devencalcutt

Looking for insight in heat treat process. Any help appreciated.

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Hey guys,
 
Hopefully I am not going to upset anyone for the nature of my post, but I feel like this community would really be able to help me.
 
I am brand new to the forum, partly because of a life interest in hand crafting my own knives/swords/tools, and partly because I work as a mechanical engineer at a plant that heat treats many automotive parts.
 
I joined the forum because I stumbled upon it once before when I was curious about choosing a type of steel for a knife I was making for my father in law. I didn't join then but it was evident that you guys were knowledgeable in this field and for that reason I am back and seeking some assistance. I am not looking for help with knives this time, but in my job as the heat treating process is something common between my work and creating knives.
 
What I am challenged with is at work we are having constant issues with oxygen "scoring" on the surface of our parts. This issue is costing the company (no joke) hundreds of thousands each year because we have to ship the parts off site to have them buffed free of the surface scoring and then shipped back before assembly. Obviously my interest as an engineer is to eliminate the need for this buffing process, but it is a difficult challenge... This is where I am looking for knowledge from those with more experience in traditional heat treating methods, who may know some trade secrets to reducing scoring on the surface of your parts.
 
I should add in case I am using incorrect terminology that by scoring I mean a buildup of (what I guess is) carbon on the surface of the parts after heat treatment.
 
The issue I face is this is not a typical heat treat process. The parts are moved into an induction coil's path on a revolving table. The induction head is them moved forward around the part, the part is raised to about 1100 degrees in 6 seconds, and then it is immediately quenched to reduce the temperature to around 200 degrees over about 10 seconds.
 
Thus far, going by my own research and taking ideas from what others in the industry have been doing I have designed an "inert environment". This consists of a box that moves with the heating head around the part. The front of the box has a constant flow of water to create a waterfall over the front of the box, sealing the air inside the box. Inside the box a constant flow of 24 cubic meters/hour of nitrogen is pumped into the box in hopes to purge the oxygen out of the environment while being heated and quenched.
 
The thing is, the box works. There is no scoring on the surface on my trial parts. My problem is that we run 6 of these heads, and anything less than the 24 cubic meters/hour of nitrogen still leaves scoring on the surface. As you can imagine, 144 cubic meters of Nitrogen per hour, 24 hours a day seven days a week is going to require a MASSIVE tank of nitrogen, plus it’s going to cost a bunch (not as much compared to buffing, but I hope for better) and we are going to have to fill the tank no matter how big on a frequent basis. It’s a pain really.
 
What I come to you guys asking is for your thoughts on the process. Is there anything that you would criticize? Improve on? Try differently? It’s something that I have been working solo on for about 4 months now, and I'm scratching my head at what else I can try. My knowledge of heat treating comes from a long time welding, and that has just taught me that you need an inert gas to prevent contaminates from getting into your weld. Beyond that, I'm still learning.
 
Any suggestions and tips would be graciously appreciated, as I think I need to look outside the box. Thank you for taking the time to read through this, and again I apologize if this post isn't something that is meant for this site, and in which case I would be more than willing to take it down.
 
Thanks in advance.
 
Deven.

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Add your location to your profile.It will help in getting you better answers and references.

 

What size and type metal are you working with?

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Welcome aboard Deven, glad to have you. Seeing as Glenn beat me to admonishments about putting your general location in the header I'll cut you a  break.

 

About the oxygen scoring, is it really CARBON residue? Oxygen and steel at high temp is going to produce scale Fe2O3 (IIRC) black iron oxide. Carbon at high temp exposed to oxygen is going to burn, not remain as a residue.

 

Isolating the parts from atmospheric oxy isn't new, we do it frequently. First is operating in a carburizing atmosphere which isn't applicable to you. The other really common way we keep oxy off our hot steel is with flux. Most fluxes used on clean metals are intended to provide a prophylactic barrier to oxygen. No oxy, no scale to prevent welding. A borax based flux wouldn't survive the quench, it's water soluble and the thermal shock causes it to flake off. A high pressure washer should blast any left quickly and easily, easy automation step.

 

About the nitrogen atmosphere. Why do it in such a resource and equipment demanding way? Simply build a heat treat room with airlock. Parts feed in through airlock, get processed and are removed through another airlock. An airlock doesn't need to be some space ship unit for this, just run the chain advancement mechanism through a "P" trap air lock like you find under the sink. The parts are going to get dipped in water anyway and the heat treat room is oxy free so no oxidization can take place. A little water soluble oil in the exit airlock takes care of keeping them oxide free when finished.

 

Those are just my first thoughts, we get some more brains firing on this and I anticipate a fine brainstorming session.

 

Frosty The Lucky.

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rather than N2 have you considered CO2 ? being less costly...

 

Sorry Steve but CO2 isn't inert at those temps there will be some breakdown and the oxy will scale the parts. N2 isn't so expensive using a reverse osmosis processor, it's the natural byproduct of an oxy generator. I looked into them some time ago but the oxy was too low psi for my needs and the compression unit was WAY more than I wanted to spend.

 

Not a bad thought buddy. More?

 

Frosty The Lucky.

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Not to insult anybody here but at "hundreds of thousands of dollars a year" your company should be hiring a knowledgeable consultant to deal with a very common problem in industry; no need to reinvent the wheel when there are lots of tested systems out there!

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If my quick calculation is right, your 144 M3/hr is around 85 CFM of N2 or 180 kg/hr (400 lb N2/hr). I assume you are using Oxygen-Free Nitrogen.

 

If you can live with lower purity, an on-site membrane-type Nitrogen generator may be a (much) cheaper option. It needs a clean, dry compressed-air supply and uses membranes to selectively remove Oxygen.

 

Pressure-Swing-Adsorption systems are also available and offer higher purity than membranes, but I have no experience of them. 100 CFM is not a big system in industrial terms.

 

I'm guessing you are not in the USA by your use of units. I'd suggest speaking to your nearest Atlas-Copco distributor to get an idea of what is available, then shop around once you have an idea of what you need.

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Since nitrogen (N2) is lighter than air, why not contruct a bell in which you put the conveyor / induction coil? Hot nitrogen (due to heating) will rise, but not escape (the bell prevents it), except from the bottom (but not to much, since the lighter nitrogen will have the tendency to float/rise on air).

 

Then use some sort of PID-controller to add nitrogen when concentration changes.

 

By the way,

 

The carbon buildup you talk about sounds like scaling to me, not carburization imho.

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A flux would be one way to go.

I was also going top suggest a nitrogen generator since that is the way we are looking yo go at work. We run anywhere from 20-100 Cubic Feet an hour. The high end was due to a leaky seal that is now fixed, so more likely 50cfh and lower now.

My concern is the water being used as a seal....water contains lots of oxygen.

What is the quench medium?

Have you looked into quenching coils? Some put a ring into the heating coil itself that the quench is sprayed out of. The part is heated, then immmediatly quenched while still in the coil.

My only addition to Thomas Powers comment would be , if it is costing hundreds of thousands a year to buff I would be looking to get set up, and do it in house. We were spending tens of thousands a year on centerless grinding, so we finally bought our own-something they should have done 10 years ago.......

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Is it possible to do the heat treating in a fluid-like medium such as sand? I'm having a hard time imagining a system which would work without also pumping in an inert gas like nitrogen, but sometimes weird ideas spark other ideas, so I'll leave it there as an improbable suggestion.

However, I also echo Thomas's statement: a prudent business that's trying to save hundreds of thousands of dollars would do well to spend money on an expert who will give you a real solution. I understand the desire to come up with a great solution on your own, but "I found the answer on the internet" is not an explanation I'd be proud to give my boss. (Well, except that I program computers for a living, where solutions are legitimately found on the internet... You get what I mean. ;) )

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Possibly with the same flux as used in submerged arc welding. The induction unit's magnetic field will penetrate insulations, fluxes, etc.

If he is overseas the time difference could account for the lack of response from him.

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It does seeem rude to start a thread, and not even return to read reply's.... then again it aint too bringht spending hundreds of thousands of dollors on a problem, and asking total strangers on a website for answers,  rather than hire a engineer to sort it out either, but I am sure he has his reasons. Maybe if he bothers to return he will enlighten us? Until then we are having fun with it.

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Seeing how this thread has gone I think we're dealing with an employee who THINKS s/he can redesign the process without knowing anything about it. We all have a little of that in us or we wouldn'tve been answering the question. The main difference being we know we're just noodling a question and not redesigning a working factory.

A local guy has taken the tendency to the point of a pychological disability. The guy is collecting disability checks because he's just not capable of showing up on time, doing what he's told and not . . . Well I don't know if he causes trouble beyond spending more time redesigning the business than doing the job. I "hired" him to help me erect my shop and made the mistake of paying him at the end of the first day. I got a call from him after 5:00pm the next day ready to come to work if I'd pick him up. He had to "help" a friend in a bar last night. <sigh>

He's not a bad guy, just psychologically incapable of NOT thinking he can design anything better than what works now. It's kind of sad but I don't know how to actually help him,nor does his Mother, Stepfather or Father.

I think the OP falls into this category, maybe a 18 yr. old janitor who thinks he should be upper management.

I don't know and by now don't much concern myself.

Frosty The Lucky.

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