Welding on Caterpillar scraper - cast section.

[621_Rocker]

I have a small crack on two different 621 (A) scrapers that is nearly identical on each machine. The crack is on the cast section on the top of the differential/transmission housing. I spoke with my local Cat dealer about the metallurgy of this and they said that they did not know and that their welder would just do a spark test of the material. So far I have gotten the advice from other people to completely grind out the crack and then preheat the area (5"-6" surrounding but I have not been told what temperature range). Possibly use a UTP 62 rod and peen the weld. Do post heating and allow the area to cool slowly by insulating it with kitty litter. This is a very critical weld and I want to make sure that I do it right because the main force of the scraper weight comes down and is transferred around the drive line housing here. I want to have a strong weld and not weaken any of the existing structure. I have no experience in doing spark testing so I am not confident about using that test to determine my material. Does anyone of any knowledge of this or any more suggestions as far as preheat temperatures and rod to use? The arrow in the first photo is where the crack is and the second is of the crack.

621 Rocker

 

[StanRAUUS]

Cast Steel – per Cat’s special instructions SEHS8851 (7/87) All foreign material like oil, grease, water, paint, rust, dirt and scale, must be removed before welding. Cracks should be cut [air-carbon or oxy-ac torch with scarfing tip] or ground out 6mm-.25” deeper than the original crack whenever possible. Fill the crack with weld material! Pre-heat kingbolt housing [your’ repair] to 260C-500F prior to welding to prevent cracks. If the welding process is completed in a reasonable time no additional preheating should be required. To ensure a good weld, the material around the weld area should be 230 +/-C // 450 +/-F during welding process [innerpass temp] on the part being repaired. NO post weld heat required!
I prefer oxy-ac torch to scarf out the crack because the high heat drives out-washes out the accumulated crap and pre-heats the area, immediately welding with Mig procedure using Outershield .045” 70 series wire or .035-.045” 70series solid wire // LH7018 if using weld rods. You DO NOT want a stronger weld material versus the base material, that can cause under bead cracking, because the weld material is stronger as the weld puddle cools [shrinks in all directions]it can pull away for the base material causing under bead cracking. Too narrow ground out-scarf area [narrow root] causes under bead cracking, a U shape [wider] is preferred versus shape V shape [narrower], adequate room to manipulate the rod or wire washing in the side-walls.

 

[Scrub Puller]

Yair . . . It's a long time ago but I seem to remember similar cracks on J621's . We centre dotted them and watched and they never got any worse . . . just say'in.

I suppose it depends on what your plans are for the scrapers . . . if I was buying I'd rather see an honest crack than a painted over weld.

Cheers.

 

[StanRAUUS]

Yair . . . It's a long time ago but I seem to remember similar cracks on J621's . We centre dotted them and watched and they never got any worse . . . just say'in.

I suppose it depends on what your plans are for the scrapers . . . if I was buying I'd rather see an honest crack than a painted over weld.

Cheers.

I wouldn't weld or worry about that crack as 1st recommendation, the tube casting is massive joining front-rear pivot bores.
Good day

 

[Reid]

Good eye spotting that Crack, I would do the Samething as Scrub puller said, Mark it and see if it grows if not then i would not worrie about it. Heck it could have been there from the factory for all you know

 

[CAT303 SR]

Common practice with in service cracks (on steel tubulars in oil platform construction) is to drill a hole at the end of the crack to relieve to surface tension - this would only be applicable if the crack was through wall
I agree center dot / drill and monitor for growth - If its prevalent on these castings its obviously a design problem, and welding may not fix the problem - long term