Plastic Screws Recommended Torque 2

[minchanin]

I am looking for standards or recommendations for maximum allowed torque for plastic screws, specifically for size 4-40 x ½ screw made of “peek” material (

http://www.berry-is.com/PEEK overview.html).

Do these standards or recommendations exist?
I would appreciate if someone could share with this information.

 

[mcgyvr]

Many times the maufacture of the screw will specify this in their documentation. This max. torque is also highly dependent on the size of the pilot hole.

Typically though #4-40 is a thread pitch for metal and #4-17 is for plastics,etc..

I would look into plastic thread forming screws like the hi-lo types or Plastite 45 from Reminc as they will allow a higher torque because thats what they are made for.

Here we torque a #4-17 screw into ABS using 7 in-lbs.

 

[drawoh]

mcgyvr,

I think minchanin is asking for the torque required to drive a plastic machine screw into a previously tapped hole. The standard torque equation should answer this question. You can get the proof stress by reading up on the material.

T = KDF...

...where T is torque in inch pounds, D is major diameter in inches, and F is clamping force in pounds. The stress area of a 4-40UNC screw is 0.00604sq.in.

Does anyone know the friction factor K would be? I have all sorts of literature on metal bolts and screws, with and without lubrication. I have seen nothing on plastic.

JHG

 

[CoryPad]

Unreinforced (and without PTFE filler) PEEK against another part should have [μ] ~ 0.15.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mcgyvr]

Sorry I missed the "made of PEEK" and assumed going into PEEK..