Bearing / Guide

Bearing industry

1. Introduction to the bearing industry:

Bearings are used to determine the relative movement position of the rotating shaft and other parts, supporting or guiding parts. Its performance, accuracy and reliability play a decisive role in the normal operation of the main body.

my country is a big bearing producer, but compared with a strong bearing industry, China has a big gap, which is mainly manifested in high precision, high technology content and low value-added products. The main products are still imported to meet. More than 75% of the global market share is concentrated in eight multinational bearing groups, namely: SKF of Sweden (SKF), INA and FAG under the Schaeffler Group of Germany, NSK (NSK), NTN (NTN) ), Koyo Seiko (KOYO), Minebea (Minebea), Nachi Fujitsu (Nachi), American Timken (TIMKEN), etc.

In addition, the well-known domestic enterprises in China are: Renben Group Co., Ltd., Wanxiang Qianchao Co., Ltd., Wafangdian Bearing Group Co., Ltd., Luoyang LYC Bearing Co., Ltd., Tianma Holding Group Co., Ltd., Zhejiang Wuzhou Xinchun Group Co., Ltd., Ci Xing Group Co., Ltd., Dalian Metallurgical Bearing Group Co., Ltd., Hubei New Torch Group Company, Harbin Bearing Group Company, Shanghai Jiyou Machinery Co., Ltd., Xiangyang Automobile Bearing Co., Ltd., etc.;

At present, foreign companies basically use CBN grinding wheels for product grinding, while domestic companies mainly use ordinary corundum grinding wheels. However, as high-performance machine tools are promoted and gradually used in the domestic bearing industry, ceramic bond CBN grinding wheels are used for internal grinding of bearings. It is gradually being adopted by large domestic bearing companies. The main advantages are: long life, high efficiency, high precision and good roughness.

2. Common problems and solutions in the grinding process of the bearing industry:

(1) Spiral line formation: Main reasons: 1. The grinding wheel is poorly trimmed, the corners are not chamfered, and the coolant is not used for trimming; 2. The table guide rail guides too much lubricating oil, causing the table to float; 3. The machine tool accuracy is not good ; 4. Grinding pressure is too high, etc.

The specific reasons for the formation of the spiral line: 1. The V-shaped guide rail is not rigid, and the grinding wheel is offset when grinding, but the edge of the grinding wheel is in contact with the working surface; 2. The reversing speed of the worktable is unstable when the noisy wheel is trimmed, and the accuracy is not high. , So that a certain edge of the grinding wheel is slightly trimmed; 3. The rigidity of the workpiece itself is poor; 4. There are broken and peeled sand particles on the grinding wheel and the iron filings under the grinding of the workpiece accumulate on the surface of the grinding wheel. For this reason, the trimmed grinding wheel should be used. Rinse with cooling water or brush clean; 5. The grinding wheel is not well-dressed, and there are local bumps.

(2) Fish scales appear on the surface: The main reason for the reappearance of fish scale marks on the surface is that the cutting edge of the grinding wheel is not sharp enough, and the phenomenon of "grabbing" occurs during grinding, and the vibration is large at this time. The specific reasons for the appearance of fish scale marks on the surface of the workpiece are: 1. There is garbage and oil on the surface of the grinding wheel; 2. The grinding wheel is not rounded; 3. The grinding wheel becomes blunt. The dressing is not sharp enough; 4. The diamond fastening frame is not firm, the diamond is shaking or the quality of the diamond is not sharp; 5. The hardness of the grinding wheel is uneven. The main reason for the reappearance of the scratches on the surface of the working face is that after the coarse-grained abrasive grains fall off, the abrasive grains are sandwiched between the workpiece and the grinding wheel.

(3) The surface of the workpiece is roughened during grinding: The specific reasons are: 1. The traces left by the rough grinding are not worn off during the fine grinding; 2. The coarse and micro abrasive particles in the coolant are not cleanly filtered; 3 .The abrasive grains are easy to fall off when the coarse-grained grinding wheel is just trimmed; 4. The material toughness is valid or the grinding wheel is too soft; 5. The toughness of the abrasive grains and the toughness of the workpiece material are improperly matched, such as the workpiece surface has straight wave marks on the workpiece we will grind the vertical axis of the workpiece Cut a cross section of the line and zoom in, you can see that its periphery is similar to a sine wave. If the center of the sine wave moves along the axis without rotation and translation, the trajectory around the sine wave is a wave cylinder, which is also called a polygon.

(4) Straight wave traces are produced: the reason is the movement of the grinding wheel relative to the workpiece or the periodic change of the grinding pressure of the grinding wheel on the workpiece, which causes vibration. This kind of vibration may be forced vibration or self-excited vibration, so the direct wave frequency on the workpiece is often more than one. The specific reasons for the straight wave marks are: 1. The grinding wheel spindle gap is too large; 2. The hardness of the grinding wheel is too high; 3. The static balance of the grinding wheel is not good or the grinding wheel becomes blunt; 4. The workpiece speed is too high; 5. The transverse knife is too large 6. The bearing of the grinding wheel spindle is worn and the matching clearance is too large, resulting in radial runout; 7. The pressing mechanism of the grinding wheel or the worktable "crawls", etc.

(5) The surface of the workpiece is burned during the grinding process: the surface of the workpiece is often burned during the grinding process. There are several types of burns. One is the burn along the processing direction of the grinding wheel and appears as dark black patches; the other is lines or broken. Continued line-like. The surface of the workpiece is burned during the grinding process. In summary, there are several reasons: 1. The grinding wheel is too hard or the grain size is too fine and the structure is too dense; 2. The feed rate is too large, the cutting fluid supply is insufficient, and the heat dissipation condition is poor; 3. The workpiece speed is too low, the grinding wheel speed is too fast; 4. The grinding wheel vibrates too much, and the grinding depth changes continuously and burns; 5. The grinding wheel is not repaired in time or the repair is not good; 6. The diamond is sharp, and the grinding wheel is not repaired well; 7 .The workpiece burns too deep during rough grinding, and the fine grinding allowance is too small, and it is not worn off; 8. The workpiece clamping force or suction is insufficient, and the workpiece stops rotating under the action of the grinding force. So how does the surface of the workpiece know whether it burns black during the grinding process? This can be checked by regular pickling. After the workpiece is pickled, when the surface is wet, it should be visually inspected under astigmatism lamp immediately, and the normal surface is uniformly dark gray. If it is a software point, it will appear cloud-like dark black spots, and the perimeter is not fixed; if it is decarburized, it will appear gray or dark mottling; if the crack is ground, the crack will appear to be cracked. If it is a burn, the first is the surface edge. The machining direction of the grinding wheel shows dark black patches, and the other is the appearance of lines or intermittent lines. If the above-mentioned burns occur during the grinding process, the reasons must be analyzed in time and effective measures should be taken to solve them to prevent batch burns.

(6) The surface roughness does not meet the requirements: The surface roughness of the bearing parts has standard and process requirements, but in the grinding and super-precision process, due to various reasons, it often fails to meet the specified requirements. The main reasons that cause the surface roughness of the workpiece to fail to meet the requirements are: 1. The grinding speed is too low, the feed speed is too fast, the feed rate is too large, and the grinding time without feed is too short; 2. The workpiece speed is too high or The vibration of the workpiece shaft and the grinding wheel shaft is too large; 3. The grain size of the grinding wheel is too coarse or too soft; 4. The dressing speed of the grinding wheel is too fast or the clearance of the dressing mechanism is too large; 5. The diamond of the dressing wheel is not sharp or the quality is not good; 6. Super precision The quality of the oilstone used is not good, and the installation position is incorrect; 7. The quality of kerosene used for ultra-precision does not meet the requirements; 8. The ultra-precision time is too short, etc.;

3. Products of our company:

In recent years, our company has successfully developed a series of ceramic bond CBN grinding wheel products based on the characteristics of inner hole processing in the bearing industry and combined with the requirements of the machine tool for the use of grinding wheels. Supporting internal grinder produced by machine tool factory