One problem is —how to judge the "tightness" in the chain transmission

Chain transmission is a mechanical transmission mode that uses a chain to transfer power from one rotating part (active sprocket) to another rotating (driven sprocket). The active sprocket merges with the chain to drive the chain movement, and the chain merges with the driven sprocket, so that the driven sprocket rotates at a certain transmission ratio. The transmission ratio is equal to the number of teeth of the active sprocket divided by the number of teeth of the driven sprocket. For example, if the active sprocket has 20 teeth and the driven sprocket has 10 teeth, then the transmission ratio is 2:1, meaning that the active sprocket turns one circle and the driven sprocket turns two laps. In general, the efficiency of chain transmission is between 92% and 98%, because the friction of rolling chain (roller chain) or engagement friction (tooth chain) between the chain and the chain wheel is relatively small and can effectively transfer power.

01How to judge the tightness of the chain?

observational method

Ssis observation: This is a simple and intuitive method for horizontal or near horizontal chains. Stand on the side of the chain, make the view parallel to the chain, and observe the chain droop between the two sprockets. If the radian formed by the chain droop is relatively flat, and meets the range of 1% -3% (generally), it can usually preliminarily judge that the chain tightness is appropriate. For example, the center distance between the two sprockets is 500mm, and the droop degree of between 5 and 15mm is considered normal.

Operation observation: initially observe the chain when the equipment is stationary, start the equipment and let the chain run at normal working speed. Observe the engagement of the chain on the sprocket, if the chain can smoothly rotate around the sprocket, there is no obvious sign of beating up and down, shaking or detachment from the sprocket, which also indicates that the tightness of the chain may be within a reasonable range. However, this method can only make a preliminary judgment, for some small cases may be difficult to detect.

Decopy measurement: Use professional measuring tools, such as calipers or ruler, to measure the droop of the chain. Place the caliper or ruler vertically at the lowest point of the chain and measure the distance from the bottom of the ruler to the lowest point of the chain. To improve measurement accuracy, multiple measurements can be taken at different locations in the chain and then averaged. Compare it with the specified droop standard range to judge whether the chain tightness meets the requirements.

Tension measurement: to use a tension meter to accurately measure the tension of the chain. According to the specifications and application scenario of the chain, contact the sensor of the tension meter with the chain, and read the tension value according to the operating instructions of the tension meter. For the equipment with tension standards required, such as some high-precision automation equipment, this method can accurately determine whether the tightness of the chain meets the standard. Different types of chain tension meters are suitable for different chain specifications and tension ranges, when using the appropriate tension meters.

antitheses

Compare with the new installation status: If the chain of the equipment is newly installed and has been adjusted to the appropriate tightness when installation, it can be compared as a standard. After the device is running for a period of time, observe the state of the chain again. If the chain is found to be significantly larger, or if the chain becomes much weaker than when it was newly installed, it may need to check whether the chain meets the tightness criteria and consider whether it needs to be adjusted.

Compared with the same type of equipment: In the case of multiple same or similar equipment, the chain status of the inspected equipment can be compared with the normal operation of the same type of equipment. Observe the droop of the chain and the stability during operation. If the chain status of the inspected equipment is quite different from that of the normal equipment, and the following vertical degree is significantly larger or the chain is abnormally shaken in operation, it is necessary to further check whether the tightness degree meets the standard.

02 How to adjust the chain tightness?

1.Adjust the center distance method

Structure of the adjustable sprocket spacing

For some sprockets with adjustable mounting seats, this is a common method. The sprocket mounting seat of many equipment is designed to have long holes or adopt a slider structure to change the center distance between the two sprockets by loosening the bolts that fix the sprocket wheel.

For example, in a small delivery device, when the chain is found to be too loose, loosen the bolts on the sprocket mount and move the sprocket away from the other one along the long hole or slide track, increasing the center distance and tightening the chain. During the adjustment process, it is necessary to check the chain tightness with the above method or measuring the tension) until the appropriate tightness is reached, and then tighten the bolts.

Increase or decrease the gasket adjustment

In some devices, the mounting position of the sprocket is controlled through the spacers to control the center distance. If the chain is too loose, the thickness of the gasket can be reduced appropriately; if the chain is too tight, increase the thickness of the gasket.

In the chain drive of a motorcycle, for example, there are usually gaskets at the sprocket and the mounting part of the engine or rear wheel. When the chain needs to adjust the tightness, the maintenance personnel can increase or decrease the number or thickness of the spacers according to the actual situation, and then check the operation of the chain after the adjustment.

2.Use the tensioning device method

Spring tensioner

Spring-type tensioner is a more common device. It usually consists of a tensioning wheel with a spring, mounted on the loose side of the chain. When the chain rela, the elasticity of the spring causes the tensioning wheel to apply pressure on the chain, thus tightening the chain.

In chain conveyors on some automated production lines, spring tensors can automatically compensate for the elongation of the chain after a long run. By adjusting the pretightening force of the spring, we can control the pressure of the tension wheel on the chain, and then adjust the tightness of the chain. Generally speaking, the pretension force of the spring can be changed by rotating and adjusting the nut, so that the tightening degree of the tensioning wheel to the chain meets the requirements.

Hydraulic or pneumatic tensioning device

In large, heavy-duty mechanical equipment or some high-precision equipment, hydraulic or pneumatic tensioning devices may be used. These devices can provide more precise and stable tension forces.

Taking the large chain scraper conveyor in the mine equipment as an example, the hydraulic tensioning device can accurately adjust the tension force through the hydraulic system according to the load situation of the equipment and the actual elongation of the chain. The operator can adjust the tightness of the chain by controlling the pressure of the hydraulic system, and the hydraulic system can automatically adjust the tension according to the sensor feedback to ensure that the chain is always in the appropriate elastic state.

3. Replace the chain method

When the chain has been used for a long time, the tightness cannot be effectively adjusted by the above methods due to wear, extension and other reasons, and the wear degree of the chain has exceeded the allowable range, it is necessary to consider replacing the chain.

When selecting a new chain, ensure that its specifications comply with the equipment requirements. After installing the new chain, make the initial adjustment according to the design requirements of the equipment and the normal installation steps to make the chain reach the appropriate tightness degree. At the same time, after the new chain is put into use, its tightness should be checked regularly and adjusted in time.