Different spark plug material!

[GreggA]

I am wondering if anyone has used "ULTEM" for their spark plug insulator?
Im working on the kerzel H&M engine chose this material over Corian. it machines very well and is a little stiffer than Corian, has good insulating quality's too. I made my plug out of it and it seems to be working very well.
just wondering if anyone else has tried it...a 3/8" rod 1' is about 6 bucks from mcmaster.

 

[lee9966]

I was just looking at various spark plug insulating materials. For "ULTEM" I found" Material Properties of Thermoplastic Ultem – Polyetherimide, PEI
"Ultem® is the ideal thermoplastic choice for demanding, high-heat applications. This polyetherimide material can withstand continuous operating temperatures of 340° F"

That seems a bit low temp for the end of the spark plug inside the combustion chamber? Corian is very cautiously mentioned as good to 212F aka boiling point. From DuPonts website:
"Corian® solid surface is heat resistant and remains undamaged in temperatures up to 212ºF. However, as with all countertop materials, it is important to minimize direct heat exposure to protect your surface and investment."

I just posted a thread question related to this about PTFE (teflon) rated at a much higher temp:
"While PTFE is stable and nontoxic at lower temperatures, it begins to deteriorate at temperatures of about 260 °C (500 °F), it decomposes above 350 °C (662 °F)"

 

[peterl95124]

so ULTEM is a plastic whose glass transition temp is 422-F,
while Corian is aluminum-hydroxide filled acrylic, and acrylic's
glass transition temp is only 221-F,
so I would expect that ULTEM is a better choice (might also depend on filler material)

 

[a41capt]

I’ve often wondered how fired clay with a glaze would work. I haven’t got a kiln to give it a try, but it sure seems as though it would possibly approximate a porcelain insulator.

Just rambling here, I haven’t the technology to attempt it, but wondering out loud…

John W

 

[merlin]

Just another thought to add to the pile. Dow Corning makes a product call MACOR which is a machinable glass ceramic. It is good to 800 deg C. It machines like steel and has good insulative qualities. Full specs can be found at their website. Not inexpensive but we wouldn't need much per plug.
Tom S

 

[michelko]

Just another thought to add to the pile. Dow Corning makes a product call MACOR which is a machinable glass ceramic. It is good to 800 deg C. It machines like steel and has good insulative qualities. Full specs can be found at their website. Not inexpensive but we wouldn't need much per plug.
Tom S

You are rigth, its machineable with hss tools but its awesome expensive.
A good fellow gifted me some of this material for building spark plugs for my Bugatti.
They worked quite a while but then went bad. The next batches i made where from Corian.
Worked also nice but is not so brittle and expensive.

Michael

 

[xander janssen]

How did it go bad? Did it crack, crumble or loosing its ability to insulate electrically.

How many hours of running did you get out of it?

 

[michelko]

SOme of them shorted internaly so i believe the isolation cracked. Maybe i used to much epoxy to glue them in and the stress cracked them?

 

[gilbycoath]

I have a stick of material I bought fifty plus years ago that was recommend by ETW.
The piece I have is 5/8 in dia. and about 12" long.
Its is grey/ brown in colour and motley/ flecky. It turns easily, though haven't made anything from it.
It could easily be split down the middle to double the amount of small plugs to be made.
Question, does anyone know the name of it and/or used it??
Thanks.
Ron

 

[Henry K]

I have not made spark plugs but I would assume potentially different theramal expansion rates between the insulator and the center electrode and the insulator and the insulator and the outer steel housing could be a real problem and cause plug failure. For instance if the center electrode has a higher expansion rate than the insulator, it will exerte an expansion stress on the insulator possibly enough to cause the insulator to break. Any thoughts?

 

[cwelkie]

I have a stick of material I bought fifty plus years ago that was recommend by ETW.
The piece I have is 5/8 in dia. and about 12" long.
Its is grey/ brown in colour and motley/ flecky. It turns easily, though haven't made anything from it.
It could easily be split down the middle to double the amount of small plugs to be made.
Question, does anyone know the name of it and/or used it??

It may be a micarta moulded rod - a common insulation material from years gone by. I've only used small pieces of it over the years as they came to hand. One piece ended up as the ignition distributor body and cap for my Aeronca E113 model.

Here is a link to a site selling what you may have:
https://www.eplastics.com/shapes/micarta