Vibration and Cracks

[6010]

There have been times when we have had to fix cracks in machinery that is subject to a lot of vibration. I would like to know how some of you do this repair work and what welding rods you use. Do you drill holes at each end of the crack, or do you grind the metal at right angles at each end of the crack. Sometimes it is the welds that crack and sometimes it is the base metal that cracks and needs repair.

Thanks

[SignWave]

theres a fellow on the motorsport side by the nic "CoalSmoke", I think he does alot of crack repair. Might try him for an answer.

Personally I like to drill the end of the crack and groove the length. Then fill it in, but as for type of rod, Ive never given that much consideration. I dont have to fix stuff that needs to stay together under any kind of load.

[KBar]

The cracks I have done was on medium grade machinery such as bush hogs. I would grind the cracks out and use a 7018 rod to weld it. The number of passes would decide on the size of the crack. I never had any reappear YET.

[burnie]

Just my 2 cents but the first thing to know in crack repair is that the crack is just the symptom of the problem. Once you know which direction(or directions) the stress load is being applied from, you can fix accordingly. Sometimes that means adding material or bracing but usually it just means adding a wrap to the end of a weld or even changing direction with your bead. I found it helpful to look at every weld (no matter how perfect) as a stress riser. Assuming that the stress will follow the weld(previously the crack), if you can point the stress in a harmless direction....end of cracking. For example, if you were to weld ears on a bucket only on 1 edge, that ear would not last 10 minutes but just by wrapping the weld around the ends of the ear you double the shear force needed to tear the ear off and you also change the direction of force needed. I use 7018 or 11018 on alot of the stuff I work on and I only drill holes on cast. Also I spent a fair bit of time on proper joint prep and then I pay extra attention to my root pass to ensure a hot pass with no cold lapping and as little undercut as possible. I tend to start my arc a step into the crack and then back up to make sure of proper fusion. Sometimes pre and post heating helps too. Alot of this effort is better suited to frame cracks than the cracked corners of an older shaker bin but hey...happy customers call you back. Sorry to be so long winded but I hope it helps.

[pthunberg]

If the crack is in plate I usually clean the area well dye penetrate test the area to ensure I know where the end of the crack really is. Then drill stop the ends of the crack using a bit size equal to the thickness of the plate. Example ¼” plate use a ¼” drill. Gouge out the crack from both sides. I usually use a grinder but have used a carbon arc gouge on thicker plate. The goal is to open up the crack and eliminate any weak area. I then weld er up with a root pass 6010 or 6011 followed by back gouging and a cap pass of 7018. This procedure works well for plate but castings are a whole different animal. Preheat and post heat are the key on castings. Like Burnie said solving the cause of the crack is the best fix. Be careful not to reinforce the original crack site and create a hard spot leading to cracks elsewhere. I once fixed a tow post on a boat, moved the crack from place to place, eventually had to build a whole new tow post. Boss was real mad.

[mustange70]

Yeah well first off the crack has to be completly removed to ganuantee it won't cause issues after the fix. But then just weld it up like you'd weld the material orginally, be sure to preheat though.