weld macros - fine-grind many for macro-etch

Hello all

I need to prepare many weld cross-section macros - tens per Company - in meeting a new European legislation without requiring the steel fabrications companies (FabCo's) to change their welding machines.

Many FabCo's have a big belt-linisher - which is useful for a first linish, where it's available.

File and use coarse and fine emerys as in welding school is a bit slow.

What would you do if you were "the expert" and were walking into FabCo's sorting out all this for them?

I have a 4inch air-powered angle-grinder. Would that be good with a linishing disk? How do you rapidly switch between linishing disks? Is there some system where you rapidly demount the backing disk (flexible(?) with its pad???

A few hundred grit final light grind / linish results in a perfect macro-etch.

I have a reducing valve which plugs into standard airlines. Then plug your air-tool into that. The regulator / reducing valve - it gives me very accurate control of air-tools in general. So I can slow down and control the torque of tools. (eg "tickling off" the sharp edges of fatigue-test samples so you are fatigue-testing the weld itself not the sharp edged and notches of the sample which are not part of the in-service weld, etc)

I see there are "pistol-grip" air-powered sanders / linishers. "Roloc" is mentioned in some.

There's no need for a "random orbital motion" (???) Can readily alternately grind in one direction then at its right-angle-direction.

Sorry about how broad questions are - have no experience of this matter...


Reply to
Richard Smith
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The machines we used to prepare metallographic microscopy specimens in college were like phonograph turntables, with water flowing onto the abrasive-charged platter. We cast the metal samples into standard-sized round pucks to manipulate them, using either Bakelite powder or acrylic resin. The student version required us to hold them ourselves while polishing. IIRC we slowly rotated them. Once the belt-sanding scratches had been reduced enough to please the teacher we etched them in nitric acid and alcohol, called "nital".

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Reply to
Jim Wilkins

Jim, all

True and that would be absolutely "the business"

- but that is for preparing micros

- which need to be planar (the depth-of-focus of a metallurgical microscope is so limited the surface needs to be machine-flat)

- and you go through to 1200grit

- then micro-polish to a mirror-finish on felt-knap impregnated with diamond paste

- then use 2%Nital for a very fine light etch

If I had to do that, I'd know exactly how to do it! - even if it was improvising a portable kit where the normal is "fixed".

Macros only need to go to about 400 grit(?), need not be machine-planar and are much-more rough-and-ready. Etchant is the much stronger 5%Nital (BTW that alcohol needs to be methanol so it cannot nitrate with the Nitric acid content). I'm using the Iodine Etchant - previously asked about this on s.e.j.w.

Fitness-for-purpose says some sort of flexible but stiff-backed linishing disk should be enough. Also - with this approach you only have to prepare the weld area - the rest of the cross-section away from the weld can be left be. The kit has to work in a FabCo with people welding and grinding away in the same shop.

For sure I thought about some some of swing-grinder (surface-grinder with a wheel-axis normal (right-angles to) the table axis) to do initial prep, then do the papers. For that good machine grind, hand-gliding the samples on emery papers on a planar surface would be just fine

- but that is fanciful and excessive for a portable kit...

Rich Smith

Reply to
Richard Smith


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about 3:30 onwards.

-- Peter Fairbrother

Reply to
Peter Fairbrother

Thanks. Is great video. Very practical person there.

Iodine etchant worked well - happy about that choice. iodine + potassium iodide + water. Went with the ASTM composition 1 part iodine - 2 part Potassium Iodide

- 10 parts water, by mass / weight. The ingredients are generally available and present very limited hazard.

The problem is now how to prepare a lot of weld cross-section samples to do macros upon.

After other discussions, I am looking at my 4inch air-powered angle-grinder. Can be fitted with a flexible-but-stiff plastic backing disk and take emery paper disks? I have a regulator / reducing-valve to control the power - for doing gentle light grinds at successively finer grits.

Holding the angle-grinder body and the handle should give the control needed. Accurately linish / grind in the right place in the chosen direction.


Rich S

Reply to
Richard Smith

The only thing I was going to add, get several angle grinder/sanders with each having a different grit. No need to keep changing grits. If you really have a LOT to do, three air hoses, so you don't need to keep swapping. (Harbor Freight?) Now where are those 10 vises to hold the samples. Mikek

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