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  1. #1
    Join Date
    Sep 2005
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    northern NJ
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    1,856

    Default Komatsu boom crack repair

    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
    Last edited by MMW; 05-04-2013 at 06:32 AM.
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  2. #2
    Join Date
    Apr 2008
    Posts
    254

    Default

    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!

  3. #3
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    northern NJ
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    Default

    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.
    MM250
    Trailblazer 250g
    22a feeder
    Lincoln ac/dc 225
    Victor O/A
    MM200 black face
    Whitney 30 ton hydraulic punch
    Lown 1/8x 36" power roller
    Arco roto-phase model M
    Vectrax 7x12 band saw
    Miller spectrum 875
    30a spoolgun w/wc-24
    Syncrowave 250
    RCCS-14

  4. #4
    Join Date
    Apr 2008
    Posts
    254

    Default

    Quote Originally Posted by MMW View Post
    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.
    Last edited by HayFarmer; 05-05-2013 at 07:17 PM.

  5. #5
    Join Date
    Sep 2005
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    northern NJ
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    Default

    Hayfarmer, The reason I used the backer was the day before I got there the rep had stopped by for something else & happened to discuss this with the mechanic. He described the way they fix it in their shop which uses the backer so that's what I did. I most likely wouldn't have backed it if it wasn't mentioned. The side plate was about 5/8" thick & the "ear" on the casting was about 1"? thick. The outsides were flush but the insides weren't. The 1/4" backer I used layed on the inside of the side plate & butted up against the casting "ear". The backer was hot rolled steel. I don't know for sure but I think the side plates are hot rolled steel also.

    As far as stress risers, I'm no engineer so I couldn't begin to figure out if this will be one or not.

    As far as ag vs. excavating equipment, I don't find them much different. At least with the newer ag stuff anyway.
    Last edited by MMW; 05-06-2013 at 06:21 AM.
    MM250
    Trailblazer 250g
    22a feeder
    Lincoln ac/dc 225
    Victor O/A
    MM200 black face
    Whitney 30 ton hydraulic punch
    Lown 1/8x 36" power roller
    Arco roto-phase model M
    Vectrax 7x12 band saw
    Miller spectrum 875
    30a spoolgun w/wc-24
    Syncrowave 250
    RCCS-14

  6. #6
    Join Date
    Apr 2008
    Posts
    254

    Default

    Quote Originally Posted by MMW View Post
    Hayfarmer, The reason I used the backer was the day before I got there the rep had stopped by for something else & happened to discuss this with the mechanic. He described the way they fix it in their shop which uses the backer so that's what I did. I most likely wouldn't have backed it if it wasn't mentioned. The side plate was about 5/8" thick & the "ear" on the casting was about 1"? thick. The outsides were flush but the insides weren't. The 1/4" backer I used layed on the inside of the side plate & butted up against the casting "ear". The backer was hot rolled steel. I don't know for sure but I think the side plates are hot rolled steel also.

    As far as stress risers, I'm no engineer so I couldn't begin to figure out if this will be one or not.

    As far as ag vs. excavating equipment, I don't find them much different. At least with the newer ag stuff anyway.
    So you had some input going in to it. I would have liked that myself. Im not an engineer (at least that type) either and I wonder how some field decsisions are made. Im not sure I would want to make those choices w/o considerably more knowledge.

    I have really no experience in heavy equipment so its a black box to me. I would have thought the arms on machines like that would be made from some high strength alloy.

  7. #7
    Join Date
    Jan 2013
    Location
    Ohio
    Posts
    55

    Default Komatsu boom crack repair

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

  8. #8
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    Sep 2005
    Location
    northern NJ
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    Default

    Quote Originally Posted by kerr74 View Post
    MMW...I'm still learning....what do you mean by stringing?...like the pics an explanation on how you did the repair
    Kerr74, Stringers are basically normal size welds overlapping each other to create a large weld. Here is a link explaining it.

    http://www.weldmyworld.com/quick_wel...ger-beads.html
    MM250
    Trailblazer 250g
    22a feeder
    Lincoln ac/dc 225
    Victor O/A
    MM200 black face
    Whitney 30 ton hydraulic punch
    Lown 1/8x 36" power roller
    Arco roto-phase model M
    Vectrax 7x12 band saw
    Miller spectrum 875
    30a spoolgun w/wc-24
    Syncrowave 250
    RCCS-14

  9. #9
    Join Date
    Sep 2012
    Location
    seaford de
    Posts
    406

    Default

    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

  10. #10
    Join Date
    Sep 2005
    Location
    Salem ,Ohio
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    3,913

    Cool

    Quote Originally Posted by weldonwelding View Post
    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
    Bob Wright, Grandson of Tee Nee Boat Trailer Founder
    Metal Master Fab Salem, Oh 44460
    Birthplace of the Silver & Deming Drill
    1999 MM185 w/185 Spoolgun,1986 Thunderbolt AC/DC
    Spool Gun conversion. How To Do It. Below.
    http://www.millerwelds.com/resources...php?albumid=48

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