Have had my D5H LGP in the shop for a while now, working on it when I've had free time. Took almost all shields off blew off with big air compressor and pressure washed to inspect. Have some cracks in the C frame and some in the back of the blade. Man it really seems like this machine was abused earlier in its life. i know the last owner and he never worked it too hard. Honestly i have asked quite a bit from it the last 5 years and its never gave me much trouble. But i like to take the time to weld up cracks and keep her running well. Anyways i took all the belly pans off and after inspecting found some cracks on two pieces that were welded together from the factory, and then someone half arsed welded it again i guess it may have cracked. I'm gonna need to plasma gouge and grind i know but it seems as tho its a cast piece welded too a different type of steel. this is on the frame where its welded to the rear axle that comes out to track frame pivot. Ive been welding for quite some time i went to a technical college and worked under one of the best welders in my area for 4 years during and after high school but i can't remember everything like what rod to use and if i even have two different types of steel here. i have a good stick welder but I'm not sure just using a 7018 will do the trick. here are some pictures from the inside. the outside has also been welded most the way up at some time but the weld appears to be fine.. funny how one side cracked. Any help would be greatly appreciated! photo bucket links are same pics but right side up all pics shown are sideways
No wonder it re-cracked, the repair welding was **** ........ Gouge/grind the cracks out properly to produce a 45-degree groove, add a bit of preheat to drive the moisture out of the steel, and weld with E7018 electrodes and it ought to last far better. If you have access to a needle-peening gun to stress relieve the weld while you're doing it so much the better. It has a secondary benefit that it removes the slag at the same time. The cast part will be cast steel so don't worry about a problem of dissimilar metals, they're not. This thread may give you some ideas. A different problem but the techniques are pretty much the same ....... HeavyEquipmentForums
May not be the tool for a full time welding shop use but even it it pukes after a couple days work it will pay for itself on this one job: http://www.harborfreight.com/air-needle-scaler-1108.html I should buy one for my self, I know I liked the one they had at the place I worked, great for knocking of build up of dry mud and rust before starting a repair.
Yup I have a needle peening gun. I thought my welding professor told me if I used it too much it would create stress? Hmm must have heard it wrong. Thanks guys!
Nige nailed it. Your root pass is where the strength comes from. A pass over the top is just dressing. Cut that grove to the bottom of the base metal and burn it in with some 7018. Good luck.
And don't even worry if you have to blow right through it with the gouging torch to get the root clean. You can make build-up passes using stringer beads on base material on both sides of the root until you close the gap sufficiently to be able to get a single root pass in there, fuse everything together and get adequate penetration into both sides. When welding don't be frightened to grind out anything up to 50% of the weld you just put in so that you are down to perfect weld metal. Any small imperfections like slag inclusions inside a weld bead are just stress risers that will create the next crack. The more you needle peen while the weld is still warm the more you remove stress ......... beat the living cr@p out of it.
Preheating to a few hundred degree's and welded properly with 7018 should do the trick. Warming the welding rods helps too. Peening is generally done on material like cast iron where the welding rod has more shrinkage forces than the cast iron. You could weld steel with something like an 8018C3 which has 1% nickel to add toughness to the weld. The welds aren't peened from the factory but on real critical weldments built of steel they are stress relieved using high heat for a determined length of time and slow cooled. I think I read where large excavator booms are stress relieved, not peened. Over peening can induce new stresses. Consider how fatigue cracks occur, constant pounding over time. Some peening can help but only when the weld is still hot. Usually about 5-10 seconds after welding. If it cools off too much and is peened to death will add new stress like fatigue stress. I think the most important thing is to make sure you have good fusion and no internal flaws in the weld. If you have slag inclusions, porosity or lack of penetration, grind it out and make sure the weld is 100% sound and you'll have a good chance at a successful repair. If you're going to fix it, take your time and do it right the first time. Repeatedly welded repairs in the same place can cause fatigue cracks as well. Grind a bevel with enough room to get full penetration. Weld inwards from each end of a crack so you don't have the crater at the end where a crack can start. Welding from both sides is best if you can get to the other side. Weld one side, then grind out the other side into your sound weld and you'll be sure to have 100% penetration. If you're not experienced enough with welding get someone who is if it's a more critical repair. I've seen people get praised for their welding repairs and when you look close it was done downhill with 7018 which has very little penetration or strength.