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Exactly the Same, Only Different

When steel flat products are thin, they are typically referred to as sheet and strip; as opposed to flats and plate. There are specific delineations separating the two types, however in general use distinction of the terms is pretty loose.

It is customary to describe flats and plate, or strip and sheet, from the smallest dimension through to the largest dimension. Thuse, 1/4″ x 48″ x 240″ would be how a quarter inch thick piece of 4ft wide 20ft long plate would be listed. It is fairly typical for the “grain” direction of the steel to run parallel to the length of the item. There is room for caution when grain is an important consideration; such as when forming is involved, since the plate may have subsequently been cut to a smaller size. In those instances, you can not be sure about grain direction unless it has been marketed. It is good practice to mark grain direction on remnants, or “drops”, once a plate has been cut. Grain is important for several reasons. First, when forming a steel plate it is generally advisable to form against (perpendicular to) the grain. In the case of wear plate, abrasive wear due to flow, may be diminished when the plate is installed so that the flow pattern is perpendicular to the grain. Unfortunately, many times this is theoretical rather than practical due to size and shape required.

Hollow materials may be pipes and tubes, or something like structural rectangular tubing. Tubes are generally more exacting in size, shape, and quality. Pipes are “big and ugly” hollow sections. Pipes are categorized as NPS, or National Pipe Size. Sizes up to 14″ NPS are described by their I.D. Or inside Diameter. At 14″ O.D. (outside diameter), the NPS refers to the O.D. Important information required would involve; O.D. I.D., and wall thickness. Generally, you would use only two of those measurements; not three. Caution must be exercised when “telescoping” one tube inside of another. Where a closer fit is desired, the two parts must be made, or fabricated in such a way to ensure that they are completely compatible; insured compatibility.

When dealing with pipe and tube you will doubtless encounter peripherals, such as elbows, flanges, laterals, T’s, etc. Configurations and cautions here are too numerous to list. If you will be involved with tubing or pipe it is recommended that you take the time to familiarize yourself with the materials and parts you will be encountering. Complex configurations require as much artistry and experience as technical knowledge.

Solid Steel Bars (Long bar products) are referred to as “bars” or “lengths”, or each (Ea). Hydraulic Pistons or shafts are referred to as “rods”.

Typically, there is a difference between the physical properties of a grade of steel and the mechanical properties. Generally, the physical properties are those properties that will be fairly uniform (common) to the grade. Those might include; thermal conductivity, thermal expansion, % elongation (%EL), %reduction in area (%RA), etc.

When discussing properties of steel, such as flatness, straightness, or out-of-round, it is best to avoid superlatives such as “perfectly flat”, or, “perfectly straight”. Presenting your requirements in that manner may result in a “No-Quote” from a potential supplier.

While there are many methods of determining hardness, it is fairly common in carbon and alloy steel to encounter Rockwell “C” hardness testing, or, Brinell (Bhn) testing. In sheet and coil you may encounter the Olson test, which involves an even larger ball impression than the Brinell ball. The Rockwell test is more appropriate for high surface finishes or finished parts, whereas the Brinell test method is used on “Big and Ugly” materials, such as hot rolled wear plate or bar.

Remember that surface decarb must be removed completely to obtain an accurate reading.

 

-Howard Thomas, July 8th 2020

 

Straightness Is Perishable

Bananas turn brown, avocados turn mushy, cars rust. Those are things we recognize as having a shelf-life. They are not permanent. They are perishable.

When discussing steel shafting, especially in the field of maintenance, straightness is an important property. If a shaft is received at the end user’s plant bent, It is not usable. You can’t grind it. You can’t machine it. You can’t install it. In fact, unless you are cutting it into little stubs for pins, or whatever, it is pretty much useless.

So, although we can all agree that straightness is important. We must understand that even if the bar has been straightened, it will not necessarily remain straightened. Straightening, and the subsequent handling, of a steel shaft is a commitment. Think of high school kids being required to carry a raw egg around for several months without breaking it. The exercise is intended to teach responsibility. It is designed to instill a sense of appreciation of the delicate nature of that item in your care.

We should think in terms of that when discussing anything about bar straightness.

Even if you require, or purchase “Pump Shaft” straightness, or, “Pump Shaft Quality (PSQ), responsibility does not end there. From the moment that product was created it began deteriorating. The severity of the deterioration will be relative to many influences. But, probably the most influential of all will be the diameter relative to the length.

A PSQ bar of 4140 Heat Treated alloy that is 3-1/2″ Dia. x 4 ft. long will be much more likely to maintain its straightened condition than will a 1-1/2″ Dia. shaft that is 16 ft. long. Then there is movement around the plant, packaging, shipping, unloading, machining, fabrication, installation, etc. It’s like those little turtles heading for the ocean once they’ve hatched. It’s a wonder any of them actually make it to adulthood.

The point is, if you are judicious, you should be able to solve most shaft problems where straightness is the rub. But know that it is not a slam dunk, just because the invoice says “PSQ”.

-Howard Thomas, May 17th 2018