Plastic Screw Torque

The best solution is to take a piece of the Nylon and screw 10 to 20 screws measuring the torque versus angle values. You will get 2 important values:

- the torque value to form the thread and

- the destruction torque

Your tightening torque should be between those 2 values (maximal forming torque and minimal destruction torque) at about 1/3 of the difference over the maximal forming torque.

Who gives you already a value takes a big responsibility since it is not possible to specify it due to differences in the thread profile, variations of material and friction, temperature and so on.

The number of measurements should be >10 for dispersion reasons and it is better to have 20 or even more. From the measurements you should make a statistical analysis in order to compute which are the extreme values mentioned above considering the statistical aspect of tightening.

Hope it will help

As far as I'm aware, RMS-01 is Richco Inc's "Raw Material Specification". Have you asked Richco for the information you require?

No tighter than you can get it by hand with a screwdriver. Or about 2-5 inch pounds any tighter an the threads start separating.

Don't ask my how i know.

At the torque you mention the stress in the screw shaft is >100 N/mm²!

The screw will be destroyed a lot earlier.

May I make a correction with respect to what I wrote in the 1st comment. The forming torque is valid for a metallic screw (profile for plastics) in a plastic part. If the screw is of plastic then only the destruction torque is important which ever is the material of clamped parts. The tightening torque should consider the function and give a good safety reserve Tightening at < 50 % of destruction torque.

I stand corrected. I failed to take into account the elongation. Typically though the amount of stress that is applied by hand when reaching the point of snug is all that is needed.

The screws that I use here are a nylon hybrid that can take a bit of stress but very little. the biggest problem I have had with them is they seem to weld themselves to the metal surfaces that they are holding and the slot strips out when you try to remove them.

I am using a slotted flathead screw for my purposes. I have no idea if it makes a difference or not but I imagine the the flat variety might sustain a bit more holding torque than a normal buttonhead screw.

Its all just theory anyhow. Until you put them in use at varying tightnesses, as is stated above by you nick, you will not know the actual destruction threshhold of the screw itself. So GA to you for that.

More information please.

Is the screw plastic? or is it a metalic screw fastening into plastic? Can probably get indicative numbers from our manufacturing guys, but the screw/plastic suppliers should be able to give you good information.

As previously suggested you would need to conduct some experiments to confirm suitability, as the hole diameter, wall section of the hole and the screw material and head details also impact the outcome.

Just an Engineer,

Jesusbravo is probably going to tell you anyway but....Nylon 6/6 is plastic - and I think my earlier post mentioned the (exact) supplier.

I was able to ask Richco for my query about the required Torque on their plastic screw part, but as of now i did'nt recieved any reply from them.