Time : August 28, 2023
Abstract: The paper proposes one kind of new support material ,ceramics material ,applied in the finishing process of bearing rings. And the respects such as the material behavior ,friction – wear mechanism ,the manufacture technology of the ceramics support material ,and so on ,are studied. The results show that the ceramics support material has an advantage over the tradi2 tional support materials for improving the processing accuracy and the surface quality of the bearing rings ,and can eliminate the defection of support trace brought by the support material.
Key words : Ceramics support ;Bearing rings;Finishing process;Applied research
Rolling bearings, as standard components, are widely used in industries such as aerospace, automotive, metallurgy, and household appliances, and have a huge domestic and international market. In order to expand domestic demand and earn foreign exchange through exports, domestic bearing manufacturing enterprises are striving to improve the internal accuracy of bearings while also paying attention to the appearance quality of bearing products. However, often due to the appearance quality of bearing products not meeting customer requirements (the host country is unable to effectively eliminate support marks), they cannot compete with world-renowned enterprises in the international market, causing huge economic losses to the country every year.
Centerless fixtures are widely used in grinding and ultra precision machining of bearing rings. Its characteristics are: high repeated positioning accuracy, no clamping deformation, convenient adjustment, easy loading and unloading of workpieces, radial runout of the spindle does not affect processing accuracy, and is easy to achieve automation. However, unintentional fixtures can easily leave support marks or cause surface scratches on the positioning surface during use. In order to eliminate support marks and surface scratches, the domestic bearing industry generally increases the polishing process, which will inevitably increase the cost of bearing processing. At the same time, improper control of the polishing process can also easily cause damage to the accuracy of ring processing. Therefore, it is necessary to find a new support material to replace the commonly used centerless fixture support material.
Ceramic materials have characteristics such as high strength, high temperature resistance, wear resistance, corrosion resistance, good thermal stability, self-lubrication, and highly accurate product dimensions, which make them unparalleled in other traditional bearing ring grinding and ultra precision machining support materials. This article will study the application technology of ceramic support materials in ring ultra precision machining from both theoretical and experimental perspectives.
2.1 Defects in Traditional Support Materials
At present, nylon and bakelite supports are commonly used in the ultra precision machining of ferrules, which are subjected to pressure and clamping force from oilstones. When the collar rotates rapidly, on the one hand, due to the high friction coefficient between nylon and bakelite and bearing steel, the generated friction force is also large, which is easy to generate support marks on the positioning surface; On the other hand, due to the low hardness of nylon and bakelite, abrasive debris and oil stone particles that fall off during ultra precision are easily embedded in nylon or bakelite under the pressure of oil stone, which can easily cause scratches on the positioning surface of the bearing ring. In addition, due to the low hardness and poor high-temperature resistance of nylon and bakelite materials, if there is insufficient lubrication and poor heat dissipation during processing, it is easy to cause serious wear and thermal deformation of the supporting materials.
2.2 Wear mechanism
The super essential oil used in the ultra precision machining of ferrules is a mixture of kerosene, No. 20 engine oil, and oleic acid additives, which plays a role in lubrication and cooling during the machining process. In recent years, many fundamental studies have been conducted on the friction, wear performance, and mechanism of silicon nitride ceramics under oil lubrication conditions, and many beneficial results have been achieved. However, there have been no literature reports on the friction and wear mechanism of Si3N4 GCr15 steel under 20 # engine oil lubrication. For this purpose, experimental research was conducted on the friction and wear performance of Si3N4 GCr15 steel friction pairs under oil lubrication on a friction testing machine, and the friction coefficient and wear amount of the friction pair were quantitatively measured, providing a theoretical basis for the application of ceramic support in ultra precision machining of bearing rings.
The experiment was conducted using a pin disc grinding method on a self-made friction testing machine. The ceramic sample block is 6mm fired by hot isostatic pressing (HIP) × 6mm × 10mm rectangular pin with a surface roughness of 0132 μ M. The coupling is a GCr15 steel disc with an outer diameter of 60mm and a thickness of 8mm. The material has been quenched and tempered, with a hardness of 62HRC and a surface roughness of 0132 μ M. The experiment was conducted at room temperature for 1 hour. During the experiment, the pin was fixed and the disc was driven by an electric motor at a speed of 500r/min. No. 20 oil was injected into the experimental contact area under the action of gravity, with an average flow rate of 0102L/min. The load was loaded using a code, and the friction force was amplified and displayed on a digital meter after signal processing on the strain gauge on the force arm uploaded by the experimental machine. The calculation formula for the volume wear amount W of ceramic pins is
The measured data of L0 and L1 pins measured on the bearing height measuring instrument before and after the experiment in the equation
The experimental results show that under 20 # oil lubrication, the ceramic friction surface is polished, and the sliding friction coefficient of the friction pair is 0109-0 17. The wear amount is less than 2%, and the friction coefficient of the friction pair decreases with the increase of load. After analysis, the low friction coefficient is related to the anti wear effect of the boundary adsorption film formed by the lubricating oil on the exposed metal surface during the friction process. At the same time, ceramic materials have a relatively obvious porous structure (porosity ranging from 2115% to 6 32% range), with pore diameters mostly ranging from 0133 to 1 fifty-two μ Between m [1], this is enough to allow 20 # engine oil to penetrate into it, forming a very thin protective oil film on the ceramic surface, and also helping to reduce the friction coefficient of the friction pair.
In addition, the hardness of ceramic materials is much higher than traditional support materials such as nylon and rubber. During ultra precision machining, the abrasive particles that come off during grinding and oilstone are not easily embedded in the support block under the pressure of the oilstone to form abrasive wear, greatly reducing the possibility of the support block scratching the positioning surface of the bearing sleeve.
In recent years, a large amount of experimental research has been conducted on the precision machining technology of ceramic materials both domestically and internationally, and rich research results have been achieved. At present, the mature precision machining technologies for ceramic materials mainly include cutting, grinding, grinding and polishing, electric discharge machining, ultrasonic machining, laser machining, etc. Drawing on the advantages and disadvantages of various processing technologies while considering the existing processing equipment of our school and cooperating units, we have decided to use diamond grinding wheel or diamond grinding as the processing method. Due to the fact that the particle size of resin bonded diamond grinding wheels is an important factor affecting the surface roughness of ceramic grinding, and the improper selection of the feed rate and grinding depth of the grinding wheel can easily cause surface cracks and damage, we have used low particle size resin bonded diamond grinding wheels during actual processing, strictly controlling the feed rate and cutting depth of the grinding wheel. The size accuracy of the processed ceramic blocks has been tested The geometric shape accuracy and surface roughness fully meet the technical requirements. In addition, we also experimented with precision machining of ceramic blocks using diamond grinding paste on a grinding machine and achieved success. However, compared to diamond grinding, this processing method has lower processing efficiency. Due to the high hardness of the ceramic support block, if the working surface of the ceramic support block and the supported surface of the ring are in point or line contact during the ultra precision machining of the ring, it will inevitably scratch the positioning surface of the workpiece. Therefore, the surface shape of the ceramic support block and the surface of the workpiece must meet the enveloping surface contact, in order to prevent the ceramic support block from scratching the positioning surface of the bearing ring during ultra precision machining.
4.1 Experimental process
(1) Experiment 1: Randomly select 100 qualified products from the outer rings of 30203 tapered roller bearings that have been processed in a small batch and are to be superfinished, and divide them into two groups of 50 pieces each. Ceramic and nylon supports are used for superfinishing on the same LZ211 machine tool, Number each group of processed products separately and use a special bearing tester to measure the dimensional accuracy of the bearing products after processing, while visually inspecting their surface quality (whether there are scratches or support marks) and the wear of the supports.
4.2 Analysis of experimental results
After comparing and analyzing the recorded experimental data, it can be seen that using ceramic support does not reduce the dimensional accuracy of the ring after ultra precision compared to using traditional nylon and bakelite support materials, but rather slightly improves it. The measured data can be calculated that the average taper deviation of the former is reduced by 3185% compared to the latter, the average taper angle deviation is reduced by 7619%, and the average wall thickness difference is basically the same. In addition, from the recorded visual inspection of the surface quality, it can be seen that there are no scratches or support marks on the surface of the workpiece supported by ceramic support and roller support, while there are scratches and support marks on the surface of the workpiece supported by nylon support. Therefore, after using ceramic supports, there is no need to add a polishing process to eliminate support marks and scratches, which can avoid waste products caused by improper polishing control and also reduce processing costs.
From the record of bearing wear, it can be seen that the wear of ceramic bearings is extremely slight, while the wear of nylon and roller bearings is more severe. Therefore, using ceramic bearings can effectively reduce the frequent downtime caused by replacing worn bearings, thereby greatly improving the production efficiency of bearing ring ultra precision machining.
More about XZBRG Silicon Carbide (SIC) Ceramic Bearings：
Full ceramic ball bearings constructed entirely of ceramic material. Inner/outer races and balls are made of either Silicon Nitride (Si3N4), Zirconium Oxide (ZrO2) or Silicon carbide (SiC). They are available as full complement (no cage) or with a cage made from PEEK or PTFE. Full ceramic bearings are for medium load and medium speed applications. It is not possible to achieve the inner and outer ring roundness that is found with precision steel bearings so full ceramic bearings have lower speed ratings.
Silicon Carbide (SIC) Ceramic Bearings have exceptional wear and thermal shock resistance for high-stress environments in various industries.
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