pre heat needs!

[BuiltnotBought]

Right guys,

I need some brain ratteling done please. I have started working for a plant hire company and have been doing bucket repairs ( oh the fun!!) And this current bucket is running 10mm plate. Is it nessissary to pre heat the weld area to stop the weld cracking? I noticed the tacks I habe put on have cracked at the ends slightly. I also read that cracks can be caused by rapid cooling or impurities such as water, because of poor surface prep. Is it more likely there was rust around the weld area that caused cracking. Im right in thinking the pre heat helps hydrogen?? Diffuse across the material and the rapid cooling causes the crack. Meaning the slower the cool ratecthe better the crystalisation and stronger the weld? Is there a rule of thumb for material thickness and pre heating??

I've typed this on my phone so sorry for any poor spellings and punctuation.
Thanks in advance

Al

 

[dan.taylor.1]

The bucket edge and maybe base may well be hardox or similar so may need heat, I assume you've cleaned round the weld area of rust etc? What process are you using as this will alter replies somewhat.

Dan

 

[BuiltnotBought]

Ha yeah fair point! So its MIG welded with standard 1.2 wire. All the buckets are plain old mild steel so I have been told.

Yeah have cleaned them, cut old broken s**te out ground it back cleaned it up and then put new sheet in to replace it. But for some reason this 10mm plus is cracking. The obvious thing I could think of was that its a bit cold and its contracting to quickly!!

Al

 

[dan.taylor.1]

It's the new sheet that's cracking? I'd have said the old plate night have been work hardened or just hard to start with so it might have cracked.

Is it pulling or warping with the heat? Can't say I've ever had much trouble with digger buckets but I've not dealt with any really bad or rotten ones.

Dan

 

[Ed.]

Hi, I used to work on agricultural machinery when I was much younger and all the buckets that were made/repaired were also made out of mild steel, with the exception being the pads and blades out of wear plate material. I don't remember any problem with cracking between the two different materials.

Although after tacking the over sized blade to the body of the bucket, I used to heat each end of the blade with an Oxy/Acet rose bud torch and when hot enough, then beat them with a sledge hammer to create a 90 degree bend. As the wear plate was already tacked to the body, we then welded them up to the bottom of the bucket and sides. Apart from that, no other heat except from the MIG when doing beads. Even when welding on the tooth holders to the wear plate we didn't pre heat. Doing this we didn't have any tacks cracking.

Bear in mind this was about 40 years ago and the wear plate material composition may have changed significantly since then, but I am guessing that one material is shinking faster than the other.

If you have cut out the damaged sections to clean metal then I don't think that it would be contamination or anything like that. Pre heat a small section and see if it helps, probably wouldn't take much heat to get an idea if that is required or not. Perhaps you may need bigger tacks, I would check to see that you are just using standard mild steel mig wire just in case you changed a roll and put on something else although that is probably unlikely!

Just my 2 cents worth.

Cheers

Ed.

 

[BuiltnotBought]

Hay guys,
thanks for the replies! I think it was just me being a slight muggings and just not doing quite big enough tacks for the thickness of the plate I was welding. I welded it all up fine on Friday without any need for heat. I guess it was just the amount of force being applied through the sheet while it was in a position it wasn't naturally sitting and me not having cooked it on there well enough.

Thank you again.