Carbide roller rings (also called tungsten carbide roller rings) refer to rollers made of tungsten carbide and cobalt by powder metallurgy. Carbide rollers are available in two types: integral and combined. They have superior performance, stable quality, high product processing precision, good wear resistance and high impact resistance.
As the market competition for steel product quality and price becomes increasingly fierce, steel enterprises are constantly updating their equipment and technology and continuously improving the rolling speed of rolling mills. At the same time, how to reduce the number of mill shutdowns and further improve the effective operation rate of rolling mills has become an important topic of concern to steel rolling engineers. Using roll materials with longer rolling life is one of the important means to achieve this goal.
Carbide rollers have high hardness, and their hardness value changes little with temperature. The hardness value at 700℃ is 4 times that of high-speed steel; and the elastic modulus, compressive strength, bending strength, and thermal conductivity are more than 1 times higher than tool steel.
Due to the high thermal conductivity of carbide rollers, the heat dissipation effect is good, so that the roller surface is at high temperature for a shorter time, and thus the high-temperature reaction time of the roller with harmful impurities in the cooling water is shorter. Therefore, carbide rollers are more resistant to corrosion and cold and hot fatigue than tool steel rollers.
Cemented carbide rollers are developed on the basis of cemented carbide tools. They are a kind of metal ceramic tool material prepared by powder metallurgy method with refractory metal compounds (WC, TaC, TiC, NbC, etc.) as the matrix and transition metals (Co, Fe, Ni) as the bonding phase.
It has a series of excellent properties such as high hardness, high red hardness, and high wear resistance. Sometimes, in order to obtain corrosion resistance, a certain amount of nickel, chromium and other elements are added accordingly.
The performance of cemented carbide rolls is related to the content of the bonding phase metal and the size of the matrix phase – tungsten carbide particles.
Different binder contents and corresponding tungsten carbide particle sizes form different cemented carbide grades. A series of cemented carbide grades suitable for different batches have been developed. Tungsten carbide accounts for about 70% to 90% of the total mass of cemented carbide, and its average particle size is 0.2 to 14μm. If the metal binder content is increased or the particle size of tungsten carbide is increased, the hardness of the cemented carbide decreases and the toughness increases. The bending strength of cemented carbide rolls can reach more than 2200 MPa, the impact toughness can reach (4 to 6) × 106 J/m2, and the Rockwell hardness HRA is 78 to 90.
According to the structural form, cemented carbide rolls can be divided into two types: integral cemented carbide rolls and composite cemented carbide rolls.
Integral cemented carbide rolls have been widely used in pre-finishing and finishing stands (including sizing stands and pinch roll stands) of high-speed wire mills.
Composite cemented carbide rolls are made of cemented carbide and other materials, and can be divided into cemented carbide composite roll rings and integral cemented carbide composite rolls. The cemented carbide composite roll ring is installed on the roll shaft; the integral cemented carbide composite roll casts the cemented carbide roll ring directly into the roll shaft to form a whole, which is used in rolling mills with large rolling loads.
New technology for manufacturing composite carbide rolls
1. Cast-in composite carbide roller ring
In order to meet the requirements of modern rolling production, a new CIC composite roll cast-in type (CAST IN CARBIDE) composite carbide roll ring is developed.
This technology is to cast the carbide ring and the ductile iron inner sleeve together. The roll ring and the roll shaft are keyed. In this connection mode, the carbide material with extremely high hardness and excellent wear resistance on the outer layer of the composite roll ring bears the rolling force, and the ductile iron with good strength and toughness on the inner layer transmits the torque. Structural features of CIC composite rolls:
The development of cast-in CIC composite roll ring technology is a new combination of powder metallurgy technology and casting technology, and a major advancement in the application of composite wear-resistant material technology on rolls.
2. Powder metallurgy composite WC roller ring
This technology combines the cemented carbide ring with a steel matrix with Ni and Cr powder added, and combines the two together through powder metallurgy technology.
The key point of the process is to first press and sinter the cemented carbide powder into a ring, and then mold and sinter it with the selected steel base powder. There is a strong metallurgical connection between the cemented carbide and the steel base.
The key to this process is to master the sintering temperature of 1100-1200 ℃ and the pressure conditions of 100-120 MPa. The sintered blank is rough turned, stress eliminated and other processes, and finally fine turned and ground to form.
By selecting the right matrix material, combined with advanced technology and proportioning, the residual stress between the cemented carbide and the steel matrix in the composite roll ring can be very low.
This powder metallurgy technology has created a new era in the preparation process of roll materials.
Application of Carbide Roller Ring(tc rings) Materials
WC roller rings are subjected to high temperature, rolling stress, thermal corrosion and impact load during hot rolling.
Sulfur and oxygen are added to ordinary cemented carbide materials to form stable gradient metal oxides and metal sulfides (Co3O4 and CoS, respectively) on the surface of the metal substrate.
Co3O4 and CoS have good lubrication and wear resistance. Industrial tests on LGM roller rings show that the sulfides and oxides in the gradient material can reduce the friction coefficient during rolling, significantly improve the lubrication performance of the roller ring under high temperature and large rolling force conditions, reduce the generation of transverse cracks, and the service life of the roller ring is 1.5 times that of ordinary cemented carbide roller rings. It can also reduce the amount of grinding and the number of roller changes, which has significant economic benefits.
Using CIC technology, we developed the carbide roll ring H6T with the least binder phase in the world. Its binder phase content is only 6%, while its hardness and wear resistance are significantly higher than those of ordinary alloys, especially the wear resistance is improved by 50%;
When used on finished product racks and finished product front racks, the roll life is twice that of ordinary carbide; it solves the problem of changing rolls together for finished product racks and finished product front racks, and can significantly reduce the number of slot and roll changes, thereby improving the effective operation rate of the rolling mill.
Composite carbide roller rings have been used in wire mills (intermediate rolling or pre-finishing rolling), bar mills (intermediate rolling, finishing rolling), small-sized steel mills (square steel, hexagonal steel, flat steel and angle steel, etc.) and three-roll mill systems (such as KOCK wire rod, seamless steel pipe tension reducer).
When composite carbide roller rings are used in the intermediate rolling unit of high-speed wire mills or the finishing stand of small bar mills, the rolling amount of each single groove is 10 times that of ordinary cast iron rollers, and the grinding amount per time is only 1/3 to 1/2 of that of cast iron rollers. Therefore, compared with traditional cast iron rollers, the total rolling amount of composite rollers is 20 to 30 times that of ordinary rollers.
When used in 3-roller tension reducing mill stands and jacking mill stands for seamless steel pipes, compared with traditional cast iron tension reducing mill rolls, when rolling larger diameter steel pipes, the single groove rolling amount of the composite roll is 20 times that of ordinary cast iron rolls, and when rolling smaller diameter steel pipes, the single groove rolling amount of the composite roll is 40 times that of ordinary cast iron rolls, and the finished product quality and dimensional accuracy of the steel pipe are significantly improved.
In order to solve the problems existing in alloy tool steel and cemented carbide roller materials used in the production of threaded steel wire, cemented carbide GW30, which is between alloy tool steel and cemented carbide, was developed.
After forging, machining and heat treatment, the “bridging” phenomenon of carbides in the alloy was weakened, and the bending strength and impact toughness of the material reached 2672 MPa and 18.0 J/cm2 respectively, which can prevent the early brittle failure of the roller.
At the same time, the wear resistance of the hard phase in the cemented carbide was fully utilized. Under the condition of keeping the strength and toughness of the roller unchanged, the surface of the roller was treated with surface boronizing, so that the boronized layer was firmly combined with the steel matrix, and the microstructure and properties of the alloy surface layer tended to be consistent, so that the wear resistance of the alloy was further improved.
The results of industrial tests show that the service life of the roller is more than ten times that of alloy tool steel, with significant economic benefits.
In the rolling of wire and bar, the use of cemented carbide rolls instead of traditional cast iron and alloy steel rolls has shown many advantages. With the continuous development of roll manufacturing technology and use technology, the use of cemented carbide rolls will continue to expand. Its position in rolling processing will become more and more important, and its application prospects will be very broad.
Tungsten Carbide Alloy Roller Ring Application Notes
When the carbide roll is working, various factors always work together to damage the groove surface and cause the roll to be damaged. These factors are mainly: cracks, wear, corrosion, and falling blocks. The factors that affect the service life of tungsten carbide alloy roll rings are mainly the following:
1. Cracks of tungsten carbide alloy rolls
The important factors that lead to the damage and rupture of alloy rolls are the generation and expansion of cracks. There are two forms of cracks: transverse cracks and longitudinal cracks. Transverse cracks are parallel to the axis of the roll ring, and longitudinal cracks are along the circumference of the roll ring. Transverse cracks are the most fatal to the roll ring. Cracks on the roll surface are caused by thermal fatigue. These cracks must be ground out during grinding.
2. Wear of rollers
During the rolling process, the changes in the quality and quantity of the roller surface caused by the physical friction between the roller and the workpiece, and the chemical corrosion and oxidation caused by contact with cooling water under high temperature and high pressure are called roller wear.
3. Corrosion of rollers
Electrolytic corrosion occurs in acidic cooling water. Corrosion causes the loss of the bonding phase on the exposed surface of cemented carbide, especially on cracked surfaces. After corrosion occurs, carbide particles are exposed, which intensifies wear and reduces the life of the roll sharply.
4. Surface falling off
The main reasons for the falling of the roller ring surface are roll explosion and surface collision during transportation and installation. No matter what the reason is, the falling of the roller ring will cause stress concentration in the rolling process, and severe cases will directly lead to broken rollers. Therefore, the storage and transportation of the roller ring should be carried out with great care.
The following points should be noted when using tungsten carbide alloy roller rings:
1. During the rolling process, ensure that there is enough cooling water in the rolling groove to avoid cracks or even breakage of the roller ring.
2. The rolling amount of a single groove of the rolling groove determines the rolling tonnage according to the actual situation. Excessive rolling is strictly prohibited to avoid cracks in the roller.
3. The pH value has a great influence on the corrosion of carbide rollers during rolling. The pH value of cooling water is required to be 7.0-7.2.
4. When re-grinding or turning the used rollers, microcracks should be completely eliminated and all surface damage should be removed.
Tungsten carbide alloy roller ring is a widely used cemented carbide product. Paying attention to the above factors that affect its life and the matters that should be paid special attention to during use can not only fully improve the use efficiency but also extend its service life. Sidi Technology Co., Ltd. has rich experience in the processing of cemented carbide roller rings and can customize the products according to the customer’s drawings or sample size accuracy requirements.
