Stainless Steel Component annealing

Question

Stainless Steel Component annealing

PH1970 (Automotive)

(OP)

26 Oct 13 04:32

My company produces industrial fasteners (rivets that have an internal thread) from 304 and 316 stainless steel. They are made by cold forming them from wire and as the fastener is a rivet (dynamic) it must be annealed at the end of the production process to stress relieve them. The finish must be bright as often they are visible in the end user application. We have a Mahler continuous feed belt furness with forced nitrogen and hydrogen to make this annealing, running at circa 1,050 degrees. We process circa 70 kg of parts per hour. But we have to often replace the belt (expensive) and the finish of the parts is often not great and occasionally, the parts don't seem to have been fully annealed. I know other company's in my industry use ovens, does anyone have any experience / advice for using an oven for this. Thanks.

MikeHalloran (Mechanical) · Answer 1 · 2013-10-26 12:44:25

Look for air leaks, especially where oven wall parts have been omitted or damaged during a belt change.

Mike Halloran
Pembroke Pines, FL, USA

berkshire (Aeronautics) · Answer 2 · 2013-10-26 15:56:17

Does the oven have a water cooled muffle for cool down of the parts. Check for small leaks.
B.E.

You are judged not by what you know, but by what you can do.

TVP (Materials) · Answer 3 · 2013-10-28 11:27:38

PH1970,

It sounds like the atmosphere in your continuous furnace is not correct. Have you worked with Air Products, Linde, or other gas supplier to optimize the existing equipment? The dew point must be below - 40 C with a minimum of 25% hydrogen. Here are two links from Linde that you might find useful:

http://heattreatment.linde.com/international/web/l...

http://heattreatment.linde.com/international/web/l...

With regards to annealing in a batch oven/furnace, this is certainly possible. Here are some links for manufacturers that supply these items:

http://www.hotfurnace.com/pdf/xlc-s.pdf
http://www.hotfurnace.com/pdf/h2-s.pdf

http://www.riva-furnaces.com/-RMKg-RMKe-

http://www.elti.fr/notices/14%20EASYBOX%20%20AC%20...

EdStainless (Materials) · Answer 4 · 2013-10-29 14:32:17

We have bought a new mesh melt annealing furnace from Abbott, we are very pleased.

I would not run 75% Nitrogen unless you can tolerate some nitriding of the parts, 50/50 is more like it.
You need to measuring dew point and oxygen in the first section of the cooling section.
While you need good atmosphere in the anneal zone, you actually need better atmosphere in the cooling to prevent tinting/discoloration. It is most sensitive in the area where the parts are about 800F.

Continuous furnaces are nice because you set the speed, temperature, and a maximum load (pounds per foot of belt) and you will always get the same results. If you have parts that are under annealed then you are either running too fast or the belt is being overloaded.
Batch ovens are a pain, harder to keep atmosphere control and harder to get good repeatability.

Check for temp uniformity and check for leaks.

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Stainless Steel Component annealing