Residual Torque Correlation Factor
The term Residual torque correlation factor is similar to a calibration and adjusts between the dynamic torque, measured in the electrical tool, and the residual torque, measured by a control tool.
The Residual torque correlation factor is available for all tools running the TurboTight strategy and the TensoPulse tightening strategy. It is also available for the battery pulse tools that are supported by the controller.
When using a Residual torque correlation factor that differs from 100, the reported Final torque is no longer the dynamic torque measured by the tool transducer.
The dynamic torque measurement uses an internal torque transducer that constantly measures the torque. When the target torque is reached, the tool stops and the result is evaluated and reported. The measured final torque in the transducer is affected by the joint condition, the tool speed, gears and sockets.
The residual torque is measured after the tightening is completed. It is the torque needed to continue or restart the tightening to a higher level. The residual torque is determining the clamping force in the joint.
A dynamic torque measurement is highly repetitive but may differ between tool type and tool speed. | A handheld calibrated torque wrench provides high accuracy measuring the residual torque but has higher variations due to joint relaxation, torque decay, friction or operator technique. |
The Residual torque correlation factor is a compensation between the dynamic torque and the residual torque. The factor should be determined by conducting tests. The selected tightening program is performed a few times and the dynamic torque is recorded. The tightenings are also manually measured to determine the residual torque.
The Residual torque correlation factor can be calculated by dividing a residual torque by a dynamic torque. TheResidual torque correlation factor is presented as percent and is by default 100%. This means the reported dynamic torque value has not been modified.
Parameters | Function |
|---|---|
Target torque | The tool target torque set for the tightening using the TurboTight strategy. |
Final dynamic torque | The final torque reported as the result of the performed tightening. |
Dynamic torque | The dynamic torque measured by a reference transducer. |
Residual torque | The desired residual torque that ensures the desired clamping force. |
Residual torque correlation factor | The compensation factor between residual torque and dynamic torque |
An example of how torque tuning can be used:
The TurboTight strategy is selected. The joint shall be tightened to 12 Nm to reach the desired clamping force. The following set up is made:
Example settings | Value | Function |
|---|---|---|
Target torque | 12 Nm | The programmed desired target torque in the controller |
Residual torque correlation factor | 100 | The compensation factor between residual torque and dynamic torque |
A number of tightenings are made. After each tightening the joint is checked with a calibrated torque wrench. The average is calculated and the following result has been found:
Initial parameters and results | Value | Function |
|---|---|---|
Target torque | 12 Nm | The programmed target torque in the controller. |
Final torque | 12 Nm | The final torque reported as the result of the performed tightening. |
Dynamic torque | 12 Nm | The uncompensated measured torque from the tool transducer. |
Residual torque | 10 Nm | The residual torque measured with a calibrated torque wrench or other test tool. |
Residual torque correlation factor | 100 % | The compensation factor between residual torque and dynamic torque |
The testing shows that the residual torque is too low to produce the desired clamp force. The Residual torque correlation factor is calculated to 0.83, which is 83 %. An adjustment of the tuning factor is made and the following result is obtained.
Final parameters and results | Value | Function |
|---|---|---|
Target torque | 12 Nm | The programmed target torque in the controller. |
Final torque | 12 Nm | The final torque reported as the result of the performed tightening. |
Dynamic torque | 14.5 Nm | The uncompensated measured torque from the tool transducer. |
Residual torque | 12 Nm | The desired residual torque that ensures the desired clamping force. |
Residual torque correlation factor | 83 % | The compensation factor between residual torque and dynamic torque. |
What this shows is that we need to tighten a bit more than the specified target, to compensate for differences and to reach the desired torque in the joint.
It is important that the correlation is made with the same tool type and parameter configuration that will be used in production.
