Cracked Boom Pictures! Suggestions?

[tctractors]

Nige, the bit I cannot see I dont think I would worry much about, I would weld it up and check things are working smoooothly, get the pilot to keep his eye on the boom and let it earn a bit of corn??, if it was new I would ask for Product Support to investigate the boom cracks, with a repair or replacement program, but I would not be cutting in to take a peep on a little swinger like this, it might need a plate improvment that often the dealers will have detail information on that might be of help, but hacking holes to get your head in " aint worth nowt" on this chariot.

 

[Scrub Puller]

Yair...hey fellers what am I missing? Comment above from tctractors #18 post.

1 cylinder would work before the other causing a twisting effort in the boom.

When I build stuff with two synchronously working rams I tee between them and feed and return down a common line.

I'm a self taught bush mechanic and (to me) this always seemed the simplest way to balance out the forces and avoid the twisting problem.

What are the disadvantages as obviously (according to the comments) this isn't common practice on diggers.

Cheers.

 

[Nige]

Nige, the bit I cannot see I dont think I would worry much about, I would weld it up and check things are working smoooothly, get the pilot to keep his eye on the boom and let it earn a bit of corn??, if it was new I would ask for Product Support to investigate the boom cracks, with a repair or replacement program, but I would not be cutting in to take a peep on a little swinger like this, it might need a plate improvment that often the dealers will have detail information on that might be of help, but hacking holes to get your head in " aint worth nowt" on this chariot.

Tony, I take your point. But the problem I have come across many times is that by the time somebody starts to think along the lines of "trying to fix it from the outside ain't working" usually the structure's been so badly buggered about by just welding it from the outside that there's almost nothing left to weld to, and the inside is proably in pieces. I know it's easy for me to say "fix it once, fix it right" because my previous experience has taught me that a large percentage of structures like this boom can generally only be successfully welded as a long-term fix by going inside and sorting out the problems there first instead of going for the quick fix and just welding the outside.

I understand your point completely about getting the machine up & running and earning, but you and I both know from past experience that today's "temporary" fix has a habit of becoming permanent and is possibly only putting off until tomorrow what should really have been done today and if it had been it would have only taken half the time if someone had bit the bullet and done it right first time.

Like you I would be looking to the manufacturer's dealer network in the first instance to help with a repair procedure before even starting to clean the paint off the cracks. It would surprise me very much if they didn't have something.

I can also understand why people who haven't previously seen repairs done by cutting holes in a structure being more than a bit wary of the procedure, but in truth it's really quite simple, and what's more it works. What I'm going on for this excavator is a load of documents I have for similar size Cat machines detailing repair methods for booms that in all probability are dam nigh identical in internal & external design even though they are painted a slightly different shade of yellow.

 

[alaskaforby4]

The cracks will be drilled, v'd welded, ground smooth and a 1/2 plate is going around the pin boss and everthing from the top to the bottom, I'll post pics once we get it finished.

 

[r_steven]

I know I'm coming in a bit late, but couldn't a hole be drilled into the boom and an inspection camera be used?

 

[tctractors]

Scrub Puller, the common practice on excavator hoist cylinders is the fitment of check valves, these are often signal pressure activated to put the boom rams to move, there is also the fact that each cylinder has its own check valve set, so if 1 cylinder valve is releasing before the other due to valve adjustment etc, the boom cylinders are working on the gimp so as to speak, I check the signal line pressure with the boom up, engine stopped, pressure gauges on both check valves, then lower boom using stored hydraulic power to lower, 1 check valve will always open before the other, it just needs to be a close thing, I myself think check valves are a pain, slowing the working rate of a swinger a good bit, but they must have saved a few lifes plus they are hear to stay so its "bend with the flow"

 

[Scrub Puller]

Yair...gotcha tctractors. Thanks for the explanation.

Cheers.

 

[Nige]

The cracks will be drilled, v'd welded, ground smooth and a 1/2 plate is going around the pin boss and everthing from the top to the bottom, I'll post pics once we get it finished.

If you like PM me with an e-mail address and I'll send you a repair procedure for a Cat boom of similar size. It might give you a few pointers, especially regarding the shape and the welding sequence of the reinforcing plates.

I know I'm coming in a bit late, but couldn't a hole be drilled into the boom and an inspection camera be used?

Good point, never thought of that. Especially with modern fibre optics to light up the inside.

 

[uffex]

Good day cracked JD
My experience of the cracks in this area are caused by a inbalance in the hoist cylinders very common when the boom cylinders are fitted with hose failure valves. I recommend you check out the cylinders a issue much the same was recorded by www.excatech.com some time ago, I hope this helps if not you can mail me for more details.
KR

 

[tctractors]

Nige on a light note, I never worry about my customers equipment, I only worry about how they intend to pay my bill, for years I have been focused on doing a good job, doing the impossible with little reward and never any thanks, in these tough times the machine owners only want them earning coins, so a crack in a light excavator boom would be drilled, welded and plated in as fast as my backside could be kicked, I might be able to get a days work out of it, but it would not be 2, this week I had to be on a site Wednesday morning at 6.30am to fix a Volvo dumper near Hereford, just as I was thowing my tools in my chariot I get a call to go to J10 of the M40 to repair a broken track on a Rock Hawg, by the time I finished pressing up the pins etc and made it home it was 1.30 am, the Volvo owner will take forever to pay up and I would be suprised if the Rock Hawg man beats him on the coin sorting deal, so thats why I dont worry about if things brake in 6 months time. blowing it on tctractors

 

[Scrub Puller]

Yair...I know the feeling tc...see my comment on "reasonable charge for repair thread".

It's not funny but it makes you laugh.

Cheers.

 

[rare ss]

worse i had was a CAT 235C which had cracked through 3 sides (bottem was holding the boom together) and the top had opened up enough to fit your hand inside the boom, funny thing was the operator was still loading trucks!

will have to find some pics, we just scrapped the boom, found another one which was differant prefix had to re-bend/remount pipes and fit sleaves in the lift ram bores, was a fun time

 

[pp13bnos]

He just wanted to get every ounce of $$ out of the machine. Pics would be great though.

 

[oceanobob]

Should the weld rod be 7018 or perhaps one of the so called 'repair weld rods' which have additional ductility and perhaps a bit more strength? I use the 7018 fresh out of an oven but the sales approach of the 'repair weld rod' I always wonder about.

 

[tctractors]

The weld could be 7016 - 7018 or MIG, that is low Hydrogen basic coated welding rods would give the best result, there is talk of pre heat etc, but I would glue it all up with 7016 3.2 rods at the correct voltage and forget the heat, but that is me doing a job and we all do things different???, any plate aditions would be welded in the same style if possible using weldox plate or 50b grade steel, then I would check out the hoist ram set up for even operation as something has caused this crack to show its face, but its a common crack to see, it also gets fixed easy.

 

[Nige]

We came across some extremely useful rods for repair welding - Eutectic Xuper Nucleotec 2222. Originally designed for the nuclear power industry. Much more ductile than a 7018 (45% elongation) but with almost identical tensile properties.

 

[Karl Robbers]

The weld could be 7016 - 7018 or MIG, that is low Hydrogen basic coated welding rods would give the best result, there is talk of pre heat etc, but I would glue it all up with 7016 3.2 rods at the correct voltage and forget the heat, but that is me doing a job and we all do things different???, any plate aditions would be welded in the same style if possible using weldox plate or 50b grade steel, then I would check out the hoist ram set up for even operation as something has caused this crack to show its face, but its a common crack to see, it also gets fixed easy.

Don't mig it whatever you do!
Solid wire mig is a low hydrogen process for sure, BUT, it has nowhere near the toughness of a 7018 electrode, particularly when an Argon based shielding gas is used. If we are talking FCAW, (flux core arc welding) then that is equal to or better than the low hydrogen electrode.
As to preheat, when in doubt preheat. When the grade of steel is unknown, particularly when dealing with heavy or uneven thicknesses preheat is a must as it reduces thermal shock, slows cooling and also has the ability to drive out moisture from the joint, all of which contribute to a sound weld.
By preheat we are talking between 50 to 200 degrees celsius.
When welding the joint full penetration is imperative and don't just chip the slag out - give it a light grind every run, make sure that your finished weld has no undercut and is not overfilled as this creates stress at the toe of the weld. Obviously cool as slowly as possible, (don't quench and try to avoid cold winds etc).
Personally, I would use a 3.2mm (10ga) 7018 electrode (due to their smoother running and better deposition rate over the 7016) although for the root ron may opt for the same electrode but the next size down if I felt I needed more control over penetration/ blowthrough.
Generally speaking, for repair work the low hydrogen stick is king.

 

[Nige]

I'd echo everything Karl has said and add to it that as an aid to stress relief I would needle peen after every weld pass. Also after completion I would recommend grinding the whole thing back smooth and tapering out any radiuses, etc, in order to further reduce stresses.

However, to disagree on one aspect. I think that the low-hydrogen stick is a good repair tool, but on long welds the number of terminations caused by the welder "running out of rod" and having to change over can easily introduce flaws in the weld however good the welder who's doing the job, which is why I would prefer a wire feeder.

 

[tctractors]

Just like to say I used to do pressurized welding (pipe Line) but now only certified for upto 2" vertical permenent work, my welding skill and prefered method is MMA, the MIG weld is avoided by myself as much as possible, low hydrogen welding rod (Basic coated) are to all intents just sand coated (silica) after welding the slag is like glass and can be hard to chip off/remove, all that grinding and needle gunning is great, but making sure the W/Rods are dried as specified on the box to reduce the Hydrogen parts per Million is the route to go, 7016-7018 are both great spec rods for this style of repair, anything is better than a crack some times

 

[Nige]

Needle gunning is a must for stress relief - it has an additional advantage that it cleans the slag off the weld at the same time. Can't argue about making sure the rods are dry, expecially in the climate condtions here where it seems so rain 330 days a year.