Applying Loctite to a screw changes the screw's axial force.

Today, we are going to discuss the "Applying Loctite to a screw changes the screw's axial force.Here is a note about "The

By applying Loctite to the screwEqualization of frictional force　The following is an example of a product that can be used for the following purposes.

This equalization of frictional force can be accurately thought of as "frictional force reduction.　When a screw is tightened, the tightening torque is affected by the friction of the screw thread and the friction of the seat surface (the seat surface of the screw neck).

For the same tightening torque, an object with less friction will have a larger axial force, while an object with greater friction will have a smaller axial force.Just as the thrust in a ball screw is different from the thrust in a trapezoidal screw, the efficiency with which the force in the direction of rotation is replaced by thrust changes. 

Today I will note that part using a formula.Please refer to this page for those who are engaged in severe design and assembly.

Loctite can "equalize the frictional force" so the axial force changes.

Now I will make a note of the calculation formula.

Tightening torque (when Loctite application is not assumed)

Tightening Axis Force1383*((Effective diameter 2.675/2)*(((Screw friction coefficient 0.25/COS(RADIANS(30)) + lead angle 0.0595)+(seat friction coefficient 0.25*(seat effective diameter 5.5/2)))/1000 = 1.6Nm

Tightening torque (when applying Loctite)

*The following formula assumes the tightening axial force to be "1737 N". Since Loctite is applied, the coefficient of friction is 0.1.

Tightening Axis Force1737*((Effective diameter 2.675/2)*(((Screw friction coefficient 0.1/COS(RADIANS(30)) + lead angle 0.0595)+(seat friction coefficient 0.25*(seat effective diameter 5.5/2)))/1000 = 1.6Nm

Thus, it can be seen that the axial force is different for the same tightening torque due to reduced friction.

Conversely, if the same axial force of "1383 N" is to be obtained and the tightening torque is assumed with and without Loctite application, then

• Without Loctite application: 1.6Nm
• With Loctite applied: 1.27Nm

*The coefficient of friction of 0.25 without Loctite and 0.1 with Loctite are my standards. These are not the instructions given by Loctite. Please understand that these are based on my experience.

The use of Loctite for screw fastening should be determined from the outset of the design process.

As shown above, it was found that the axial force changes when Loctite is applied to the screw. What we need to be aware of here is that there is variation. As a recommendation for applying Loctite

• For through holes, apply a few drops to the threads at the point where the nut is tightened.
• In the bag hole, put a few drops of thread-loosening adhesive at the bottom of the hole.

but if the amount of this Loctite application is increased, the

Frictional force decreases → Axial force exceeds bearing capacity → Screws are loaded more than expected → Failure occurs unexpectedly

This is the case.When Loctite is applied for sealing as well

• Apply 360° to the screw side to ensure complete filling of the gap.
• For large screws and gaps, apply 360° to the tap side as well.

There is a

In reality, screws are rarely torn off due to "reduced frictional force," but vibration or impact may cause the screw to stretch after a while, resulting in a reduction in fastening torque (lack of axial force), which may cause the fixed object to move.

Therefore, the design must indicate whether or not Loctite should be applied to a given screw, or the appropriate amount of Loctite to be applied.　Particular attention should be paid to last-minute designs.

Finally, if you want to figure out how to include this coefficient of friction in the calculation by changing the bolt size and so on...Calculation Formula for Screw Tightening Torque and Axial Force　Please use the calculation sheet located at

That's it.