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”.
While there may be typical answers to that question, it is still a little like asking “What is the price of a car?” It depends on a lot of variables.
The most universally accepted random bar length would be 12ft random. A close runner-up would be 20ft random. The problem that comes into play is relative to the fact that there is no literal interpretation for random bar lengths.
Further, in the steel industry, twelve food random may imply 10ft to 12ft random; which in reality could actually be 10ft to 13ft, or even 14ft random. If the shaft you are making has a finished length of 12ft, you would not want to order a 12ft random bar without specific clarification. Communication with your vendor goes a long way. Discuss your actual needs (“Finished Length”), with the supplier.
Perhaps, if you consider the cut-to-length price as the standard, or normal, price, then random lengths would be those lengths that are advantageous for the vendor to sell. One vendor may decide to sell 3ft, 4ft, or 6ft random bars. That allows them to utilize their end cuts. By selling “random bar lengths” they can make best utilization of their stock and pass savings incentives along to their customer.
If the customer is actually cutting the bar into short pieces, it is in their best interest to share that information with the vendor. Many times we will end up shipping 26ft bars across the country for years before we finally find out that those bars are being cut into 3″ pieces. Somehow, the total footage required to yield the number of small cut pieces was taken to be the minimum bar length. Shipping shorter pieces represented many advantages to both the end-user, and the supplier, that were unfortunately never capitalized on. Most sellers will cut a long bar in half as a courtesy to facilitate shipping; sometimes they will cut it into three equal pieces, also at no additional charge.
This minimizes potential damage in transit and often results in much lower shipping charges; not to mention potential incentive savings from purchasing end-cuts.
https://www.associatedsteel.com/wp-content/uploads/12_ASC_logo-1.gif00Michael Rosshttps://www.associatedsteel.com/wp-content/uploads/12_ASC_logo-1.gifMichael Ross2018-04-02 16:00:522018-04-02 16:30:49What is the Length of a "Random Steel Bar"?
“If you live in a hard-partying area of the country, you may not want to buy a new car that was assembled on a Monday. And, you may not want to shoot pool with someone whose first name is the name of a major city”. Just some considerations learned from experience.
In heavy industrial maintenance, seasoned professionals have their own hard-won cautions like the above. Those may not always be obvious. Wouldn’t it be great if those tidbits of knowledge, however, were somehow automatically transferable through the generations? However, natural powers, or gremlins, seem to insure constant attrition; constant turnover of experienced maintenance personnel, and the subsequent loss of their esoteric talents.
It’s a terrible thing to know you have solved a problem only to see things go from bad to worse because of a less-than-obvious semi-related circumstance.
Let’s say you are trouble shooting a problem where there is obvious “pitting” on the surface of a stainless shaft. For a host of reasons, pitting will eventually lead to a shaft failure. Before you begin looking into the usual suspects related to corrosion, do a little forensic investigation and see if that is really the main problem you want to solve. Pitting may not be The Big Offending Kahuna.
The shaft in question may be extra long with a small diameter (Linguini). Straightness, as in the case of a vertical mixer shaft, may be a primary concern. Let’s assume the opposite configuration of a larger diameter shaft with relatively short length (fat and stubby). In either case, straightness happens to be a key element. So, in the hierarchy of concerns; pitting is subordinate to straightness.
Most stainless-steel shaft grades, by nature of their chemistry and grain structure, retain substantial amounts of stress. Those retained stresses contribute to bow, twist, or fracture. There are grades of stainless steel, however, that respond well to thermal stress relief. Most of the retained stress is able to be removed. (less retained stress, less movement in machining and in subsequent service). These grades resist pitting, but maybe not as well as other grades. Remember though, if the shaft never makes it into service, the potential life expectancy is irrelevant.
You know steel shafts may be straightened mechanically; so, just solve the pitting problem with a material change and then straighten the shaft. But, if the shaft configuration, or the final machined configuration, does not allow for conventional mechanical straightening, or that process would require equipment that is not readily available, or the straightener guy is just plain incompetent, experience may have opted for a steel chemistry that would be less susceptible to warp and bow; either in machining or in service. The luxury of post machining straightening was not considered an option. The best steel choice in this case may not be the one with the best Pitting Resistance Equivalency (PRE). (If the shaft never makes it into service, service life is irrelevant).
To be effective in the industrial maintenance field you must be intuitive and organized. Assuming you are, then pointing out the need to look at more than one contributor to material failure is obvious. Considering the relativity of an incompetent straightener to a pitting condition, is not so obvious.
https://www.associatedsteel.com/wp-content/uploads/12_ASC_logo-1.gif00Michael Rosshttps://www.associatedsteel.com/wp-content/uploads/12_ASC_logo-1.gifMichael Ross2018-03-06 14:16:342018-03-06 14:18:53It's Not So Obvious
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