Did you know you can buy precision finished high-strength shafting that already has a keyway machined in it? You can. You can purchase sizes from ½” Diameter through
2 15/16” Diameter. This product is available to ship from stock from Associated Steel.

The product name is Mirraloy FM (Free-Machining) Pre-Keyed. It is an elevated strength material that is also precision finished and polished, In most sizes accurate within a couple of thousandths. The keyway runs the entire length of the shaft.

For some, that configuration may work just as received; just cut it to the length you need. For others, it will be sufficient to get you back up and running quickly while you wait for an OEM part or custom machined part.

The main thing is, be aware that it is available, and the standard length (10/12ft rdm) can be cut-in-half as a courtesy, and rushed out via an expedited package service.

Cutting keyways can be a fun and surprising endeavor. Some materials, particularly stainless grades and hardened alloy, can move and bow, and not just a little. Re-straightening is often required; sometimes even an additional stress-relief is needed. When you purchase the shaft pre-keyed, Associated Steel has already insured you get a prime, accurate, usable shaft. Just install it and carry on.

-Howard Thomas, August 24th, 2022

IT IS A HUGE BENEFIT TO THOSE CUSTOMERS WHO PURCHASE ASSOCIATED STEEL KROMITE CD60 FINISHED RAIL TO BE ABLE TO JUST BOLT IT IN PLACE AND GET ON WITH THEIR LIFE. The manufacturer assumes the risk and accepts the liabilities associated with the production of the product.

ASSOCIATED STEEL;
“If we supply it, we stand by it”. We cannot guarantee the workmanship of our customer or their agents. Making finished hardened and machined custom wear rail is not for the faint of heart. Anyone who has done so knows there is truth in that statement.

Associated Steel has a Special Services Department (SSD) dedicated to custom fabrication. They have developed a specific fabricated rail from Kromite Cold Drawn Stock. Because of unique properties and characteristics, that product has been trade named; “Redi-Rail / Kromite CD60”.

Kromite CD60 is a semi-finished or finished rail that has been fabricated, to the customer’s specifications. Much like the unique processing technique used in the production of I.D. hardened wear pipe, the processing sequence and technique for Kromite CD60 is an inseparable component of the finished product. It is only CD60 when Associated Steel supplies it complete. Associated Steel has dedicated inventory, and devoted countless hours of engineering and refinement, toward making the highest quality product. CD60 is the product of an esoteric process. It has been field tested and proven to work exceptionally well. We do not share, nor do we release esoteric production technique or production sequencing information.

There is an “art” to making exceptional surface hardened rails, and that is why we trade-name finished and semi-finished rails. The actual process is an open-air process that is accomplished as much by sense and feel as by instructions and manuals. We have been supplying custom automation rails for over 50 years.

Occasionally, we will get a call from a customer who has made their own rails, advising they are getting low hardness readings. There are times where the actual hardness testing is the culprit. However, the majority of the calls could be avoided with a little bit of education. During the flame hardening process, De-carb is created on the surface of the bar. De-carb is that grey powdery coating that is visible on the surface that has been heat treated.
During the hardening process, carbon in the steel, at the surface, is burned off and disburses into the atmosphere. (No carbon, no hardness). Carbon near the surface can also burn off, although not completely. Testing into the De-carb will result in hardness readings that are not accurate, therefore a grind spot is recommended. A refined grain structure ensures the higher hardness range that we achieve after processing.

Surface hardening, when done correctly, allows the core of the bar to remain somewhat softer in order to maintain limited ductility. That is necessary for subsequent straightening and various other installation operations.

Heavier cross sections of flat bar retain more ductility. They are easier to work with during production and installation. Thinner flat bar will be more brittle and subsequently more difficult to manufacture and install. So, a 1” x 4” bar will generally be less troublesome than a piece of ¼” x 4”. On thinner sections, “crowning” across the flat becomes an issue and brittleness can come into play. At some point, if the ratio of thickness to width to length becomes unreasonable, Associated Steel will decline to quote. There are no charts to determine the exact point of concern. Experience and familiarity is required to make those determinations.

OUR COMMITMENT
To insure we provide the best possible hardened rails, we have developed unique jigs, fixtures, custom quenching mediums and procedures, at great expense to our company. There are times when we recognize that costlier additional processing procedures may be required. In rare instances, we may decline to quote certain configurations.

Associated Steel has the ability to provide custom surface hardened railroad type rails and custom hardened rail configurations specific to beef processing and other automation industries.

 

-Howard Thomas, August 6th, 2022

Part 2 of 3

MAKING RAILS
a. if you start with cold rolled or cold drawn material remember that the manufacturing process for that product generally contributes to a noticeable amount of “retained stress”. That stress will tend to be released by temperature, and/or, vibration; meaning, while you are making the rail, or when the rail is in service.

b. if you start with a hot rolled bar, you must allow more stock removal, not only for potential decarb on the surface, but also distortion in shape (out-of-square, etc.). The mill allowance for out of square with hot rolled bars is significantly more than it is for cold drawn material. Often, a final grind is needed after processing.

So, there will be limits of what you can do to that piece of steel. Many variables will have to be taken into consideration. When we say, “Our steels machine better, weld better, or wear longer”, you must understand that is within a certain context. The statements we make are relative to other high strength steels used for maintenance applications (apples to apples). We are not saying they machine better than free-machining steel, or mild steel, or copper, or plastic.

A round bar that has been supplied as hardened from the mill, may not want to be straightened to a very tight T.I.R. To achieve a specific T.I.R. the straightener will have to overcome many factors. Consideration will have to be given to size vs length, the bar’s propensity to retain stress, etc. The operator will have to know something about the specific material’s “memory” properties and be familiar with all the potential conditions that might prohibit the required end result.

Conditions that might prohibit achieving that, are present in different forms for all fabrication jobs. They may relate to; number of pieces, grade, hardness, length, configuration, tolerance, surface finish, service temperature, etc. In addition, there are a limited number of companies offering value added services who are comfortable dealing with maintenance steels.

Metals fabrication shops only work with “serious” experienced companies, or the people they trust at those companies. They can easily lose faith in a job if you don’t have all the information needed. They can back away from a job if you keep feeding them additional or changing information every couple of days. Maintenance jobs cannot afford delays.

Metals fabrication is serious business. It is not a training ground for eager novices. Some words of wisdom you might want to tattoo somewhere on your person are: “Fabrication may be late, wrong, and dangerous.”, “Wear Plate is big and ugly!” and,” If you can’t stand the heat, stay out of that kitchen.”

Rule #1
Steels for maintenance and tooling need to be hard and tough. They need to resist abrasive wear, or gouging, or bending, or fatigue failure, or all of those issues.

Rule #2
Once you have made the base metal hard and tough, you have made a material that does not want to be messed with.

Let’s review
Making finished hardened and machined custom wear rail is not for the faint of heart. Anyone who has done so knows there is truth in that statement. If you are familiar with Murphy’s Law, when rail is being discussed, think of it as “Murphy’s Rail”.

 

-Howard Thomas, June 21st 2022

Cold Drawn – a Process Not a Material 

Cold Roll or Cold Drawn bar is often requested from a supplier as if the term indicated a grade of steel. Those terms refer to production methods not chemistry or grade. I point this out not to be stuffy, but to try to eliminate potential safety problems in the field.

Cold Roll, Cold Drawn, or Cold Finished bars may be made from 1018, 1020, 1045, 8620, 4140, etc. While most often they would be annealed (soft), there is the chance a cold drawn bar could be supplied in a hardened condition. The real problem is somewhat related to geography. In certain parts of the country, Cold Roll (Cole-roll), is most often produced as 1018 or 1020. Elsewhere, in other mills, the preponderance of production might lean toward 1045. The 1045 grade is hardenable; 1018 and 1020 are not. Expecting a material to be ductile in all circumstances could lead to significant problems should that steel turn out to be brittle.

Cold Drawn or Hot Rolled – When?
Cold Drawn steel materials may be used for various types of rails in heavy industrial applications. Hot Rolled Hardened wear bars may also be used for types of rails. If smooth and accurate travel along a rail is a concern, or if a finished cam/wheel is riding on it, you will probably want Cold Drawn, Cold Rolled, or Cold Finished (all the same) bars. If the application is “Big & Ugly”, let’s say a large heavy tank car is rolling over the rails and the rails eventually fail due to gouging, deforming, weight and wear, think Hot Rolled and Hardened. (Q&T).

Basically, a flat bar (cold drawn or hot rolled) is referred to as a rail when it has undergone some machining, and/or, hardening, or is used in an application where something is conveyed along it, or guided by it. A roller cam or trolley may ride along any surface of the flat bar, whether the bar is lying down flat, or is positioned up on end. Product may simply be slid along one surface of a flat, with no cam to assist movement. In the case of sliding, you will want to review “galling”.

If the application is “Big and Ugly”, such as moving bins of molten metal in a steel mill, the rail may be just hardened hot rolled bar stock. Pay close attention to the “out-of-square” allowable tolerance on hot rolled hardened mill bars. It is much more open than the tolerance of cold drawn bar.

WEAR BARS OR HOT ROLLED FLATS AS RAIL
Where the configuration is not sensitive to smooth uninterrupted movement (such as is required in an automation facility), hot rolled hardened bars may be used. These could be sizes like 3/8” x 2 ½”, or 5” x 8” depending on the weight of what is travelling the rail.

Generally, these types of rails will be welded or bolted to a substrate. Even Big and Ugly rails may require precise hole locations on the bars for alignment to pre-drilled holes in the substrate. When this is a requirement it is important to measure the holes centered on the length of the rail. So, you would not measure from the outside length dimension of the flat bar. You would find the center of the bar length and index the holes from that point radiating out in both directions. Otherwise, if the length was a bit oversize or undersize, the holes would not line up. The same goes for the width of the flat bar.

Our next post will focus on fabricating finished “Rails”; specifically impediments to fabrication and subsequent service-life. The third, and final post on CD bars will be an introduction to the trade-name rails produced and marketed by Associated Steel.

-Howard Thomas, May 9th, 2022

ASSOCIATED STEEL PRODUCTS: KROMITE® #3 (Hot Roll) & MIRRALOY® (TG&P)
The following tips assume you have an existing piece of shafting in 4140 or 4150 alloy steel, that is presently at a through hardness of approx. 30RC. And, that you require an increased hardness of approximately high 40’s to low 50’s RC.

PREFERRED METHOD: Long cycle anneal
Anneal at 1525F, one hour per inch of greatest cross section.
Cool in a furnace to 800F, at a rate of about 20F per/hour.
Re-heat to 1525F, one hour per inch of greatest cross section.
NOTE: In the event you have to move the material a significant distance between the heat temp and the oil quench, take precautions not to let the temperature drop below 1525F between the heat and quench. Cool in oil until smoking but no flame, approximately 250F to 300F.

NOTE: Alternate is a “sub-critical anneal”. Heat the bar to 1350F – 1400F, hold for one hour per inch of greatest cross section, atmosphere cool (in a protected atmosphere) to 350F. If the carbon is closer to .50, temper at approx. 700F to 800F for three hours per inch of greatest cross section (even for small diameters) should yield about 50 to 54RC. If carbon is closer to .40, lower the temp to approximately 400F to 600F.

NOTE: These are intended to be, and should be taken to be, suggestions for consideration, not instructions. This is not exact. If the material is too hard, repeat the cycle and try a higher tempering temperature. Repeated thermal cycling is not detrimental to the material, provided excessive temperatures are not encountered. If you do have to try several times, you may develop significant surface de-carb (powdery surface coat), which you will have to remove if you are not getting the results expected. CAUTION: Do not overlook removing all decarb in the area you will be checking hardness, no matter if using Rockwell “RC” or Brinell (bhn) equipment. Just grinding to “bright metal” does not mean you have removed all decarb. If your tests indicate you are only getting 18RC or lower, you are probably still into decarb. Even in an annealed condition those alloys would likely register a higher hardness than that.

Simply reaching for a higher hardness is not always the answer. If you try to go too high, brittleness may become a factor. In shaft applications where 28 to 32RC are deemed to be insufficient, you may want to try 32RC to 38Rc. Years ago, I was advised by an old friend; “With 4140 and 4150, “funny things begin to occur when you exceed 40RC (they tend to spit carbides). Don’t ask me what that means. I just got a strong negative visual and have been happy to follow that little gem for many years. (Real hard things can shatter like glass).

The above “tips” are just that; TIPS, as in “Hey, my brother in law’s uncle’s wife tried this once.” Plus, they are reduced to the simplest form. These basically relate to shaft stock and do not take into account a host of variables that may affect your safety and results. Part configuration, cross sectional differences, experience, etc. In all instances it is our recommendation that you utilize experienced thermal treatment personnel familiar with thermal conditioning alloys, who make use of all appropriate safety gear.

 

-Howard Thomas, April 8th, 2022

4140 and 4150 – KROMITE #3 AND MIRRALOY – modified grades of high strength alloy.

Last month, we talked about the word “modification” appearing on a Mill Test Report (MTR). This month I have been asked to clarify just how modifications have been incorporated into two key shaft materials provided by Associated Steel. Those items are Kromite #3 and Mirraloy. Both of those products incorporate changes (metallurgical and non-metallurgical), that address requirements of Heavy Industrial Maintenance.

Many times, in fact in most cases, modifications incorporated into the production of a grade of steel fall within the parameters of an established grade. They are usually adjustments to processing requirements and are specific to a particular customer. Modifications will appear on the MTRS. Some will change the allowable range of a chemical element but still carry the original numeric grade identifier, such as in the case of “H” Band Steel. H-Band steels have altered chemical ranges of certain elements to assist in thermal treatment. The change may allow slightly higher Carbon and Chromium content. The grade, however, remains basically the same. It retains the base metal grade numeric designation, plus a suffix addition. In this case “H”.

There are times when the modifications, intentional or not, may change the grade, i.e., prohibit the intended grade from being certified without an exception noted. Even a very small change in the content of an element may be sufficient to change the grade.

Many years ago, a manufacturer required a slight increase in resistance to service temperature for a part made of 4150. Over time, fatigue from repetitive motion, in elevated temperature, contributed to failure. One of the effects of vanadium is that it increases temperature resistance. The addition of approximately .15 vanadium content, to the 4150 chemistry resolved the customer’s problem and introduced a new grade of steel, 6150. In applications involving stainless steel, lowering the carbon content to .030, in type 304 stainless, created 304L, a modified grade. An “H” suffix in grades of stainless steel indicates elevated carbon content; again, a modification to the base grade.

The point is modifications are neither good nor bad. You just need to know how they will affect your application. The alloy steel grades Kromite #3 and Mirraloy, supplied by Associated Steel, are chemically modified to improve cleanliness of the melt. They incorporate bracket restrictions, (high-side for beneficial elements, low-side for detrimental or tramp elements). Improved cleanliness results in improved “toughness”, the key property that resists fatigue failure in shaft applications.

Associated Steel has been in continuous service to heavy industrial maintenance customers for nearly a century. Their products have been field proven in critical service.
The round bar shafts Kromite #3 and Mirraloy are both the same chemistry and follow the same thermal processing and grain refinement. Mirraloy is the precision finished product produced from Hot rolled Kromite #3.

 

-Howard Thomas, March 7th, 2022

Part One of Two

Steel grades in the U.S. are generally referred to by the materials standards and grading systems presented by various entities. The most common being: SAE (Society of Automotive Engineers), ASTM (American Society of Testing Materials), AISI (American Institute of Iron and Steel), and ASME (American Society of Mechanical Engineers). Those are certainly not all of them. Add to those an entire host of international agencies and it becomes a very large index. Grading systems are often common within a particular industry. Automotive may primarily use one numbering system, while pressure vessel operations would typically use another. As your time in a particular job builds up, it will serve you well to become familiar with the “esoteric” agencies and specifications typically used in that job. Be cautious, however, that your familiarity does not lead to assuming that grading systems used by your suppliers are the same because you recognize similar numbering. Be certain that the agency matches the specification referenced. Then pay special attention to any prefix, suffix, or reference to nomenclature, such as, “Modified”. The presence of that word does not have any specific connotation or purpose, other than to alert you to the fact that something relative to the specification is noteworthy. Nor does it mean that the original specification is no longer valid. While it may well mean an improved grade for one application, it may not affect your application at all.

The scope of potential modifications is broad. For instance, the content brackets for a certain element that the grade allows may have been tightened (restricted) for a particular heat-lot (melt) of steel, the bulk of which may have been destined for a particular industry. Let’s say the standard grade allows a carbon content of .38 to .42. If the melt content simply happens to fall within that grade, no modifier will be shown. However, if the ladle metallurgist has intentionally restricted the low-end content to be no less than .40, or a new restricted range of .40 to .42, the words “modified analysis” should be shown. For your needs, there may be no concern, since the content still falls within the range for the original grade. But, for the customer whose parts must hit a minimum hardness, it is very important that the carbon content is higher. For that privilege, that end-user will have paid an up-charge. Modifications may be made to element content to facilitate temperature resistance in service, strength, cleanliness, etc.

Prefix and suffix indications are more specific. An “E” prefix may mean Electric Furnace, which is a specific type of furnace treatment. An “H” suffix (H-band) relates to a chemistry adjusted to insure specific hardening results. An “H” modifier does not change the grade of the steel, it does change the hardenability potential. There may be “S” for sulfur additions, “L” for lead additions in steel, or low-carbon for stainless.

If you are not charged with the actual engineering and safety of the job, but are in an affiliated support position, you are not required to understand all of the specifics that relate to the metallurgy involved and the certification of the grade of steel. The thing to understand is that steel grades commonly bantered about in the industrial marketplace are a means of dialog. But, by the time the pen hits the paper on a requisition or purchase order, it is important that all parties are on the same page. Your general familiarity with numbering and grading systems will help you to effectively accomplish your tasks from a non-engineering position. The action you take will differ with each situation. It may be as simple as pointing out that a modifier appears. Expect a response like; “Thanks for the heads-up dimwit,” whether they were aware of it or not. Be forensically functional in whatever you do. Pay attention wherever you see the word “modified”, whether on your lunch order or marriage license.

 

-Howard Thomas, February 7th, 2022

MECHANICAL PROPERTIES: Generally, density, thermal and electrical conductivity are considered to be PHYSICAL PROPERTIES. The following represent MECHANICAL PROPERTIES.

If you expect a piece of steel to make a certain part, or provide certain benefits, you should know something about the nature of the steel you are purchasing. Understanding the mechanical properties of the steel will give you a better understanding as to how hard it will be to fabricate (cut, form, drill, tap), as well as an idea about how the steel might perform in your intended application (wear resistance, twist or bow, gouging, etc.).

HARDNESS How hard is it? This relates directly to strength, and/or brittleness.
Note: Hardness could well be an entire study i.e., variables affecting results, and interpretation.

YIELD At what point will it bend? (Plastic Deformation)

TENSILE At what point will it break? (Ultimate Tensile)

% REDUCTION IN AREA Pull it from both ends to the point of fracture. This measures the ratio of the reduced diameter at the break, to the original diameter. FUN WITH MECHANICAL PROPERTIES; roll a piece of Playdough to a pencil shape. Then pull it from each end until it breaks. The longer you can pull it and the smaller the diameter at the break, the more desirable.

% ELONGATION When pulled from both ends to the point of fracture, this measures the ratio of the length, at fracture, to the original length once it has been pulled apart from both ends. FOR MORE FUN SEE ABOVE. Once again, the longer you can pull it, the more desirable it is. There are always exceptions to your particular needs, but greater Reduction and Elongation are most often desired.

LCVN (Longitudinal Charpy “V” Notch) How much impact will it withstand?
Stick a short test specimen vertically protruding from a vice.
Notch it, then strike it above the notch with a weighted pendulum. Measure how far the pendulum travels after the specimen breaks
This is the closest indicator of “Toughness.” (Generally accepted as the standard for measuring impact strength.). “Toughness” is the main deterrent to Fatigue Failure, one of the greatest causes of shaft failure in heavy industrial applications.
.

RULES OF THUMB – NOT FOR ENGINEERING PURPOSES!
Two of the most common hardness testing methods are The Rockwell Test and The Brinell Test.
30 RC Hardness, in Rockwell “C” scale equals roughly 300BHN in The Brinell Test, 40RC = 400bhn, and so on…
Tensile (Breaking Point) equals about one half of The Brinell (BHN) reading.
EXAMPLE: Where BHN is 300, the Tensile will be approximately 150,000psi.
Yield (Bend Point, or point of plastic deformation) = is approximately 70% of Tensile
Generally, you want the yield strength to be somewhat lower (by 20 to 30%) than
the tensile. “Gives you a chance to get out of the room before the shaft breaks.”

THOUGHTS TO REFLECT ON: The test reports (TRs) for steel mill heat lots (batches of steel), are simply random checks. For 5000pcs of ½” Diameter steel bars, only a sampling will be tested. Even within those tests, results will vary. Recorded readings will usually show some variation which may be due to interpretation of results, test preparation, instrumentation, location in furnace, bar ends, etc. The surface of a wear plate may display several different hardness readings when tested in different places on the plate, by different facilities or by different people. This is not to suggest that readings recorded on Test Reports (TRs) are invalid. It is to encourage perspective within the realm of any mechanical testing. In fact, in situations where criteria are highly critical, the best method is to statistically check the actual finished part. Endurance limit testing is an excellent example of this. Many times, customers will request endurance limits on raw steel. Unless the actual finished part is tested, endurance limits posted on any raw steel product are useful only for the broadest suggestion of potential performance.

There is an excellent movie that illustrates this perspective; I believe it is “No Highway in the Sky”, starring Jimmy Stewart. It is an old movie (1950). Very popular among metallurgists and engineers. Enjoy.

 

-Howard Thomas, January 7th, 2022

From January 2020 post: NOTE: These are tips and guidelines/suggestions, acquired over the years. Not instructions.

There are steel grades (Mild Steel) that pretty much won’t harden by heat treatment. There are steel grades that are hardenable by thermal treatment. And there are steel grades that won’t harden during heat treatment but will harden if you whack em’ around; known as Work Hardening, Strain Hardening, or Cold Working steels. The most common of the work hardening grades (Austenitic) are the stainless grades 304L or 316L. They belong to a group of steel, categorized by grain type, as the austenitic stainless grades (typically 300 series, and the less common 200 series).

However, there is a non-stainless alloy steel that also work hardens; Hadfield Manganese Steel (or 11 to 14% Manganese, Austenitic Manganese Steel, or simply Manganese). It is a somewhat unique product that has found a home in heavy industrial applications where a combination of impact and abrasion tear up perfectly good steel. The railroad industry and the shot-blast industry are two of the prime venues for this product. As good as Manganese is in brutal service, it can also be somewhat “user adverse”; difficult to fabricate pretty much in every operation you might consider. It wants to work harden. During machining, it will harden ahead of your tooling, it will harden in the forming process, and it will be unforgiving of any misadventures in the welding process. Lack of attention to some simple details during welding, and you will be rewarded with embrittlement and fracture.

WELDING MANGANESE STEEL is not exotic or complex. The steel is just big and ugly, has a hard time making friends, and you need to respect some simple precautions. Think of everything you know about welding hard alloys, and pretty much reverse most of it. Don’t preheat Manganese Steel. Keep it cool, keep the interpass temp cool. Assist the welded unit to cool quickly; even if you have to spray some water to cool it. Employ techniques that tend to minimize welding temperature i.e short arc, minimize puddling, skip and backstep.

Don’t use carbon or low-alloy rods. Use Manganese Electrodes

If welding Manganese to Manganese:
Use Covered Electrodes (AWS A5.13, EFeMn-A) E-FeMnA
If welding Manganese to carbon or alloy
Use Covered Stainless Electrodes (AWS A5.4, E309) E-FeMn B
Use High Speed GMAW and FCAW not SMAW

If the Manganese has work-hardened in service (such as may likely be encountered in repair jobs),
cut away the hardened surface. Then apply a “butter-coat” of 307 stainless. The hardened surface, if not removed, will contribute to embrittlement and eventual fracture at the welded area.

Peen the welds while hot
Arc Welding is Good Don’t use OxyAcetylene (contributes to embrittlement)
Lean rod into direction of travel – flow the bead, don’t push it
Minimize energy input (65,000 joules max).

So, when welding hardened alloy steel, you are trying to get sound welds and maintain the hardness.
When welding Manganese, you’re trying to get sound welds period. Not protect any pre- hardened condition. Hardness will occur (or reoccur) when placed or placed back into service.

-Howard Thomas, December 7th 2021

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