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Thread: Finding appropriate bolt torque when bolt bolt is used on PVC surface

  1. #1
    Associate Engineer
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    Finding appropriate bolt torque when bolt bolt is used on PVC surface

    I am currently bolting a sheet of PVC to a steel frame.

    For an M6 8.8 bolt the standard torque is 9.3Nm, according to various

    However Im not sure if this takes into consideration the strength of the bolted material. Im a little worried that the PVC may be damaged by the clamping force (The compressive strength of the material is 67MPa). According to my calculations the clamping force and washer area would lead to a stress of 24 MPa.
    My concern is the factor of safety could be too low.

    Are there any standards that help the user find what bolt torque should be applied with the bolted material properties taken into consideration.

  2. #2
    Lead Engineer Cake of Doom's Avatar
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    Do you have enough material to run practical tests?

  3. #3
    Administrator Kelly Bramble's Avatar
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    Standard torques assume that both materials at of equal strength..

    To estimate the number of require threads of engagement required of the weaker material see:

    Threaded Hole Fastener Pullout Stress

    https://www.engineersedge.com/thread...olt_stress.htm

    If you can use a bolt-not design and don't exceed compressive force that would crush the installation.

    Axial force torqued bolt.

    https://www.engineersedge.com/materi...alculation.htm
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  4. #4
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    Quote Originally Posted by okelly37 View Post
    Are there any standards that help the user find what bolt torque should be applied with the bolted material properties taken into consideration.
    I am not aware of any such standard. This is quite application specific. Maybe if you have an option to use a washer of material like teflon or polyurethene with toughness between steel and pvc that might help you to use more torque. Its all depends on the dimensions of the sheet and frame.

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