non conductive high temperature structural material for induction heating fixture

[Tmoose]

Good morning,

We need to hold some tungsten carbide plates/tiles ( roughly 1" square, less than .25" thick ) in position on a two pound steel part when heated for silver brazing . Possibly to 1500° F.

I'm picturing a springy finger bearing gently against the tiles.

Any metallic spring would likely get real hot during the brazing process and wilt.
I'm wondering what easily available materials would stay cool and be fairly rugged to survive hundreds of uses and shop handling.

thanks,

Dan T

 

[EdStainless]

Can you use pins or arms with the springs mounted outboard?
My first thought is to use H13 for the actual hot parts.
But maybe a ceramic would be better, a TTZ might be rugged enough.

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[dik]

Can you increase the distance, to allow more air circulation?

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-Dik

 

[Tmoose]

I tragically and unforgivably failed to say we use some kind of induction oven. I am mortified, and sorry.

A manufacturer of induction heaters mentions this - "Some manufacturers will hold the carbide in place with a non-conductive rod to ensure the carbide remains in contact with steel."
In previous episodes Google came back with dry wood, mica and teflon.

Hence my question. I //think// non-conductive ( to prevent inductive heating) //may// be the key.
Even if some steel spring could handle 1200+°F I was thinking the small spring might get way hotter by the time the 2 lbs of steel was up to brazing temperture.

 

[dik]

I don't know how teflon works with high heats...

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

Teflon decomposes into perfluorocarbons at high heats. Probably not something you want going on in your furnace.

Why try to keep things cool? Use materials that can operate at the temperature in the furnace. Tungsten and tungsten-moly should be able to maintain mechanical properties at your listed temperature.

https://ucfilament.com/high-temperature-springs-and-supports/

 

[dik]

Thanks, Tug

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Tmoose]

Teflon SELF IGNITION TEMPERATURE, METHOD 520-560 deg C (968-1040 deg F), ASTM D1929

https://www.icorally.com/pdf/ProTECT/MSDS-PTFE.pdf

Dry wood spontaneous ignition requires a temperature of approximately 600 °C.

Those were the Google hits for materials non conductive and thus presumably would not be heated in an induction heater.
Not candidates I was considering for my tungsten brazing retaining clips.

thanks All,

Dan T

 

[3DDave]

Fused quartz rod?

 

[MintJulep]

Could you just turn it upsidedown and let gravity work for you?

 

[TugboatEng]

The attachments may float on the braze material. A simple spring should work. The temperature isn't high enough to require exotic materials. Then again, lightbulb filaments (tungsten) have suddenly become exotic.

 

[3DDave]

Fused quartz rod sells for as little as 50 cents a foot for 1mm diameter if you are worried about "exotic."

 

[TugboatEng]

Does it have resilience? The dimensions of the system are going to change a lot while quartz will be very stable. That means tension may vary widely over the temp range.

 

[3DDave]

young's modulus 10e6 and tensile strength of 7 ksi. Not great, but if it's only holding an item from sliding around that should be enough.

https://technicalglass.com/technical_properties/

It will bend and be a bit springy - more force = more rods. Or make the mounts that hold it springy. It's not going to carry heat from the induction volume.

 

[dik]

Quartz has interesting thermal properties for dimension/phase changes.

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[IRstuff]

Quartz boats and tubes are used in silicon integrated circuit processing, with typical process temperatures on the order of 1000C. with max process temperatures up to 1200C. Continuous process temperatures at and above 1100C will tend to degrade the quartz, but that's a process cost issue, mostly.

https://www.made-in-china.com/products-search/hot-china-products/Quartz_Diffusion_Tube.html

Another possibility would be alumina and other high temperature ceramics, which can actually do better than quartz.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[Tmoose]

Most of our brazed parts have tiles on one face, so gravity mostly works OK.
We have a design with tiles brazed to two perpendicular faces. That is the problem part for gravity fixturing.
My thoughts so far have been along the lines of long cantilever spring for low stress and compliance using non-metallic materials.

My concern with an electrically conductive (metallic) spring is my ignorance of induction heating,and not knowing how it will respond to the induction heating during brazing.
I wonder if the spring, being fairly small relatively speaking, will get way hotter than the nominal 1200-1400°F we shoot for with timed heating.

In the previous century my company started using brazed TC tiles for erosion resistance. Among their developments was a patent earned for a metallic scrim used to control the gap of the finish brazed joint.
We don't use the scrim on brazed assemblies any more. Several assemblies evolved to a more elegant design using TC tiles on a single face.

I was thinking such a scrim might be necessary if the spring loaded fixturing squeezes the braze joints too thin.
As it turns out, the assembly drawing and BOM show the scrim on the side tiles.
Obviously still trying to round up all the pertinent info to best complete the given task of "design fixture."

thanks All,

Dan T

 

[EdStainless]

TTZ, transformation toughened zirconia.

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P.E. Metallurgy, consulting work welcomed

 

[Tmoose]

I just found out the brazing fixtures are made from this -

http://zircarchina.com/rs200.htm

Also in response to my question if the fixture or furnace " buzz" when the induction coils are powered - " There is some buzzing on the tungsten tiles when the brazing prosses starts but we hold them down with a stick which is nonmagnetic, so it does not affect it.

Still gathering facts.

Artisi and Sherlock Holmes sure got it right.
It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.

 

[EdStainless]

Zircar makes a wide range of products.
Various materials, densities, and product forms.
In the old days we would have used Transite, with asbestos for this.

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P.E. Metallurgy, consulting work welcomed