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De-scaling


P.Abrera
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One worn out file later, Im wondering what are the other approaches others take to de-scaling when profiling/finishing without grinders etc. (...i've read about the vinegar pre-soak and will try that next time)

 

And what are the best techniques and abrasives that have worked well for you guys when hand finishing?

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A coarse stone works well.

Sandblasting is very fast.

Stiff wire wheel on bench grinder.

Use the corner of an edge of a worn out file.

 

You don't have to get it completely clean, but the more the better. Start with a single edge scraper, sen and rough it down, or use an older file to begin with before you use a new file.

Don Fogg

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I'll vouch for the vinegar method. If you aren't in a hurry, an overnight soak will often remove 90 to 100 percent of the scale. Try to have the entire knife tang and all submerged, if you leave some out of the vinegar you will get a severe etched line where the surface of the vinegar crosses the blade/tang which may force you to remove more steel from that area during the shaping than you intended. PVC pipe works well as a container for this and other etching processes. On a side note, the used vinegar/iron solution also works pretty well as a black stain for vegetable/oak tanned leather or even on oak itself as my work bench can attest. :blink:

 

If you are in a hurry and want to go from the forge straight to working the blade the methods Don outlined can't be beat. A wire wheel for my bench grinder is on my shopping list!

Guy Thomas

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If you heat or simmer the vinegar it will work faster. If you do this make sure you are properly ventilated. The problem with vinegar is that it also eats away at the steel. The best chemical method is with Naval Jelly. It won't eat away at the steel, just the scale. With the Naval Jelly it will take many applications before the steel is clean. This takes time.

 

A combination of stoning and chemical pickling is my favorite.

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I find that when I am forging it is good to brush the steel with a stiff wire brush when it is still hot, as Don was saying. Do this about every couple of re-heats. My biggest problem is that if I don't keep the scale down to a minimum while I am pounding the steel, it will start to infuse with the steel. This leaves a lot of pits and other problems that are a pain in the butt to fix later. Just my 2 cents

Jordan Sahlberg

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I'm a firm believer in the wet forging method too! Not only does it keep the scale to a minimum but it's just plain cool when the scale pops of off loud as a firecracker! :D

Guy Thomas

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i just did my rough shaping the other day on my second knife using gas and the scale was indeed thick, i soaked it in vinegar for an hour and that made it alot easier to grind off.

Michael

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Quick follow up:

 

-What causes scale to form in the first place?

 

-do you get as much scaling with gas forges?

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I may be wrong but my understanding of it is scale is a form of iron oxide that forms at temps over 1200 degrees or so. The only way to completly avoid it is to forge and heat-treat in an atmosphere devoid of oxygen... So scale forms when steel and oxygen get together at high temps.

 

It happens in a gas forge too, and has an ugly reddish tone to boot.

 

I've found that wire brushing while the steel is still hot, then soaking in a ferric chloride solution for 15 minutes or so, goes a long way towards dealing with scale. The FC solution loosens the scale, making it easier to remove.

George Ezell, bladesmith

" How much useful knowledge is lost by the scattered forms in which it is ushered to the world! How many solitary students spend half their lives in making discoveries which had been perfected a century before their time, for want of a condensed exhibition of what is known."
Buffon


view some of my work

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Yes - scale is simply iron oxide formed at higher temperatures - depending on the temperature & availibility of oxygen one of 3 iron oxides forms. Fe3O4, Fe 2O3, or FeO. They have different crystalline structures and adhere differently to the base metal. At one furnace company I worked for, we recommended that customers use a slightly oxidizing atmosphere in slab reheat furnaces fired with natural gas burners. The reason - the fully oxidized scale was less adherent & easier to remove with a high pressure water jet ahead of the hot rolling mill and produced a better surface finish. We were primarily working with low carbon steels, not a mid-range or higher carbon level plain or alloy steels, where surface decarb versus end use is important.

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