What Material to Use for an Insulating Coating on Industrial Tongs?

[Maui]

We have different sets of steel tongs that are used for manually transferring hot parts out of our austenitizing furnace and into our fixture quenching machines. At the point where the tongs contact the hot parts, there is some heat transfer. For the thicker parts this doesn't really cause any significant problems. But with the thinnest walled parts, the heat loss at the point of contact is large enough where we do end up with low hardness readings after quench and temper in those isolated areas sometimes. What I am looking for are suggestions about what types of coatings could be applied to the ends of the tongs that would act as an insulting layer that would minimize heat transfer during this step in the process. But the coating can't be slippery - the tongs still have to be able to grip the parts. And the coating has to be able to put up with some mechanical abuse without breaking. Suggestions are welcome.

Maui

 

[TVP]

There are a number of options that can be considered for this application. I would contact some vendors of HVOF, plasma spray, and other coatings in your neck of the woods.

http://www.thermalspray.org/index.p...sk=search&Itemid=68&cat_id=42&searchword=HVOF

http://www.thermalspray.com/plasma-spray-materials/

http://www.flamesprayusa.com/flame-sprayed-coating-materials.php

http://plasma-tec.com/coating-application-chart

 

[racookpe1978]

I think you need to go back to the woven asbestos pads: Somewhat "rough" so they grip at all angles of contact, flexible, "formable" so they fit onto the end of the tongs, can be replaced when worn out, abrasive-resistant - but will erode away over time!, highly heat-resistance (won't burn out) and very low heat transfer coefficient. Won't burn off and will resist industrial use with due care so the fibers don't get in the air.

 

[btrueblood]

Foamed silica (space shuttle tile material), with suitable metal backing to hold it in place, and suitable shaping of the jaw faces to conform to the parts. Has good compressive strength, but poor tensile, like most ceramics. An alternate would be pressed+sintered boron nitride. Both materials can be fairly easily shaped/machined so you can have several replacement sets ready when one breaks. The foamed silica has ridiculously low thermal conductivity and thermal mass. See

http://www.cotronics.com

- they have lots of stuff that might work there.

Quartz/silica fiber woven cloth, or partially sintered "boards" would be a possible replacement for racooke's asbestos pads, which are probably tough to find these days.

Do realize that inhaled powdered silica dust can be as hazardous to people as asbestos fibers.

 

[arunmrao]

A not so elegant protection I wish to suggest.

Dip the tongs in a slurry paste of any refractory (fire clay, alumina etc) and then allow them to dry. You could repeat the process easily .

I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)

 

[Compositepro]

Apply baling wire hangers to your parts before they go in the furnace.

 

[btrueblood]

Or put them in ceramic "boats" ...