Undersize 316 Shaft Repair

[Fracball]

I have a shaft made from cast 316 SS which has been machined undersize approximately .035 inch. The undersize surface is used to support a roller bearing. It has been recommended to buildup this surface by "spray welding" and then re-machine to the correct diameter.

Is spray welding the preferred method of repair in this case? Would chrome or nickel plate be better? Comments?

Thank you for the help.
Fracball

 

[unclesyd]

You should build the shaft up by welding instead of try to plate sue to the problems with plating of the cast material and thickness. I am assuming that you are referring to MIG welding by "spray welding". If you are talking about thermal spray/metallizing of any sort please comeback with more detail as to the process and the physical dimension of the shaft.

We repaired SS shafts, all were wrought material, by welding or installing a shrink fit sleeve.

To weld this I would undercut the shaft in the undersized area to give at least an 1/8" diametrical undersize. Slightly taper the ends of the under cut. You might want to weld with longitudinal stringers rotating 180° on each pass depending on the diameter. Once you start, keep welding.
Being cast SS it is extremely hard to predict which direction it will go.

Come back with the Dia.

 

[Cockroach]

I totally agree with unclesyd, weld and machine back is the only way to go.

Plating the shaft up to 0.035" is kind of thick for this application, typically you only want one thousand of an inch or so for coat thickness. Anything more and flaking, peeling, cracking become a problem. Adhesion works best with thin coating followed by baking, like in the electroless nickel application.

Weld repair is indeed the industry standard for repairs of this nature. I like the longitudinal stringer idea, diametrically opposed would provide surface strata strength. Note also since you are to machine back the shaft to the correct diameter, any warpage due to thermal stresses would be corrected.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Fracball]

Thank you for the help.

unclesyd: I am referring to a thermal spray/metallizing process. I do not know any more details about the process - yet. The diameter is approximately 3 inches.

Thanks again.

 

[Carburize]

There are number of HVOF applied coatings available from Praxair for example LC-117 may work. Check with your local Praxair facility.
The problem with these types of coatings as with the "metal spray" type repair is low bond strength. Typically HVOF coatings have about a 10,000 psi bond strength.

 

[profengmen]

Welding the shaft is going to distort it, warp it, and make it hard to machine back into a concentric part, it would be easier to get a new one.

Machining a press fit or shrink fit sleeve is what we do, it's faster and holds concentricity without damaging the shaft.

 

[quark]

If we hold the shaft on a lathe at its ends before performng welding, there should not be any problems with concentricity. This is the standard procedure we follow.

Shrink fit sleeve is also a good option.

Welding a cast SS shaft may create some problems (as the temperature will be above recrystallization temperature and subsequent problems with carbide precipitation). But Unclesyd has profound knowledge in these matters and I think he will clarify my doubt.

Regards,

 

[boo1]

For a quick repair consider Speedy-Sleeves from Chicago Rawhide

 

[arto]

How about Roller Burnishing? [unless the shaft area need to go through a seal]
work-hardening might be an additional benefit?

 

[arto]

Roller Burnishing info:

http://www.cogsdill.com/pdf files/usbur_overview.pdf

 

[johnchrc]

I don't think welding is the way to go.

What type of tolerances end to end and surface do you have. Also, weld will not clean up worth a damn so your surface finsih will be spotty in areas.

The shrink fit has the most promise. However, for a 316 shaft at 3" dia., at what point do you punt and make new. IT doens't sound like an expensive part relatve to the work your about to put in it.

 

[unclesyd]

Our luck with spray welding, especially with Oxy-Acet was not very good on SS. Very good on motor end bells if we didn’t have a sleeve. On SS if we used metallizing we used a higher energy, thus higher density, type spraying process.
We had no problems with welding SS shafts and were able to achieve most any finish required. We never had problems with bearing areas. We found it expedient to finish in the weld metal not in an weld interface, that is the reason for the slight under cut suggested. The slight taper keeps a demarcation line from being a problem.