cracked platen on Pexto shear

Hello, all,
I have a Peck, Stowe and Wilcox 30" shear that has a crack in the platen
(The "bed" of the unit that holds the fixed blade). It first cracked
right across where one of the bolts that supports the fixed blade is,
parallel to that bolt. This is the vertical bolt that presses upward on
the bottom of the fixed blade, not the bolts that clamp the blade to the
platen.
Anyway, someone had made a horribly amateur attempt at welding it, and
it cracked immediately. I took a shot at TIG welding the crack, knowing
it had about zero chance of working. Exactly. So, then I welded a
piece of 1/4" steel plate about 6" long, underneath the rib of the
platen, running about 3" each side of the crack. I made a number of
small weld beads there, essentially butt welding the plate onto the edge
of the rib. (The plate hangs straight down from the platen.) I used
TIG at ~100 amps (had the welder set for 150 A max) and went slow so as
to at least partially preheat the area, and then just make a 1/2" long
bead at a time. This weld has held quite nicely!
But (there's always a but) now the platen has cracked again, right at
the end of the welded area. This is right down the center of the platen
too, heading toward the front of the platen, where you stand to stomp
on the pedal. (There is a possibility this crack was already there, or
at least starting to develop, and when the other crack was secured, the
load all jumped to this one. But, the location RIGHT at the end of my
weld is suspicious.)
Well, I certainly don't have a heat treat oven where I can preheat
something as big as this. Has anyone ever succedded in repairing cracks
on a stomp shear like this? Especially if it is a Peck, Stowe & Wilcox,
(not their later PEXTO label) so it must be PRETTY old, I'm guessing
1900 - 1920 at the latest. (Hope this thing isn't made of the same iron
that went into the Titanic! That would explain this damn thing cracking
so easily.) And, of course, the real question is, should I try to
repair this crack, too, or is this a totally lost cause? Without a heat
treat oven, is every weld repair going to end up producing another crack?
Thanks in advance for any thoughts on this!
Jon
Reply to
Jon Elson
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I've brazed pretty heavy castings using a space heater (or two) to preheat.
John
Reply to
JohnM
Jon at this point its largely..IMHO a lost cause. Not that it cant be repaired with replacement parts from another shear.
Drop Leigh at snipped-for-privacy@aol.com with a question about replacement parts from carcasses. If he doesnt know where to find them...few others will either. The dude is good with Pexto stuff.
Gunner
"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown
Reply to
Gunner
Did you drill the end of the crack? You should do this! carefuly check that you drilled out the end of the crack (oil and chalk) or it will certainly crack again. Preheating by any means will reduce inner tension.
HTH, Nick
Reply to
Nick Müller
You can easily heat up the bed to 600 degrees using a propane weed burner and some sort of metal enclosure. A 30" bed should be about 36"x18", that would fit nicely inside the shell of a 50 gallon water heater. If you can't find a weed burner, try one of the cheaper gas burners
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J> Hello, all,
Reply to
RoyJ
That's what I was thinking too, Nick. I've drilled out the end's of cracks in fiberglass panels to prevent them from cracking further before repairing them. Works like a charm.
How do you use oil and chalk to find the end of a crack?
Reply to
Artemia Salina
snip----
It's much like a spray penetrant inspection. The crack holds some oil, which is wicked out by the chalk and is easily visible from the discoloration. It defines cracks quite well.
Harold
Reply to
Harold and Susan Vordos
Pour some thin oil on the suspect place, let it penetrate, whipe it carefuly off, and dust some powdered chalk over the place. The chalk will suck the oil out of the crack and will get dark. voila! Well, you can also buy expensive super space science spray for that ...
Nick
Reply to
Nick Müller
The new crack is 3 inches away, and parallel to the old crack. It is at the end of the gusset patch, where stess may have been concentrated both by the application of the patch and by the patched area now being stiffer than the rest of the platen.
So, this has nothing to do with the end of the crack propagating farther.
Thanks,
Jon
Reply to
Jon Elson
Hello Jon,
Somebody posted this URL here a while ago:
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It seems to me that what you are experiencing agrees pretty well with their explanation as to the mechanisms involved, though I'm only going on recollection. It may be that either their products or their data could help.
BTW your EDM power supply worked exactly as I hoped on eroding a square socket into the hardened stud we were discussing a while back. So, thanks once again on that.
Regards,
Adam Smith Midland, ON
Reply to
Adam Smith
This stuff seems to be about sealing leaks in the non-structural part of engine blocks. Maybe I was reading the wrong part of the site. The problem I have is this is in the highly stressed part of the platen, where it experiences great tension loading!
Hey, great! Glad it worked out for you. How long did it take?
Jon
Reply to
Jon Elson
OK, this seems to have to deal with thermal tension from welding. I am _not_ a welding instructor, so don't read my answers like a bible.
What could you do to reduce thermal tension? - use MIG/MAG - weld quick and not make the fillet in one pass (we call it "pilgrim's step", one back two forth) - weld on both sides intermittent - leave time between welding passes - preheat
One last resort might be MAG-brazing*). But if that fails, your piece might be ruined. MAG-brazing is a "welding" with a CuAl-alloy wire (Or CuSi, about 95% Cu) in your MAG with Argon. The wire is quite expensive but will be more flexible. But I don't have enough experience to stand full behind this advice! Maybe someone else has something to say?
*
) That's how about how I would translate it from German, your naming might vary.
HTH, Nick
Reply to
Nick Müller
I've also heard of using pure nickel rod, and peening the weld before the part cools. I used some stainless steel filler wire, as it has SOME nickel in it. That weld has held! I did do the weld slowly, ie. in a small spot at a time, then working on the opposite end of the patch.
What's really driving me crazy is why this platen keeps cracking when I'm cutting thin aluminum sheet. I am operating at half or less the capacity the shear should be able to handle.
One "plan B" solution is to remove my patch and make a patch that runs the full length of the platen, welding it in just to the side of the two cracks. And, then jam in shims or weld on little blocks that support the platen along the full length. That ought to work, and should prevent any more cracking, but it will be a lot more work.
Thanks to everybody for the help with this.
Jon
Reply to
Jon Elson
Silly wild-ass guess non-expert off the cuff analysis from a hundred miles away comment... In other words, Feel free to ignore me, I'm just thinking out loud here. ;-P
(Oh, and after a quick bit of research... From here to your address in Kirkwood MO
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- I'm not psychic] Mapquest says it's 1838.67 miles, 27.5 hours. Seems my initial silly guess of 100 miles was a /bit/ low. But I digress...)
If this area is cast iron that gets shock-loaded in tension during use, it won't take much to make it crack again. Since you tried a fishplate on the bottom side, and it just cracked where the loads were moved to one end of the fishplate, I'm thinking there may be an inherent design weakness in the platen. (Bet you when they changed over from "Peck Stowe and Wilcox" to "Pexto" they made it heavier...)
How about putting a tension rod through or under the platen, right below the shear throat edge, thread the ends and use some fine thread nuts to put some external compression on the platen? Maybe even a V-block (or two on the webs) at the center like the tensioning rod on your garage door, to counter any downward forces in the unsupported center of the platen? THEN you remove the old fishplate, drill the ends of the cracks, preheat and weld them up again.
You can check the finished side of the platen for bowing, and stop tightening the tensioning nuts when it gets a very slight positive arch from the preload.
Better than throwing it out.
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Reply to
Bruce L. Bergman
Yes, that's the main problem. Since you tried a
Maybe, this is a 30" shear, I can't find a gauge rating on it, and it only weighs 150 Lbs. It has 18 (nameplate) 90 cast into the upper blade support, so it must be a very early design.
It seems to me that compressing the piece first and then welding is going to cause even worse problems (unless you never remove the preload again). If you do ever remove the preload, it might just crack right then. I arranged to leave the first crack slightly spread (maybe .020") before doing all the welding. After I was done, the crack had closed up quite nicely.
I'm not sure this is going to be stiff enough. I think having a thick piece of steel sheet that supports the platen along the entire length would be a lot stiffer than a rod. It might not even need to be welded to the platen at any point, just attached to the legs.
Jon
Reply to
Jon Elson
Ok, thanks. That almost sounds like my "dirty thumb" method of crack detection: Clean suspect area well, then wipe with dirty thumb.
Reply to
Artemia Salina
As an retired farmer I used to keep a stream of water running on my chunks of cast iron , always able to hold it in bear hand. Can be very slow filling in.
Reply to
hvacr
I have a friend who uses nickel. I have also had engine blocks nickel welded.
Who knows why it keeps breaking, perhaps it is jus old!
If you fix it, try bolting the legs to each other, or bolting it to the floor really well. Stopping leg spread under load may reduce the cracking. MAybe
Reply to
yourname
I have had good results welding cast iron with two different rods- the nickel tig rod, and silicon bronze- tig brazing the cast iron. With the nickel, a preheat really helps, but just using the rosebud on the oxy fuel torch will do it- 500 or 600 degrees is plenty, you dont have to get it red. The silly bronze rod is more forgiving, as you dont have to get the base metal as hot.
The small Pexk Stow and Wilcox 30" shears were 18ga max. And most of those weighed in at 400lbs. My guess is yours is a No. 30, or a No. 130- the only difference is the 130 had little fold down tables left and right. My guess is years of people ignoring the 18ga rating, and cutting 16ga stressed the machine out.
Reply to
rniemi

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