I have a 450lc-3 Hitachi excavator and I have a crack in the boom. I is located about one foot behind the boom cylinder. It runs vertically to the top of the boom and stops. I want to put a backing plate in behind it and fish plate it. I don't know what type of steel to use, and also what type of design of fish plate to make. Has anyone has done this before, and any kind of info would help me along to fix and keep running. I'm a H.E.T. mechanic but not a welder fabricator so I'm going into new ground on this project.
Can you post some pics? I have a welding guy who is about as good as they get. I'll show him the pics and give you his advice.
Also, is the top plate broken too? All booms I have seen have a top and bottom plate. Without seeing it, I'm guessing what you need to do is air arc out the crack, weld it back up, then your plate probably should be fitted up past the boom bore so you can weld around the bore, but the rest of the plate you want to only weld top and bottom. I have drawn a crude diagram to show how I would probably attempt to fix. You DO NOT want to weld to the side plates of the boom. Around the boom pin boss would be fine because it is already welded there.
Good day Dr.Dc May we suggest it may well be in your best interest to address cause as a first step, in our experience such equipment failures occur as a result of side sweeping, other instances have been to unequal boom hoist pressures primarily from the boom cylinders so this also is worth a check. Reinforcing a boom structure with plate should never exceed the parent metal in thickness (Or results in high stress concentration ). Plate should terminate in “fish tail” or “Birds nose” I 'm not sure about your local terminology. Welding with low hydrogen in all such case's. There is well documented advice available at the excatech.com web site it costs nothing only a request from you if the information proves useful. Kind regards Uffex
If your have a good local dealer they can submit all your info and pictures to DTAC and they will send back the factory recomended repair for your boom. All material on the booms are standard mild steel. I agree with the side sweeping as a cause, but the lift cyl circuit has to be the same for both of them as they are connected at the base to a single tube from the control valve, not two seperate circuits.
Those cracks were common on some models of the EX machines and there was a factory designed fix for it. Get in touch with your local dealer and see if they can find some info on it. The fish plates they installed had a reverse curve in the middle and a specific weld procedure.
The picture from shimmy1 is exactly were the crack is and no the top plate did not crack. I believe its from side sweeping or uneven load. These machines have the sticks removed and a shear is installed in its place. Some of the jobs that are performed with the machines amazes me. I did contact the dealer for Hitachi and they didn't have a procedure and also couldn't tell me what the type of steel they were made of. I will contact a Deere dealer and try to find any info from them(hopefully they will contact DTAC). I also came across a design from a cat that might work. Since I'm learning about this as I go it might be a trial and error situation. Thank you very much on the info you all provided at least if have a direction to go with, and repair and questions to ask certain people.
Looking at a 450 I don't see any extra plating along the sides of the boom around the cylinder area . http://www.machinerytrader.com/listingsdetail/detail.aspx?OHID=10169671 My excavator had a factory plate on the boom . Continuous welded everywhere , with additional elongated holes in the center of the plate welded to the boom structure . Might be an idea for a repair . Use low hydrogen rods as suggested . Make sure there is enough clearance for the new repair plate between the boom & cylinder body . Hard to tell in the pictures on the machinery trader link but it looks close . Just something to keep in mind . Good luck with the repair .
I cracked my boom, this is how we went about repairing it. Still holding
Yair . . . Good one alaskaforby4 , that was a good discussion and there is no point in repeating the same stuff here. The one thing I would say is that I believe the practice of leaving the ends of doubler plates unwelded is poor practice. Cracks will propagate from the ends of the welds particularly on a small stick when they are opposite each other as Shimmy1's sketch in the #3 post. I feel it is far better to weld all around and plug weld as in td25c's picture . . . . I prefer that to the reverse curve shown on the original thread. The unwelded plates look very unprofessional and if used around saltwater are going to bleed some rust. I have always tried to make my repairs look as though it part of the original equipment. Cheers.
Hi Scrub Puller, the practice of whale tailing the weld on any doubler plate is generally accepted practice in this country. You will see manufacturers doing in on original weldments all the time. The idea is that you couldn't point load a curve like you can the end of a pointed plate.
Yair . . . Gotcha John C. Interesting. It may well be common practice here now as well . . . I never saw it much in my time except perhaps on truck chassis repairs. The rule of thumb was that the doublers were radiused about one third the width of the section being strengthened which would make the plate in td25c's picture a little too "pointy". . . no criticism intended, the comment was just to explain my meaning. Cheers.
the final product was doing a plate that followed the curve of the boom on the top and bottom with about a half inch gap between the top plate welds and the bottom plate weld. Put 4 smaller oval shaped holes in 4 corners. not to close to the edge. I whale tailed each end stopping before the main boom pin. welded it all solid. where the pate came to points on the four corners I keep the weld going and blended it into the existing welds on the boom . I will get some pics and post at a later date. so far so good.
You must check the lift cylinders for leakage! In my experience failures in this area are do to one of the cylinders doing most or all of the lifting. How to test in the field? 1) support bucket above ground elevation with a big rock, concrete block or another machine. Best done with the stick all of the way out to test at the highest static pressure. 2) with machine turned off remove both hoses connected to the rod end of the cylinders. Do this at the machine and leave hoses attached to the cylinders. Place hoses in five gallon buckets. 3) if you used another machine and with your machine still not running remove the support on the bucket, at this point a small amount of oil should come out of the hoses then the boom should not settle any more. If the boom continues to drop oil will continue to come out of the hoses and this will be a sign of a failed cylinder, at this point take them both off and fix them both. 4) if you used a rock or block start your machine temporarily and swing until your off the support. This can be dangerous and very messy. Be careful with pressurized or hot oil! Use appropriate methods to contain oil! If you need more info just post back here! Again you most likely have a bad boom cylinder breaking your boom!....TIO
very good point, root of the problem. Ill try it .
Unfortunately Hitachi's weaknesses is cracking I've seen many cracked boom's on hitachi's .
I see very few cracked Hitachi booms in the 40 ton and smaller class. Maybe 2 in 28 years and then they were minor. I've seen plenty in 100 ton and up but mining work doesn't compare to anything else. There are plenty of heavy diggers that crack more than Hitachi's in my experience.