Q: Nylon or UHMW or Garolite for a small structural member?

The real Leigh · Jun 22, 2017

I have to make a couple of component supports for a radio transmitter.
These are 0.5" thick, 4" wide, and 6" tall. They mount vertically (6" up, 4"x0.5" footprint).
There is no lateral stress. The component only weighs 2 pounds.

There's a hole about 2.5" diameter near the top through which the component protrudes. The support is cut through the middle of that opening, with the top held in place using high-temp PEEK screws.

These must be electrical insulators, capable of operating continuously in a high-temperature (200F) environment.

I do plan to roll-tap a couple of holes for #10-32 screws.

I have nylon, UHMW, and Garolite. Which would you suggest, or something else ???

TIA.

- Leigh

Finegrain · Jun 22, 2017

As much as I detest machining it, Garolite sounds like the right material for the described parameters.

Regards.

Mike

Limy Sami · Jun 22, 2017

IMHO it's the long term service temp that is going to be a big factor

If you go here https://www.directplastics.co.uk/?gclid=CPOyqseC384CFdRAGwodxNkODw, click on a material and you will be able to find the date sheet for it somewhere on the page

Your Garolite which comes up as G10 or something looks good for heat http://www.matweb.com/search/datasheet.aspx?matguid=8337b2d050d44da1b8a9a5e61b0d5f85&ckck=1

FWIW I would not like to try winding PEEK screws in to form tapped holes in plastics, ........cut threads or pound to a pinch you will wring the PEEK screws off .

Finegrain · Jun 22, 2017

The real Leigh said:
I do plan to roll-tap a couple of holes for #10-32 screws.

Unless you are using "roll tap" in a different context, I should think this will not work well in any of those three materials. You must cut the threads IMO. Ida Know, maybe someone makes form taps for plastics?

Regards.

Mike

The real Leigh · Jun 22, 2017

Finegrain said:
As much as I detest machining it, Garolite sounds like the right material for the described parameters.
Regards.
Mike

Hi Mike,

Yeah, I'm sorta of the same mind.

I was hoping someone could suggest a different product since I hate working with Garolite (Bakelite).

But I may have to bite the bullet.
Long-term (years) untended reliability is the prime concern.

Thanks.

- Leigh

The real Leigh · Jun 22, 2017

Limy Sami said:
FWIW I would not like to try winding PEEK screws in to form tapped holes in plastics, ........cut threads or pound to a pinch you will wring the PEEK screws off .

Hi Sami,

The PEEK screws were chosen for their high temperature rating.

Perhaps a different material would be appropriate.
They cannot be metal, as this is used in a high-intensity RF environment.

Thanks.

- Leigh

Limy Sami · Jun 22, 2017

The real Leigh said:
Long-term (years) untended reliability is the prime concern.

- Leigh

In that case I'd be tempted to at least look in to the viability of PEEK,but it' $$$$$$ ........ IME laminated materials have a tendency to de-laminate over time in the wrong application etc etc etc.

TDegenhart · Jun 22, 2017

Garolite is a trade name for a group of thermoset plastics. Which one do you have?

McMaster-Carr

Tom

The real Leigh · Jun 22, 2017

Limy Sami said:
In that case I'd be tempted to at least look in to the viability of PEEK,but it' $$$$$$ ........ IME laminated materials have a tendency to de-laminate over time in the wrong application etc etc etc.

Hi Sami,

That's certainly a consideration.

Garolite (Bakelite) was invented in the 1930s. Much equipment exists that was built before WWII and is still in excellent condition. It's not a "layered" product like some more modern ones.

Thanks for the observation.

- Leigh

Milland · Jun 22, 2017

The real Leigh said:
Hi Sami,

The PEEK screws were chosen for their high temperature rating.

Perhaps a different material would be appropriate.
They cannot be metal, as this is used in a high-intensity RF environment.

Thanks.

- Leigh

You can get ceramic (Alumina) screws/bolts McMaster-Carr
but you will need cut threads on the garolite.

Just checked the price of the ceramic bolt I posted - ~$33 each. Use peek...

The real Leigh · Jun 22, 2017

TDegenhart said:
Garolite is a trade name for a group of thermoset plastics. Which one do you have?

Hi Tom,

This is Phenolic, the original Bakelite, from McMaster-Carr.
8525K32

Thanks.

- Leigh

The real Leigh · Jun 22, 2017

Milland said:
Just checked the price of the ceramic bolt I posted - ~$33 each. Use peek...

Yeah. The PEEK screws aren't much better at $6 each.
But I only need 4 of them.

- Leigh

TDegenhart · Jun 22, 2017

The real Leigh said:
Hi Tom,

This is Phenolic, the original Bakelite, from McMaster-Carr.
8525K32

Thanks.

- Leigh

That is a paper laminate, a so-so material. Its not solid phenolic like you thought. Also, Bakelite was developed in 1907 by Leo Baekeland. For you application I would choose glass epoxy or glass polyester.

Tom

xplodee · Jun 22, 2017

Check out ultem for screws. Its a good material for very hard plastic screws, easy to machine too.

The real Leigh · Jun 22, 2017

TDegenhart said:
That is a paper laminate, a so-so material. Its not solid phenolic like you thought. Also, Bakelite was developed in 1907 by Leo Baekeland. For you application I would choose glass epoxy or glass polyester.
Tom

Hi Tom,

The label on the product, from the manufacturer, says Phenolic.

- Leigh

Finegrain · Jun 22, 2017

I would suggest G-10: McMaster-Carr

Truly horrible to machine, but indestructible.

Regards.

Mike

Limy Sami · Jun 22, 2017

The real Leigh said:
Hi Sami,

The PEEK screws were chosen for their high temperature rating.

Perhaps a different material would be appropriate.
They cannot be metal, as this is used in a high-intensity RF environment.

Thanks.

- Leigh

High RF environment you say? .....now I'm right out of my depth here so bear with me, ...I'm not quite sure what a high RF environment means, ........but I make all sorts of parts for sputter magnetrons - used in the manufacture of touch screens, and included in the parts are several large PEEK jobbies, where the material is eye wateringly expensive, like ex 4'' dia x 4'' long @ around £300 per each.

In discussions with my client I'm told - (in terms I can understand

) that they have to be PEEK because they're in the RF hotspot, and they would definitely use a cheaper material if they could, but nothing else stands the pace,.......they've been there and tried that.

So I suppose what I'm saying is, if you don't know, get some hard information on suitable materials for the application - preferably getting the end user to spec it in writing.

TDegenhart · Jun 22, 2017

High intensity rf environment? You better get more information on the application and rf characteristics of the materials you suggest. Phenolic does not come to mind as a good application for that. The other materials - not sure.

Tom

jim rozen · Jun 22, 2017

Bakelite was a non-reinforced engineering polymer.

Bakelite =/= phenolic of any flavor.

For this application, if the rf loss tangent of the material is acceptable, then
I do suggested LE grade phenolic. This is linen-based phenolic and can be tapped.
Paper based phenolic will hold tapped holes very well. Avoid that.

The spec sheet for the material will give the rf absortion numbers as a function of
frequency. Inspect the data there to see if it's acceptably low.

Limy Sami · Jun 22, 2017

thanks for that Car 2, I will read it over and over and it might make sense to me - don't put your pension on it mate

But like I said ;- just passing on what I've been told, for IME it's often the little asides (oten from those not fully in the know)that cansave your ass

Q: Nylon or UHMW or Garolite for a small structural member?

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