Torque For Plated Hardware:More or Less?
Torque For Plated Hardware:More or Less?
(OP)
An argument has erupted as to the correct installation torque for zinc and cad plated hardware as compared to plain clean steel hardware; our joint assy torque calculations are based on "K" factors suggested by Shigley which shows zinc or cad plating factors to be significantly lower than nonplated steel i.e., 0.2 and 0.16 (plated) versus 0.3 (nonplated). These factors result in lower torque for a desired preload when using plated vs. non-plated hardware [we use the simple equation(T=fKd)].
However, our lead engineer insists that zinc plated hardware requires 1.4x greater torque than for unplated hardware and will only provide an anecdotal reference which we cannot verify. Can anyone please resolve this with specific literature references?
Thankyou if you can.
Tom
However, our lead engineer insists that zinc plated hardware requires 1.4x greater torque than for unplated hardware and will only provide an anecdotal reference which we cannot verify. Can anyone please resolve this with specific literature references?
Thankyou if you can.
Tom





RE: Torque For Plated Hardware:More or Less?
Coating Nut factor
------------- ----------
bare steel 0.2
Cd plate, dry 0.2
Zn plate, dry 0.295
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Torque For Plated Hardware:More or Less?
I will be very carefull with those coefficients for critical use and I would recommend actual testing for every new batch of fasteners and clamped surfaces. It is best to use the largest fastener available that will give the desired clamping force even with the largest possible K while will be able to hold without failure if the actual K will be the lowest available.
RE: Torque For Plated Hardware:More or Less?
Take a look at this site it as some excellent tables regarding friction factors and also supplies formula for torque and pre-load.
http://www.torqueleader.com/specify.htm
regards
desertfox
RE: Torque For Plated Hardware:More or Less?
I like the NASA Design Manual approach for calculating the K value for each particular application, but this requires data on helix angle and thread angle (same as lead angle???) which do not seem to be tabulated in H28 or ASME B1.1 or Machinery Hdbk. Do you know where to find this data?
Thankyou again,
T
RE: Torque For Plated Hardware:More or Less?
The thread angle α shown in NASA RP 1228 is 30 degrees. This is actually half the true thread angle α as defined in ISO 5408, so it is important to know from where your equations and data come.
You can calculate λ easily:
tan λ = l/π dm
where
π = 3.141 592 654
dm = mean diameter or pitch diameter
I recommend dispensing with K altogether and using friction coefficient equations. You can find them in VDI 2230, see FAQ725-600.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Torque For Plated Hardware:More or Less?
T
RE: Torque For Plated Hardware:More or Less?
l = lead or pitch
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Torque For Plated Hardware:More or Less?