Cracked Boom Pictures! Suggestions?

[Nige]

IMO we have got past the repair on the Deere that was the OP's problem when he originally posted, and on to the subject of structural repairs in general. For me this discussion is a valid one if it helps someone else in the future with a structural crack on any machine, not just an excavator.

 

[Scrub Puller]

Yair . . .as Nige mentions this has gone way beyond the original posters repair which I reckon will be fine . . . (to me) it almost goes without saying that you would carry out such a procedure on both sides of the structure.

The inward curves of the plates of the repair technique are unfamiliar to me. I don't like the sharp corners either.

The old boilermaker who kicked me off reckoned that the plates should be tapered outwards at forty five degrees top and bottom and terminated with a radius one third that of the structure being stiffened.

He would put two inch "plug welds" or, as they are called here, "rossetes" on about twelve inch centres . . . good advise I reckon and it has always worked for me.

We were working in salt water and it was not an option to not fully weld a doubler . . . it would be bleeding rust in about a week.

Cheers.

 

[T.O.]

found a crack in the boom on 200 clc, new to this forum and would like some input.

 

[icestationzebra]

found a crack in the boom on 200 clc, new to this forum and would like some input.

If you want specific suggestions you will need to post some pictures. ISZ

 

[T.O.]

 

[T.O.]

I'm planning on removing hyd lines, cover ram on cylinder, grind off paint, drill relief holes at each end, grind down to the vertical plate, preheat with torch, make root pass with 6010, stringers with 1/8 7018. Machine sees farm use, tree digging now, but was prior rental, had seen some jackhammer use most likely.

 

[oceanobob]

Thank you for signing up on the forum....I figure this could be a new thread were you able to do so...maybe it will get moved into such a status, but for now here it is.

I am not sure but: there may be some concern the interior section parts may be cracked and these are transferring forces to the exterior....the crack looks tight and you are to be commended for detecting this at this point (unlike the kubota dipper show on another thread where it darn near parted)...

This crack appears to extend in the distance from the boom rams toward the dipper? but not the other direction toward the boom pivot....and then once it gets to the dipper ram mount on the boom, the crack stops...
does this match what you are seeing?

This area is the section of the boom that is unbraced (without a ram forming a triangle) ....

Assuming all the above is the situation, the overall bending moment has exceeded the material strength - but maybe not. If the crack is fatigue, that is. Since there is little deformation, fatigue is a strong candidate.

One way for fatigue to show up is if the web didnt fit that well to the flange....and the factory weld, not being a full pen would allow an eccentric force to cause rotation as the web moved toward the flange and vs vs. This is why web stiffeners are usually fitted tightly. That rotation would be applied to the last portion of the web near the end of the weld (HAZ) and change in section thickness ergo stiffness profile .... and the fatigue crack occurs.

So, my earlier suggestion there may be cracked parts inside may be just a worrisome thought and perhaps simply welding the crack down to the web is in fact a good idea.

Soon you will have other opinions as to this machine and their other experiences in particular, as well as general direction for your repair plan.

 

[lantraxco]

I'm planning on removing hyd lines, cover ram on cylinder, grind off paint, drill relief holes at each end, grind down to the vertical plate, preheat with torch, make root pass with 6010, stringers with 1/8 7018. Machine sees farm use, tree digging now, but was prior rental, had seen some jackhammer use most likely.

That's an unusual looking crack. I'll bet if you get up farther you will find that the crack started at the butt end of the stick cylinder mount plate. Just a guess.

 

[Oxbow]

Oh boy, here we go again! I would do just as you suggest T.O., but relative to the knowledge of the bright folks on this thread I have very little.

In reference to all the previous posts I have learned an awful lot on this thread. One thing that I didn't see discussed was metal fatigue. On other posts Nige has written about the rebuilds of D10s etc., and I believe that in some cases the main frame is replaced. Is this not due to fatigue? Surely after 20,000 hours it can't be blamed on greedy corporations building something that they know will fail in order to compete with off shore companies. Heck, in Caterpillar's world off shore would mean another planet as they are as global as any corporation that I can think of. Maybe sometimes things just wear out! The comment that someone made about the absence of "welding engineers" in the manufacturing process must be horse poop in my mind as 20,000 hours on the main frame of a D10, or 11, or whatever just could not occur if there weren't a bunch of brilliant people involved in the design and manufacturing of such equipment.

While many of the contributors to the thread who suggested cutting a whole to see the inside, removing the boom, heating in an oven etc. were certainly not wrong, I think it is important to remember that for a small operator such as myself and the OP, removing the boom is a monumental task. I would guess that the 490 in question runs between 500 to maybe 1000 hours a year at most. Considering the seasonal work in Alaska it may be much less than that. I would have followed along the lines of what Scrub Puller suggested as far as the repair goes, and I think that it would have outlived the remainder of the machine.

T.O. you have bumped the old thread here, and I am sure that you will get some great advice soon, let's just keep it in perspective folks!

 

[Scrub Puller]

Yair . . . Well said Oxbow and for or what it's worth I never get too fixated on different rod types, I use a GP 6013 for about 90% of what I do.

Sure I use a low hydrogen if I have them and iron powder can be handy for some applications but as I say the old GP is the go to rod . . . even fabricating implements from cutting edge I never bother with low-hydrogen, I'd rather do a couple of extra passes with GP's.

Preheat . . . well maybe. It's all there in the text books. In the real world when you're a days drive from the oxy-shop jobs tend to miss out on the fancy stuff, the main thing in most cases is to keep on welding and putting in the heat.

On a big weldment, say a cracked main frame or saddle on a dozer there's no time to eat or sleep . . .and never ever cool it. When the thunder storm comes over protect it from the rain.

I'm not advocating short cuts, or iffy workmanship, I'm just saying how it is . . . in my part of the world.

Cheers.

 

[kevin37b]

Grind it out and WELD it . I could fix that in an hour .

 

[T.O.]

Deere actually has a repair procedure for this specific repair since it is so common, they recommend cutting a hole in the web to weld the inner. I'm confident that thorough repair from the top will be all that's needed.

 

[Scrub Puller]

Yair . . . By coincidence as of yesterday I'm going through the same thing here. A bloke just bought an old digger and is paranoid about cracks and "correct procedure" to repair them.

Sheesh, I told him to get outa my face.

Sure it needs fixing but the bloody thing has been working for years with rust bleeding out of the cracks . . . anything is an improvement on what's there. As kevin37b says I'm suggesting just a grind out, weld and watch it approach.

If he wants the full monte with pre-heat and plating that's up to him, I just don't think it's worth spending that kind of money on a digger that does a few hundred hours a year.

Cheers.

 

[Nige]

As everyone who's anyone has already expressed an opinion on how easy this job is I'm not going to even bother pi$$ing on anybody's chips at this point .........

The only thing is this. If according to the OP it's a known problem area to Deere and the root cause lies in a crack inside the structure which is not addressed at the time of repairing the outside then I can 100% guarantee the crack will appear again in the external weld repair at some point. If the life of the repair until it cracks again is judged by the owner/operator to be "acceptable" (and for the type of work the OP describes this might well be the case) then no harm no foul. On a machine that had to earn its corn on a day-in day-out basis anything less than a full-blown repair might not give satisfactory results in the long-term.

OK, as you were ...............

 

[Nige]

In reference to all the previous posts I have learned an awful lot on this thread. One thing that I didn't see discussed was metal fatigue. On other posts Nige has written about the rebuilds of D10s etc., and I believe that in some cases the main frame is replaced. Is this not due to fatigue? Surely after 20,000 hours it can't be blamed on greedy corporations building something that they know will fail in order to compete with off shore companies.

Sorry Ox, I need to correct this information. As far as I'm concerned the frame is the one critical component of any machine that determines its "rebuildability" - in other words if the frame is good at overhaul after shotblasting down to bare metal then the whole machine is good to go again because everything else is effectively bolt-on. the D10 overhaul I was posting in another thread is from a machine that had 17,000 hours from new. There wasn't a single crack in the frame so I have every reason to believe it will go 17,000 more in its new "life", and even 17,000 more after that. When it gets to the 3rd time round at 51k then we would likely be looking really closely at the frame and wondering how much longer it would last. But that's a track-type tractor, I've seen big off-highway truck frames go past 100,000 hours and still be good. The last I heard the highest hour Cat 785 truck in the world was approaching 140,000 hours on the original (albeit repaired) frame.

 

[RayF]

I'm with Nige on this. I won't upset the apple cart except to say I've seen many, many grind and weld repairs done on booms and then when it fails again its a major job that could have been avoided. As some have said its not in full time production so that can be a factor.

 

[Oxbow]

Heavy manufacturing industries have embraced almost every welding technology that has come down the pike which has been touted as being able to decrease production costs, often for no better reason than to more effectively compete against ‘off-shore’ competitors. What other possible motivation does a global corporation have?

Rarely are the decision makers in these enterprises trained welding engineers. Nor should they be, there is much more to building a productive piece of equipment than the welding. It is but one of thousands of considerations that must be made.

Process control in most welding establishments in 2012 still involves nothing more than twiddling dials, and listening for the resulting sounds!

The underlying problem is that production decisions are too tightly focused on cost issues, while the engineering solutions require a level of technical understanding and insight that appears sorely lacking. When the military developed the Abrams tank, they had a prototype that was much superior to what was actually produced because of cost constraints. I suspect that equipment manufacturers constantly deal with balancing "how good can we make it" with "how good can we make it and still produce it in a price range that is cost effective to the consumer".

Yank, I appreciate your point of view, but I feel that the technical understanding within the hallowed halls of Caterpillar is hard to beat. Do they make mistakes? Yes, of course, but they pay for those mistakes in the market share arena. Caterpillar's one and only purpose is to provide profit to it's shareholders, and as any business, they must make cost saving decisions in order to do that.

Nige, I had no idea that the main frames of the 10's and 11's lasted that long. I am not in the portion of our industry that utilizes that size of equipment, or puts that many hours on them. I feel that that is proof that Cat, and other companies, put plenty of emphasis in the quality of the welds.

I guess that while I have never been acquainted with anybody that has a better grasp on what maintenance and repair procedures provide the least cost per hour as you, I suspect that it is not directly proportional as the scale of the operation is reduced to the typical owner operator. In simple terms, the cost of the best repair procedure may not be warranted in a machine that might be billable for only 500 hours per year.

This has been an educational discussion, and I for one thank all that have contributed!

 

[Nige]

I'm with Nige on this. I won't upset the apple cart except to say I've seen many, many grind and weld repairs done on booms and then when it fails again its a major job that could have been avoided. As some have said its not in full time production so that can be a factor.

+1. Fix it once, fix it right, because if you don't it'll come back and bite you in the ass at some point when you're not expecting it ............... I've seen too many "bush repair experts" using their easy-to-weld electrodes produce really pretty welds on the outside that weren't worth Jack Schitt on the inside. There is some serious metallurgy involved in a repair weld and those people who understand said metallurgy will produce a repair that's light years ahead of those who don't.

 

[Dad5]

I'm with Ray on htis one. FFS don't try to "butter this over" by just working from the outside, it will only crack again but 100 times worse the 2nd time. Even though cutting a hole in "good" steel might seem a bit drastic you have to cut a window in the boom so that the inside can be inspected and accessed for welding, repairing cracks in the casting if necessary. You may find that it was a crack in the casting that caused the outside of the boom to crack but you have no idea until you cut a hole in the boom and go looking.

I'd go a bit different to Ray and suggest that if the external boom crack is easily accessible from the inside, then put the backup strip on the outside of the structure and then make the repair weld from the inside. After welding then grind the interior weld smooth and make sure where it transitions to the casting it's well ground to smooth off the radius. Finally the backup strip can then be cut off and the weld can be back-gouged and the final passes made on the outside. Again grind smooth after finishing. Get some preheat in the structure from the get-go to make sure you drive all the moisture out and beat the crap out of every weld pass with a needle gun to stress-relieve it. Possibly add a stiffening plate over the top if it's recommended by the manufacturer. Maybe your Deere dealer can help you, they may have a repair procedure already.

To fix this one correctly is not going to be quick or cheap. If it was me I'd have the boom off the machine so that the repair work didn't have to be done off a ladder. You don't need to make a difficult repair job any harder than it already is.

Definitely open a window and look inside. I have seen tack welds inside booms and sticks cause stress risers which eventually lead to cracks like you have.

 

[oceanobob]

What exactly would be seen if one looked inside the boom? A big beautiful investment casting? or some plates fabbed into a notable weldment? perhaps just a simple heavy wall tube sleeve that goes from one side of the boom to the other with some bushings in it? could it be just the sleeve and maybe a simple stiffener?
*
With great respect to all, for us who've not seen inside a boom it's hard to get the idea to cut a hole in the boom to look inside when one isn't sure where or what to look for...