Steel Recommendation for Tool (Not Knife)

A

Animatronic Fireman

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Sep 16, 2011
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Hi everyone

I'm an engineer underground in a potash mine and though I am really interested in material science, since university I haven't had a tonne of experience with tool design in my professional career.

The tool in question is called a Spad Gun, which is kind of like hammer. A spad is long flat narrow triangular piece of metal is hammered into the rock wall used to hang up brattice (brattice is like a tarp that is used to control mine ventilation and potash is a salt and so the rock wall is actually quite soft). The tool itself is consists of a pipe, rod, hammer, and hammer guide. The spad is loaded into the hammer guide and the rod is pulled out from inside of the pipe and then pushed up. There is a thin narrow rectangular hammer that slides up into the hammer guide and hits the spad into the rock wall.

The problem is, is that the steel of the spad is a lot harder than the steel of the hammer. After less than a day of hammering spads into the rock, the hammer will have deflected so bad that it deforms the steel of the hammer guide and will no longer slide the whole way through it, making hammering impossible. The hammer is made of AISI 4140 . One of the operators took a torch to the hammer and we think quenched it in water but it possible that he let it air cool and this hammer lasted for a month before breaking (no mushrooming....the hammer eventually broke in half). We used to have an old spad gun made by another supplier that according to some of the senior miners never deformed but is no longer available to us. (We found an old model that is completely rusted up but still works fine).

So to make a long story short I'm wondering what some good steels/heat treatments that would provide some good impact resistance but enough hardness/stability so that the thin hammer doesn't deform. I was thinking A6, A2 or O6, O1, O2.

I've never actually knowingly worked with any of these steels before.

Thanks for your help!
AF
 
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Pictures would help, as well as dimensions of the hammer. Are the spads single use? Any concern about damaging them?
 
Spads are single use, no concern of damaging them....apparently hammering two spads has in some case destroyed the hammer.
Thanks for the help Brian.
 
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attachment
 
Sounds like you guys have a heat treat problem.
Pictures and dimensions of the hammer would be good too. As well as the hardness of the material being hammered.

I have used cheap India/chinese mauls and splitting wedges that have been ruined after an afternoon of splitting wood.
I have also used USA made mauls and splitting wedges doing the same work for several days on end, loaned the tools out to family members and they have come back worn, but not mushroomed.

4140 can be tough stuff when heat treated properly.
Hopefully an expert will step in on this one and perhaps you can send some new one's out to get heat treated differently so that you can figure out what works the best. I imagine that a hammer that lasts longer and has less down time saves on labor.
It definitely has me interested.
 
Thanks Dave

That punch that I posted is the hammer. The hammer guide is two pieces of a rod that has essentially been cut in half and have the keyway milled in. The hammer is attached to the top of the rod and at bottom end of the rod there is a handle attached which you grab and slide up and down through the pipe to hammer the spad into the wall. This picture from Wikipedia is basically large scale and more complicated version of the hand tool I'm trying to describe. I'll try figure out the material and hardness of a spad tomorrow when I can talk to my coworkers who use this tool underground.

http://en.wikipedia.org/wiki/File:HammerSRM.jpg
 
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I wonder if that 4140 was really heat treated. 4140 is used by blacksmiths for hammers and anvils so it does hold up to hammering well .If heat treated to 50-52 HRc it should hold up. 4340 would be an improvement and S7 an improvement on that.
 
mete said:
I wonder if that 4140 was really heat treated. 4140 is used by blacksmiths for hammers and anvils so it does hold up to hammering well .If heat treated to 50-52 HRc it should hold up. 4340 would be an improvement and S7 an improvement on that.
Click to expand...
:thumbup::thumbup:
 
It sounds like someone had success re-heat treating the hammers. With the thinking that these hammers are being mass produced cheaper than you can get them custom made, you should try that route first.

If that does not work, this should...
JBS TOOLMAKER said:
S-7 Tempered in the low 50's.
Click to expand...
 
Just my two cents, but the 4140 should do ok, as mete said 4140 is used for anvils and blacksmith hammers, and can take allot of abuse. Is the 4140 you are using heat treated? it sounds like it is not. your operator did a very rudimentary heat treat with a torch that seemed to help allot, but his heat treat job may not have been the best. 4140 needs to be heated to about 1550 F then quenched in oil, following that it needs to be tempered at at least 500 F (this is only a brief description, and if you are going to attempt this yourself you should definitely get some more exact specifications). I think your operator might have forgotten the temper part. The temper makes the part much tougher by reducing residual stress from the quench and stabilizing everything.
If you want significantly better S-7 or any of the S series steel (s stands for shock) should do very well indeed, but again it all depends on the heat treat
 
Alright so today I spoke with the manufacturer's rep and when I initially asked with what the 4140 was hardened to he said 38 to 40. I shuddered when I heard this but when I took a look at his drawings it said harden to 50 HRC after machining. He said that they ship out the punches to be hardened but I'm very suspect as to whether this actually happened but regardless they're going to build some prototypes with different steels that we can try out. I've received quotes from a steel supplier for 4340 and S-7 bar stock....wow the S-7 is expensive!!!
 
I would suggest posting this very same question in Weldingweb. Lots of machinist there that could give great advice as well. Not saying that advice here in Bladeforums is not sufficient or anything! Don't take me wrong.
Mikel
 
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