An interview with Robert F. Spangenberg, vice president, engineering and quality assurance, in which is discussed the use of polymer quenchant from Tenaxol, Inc., in heat treating compressed gas cylinders.

Mr. Spangenberg, in walking through the Pressed Steel Tank Company plant it becomes obvious that you produce a great variety of compressed gas cylinders.
    That's true. I think it's safe to say that our company produces the biggest variety of compressed gas cylinders, including both sizes and types, that you'll find anywhere.

In view of the variety, is "cylinder" the proper terminology in all cases?
    I don't think there's any hard and fast rule, but cylinder is good enough. Out in the field they occasionally are referred to as bottles or tanks, and, of course, our company name has the word "tank" in it, but on balance cylinder seems to be the best all-round word.

You produce them all here at the Milwaukee plant?
    That's right. This is our only plant and is the largest of its kind in the world, to the best of our knowledge. It's situated on 10 acres of land.

What are some of the end uses for the cylinders you manufacture here?
    When the company was established back in 1902 it was for the purpose of manufacturing acetylene cylinders for automobile head lamps. Today our cylinders are used for Scuba diving, breathing air for firemen, carbon dioxide for vending machines, medical gases, fire extinguishers, acetylene, chlorine, ammonia, refrigerant gases, and so forth. I could name a lot more, but these might give you an idea.

Cylinders are your only product then?
    Not really. Over the years we have developed a good deal of expertise in forming seamless shells which are the bottoms and tops of many of our cylinder and tank products. We sell literally thousands of these shells to other companies who complete the welding process to make their own containers, and then some of these shells are used for other purposes as well.

Getting back to your basic cylinder lines for a moment, how do you bracket these size-wise?
    The variations sometimes seem countless, but on balance I'd say that diameters range from 2 inches up to 24 inches, and nearly all the lengths would fall somewhere between 7 inches and 54 inches. Wall thicknesses range from .050 inches up to .750 inches.

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"We began production use of Tenaxol quenchants in 1964.  Tenaxol has worked satisfactorily the whole time."

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What about the materials you use? 
    We use 12 basic steel compositions, all of which are to our own specifications.

You mean every steel you use is custom-produced?
    That's right. These are specifications we've drawn up to provide material that gives us good metallurgical properties in our finished products as well as adaptability to our manufacturing methods.

Would you describe some of these for us?
    They range from mild steels -- below .10 carbon -- and around 1015 to 1020, through high strength low alloy steels, still below .20 carbon, up through 4130 which is what we use for the bulk of our high pressure vessels. Also, some steels are to ASME specs which are employed in the manufacture of ASME vessels.

Would you digress a moment? What's the technical difference between a high-pressure and low-pressure cylinder?
    The commonly accepted dividing point is 900 psi service pressure. Above that is high-pressure, below 900 is low-pressure.

Does Pressed Steel Tank produce a preponderance of one over the other?
    No, actually it's about half and half, I think, without looking it up. 

Is the manufacturing process the same for both?
    Oh, no. High-pressure cylinders are seamless, that is, produced from one piece of raw stock. Low-pressure cylinders generally are made by welding two cups, or halves, together. This is not exclusively the case, however.

Getting back to materials, then, do you use one type more than any other?
    Yes. All of our high-pressure cylinders are made of 4130. As high-pressure cylinders are roughly half our output, it figures we use a great deal of our 4130 specification. This material also is the only one we quench and temper. 

The last statement prompts a number of questions, but before we get into that, just what is the base stock you work from?
    Except for rare instances, such as tubing, we work with "circles" which are discs blanked from sheet or plate. Thicknesses range from .090 inches up to .750 inches, with diameters from 10 inches to 42 inches. There are exceptions, but these ranges cover the bulk.

Then what happens?
    The manufacturing process consists of taking the circles from flat discs to cups or complete cylinders by means of presses and progressive dies. Once the basic shapes are achieved, the second half of the sequence consists of various finishing operations such as welding halves together, forming necks and closures, welding on fittings and attachments, heat treating, cleaning, painting, and so forth.

It seems you have furnaces located throughout this plant. Would you comment on this?
    We have eight furnaces, totally, five on what we call the "finishing" side of the plant, and three on the press side. Six of the furnaces, all of which are gas-fired and continuous, are used for stress relief-anneal or normalize operations during or after forming. The other two facilities are heat, quench and temper furnaces, and these are the ones that process all of the 4130 material. The stress-relief furnaces are located to be essentially in-line with the forming operations so that we can minimize materials handling and movement.

So it should be safe to assume that the two furnaces you just mentioned are the ones that utilize Tenaxol as a quenchant?
    That's right.

Would you elaborate on these, please?
    The bulk of our 4130 cylinders -- probably 90% of them -- are heat treated in a single-row pusher-type furnace using fixtures and trays. At the discharge end is the Tenaxol quench tank, and at the discharge end of the quench tank is a two row pusher-type tempering furnace positioned parallel to the hardening furnace. These furnaces can handle cylinders up to 30 inches high, which covers the bulk of our 4130 product line. Another furnace handles the 4130 cylinders that are too large for the 30-inch line.

Let's talk about Tenaxol and the first furnace then. How big is the quench tank?
    It holds 1,200 gallons.

Which type of Ucon* quenchant from Tenaxol do you use?
    We've always used Ucon A, mostly in a 11-12 percent concentration. Occasionally, but not too often, we run it up to 15 percent.

Why this concentration?
    It's the one we've found to be most effective for our operations. We have to obtain full hardness, right around 44 to 48 Rockwell C, as quenched, quenching from the outside only.

The cylinders are not totally submerged in the quenchant?
No. The necks, or openings, are always above quench level.

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"Metallurgical requirements must come first as safety is most important. Incidentally, Tenaxol gave us better properties than oil. On top of this is the fact that we have no fire hazard, we don't have to clean quenchant off the cylinders prior to tempering, and further, there's no smoke from the quenching process."

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How long has Pressed Steel Tank been using polymer quenchant from Tenaxol?
    That's an interesting question. To the best of our knowledge, we're one of the "oldest" Tenaxol users around. Matter of fact, our company was intimately involved in development of the data that got Tenaxol on the approved quenchant list for compressed gas cylinder manufacture.

Say again, please?
    Well, Federal regulations some years back specified that cylinders be quenched in oil. We started experimenting with Tenaxol in 1963 and the data we developed in joint effort with the people at Tenaxol were fundamental ingetting this type of quenchant approved for use in industrial cylinder manufacture. The effort required obtaining a change in specifications, and as you might expect, getting a change in any Federal regulation or specification is a major task. Even so, the results of the work were impressive enough so that the Bureau of Explosives issued an exemption -- the BOE responsibilities later were assumed by the Department of Transportation -- and we began production use of Tenaxol quenchants in 1964. The new specifications ultimately were approved in 1971.

So, you've been using Tenaxol for what, nearly 14 years now?
    That's right.

Any problems?
    No. Tenaxol has worked satisfactorily the whole time.

Do you do anything out of the ordinary to maintain it?
    Nothing out of the ordinary. We check the concentration once each shift with a refractometer. We have an adjacent tank and pumps to use whenever the quench tank needs pumping out for whatever reason, routine maintenance and so forth.

It's obvious that Pressed Steel Tank is satisfied with Tenaxol's performance, then, right?
    Very satisfied. The thing is, our products are critical. Metallurgical requirements must come first as safety is most important. Incidentally, Tenaxol gave us better properties than oil. On top of this is the fact that we have no fire hazard, we don't have to clean quenchant off the cylinders prior to tempering, and further, there's no smoke from the quenching process. We think Tenaxol is an outstanding quenching material.

*Ucon is a trademark of Union Carbide Corp.