Galling while continuous annealing 304SS

[racy10]

We are continuous annealing 304 SS tubing between drawing passes to thin the tubing wall. We get galling of the outer surface of the tubing as it moves through and contacts the muffle tube in the annealing furnace. The furnace is about 2000F. We use disassociated ammonia for the atmosphere. What causes the galling of the 304 tubing? How can it be prevented?

 

[israelkk]

What the material the muffle tube is made off? If it is too an austenitic stainless steel it will gall with the 304. Even if it is a different alloy it still may gall with the 304.

 

[CoryPad]

You have sliding contact at 2000 [°]F? That is the problem.

 

[EdStainless]

The tube isn't' supposed to touch the muffle. Hot SS is so soft that any contact will result in galling. there should be rollers that support the tube in anneal.

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Plymouth Tube

 

[racy10]

To answer some of the questions:

The muffle tubes are 4 inches ID and 10 ft long. They are made of RA330, an austenitic alloy.

Depending on the wall thickness of the 304SS tubing we're processing, speed through the annealing oven varies from 24 fpm to 55 fpm @ 2000F. If 2000F is too hot, then what is the upper limit to prevent galling?

As the tubing moves through the muffle it undulates or becomes 'snake-like', so it's touching the ID of the muffle tubes in several places. Supporting it somehow to avoid tubing-to-muffle contact looks impossible.

I appreciate the help.

 

[EdStainless]

You could lower the temp a bit, say to 1950, but you may need to then use slower speeds to get the same results that you are accustom to.
If the tubes are snaking then I suspect a combination of crooked tubes going in and uneven heating. Try attacking those two issues.

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Plymouth Tube

 

[rayband]

A ceramic coating on the muffle tube ID might help; it has been used in other applications to reduce galling of stainless.

RAYBAND
Rock Island Arsenal
AMSTA-RIA-SEM