torque values for joining hot plates

[duk748]

hello - i was wondering if there was a different torque value for joining 2 plates which are at a temperature of 150 degrees each or when the 2 plates are at room temperature - i believe there is but i cant seem to find what the variation or conversion is per unit of increase in temperature - we have a platen in a plastics machine that has worked loose & the customer wants to tighten it back up w/o shutting down the machine & letting it cool - any info would be greatly appreciated - thank you

 

[EdStainless]

150C I suppose?
If these are high strength steel bolts they should have the same strength as the do at room temp.
The big problem will be thread lubrication, are you sure that your anti-seize is up to it?

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P.E. Metallurgy, Plymouth Tube

 

[MintJulep]

The reason the platens became loose is because torque control is not typically adequate for things that experience fluctuating temperatures.

You need to use elongation control, and give consideration to the expansion coefficients of the fasteners and the platen.

You could try to calculate elongation as a function of torque, but that won't be very accurate.

 

[chicopee]

150dC would be around 300dF and for plastics we are close to the melt temperature; that would be problematic.

 

[EdStainless]

And with temperature cycling you may want to use bellville washers to help maintain clamping force.

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P.E. Metallurgy, Plymouth Tube

 

[tbuelna]

The biggest issue is any CTE mismatch between the fastener and plate materials. If the plate and fastener materials have similar CTE rates, and do not experience any significant difference in temperature during operation, then it should be OK to torque the fasteners while hot.

 

[duk748]

hello again & thank you for the replies - it is much appreciated