Tempering Oxide Scale Flaking Issue

[jvalent]

I'm having an issue where our desired oxide scale is flaking off in our process leaving the product with a spotty oxide scale coating at the finish. Here is some information on our process:

We start by taking the drawn wire and cleaning it in an inline tank to remove drawing lubes and other surface contaminants, then we use an induction heating unit to bring the wire up to temp more quickly, then it runs through a muffle tube furnace with a wet nitrogen/propane atmosphere, followed by an oil quench, then a cold kettle lead bath, water rinse and oil spray before the take up. We are having an issue with one product that is a chrome silicon vanadium composite. The scale is flaking off between the oil quench and the take up after being formed in the muffle furnace. This issue seems to be even worse after a start up from a PM. Any ideas on things to look at that could be causing this to flake off? If you need any specifics please let me know.

 

[redpicker]

High silicon content will lead to a thicker scale. Perhaps adjustment to the atmosphere composition in the muffle furnace. I am assuming that you cannot adjust the chemistry of the wire.

rp

 

[jvalent]

Thank you very much for responding. You are correct and we cannot adjust the chemistry of the wire. I will experiment with trying to produce a thinner scale in hope that it will not flake off. In our process it is typically the more scale you can produce the better. Maybe that has an adverse effect with this product? Do you know if a caustic solution after the initial clean, but before the furnace, would help at all?

Thanks again

 

[tomwalz]

What is the cleaning bath? How does it change after PM?

If they are solvent cleaning they may be diluting the oils, greases, etc. A caustic solution will saponify the oils and greases so there can be 100% removal. A commercially prepared caustic solution will also have additives to aid rinsing.

There are two cultural issues that often come into play in this kind of situation. 1. The practice of using solvents as cleaners has a much better reputation now than it deserves. Most of the really good solvents are now either illegal or so highly regulated that their use is impractical. 2. People play with baths.

A classic industry story has the night shift operator adjusting the pH up to improve performance and the following day shift operator adjusting pH down to improve performance. And so on.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[EdStainless]

No, you don't want more scale.
At some point it becomes so thick that it is porous and fractures.
You need less moisture with this product.

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Plymouth Tube

 

[jvalent]

I did experiment with creating a thinner oxide coating by increasing the line speeds. This did help and I was able to achieve a better oxide coating without flaking. The scale is still a little lighter than we would like, but I will continue to play with the atmosphere to achieve the desired results. Thank you all for your help.

We will also be looking into our cleaning bath solution and trying to make some changes there. I am not very familiar with what we are using in that part of the process, but I will be working with another process engineer on this.