The power transmission belt is used to transfer the rotational energy of a prime mover such as an engine or motor to a driven machine.

When the motor is rotated clockwise, the belt is pulled and the driven pulley rotates. In this process, the upper side of the belt is pulled (tension side) and the lower side of the belt is loosened (slack side). A "tension difference" is generated between the tension side and the slack side. This difference is called "effective tension," and effective tension is generated by rotating the driven pulley under load.
　Figure 2 graphically illustrates this relationship. The graph shows that effective tension starts at 0 before power and load are applied, but after operation, when power and load are applied, the tension on The graph shows that effective tension starts at 0 before power and load are applied, but after operation, when power and load are applied, the tension on both sides gradually begins to differ, and effective tension is generated.

Next, look at Figure 3.

The graph on the left shows a case where the belt is operated at an appropriate tension, ensuring sufficient effective tension. On the other hand, the graph on the right shows a case in which the belt is installed and operated at a low tension, and as the power and load increase, the slack side tension drops below 0, and sufficient effective tension is no longer ensured.

Thus, if the slack side tension falls below 0, there is a risk of excessive slippage in V-belts and jumping (hereinafter referred to as "tooth skipping") in synchronous belts, etc. Because effective tension is directly related to belt performance, Since effective tension is directly related to belt performance, it is important to Since effective tension is directly related to belt performance, it is important to install the belt at the proper tension so that the slack side tension does not fall below zero.

We have explained that a certain amount of tension is required when installing a power transmission belt. The answer is NO. Power transmission belts must be tensioned at the "optimum tension".
The table below explains how improper tension affects belt product quality by classifying belts into two categories: V-belts and synchronous belts.

As you can see, improper tension of the power transmission belt increases the possibility of premature belt failure. Under such conditions, the transmission performance of the belt cannot be fully demonstrated.

There are various methods to calculate the appropriate tension, and one of the most recommended methods is to use our "Industrial power transmission belt design support" (Windows application). The main function of the "Industrial power transmission belt design support" is to calculate the design for appropriate belt selection, but it can also calculate the appropriate tension. By entering machine operating conditions, belt type, and other information, the application calculates the appropriate tension for belt installation along with the design calculation results. In this application, the appropriate tension is displayed under "initial tension" for V-belts and "installation tension" for synchronous belts.

In the next section, we will explain how to actually install the belt with the calculated "initial tension" or "installation tension" and how to manage it afterwards.

This section describes how to tension the belt and how to check and re-tension the belt after operation.

For both V-belts and synchronous belts, install the belts according to the above procedure using the calculated installation tension. Please note that the tension is multiplied by 5.

In the case of V-belts, due to their structure, the tension gradually decreases as the belt becomes more familiar with the pulleys and the side In the case of V-belts due to their structure, the tension gradually decreases as the belt becomes more familiar with the pulleys and the side. For this reason, it is necessary to check the tension using a tension measuring device one day to one week after installation. If the tension is lowered at this time, the initial tension should be 1. 5 to 1. 5 times higher than the initial tension. The belt should be re-tensioned at 3 times the installation tension. After that, the tension should be checked periodically at intervals of 3 to 6 months. If the tension is lowered at this time, the initial tension should be increased by 1. 5 times. Re-tension the belt with 3x installation tension.

On the other hand, once the synchronous belt is tensioned and installed, it has a structure that allows it to flex easily and to fall into the pulley groove On the other hand, once the synchronous belt is tensioned and installed, it has a structure that allows it to flex easily and to fall into the pulley groove less frequently. (See Fig. 5)

We have discussed the need for proper tension management. However, no matter how much we understand the importance of tension management, it is impossible to manage tension without equipment to measure tension.
Therefore, we would like to introduce our tension measuring instruments. We offer the TENSION MASTER™ (acceleration sensor type) and the Tension Meter (spring type). The features of each are shown in the table below.

Since each of the two tension meters/tension gauges has its own advantages, please select the appropriate tension measuring device according to your usage conditions and belt layout.

We hope this explanation has answered any questions you may have had about power transmission belt tension. If you have any questions about proper tension and management, please feel free to contact us. We will continue to support your safe and efficient use of power transmission belts.