Talk:Galling

Focus on sheet-metal?

I'd like to start by saying that this article is very well constructed and written. However, there seems to be too much focus on the process occurring in sheet metal forming, rather than on the process itself. Galling can, and often does, occur whenever any type of metal surfaces are in contact and moving transversely to each other. It's more apt to happen if there is a high load at the point of contact and little lube, but also happens frequently in high-speed/low load contact as well. For instance, it is a common problem in air motors, like are used in impact wrenches and hoists, where the rotor contacts the end plates, or in crankshaft journals. It's also a bigger probelm with certain metal interfaces than with others. Aluminum end plates against a steel rotor, for instance, are far more prone to galling than a steel-steel interface, and a brass-steel interface performs even better yet. Zaereth (talk) 00:21, 1 May 2012 (UTC)

Well I wrote most of the present galling article and I thank you for giving me some credit.

And you are quite right. Much of the article is dedicated to metal moving transversely against fresh “un spoiled” metal.

The following hopefully explains why:

1. My Master thesis (Swedish university D-level scientific report) was dedicated to metal moving transversal against fresh “untouched” metal.
2. My pictures, found in the article and my Master thesis, are the only free pics on galling build up, availed on Wikipedia commons with a reference describing circumstances and application data.
3. It´s easy to write about your own empirics, rather then trying to figure out the origin and circumstances of others.
4. I tried making the article general and provide a uniform theory for all types of friction related plastic deformation.
5. Galling found in repeated metal/metal contacts, such as in air-motors, are much harder to theoretically and scientifically break down into discreet (single) events.
6. There are contributions about other forms of galling written by succeeding writers but they are few and of the quality seen in the present galling article.

If your are interested about background data and circumstances of the pictures found in the Wikipedia article look up, https://libris.kb.se/form_extended.jsp?f=ext, click on the link “uppsök” and then use search words: Wallin Harald & galling

I just found out that somebody recently have changed something and made my report hard to find using the search engines of Kungliga-Biblioteket, National Library of Sweden/LIBRIS, I will address the matter on Monday June 30, 2012.

--Haraldwallin (talk) 18:42, 30 June 2012 (UTC)

Thanks for the response. I hope I wasn't sounding critical, because, aside from what I see as a few minor details, the article is very good and I learned quite a bit from it. I've been working on heat treating articles, and found this one after providing a link to it from the tempering article. I understand about working form your own knowledge base, for instance, I often use steel as the main example, because that's the metal I understand the best. I usually leave comments like this, not only to invoke comments from others, which are very helpful in organizing my own thoughts, but also to help plant a seed in my own mind of what could be improved. My typical M/O is to let it stew in my subconscious for a while, and come back later with some changes or additions. With this article, the changes I would make are probably rather slight.

What really caught my eye was the first sentence. Although it's not unusual to provide examples in the first sentence, typically these are saved for a summary sentence or paragraph. However, like I said, it's not unusual to go against the norm, and often is refreshing. The thing I would probably change there is the example "other industrial applications" to be more specific. Other than that, I would probably try to include some other examples in the body of the article. Or, perhaps, the first section could be about galling in sheet metal forming, and titled such, followed by a section describing other types of galling. The possibilities are really endless. (I'm still stewing.) I hope you find my comments constructive and helpful. I'm still working on other articles at the moment, but am keeping this one in the back of my head. I'll probably be back at some time in the future, and maybe we can help each other to make a good article better. Zaereth (talk) 20:23, 30 June 2012 (UTC)

On a quick reading, at this time, I did not notice any such focus. It seems good work. David R. Ingham (talk) 05:52, 15 October 2013 (UTC)

Technical Level

I join Zaereth in complimenting the writer Haraldwallin, who's done most of the work on the article. What I'd like to ask, however, is if it's possible to reduce the technical level a bit so a layman looking to understand what "galling" is can do so with greater ease. This doesn't necessarily require re-wording the entire piece. Perhaps the writer who did the bulk of the work (or others, if he/she is no longer available) can provide an opening paragraph which speaks to the layman in simpler language, presenting the general concept for a quick grasp by those who encounter the word in other articles and wonder "what is this?". The rest of the article can then proceed as it does with greater technicality for those more familiar with the industries in which galling occurs. Cosmo1976 (talk) 13:31, 23 January 2013 (UTC)

Thanks for the comment. I have been meaning to do exactly that. It just hasn't come to the top of my list yet. I'm really busy in real life, and most of my wiki-energy is going to creating a readable introduction for the entropy article. However, per your request, I'll try to move this article up the list, and maybe I can get to it within the next month or so. Zaereth (talk) 00:47, 24 January 2013 (UTC)

This problem also appears to me to have been overcome. David R. Ingham (talk) 05:56, 15 October 2013 (UTC)

Open questions

One system that I don't find an explanation for here is automotive straight crank shaft bearings. These, as I understand, are very soft (but heavy) metals backed by moderately hard metal, in contact with the hard steel of the crank shaft. The reason for this, I read somewhere, is that this combination leads to less galling than when harder bearing materials are used. Most of the time, the metals are not in contact, because of the hydrodynamic lubrication, like that of a hard drive head. But on start-up only the thin film properties of the lubricant separate the metals. I don't see this article shedding light on this particular subject. David R. Ingham (talk) 06:14, 15 October 2013 (UTC)

Automotive-crankshaft bearings consist of two surfaces of interest: Steel and babbitt. The crankshaft is usually thoroughly heat-treated to a rather low hardness, making it tough in order to prevent breakage. However, this leaves the bearing surfaces (journals) much too soft and prone to galling. To fix this problem, the journals are induction hardened, which hardens only the bearing surface to the highest possible hardness the steel can become. This differential heat treatment greatly reduces the steel's chances of galling.

The babbitt is an alloy which the bearings themselves are lined with. The reason for using babbitt is two-fold. First, it has vey low stacking-fault energy, which means it will resist the slipping and tearing of the crystal structure, making it very resistant to galling. Second, babbitt has a very low coefficient of friction (it's a slippery metal) --even better than bronze-- which reduces all forms of wear, including galling. (To test this, simply try hacksawing through it, and you'll see how the blade glides across the metal more than it cuts.) I hope that helps. Zaereth (talk) 07:46, 15 October 2013 (UTC)

I might add that when two surfaces are sliding without much lateral load, two very-hard surfaces will work well together. Therefore, the piston rings and cylinders of engines are usually made of hardened steel. (Tungsten carbide or ceramic seals can be used in water pumps, etc...) However, in crankshaft bearings, lateral load plays a big role, as the pistons are literally hammering the bearing surfaces. Therefore, babbitt is also used for its combination of low yield-strength and high toughness, and its relatively high shear and tensile strength. (In contrast, most other types of bearings, like ball or needle bearings, are more concerned with radial load and thrust load, but babbit bearings provide better lateral-load distribution than those types, which reduces the chances of another type of wear, called Brinelling.) Zaereth (talk) 09:49, 15 October 2013 (UTC)

"Slippery" is clear, since galling is caused by adhesion. Perhaps the tendency of differing material to have less adhesion that similar materials should be explicitly mentioned in the article. I do not understand the difference between low stacking-fault energy and hardness. Perhaps I don't know the definitions of the bulk properties well enough to follow the chain of thought. Anyway, that part of the above is a long way from being in shape to add to the article.David R. Ingham (talk) 00:12, 19 October 2013 (UTC)

Isn't it mainly shear strength that resists penetration in a hardness test? Does babbit yield differently than ductile materials do? If it is tough then it must not crumble. David R. Ingham (talk) 00:32, 19 October 2013 (UTC)

Hardness usually refers to two different properties of a surface: Resistance to abrasion or resistance to indentation. Steel has very high stacking-fault energy, so it is a metal that is prone to galling. Increasing the hardness decreases the chances of surface deformations occurring, so hardened steel has a much lower chance of galling than softer steel.

To describe stacking-fault energy, it may possibly be easiest to use a stack of paper as an analogy. If you set a stack of paper next to a wall and slide your hand across the surface, some of the sheets will likely adhere to your hand and move toward the wall. The adhesion to your hand outweighs the cohesion with the stack, so the stack of paper can be said to have very high stacking-fault energy. When the paper adheres to your hand and slides toward the wall, it will bunch up and rise from the surface. This action can be compared to the process of galling.

Now, lets say you take a stapler and drive a bunch of staples through the stack all over the place. When you slide your hand across the stack, the pages will not move with your hand. By creating intersections between the planes, you have decreased the paper's stacking-fault energy, thus, decreasing the stack's chances of galling. The paper is no harder, but resists the slipping of its planes. Therefore, very soft metals like gold can be very resistant to galling. However, even a soft metal's resistance to galling can be made better by hardening it, even if only by work hardening.

The slippery aspect of babbitt is due primarily to its low shear strength (sorry, my mistake, I meant "low" in the statement above, not high) similar to teflon. What's needed besides this is good compressive strength and low work-hardenability (high ductility) to also prevent cracking and spalling. Zaereth (talk) 01:04, 19 October 2013 (UTC)

Is galling technically applicable to other materials, e.g. compacted snow? the first image resembles what sometimes happens when skiing, where a lump of snow gets detached from the ski track and and attaches to the ski. It occurs to me that fundamental principle is the same. — Preceding unsigned comment added by 164.40.242.212 (talk • contribs) 09:47, 20 November 2013

I've never heard the term used in respect to snow. Snow is typically a collection of ice crystals, similar to sand. For something to gall, it typically requires a solid surface and some plasticity, like metals. I've never heard of galling in ceramics or glass or other types of materials; just metals. Galling does occur in plants, but are more like growths or burls, and are caused by insects like galling sawflies or aphids. Zaereth (talk) 17:51, 20 November 2013 (UTC)

"the present research" in the second to last paragraph

The meaning of this phrase is not made clear, and it suggests that a source has been too closely followed. David R. Ingham (talk) 00:18, 19 October 2013 (UTC)

Most of this article, beyond the introduction, is based upon (if not a direct copy of) the author's college thesis. I very much commend them for their work, but the article is still too focused on galling as it occurs in one particular application and, most importantly, between only one kind of metal (stainless steel, which is very susceptible to galling). In such a case, there was probably no need to go into different aspects such as why stacking-fault energy plays such a big role. I plan to work on this article more, and work to change things too. (For example, the style is academic, using first-person narrative and photos as the main focal points, and need to be changed to encyclopedic style.) I don't have much time to work on these thing, but try to get in a little here and a little there when I can. Zaereth (talk) 02:01, 19 October 2013 (UTC)

Strange wording

Article has "In extreme cases, the bolt may lock up to the point where all turning force is used by the friction..." What does that (in italics here) mean ? Perhaps that entire italic phrase can be removed without changing the sense ? - Rod57 (talk) 22:26, 20 December 2019 (UTC)

I think it's saying that the problem can be so severe that any additional force applied to unscrew the bolt (trying to turn the bolt) is absorbed by the frictional process with more galling being the result. We need a reference and the time to digest it. Or, a question could be asked at Wikipedia:Reference_desk/Science. Johnuniq (talk) 22:47, 20 December 2019 (UTC)

Honestly, that's almost exactly what the source says. Perhaps a little too closely paraphrased, but being so short it doesn't violate copyright.

Scientifically speaking, unless you're in space, anytime you apply force to an object there is resistance in the form of friction. Without resistance, there is no force. There are two types of friction: static and kinetic. If you push a brick across the concrete, static friction keeps it from moving. When you reach the break-away point, the force required goes down and kinetic friction takes over.

When turning a bolt or screw, you encounter kinetic friction while it's moving. As it begins to seize up, it requires more and more force to overcome the resistance. Once it reaches the point where you can't turn it anymore, it becomes all static friction holding the bolt in place. You can get a cheater bar and maybe get another turn or two out of it, but if it keeps galling the friction keeps increasing and sooner or later something's going to give. (That's why if you use stainless-steel NPT pipe-fittings you may as well have just welded them together, because they ain't coming apart in one piece.) The energy you expend pushing the wrench has to go somewhere, and that place is in the friction; whether moving or stationary. I hope that helps explain. If you can find a better way to phrase it, then please feel free to give it a try. Zaereth (talk) 22:52, 20 December 2019 (UTC)

ASTM G40 Galling definition typo

There is an important typo in the ASTM G40 definition of galling. The page says "Galling is a form of surface damage arising between sliding solids, distinguished by microscopic, usually localize, roughening and creation of protrusions (e.g.: lumps) above the original surface".

Should be macroscopic instead of microscopic. This is an important detail.

Additionally, the "(e.g.: lumps)" is not in the ASTM G40 definition. I suggest removing it from inside the quotation marks, and adding a separate sentence of explanation of the word "protrusions".

Thanks for the suggestion. Since you obviously have access to the source, and know exactly which sentence needs to be changed, it would probably be easiest if you simply change it yourself. You are most welcome to do so. Just leave an edit summary in the little box at the bottom, explaining what you're doing and why. (You can simply point people to this discussion on the talk page.) I should point out that "protrusion" and "lump" in this context are completely synonymous. Also, this leaves an inconsistency with some of the other sources. Galling, by the time we typically notice it, is definitely a macroscopic lump or protrusion, but it always begins at the microscopic level, long before it becomes noticeable to the naked eye. I hope that helps. Zaereth (talk) 19:57, 21 April 2022 (UTC)