Ceramic Coating Needed For Steel Ring used in Heat Treating Fixture

[Maui]

We have a die set-up for fixture quenching parts during heat treatment. The parts are removed from the austenitizing furnace at 1560F, and placed onto a room temperature steel table ring and then retracted into the machine where they are oil quenched. The elapsed time from furnace to quench generally takes less than 30 seconds. One of the issues that we are having is that heat is being drawn out of the part by the table ring before the part makes it into the oil quench, which results in a slack quench and hardness variations on the part surface. We want to prevent this from happening. If we apply a ceramic coating to the hardened steel table ring it should minimize the conduction of heat between the hot part and the table ring prior to oil quenching. My question is this: what ceramic coatings are available for this type of application that could be applied in a relatively uniform thickness over the surface of the table ring? Is there a particular supplier that you have used for a similar application that you can recommend? Thank you for any help that you can provide.

 

[CoryPad]

This sounds like a good application for a ceramic coating applied via thermal spray or similar technique. One type of coating is known generically as Thermal Barrier Coatings. You can learn more from vendors like Oerlikon Metco, Praxair Surface Technologies, and Bodycote.

 

[arunmrao]

Maui, you may try on a first time basis, zircon based coatings, used in steel foundries. I use them, for want of an alternative in Nigeria. I am sure, there are better products available .


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[tbuelna]

Maui-

What does your quench plug look like? Quench plugs usually have a "toothed" OD profile that minimizes the total contact area with the mating part ID. The spaces between the quench plug "teeth" also allow greater oil flow over the part ID surface. The same is true with quench press plates. They typically have grooves that minimize contact area with the part faces, while also maximizing oil flow over the part surface during quenching. Here is an example:

 

[CoCoE]

Dear Maui,

Can you post some photographs?

I would like to see it and study!!

Regards

Cococa

 

[Maui]

Cococs, tbuelna just did.

Maui

 

[tbuelna]

Maui-

You can try applying some type of thermal sprayed ceramic coating to the contact surfaces. Then give the coated surfaces a very careful finish grind/hone to bring them into the tolerance required. As you are probably aware quench plugs require fairly precise control of the outer profile. Tight enough to keep the part round, but loose enough to prevent the plug from getting stuck. Hard ceramic coatings will likely require diamond tooling to finish grind. You need to take care when finish grinding a thin ceramic barrier coating on a metal substrate, since it is very easy to create excessive heat at the grinding contact which will cause the ceramic coating to crack and spall. Spalling of the coating is also something that might be an issue in service after repeated rapid heating/quenching cycles, due to the thermal expansion/conductivity mismatch between the metal plug and ceramic coating.

If spalling/cracking of a thermal sprayed ceramic coating becomes a problem, you might look at attaching small ceramic pads/inserts to the (austenitic?) metal plug. The pads/inserts can be attached mechanically using something like a press fit hole or a dovetail joint. Or they can be attached by brazing, similar to how carbide inserts are attached to steel cutting tools. Unfortunately, this approach would add cost to the quench plug. But it may be justifiable for a large production run, or high value parts.