welder on crack

[wilajo]

Howdy folks. This is my first time posting, though I’ve been following your conversations for awhile. You’re a helpful and amiable group.

On the advice of a friend, I recently purchased a Miller 251 mig welder (1/2” penetration) set up with .035 wire and argon/co2 gas. To date, I have done no more than practice laying down a bead on various pieces of steel.

I am going to repair a crack in my 2’ backhoe bucket. The 8” long crack runs parallel to the center tooth assembly, starting at the buckets cutting edge and heading toward the rear of the bucket. The crack has completely penetrated the ½” thick, beveled cutting edge, and the overlapping 1/4 +” steel of the bucket itself.

I have been told to find where the crack ends and drill a hole at that point to stop the crack from lengthening. I have been told to grind a groove down the length of the crack to clean it out. I have been told to grind the metal around the crack to clean it up. After welding the crack, I intend to weld a plate over it for added strength.

Questions: /forums/images/graemlins/confused.gif Do I grind the crack following groove completely through the total thickness of the steel?
Do I fill the crack stopping drill hole with weld or leave it unfilled?

Thanks,
Bill J.

 

[Henro]

In addition to asking the question here, I would highly recommend you stop by the following site and ask there too.

Hobart welder's Forum...

Hobart is owned by Miller and there are a lot of experienced welders there who can give great welding advice.

It is the "TBN" for weldor's I think. /forums/images/graemlins/smile.gif

 

[RICHARDG]

You need to find where crack starts and ends,yes,,if its a big enough crack to let you see where it starts and stops,than you grind past the ends an inch or so,on both sides,if you can't tell by your eye where crack starts and stops,than drilling a hole on each end will serve no purpose,,and if you can tell by your eye,just grind past the ends,like I said,,,,they make stuff to check where exactly the crack stops,,its called dye penatrant,,,comes in spray cans,,,you spray the area with the red penatrant,,let it soak for 5- 10 min,,than dampen a rag with the remover,and whip off all you can see,,than you spray the developer on,[its a white powder],the penatrant in the crack will bleed up into the white stuff and you can than see where crack is,,,grind,,repete,,untill there are no more red lines,,,welding supply place should be able to get you a kit,,,don't cost all that much,,,,,,a magnifying glass may also help,,,,if you don't get all the crack out,,,it may just start cracking where you didn't grind it out and weld up area. If you can weld both sides in the flat postion,I would grind down about half way on each side,,weld one side,turn it over,grind your dingle berries and smooth out the other side down to solid weld metal,than weld the second side,,,depends on your skill level how you go about it,,you could grind one side 3/4 through,weld it up,than second side grind down to solid weld metal from your first side and than weld. As far as your mig machine having 1/2 inch penatration,,,you better hope not,,or you will make some pretty big holes in your bucket,,,when they say that,,they shouldn't,,,penatration depends on several things,,,how many amps you are running,,,travel speed,,how you move you gun,,etc,,,to weld thicker stuff,,you just make more passes,,filling groove up,real thin stuff,turn your machine down,,get it running right,,,and one pass may be all you need. As far as putting a patch over it once you get area fixed,,,the patch will serve no purpose,IF, you get the crack out,and IF,you weld the area up,with a good solid weld,,,the bucket will than be as good as new,at least in that area,,,,,thingy

 

[aardvark]

If I were doing it, I would grind the crack about one quarter the depth of the steel, on each side. I would try to keep the ground groove relatively narrow. Maybe 1/8"-3/16" wide if possible, but wider can be filled as well, it just takes more time. I would run the voltage setting slghtly higher than required, and run the wire speed a little faster than required, in order to fill the groove. You will have to practive this to get a nice setup on your machine. Grind some practice grooves in pieces of scrap steel which are the same thickness, so you can get a good weld on the bucket the first time. I might also run the torch so that I was pulling the weld puddle rather than pushing it. I find I can fill more easily while dragging the weld puddle than I can by pushing the puddle. If you can weld with the groove flat and level, then that would be best. If the bucket wall is vertical while welding, I would start at the bottom and work my way upwards with the weld bead. I personally would fill the drilled hole with weld. You sould practice filling holes before you try this, because filling holes typically is a pulsed operation. IOW, pull the trigger, make an weld puddle and fill for a few seconds, and then release the power. Let the puddle cool and then repeat the cycle. Once you have built up a bottom, you should be able to run a bead around the perimeter of the hole unitl it's filled. You don't HAVE to fill the hole if you don't want to. Unless you want to carry liquids in the bucket. /forums/images/graemlins/smile.gif

How wide is the crack? What diameter hole do you plan on drilling?

 

[RICHARDG]

Why drill a hole? This is steel,not cast iron,,,,the hole theory is supposed to stop the crack from speading,,right? Well if you don't know where it stops at,,you won't know where to drill the hole,,,,and if you know where it stops at,just grind it out,and then some,,and its gone,,,than weld,,,if you want to make for sure,than do the dye penatrant test,,,that hole drilling stuff is for cast iron,,when you are just sealing up a crack that will leak,plus you have to preheat cast iron to weld it,,that alone may make crack spread and you just keep chasing it,,,,this is a full penatration weld,,or should be,welded from both sides,,,,,,,however deep you grind it,it still needs to be solid weld from one side to the other,,you can't get the crack out any other way,,if you only grind 1/4 way,,weld it,,grind a 1/4 way on other side,weld it,,,how are you making sure that the second weld tied into first with complete fusion? Now it might,,and than it might not,,,thats why I suggested to grind both sides,,,weld one side,,than on second side grind again down to solid weld metal,,that way you are pretty much assured that you have soild weld metal the complete thickness,and no voids or crack left. I wouldn't make the groove to wide either,,,but wide enough to where you can tie in the sides,,I would put a little bevel on the sides,,,you can always run a two or three bead cove,,or again,,depending on skill level,,a weave cover. I can't follow the changing of the amps and volts either,,,I use about 120 amps and about 19 volts with .035 wire,,thats on the hot side,,,if I want it colder,,than I turn it down a little,,play with the wire speed untill it sounds good and try it,,should be a nice even paper tearing kind of a sound,,,thingy

 

[wilajo]

Henro, thanks for the Hobart lead. I have been reading their forum, but I felt a little more comfortable posting at TBN. I know there are folks here that know their way around the metal shop. Not only am I green at welding, I’m considering buying Green (110 tlb).

RichardG and Aardvark, thanks for your advice. I hadn’t heard of a crack clarifier. I’ll pick some up at my local supply shop for future use. In this case the crack is 1/16” wide on one side, thinner on the other. You both answered my questions. I hadn’t thought of grinding one side, welding, and then repeating on the other side. The crack gets ground out, using one of your several offered methods. The logic for not drilling a hole is impressive. If I know where it stops, grind past it. If I don’t know where it stops, what is the use of a hole? I’ll remember the approach for filling holes, though in this case, it sounds like the hole is history. I am beginning to see that welding, like the other arts/crafts, offers differing approaches and methods to accomplish a given end. In any case, this sounds like a lot of grinding with a little welding. I can manage the grinding, we’ll see about the welding. We could go further, into wire speed and voltage, but perhaps I should just learn this like I learn most things, through my own flirtations with disaster and near disaster. /forums/images/graemlins/tongue.gif

Thanks guys,
Wilajo

 

[SPIKER]

wilajo:

several good posts, remember this is a back hoe bucket and will get more and more abuse as time passes, you already bought the welder so if you weld it up this time and 10 years form now it breaks againe, well you will be a more experianced welder by then and will not need to ask for help. I would remove the tooth bar part and weld it sepperate, as you don't want to weld that to the bucket. lay it flat and clean both faces of the weld area with a wire brush and grinder. grind a nice 2/3 bevel leaving a small amount (1/3 thickness) of material in the ceter and enough bevel on each side (1/3 thickness) to get a good fill in there. the grind should vbe V shaped or a slight U shaped.

With teh bucket wire brushed and gorund take a heavy hunk of steel chanel or something similar and clamp across the front edge to hold it falt and back into shape as best as possable, you MAY need to use some pipe clamps at the end/edge to squeeze the crack back together a bit, maybe have to use a bit of clamp and bang. (clamp tight wack with big hammer.) once it is held in factory spot, then tack weld it with small spots 1/2" long just ewnough down in the grouve to get the parts back together firmly. you can then begine the welding process weld it up with beads no more than 4" long with a good weave, makeing sure the weld bead fills the V from each side adn leaves the bead slightly higher than the surrounding metal, after you go that 4" max lenght then stop and move to next spod and do the same untill the weld is done fully, switching back and forth between sides is good idea, let it cool and grind the bottom edge bead flat where the tooth bar will go, then bolt up the tooth bar and tack weld it back together too. remove it and weld it up using the same way, grind the top mating edge and bolt it back on...

pretty simple process and I'm sure you can get it done, as for the CO2 it is OK, but the MIX 75/25 is a bit better for all aound use. with that bucket and steel the CO will work for you fine. get into some other coated stuf then you will want to get the mix. it is a bit more expensive but also cleans a bit better.

mark m /forums/images/graemlins/smile.gif

 

[MadReferee]

Over the years I have made several repairs of this type and I agree with SPIKER in that you got to grind your V about 2/3 of the way thru the metal and the width of the V should be at least twice the depth (half on each side). Do the weld in sections so you minimize warping.

One thing, get some scrap metal the same thickness as your bucket and practice a few V-groove butt welds. Once you get the machine settings and your welding technique where you are comfortable and the weld is solid, then do the bucket. You really need a solid weld here so don't just lay filler into the groove. Remember, penetration is the key to a good weld.

 

[RICHARDG]

I don't think warping will be much of a concern,,,if your worried than but a bead on one side of your groove,,flip it over,backgouge to solid metal,put a bead on that side,and since it will probably,[should],take more than one pass per side,,flip it back,wire brush bead,and put next bead on ,,so on,,if he tries and stitch it,,he is going to have a lot of starts and stops,,,which he will than need to feather down,,,he sounds like he is just learning,,,so all that may be beyond him,,,plus,,I don't think it will warp much,,just give it a few min. between passes,,,bucket is a pretty big heat sink,,plus the way a buckets formed,,,should reduce warpage,, by the time he puts a few good solid tacks,its going to be stitched anyways,every 5 or 6 inches,put a good tack about an inch long,than feather the ends down a little,,,,,mig can be tricky for beginner,,,cause it looks good,[generally],and is easy to lay a bead down,[after you learn how to set up machine],you think,I got this welding stuff,,,till it breaks,,,because you were not using enough heat,or not pointing wire in right spots,,getting cold lap and lack of fusion. One more thing,,he needs to make sure area is shiny and dry,,might be a good idea,[if you got a oxy torch,,to warm it up to hand warm,before welding,,that will dry it off... thingy

 

[Kevin_in_VA]

Thanks for the link to the Hobart forum. I have been looking for something like that recently.