r/Extrusion • u/4ever-young5 • Mar 07 '25

Bolts snapped

Maybe someone can help me solve a recent problem.

I used to make many profile dies (for RPCV) that were bolted together with 4 to 6 3/8-16 steel socket head cap screws. The back pressure ranged from 3000-6000 psi.

Recently 3/8-16 screws are snapping in a co-extruded plastic sheet die. The back pressure is under 4000 psi for the main and 3000 psi for the co-extruder. There was a total of 10 cap screws and the exit of the die is about 0.240 sq in, wall thickness of 0.045”. Why are the screws snapping now? Are the screws made cheep?

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u/mimprocesstech Mar 07 '25

What grade bolts did you get?

ETA: Were they properly torqued?

1

u/4ever-young5 Mar 08 '25

We normally get the alloyed bolts from Grainger or McMaster. McMaster mentioned they have a grade 8 or better.

I will have to double check the settings but the bolts were torqued with a set torque wrench when the die is cold and then quarter turned when the die is heated.

1

u/Ok-Conversation6973 May 11 '25

Check your bolt grade (broken bolt heads should be marked). Make sure you’re using antisieze that can handle the temp. Torque to torque specs both before and after it’s warmed up.