Common Failure Phenomena of Tungsten 炭化物 Roll Rings

Sand Holes Inside the Roll Ring

The production process of tungsten carbide cemented carbide roll rings generally includes hot pressing, cold pressing, hot isostatic pressing, and cold isostatic pressing to achieve the densification of the internal structure of the roll ring and ensure its wear resistance and sufficient strength. However, due to various factors during the production process, sand holes similar to those produced by casting processes can occur within the roll ring’s structure, leading to failure in use. When slotting or grinding the roll rings, we often encounter this phenomenon. The sand holes vary in size; smaller ones can be eliminated by increasing the grinding amount during the roll ring processing, and their elimination does not affect the use of the carbide roll ring. Larger sand holes cannot be removed by general grinding and sometimes require abandoning a particular roll groove during processing. If the sand hole is located exactly in the middle of the roll ring’s width and is large, the roll ring can only be scrapped.

Cracks at the Bottom of the Roll Ring Groove

Under normal production, each rolling groove can guarantee a certain amount of rolling. However, some carbide roll rings wear too quickly during the rolling process and fail long before reaching the rated rolling amount. During inspections, it can be found that some roll rings have regular nail-like microcracks at the bottom of the rolling groove (see Figure 1); while others may have a craze pattern. These two types of cracks are dangerous for carbide roll rings. If the roll is not replaced in time, the cracks will expand, leading to the scrapping of the carbide roll ring.

Roll Ring Bursting

During the production process, there are two phenomena of roll ring bursting: circumferential fracture and radial fracture. In circumferential fractures, cracks occur at the bottom of the roll ring’s axial hole grooves and spread in a ring shape along the rolling groove; in radial fractures, the roll ring cracks radiate radially. In production practice, circumferential fractures of roll rings are relatively rare, with most occurrences being radial fractures (see Figure 2).

Roll Ring Shattering

Shattering of roll rings is another major phenomenon of roll ring failure and is a more serious accident that occurs during the rolling process. The hazard of roll ring shattering is extremely high because during the rolling process, the rolling mill operates at high speed, and the explosive fragments of the roll ring can damage other roll rings, leading to the expansion of the accident. When a carbide roll ring shatters, fragments often strike and injure the carbide roll rings of adjacent frames, damaging the taper sleeve and aluminum cap.

Analysis of Roll Ring Failure Causes

Cracking Due to Repeated Thermal Stress

During the rolling process, the hot rolled piece comes into contact with the surface of the rolling groove, causing the temperature of the roll surface to rise. This part of the metal will expand, while the metal temperature in the deeper layers of the roll rises less, resulting in compressive stress on the surface metal of the roll. Conversely, when the roll surface is quenched by cooling water, the surface metal contracts, while the deeper metal does not contract as much as the surface metal, creating tensile stress in the surface layer. This repeated alternation of thermal stress easily generates thermal fatigue cracks, causing the roll ring groove bottom to appear nail-like microcracks and crazing.

Optimizing Cooling Water Pressure

Insufficient cooling water pressure is also one of the causes of carbide roll ring fatigue cracks. To reduce the cracks caused by fatigue, it is necessary to use cooling water to carry away the heat obtained from the rolling piece, thereby reducing the temperature rise of the roll ring and the thermal expansion of the surface metal. When the rolling piece comes into contact with the roll ring surface, the surface metal of the carbide roll ring can reach 500~600°C. When cooling water is sprayed onto the hot roll ring surface, it forms a layer of steam film that covers the underlying roll surface, severely affecting the cooling effect. Studies have shown that when the pressure of the cooling water is less than 0.5MPa, it cannot break through the steam film, and even with sufficient water volume, the desired cooling effect cannot be achieved.

Maintaining Water Quality

Water quality can have a significant impact on the life of the finishing mill roll rings. Tungsten carbide roll rings have special requirements for the acidity of the water quality. Generally, acidic water quality can cause corrosion of the hard alloy rolls. When the pH value of the water is below 7, the cobalt alloy begins to corrode, exacerbating the propagation of thermal cracks and greatly reducing the life of the roll rings. Therefore, in addition to maintaining cleanliness, the acid-base balance of the water must also be maintained.

Quality, Operation, and Production Factors

The circumferential fracture of the roll ring is mainly caused by the propagation of fatigue cracks, while the reasons for the radial radiating fracture of the roll ring are more complex. Summarizing practical experience, the following are several causes of radial fracture of carbide roll rings:

Material Deviations and Sintering Process Defects

There are issues with the quality of the roll ring itself. The material formulas of roll rings produced by different manufacturers are distinct, resulting in different grades of roll rings. Even carbide roll rings of the same grade produced by the same manufacturer may have deviations in material proportions, leading to unstable quality of the roll rings. Another reason is that during the manufacturing process of the roll rings, improper control of the sintering process parameters can lead to defects in the quality of the carbide roll rings. We have experienced continuous radial fractures of roll rings provided by a domestic manufacturer, and the manufacturer admitted that there were issues with the sintering process after analyzing the causes of the accident together.

Overlooked Process Requirements and Excessive Pressure

Improper operation during roll mounting. There are clear process requirements for the mounting and dismounting of finishing mill roll rings, but in the production process, operators often overlook these requirements in order to work faster, resulting in insufficient cleaning of the roll rings and the taper sleeves. Moreover, operators may not control the pressure properly when using the roll mounting cart, and excessive pressure can easily cause roll ring fractures during the rolling process. Additionally, if the temperature of the roll box shaft head is not sufficient when the operator mounts the roll, it can also easily cause roll ring fractures during the rolling process.

Taper sleeve quality issues

Because the inner surface of the taper sleeve contacts the roll shaft of the roll box, and the outer surface contacts the inner surface of the roll ring, the process requires high precision in terms of concentricity and ovality. If the concentricity and ovality are out of tolerance, uneven contact between the taper sleeve and the roll ring can cause local stress during production, leading to carbide roll ring fractures.

Steel stacking

It is inevitable that steel stacking accidents occur during production. If such an accident occurs in the finishing mill, it can cause significant damage and harm to the roll rings, as the rolling pieces are rolled at high speed with temperatures above 1000°C. When steel stacks, the metal accumulates around the roll ring groove, and due to high temperatures, the metal adheres to the roll ring surface, forming a “turtle shell” phenomenon. At this point, the local heating of the roll ring generates thermal stress, easily forming thermal fatigue cracks, which can lead to fracture failure when the roll ring continues to be used.

結(jié)論

The reasons for roll ring shattering are also multifaceted. Generally, it is an expansion of the roll ring fracture accident, as the roll ring fractures while the mill is still operating at high speed, and the tremendous centrifugal force causes the fractured roll ring to break apart. Another reason is the impact of the rolling piece on the roll ring

Development of Grades

Due to the combination of coating technology and the carbide matrix with high toughness and high hardness, the market segmentation of standard K and P type carbides is changing, and the application range of K type carbides is still expanding. The development process of extruded grades is as follows.

K10/20, with a cobalt content of about 6%, contains approximately 0.2% VC and 1% TaC, and the grain size of WC is between 1.0 and 1.5 μm. Since large TaC grains (>2 μm) are prone to premature shedding during cutting, and also reduce the toughness of the carbide, which is the biggest taboo for K-type carbides, the TaC in this grade carbide?has been replaced by Cr?C?. Subsequently, the K20F grade appeared, with a cobalt content of about 8%, and the WC grain size reached 0.7 μm, mainly used for PCB micro-drills and twist drills. When extended to cutters for paper processing, the cobalt content increased to 8.5%, and the WC grain size was 1.0 to 1.5 μm. Jinlu Company’s GK10, GK20, and GK20UF correspond to these grades. The typical microstructures of GK10, GK20, and GK20UF grade carbides are shown in Figures 1, 2, 3, and 4.

ISO grade K30-K40, with a cobalt content of 10%, also adds Cr?C? and VC. The WC grain size is between 0.6 and 0.8 μm. This grade of carbide?has high strength (TRS reaching 4000 MPa), high hardness (HRA 92.2), and high wear resistance. It is important to note that the total content and the ratio of Cr?C? and VC have a significant impact on the hardness and strength of the carbide, and for different processing objects, the content and proportion of Cr?C? and VC need to be selected. To this day, this grade is still one of the main grades for rods. Jinlu Company’s GK30F grade corresponds to this. The typical microstructure of the GK30F grade carbide?is shown in Figures 5 and 6.

Japanese manufacturers were the first to develop hard metal drills and end mills with a cobalt content of 12%, while also adding Cr?C? and VC (totaling 1.2%), with a WC grain size of 0.4 μm. The wear resistance and toughness of this grade of carbide?are significantly improved, thereby significantly extending the tool life. It has outstanding advantages in the processing fields of hardened steel, stainless steel, titanium carbides, and glass fiber-reinforced plastics. The processing performance advantages of this grade are becoming more apparent and it is replacing the GK30F grade in many application areas. Jinlu Company’s GK40UF grade corresponds to this. The typical microstructure of the GK40UF grade carbide?is shown in Figures 7 and 8.

The ultra-fine grade currently under development, which contains a cobalt content of 12% and a WC grain size of 0.2 μm to 0.3 μm, and also contains VC and Cr?C? inhibitors, is widely favored by the industry. The microstructure of the test sample for Jinlu Company’s GK30SF grade is shown in Figure 9.

Tables 1 and 2 list the composition and performance indicators of the aforementioned grades.

Development of Production Technology

Production Method of Extrusion Materials

The production process of extrusion materials is as follows: wet grinding (both rolling ball milling and stirring ball milling can be used) → slurry drying → blending with a forming agent → screening and granulating. It must be noted that a considerable number of extruded product grades contain one or two types of trace grain growth inhibitors, therefore the selection of WC powder and cobalt powder grades and the method of adding grain growth inhibitors will fundamentally affect the performance of the carbide.

Extrusion Methods

Currently, the extrusion machines used in the production of hard metal extrusions include plunger extruders and screw extruders.

Plunger extruders’ output per working cycle is limited by the volume of the plunger cavity. Different tonnage plunger extruders have varying single loading quantities, ranging from a few kilograms to several dozen kilograms. Their advantage is flexible production scheduling, convenient switching between different grades of materials, and minimal material loss.

Screw extruders have almost unlimited production capacity, with continuous feeding and extrusion, which is highly suitable for the mass production of established grades. The downside of screw extruders is that equipment cleaning and installation are time-consuming when switching grades, and there is a significant waste of materials.

Both plunger extruders and screw extruders, advanced extrusion technology manufacturers have made progress in the automatic placement and automatic cutting of the compact. The extrusion molding of porous synchronous extrusion and double helix cooled bar stock is a reflection of the overall advancement of extrusion technology (see Figures 10 and 11).

Method of Removing Forming Agents

The composition of the extrusion forming agents and the corresponding process for removing them are topics that manufacturers have continuously researched. The motivation for this research comes from reducing costs and improving the dimensional limits of extruded molding. The traditional process involves removing the forming agent in a hydrogen atmosphere, followed by vacuum low-pressure sintering. Technologically advanced manufacturers have made breakthroughs in forming agent research, with the extrusion blank first being dried in an oven (without the need for a protective atmosphere) before undergoing vacuum low-pressure sintering. The drying process and equipment are shown in Figures 12 and 13.

Sintering Technology

Extruded profiles all use vacuum low-pressure sintering processes to ensure the uniformity of the product’s material and the stability of production.

Inspection and Performance Evaluation

In addition to the conventional analysis indicators of the carbide, the quality inspection of extruded profiles also includes ultrasonic testing for the sintered blanks of rods with a diameter of more than 12mm. Attention should be paid to the dispersion of the product’s bending strength and the fluctuation of the coercive force. For micro-drill rod materials used in PCBs, special attention must be given to controlling the carbide’s hardness, bending strength, and magnetic saturation value; all three indicators must be controlled simultaneously.

結(jié)論

Just like with die-pressed cemented carbide products, there is a significant gap between China’s extruded cemented carbide profiles and the world’s advanced level. The main aspects of this gap are as follows:

• Material quality disparities
• Disparities in binder and pre-sintering technology
• Inability to produce, or produce stably in bulk, cutting-edge products
• Automation disparities
• Stability of industrial production (within the same batch or between different batches)

Therefore, we should increase our research and development efforts in the aforementioned areas to quickly narrow the gap with the world’s advanced level. This will provide reliable domestically produced cutting tools for China’s emerging electronic industry and machinery manufacturing industry.

Firstly, the connection method between the saw tooth insert and the saw blade body has been changed from the traditional welding method to a machine-clamping method. Secondly, the saw tooth inserts of the saw blades are coated using Chemical Vapor Deposition (CVD) technology.

Design of Machine Clamped Carbide Toothed Circular Saw Blades

Material and Manufacturing Process of Machine Clamped Circular Saw Blades

(1) Material of Circular Saw Blade Body

The material selected for the machine clamped coated carbide toothed circular saw blade body is 75Cr1, with a material hardness of 35HRC. 75Cr1 is a specialized steel for saw blades, with a carbon content of 0.70%-0.80%. Due to its higher carbon content and the addition of Cr elements, 75Cr1 can obtain high hardness and strength after heat treatment, and its impact resistance is significantly improved. It is widely used in carbide saw blade substrates and diamond saw blade substrates.

(2) Material of Saw Blade Saw Tooth Insert

The insert material uses ultra-fine grain carbide with a grade number of P25-P40 series. The WC grain size of ultra-fine grain carbide is below 0.5μm, which is a fraction to several fractions of the WC grain size of ordinary carbide. After grain refinement, the hardness, wear resistance, bending strength, and chipping resistance of the alloy are significantly improved. It is widely used in the processing of difficult-to-machine metal materials such as stainless steel, hardened steel, and chilled cast iron. P-type ultra-fine grain carbide is particularly good at processing long chip-producing black metals (such as stainless steel). Its lifespan is 3-10 times higher than that of ordinary carbide.

(3) Manufacturing Process of Machine Clamped Circular Saw Blades

The processing of the machine clamped saw blade body involves laser cutting for blanking, followed by heat treatment, flattening, grinding of the inner hole and surface, and other machining processes. The processing of the blade body is completed through the detection of hard indicators such as end runout, diameter runout, and flatness.

The tooth seat structure model of the saw blade body is shown in Figure 1. The processing of the machine clamped saw blade body tooth seat structure involves milling the tooth seat, milling the semi-circular groove, drilling the fastening holes, tapping threads based on the fastening holes, and other processes, and the end runout of the tooth seat is detected and checked to complete the processing.

Geometric Parameters of Machine Clamped Circular Saw Blades

(1) Geometric Parameters of the Machine Clamped Circular Saw Blade Body

The diameter of the machine clamped circular saw blade body is 965mm, with a thickness of 9mm. The surface roughness of the saw blade is R≤3.2μm, and the end runout is ultimately guaranteed to be within 0.07mm.

In the tooth seat structure of the machine clamped circular saw blade body, the width of the semi-circular positioning groove is 6-8mm, the depth is 0.4-0.6mm, and the clamping screw selected is M4×12mm.

(2) Geometric Parameters of the Machine Clamped Saw Tooth Insert

The machine clamped saw tooth insert is a non-standard insert, and its geometric structure requires independent research and development design. Based on the thickness of the saw blade body and the tooth seat structure, the insert’s thickness, width, and height are designed to be 15mm, 10mm, and 6mm, respectively. The model schematic of the machine clamped insert is shown in Figure 2. The clamping part is designed with a countersunk screw connection. The specific structural geometric parameters are as follows:

Front Relief Angle: The sawing process is a discontinuous cutting operation, during which the insert will continuously receive impacts. Considering the brittleness of the carbide tool material, the front relief angle should not be too large. Therefore, based on past sawing experience, the front relief angle of the saw tooth insert is chosen to be 6°-8°, as shown in Figure 3.

Rear Relief Angle: A rear relief angle that is too large will lead to a decrease in the insert’s ability to withstand impacts. Therefore, considering the above factors and sawing experience, the rear relief angle of the insert is selected to be 8°-12°, as shown in Figure 3.

Negative Chamfer: A negative chamfer needs to be ground on the front cutting edge. The chamfer can not only further enhance the strength of the insert’s cutting edge but also increase the insert’s wedge angle to improve heat dissipation conditions. Based on relevant theoretical research and sawing experience, the negative chamfer width is chosen to be 0.3-0.5mm, with a chamfer angle of 14°-18°, as shown in Figure 3.

Chip Groove: Chip grooves can be divided into three shapes: rectangular, angular, and circular arc. The machine clamped saw tooth insert will use a circular arc-shaped chip groove. The groove width and depth are 0.2-0.4mm, with a circular arc radius of 0.3-0.5mm. The chip grooves between adjacent teeth are symmetrically distributed. The chip grooves on the saw tooth insert are shown in Figure 2.

Coating Materials and Parameters for Saw Tooth Inserts

Based on the theory of coating technology and the actual sawing conditions, the saw tooth inserts will be coated using CVD technology with TiAlN and AlCrN coatings for comparative testing. The characteristics of the two coating materials are as follows:

TiAlN Coating: This is a widely used coating material with a hardness of 3400-3600HV and an oxidation resistance temperature up to 800°C. During cutting, it can oxidize to form Al?O?, thus creating a hard, inert protective film that serves as an antioxidant and resistant to diffusion wear. It is the preferred coating for processing difficult-to-cut metal materials such as high-alloy steel, stainless steel, and titanium alloys.

AlCrN Coating: This is another new type of coating material developed after TiAlN. Its unique cubic crystal lattice structure endows it with high red hardness and wear resistance, with a hardness of 2800-3200HV. It can maintain high hardness at temperatures up to 1100°C. Its toughness is superior to TiAlN, making it more suitable for intermittent cutting. It is applicable to various cemented carbide tools, including gear hobbing cutters and end mills, especially when cutting stainless steel, it exhibits good chip breaking performance.

The finished machine clamped saw blade is shown in Figure 4.

Performance Testing of Coated Cemented Carbide Toothed Circular Saw Blades

Test Conditions and Methods

The coating performance test sawing experiment was conducted in a sawing workshop at a certain steel pipe factory. The sawing machine used in this test was produced by Wagner, model WHC1000. The workpiece to be sawed was solid round steel, with a material composition of 13Cr (stainless steel) and a diameter of φ270mm. The saw tooth inserts to be used included uncoated inserts and inserts coated with TiAlN and AlCrN vapor deposition coatings, both with a coating thickness of 4-5μm, which is a conventional thickness for coatings.

Sawing Test Process

First, the uncoated welded carbide toothed circular saw blade was mounted for testing. During the trial cut, it was found that the sawing machine consumed a high amount of power. After 5 cutting cycles, the machine was stopped, and it was observed that the insert cutting edge had already shown signs of wear. After adjusting the sawing parameters, the test continued. During the process, the sound of the saw entering the material gradually increased, and after more than 20 cutting cycles, sparks appeared at the cutting area with red chips flying out, and the sawing machine vibrated significantly. After 30 cutting cycles, the machine was stopped for observation, and it was found that the saw blade cutting edge was significantly worn, with severe edge chipping. The cross-section of the workpiece had a large number of burrs. Since the saw blade was scrapped, the test was immediately stopped.

Next, the TiAlN coated carbide toothed circular saw blade was installed on the sawing machine and no abnormalities were found during the trial cut. After adjusting the parameters, the cutting continued until more than 80 cutting cycles, when it was observed that the power consumption of the sawing machine had increased. After the 90th cutting cycle, the machine was stopped for inspection, and it was found that there were a few built-up edges at the insert cutting edge, and three saw tooth inserts had?slightly?chipping.

Finally, the AlCrN coated carbide toothed circular saw blade was installed. After the trial cut phase, the machine was stopped for observation, and the saw blade was found to be in good condition with no abnormalities. After adjusting the sawing parameters to the normal range and continuing the observation, the sawing process was smooth, with no abnormal changes in sound or chip ejection. After more than 130 cutting cycles, the cutting sound slightly increased, and the sawing machine showed slight vibration. After 140 cutting cycles, the machine was stopped, and the blade was removed for a detailed inspection. It was found that there were a few built-up edges, but all insert blocks showed normal wear with no chipping. The surface roughness of the workpiece cross-section was low, meeting the precision requirements.

Test Results and Discussion

The test conditions for the three types of saw blades are shown in Table 1.

Based on the analysis of Table 1, it is understood that the tool coating can significantly improve the cutting performance of carbide toothed circular saw blades, and the service life of the saw blades is extended to 3-5 times that of traditional uncoated welded saw blades. A comparison of the two coating materials found that AlCrN coating has superior performance compared to TiAlN coating.

(1) Compared to uncoated circular saw blades, coated circular saw blades demonstrate superior cutting performance, mainly because the coating material has good comprehensive properties. This is mainly manifested in the following aspects:

The hardness of the coating is about twice that of the carbide material used for the saw tooth inserts, which reduces the frictional wear and adhesive wear between the saw tooth inserts and the workpiece being cut, and improves the wear resistance of the saw tooth inserts; the inert Al?O? film generated by the coating material during the sawing process can enhance the oxidation resistance of the saw tooth inserts; the low friction coefficient between the coating material and metal can reduce the cutting force and cutting temperature, thereby greatly improving the durability of the tool; the low thermal diffusivity of the coating material can slow down the rate at which cutting heat diffuses to the carbide substrate of the saw tooth insert, thereby reducing the thermal load on the insert substrate, which is particularly important during intermittent cutting processes.

(2) Through the comparison of sawing tests with the two coating materials, it was found that AlCrN coating is more suitable for sawing stainless steel than TiAlN coating. Therefore, an analysis of the properties of the two coating materials was conducted: According to the metal lattice theory, the lattice structure of AlCrN is superior to that of TiAlN in its ability to solid-solve Al, so the AlCrN coating will generate more Al?O? during the cutting process, and the formed Al?O? film is more stable. Moreover, Cr has a higher melting point than Ti, therefore, the AlCrN coating with Cr substituting for Ti has significantly improved resistance to high temperatures and oxidation compared to the TiAlN coating, with a smaller friction coefficient and stronger chip evacuation capability. Although the hardness is slightly reduced, the comprehensive performance is more excellent.

結(jié)論

Through the comparison and analysis of the cutting performance tests of uncoated, TiAlN, and AlCrN coated carbide toothed circular saw blades, the following conclusions are drawn:

(1) Coated carbide toothed circular saw blades significantly improve the cutting ability and extend the service life of the saw blades.

(2) Coating material: Based on theoretical analysis and test results, the novel AlCrN coating can be preferentially selected.

Wire drawing process parameters and dies

Die Material: Cemented Carbide Wire hardness: 65＃
Lubricant: Soap Powder
Drawing Speed: 150 m·min?1
Inlet Diameter: 4.6 mm
Outlet Diameter: 4.2 mm
Production Volume: Approximately 12 tons

Take a set of five normally worn cemented carbide wire drawing dies that have failed due to wear. Cut them along the die hole axis using wire cutting, and clean the residual substances on the die hole surface with carbon tetrachloride. Observe the wear morphology of the die hole. Select a typical one from them and mill away most of the die sleeve to facilitate placement during observation with a scanning electron microscope and for energy spectrum analysis.

Analysis of the Wear Morphology of the Wire Drawing Die

Based on the shape of the wire drawing die hole and its wear morphology, it can be divided into four regions (see Figure 1), namely the entrance zone, the transition zone between the entrance zone and the compression zone, the compression zone, and the sizing zone.

Taking the wire drawing dies from a steel rope factory that have failed due to wear during wire drawing as samples, this paper analyzes the wear morphology and main wear forms of cemented carbide wire drawing dies, providing a basis for the rational design and use of drawing dies to extend their service life.

Entrance Zone

The surface of the die entrance zone is relatively smooth, with the bonded WC particles being almost completely coated, and the surface is relatively intact. There are no extensive friction and wear marks, only a few pits left by grinding.

Under high magnification SEM images (see Figure 2(a)), it can be observed that there are a small number of scratch marks at some positions in the die entrance zone when the wire is being drawn through. It is evident that during the wire drawing process, the entrance zone does not come into contact with the wire, the compressive stress is low, and the wear is not significant, but it is prone to a small amount of scratching.

From the EDS analysis results (see Figure 2(b)), the surface of the die hole in this area contains not only the basic elements C, W, and Co but also a small amount of oxygen (O) elements.

Transition Zone between the Entrance Zone and the Compression Zone

In the transition area between the entrance zone and the compression zone, along the circumferential surface of the die hole, some parts are smoother while others are rougher. The smooth parts are similar to the surface morphology of the entrance zone, while the rough parts are closer to the compression zone, indicating that during wire drawing, the axis of the wire drawing die does not align with the die hole, resulting in the die at the entrance contacting the steel wire along one side, leading to uneven wear.

Under low magnification, the smooth surface parts are less even than the entrance zone, with an increased number of pits on the surface. Observing under high magnification SEM, as shown in Figure 3(a), the adhesive phase and skeleton particle shedding are more obvious, with wear traces scattered everywhere.

EDS analysis shows that the surface of the die hole in this area contains not only the basic elements C, W, and Co but also a small amount of oxygen (O) elements, as seen in Figure 3(b).

Compression Zone

The surface is almost entirely composed of continuous protrusions and pits, making the entire surface rough. Under high magnification SEM, as shown in Figure 4(a), the binder phase Co on the die surface is almost completely extruded, and the entire surface layer consists of W and C skeleton particles, with significant particle shedding and wear. According to the EDS analysis results in Figure 4(b), the surface of the die hole in this area contains not only the basic elements C, W, and Co but also foreign elements O, Fe, and Ca.

Sizing Zone

The transition part between the sizing zone and the compression zone has worn down, and the length of the sizing zone after wear exhibits a?fact?where one side is longer than the other along the die hole surface, further indicating that the wire at the exit is not concentric with the die hole. Under low magnification SEM, the entire sizing area surface appears rough, with the morphology mainly characterized by wear stripes parallel to the drawing direction, as shown in Figure 5(a).

Under high magnification SEM, the binder phase Co is also almost completely extruded, leaving mostly W and C skeleton particles on the entire surface, accompanied by furrow-like wear morphology, with the furrows parallel to the drawing direction, as shown in Figure 5(b). According to the EDS analysis results, similar to the compression zone, the die hole surface in this area contains not only the basic elements C, W, and Co but also foreign elements O, Fe, Ca, and P.

Analysis of the Wear Mechanism of the Wire Drawing Die

Abrasive Wear

The uneven, convex-concave morphology on the die hole compression zone is primarily caused by abrasive wear. The process of abrasive wear in cemented carbide can be detailed as follows: ① movement of the binder phase on the alloy surface layer; ② plastic deformation of the binder phase; ③ increase in plastic strain of W and C grains; ④ fracture of individual W and C grains; ⑤ intergranular fracture; ⑥ grains being pulled out from the matrix.

During the steel wire drawing process, the normal stress on the die hole compression zone gradually decreases from the entrance end to the exit end. However, for drawing high-strength steel wire #65, the stress values at each point are quite high. Under the action of surface normal stress and frictional force, the binder phase Co within a certain depth of the material contact surface undergoes plastic deformation and micro-abrasive wear, resulting in the extrusion of the surface Co from between the grains and the formation of an uneven morphology. As the binder phase is lost, the surface integrity of the cemented carbide is damaged, the skeleton becomes unstable, and cracks form between the grains, causing some W and C particles to fall off from the matrix surface, creating pits on the die hole surface.

Oxidation Wear

During the steel wire drawing process, the heat generated by deformation work and friction work causes the temperature of the steel wire itself to rise, typically reaching up to 200°C. On a continuous wire drawing machine, without cooling measures, after multiple draws, the accumulated temperature of the steel wire can reach 500~600°C. It is evident that the cemented carbide wire drawing die gradually oxidizes due to working at higher temperatures. According to EDS analysis, a certain amount of oxygen (O) elements is present in various regions of the die hole surface, and the content of O elements is consistent with the distribution of the die wall temperature, with the highest in the compression zone, followed by the sizing zone, and the least in the entrance zone.

Adhesive Wear

According to EDS analysis, there are elements of Fe and lubricant components on the die hole surface, indicating the presence of adhesive wear.

Adhesive wear is mainly related to high contact stress and significant sliding. When the drawing metal comes into contact with the die surface, microscopically, the actual contact area is only on some isolated peaks. Additionally, the high normal pressure in the die hole during drawing results in enormous contact stress on these peaks. Even with the presence of a lubricant, the contact is in a boundary lubrication state. Under the combined action of the drawing force and the die hole pressure, the temperature rises, the lubricating film breaks, the peaks undergo plastic deformation, and adhesion, welding, and tearing occur, leading to metal transfer and adhesion to the die surface.

結(jié)論

(1) The most severe wear areas of the wire drawing die hole are the compression zone and the sizing zone, with the main wear mechanisms being abrasive wear, oxidation wear, and accompanied by adhesive wear. Therefore, to reduce the wear of cemented carbide wire drawing dies, efforts should be made to reduce abrasive wear, oxidation wear, and adhesive wear.

(2) The misalignment of the steel wire at the entrance and exit of the die hole with the die hole axis can lead to uneven radial wear of the die hole. Therefore, it is important to properly straighten the wire before drawing and ensure that the wire entry direction is as aligned as possible with the wire drawing die axis to reduce uneven radial wear of the die hole, which can cause premature die failure.

Requirements for Seal Face Materials in Mechanical Seals

To ensure the proper operation of sealing rings in mechanical seal devices, they are typically configured as a pair consisting of a hard ring and a soft ring with different hardness levels, considering aspects such as wear reduction, corrosion resistance, and prevention of galling. During operation, the sealing rings may come into contact and generate friction when starting, stopping, or experiencing fluctuations in working conditions. Therefore, the material for the hard ring needs to have sufficient strength, rigidity, wear resistance, and thermal conductivity. Friction and fluid shear forces can elevate the temperature of the sealing rings, so the sealing material must exhibit good thermal conductivity, heat resistance, and thermal shock resistance. To ensure a long service life, the sealing ring must also have good corrosion resistance. Additionally, the hard ring should possess good formability and machinability, low density and permeability, and excellent self-lubricating properties. No single material can fully meet all these requirements, so typically, the main performance criteria for sealing materials are defined based on the operating environment, and suitable materials are selected accordingly.

Application of WC-Ni carbide as Mechanical Seal Materials

To ensure the longevity and stable operation of mechanical seal materials, the sliding materials should have appropriate thermal compatibility and thermal conductivity, as well as suitable coefficients of thermal expansion, elastic modulus, and friction factors. WC-Ni carbides are known for their excellent performance in mechanical seals, making them suitable for applications in high-pressure, high-speed, high-temperature, corrosive environments, and media containing solid particles.

Characteristics of WC-Ni carbide

Since the introduction of carbides in the 1920s, cobalt has been regarded as the best binder phase and continues to play a significant role in the preparation of carbides. With the rapid advancement of science and technology, the applications of carbides have expanded, leading to a surge in demand. Due to the scarcity of cobalt resources, scientists worldwide have prioritized cobalt as a strategic material and have been researching ways to reduce or substitute cobalt in carbides. Nickel, being close to cobalt in the periodic table, with similar density, melting point, and atomic radius, can effectively wet and support the hard phase and has lower radioactivity compared to cobalt, making it a common substitute.

The characteristics of WC-Ni and WC-Co carbides during the sintering process are similar. However, due to the different strengthening effects of Ni and Co on the hard phase, WC-Ni may exhibit slightly lower performance in certain aspects compared to WC-Co carbides. By adding a small amount of metal elements to enhance the binder phase, using fine low-carbon WC particles, and employing vacuum sintering processes, WC-Ni carbides with lower porosity and a uniform, fine-grained structure can be achieved. Their hardness, bending strength, and tribological properties can meet or exceed those of WC-Co carbides, while their corrosion resistance is also significantly improved. Additionally, as Ni replaces the radioactive element Co, it provides good radiation protection when used under radioactive conditions. By carefully controlling the total carbon content and grain size of the alloy, and adding appropriate amounts of Mo and Cr, WC-Ni carbides can be produced with non-magnetic properties and excellent physical and mechanical performance, thereby mitigating the effects of special working conditions and environmental factors.

Physical and Mechanical Properties of WC-Ni carbide for Mechanical Seals

WC-Ni carbides are made by mixing WC and Ni powders in a specific ratio, adding a binder, and then pressing and sintering the mixture. With a melting point of approximately 2700°C, WC particles are primarily bonded together during the sintering process through the melting of Ni. At high temperatures, some WC dissolves into Ni, forming a WC-Ni eutectic with a lower melting point than Ni. Consequently, the sintering temperature varies with changes in Ni content and WC grain size. For composite materials, physical parameters such as elastic modulus, coefficient of thermal expansion, Poisson’s ratio, thermal diffusivity, and thermal conductivity can vary based on the proportion and distribution of each phase.

Application of WC-Ni carbide Materials in Mechanical Seals

Due to their exceptional toughness, rigidity, high hardness, good wear resistance, high bending strength, and high thermal conductivity, both WC-Ni and WC-Co carbides are notable. WC-Ni carbides offer superior corrosion resistance compared to WC-Co alloys and do not emit radiation under neutron exposure, making them suitable for use in mechanical seals operating under high pressure, high speed, high temperature, corrosive media, media containing solid particles, and radioactive environments. Currently, WC-Ni carbides have significant application value in vehicle transmission shaft seals, power shift transmissions, pumps in special operating conditions, and rotary seals for aircraft, as well as in the petrochemical industry and nuclear power seals.

Influence of Microstructure on the Properties of WC-Ni carbides

The unevenness in microstructure can adversely affect the strength of carbides. Minor variations in the binder phase content and distribution, WC grain size, carbon content, and any form of impurity contamination can lead to an uneven microstructure that negatively impacts the mechanical properties of WC-Ni carbides.

Influence of WC Grain Size on the Properties of WC-Ni carbides

WC-Ni carbides use Ni as the binder metal. During the sintering process, Ni melts at the sintering temperature and bonds the WC particles together into a solid mass. These alloys exhibit very high hardness, are difficult to machine, and possess excellent wear resistance. Variations in the processing methods can lead to significant differences in the alloy’s composition and properties, and the morphology of the WC grains can also affect the performance of WC-Ni carbides.

3.2Changes in WC Grain Morphology During Liquid Phase Sintering of WC-Ni carbides

The coarseness of WC grains can significantly affect the bending strength of carbides, while uneven distribution of Ni can lead to brittle fracture of the alloy. To improve the fracture toughness of the product, it is essential to strengthen the interface between WC and the binder phase or to enhance the strength of the binder phase. Therefore, controlling the sintering process and conditions will impact the mechanical properties of WC-Ni carbides.

During sintering, the shape of WC grains in the carbide?is also influenced by shape relaxation and the grain growth process. The higher the ratio of the average intercept length of the binder phase (the average length of each grain intersected by any testing line on a cross-section) to the WC grain size, the less impact it has on the shape of the WC grains, resulting in a more equiaxed grain morphology.

Effect of Binder on Temperature Residual Stress in WC-Ni carbides

When the content of the metallic binder Ni in WC-Ni alloy materials is relatively high, the compressive stress in fine WC grains is greater than that in coarse grains. This is because, with a constant WC content, the average free path of the binder in fine powder is shorter than in coarse powder. When the WC-Ni alloy contains less binder, the difference in the average free path of the binder is minimal, and the variation in residual stress with temperature is not significant. Therefore, if conditions allow, the Ni content in WC-Ni alloy sealing rings should be reduced to minimize the uneven distribution of residual stress due to temperature changes, thus reducing or even preventing thermal cracking in the sealing rings.

Current Research Status on the Application Performance of WC-Ni carbides

?Corrosion Resistance of WC-Ni Alloys

Compared to WC-Co carbides, WC-Ni carbides exhibit superior wear resistance. This is due to the binder in WC-Ni alloys having excellent corrosion resistance, with both passivation and electrochemical corrosion rates for WC-Ni carbides being significantly lower than those for WC-Co carbides. Under acidic conditions in practical production processes, WC alloys with Ni as the binder show better acid resistance than those with Co as the binder.

Table 2 compares the corrosion resistance of WC-Ni and WC-Co carbides. The results show that substituting Co with Ni significantly enhances the corrosion resistance of WC carbides. However, the corrosion resistance of a material is specific to its alloy composition, grain size, and the corrosive conditions (including temperature, concentration, time, and corrosion state). For example, the corrosion resistance of YWN8 in 68%-90% HNO? is not significantly different from, and even slightly lower than, that of YG6 alloy. This is primarily due to the poor resistance of metallic Ni to strong oxidizing acids like HNO?; as the concentration of HNO? and the Ni content in the alloy increase, its corrosion resistance decreases.

Table 2 Corosion resistance performance comparison between WC-Ni and WC-Co cemented carbides

Tribological Performance of WC-Ni Alloy Mechanical Seal Rings

WC-Ni carbide?sealing rings exhibit excellent wear resistance. This is because WC-Ni carbides possess strong oxidation resistance and corrosion resistance in fluid sealing media, which contributes to their superior wear resistance. The friction coefficient of WC-Ni carbides is related to the content, grain size, and distribution of the binder phase. A softer binder phase can lead to adhesion during friction. Additionally, the content and composition of the binder phase can affect the hardness of WC-Ni, thereby influencing the wear resistance of the WC-Ni carbide.

結(jié)論

Mechanical seal materials are a crucial area of research in sealing technology. With the advancement of modern science and technology and the increasing demands of production and daily life, the requirements for sealing technology have become more stringent. However, research in this field in our country is still relatively behind. Strengthening interdisciplinary collaboration and continually improving experimental and theoretical research are key to overcoming the technological barriers in mechanical seals imposed by foreign countries.

Overview

In recent years, research on coarse grain carbide grades and materials has been advancing in two different directions: ultra-coarse and ultra-fine grains. Ultra-coarse grain cemented carbides have been widely applied in mining rock drilling tools, roll mills, and stamping molds.

Studies have revealed several primary forms of carbide failure during drilling: impact fatigue, abrasive wear, and thermal fatigue. For hard rock formations, such as granite (drilled with impact or rotary impact drills), abrasive wear is relatively lower, and carbide failure is primarily caused by impact and impact fatigue. The compressive strength and bending strength of the carbide are directly related to its impact fatigue resistance; additionally, this resistance is associated with the carbide’s purity, WC grain size, and Co phase’s average free path. Furthermore, the carbide’s impact fatigue resistance is directly related to the impact energy.

Reasons for Issues in Cemented Carbide Rock Drilling

For medium-hard rock formations, such as quartzite (drilled with impact drills), abrasive wear dominates. Abrasive wear generally consists of two aspects: micro-cracks at the contact points of abrasive particles and premature wear of the Co phase. The former primarily occurs on hard and brittle carbides, especially when abrasives have high fracture strength; the latter occurs on softer carbides with higher Co content, particularly when abrasives are very brittle. Figure 1 shows a scanning electron microscope (SEM) image of the wear surface of a GF20D grade drill tooth, produced by Xiamen Jinlu Special Carbide Co., Ltd., after drilling about 500 meters into quartzite. The YG6 grade carbide, composed of 94% WC with a grain size of 2-3 μm and 6% Co, has a hardness of HV30:1430. The image illustrates typical abrasive wear, characterized by premature Co phase wear and cracking and spalling of the WC phase.

For soft rock formations, such as sandstone, thermal fatigue is the primary cause of carbide failure, accompanied by abrasive wear. For ultra-soft rock formations, such as calcite and limestone, thermal fatigue is the main cause of carbide failure. The propagation of cracks and premature wear of the Co phase directly impact the drill tooth’s lifespan. Especially when drilling magnetite, thermal fatigue cracks, also known as creep cracks, dominate. Figure 2 shows a typical undulating cracking morphology of cemented carbide drill teeth formed while drilling magnetite. Figure 3 is an SEM image of a traditional polished cross-section of a carbide drill tooth that drilled about 5 meters into magnetite, composed of 94% WC with a grain size of 5 μm and 6% Co, with a hardness of 1230 HV. The image reveals that the thermal fatigue cracks on the carbide surface have extended into the carbide’s interior.

Figure 1: SEM photo of the wear surface of the quartzite at a depth of about 500 meters on the YG6 drill tips inserted in drill bits

Figure 2. Typical ups and downs of crack morphology formed when carbide drill teeth drill magnetite

Figure 3. The carbide drill teeth drill a conventional polished cross-section of about 5m into the magnetite. The grade consists of 94% WC with a grain size of 5um and 6% Co with a hardness of 1230HV(SEM).

Reasons for Developing New Rock Drilling Cemented Carbides

The fundamental reason for developing new rock drilling carbides lies in the continuous advancement of mining and drilling technology both domestically and internationally. As drilling equipment becomes more advanced and drilling efficiency improves, there is a growing use of fully hydraulic, high-power, and high-efficiency rock drilling rigs and rotary-percussion drills. This advancement has raised higher demands for the quality and lifespan of rock drilling cemented carbides. When drilling tools penetrate rock, the pressure rises from 0 to 10 tons within 1/10 of a second, and the temperature increases from 20°C to 1000°C. During impact and rotation, drilling carbides generate extremely high temperatures. Especially when drilling magnetite, rapid formation of thermal cracks, commonly referred to as “snake skin” or “tortoise shell” cracks, occurs.

To meet the requirements of modern rock drilling technology, the performance of rock drilling cemented carbides needs to be improved and optimized in several key areas: the thermal conductivity (the ability of the material to conduct heat) should be as high as possible; the thermal expansion coefficient (the linear expansion of the material when heated) should be as low as possible to ensure minimal growth rate of thermal cracks; high-temperature hardness should be further enhanced to guarantee good wear resistance at high temperatures; in addition, the transverse rupture strength (TRS) and fracture toughness (Kic, the material’s ability to resist sudden fractures caused by micro-cracks) should also be improved.

Table 1 lists the thermal performance data of pure WC, pure Co, three commonly used WC-Co carbide grades, and three types of rock. These three grades, with varying Co content and WC grain sizes, are suitable for different rock drilling teeth, hot-rolled rolls, and multi-purpose applications.

Directions for Developing New Rock Drilling Cemented Carbides

It is well known that Co has low thermal conductivity and a high thermal expansion coefficient. Therefore, the Co content should be minimized as much as possible. On the other hand, cemented carbides with high Co content exhibit better strength and fracture toughness. From a mechanical perspective, especially when carbide drill bits penetrate rock surfaces at high speeds, the drill bits endure high impact and loads, or mechanical vibrations under hard cutting conditions, necessitating improved strength and fracture toughness in the carbide. Additionally, compared to fine-grained carbides, coarse WC grain sizes contribute to greater strength and fracture toughness of the cemented carbide.

As a result, the preparation of rock drilling cemented carbides tends to use lower cobalt content and increase WC grain size to achieve good mechanical properties and the required high-temperature wear resistance. This approach results in ultra-coarse grain carbides. Traditionally, the production of ultra-coarse grain cemented carbides involves high-temperature reduction of coarse grain tungsten powder followed by high-temperature carburization to produce coarse grain WC powder. This powder is then mixed with Co powder and ball-milled to form a mixture, which is subsequently pressed and sintered to create the cemented carbide. However, coarse grain WC powder produced from tungsten powder via high-temperature carburization generally consists of polycrystalline particles, where each WC particle is composed of multiple WC single crystals.

Figure 4 shows a scanning electron microscope image of coarse grain carbide powder with a Feret diameter of 23.20 μm. The image reveals that each WC particle contains multiple WC single crystals. Although the original powder has a coarse grain size, after grinding, the polycrystalline particles easily break down into fine single crystal particles. Consequently, the ground WC powder has a Feret diameter of only 4.85 μm. Figure 5 shows the metallographic photo of a cobalt-containing carbide with 6% Co produced using conventional carbide production processes. The average grain size of this carbide is approximately 4.0 μm.

Figure 4: SEM image of coarse grain WC powder with a particle size of 23.20 μm.

Figure 5: Metallographic photo of WC-6% Co alloy produced from coarse grain WC powder with a particle size of 23.20 μm using conventional processing methods.

U.S. Patents 5505902 and 5529804 disclose methods for producing ultra-coarse grain cemented carbides. The methods outlined in these patents involve the dispersion and classification of coarse grain WC powder through jet milling and sieving to remove fine WC particles, selecting only the coarse-grained carbide, and then coating these WC particles with Co. Patent 5505902 utilizes the sol-gel method, where WC, methanol, and triethanolamine are mixed in a reactor. During heating, methanol evaporates, and Co precipitates onto the WC grains, forming a sol-gel.

Patent 5529804 employs the polyol method, where Co acetate, water, and WC are mixed and then spray-dried. The mixing process is optimized to prevent the breaking of coarse WC particles. The mixture produced using these patented methods is then subjected to conventional pressing and sintering processes to create cemented carbides with 6% Co and an average grain size of 13-14 μm, with porosity easily controlled between A02 and B02. This new carbide shows better WC matrix adjacency compared to carbides produced by traditional ball milling. Consequently, this new carbide has been successful in specific applications where conventional carbides fall short, such as in hard rock layers like granite and hard sandstone. In these cases, conventional column teeth fail due to Co dissolution at high temperatures, leading to spalling of elongated or hexagonal WC grains, and eventually, complete spalling of the drill bit within minutes, causing rapid crack propagation and subsequent fracture. In contrast, carbides produced with new technology can be used for extended periods in hard rock layers, displaying stable wear resistance without deep cracks. Due to the high adjacency of the WC matrix, the thermal conductivity of the 6% Co carbide with a WC average grain size of 14 μm can reach 134 W/m°C, which is 20% higher than that of coarse-grained carbides with the same Co content produced by traditional methods and comparable to the thermal conductivity of pure WC.

Application Examples of New Ultra-Coarse Grain Cemented Carbide Production Technologies

Two types of impact drilling cemented carbides were simultaneously produced using both traditional and new methods and tested in iron ore. Both samples had a WC average grain size of 8 μm, 6% Co, and 94% WC content.

Sample A: Produced using traditional ball milling, drying, pressing, and sintering processes. This carbide has a wide distribution of crystal sizes.

Sample B: The WC powder was subjected to jet dispersion and classification to remove coarser and finer WC particles, selecting 6.5-9 μm WC powder. The WC grains were pre-coated with 2% Co, and then 4% pure Co was added to achieve a 6% Co content. After wet mixing (without ball milling) to obtain the desired slurry, a thickening agent was added if necessary to prevent coarse grain WC sedimentation. The slurry was dried, shaped, and sintered, resulting in a narrower particle size distribution, with over 95% of the grains ranging from 6.5 to 9 μm. The adjacency of these carbides was measured: Sample A had an adjacency of 0.41, while Sample B had an adjacency of 0.61.

Testing was conducted in magnetite, which is prone to generating high heat and thermal fatigue. After drilling 100 μm, Sample A exhibited thermal cracking. Cross-sectional observation of the used carbide revealed small cracks extending into the carbide, damaging its microstructure and reducing its lifespan. With regrinding after every 100 μm of drilling, the carbide’s drilling lifespan was 530 meters. Sample B showed no or only minimal thermal cracking after drilling 100 meters. Cross-sectional observation showed no internal cracks, only some fractured surface grains. With regrinding after every 200 meters, the average drilling lifespan was 720 meters.

Carbide?Valve Seat

carbide?valve seats can also be called tungsten steel petroleum valve heads. carbide?valve seats, valve assemblies, or carbide?ball valves evolved from traditional plug valves, with the opening and closing component being a sphere, achieving opening and closing purposes by rotating the sphere around the valve stem axis. The main function of carbide?valve balls in pipelines is to cut off, distribute, and change the direction of fluid flow.

Production Process of Valve Seat

carbide?valve seats are made using the carbide?cold extrusion process. Cold extrusion is a metal fine forming process with minimal or no cutting, and very low power consumption. Using cold extrusion to produce metal formed parts has unparalleled advantages in machining, especially suitable for the production of large batches of metal parts, among which carbide?valve seats are one of the applicable parts. It can also serve as a forming process for products.
There are many advantages of the carbide?cold extrusion process. Firstly, it saves raw materials. Cold extrusion uses the plastic deformation of carbides to produce parts of the required shape, thus greatly reducing machining and improving the utilization rate of raw materials. The material utilization rate of cold extrusion generally exceeds 80%, which is advantageous for the carbide?industry production.

Carbide Ball Valve

The ball valve emerged in the 1950s. With the rapid development of science and technology and continuous improvement in production processes and product structures, within a short span of 40 years, it has rapidly developed into a major type of valve. In countries with developed industries in the West, the use of ball valves is increasing year by year. In China, ball valves are widely used in industries such as petroleum refining, long-distance pipelines, chemicals, papermaking, pharmaceuticals, water conservancy, electricity, municipal engineering, and steel, occupying a pivotal position in the national economy.

Carbide?ball valves are mainly used for cutting off or connecting the medium in pipelines and can also be used for fluid regulation and control. Among them, hard-sealed V-shaped carbide?ball valves have strong shear force between the V-shaped ball core and the carbide?metal seat, especially suitable for media containing fibers, tiny solid particles, etc. Multi-way carbide?ball valves can flexibly control the confluence, diversion, and flow direction switching of the medium in pipelines, while closing any one channel to connect the other two channels. Such valves should generally be installed horizontally in pipelines. Classification of carbide?ball valves: pneumatic carbide?ball valves, electric carbide?ball valves, manual carbide?ball valves.
It has a 90-degree rotational action, with the closure body being a sphere with a circular through-hole or passage along its axis. carbide?ball valves are mainly used in pipelines for cutting off, distributing, and changing the flow direction of the medium. They can be tightly closed with just a 90-degree rotation and a small turning torque. carbide?ball valves are most suitable for use as on-off and cut-off valves, especially V-shaped carbide?ball valves.They are also widely used in vacuum systems.

Features of carbide ball valves

Carbide?ball valves not only have simple structure and good sealing performance but also within a certain nominal diameter range, they are small in size, lightweight, consume less material, have small installation dimensions, and require low driving torque. They are easy to operate and achieve quick opening and closing, making them one of the fastest-growing valve types in recent decades. carbide?ball valves evolved from plug valves, with their closing member being a sphere, which rotates 90° around the valve stem axis to achieve opening and closing. carbide?ball valves are mainly used in pipelines for cutting off, distributing, and changing the flow direction of the medium, and carbide?ball valves with V-shaped openings also have good flow regulation functions.

Applications of Several Common Carbide Ball Valves

Especially in industrialized countries such as the United States, Japan, Germany, France, Italy, Spain, and the United Kingdom, carbide?ball valves are widely used, with the variety and quantity of use still expanding. They are moving towards high temperature, high pressure, large diameter, high sealing, long life, excellent regulatory performance, and multifunctional direction. Their reliability and other performance indicators have reached a high level, and they have partially replaced gate valves, globe valves, and throttle valves. With the technological progress of carbide?ball valves, they will have broader applications in the foreseeable future, especially in oil and natural gas pipelines, refining and cracking units, and nuclear industry. In addition, in medium and large-caliber, medium and low-pressure fields in other industries, carbide?ball valves will also become one of the dominant types of valves.

carbide?ball valves are suitable for double-position adjustment, high sealing performance requirements, fast opening and closing (1/4 turn), high pressure drop, small operating torque, low flow resistance, and erosion in pipeline systems or vaporization.
In pipelines with certain corrosive media.
In low-temperature devices or high-temperature and high-pressure pipeline systems.
Full-bore welded carbide?ball valves can be used in petroleum pipelines and natural gas pipelines buried underground.
Specially designed V-shaped carbide?ball valves also have certain adjustment functions.

Assembly of carbide?Ball Valves and Valve Seats

1.Ball Processing

The core component of a ball valve is the sphere, so ball processing is the most critical part of ball valve manufacturing. Common ball processing materials include copper, iron, stainless steel, etc., and processing techniques include forging, casting, etc. The production of ball valve balls requires multiple processes such as rough machining, finishing, surface treatment, and carbidespraying to meet production requirements.

2.Valve Body Casting

The valve body of a ball valve is usually made of cast steel or forged steel. Casting methods include sand casting, pneumatic mold casting, etc. Before casting, mold design, casting process, and procedures need to be formulated, and strict material selection and quality inspection are required to ensure the reliability and durability of the valve body.

3.Stem Processing

The stem is the connecting part between the ball and the actuator of the ball valve, so the processing and production of the stem are very important. Chromium-molybdenum alloy steel is commonly used for stem materials, and processing techniques include turning, grinding, etc. During stem processing, attention should be paid to accuracy and smoothness, and heat treatment and surface treatment should be carried out to improve corrosion resistance.

4.Seal Installation

The seals of a ball valve include valve seats, sealing gaskets, etc., which must be installed in the appropriate positions to ensure the sealing performance of the ball valve. When installing seals, correct assembly and installation operations should be performed according to the structure and requirements of the ball valve.

5.Testing

After the manufacturing of the ball valve is completed, testing is required to verify its good performance and reliability. Testing includes hydrostatic testing, airtightness testing, pressure resistance testing, etc. Only ball valves that pass the test can be put into use.
In summary, the manufacturing process of ball valves includes multiple steps such as ball processing, valve body casting, stem processing, seal installation, and testing. Each step requires strict manufacturing standards and control to ensure the quality and performance of ball valves.

結(jié)論

High-precision customized production and processing of carbide valve seats, valve assemblies, and carbide ball valves are used in oil drilling, deep-sea drilling pump valve balls, and seats, which are critical supporting parts in oil pump equipment. The use of valve seats and petroleum valve heads is mainly for petroleum equipment production purposes.Meteou specializes in the technical and professional production of carbide products, providing customized carbide valve seats, petroleum valve balls, petroleum valve assemblies, and other series of wear-resistant and corrosion-resistant carbide parts tungsten steel fittings that meet the requirements of petroleum equipment usage.

Selection of carbide?Brazing Materials

The brazing materials for tungsten carbide and steel brazing are divided into three categories: high-temperature brazing materials, room-temperature brazing materials, and low-temperature brazing materials according to their melting points and brazing temperatures.

High-temperature Brazing Materials

Brazing materials with a brazing temperature above 1000°C are called high-temperature brazing materials, such as purple copper and 106 brazing materials, etc. Medium-temperature brazing materials have a brazing temperature between 850 and 1000°C, such as H62 and H68 brass brazing materials, etc. Low-temperature brazing materials refer to brazing materials with a brazing temperature between 650 and 850°C, such as B-Ag-1 and L-Ag-49 silver-containing brazing materials.

Room-temperature Brazing Materials

Purple copper brazing materials have a high brazing temperature and low weld seam strength, and are mostly used for vacuum brazing. Pure copper brazing materials have a single-phase structure, are relatively easy to control the brazing temperature, have good wetting ability for various types of carbides, good plasticity, and are the cheapest. The shear stress of purple copper brazing weld seam is about 150MPa, and it can be used below 400°C. The brazing temperature of H68 brass is much lower than that of purple copper, but because of its low weld seam strength, it is not commonly used. The melting point and brazing temperature of H62 brass are relatively low, and the weld seam has certain room temperature strength, making it a commonly used carbide?brazing material. It is generally used for carbide?tools under medium and small loads. When high temperature strength of the weld seam or small welding area is required, 105 brazing material should be used.

Low-temperature Brazing Materials

L-Ag-49 low-temperature silver brazing material is widely used abroad because of its low melting point (690-710°C), good wetting ability for tungsten carbides, and advantages such as convenient brazing and low stress. When necessary, purple copper sheets can be used as compensating shims, which can almost completely eliminate brazing stress and prevent brazing cracks. It can be used for brazing some easily cracked carbides or some large brazing surface carbide tools. Since the workpiece brazed with L-Ag-49 silver brazing material will rapidly decrease in weld seam strength as the operating temperature increases, the working temperature of the workpiece brazed with L-Ag-49 brazing material should be limited to below 200°C. The brazing fluxes used in conjunction with L-Ag-49 brazing materials contain more fluorides and chlorides, requiring higher cleaning requirements after welding, otherwise, surface corrosion of the workpiece may occur due to inadequate cleaning.

Ultra-low-temperature Brazing Materials

B-Ag-1 brazing material is an ultra-low-temperature silver brazing material with a melting point around 600-610°C, which can further reduce the residual stress of tungsten carbide joint and can also be used for brazing some easily cracked workpieces with purple copper sheets as compensating shims. Due to the ultra-low melting point of B-Ag-1 silver brazing material and its good wetting ability to tungsten carbide, it is also suitable for brazing certain diamond tools such as large diamond saw blades. However, the price of B-Ag-1 silver brazing material is high, and its high-temperature strength is low, so it is only suitable for use at temperatures below 150°C. The cadmium content in this brazing material is 24%, which is easy to evaporate at high brazing temperatures, harmful to human health. In addition to controlling the brazing temperature during brazing, exhaust devices should also be installed at the brazing operation site. After brazing, attention should also be paid to cleaning the workpiece thoroughly to prevent corrosion of the workpiece.

Selection of Brazing Flux

The function of brazing flux is to reduce the oxides on the surface of the shank and tungsten carbide, enabling the brazing material to wet the metal surface to be brazed effectively. Generally, the melting point of brazing flux is at least 100°C lower than that of the brazing material, with good fluidity and low viscosity. The melted brazing flux during brazing serves to protect the brazing material and brazing surface, while also acting to reduce oxides.

The main requirements for carbide?brazing flux are as follows:

1.The flux should exhibit good wetting ability on both the carbide?to be brazed and the steel substrate, ensuring that it possesses good fluidity and penetrability.

2.One of the characteristics of carbide?use is its high red hardness, so it’s crucial to ensure that the brazed weld seam has sufficient strength at both room temperature and high temperatures.

3.The melting point of the flux should be as low as possible to minimize brazing stress and prevent cracking. However, the melting point of the flux should be at least 300°C higher than the working temperature of the weld seam to ensure that the tool can function normally at high cutting speeds.

4.The flux should not contain elements with low evaporation points to avoid affecting joint quality during brazing heating or posing health risks.

Preparation Before Vacuum Brazing

1.Prior to vacuum brazing, check whether the tungsten carbide has cracks, bends, or uneven surfaces. The brazing surface must be flat. If the brazing surface is spherical or rectangular, it should conform to certain geometric shapes to ensure good contact between the alloy and the substrate, thus guaranteeing brazing quality.

2.Perform sandblasting treatment on the carbide. If sandblasting equipment is not available, the oxide layer and black grade letters on the brazing surface can be removed by holding the tungsten carbide by hand and grinding it on a rotating green silicon carbide wheel. If the oxide layer on the brazing surface of the carbide is not removed, the brazing material will not wet the carbide easily. It has been verified that if there is an oxide layer or black grade letters on the brazing surface, sandblasting treatment should be carried out. Otherwise, the brazing material will not wet the carbide easily, and black letters will still appear in the brazing seam, reducing the brazing area and causing brazing defects.

3.When cleaning the brazing surface of the carbide, it is best not to use chemical mechanical grinding or electrochemical grinding methods. Instead, wire cutting by electric spark erosion should be used. The processed tungsten carbide can then be sandblasted again or ground with a green silicon carbide wheel to remove the surface layer. The sandblasted carbide can be cleaned with gasoline or alcohol to remove oil stains.

4.Before vacuum brazing, carefully check whether the groove shape on the steel substrate is reasonable, especially for carbide grades prone to cracking and tungsten carbide workpieces with large brazing surfaces. Stricter requirements should be imposed. The grooves should also be sandblasted and cleaned to remove oil stains. When the cleaning volume is large, an alkaline solution can be boiled for 10-15 minutes. For multi-blade tools and complex gauges brazed with high frequency or immersed copper, it is best to boil them in a saturated borax water solution for 20-30 minutes, take them out to dry, and then carry out welding.

5.Before using the brazing material, wipe it clean with alcohol or gasoline and cut it into shape according to the brazing surface. When brazing general carbide cutting tools or molds, a brazing material thickness of about 0.4-0.5mm is suitable, and its size should be similar to the brazing surface. When using continuous nitrogen protection for brazing furnace heating, the brazing material can be appropriately increased. When brazing tungsten carbide multi-blade cutting tools, gauges, etc., the brazing area should be minimized. Generally, the brazing material can be cut to about 1/2 of the brazing surface. When the brazing technology is proficient, the brazing material can be reduced to 1/3 of the brazing surface or even smaller. Reducing the amount of brazing material can make the appearance of the welded workpiece more beautiful and facilitate grinding.

Vacuum Brazing Process

Uniform Heating of the Shank and carbide Inserts The correct vacuum brazing process for tungsten carbide tools plays a crucial role in welding quality. The heating rate significantly affects the quality of the weld. Rapid heating can cause cracks and uneven temperatures in the carbide inserts. However, heating too slowly can lead to surface oxidation, reducing joint strength.

During vacuum brazing of carbide tools, uniform heating of the shank and carbide inserts is one of the basic conditions to ensure welding quality. If the temperature of the tungsten carbide inserts is higher than that of the shank, the melted brazing material wets the carbide inserts but not the shank, leading to decreased joint strength. In this case, when shearing the alloy insert along the weld layer, the brazing material remains intact, detaching along with the alloy insert. Milling marks from the shank support surface can also be seen on the weld layer. Conversely, if the heating rate is too fast and the temperature of the shank is higher than that of the alloy inserts, the opposite phenomenon occurs.

Arrangement of Flux, Brazing Material, and tungsten carbide Inserts

The sequence and positions of flux, brazing material, and carbide inserts directly affect brazing quality. The correct arrangement method is as follows: place the brazing material on the groove, sprinkle flux, then place the carbide inserts, and sprinkle another layer of flux along the side weld seam on the top surface of the carbide inserts. This facilitates temperature control during brazing, reducing excess brazing material adhering outside the weld seam. It’s crucial to control the vacuum brazing temperature of the workpiece correctly. Excessive vacuum brazing temperature can cause weld seam oxidation and zinc evaporation from zinc-containing brazing materials.

Brazing Parameters

During vacuum brazing, maintain a vacuum degree of about 5 X 10-2 Pa. The heating rate is an important parameter during vacuum brazing, as excessive heating rate leads to a sharp drop in vacuum degree, which can cause oxidation of carbide and brazing materials. In production, the vacuum brazing process is as follows: increase the temperature from room temperature to 800°C at a rate of 10°C/min, hold for 30 minutes, then increase the temperature to the set temperature at a rate of 9°C/min, hold for 10 minutes, and then cool down with the furnace. The 800°C holding temperature ensures uniform heating of the base material. Increasing the temperature to the set temperature at a rate of 9°C/min ensures that the vacuum degree does not decrease significantly, and the short-term holding at the set temperature allows the brazing material to melt fully and prevents excessive evaporation of particulate magnesium in high vacuum.

Cooling Speed After Vacuum Brazing

The cooling speed after vacuum brazing is one of the main factors affecting brazing cracks. During cooling, instantaneous tensile stress occurs on the surface of carbide?inserts, and the tensile stress of carbide?is much lower than the compressive stress. Especially for carbide?grades such as YT60, YT30, and YG3X, which have large brazing areas and small matrices but large carbide?inserts, attention should be paid to the cooling speed after brazing. Usually, the post-welded workpiece is immediately immersed in lime or charcoal powder to cool slowly. This method is simple but does not control the tempering temperature. If conditions permit, the workpiece can be immediately placed in a furnace at 220-250°C for tempering for 6-8 hours after brazing. Low-temperature tempering can eliminate some brazing stress, reduce cracks, and prolong the service life of carbide?tools.

Cleaning After Vacuum Brazing

After vacuum brazing, the product can be polished with sandpaper and then polished with polishing paste. Post-brazing cleaning of well-brazed carbide?parts is necessary to remove residual flux around the weld seam. Otherwise, excess flux will clog the grinding wheel during tool sharpening, making grinding difficult. Residual flux after brazing can also corrode the weld seam and base material. Common cleaning methods include boiling the cooled workpiece in boiling water for about 1-2 hours, followed by sandblasting to remove residual flux and oxides adhering to the weld seam surroundings. Alternatively, the workpiece can be immersed in an acid bath for pickling (nitric acid concentration of 3%-5%) and washed with NaOH solution. The pickling time is about 1-4 minutes, followed by thorough rinsing in cold and hot water tanks.

Quality Inspection of Vacuum Brazed Products

The main inspection focuses on the quality of the brazed joint between the carbide?and the steel shank, as well as the presence of cracks in the carbide. A normal weld seam should be uniform without black spots, and the unfilled portion of the weld seam should not exceed 10% of the total length of the weld seam. The width of the weld seam should be less than 0.15mm. If the brazed blade is skewed and does not meet the drawing requirements, it should be re-brazed. The tendency for cracks in carbide?blades can be checked using the following methods:

1.After cleaning the tool with sandblasting, wash it with kerosene and then observe it with the naked eye or a magnifying glass. When there are cracks on the blade, obvious black lines will appear on the surface.

2.Prepare a solution by mixing 65% kerosene, 30% transformer oil, and 5% pine oil, and add a small amount of Sudan red. Immerse the pre-checked tools in this solution for about 10-15 minutes, then remove and rinse them with clean water. Apply a layer of kaolin clay, dry it, and then inspect the surface. If there are cracks on the tool, the color of the solution will be displayed on the white clay, which can be clearly seen with the naked eye.

概要

The characteristics of using carbide?tools in mining are large impact loads and vibrations, requiring the carbide?inserts to be firmly brazed with minimal brazing stress. The surface roughness of groove machining has a significant impact on the strength of the weld seam. The lower the roughness, the higher the strength of the weld seam (although lower roughness makes machining more difficult). Generally, a roughness of around Ra6.3 is sufficient. To obtain weld seams that are thin and uniform in appearance, the groove machining accuracy of carbide?gauges should be higher.

In conclusion, the vacuum brazing and quenching of cutter teeth are becoming increasingly common due to their high production efficiency, stable quality of brazed joints, and complete heating, brazing, and quenching in a vacuum environment, which avoids oxidation and decarburization of the cutter teeth. Therefore, the vacuum brazing and quenching process for cutter teeth will be more widely adopted.

The wear forms on valves

Based on the conditions and mechanisms of friction, wear can take various forms, with common types including abrasive wear, adhesive wear, fatigue wear, corrosive wear, and erosive wear.

Common parameters used to characterize material wear performance include wear volume, wear rate, wear depth, wear resistance, and relative wear resistance. The fundamental requirement for abrasion resistance is that the surface of the object must have high hardness (surface hardness should exceed the hardness of the abrasive). Additionally, it should exhibit good oxidation resistance at the operating temperature. The most effective way to control or minimize wear is to enhance material hardness and wear resistance.

Sintered tungsten carbide has high strength, a smooth surface finish, and a lower coefficient of friction compared to steel when used in conjunction with other materials. This significantly reduces contact surface frictional forces, effectively lowering operating torque.

Material features of carbide

Whole sintered carbide?is produced by high-temperature heating of a mixture of tungsten and carbon. The hardness of most tungsten carbides is very high, with microhardness second only to diamond. It has a melting point of 2870°C and a boiling point of 6000°C, with a relative density of 15.63 (at 18°C). It is resistant to decomposition at high temperatures and exhibits excellent oxidation resistance.

Field investigations indicate that tungsten carbide demonstrates wear resistance in situations such as abrasive wear, erosive wear, and abrasion, which is about 100 times higher than that of tool steel, stainless steel, iron, and brass. It has 2-3 times the rigidity of steel and 4-6 times the rigidity of cast iron and brass, with impact resistance similar to that of quenched tool steel.

The reason carbide is needed in valves

In conditions involving high temperature, high pressure, strong corrosion, and slurries or powders with solid particles such as in gasification and polycrystalline silicon, the sealing surfaces of conventional hard-sealed ball valves, V-port control valves, coal powder control valves, butterfly valves, and slide valves use carbides as the sealing materials for the valve disc and seat. However, due to the limitations of the sprayed tungsten carbide coating—thickness <2mm, hardness <60HRC, and coating adhesion to the substrate <1000psi—the spraying process is typically conducted under harsh conditions at temperatures as high as 10000°C. Valve lifespans are challenging to guarantee for 10,000 cycles, making it difficult to meet the long-term stable production requirements of systems handling coal chemical slurries and polycrystalline silicon powders.

On the other hand, the strength of sprayed tungsten carbide mainly relies on the base material, and when the coefficients of thermal expansion of the two materials are significantly different, the usage is limited by temperature and cannot exceed 450°C. The valve performance has seen significant improvements with the adoption of integral sintered carbides for the valve disc and seat in new types of hard-sealed ball valves (Figure 1), V-port control valves (Figure 2), coal powder control valves (Figure 3), butterfly valves (Figure 4), and slide valves, addressing these challenges.

Fig1 Sealing ball valve

Fig2 control valve

(1) High Hardness: With a hardness greater than 80HRC, it can withstand the high-speed scouring of multiphase particle media such as water-coal slurry, coal powder, and silicon powder.

(2) High-Temperature Resistance: Capable of prolonged operation at temperatures up to 750°C, it is not limited by temperature in terms of strength, adhesion, and thermal expansion. This completely meets the requirements of high-temperature conditions, such as those encountered in coal chemical processes.

(3) High Pressure Resistance: The transverse fracture strength of integral sintered tungsten carbide reaches 4000MPa, more than 10 times the strength of conventional steel. It can operate long-term under working pressures up to 25MPa.

(4) Corrosion Resistance: Integral sintered tungsten carbide exhibits stable chemical properties. It is insoluble in water, does not react with hydrochloric acid and sulfuric acid, and is not dissolved even in aqua regia. This corrosion resistance satisfies the special requirements of industries such as coal chemical processing.

Fig3 Coal powder control valve

Fig4.?Butterfly valve

(5) Wear Resistance: The high hardness and stability of integral sintered tungsten carbide ensure excellent anti-wear properties for sealing components. This meets the special wear requirements of media such as coal powder and organosilicon (silicon powder particle hardness is 62HRC).

(6) Erosion Resistance: Conventional valves with sprayed tungsten carbide coatings on sealing surfaces often suffer severe erosion, exhibiting honeycomb patterns within a month under conditions of 250°C and losing functionality completely. In contrast, V-port control valves and coal powder control valves, which use integral sintered tungsten carbide as control components, have a lifespan of 12 months under 450°C (other conditions remaining the same). Disc valves and slide valves, subjected to more than 300,000 switching cycles, fully meet the long-term operational requirements of industries such as coal chemical processing for 8000 hours.

(7) High-Temperature Flexibility: Both the ball and seat are made of integral sintered carbides, with coefficients of thermal expansion ranging from 1/3 to 1/2 of conventional steel. This effectively prevents the common issue of valve sticking at high temperatures, ensuring excellent operational performance under high-temperature differential conditions.

(8) Low Friction: The use of sintered carbide?anti-wear pads not only extends the high-temperature lifespan of the pads but, due to their lower friction coefficient, typically only 1/3 to 1/2 of conventional paired materials. This significantly reduces frictional forces between components, lowering valve operating torque.

結(jié)論

Integral sintered carbide?possesses high strength, high hardness, a high melting point, stability, a low friction coefficient, wear resistance, erosion and cavitation resistance, and corrosion resistance. Manufacturing wear-resistant valve sealing components for demanding operating conditions has enhanced the applicability of valves, expanded their range of use, prolonged their operational lifespan, ensured various performance indicators, and met the development needs of the chemical industry.

As the competition in the steel product quality and price market intensifies, steel companies continuously upgrade their equipment technology to enhance rolling mill speeds. Simultaneously, reducing downtime and further improving the effective operation rate of rolling mills have become crucial concerns for steel engineers. The adoption of rolls made from materials with higher rolling life is one of the essential means to achieve this goal.

Classification of carbide rolls

carbide?rolls can be classified into integral carbide?rolls and composite carbide?rolls based on their structural forms.

Integral carbide?rolls are widely used in the pre-finishing and finishing stands of high-speed wire rolling mills, including fixed reduction stands and pinch roll stands.

Composite carbide?rolls are made by combining carbide?with other materials and can be further divided into carbide?composite roll rings and integral carbide?composite rolls. carbide?composite roll rings are installed on the roll shaft, while integral carbide?composite rolls have the carbide?roll ring directly cast into the roll shaft, forming a single unit. The latter is applied in rolling mills with higher loads.

Performance of carbide?Roll Rings: The performance of carbide?rolls is influenced by the content of the bonding phase metal and the size of the tungsten carbide particles in the matrix. Different levels of bonding agent content and corresponding tungsten carbide particle sizes result in different grades of carbide. Series of carbide?grades have been developed for various rolling mill stands. Tungsten carbide typically constitutes 70% to 90% of the total mass composition in carbide?rolls, with an average particle size ranging from 0.2 to 14 μm. Increasing the metal bonding agent content or enlarging the tungsten carbide particle size can reduce the hardness of the carbide?while enhancing its toughness. The bending strength of carbide?rolls can exceed 2200 MPa, impact toughness can reach (4–6) × 106 J/m2, and the Rockwell hardness (HRA) ranges from 78 to 90.

Quality standard elements for carbide roll rings

The quality standards for tungsten carbide rolls include material porosity, WC grain size, total carbon and free carbon content, density, hardness, magnetic saturation intensity, coercivity, bending strength, impurity content, as well as the processing precision and surface roughness of the rolls. Each indicator reflects the quality of the roll and predicts its performance. Factors influencing the quality of the rolls include the dispersion, particle size, and size distribution of WC powder and Co powder in the mixture, as well as total carbon, free carbon, oxygen, iron content, etc. The type and quantity of adhesive used for molding, the temperature and time for degreasing, and the temperature, time, and atmosphere for sintering are also crucial.

Moreover, the precision of the grinding machine used for roll processing, the quality of the diamond grinding wheel, and other factors can impact the quality of the rolls. In 2009, Meetyou?cemented carbide?Co., Ltd. obtained ISO9001 international quality assurance system certification, ensuring the provision of high-quality and stable tungsten carbide roll ring products to customers.

New tech for WC roll rings

LGM Technology

WC roll rings undergo high temperatures, rolling stresses, thermal corrosion, and impact loads during the hot rolling process. Consequently, they exhibit poor wear resistance and are prone to fracturing during use. Building upon conventional carbide?roll ring materials, we have developed a Lubrication Gradient Material (LGM) roll ring by introducing Lubrication Gradient Material (LGM), a lubrication-resistant gradient material.

This technology involves adding sulfur and oxygen to conventional carbide?materials, forming stable gradient metal oxides and metal sulfides (Co3O4 and CoS, respectively) on the surface of the metal substrate. Both Co3O4 and CoS demonstrate excellent lubrication and wear resistance properties. Industrial tests of LGM roll rings have shown that the sulfides and oxides in the gradient material can reduce the friction coefficient during rolling, significantly improving the lubrication performance of the roll ring under high-temperature and high rolling force conditions. This leads to a reduction in the generation of transverse cracks, and the lifespan of LGM roll rings is 1.5 times that of conventional carbide?roll rings. Moreover, it decreases the amount of grinding and the frequency of roll changes, resulting in significant economic benefits.

Cast In Carbide (CIC) Composite Carbide Roll Ring

To meet the demands of modern rolling production, a new type of carbide?composite roll ring, known as Cast In Carbide (CIC) composite carbide?roll ring, has been developed. This technology involves casting the carbide?ring and ductile iron inner sleeve together. The connection between the roll ring and the roll shaft is key-linked. In this connection method, the outer layer of the composite roll ring, composed of carbide?material with extremely high hardness and excellent wear resistance, bears the rolling force, while the inner layer, made of ductile iron with good strength and toughness, transfers torque.

The development of the Cast In Carbide (CIC) composite roll ring technology represents a new combination of powder metallurgy and casting technology. It signifies a significant advancement in the application of composite wear-resistant materials in roll rings.

Composite WC Roll Ring

This technology involves combining a carbide?ring with a steel matrix containing added Ni and Cr powder through powder metallurgy. The key process involves first pressing and sintering the carbide?powder into a ring, followed by molding and sintering with the selected steel matrix powder. There is a strong metallurgical connection between the carbide?and the steel base. The crucial elements of this process include maintaining sintering temperatures between 1100 to 1200 ℃ and pressure conditions of 100 to 120 MPa. The sintered blanks undergo processes such as rough turning and stress relief, followed by precision turning and grinding for the final shaping.

By selecting appropriate base materials, coupled with advanced processes and proportions, it is possible to minimize residual stress between the carbide?and the steel matrix in the composite roll ring.