Komatsu boom crack repair

[MMW]

Started this on Thursday afternoon & finished up on Friday. Cracked twice & welded by the companies mechanic (he's good but always rushed). This time he wanted me to do it. Right where the side plate meets the casting. Gouged it out completely so I had a 3/8" open gap to the inside. Snaked a piece of 1/4" bar inside with a rod tacked to it to hold onto. Pulled it tight up against the inside & tacked it good. Preheated, then welded it up.

Not really much to see. Basically like a weld test.

0502031611.jpg0502031612.jpg0503031324.jpg0503031613.jpg0503031614.jpg

[HayFarmer]

I never realized there was a casting on the end. Thought it was all built from formed steel. The casting then is steel?

Is this a usual location for failure ie is this an engineering design issue or working outside of engineering specs?

I assumed you used wire as in other projects? How did you figure the preheat..was it just to warm it up or were you trying for a certain range? Did you attempt to maintain a certain temp interpass?

Thanx again for taking the time to post pics, real interesting!

[MMW]

Yes it is cast steel. Not sure if it's common but the rep said he has seen this before on this model (PC400). The machine also has 11,000 hours on it.

The first passes I used 7018. One from the backer strip to the side plate & one from the backer to the casting. I did this because stick usually burns out any contaminants better than wire & I wanted to make sure I had a good root in there. I then finished with innershield wire doing stringers. I had about a 3/8" gap at the root & maybe a little more than 1" gap at the outside.

I didn't have my temp gun with me but tried to get it to about 300* at the start. There is so much steel there that I didn't worry to much about interpass temps. I just didn't rush it & cleaned each pass real good.

[kerr74]

MMW...I'm still learning....what do you mean by stringing?...like the pics an explanation on how you did the repair

[weldonwelding]

i have fixed about 5 of these so far on pc400's.. and also where the main boom cylinder goes into the bushing. The last one i fixed was from a bad weld, it was full of porosity on the whole bottom half of the weld. Not real good QC to let something like that come off of the line

[aametalmaster]

i have fixed about 5 of these so far on pc400's.. and also where the main boom cylinder goes into the bushing. The last one i fixed was from a bad weld, it was full of porosity on the whole bottom half of the weld. Not real good QC to let something like that come off of the line

Prob robotic welded and the 18 yo QC guy didn't care or didn't know. I saw it alot...Bob

[admweld]

i have fixed about 5 of these so far on pc400's.. and also where the main boom cylinder goes into the bushing. The last one i fixed was from a bad weld, it was full of porosity on the whole bottom half of the weld. Not real good QC to let something like that come off of the line

Of course you have.You,ve seen it all.

[JSFAB]

Of course you have.You,ve seen it all.

lol ......

Thanks, Billy, you just made my day.

[admweld]

lol ......

Thanks, Billy, you just made my day.

Not just once either Joe.Five times.

[HayFarmer]

Yes it is cast steel. Not sure if it's common but the rep said he has seen this before on this model (PC400). The machine also has 11,000 hours on it.

The first passes I used 7018. One from the backer strip to the side plate & one from the backer to the casting. I did this because stick usually burns out any contaminants better than wire & I wanted to make sure I had a good root in there. I then finished with innershield wire doing stringers. I had about a 3/8" gap at the root & maybe a little more than 1" gap at the outside.

I didn't have my temp gun with me but tried to get it to about 300* at the start. There is so much steel there that I didn't worry to much about interpass temps. I just didn't rush it & cleaned each pass real good.

I was thinking about the backer and theres no danger of it becoming a problem later on? My familiarity w/ backers is they must come off. I think they can become stress risers. Also did you try to match the backer to the original material or just use mild steel/whatever you had on the truck?

To me it seems very difficult to repair heavy equipment. There are so many variables you may or may not know or be allowed to know. Ag equipment seems a lot more doable. Guess its all about what you know....

I find these threads very interesting! Thanks a million for explaining what you did and why.