The tungsten carbide bush also known as tungsten steel bushing, is a kind of component that protects the equipment, using the bushing, can effectively reduce the wear between the punch or bearing and the equipment and achieve a guiding role. The tungsten carbide bushing is mainly applied for stamping, with the features of wear resistance and impact resistance.
Excellent Characteristics Of Tungsten Carbide Bush
The tungsten carbide bushing has a series of excellent performances with high hardness, good concentricity, good perpendicularity, high wear resistance, high toughness, heat resistance and corrosion resistance. It has greatly improved the service life of the mold and has reduced the cost of molding manufacturers.
1. Advanced molding techniques can be adapted to produce a variety of shapes for carbide bush.
2. Small deformation with high accuracy.
3. High chemical stability.
4. High bending strength.
The Machining Method Of Tungsten Carbide Bush
The tungsten carbide bushing adopts CNC precision angles, inner hole grinder, precision surface grinding machine, precision internal and external round grinder, centerless grinder. The inner hole is grinded many times and polished into a mirror. The most suitable tool material for machining carbide bushing is a PCBN cutting tool.
The spray welding technology is adopted sometimes to increase the durability and service life of cemented carbide bush, which can reach HRC60 with better wear resistance. But the carbide bushing after welding needs turning machining to ensure the requirements for size and accuracy of the drawings.
Wide Applications Of Tungsten Carbide Bush
In the industrial fields, the application of cemented carbide bushing is very wide. The tungsten carbide sleeve is related to the role and purpose of its application environment in practical applications. In the valve application, the bushing should be mounted in the stem cover trap to reduce the valve leakage, for sealing. In the bearing application, the carbide bushing is adapted to reduce the wear between the bearing and the shaft seat, avoiding the clearance increasing between the shaft and the hole.
The tungsten carbide bushing is mainly used in the fields of stamping and stretching. The widely used tungsten carbide as tool material, includes a turning tool, a milling cutter, a planer, a drill bit, a boring cutter, etc, for cutting cast iron, non-ferrous metals, plastic, chemical fiber, graphite, glass, stone and ordinary steel, which can also be used for cutting materials which are difficult for machining, such as heat resistant steel, stainless steel, high manganese steel, tool steel.
In terms of stamping dies, the tungsten carbide bush is widely used because of high wear resistance, good finishing and no needing frequent replacement, thereby reaching the higher usage rate of equipment and personnel.
The carbide bushing has excellent chemical stability, which is widely applied in the industries of petrochemicals, submersible oil pumps, slurry pumps, water pumps, centrifugal pumps. With the increase in oil production, the shallow surface of the oil is reduced, In order to ensure oil usage, people have gradually developed to extract from the large deep well, but the difficulty of mining gradually increases and the mining components have high requirements for wear resistance, corrosion resistance or impact resistance. The tungsten carbide bush used as the wear-resistant component in the oil machinery, has high hardness, excellent wear resistance and a high degree of surface finishing, satisfying the use requirements for a daily and special performance in the oil machinery industry.
High performance tungsten carbide bush is a type of protective component with wide industrial applications, with high hardness, superior wear resistance, high strength, high toughness, heat resistance and corrosion resistance.
With the rapid development of the steel industry, in order to improve the output of steel and improve the utilization rate and productivity of the rolling mill, reducing the shutdown times of the rolling mill, adopting a tungsten carbide roller with long service life is an important method. For the rolling of wire, rod, tungsten carbide roller replacing conventional cast iron rolls and alloy steel rolls, has exhibited a lot of superiority, with the continuous development of roller manufacturing techniques and use technology, will continue to expand the applications of carbide roller rings and they will become more important in rolling machining with wider applications.
What Is The Tungsten Carbide Roller
The cemented carbide roller, also known as cemented carbide roller ring, refers to a roll made of tungsten carbide and cobalt through the powder metallurgical method. The tungsten carbide roll has two types of integral and is combined. It has superior performance, stable quality, high processing accuracy with excellent wear resistance and high impact resistance. Carbide roller is widely used for the rolling of the rod, wire rod, threaded steel and seamless steel pipe, which greatly improve the operation efficiency of the rolling mill.
High Performance Of Tungsten Carbide Roller
The carbide roll has a high hardness and its hardness value varies very small with temperature. The hardness value under 700°C is 4 times higher than the high-speed steel. The elastic modulus, the compressive strength, the bending strength, the thermal conductivity are also 1 times higher than the tool steel. Since the thermal conductivity of the cemented carbide roll is high, the heat dissipation effect is good, so that the surface of the roll is under high temperature for a short time and thus the high-temperature reaction time of harmful impurities in the cooling water and the roll is shorter. Therefore, the tungsten carbide rollers are more resistant to corrosion and cold and hot fatigue than tool steel rollers.
The performance of the tungsten carbide rollers is related to the content of the bond metal phase and the size of the tungsten carbide particles. The tungsten carbide is about 70% to 90% of the total composition and the average particle size is μm of 0.2 to 14. If the metal bond content is increased or increases the particle size of tungsten carbide, the hardness of the cemented carbide decreases and the toughness is improved. The bending strength of the tungsten carbide roller ring can reach 2200 MPa. The impact toughness can be reached (4 ~ 6) × 106 J / ㎡, and the HRA is 78 to 90.
The tungsten carbide roller can be divided into two types of integral and composite according to structural form. Integral tungsten carbide roller has been widely used in pre-precision rolling and finishing stand of high-speed wire rolling mills. The composite cemented carbide roller is composited through tungsten carbide and other materials. The composite carbide rollers are cast directly into the roller shaft, which is applied to a rolling mill with a heavy load.
Machining Method Of Tungsten Carbide Roller And Selection Rules Of Its Cutting Tools
Although the tungsten carbide material is better than other materials, it is difficult to machining due to extreme hardness and it is more widely used in the steel industry.
1.Concerning hardness
When machining the tungsten carbide rolls with a hardness smaller than HRA90, select HLCBN material or BNK30 material tool for a large amount of turning and the tool is not broken. When machining the carbide roller with a hardness of greater than HRA90, a CDW025 diamond tool is generally selected or grinding with a resin diamond grinding wheel. Generally, the higher the hardness is, the material is crisper, so it is more cautious for cutting of high hardness materials and the exact reserved finishing grinding allowance.
2.The machining allowance and processing methods
If the outer surface is machined and the allowance is large, generally adopts the HLCBN material or BNK30 material to be roughly processed, then grinding with a grinding wheel. For small machining allowance, the roller can be grinded directly with a grinding wheel or profiling processed by diamond tools. In general, cutting alternative grinding can improve machining efficiency and the cutting method is more conducive to improving the production lead time.
3.Passivating treatment
When machining a cemented carbide roller, passivating treatment is necessary to reduce or eliminate the sharpness value, for the purpose of flatness and smoothness with high durability. However, passivation treatment should not be too large, because the contact surface of the tool blade is large after passivation and the cutting resistance is also increased, which is easy to cause a crack, damaging the workpiece.
What Should Be Paid Attention To For The Production And Use Of Tungsten Carbide Roller
In recent years, the tungsten carbide rollers have gained more and more extensive applications in steel production with their excellent performance. However, there are still some issues in the production and use of cemented carbide rolls.
1. Develop a new type of roller shaft material. Conventional ductile iron roller shafts will be difficult to withstand greater rolling power and deliver a larger torque. So high-performance cemented carbide composite roll shaft materials must be developed.
2. During the manufacturing process of carbide rollers, the residual thermal stress caused by thermal expansion between the inner metal and outer cemented carbide must be minimized or eliminated. The carbide residual thermal stress is a key factor affecting the life of the roller. Therefore, the coefficient of thermal expansion difference between the selected inner metal and outer cemented carbide should be as small as possible, while considering eliminating the residual thermal stress of the carbide roller ring through heat treatment.
3. Due to the differences in the rolling force, rolling torque, heat transfer performance on different racks, the different racks should adopt different grades of carbide roller rings to ensure a reasonable match of the strength, hardness, and impact toughness.
The tungsten carbide is an alloy which has the main component of powders including tungsten carbide, titanium carbide and metal powder such as cobalt, nickel, etc, as an adhesive, obtained through the powder metallurgical method. It is mainly used to make high-speed cutting tools and hard, tough material cutting edges, and high wear parts for fabrication of cold dies, measuring tools.
Mechanical And Physical Properties Of Tungsten Carbide
1.Wear resistance
The wear resistance of the tungsten carbide is its most important feature. In practical applications, carbides are 20-100 times longer than some wear-resistant steel alloys.
2.Bending resistance
The sintered carbide has a high elastic modulus and the smallest bend is obtained when subjected to bending force.
3.Corrosion resistance
It is usually used in many chemical and corrosive environments because carbides are typically chemically inert.
4.Torsional strength
The amount of torsion is two times than the high-speed steel and the carbide is the preferred material for high-speed operation applications.
5.Compressive strength
Some grades of cobalt carbide and cobalt have perfect performance under ultra-high pressure and is very successful in pressure applications of up to 7 million kPa.
6.Toughness
Cemented carbide grades with high binder content have excellent impact resistance.
7.Low temperature wear resistance
Even at an extremely low temperature, the carbide remains good to wear resistance and provides relatively low friction coefficients without using a lubricant.
Applications Of Tungsten Carbide
Cutter tool
Tungsten carbide cutter tool is the widest application, used for making lathe tool, milling cutter, planner tool, drilling bit, etc. Among them, the tungsten cobalt carbide is suitable for black metal, non-ferrous metals, processing of non-metallic materials, such as cast iron, cast brass, colloidal wood, etc. Tungsten titanium cobalt is suitable for long chip processing of steel and other black metals. In the same alloy, what has more cobalt content suitable for rough machining, what has less cobalt content suitable for fine machining.
Mold material
The cemented carbide is mainly used for cold wire drawing dies, cold stamping dies, cold extrusion dies, and other cold work molds.
Under the wear-resistant working conditions of the impact or strong impact, the tungsten carbide dies are required to have good anti-polishing toughness, fracture toughness, fatigue strength, bending strength, and good wear resistance.
In general, the relationship between the wear resistance and toughness of the carbide is contradictory, the increase in wear resistance will result in a decrease in toughness, and the increase in toughness will inevitably lead to a decrease in wear resistance. Therefore, when choosing a tungsten carbide grade, it is necessary to meet specific usage requirements based on the processing objects and machining conditions.
If the selected grade is easy to produce early cracks and damage, it is advisable to use the grade with high toughness. If the selected grades are easily damaged as the wear, it is appropriate to choose a grade with a higher hardness and better wear resistance.
Measuring tool and wear parts
The tungsten carbide is used in the easy to wear surface inlay and parts of the measuring tool, grinding machine precision bearing, the wear parts such as guide plate and guide rod of centerless grinder, lathe center.
Heat Treatment Of Tungsten Carbide
The hear treatment process of tungsten carbide can be divided into four basic stages
1.Removal of the molding agent and the pre-sintering
In the initial stage of sintering, the molding agent gradually decomposes or vaporizes, excluding the sintered body, while at the same time, molding agents carburize sintering and the amount of carbon will vary depending on the type, quantity and the sintering process. The powder surface oxide is reduced, and hydrogen can reduce oxides of cobalt and tungsten at a sintering temperature. When the reaction between carbon and oxygen is not strong, the contact stress between the powder particles is gradually eliminated. The bonding metal powder begins to generate reply and recrystallization and the surface diffusion begins to occur. The strength of the block is improved.
2.The solid phase sintering stage (800°C - eutectic temperature)
In the presence of the liquid phase, in addition to the process of continuing the previous stage, solid-phase reactions and diffusion exacerbating with plastic flow enhancement, and the sintered body appears obvious contraction.
3. Liquid phase sintering stage (eutectic temperature - sintering temperature)
When the liquid phase of the sintered body occurs, the contraction is quickly completed and then a crystallization transition is generated. The basic organization and structure of the carbide are formed.
4.Cooling stage (sintering temperature - room temperature)
At this stage, the organizational and phase components of the tungsten carbide have certain changes with the different cooling conditions, which can utilize this feature, heat treatment of the cemented carbide will improve its physical-mechanical performance.
High performance tungsten carbide has excellent mechanical and physical properties including high wear resistance, corrosion resistance, bending strength, torsional strength, etc, widely used for the making of cutter tools, cold mold, wear parts, etc. The article also briefly introduces the four basic stages of tungsten carbide heat treatment which can improve physical mechanical performance of the cemented carbide.
Tungsten carbide precision part machining technology is more and more widely adopted. It is essential and important in the precision part factory. The article mainly introduces useful knowledge about carbide precision part processing, such as four preparation work, heat treatment of the precision parts.
Four Preparations Must Be Done For Machining Tungsten Carbide Precision Part
There are three preparation stages when performing carbide precision parts machining.
1.Preparation stage
Before the precision machining of tungsten carbide, you need to analyze the pattern of processing parts, then determine the machining scheme, such as a process, selecting machine tool, processing cutting volume, tool, fixture, etc, and calculate the coordinate value of the tool path. It is worth spending some time for these necessary preparations, which can make your tungsten carbide parts machining are more smoothly completed.
2.Programming stage
After getting the process route and drawings, we need to write a CNC machining program language describing the processing based on the processing technology information, which can be identified by the system. Do a good job in programming, which isone of the key steps for precision parts machining.
3. Machining stage
When the program is executed, the machine tool system decodes, registers, and calculates the program, and sends a motion command to the machine servo mechanism, driving the moving parts of the machine tool automatically completing the precision parts processing.
The above three preparation stages are the indispensable steps before processing precision parts, which is a process from the drawing to the machining.
Points For Attention In Heat Treatment Of Tungsten Carbide Precision Part
In order to improve the performance of tungsten carbide precision parts, material cutting performance and eliminate the internal stress of the workpiece, some heat treatment procedures should be arranged in the machining process.
1. Preparatory heat treatment
The purpose of pre-heat treatment is to improve the cutting performance of the material, eliminate residual stress during blank manufacturing. Commonly used methods include annealing, normalizing.
2. Eliminate residual stress
Since the internal stress generated during the fabrication of the blank will cause the workpiece to deform and affect the machining quality, heat treatment must be arranged to eliminate residual stress. The best arrangement of the heat treatment for eliminating residual stress is after rough machining and before fine finishing. For parts that do not require high precision, annealing is usually performed before the blank enters the workshop to eliminate residual stress. For high-precision cemented carbide parts, such as precision screws, precision spindles, multiple heat treatments should be arranged to eliminate residual stress, and even ice-cold treatment is often used to stabilize size.
3.Final finish
The purpose of final processing is to increase the strength, surface hardness and wear resistance and is usually performed prior to grinding of tungsten carbide precision parts. Commonly used are quenching, carburizing, nitriding and carbonitride.
Therefore, in the tungsten carbide part machining, in order to improve the mechanical properties of the precision parts, heat treatment is essential, so that the processing quality conforms to the product requirements.
Cutting is one of the common methods used in a tungsten carbide rod, carbide sheet and cemented carbide wire. For cutting the material of 1 mm or less, diamond ultra-thin cutting pieces are commonly used for machining.
The diamond resin matrix cutting piece, wherein the outer ring belt is a resin binding agent abrasive working layer, and the central portion is a high-strength metal, mostly for medium, large cutting slots and cutting.
During the tungsten carbide machining, the cutter tool itself must be higher than the hardness of the machined workpiece. At present, the cutting tool materials for turning tungsten carbide parts are mainly made of high-hardness high-resistant non-metallic adhesive CBN and the diamond PCD.
1. The tungsten carbide components which have a hardness of less than HRA90, select the BNK30 material CBN tool to carry out a large amount of turning and the tool is not broken. The carbide components which have a hardness greater than HRA90 generally select CDW025 Material PCD cutter tool or grinding with a diamond grinding wheel adopting a resin binding agent.
2.To process R3 groove or more of the carbide precision parts, for large machining allowance, generally adopts BNK30 CBN tool for roughing processing, then grinding with grinding wheels. For small processing margins, the grinding can be done directly with wheels , or adopting PCD tool for flush processing.
3.When the crescent groove rib of the tungsten carbide roller is processed, the CDW025 diamond carving milling cutter tool also known as rotary milling cutter is adopted.
For the milling process of carbide parts, according to customer needs, CVD diamond coating milling cutters and diamond insert milling cutter can be provided to perform tungsten carbide precision parts machining, which can replace electrolytic corrosion technology and electric spark process, improving production efficiency and product quality, such as a CVD diamond coating milling cutter to micro-milling the cemented carbide, and the surface roughness can reach 0.073 μm.
What Are The Factors Affecting The Machining Accuracy Of Tungsten Carbide Part
1. Machine tool error
The machine tool error refers to the manufacturing, installation errors and wears of machine tools. It mainly includes guide error of machine tool guide rail, machine tool spindle rotation error, transmission error.
2. Machining principle error
The machining principle error refers to an error generated by adopting the approximate blade profile or approximate transmission relationship for machining. The principle error often occurs in a thread, gear, complex surface machining.
3. Residual stress inside the workpiece
The residual stress is generated during the blank manufacturing, heat treatment process, cold strengthening and cutting processes.
4.Machining environment
The machining site often has many small chips. If there is a part locating surface or location of locating hole, which affects the processing accuracy of the parts, for high-precision processing, some small particles will affect the accuracy.
5.Manufacturing error and wear of the fixture
The error of the fixture is mainly referred to as the manufacturing error of positioning elements, tool guiding elements, an indexing mechanism. The fixture is assembled, with the relative dimensional error between the various components and worn on the working surface during use.
6.Manufacturing errors and wear of tools
The influence of tool error on machining accuracy varies according to the type of tools.
7.Thermal deformation of the processing system
During the machining process, due to the internal heat source, such as cutting heat, frictional heat or an external heat source such as temperature, heat radiation, the processing system is modified, thereby affecting the machining accuracy. In large workpieces and precision machining, the processing error caused by the thermal deformation of the processing system accounted for 40% -70% of the total processing error.
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