This article quotes the customer’s long-term experience of using the expansion sleeve, and the transformation and redesign of the expansion sleeve connection structure not only meets the repair requirements, but also successfully applied in production practice and achieved good results.
Mechanical transmission is widely used in mechanical engineering, mainly refers to the transmission of power and movement by mechanical means. According to the force transmission method, mechanical transmission mainly includes chain transmission, gear transmission and belt transmission.
Belt transmission is a transmission method with intermediate flexible parts. Because the transmission belt is elastic and relies on friction for transmission, it has a simple structure, stable transmission, low noise, and can buffer and absorb vibration. When overloaded, the transmission belt will slip on the pulley. It acts as an overload protection for other parts, and is suitable for transmissions with large center distances. It is most commonly used in mechanical transmission, especially the V-belt transmission in belt transmission, which is extremely widely used.
The most common method for assembling the belt wheel and the shaft is the keyed connection; however, the keyed connection is often used on some high-speed machine tools and high-precision machine tools because the concentricity of the belt wheel and the shaft is not good, and large vibration will be generated during high-speed rotation. The structure of the expansion sleeve.
For the grinding disc power head (diameter 800mm) of the customer's CGK62 combined milling and grinding line, the power transmission is driven by a pulley with a diameter of 300mm, which is connected by an expansion sleeve and a shaft assembly. In the process of long-term operation, due to the frequent start and stop of the grinding disc, the expansion failure between the shaft and the expansion sleeve, the expansion sleeve and the pulley will fail and slip, and the transmission capacity will be lost. The structure is shown in Figure 1. The partial structure of the expansion sleeve is shown in Figure 2, which consists of an open outer sleeve, an open inner sleeve, a tension sleeve and 12 M8 hexagonal bolts.
Expansion sleeve and pulley assembly drawing Expansion sleeve drawing
Expansion principle: Pull the tension sleeve 2 and the tension sleeve 4 to the middle through the bolts. Because the tension sleeve and the opening inner sleeve are in bidirectional conical contact, the opening gap and inner diameter of the opening inner sleeve are reduced, thereby allowing The inner sleeve is tightened on the drive shaft; similarly, the tension sleeve and the open outer sleeve are also in bidirectional taper contact, which increases the opening gap and inner diameter of the open outer sleeve, so that the outer sleeve is swollen in the pulley hole.
Through analysis, the structural expansion sleeve needs to be controlled in the following two points during the manufacturing process:
①The two-way taper of the inner jacket and the taper of the two tension sleeves (total of 4 contact surfaces) must be consistent. ②The matching clearance requirements between the inner diameter of the inner sleeve and the shaft diameter, and the outer diameter of the outer sleeve and the inner diameter of the pulley must be the same.
The guarantee of the above two points is very difficult in the part manufacturing process, and there will inevitably be errors in mechanical processing, and the improvement of manufacturing accuracy will inevitably increase the manufacturing cost. Especially the difference between the inner diameter of the inner sleeve and the shaft diameter, the outer diameter of the outer sleeve and the inner diameter of the pulley will cause: ①The inner sleeve and the shaft are locked, and the tension sleeve cannot be pulled, but the outer sleeve and the pulley are swollen. The force is not enough, and the slippage occurs between the jacket and the pulley during transmission. ②The outer sleeve and the pulley have been swollen, and the tightening sleeve cannot be pulled, but the tightness of the inner sleeve and the shaft is not enough, and the inner sleeve and the shaft slip between the inner sleeve and the shaft during transmission and the phenomenon of loss of rotation occurs.
Through careful analysis and on-site observation of the slipping and grinding conditions of the expansion sleeve, it is found that it mainly occurs between the outer sleeve and the pulley. After contacting the manufacturer, it is necessary to send the pulley and shaft to the manufacturer, repair the inner hole of the pulley, and then equip it with an expansion sleeve. This requires a one-month construction period and the machine tool needs to be stopped and waited.
2. Structural improvements
After on-site discussion, it was decided to transform the expansion sleeve structure and use the company's internal machine tools to process and manufacture it on its own. The new structure of the improved expansion sleeve is shown in Figure 3. The partial components of the improved expansion sleeve are shown in Figure 4. The structure is also composed of five parts: outer sleeve flange, open outer sleeve, open inner sleeve, inner sleeve flange and 12 M12 hexagonal bolts. Bolt holes are drilled on both ends of the pulley for the inner and outer pressure flanges.
Improved expansion sleeve Improved expansion sleeve
Expansion method: First put the opening cover in the inner hole of the pulley, and fix the outer cover with bolts and the pulley. The belt wheel and the opening cover are put on the shaft to adjust the assembly position (the positioning sleeve can be processed separately to achieve positioning ); Put the opening inner sleeve on the shaft head and insert it into the outer sleeve, press the inner sleeve pressure flange on the other end of the pulley with a bolt, and push the inner sleeve into the outer sleeve at the same time; continue to tighten the inner sleeve pressure flange bolt to make the inner sleeve While the sleeve is tightened on the shaft, the sleeve is swollen in the pulley hole.
Advantages: The component has a simple structure, only one contact surface produces relative sliding during the expansion process, only the taper of this contact surface is the same (the original structure has four contact surfaces with the same taper); there is no need to require the inner sleeve, shaft, and outer sleeve The fit clearance is the same as that of the belt wheel; except for taper fit, there is no precision requirement for machining accuracy, simple manufacturing and short machining period.
3. Effect analysis
The improvement of the expansion sleeve structure greatly shortens the repair time. According to the normal return to the factory, it will take at least one month or more, and the power head shaft of the machine tool grinding disc needs to be disassembled and reinstalled after the repair. The power head is a precision machined power head, and the accuracy will change after reassembly; there is no need to disassemble the power head shaft after the transformation, so the accuracy will not change.
The repair cost of using the expansion sleeve is low, and the normal return to the factory for repair, the round-trip transportation cost plus the repair cost requires tens of thousands of yuan; after the transformation, the internal processing cost of our customer's company is less than 1,000 yuan.
This component has been used continuously for 7 months after the transformation, the effect is very good, and it has certain promotion value.
The above is the fact that our customers have used the expansion sleeve for many years. We developed the self-developed countermeasures for the problems in the use of the expansion sleeve. Hope that the majority of customers and friends will find it helpful to the similar problems encountered in the use of the expansion sleeve.