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foxint

2015-10-25: Galling on Stainless Fasteners

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Hi

Just a very occasional note on things that I find interesting. We watched the latest episode of Doctor Who and while this did inspire me to time travel, I seem to have misplaced my Tardis.

I really no not want to tell you about the less than communitive case maker, or the movement maker who apparently only has one English speaker to deal with all us lesser beings. The Swiss assembly house was less than Swiss, producing only 5 out of the 10 watches to my satisfaction. Yes we will rebuild 50% of the Swiss Made production.

 

So situation normal. I am taking orders for the current range: Snowflake and Sword (MS-9411 & MS-5517) with Soprod and Seagull movements. All pricing on the website includes shipping…. www.orangewatchcompany.com  

 

How about we move onto to something of less interest but possibly somewhat important. Galling…

Galling or Cold Welding is alive and well and may be experienced by some. This quote from Joe Greenslade identifies the problem well:

“A few times each year we receive calls from fastener suppliers who are in conflict with their customer over the quality of stainless steel bolts and nuts. The customer's complaint is that during installation the bolts are twisting off and/or the bolt's threads are seizing to the nut's thread. The frustration of the supplier is that all required inspections of the fasteners indicate they are acceptable, but the fact remains that they are not working.” (http://www.estainlesssteel.com/gallingofstainless.html)

Thread galling is most common with fasteners of stainless steel, aluminium, titanium and other alloys that self-generate corrosion protective oxide surface film.

As Greensade points out: “During fastener tightening, as pressure builds between the contacting and sliding thread surfaces, protective oxides are broken, possibly wiped off, and interface metal high points shear or lock together. This cumulative clogging-shearing-locking action causes increasing adhesion. In the extreme, galling leads to seizing - the actual freezing together of the threads. If tightening is continued, the fastener can be twisted off or its threads ripped out.”

Galling simply put, occurs when applying too much rotational speed and torque while tightening or undoing screws of these metals (we will limit this to stainless steel for simplicity) will then see the nut/threads bite, seize or break. The smaller the size, the easier it is to replicate this action and the lower the speed and torque needed to avoid galling.

Most people have never heard of this term and most are more familiar with automotive sizes nuts, bolts and screws and will have limited experience with stainless and alike. Hence when presented with watch-sized fasteners, many can become quite excited and remove and action screws far too quickly and with far too much torque. Galling and cross threading are some common results of an overzealous application of a driver. This happens occasionally and we have experienced these issues occasionally.

It has happened to me, and like a kid who is overly keen to eat the next slice of pie, gets it stuck in his throat and the happiness soon ends. As I have heard on a cooking programme: “low and slow”.

In my experience, small fasteners need to be approached slowly, with respect and with care. Overly zealous action on watch sized screws can result in galling, seizing, breaking and thread damage.

This has worked for me, and while some of it may seem counter intuitive, it works: slowly insert the screw until it stops: then start turning it anti-clockwise; you will feel the thread bed in (albeit in reverse); when you feel this bedding, slowly reverse the rotation and turn the driver clockwise; it should have found the thread channel and action should proceed smoothly and easily; if it does not proceed easily, stop and reverse the rotation – it may take several times to align the threads so the progression is easy and smooth; proceed slowly; when you feel the screw bottom – stop.

Sometime it will take what seems like an eternity to get the threads aligned…but patience will result in success and undamaged threads.

If one feels that one’s activity (e.g. using percussion equipment or overly active life style) will cause screws to work out, wipe the screw clean with methylated spirit (or similar) and coat the screw threads with Loctite 222.

We use Loctite 222 on the screw bars that attach the SEL to the watch head, but not on the bracelets that generally received less rotational movement. If you regularly change bracelets and bands we highly recommend you get a small bottle of Loctite 222.

**** happens and if this happens to you (and we hope not) we will do all we can to assist.

Hope you enjoyed my piece on Galling.

Dan

foxint@foxint.com.au

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:thumbsup:

deal with this quite often at work on various bits of kit.

the correct screw, well fitted with the right loctite applied makes for an easy life.

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