Loss of preload

The biasing force loss due to setting is that portion of the biasing force which, after tightening of a screw connection is lost because roughness planarizing the materials (plates, screws and threaded head) in the contact surfaces. In addition to the intended clamping force, this must be applied with the assembly preload. If it is not observed, the connection can lose its pretension if the clamping force and operating force are superimposed . Depending on the type of connection, leaks or premature failure of the screw connection are the result. ${\displaystyle F_{\mathrm {Z} }}$

The force is composed of three sizes:

• The flexibility of the screw , ${\displaystyle \delta _{\mathrm {S} }}$
• the compliance (or compression) of the plate and ${\displaystyle \delta _{\mathrm {P} }}$
• the set amount . ${\displaystyle f_{\mathrm {Z} }}$

The preload loss is required to calculate the assembly preload.

${\displaystyle F_{\mathrm {Z} }={\frac {f_{\mathrm {Z} }}{\delta _{\mathrm {S} }+\delta _{\mathrm {P} }}}}$

Setting amount ${\displaystyle f_{\mathrm {Z} }}$

The amount to be set is obtained from the number of joints and the type of processing of these joints: ${\displaystyle f_{\mathrm {Z} }}$

Care must be taken to ensure that an additional joint for the thread is added to the separating joints , since here, too, unevenness between the threads of the internal and external threads is smoothed.

Parting line influence
Number of joints	rotated [µm]	ground [µm]
2	13	10
3	16	12
4th	20th	14th
5	25th	16
6th	30th	18th

See also

• Joining (manufacturing technology)