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Repair or replace cracked boom???

D

Delmer

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Sure wouldn't hurt to find the part number for the boom, go on machinerytrader and see if there are any cab fire machines with a salvageable boom.

Obviously it was designed by humans, welded together by humans, and can be fixed by humans. But I don't know where you'd find a shop that I'd trust, and I wouldn't guess what it would cost you these days, or how long it would take them. If this was an old farm backhoe, then you could probably get away with grinding it out, welding it up and keeping an eye on it. Can't do much to this without removing all the hydraulics, then you might as well remove the boom. Have to at least try the manufacturer to see if they have a procedure. If you have it sitting on the ground, then you want it done right. No reason in my mind not to do it yourself if your welding is up to snuff, the design of the repair is critical, the welding in position with the proper prep isn't especially difficult.
 
W

Welder Dave

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I think it needs a very competent weldor(s) for the repair. They are out there. Can't take any short cuts and preheat needs to be maintained. If could find a good used boom, great.
 
A

aongheas.macask

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Nige said:
Usual SOP for cracked booms is to remove from the machine then the boom can be rolled over to make access & welding easier. Repair often involves cutting holes in the box structure of the boom in order to repair cracks in internal bulkheads that can’t be seen. If the internal cracks aren’t fixed properly then any external repairs are literally “papering over the cracks” and are a waste of time and money IMHO. My 2c, YMMV.
Click to expand...
totally agree with Nige
 
John C.

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When I started making a living at this we used a lot of 1/4” mild or HY80. In the last twenty years or so we used 3/16” T1 for the fish plates. The stick welding was done with 5/32 7018 when flat and 1/8” when out of position. When the squirt guns became popular, I recall using E70T dual shield in .045 size. The cracks were air arced out, ground smooth and welded. The weld was ground smooth and the surfaces cleaned of paint. The fish plates were cut so they had no points and there were holes cut for plug welding. Keep in mind that in those days the makers never admitted that there were any faults in their designs. The failure in the photo has a workmanship or design failure inside that will need to be addressed.
 
Nige

Nige

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Regarding steel the usual was something of a similar or identical specification to the original plate, thus removing any issues of fusing dissimilar metals with the welding repair.
John C. said:
The fish plates were cut so they had no points and there were holes cut for plug welding
Click to expand...
A fishplate for the top/bottom of a boom would look something like the example below. The quantity and size of the holes for the plug-welds would be dependent on the overall dimensions of the reinforcement plate.

upload_2021-5-13_18-37-34.png
 
W

Welder Dave

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Fish plates could be concave like Nige shows or convex. As long as they are rounded. Air ArcIng is great for speeding things up BUT you have to make absolutely sure everything is ground to clean steel. A tiny spec. of carbon would produce a weld flaw. What a waste of time if this happened.
 
John C.

John C.

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There was no such thing as a plasma cutter when I was putting booms back together. Fish plates for booms looked sort of like what Nige shows but were never straight like that and always had a radius where is drawing shoes the end points. I'll have to look for some old photos. I don't know anything about the names of the newer materials. I would be curios about the costs and if those materials are a bit exotic for repairing booms with. 7018 was used because it would work with any different material. The tensile would allow for expansion and contraction between the T1 on the fish plate and the mild steel in the boom. What we were doing back then was standard for the industry.
 
Nige

Nige

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That drawing above was a bit on the small side John. I know where the document was and lifted it straight from there.
In the flesh the plate had a 5/8" (15mm) flat on the corner and the ends were welded as shown in the photo. At least one bead of the fillet weld down the side was run out 3" past the end of the plate, and the fillet weld in the radius terminated about 1-1/2" short of the end of the plate.

Another snippet is that Cat booms are manufactured from A572M steel and have been for around the last 20 years to my knowledge.

upload_2021-5-14_0-37-42.png
 
Nige

Nige

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skata said:
Click to expand...
After John Canfield's recommendation on the previous page I took a look at the guy's channel and saw that one too.
I like the comment he made at the end - "Not the best, but not the worst either"
Note that he entirely reconstructed about a foot and a half of the bottom end of the stick in a number of steps to keep everything in alignment.
One thing I didn't hear mentioned was how long it took to make the complete repair. I bet it was a while.
 
J

JLarson

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We always try and find out and match the existing material as best as possible. Same goes for truck and trailer frames.
 
John C.

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Didn’t matter what the name was attached to the steel. They kept breaking and were still welded back together with 70K tensile wire or stick.
 
S

suladas

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For that Volvo repair video above, I thought you weren't suppose to weld across the top of bottom of the boom?
 
W

Welder Dave

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Nige said:
That drawing above was a bit on the small side John. I know where the document was and lifted it straight from there.
In the flesh the plate had a 5/8" (15mm) flat on the corner and the ends were welded as shown in the photo. At least one bead of the fillet weld down the side was run out 3" past the end of the plate, and the fillet weld in the radius terminated about 1-1/2" short of the end of the plate.

Another snippet is that Cat booms are manufactured from A572M steel and have been for around the last 20 years to my knowledge.

View attachment 239155
Click to expand...

Welding past the fish plates and always putting end of weld craters somewhere in the middle of the welds is something I forgot to mention. T1 is great for strength but requires a 11018 rod that may not be suitable for the boom material. I would think that current booms like the OP's would use a better a steel than a boom from say an 80's machine. Try to find out the type of material and then match a filler metal and possible reinforcing plates to that. I'm guessing it might be something a little stronger than 7018.
 
Nige

Nige

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skyking1 said:
Would you plug weld a larger fish plate?
Click to expand...
Yes.
Some prefer to use a "plug hole" shaped like an athletics track, basically a rectangle with a half circle at each end. The long sides of the rectangle would run lengthwise down the structure. Depending on the size of the hole it might be practical to only weld the long sides of the hole and not the ends, then all welds would be parallel to the structure.
 
John C.

John C.

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All the large plates had round plug holes. Stacker booms, large excavator boom and such. We used the race tracks on things like loader bucket floors and dozer push plates. I also used the race tracks on reinforcement plates on excavator sticks when we were installing thumbs back in the days. We were always told the plug welds were to go all the way around and there should be no points. We picked that up from factory drawings on repairs. It might be a preference of the engineer, or not.
 
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