Dealing with scale

A

AWGunS

Joined
Sep 16, 2006
Messages
616
Well, I had a 3-V blank all profiled out. Still had surface scale, but I did not really think about it prior to profiling the blade. Mounted up the wheel, and ran the blank on the bottom side. I rounded over the edges a little (lesson learned), but not a big deal. But after I got the layer of scale off, I noticed some pretty deep pits. More time on the wheel resulted in more rolled edges, but little improvement in the way of pitting. In a stroke of brilliance, I took the magnetic base of my indicator holder, popped the blade on, mounted up the platen and went to work on getting the pitting out.

I accomplished nothing. THe front side of the platen has been grooved from grinding, and when I applied the blank, it chattered and left some very odd circular indentations in the blank. I flipped the plate over to the virgin side, and tried to remove the pitting and the new indentations. Apparently I applied pressure unevenly, and put a nice tapered flat on one side, and failed to touch the other. The blank now resides in the scrap bucket. And to add insult, the brand new 80g belt is smoked.

I know I can get precision ground stock, but it is pricey (and I understand why). Is there a better way to deal with scale without tearing up belts? Nothing can be done with pitting, it simply has to be ground out, and I will be sure to do it prior to profiling, and use patience. I may go with PG stock in the future to avoid this, but I have many feet of D-2, 154CM, and a significantly shorter piece of 3V.
 
Soak in HCL , you can use the hydrochloric acid you can get in a hardware store .It's used for cleaning concrete. Do it OUTSIDE otherwise everything in your shop will rust.
Another benefit for PG is that it should also be decarb free.
 
I have in the past used a 41/2 hand held grinder to get scale off. Nothing kills a belt faster than scale as you have now seen.
I have been told overnight in vinegar will remove it but never tried that yet.
CW
 
AW,

If you have a milling machine you could mill a few thou off each side then cut your profile and finish the surface on the grinder.
 
A very thin layer of clay, refractory cement or anti scaling compound on the blade before HT will reduce the scaling significantly.
 
It sounds to me like your biggest problem is re-surfacing the bar and keeping it flat. The scale may be eating the abrasive off your belt, but if the scale were gone you would still have some grinding to do to get rid of the pitting, and my experience with 3v is that it can take a lot of grinding to get a clean surface.
The easiest way to deal with this is to buy from Aldo and have him grind it for you. The next best alternative I have found is to rough in the bevels and taper the tang (if the latter applies), then re-surface the much smaller amount of flat area that is left. You can do this on the platen but as you have seen, it is easy to create unwanted tapers, rolled edges, etc. I do what I can on the grinder and then go to the hand sanding block to deal with this. I guess I'm lucky that I prefer high grinds, the flats are very minimal in area once the bevels and tapered tang are ground.
I think this is one of the main uses of the 9" disk grinder, but I don't have one. I assume there is a bit of a learning curve with them, as with all things, that may lead to a few screwed up blades in the beginning.
 
Aside from the grinding problems, vinegar (or concentrated vinegar -- probably most acids) will eat/soften forge scale if you let it soak in there for a while.
 
HCL or vinegar? I think I will try the vinegar first and see if it helps out.

Just for the record, this was scale off an annealed blank, pre HT. Experience with O-1 after HT and scale was minimal, and I quickly and easily removed it on the grinder, with minimal pressure.

Mill is not up and running yet Zander. AS soon as I saw the pits, I saw the mill and thought the same thing.


I intended to do a hollow grind and leave a large flat. Funny thing is, Once I removed the dark scale and noticed the pits, I would say 90 percent of them were in the area of the actual blade. The handle area was mostly free of them. Had it been the other way around, I think I could have ground out the bevels and eliminated most of them that way. Another reason to develop a standard operating procedure.
 
Like Justin mentioned above, I've resorted t paying Aldo to do it for me. Saves me a bunch of time, I get a completely flat bar and I don't burn up that many belts.

I've tried the vinegar-soaking on O-1, and it helped a bit, but I still went through an 80-grit belt to get a 10" knife blank clean, and then I had to deal with the rolled edges, etc.
 
Vinegar helps but it has not been magic for me. I let it soak for a while, like over night, then I scrub it with a stainless steel scouring pad. A lot of scale comes off but not all of it so it goes back in the vinegar and I keep doing this until the scale is gone. It can take from three to five treatments for me to get it all off.

- Paul Meske
 
I tried the apple cider vinegar, and even the high concentration stuff was really slow -- you have to turn the blades a lot to get good coverage, and it takes overnight so the logistics are a pain.

Someone here suggested Sodium Bisulfate, which is Pool PH Decreases at Home Depot or Lowes. Works *great*, and I paid $10 for 4 lbs.
 
lazlo said:
I tried the apple cider vinegar, and even the high concentration stuff was really slow -- you have to turn the blades a lot to get good coverage, and it takes overnight so the logistics are a pain.

Someone here suggested Sodium Bisulfate, which is Pool PH Decreases at Home Depot or Lowes. Works *great*, and I paid $10 for 4 lbs.
Click to expand...

Do you add it to the vinegar? If so, what ratio do you use?
 
Sodium Bisulfate (commercially sold as PHDown in your friendly pool and hot tub dealer's store) should not be mixed with ANYTHING except water. It is a buffered acid product, jewelers use it as "pickle" to clean metal after soldering. In our world it is sold under the brand name "Sparex" if you want to google it. Personally I do not buy the Sparex brand as whatever process it is a byproduct of leaves the Sparex brand with a nasty brown oily scum that the Rio brand and the PHDown do not have. Sodium Bisulfate should be treated as acid (no contact with bleach, bleach fumes, cyanide based plating baths ammonia etc.) and used with adequate ventilation when used with steel. Also do not ever bring copper bearing products into contact with bisulfate that will be used with steel, the copper will plate out

_page
 
Wait until the wife goes to Wal Mart. (Important... wait until she is gone). Put some vinegar in the microwave in an open container. Nuke it until it boils. Soak your blade in the hot vinegar. Sure speeds things up, but after it cools, the cleaning effect takes longer. You can always nuke it again to get it hot.

Robert
 
What Page said is probably the best answer to the scale problem and PLEASE take note of the safety issue's he speaks of. As for the pitting issue with the CPM steels and a lot of other types of steels, in the rolling process you will inevitably have a layer of decarb. Most companies order there steel with this in mind and will order in steel thick enough to remove this layer in the process of making whatever it is they're making. In the case of Carbon steels it's no big deal and in the as rolled or annealed condition it's pretty easily removed. In the case of CPM steels and some tool steels this layer also contains all sorts of nasty carbides from Tungsten, Vanadium, Chromium, and Molybdenum all mixed in there along with the scale which can be as hard as 70+ Rc.

Along with that there is also the issue of hand rolling. In the case of Crucible CPM's and others it is the best way we have to do it. Although the rollers are change quite often they still take a beating. I've had sheets come in that cleaned up in no time at all and others that will have to be taken right to there finished sizes.
 
You must log in or register to reply here.
Back
Top