Q: What are the advantages and disadvantages of cold-forging tapered rollers for rolling bearings?
A: Cold-forging tapered rollers are produced by forcing a metal section to plastically roll at room temperature using a die, filling the space formed by the die and punch. The advantages are as follows:
① Improved mechanical properties of the rollers: Because the metal undergoes plastic deformation at room temperature during cold forging, work hardening is necessary. Furthermore, the original fibers of the bar stock are not cut, and any minor defects within the metal can be compacted, which helps improve the strength of the rollers;
② Saving of raw materials: Cold stamping itself is a low-chip, low-destruction plastic forming method. If the process is handled well, the ring size can be very small, thus greatly saving metal materials;
③ High productivity: Cold forging machines are generally highly automated and easy to operate. With proper adjustment, the production efficiency is relatively high, typically 70-100 pieces/min;
④ Precise roller shape and dimensions, and low surface roughness. The shape and dimensional accuracy of cold-forging rollers are primarily ensured by the precision of the mold and machine tool adjustments. During cold forging, the metal surface is smoothed by the smooth surface of the mold under high pressure, resulting in a low surface roughness value for the rollers, typically Ra 0.25~2.0 μm. If the machining and adjustment are well-done, the quality is stable, and the rollers can even be directly heat-treated without soft grinding.
Because cold forging uses cylindrical bar stock, before forming tapered rollers, except for the chamfered area at the small end and the core portion which are subjected to triaxial compressive stress, most of the matrix is subjected to uniaxial compressive stress and biaxial tensile stress, with the tensile stress increasing closer to the large end of the roller. Experiments show that tensile stress leads to intergranular deformation in the metal, reducing its plasticity; compressive stress promotes intragranular deformation, thus increasing the metal's plasticity. Therefore, when the shape and dimensions of the blank or mold are poorly designed, the material quality is poor, or the cold forging process is inappropriate, cold-forging rollers often crack at the chamfered area at the large end.
Furthermore, during cold heading, friction between the workpiece and the die surface, uneven internal material structure, and unreasonable die shape and dimensions can all induce additional stress within the cold heading roller. This reduces the metal's plasticity, increases its resistance to deformation, and generates residual stress within the roller. This residual stress can cause changes in the roller's shape and dimensions and reduce its processing performance. In particular, the additional stress caused by external friction negatively impacts the quality of the cold heading roller and the machining process. External friction mainly occurs in the axial region of the chamfer at the small end of the roller, reducing the internal and external mass of the chamfer, increasing mold wear, and shortening die life. Therefore, friction between the workpiece and the die should be minimized during cold heading. The main factors affecting friction in cold heading are material properties, die structure and shape, surface quality, and lubrication effectiveness. Because cold heading rollers are formed at room temperature, their deformation resistance is very high, especially when the blank fills the mold space. At this point, the entire roller is essentially under triaxial compressive stress, resulting in extremely high deformation resistance. The larger the roller size, the greater the stamping force during cold heading. Therefore, the size of cold heading rollers is often limited by the power of the cold heading equipment and the strength of the mold. Furthermore, when the degree of cold deformation exceeds the maximum allowable deformation of the metal material, cracks will form on the roller's circumference, resulting in scrap. Therefore, an appropriate degree of deformation should be selected for rollers of different shapes and sizes.
About LJHB:
LuoYang JinShuo Precision Bearing Co., Ltd. is mainly committed to the R&D and sales of high-precision bearings and other special products, and provides bearings and transmission parts with high performance for customers' equipment. With quick response, from pre-sales technical communication to on-time production delivery, as well as perfect after-sales service, we win the recognition and trust of customers.
Our main products include cylindrical roller bearings, tapered roller bearings, slew bearings, gear drives, spindle bearings, crossed roller bearings, turret bearings, thin-wall bearings, tandem roller bearings, spherical roller bearings, etc. The bearing dimensions rang from 100mm to 6000mm, the accuracy reaches P5, P4 and P2 levels. The bearing are widely used in mining and metallurgy, industrial equipment, industrial gearboxes, petroleum equipment, cranes, medical equipment, robotic equipment, etc. Among them, cylindrical roller bearings with better performance and high-precision deep groove ball bearings have been explored for high-speed tubular strander rotating cable equipment, which have completely replaced imports, saving customers costs and time, and improving work efficiency. It has been recognized and widely praised by customers.
Contact LJHB:
Address: Yiyang Bearing Industry Zone, Luoyang City, China 47100
Tel/Wechat: +86-18037970383
Whatsapp: +86-18037970383
Fax: 0086-379-65199160
E-mail: lyjh@lyjhbearing.com
Website: www.chinajhbearing.com
