Lubrication of screws

Function of a screw

Screws are used to fasten components and machine elements that can be loosened again. A screwed connection is based on the conversion of a defined tightening torque (MT) via the screw head to the nut or inner thread into a pre-tensioning force (clamping force Kp) in the screw shaft with which the parts   to be connected are compressed. The clamping force generates the frictional adhesion of the screw in the thread. Only if the clamping force is sufficiently large, is the screwed connection of the component secure.

Relationship between tightening torque, coefficient of friction and pre-tensioning

The frictional resistances in the thread (µ_thread) and under the screw head (µ_H) )  impair the conversion of the tightening torque (M_T) to the pre-tensioning force (Fp). However, the frictional resistances also make a fastening thread self-locking. Only approx. 10 % of the tightening torque is actually converted into the pre-tensioning of the screw. The remaining 90 % is required in order to overcome the friction in the thread and under the screw contact surface. The coefficient of friction of the screwed connection depends in particular on the material and the surface of the thread and the screw. The size of the screws does not have any influence.

Use of lubricants in screw lubrication

In industrial mounting it is of particular importance to achieve a defined clamping force. Through the use of special screw lubricants the required coefficient of friction of the screwed connection can be "set" correspondingly. Dismantling of a screwed connection should be possible without any problems in reality. However, this is usually not the case, because screws may corrode into a "permanent lock" in particular at long periods of use and under aggressive conditions of use. The use of special lubricants prevent corrosion and seizing of the screwed connection. The time required to loosen these connection for example during the inspection of supply lines, fittings and machines is reduced notably. This results in a direct reduction of the costs.

Choosing the right screw lubricant thus not only ensures the reliability of a screwed connection, but also facilitates dismantling later on - including corresponding cost advantages.

OKS lubricant for screw lubrication

The reliability of a screwed connection and its trouble-free dismantling place high requirements on the lubricants, such as pastes, oils or antifriction lacquer, used to this purpose. In addition to an optimum coefficient of friction and excellent corrosion protection, properties such as water and chemical resistance, suitability for food processing technology, compatibility to plastic, environmental compatibility, work safety and user friendliness have to be fulfilled.

Experts from a wide range of different disciplines work in our laboratories with state-of-the-art systems and test equipment in order to develop lubricants that fulfil these requirements optimally.

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