Spring relaxation

[koza19]

I have a technical question about a compression spring we make for a customer. The spring is made of 316SS spring temper per ASTM A313. The problem that occurs is the customer places the compression spring into a mold so the spring is under some compression, about 20% of the deflection and the stresses at the compression point are lower then 10% MTS [Minimum tensile strength], the mold and spring get heated to 300F for 15 min and after the heating cycle the customer is finding that the springs are approximately 10% shorter. When we manufacture the spring we coil it and then stress relieve at 400F for 30 min in a inline oven.

The question I have

Is this spring relaxation due to temperature or insufficient stress relieving after the coiling process.


We are running some tests but I was hoping to give some preliminary info to the customer based on any feedback.


Thanks much

 

[TVP]

It's a combination of the stress at the elevated temperature. Have you investigated coiling the spring longer and then hot setting the springs? This is the typical method for removing undesired compression set that occurs during the use phase at elevated temperatures.

 

[koza19]

Thanks for the feed back that is a option we are discussing.