Over the years we have looked at the nuisance of galling in several separate blogs.

That is because, every year galling makes it to the leader’s group of “Heavy Maintenance Royal Pains”, alongside, magnetism, barber pole-ing, and cupping or oil-canning.

So, let’s begin with this for anyone absent those days; Galling is the seizing of mating parts. A sort of Cold-Welding as it were.

When it is time to disassemble for inspection or repair, often the parts (hubs, casings, flanges), won’t come apart. That leads to hours of lost time and materials, often to find internal parts were savable, had you not destroyed the case. One industry I occasioned to visit finally gave up and inspections switched to mandatory replacements. Ouch!

Galling is a special thrill with the stainless assemblies often found in industries that prohibit the use of lubricants (food service and production).

Parts tend to gall as a response to friction and low-yield strength deformation. Eliminate the friction, eliminate the deformation, minimize galling. Not so fast. Can’t use most lubes in food service due to contamination.

If you’re using stainless shafts, you are most likely accustomed to a certain amount of gumminess in machining; a product of reduced strength that also contributes to deformation.

When mating parts encounter friction (resistance) they bind. Subsequently, they may deform and “cold-weld” together (gall). You can try minimizing binding during installation by slowing the installation speed; perhaps use a hand feed to detect potential galling areas; then back off pressure and speed. You can make sure the parts fit nicely (snug) to eliminate pulling the part together using the threads like a turnbuckle.

SMOOTHER & STRONGER THREADS would help as they would minimize friction and resist deformation. Using dissimilar steel parts with dissimilar hardness would also help deter galling. Try using “Rolled Threads”. Rolled Threads are smoother than cut threads so they have less surface defects which means less propensity for fatigue failure. But let’s keep the focus on galling. Rolled Threads are stronger because they are compressed or displaced into shape. That work-hardens (strain-hardens, cold-works) the thread; especially if it is a stainless steel.

“Roll-Threaded Rod Minimizes Galling”, may not be headline-making news. But it is a byproduct of that thread production method. Life is short. Be easy on yourself. Take advantage of available benefits before reengineering the whole job.

-Howard Thomas, November 8th 2021

Let me know if this reads a better, changed the order and made it (in my opinion ) a little easier of a flow without altering the message

Are there hardened (400bhn) wear plate angles and channels? November 2021 Blog

NO SUCH THING AS WEAR RESISTANT STRUCTURALS? (Other than low-hardness A588)

It is possible to make your own!

We stock a true 400bhn wear plate (sheet), 1/8” x 60” x 120”. It is clean, flat, and easy (relative to wear plates) to fabricate. We can Hi-def-plasma-cut pieces to order; simple rectangles and strips, or configurations per sketch. The cuts look almost like laser-quality with very little heat effected zone along the edge.

If you are involved with heavy plate maintenance and fabrication; more specifically, if you occasionally handle hardened wear plate, you will have a need for this unique product.

It forms well, is readily weldable (not too rich of a chemistry to cause problems), and it provides weight reduction where installation and handling might be a problem; not to mention you can make wear resistant containers, hoppers, tanks, that are lighter and therefore increase payload.

Where can it be used?

Strip it and tack weld it into the high wear areas of structural (A36) shapes. Tack it into the throat of a “U”, or, on the inside of one or both legs of an angle. You now have wear resistant structural steel.

Is a cart riding on top of a rail wearing down the top surface? Tack on a strip of this to add a 400bhn wear surface.

The material is perfect for emergency temporary patching of blow-outs on job sites until heavier fabricated pieces can be delivered. An installer can get the pieces into hard-to-reach places where a repairman could handle the plate by hand. This is an alternative to 3/8” and ½” thick A36 liners. That’s a big reduction in weight! You may even find you benefit from the competitiveness of your bids.

Cutting: oxy, plasma, band saw (use blades for hardened alloys), abrasive wheel, laser, and water-jet.

Welding: Standard Low Hydrogen Method (7018, 8018)

Form: using standard precautions for working with wear plate. Form against the grain. Leave a large radius at the bend (when wear-lining angles and channels utilize a cut-and-weld operation)

I know this reeks of a sales pitch, but, we have customers who keep this on hand around the plant for; “As Needed by Anyone Needing It” purposes. It is a life-saver for keeping things moving while you are otherwise attempting to resolve the issue.

CAUTIONARY NOTE; Working with hardened steel, anyone’s hardened steel, involves risks. Be sure to use appropriate safety gear (hot-mill gloves, hard hat, safety glasses, etc.), Utilize persons experienced in handling hardened steels, including certified welders, etc. Try to form against the grain, incorporate the largest bend radius the application will handle. And, COMMUNICATE, COMMUNICATE, COMMUNICATE.

If there is something you are not sure of; ask your vendor!

-Howard Thomas, October 27th, 2021

Or, “Keystock, we hardly knew ye. . .”

So, back in April of last year I was eulogizing Keystock; at least the longer length, higher strength, plus-tolerance kind, that for years had been a “go-to” product for a lot of people. It seemed Keystock would be going the way of the Dodo bird. But, I was apparently wrong. More correctly, it was going the way of Coke, or New Coke, or Original Coke, whatever. The point is . . . “It’s baaaack.” And, that’s a good thing.

As I mentioned then, in the steel business in most general terms, anytime you see the word “stock” attached to another word; think, “stock used to make”. Bar-stock, Bushing-stock, Brake-Die-Stock, Rifle-Barrel-Stock, Pump-Shaft-Stock, etc., would be stock that might typically be used to make those items. While it may seem to infer that there are other attributes specifically suited for the particular application specified, it may simply mean this is a material some people have chosen to make this type of part. Details should be clarified; is it closer tolerance, harder, squarer, whatever? Facetiously, a tree might be “Tooth-Pic Stock”. Works the same with the term Quality, as in; Rifle barrel quality, or Military Quality, or Drawing Quality. The explanation and caution remain the same; It may mean the steel possesses a special grade certification, but it may as likely mean that “Someone, at some time, used it for that.” So, “Trust but verify”.

Keystock is generally a low to mid-strength mild or carbon steel square or flat bar, used to make keys. Those keys are inserted into shafts. A drive motor chuck will engage with the protruding key, and rotate the shaft. The idea is that the key is of less cost and strength than the expensive shaft. If something interrupts the motion of the shaft and causes failure, it should be the cheap little key that fails not the big expensive shaft. Clear the obstruction, put a new key in, and you’re good to go, hopefully with an undamaged shaft.

The perfect piece of keystock would have less mechanical strength than the shaft, but tuned to the actual application, close enough that the shaft doesn’t fail prematurely, contributing to expensive downtime. There is the conundrum; too soft of a key and you have frequent expensive delays. Too hard of a key and you risk damaging an expensive shaft.

Ideally, commercial Keystock would be a precision cold drawn bar possessing slightly elevated strength properties, with good cross-sectional accuracy and a close oversize tolerance. The ideal oversize tolerance for many years was considered to be +.002”/ .000”. That tolerance would allow you to cut a standard keyway that would fit nice and snug. Undersize tolerance resulted in sloppy, loose keys. Too much oversize required unwelcomed machining.

Unfortunately, over the past decade or so, tolerances on commercially available Keystock gradually opened up to +/- .004 to .007” (plus or minus); even with sources that promoted “Keystock”. For several years now, it has been common to only be able to source low property mild steel, undersize Keystock, in short lengths (12” and 36”).
Longer lengths, no matter how beneficial to the end user, require expensive additional processing to eliminate camber and bow.

Running multiple draughts (passing the bars repeatedly through drawing dies) is a good practice to increase strength (strain harden) and refine tolerance. However, that process adds cost, as does additional straightening. Those expensive practices were eliminated as the marketplace shrank.

Hardness (through multi-pass cold drawing/strain hardening), tolerance, cross-sectional accuracy and straightness, are all doable. Expensive, but doable. It requires a bit of fiddling in production for an item that does not represent significant tonnage. This current economic burst has allowed “The Return of Keystock”. Check with your vendor and take advantage of a simple perk that will make your life easier.

-Howard Thomas, September 15th 2021

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Howard Thomas

Howard Thomas

Experience

Sr. Acct. Mgr. (US Southwest) / Metallurgical Consultant
Associated Steel Corporation
Jan 2017 – Present

Past Vice President / General Manager
Associated Steel Corporation
Apr 1998 – Jan 2017

Past Vice President / General Manager
Baldwin International
Apr 1974 – Mar 1997

Education

Cleveland State University
Kent State University
University of Denver

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