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.

Stress relief heat treatment is used to remove stress induced in metals from various manufacturing methods. Some of these methods include: milling, turning, welding, bending, heating, cooling, shearing, forging, sawing, grinding, not to mention the steel making processes that leave the metal full of residual stresses. These stresses can cause harmful distortion, brittle fracture, and stress corrosion cracking near welds and within some grades of metal.

Removing residual stress is a time/temperature related event with a very controlled cooling cycle using your Cress Furnace. If not carried out correctly, new residual stresses can be produced that will result in greater stresses than the part had originally. To remove stresses it is recommended that you consult the mill literature for the grade of metal to determine what the Ac1 temperature is for your application. There are several methods to remove stresses successfully, but the most commonly used method is heat treat stress relief. The main criteria to use for choosing the correct temperature is to heat below the lower austenizing temperature (Ac1). Decarburization will take place above 960oF, so protect the surfaces if the surface is not going to be removed by machining.

Thus, if we have a 4140 steel part, (4140 has a 1380oF Ac1) that we want to stress relieve, we could place it in our Cress furnace, take it up to 1100oF and soak it for 6 hours, followed by controlled cooling at a rate of lowering it at 50 to 75oF per hour, in a closed furnace, to below 400oF, at which point it can be removed from the furnace, and it would be stress relieved. However, if you heated it to 1300oF, you can soak it for just an hour, followed by the controlled cooling and also stress relieve the part.