Two main processing methods, raw materials, process equipment, quality control method, contact fatigue failure and summary.
As the key part of rolling bearing, steel ball plays the role of bearing and transferring load and motion in the bearing, which has a great impact on the life and vibration noise of the bearing.
Any point on the surface of the steel ball is a working surface that bears loads. It bears variable loads with uncertain periods. The contact area is small, the contact stress is large, and the stress condition of the steel ball is relatively bad, which is very easy to cause fatigue damage. The entire surface of the steel ball is both the processing surface and the supporting surface, so the steel ball processing technology is also very unique and specialized in the machinery industry, and has very high requirements for raw materials, process technology, processing equipment, tooling and abrasive tools, grinding fluid, etc.
At present, the domestic steel ball process technology level, equipment level, quality control level and tooling and grinding tool level have reached or close to the international advanced level, the management has become more sophisticated and perfect, large-scale production and operation are prominent, and the total production has been expanding. Quality level of steel ball: the tolerance grade of batch production is G5, the specifications and materials are complete, the single particle vibration reaches 26 dB, and the service life K value reaches more than 12 (the ratio of the basic rated life test value L10t to the basic rated life L10).
1) Processing process
Two main processing methods:
-Large cycle processing process of aqueous solution:
Raw material procurement (incoming inspection) → cold badge → smooth grinding → (soft grinding) → heat treatment → strengthening → hard grinding → preliminary research → fine research → super fine research → cleaning → appearance → anti-rust packaging → inventory
-Grinding process of resin grinding wheel:
Raw material procurement (incoming inspection) → cold badge → smooth grinding → (soft grinding) → heat treatment → strengthening → hard grinding → rough grinding → fine grinding → fine grinding → cleaning → appearance → anti- rust packaging → inventory
2) Raw materials
GCr15 wire is widely used, accounting for more than 85%, due to its moderate price and easy heat treatment. For other applications, stainless steel balls are used when corrosion resistance is more important than durability; For aircraft and other special purposes, it is required to use high-speed tool steel (tungsten steel) and heat-resistant steel (M50) with heat resistance better than GCr15. Steel balls for special purposes usually have higher material costs and processing costs due to the implementation of complex heat treatment processes (such as high temperature quenching, multiple tempering, cold treatment, etc.).
3) Process equipment
A complete set of main steel ball processing equipment has been formed in China, including Z32, Z32G series steel ball cold heading machines and high-speed cold heading machines, 3M49, 3M79 series light ball machines, 3M46, 3M76 series ball grinders, 3M47, 3M77 series ball grinders, protective atmosphere heat treatment furnaces, steel ball surface strengthening machines, cleaning machines based on brush cleaning and high-strength sponge rotary extrusion cleaning, etc. The inspection equipment mainly includes visual system based steel ball surface quality appearance tester, eddy current photoelectric appearance tester with optical and vibration channels based on eddy current flaw detection principle. The diameter of lapping plate of polishing, grinding and lapping machine tool is φ 300~950 (1000) mm, ball load 20~1000 kg, the machining accuracy of the machine tool can meet the requirements of G5 steel ball.
Problems needing attention: 1. The quality of domestic high-speed cold heading machine is still unstable, the reliability is poor, and the quality of cold heading die is low; 2. The optical, grinding and research equipment are generally general equipment, and the layout design of specialized lines has been improved, and the efficiency still needs to be improved; (3) The automatic control and automation level of polishing, grinding and grinding equipment need to be further improved; (4) The connection equipment for cleaning, drying and quality control in the steel ball processing process is still lack of professional layout and production; (5) The applicability and reliability of steel ball finished product cleaning equipment need to be improved; (6) The appearance inspection instrument for steel ball products still needs to be improved to improve the reliability.
4) Quality control method
A set of methods have been formed for the quality control of steel balls in China. The quality indicators and methods are mainly: raw material quality, size and dimensional accuracy, heat treatment hardness, metallographic structure, and surface defects. With the improvement of steel ball processing technology and processing equipment, all steel ball manufacturers can basically meet the standard requirements in terms of size and dimensional accuracy, heat treatment hardness, etc. The following problems should be paid attention to: 1. Quality control of raw materials and material selection according to the use of steel balls; 2. Detection and control of steel ball size stability; 3. Steel ball surface strengthening and surface stress control; 4. Detection and control of steel ball surface morphology; 5. Monitoring and control of ball surface waviness; 6. Confirmation of steel ball delivery quality; 7. Steel ball contact fatigue life test and control.
5) Contact fatigue failure
The mechanism of rolling fatigue can be roughly divided into two types: internal origin type spalling and surface origin type spalling. Internal origin type spalling is mainly caused by non-metallic inclusions under rolling contact surface, which needs to be dealt with by improving the purity of raw materials. Surface origin type spalling is directly related to the service environment, lubrication state of rolling bearing, and the state of the upper surface of rolling contact rolling surface (surface roughness and scars on rolling surface). It has a shorter life than internal origin type spalling, and the proportion of bearing damage is larger. The coping strategy for surface origin peeling, such as carbonitriding on the surface of GCr15 steel ball, is to improve the surface hardness of steel ball by using ordinary overall quenching, which makes it difficult to form indentation and improve the durability in the presence of foreign matters due to the high cost of carbonitriding.
6) Summary
The steel ball still needs to further improve the quality as the primary goal. It is necessary to adopt a reasonable material purity evaluation method to thoroughly carry out quality management from the blank. At the same time, in order to prevent unqualified products from leaving the factory, it is necessary to develop a more functional automatic appearance tester. In addition, in order to improve the durability, steel mills are required to further improve the purity of materials, and at the same time, they are required to develop the steel ball heat treatment technology suitable for the application, which endows the traditional GCr15 steel ball with various additional values.
In recent years, with the increasingly diversified demand for bearing applications, ceramic balls (such as Si3N4 balls) have been used to replace new steel balls under high-speed, high-temperature and other application conditions. At present, the output is rising rapidly and the application demand is strong, but the problem of high price remains to be solved.
More about WBM Steel Ball:
Quality precision：G5，G10，G16 Our Chrome ball usually produce according to GBT 308.1-2013 and ISO 3290-1:2014 standards. Hardness will be customized base on your requirement.
We are professional steel ball manufacturers and suppliers in China, with bulk high quality products in stock. If you are going to buy customized steel ball at competitive price, welcome to get quotation from our factory. We are working hard to develop various chrome ball, Inch Steel Ball, Din 5401 Steel Ball products with broad market prospects and market competitiveness, and we have achieved fruitful results.
