First, high-quality bearing steel tubes are prepared, and then the steel tubes are processed into precise bearing rings.
Step 1: Preparation of steel tubes (from steel bars to specialized steel tubes)
The steel tubes used for manufacturing bearing rings are not ordinary steel tubes but specially prepared seamless steel tubes. The mainstream production process is “punching + cold rolling (drawing)”.
This process can be simply understood as:
Heating and punching: Heat the bearing steel (such as GCr15) bar to 1100°C – 1180°C, then punch it into a hollow “flow tube”.
Cooling and annealing: After punching, quickly cool it and then perform annealing (spheroidizing annealing) to soften the steel and optimize the internal structure, preparing for the subsequent cold processing.
Cold rolling and cold drawing: Through multiple rounds of cold rolling and cold drawing, the pipe material is precisely processed to the target size. This process may include stress relief annealing in between.
Pre-treatment: The steel tube undergoes acid washing and phosphating treatment to remove surface oxides and form a lubricating layer.
Finished product heat treatment: Finally, the finished product is subjected to heat treatment to obtain precise dimensions and performance-compliant bearing steel tubes.
Step 2: Forming and precision processing of the rings (from steel tubes to finished rings)
With high-quality steel tubes, the rings can be manufactured. Currently, there are several core forming processes:
1. Turning forming
Process: This is the most direct method. Cut the steel tube into sections (cutting), and then use a CNC lathe to perform turning to process all the structures such as inner and outer rings, raceways, chamfers, etc.
Advantages: The process is simple and direct, but it wastes a lot of material and has relatively low production efficiency.
2. Cold rolling expansion forming
Process: This is an advanced chip-free processing technology. Place the cut steel tube ring pieces in the cold rolling machine and through rolling, the metal undergoes plastic flow, gradually expanding the diameter, reducing the wall thickness, and forming the raceway shape.
Advantages: Material saving: The material utilization rate can be significantly increased from the traditional turning’s 44% to 55% – 75%.
High performance: It can improve the internal structure of the metal, making the product more dense and durable.
High efficiency: The processing speed is fast, and the subsequent grinding allowance is small.
3. Cold (warm) extrusion forming
Process: Under room temperature or slightly above room temperature conditions, use a press to extrude the tube billet in the mold.
Advantages: Suitable for specific types of rings and is also an efficient and material-saving process.
Regardless of which forming method is used, the resulting rings still need to undergo a series of subsequent precision processing:
Heat treatment: Perform quenching and tempering to give the ring high hardness and wear resistance.
Milling processing: Perform precise milling on key parts (such as inner and outer circles, end faces, raceways) to meet the final precision requirements.
Inspection and flaw detection: Use magnetic particle flaw detection or eddy current flaw detection methods to check whether the parts have cracks or other defects.
Cleaning and assembly: Finally, perform cleaning and demagnetization, and qualified rings can enter the bearing assembly process.
Process summary: For large-scale production of medium-sized bearings, cold rolling expansion process is favored due to its high efficiency, material saving, and high performance. For some large, complex structures, or small-batch rings, the traditional turning process is still in use. Our VPN bearings use bearing steel, which is GCr15 (high-carbon chromium bearing steel), and undergo martensitic heat treatment for processing. The retainers can be nitrided, but ordinary bearing retainers have not undergone nitriding treatment. The VPN bearing process absolutely ensures the integrity of the product process, thereby ensuring the quality of raw materials to the final product.