EPS Heat Treat Headlines

This four-part series from EPS President Ken Klein, “Oven Selection and Specifications,” shares tips and tools for customers looking for large industrial oven applications.

In this first post, Ken talks about three customer categories for large industrial oven purchases:

One of my college professors started each day’s lecture with the words “today we’re going to talk about…” So, everyone, today we are going to talk about selecting and specifying an oven, a subject near and dear to every oven builder’s heart.

This is a challenging industry, especially where large industrial ovens are concerned. If we’re talking small lab units or other small standard catalog ovens, the process is easy–unless the customer’s requirements are misinterpreted. For larger units that must be designed for the application I tend to group customers in three general categories. That’s not to say some don’t slop over from one category to another, but in general they fit into distinct categories:

Category #1: The primary contact is inquiring on the behalf of others and has very little information on the application. He or she can try to get more information for you, but they may or may not repeat the requirements accurately and additional questions may or may not yield helpful answers.

Category #2: Primary contact is inquiring on behalf of others and is passing on a spec that makes it sound like they are constructing the next great missile system. Every detail is spelled out in exact terms. There are paragraphs and sub-paragraphs, ranging from those that are straightforward to those that ask for features either extremely complex or plain impractical.

Category #3: Primary contact is the end user and can tell you anything you want to know.

Of these three the second is received with mixed reactions by most builders. Certainly you have an apparently unyielding spec which should make it easy for the customer to evaluate all bids on an apples-to-apples basis, but most often the requirements are seen to be over the top or unrealistic, meaning many builders will need to take exception to a number of the requirements. That’s where things get murky. The builder wonders if he has a chance at getting the order. He may feel that if he quotes exactly to the spec the unit is going to be so expensive that the customer is likely to buy from another bidder who had the sense to take exception to the requirements he feels pile on the costs unnecessarily. In addition, the customer has a lot of technical exceptions to wade through. He may or may not have the expertise to evaluate the exceptions properly and may end up tossing the quotes that are too difficult to wade through.

So – let’s guess at which one is my favorite. The third of course. Easiest to understand and respond to. This article is addressed to those of you who need an oven and want to get a good comprehensive bid on your requirements. We are going to concentrate on forced convection ovens. Here’s what you should be thinking about when you talk to prospective bidders.

Next up: Ken Klein talks about the characteristics that matter when choosing an oven.

Our company is using a commercial heat treater and we’re getting good results. Why should we buy a Cress furnace and do the heat treating in house?

This is one question that we hear over and over again and there are arguments to steer the answer in both directions.  We’re going to look at several scenarios so that you can select the correct solution for your company.  Not all heat treaters operate this way, but with the high cost of energy, some are forced to take steps to keep costs low to stay competitive.

Background

You’ve created a tool, a part or series of parts in your machine shop that you need for your operations, or your customer’s requirements.   The designer has chosen A2 tool steel and specifies a hardness of 60 to 62 Rc is needed.  The part or parts could weigh 2 pounds, or 50 pounds and may have taken five hours, five days, or five weeks to make.  Regardless of the time, your company has invested time and money into producing the parts to satisfy a need.  You package the parts up, ship them off to the heat treater and ask them to be heat treated to 60 to 62 Rc.

Scenario Number Two

This is one of my biggest complaints about commercial heat treaters.  The parts arrive, a job ticket is written up.  The job is assigned to a person on the floor who often has no formal training in handling parts or heat treating for that matter.  The company metallurgist sat in their lab and only is called to verify the process to be applied if the leadman, or shop foreman can’t find the process in his private notebook.  The only time the metallurgist gets involved is if the hardness level is incorrect, and you know that the owner of the company will always be in his office concerned with bill paying or sales.

Bottom line of this scenario….. Even if the hardness reads correctly, you have no absolute assurance the times, temperatures, pre-heat, quench or tempering cycles were followed to the prescribed recipe.  Your part quality is at risk.  The life of the part is at risk along with your reputation. Your only hope is to request and pay extra for strip chart recordings of every step of the parts in process.  Even then there are things that can effect the quality of the finished product.

DISCLAIMER OF LIABILITY
The material presented in this article is intended for general educational information only.  It should not be used for a specific application without careful analysis and study of the in¬tended use.  Anyone using this information or relying on it assumes all risk and any liability arising from their applications and use.

I’m not sure there is one pat answer to that question because there are some heat treating processes which are not always economically feasible. But first, let’s consider what you might be getting for your money when you use a commercial heat treater.

Commercial heat treaters are in business for one purpose… Making Money. Most commercial heat treaters have large or medium size furnaces and they must have a sufficient volume of metal in that furnace to justify turning it on. Thus, if you send them 2 lbs or 100 lbs of A2 tool steel, they may not be able to justify running the furnace until they have 300-400 pounds collected. So delivery time becomes an issue.

But worst yet, is if the commercial heat treater is not quite ethical, they may load your A2 tools, which require 1775F, in with some S7 that requires 1725F and D2 or H13 which requires 1850F and heat treat all at 1825F. What that does is over cook your A2 and S7, resulting in a low hardness and excessive retained austenite, which they fix by freezing in a mechanical freezer to –150F. That transforms enough austenite to martensite to get by and raises the hardness back to an acceptable level. But even though the hardness reads fine, the grain structure is not correct and the tool’s life is affected. The D2 and H13, on the other hand, are not quite cooked enough, which means you are missing all the carbides the steel could offer because they did not get into full solution during the soak. Again, the deep cold will bump the hardness up to acceptable levels but, again, your tools will not wear as long as they should and may even chip easily.

So far we haven’t even discussed the various sizes of the parts in the mix. A2, D2, H13 and S7, plus other air hard steels, require a soak at austenizing temperatures of 1 hour per inch of cross section. So, if the load contains small parts and larger parts, they must heat treat based on the size of the larger parts in order to get any hardness at all. This over cooks the smaller shape parts and again using deep cold they gloss over the problem and fool the customer.

Next is tempering. Tempering should be started once the metal is quenched to below 150oF, and never allowed to reach room temperature and if it does absolutely should it never be allowed to sit at room temperature for more than 2 hours before the tempering begins. This is something that happens very commonly at many commercial treaters. It is so important that from a mill stand point a piece of steel that has been allowed to sit longer than 2 hours at room temp should be annealed and re-heat treated because that much damage; that much life has been lost. And, all steels require a minimum temper of 2 hours per inch of cross section. This does happen in some reputable commercial shops, but, again, is a major value concern if it doesn’t. One hour of soak is not sufficient because the entire mass does not get to the tempering temperature.

Please remember, most commercial heat treat companies hire lower cost workers to actually handle your parts during the processes, normally with little or no supervision. Having visited over 100 commercial heat treat shops in New England, NY and NJ, I’ve only found a small hand full that actually have their act together and the life of your tools and parts are in their hands.

No, I’m not against all commercial heat treaters. There are good ones out there, but often they are hard to find without a lot of evaluation. And there are times that you will need them when specialty processes can’t be done in smaller in-house heat treat equipment. But it’s wise to be careful when choosing or specifying the use of a commercial house. A machinist can work for days to make a tool that can be ruined in a couple hours by a poorly controlled process.

With a Cress Heat Treat Furnace you can take control of your own destiny as far as heat treatment and turn around time is concerned.

COPYRIGHT © September 2007, by Advisor In Metals

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