Bowed castings straightening

[macmet]

We use castings that are made of astm a297 grade hh - type 2.

These are about 30" L by 3" wide and 1" tall. There is a drive lug on at the centre of the part.

For our application it is very important that these pieces are straight. We just had to send a shipment back for straightening b/c they were off by about 1/4" at the centre.

We have had this problem before, some suppliers heat and straighten while others cold press them. Is one way better than the other? Anything I should keep an eye out for?

Thanks

 

[metengr]

macmet;
I have been in the same situation for misc boiler parts exposed to elevated temperature service. I see no problems with using either method other than when the part is placed into elevated temperature service it may warp again especially from cold pressing.

However, in the case I mentioned above, straightness is needed for alignment for fit-up, which is achieved using cold pressing or local heat.

 

[arunmrao]

concur with metengr. I have adopted both the methods to salvage my castings.There have been no problems reported later. 30" is not a very long casting for it to bow.

Cold pressing involves the risk of cracking,especially if the carbon is at the higher end. It also runs the risk of causing harm to the operator.

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[EdStainless]

If the guys that do it warm have good temp control I would prefer that, but you can cause damage by localized overheating.
Either method will work and neither is risk free.

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[macmet]

OK, so we got most of the castings back and they meet our straightness specs. However, they are a darker shade of grey now. Appearance is not a factor with us, is this a sign of a possible problem or should I not worry about it?

Thanks.

 

[macmet]

I should say they are much greyer (if that's a word). But, it was the first thing I noticed, it's not like they are slightly more grey, but significantly darker. At the same time, they still aren't black.

 

[metengr]

macmet;
Color appearance is only an observation related to surface oxidation, nothing more at this point. I would perform a detailed visual inspection of the castings just to be sure. More importantly, I would certainly contact the supplier and inquire as to what exactly was done to the castings to meet your straightness requirements.

 

[arunmrao]

A sharp inspector looks for such telltale signs of discoloration,mismatch in color,fresh signs of grinding etc. This indicates that the job has undergone further processing,beyond what was essential.

In your case such minor discoloration should not be a cause of worry. Only it might call for an additional explanation to be given to the inspector.

You may sand blast the part now which will make it look uniformly good with no traces of rework.

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[macmet]

Thanks for the help guys.