2023 June The Fourth Week WBM Technical Knowledge on The Application Of Grinding Method in Screw Repair
Abstract: The screw is worn during work, and the grinding method is used to repair the screw. Only an ordinary lathe and grinding sleeve with a distance between the tips greater than the length of the screw can be used for grinding, ensuring the repair quality of the screw. The method is simple and feasible, and the use effect is good.
Keywords: lead screw; Grinding; Spiral surface; Wear and tear; Processing accuracy; Straightening; repair
0. Preface
To achieve precise movement and ensure the machining accuracy of the parts during the cutting process, the machine tool must ensure that the transmission of the lead screw has a certain degree of accuracy and uniformity. The lead screw may wear due to poor lubrication, dust, and chips falling into the spiral surface during operation, and can be repaired by grinding.
Lathe often affects machining accuracy due to wear of the screw during precision machining. The manufacturing process of lead screws is relatively complex and costly, so they are generally not easily replaced after wear and tear, and should be repaired as much as possible. For this reason, we use the grinding method for repair.
1. Straightening of lead screw
Due to the fact that worn screws rarely do not bend, they should be straightened first before being restored. The main methods for straightening the lead screw include pressing bending straightening method and smashing bending straightening method. Usually, smashing bending straightening method is used, and the straightening effect is relatively good.
2. Tools for grinding the lead screw
The grinding sleeve used for repairing the screw is shown in Figure 1, and the internal thread of the grinding sleeve is tapped using a special tap. Two taps with different specifications are required, one of which has a pitch diameter value 0.05~0.1mm greater than the ground lead screw thread Z for rough grinding of lead screw threads, and the other is about 0.05mm greater than the ground lead screw thread Z for fine grinding of lead screw threads.
3. Repair the lead screw using grinding method
When grinding, first apply a thin layer of grinding agent to the inner layer of grinding sleeve 2 (Figure 1), then screw it onto lead screw 1 (Figure 1), and push the lead screw between the two tips of an ordinary lathe. Then, grind according to the wear of the lead screw.
Figure 1 Schematic diagram of single-sided grinding on the working surface of the lead screw
Lead screw; 2. Grinding sleeve
After a working surface of the screw tooth profile is worn, during grinding, the grinding sleeve only contacts the worn surface, and the grinding agent only needs to be applied to the surface that needs to be ground. Start the machine tool to grind at a grinding speed of 2-3m/min, and hold the grinding sleeve with your hand to prevent it from rotating with the lead screw. Follow the lead screw to generate grinding motion between the grinding sleeve and the contact surface of the lead screw. During rough grinding, starting from the position of Z with a large grinding amount, grasp the grinding sleeve and gradually move from the position of Z with a large grinding amount to the position of Z with a small grinding amount. In areas with a large grinding amount, as the grinding amount decreases slightly, the error gradually disappears, and the entire lead screw pitch diameter gradually tends to be consistent. Axial sliding, when it is felt that the resistance of the grinding sleeve along the entire length of the lead screw is not significantly different, clean the lead screw with kerosene, replace the grinding sleeve, and apply precision grinding agent to grind until it is qualified.
When both working surfaces of the lead screw tooth profile are worn, both need to be ground. Apply abrasive on both surfaces during grinding, and the grinding sleeve adopts the structure shown in Figure 2. The grinding sleeve used for two working surfaces of the lead screw being worn is different from that used for one working surface being worn. As shown in Figure 2, an additional researchable grinding sleeve 2 is attached to the grinding sleeve 1. The contact surface between the grinding sleeve and the lead screw is adjusted through the connecting threads of 1 and 2 to form a double-sided tooth profile contact with the lead screw (as shown in Figure 2), which is fixed by nut 3. The specific grinding process is basically the same as when one working surface of the screw is worn.
For screw threads with severe wear and tear, if grinding is difficult to repair, the following method can be used for repair.
Figure 2 Schematic diagram of double-sided grinding on the working surface of the lead screw
Grinding sleeve; 2. Can investigate the grinding sleeve; 3. Nut
For square screw threads, the thread can be turned along the axial direction, gradually increasing the distance B1 between adjacent threads, as shown in Figure 3. However, the reduction in thread thickness B should be less than 10% of the original thread thickness. Then grind the repaired screw threads using a grinding tool.
Figure 3 Schematic diagram of grinding square threaded screw
For trapezoidal screw threads, the screw thread can be turned deep and the outer diameter with burrs can be slightly repaired. The reduction in the bottom diameter of the thread should be less than 5% of the original thread inner diameter, and then a grinding tool should be prepared according to the repaired screw thread for grinding.
4. Precautions for Repairing Lead Screws by Grinding Method
Repairing the screw using the grinding method is a very meticulous task. In order to achieve an ideal grinding effect, the following points should be noted during the grinding work:
The grinding sleeve must ensure that the grinding screw can be completely ground at the effective tooth profile height.
Before grinding the lead screw, the center hole should be repaired based on its journal.
In order to improve the grinding efficiency and ensure the grinding quality, the preparation of the grinding agent should be appropriate. During rough grinding, 10% silicon carbide, W10 grinding powder, 90% Spindle oil No. 1 and appropriate amount of white coal oil should be added; When finishing, it is 5% silicon carbide, and its particle size is W5. Add 90% of No.1 Spindle oil and appropriate amount of white coal oil.
During the grinding process, overheating should be avoided. During operation, the lead screw can be frequently touched with your hand, and there should be no feeling of heat.
5. Conclusion
The lead screw is often used in machine tool equipment and is prone to wear and tear during operation, which affects product quality. The grinding method is used to repair the lead screw. The method is simple and easy, without the need for complex equipment. Only an ordinary lathe and grinding sleeve with a distance between the tips greater than the length of the lead screw can be used for grinding, and the accuracy of the lead screw can be improved to ensure the repair quality of the lead screw. This not only ensures the smooth progress of production, but also saves spare parts funds. Practice has proven that, The use of grinding method to repair the screw has shown good results in work.
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