Strongest plastic thread

[charjacq]

Hello!

I'm searching information on plastic threads, especially on how to optimise the thread to get the maximum tensile force.

Any pointers would be appreciated.

 

[MikeHalloran]

1. Make it bigger and coarser.

E.g. 1-3/4-4 Acme vs 1/4-28UNF.





Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

Oh. I thought he meant threads like you'd stitch with (i.e. fibers), and was gonna answer "spider silk".

 

[MikeHalloran]

I've worked with fire- resistant sewing thread comprising 3 strands of Dacron and 5 strands of stainless steel. It looks and feels pretty much like ordinary Dacron thread until you try to bend it.

I'm still trying to figure out how to use it in a sewing machine; it's so stiff that it doesn't always buckle when the needle backs up to make a loop for the bobbin to jump through. Barred needles help, but not enough.

[ The job is gone, but I'm still trying to solve the problem. All engineers are lunatics that way. ]





Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

Ick! We had some insulation for a rocket engine that had to be stitched; it was nomex fiber with s.s. threads, and had to be hand-stitched due to the thickness and strength of the materials being stitched. Later on, I found a gal who would assemble (stitch) multi-layer insulation blankets for an IC engine, she used nomex and fiberglass thread, it held up well and fed okay thru her sewing machine. The machine was built for curtain-making I think she said.

 

[MikeHalloran]

We used 'fiberglass' thread when the stainless didn't work out. The stuff was light brown. I think it comprised glass fibers held together with FEP. It fed okay through commercial sewing machines, but it would separate when it got really hot.

By really hot, I mean in direct contact with cast iron that was glowing red-orange. The stainless thread took that abuse a lot better, but the machines dropped every other stitch, so the seams had to be done twice and looked like crap.



Mike Halloran
Pembroke Pines, FL, USA

 

[wes616]

a side note: a single thread of glass fiber or carbon fiber is called a filament. Filaments are twisted together, typically with a "z" twist or an "s" twist into a yarn.

In glass, several yarns are wound together to create balanced yarns. It is not uncommon to find yarns with over 100 miles of filaments per pound of material.



Wes C.
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[RPstress]

Performance yacht rigging probably makes use of the highest performing practical ropes and yarns.

 

[charjacq]

Thank you all for your reponses.

I should have been more specific. I am inquiring about bolt threads, how to make the plastic threads stronger.

 

[zerosum]

Priceless information of no value here, but fascinating none-the-less

 

[CoryPad]

When you say plastic, do you mean a thermoplastic polymer? Is this a molded part?

Larger diameter & finer pitch, maybe rolling the threads instead of molding, use fiber and/or mineral reinforcement

Regards,

Cory

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

 

[charjacq]

Yes, molded part. Plastic threads cannot be rolled, they must be molded. I'm intesrested in finding out which shape of thread will yield the best results.

 

[RPstress]

http://www.icotec.biz/

seem happy enough to use standard fine threads (UNJF, I think).

Using a suitable plastic and getting some sort of fibre reinforcement in there makes the real difference. Icotec use continuous glass and carbon, but short fibre will be quite good as well.

 

[wes616]

RP,

The "J" in UNJF implies rolled threads. Cut threads are called out as UNF. Plastic threads can be cut though.

I worked at an injection molder when I was in high school, and we produced several types of thermoplastic screw. Some threads were molded. Others were shank only, and the threads were cut with a die.

Wes C.
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No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.

 

[btrueblood]

wes,

I thought UNJF just meant "controlled root radius" for the male threads, with no real restriction on how the thread is formed. Rolled threads do offer strength improvements on metal fasteners...and I don't know if one can buy UNJF series thread-cutting dies or not.