PlasmaTransferred Arc Powder

Normally, one puts the horse in front of the cart.

In other words, all these details should have been resolved LONG before the motor was "being overhauled".

You seem to have committed a motor to a vendor without doing proper due diligence.

Be prepared to live with the result.

Lyn

Thanks for your input, can you help with a known standard as per my post?

No.

This "standard", if it exists, should have been included in the request for quotation long before the job was undertaken.

Lyn

Thought this was a friendly forum to help each other out with similar issues. You have now stated the obvious twice. This issue has fallen back to me, yes the repairer should of covered all these bases. A NATA approved NDT testing company was requested for the post analysis of the repair. The issue now is there apparently is no standard as far as NATA is concerned nor with the NDT test company. But thanks anyway.

I know that VFD operation can induce eddy currents in the shaft, what effect the porosity would have on the repair, I have no idea.

Beside all comments, justified, but which do not help may I try a constructive suggestion.

First where the shaft had to be repaired ? How high is the loading in the section ?

How are the "pin holes" as dimension and as number ?

The problem is even in the case that a norm does not exist to estimate if the obtained solution can or cannot be acceptable for the further use of your motor, or if it has to be again repaired.

The best would be to give more QUANTITATIVE input since what you gave is only qualitative.

As for the verification even if norms are not available there are experience indications and I am sure some research has been done on the subject.

May I also mention that this technology is mostly used to cover a piece with a hard layer and for this case only the wear (abrasive) is of importance. In your case it is a problem of resistance and fatigue which a different loading.

Thank you to all very much appreciated taking time out......The repair was on the DE under the coupling. I am project managing this repair for a customer. My stance was not to repair, however, the repairer made recommendations and the customer decided to go with the repair. I requested a NATA certified NDT test, first test report made no conclusive statement if it was acceptable or not. Another NATA NDT company tested the repair area and deemed it not acceptable. The repairer decided to get a third company (NATA) to test, they to identified the porosity/pin hole affected area. The third company identified no standard to compare to. The second company quoted a standard not suitable for this application, they were using traditional weld method standard. We had industry experts in this field discuss this having myself, customer and repairer present in a phone hook up. All stated there is nothing wrong with the repair but would not put it in writing. As you all know in this day and age we live in a legal world. An opinion from somebody in the field does carry weight, however, when they do not put on paper and if it goes to court if a failure occurs in gets very messy. There is a light at the end of the tunnel, we have decided to get a new coupling, machine the shaft down by 1mm. I am an electrical engineer I have been told by the mechanical guys this will not effect the shafts performance or strength. We will have a shaft using its own material and a coupling to suit. Once again thank you all for your input.

Which is the shaft nominal diameter ? In torsion the diameter enters power 3!

The coupling is connected to the shaft by a key ? If so the reduction of the side contact area shaft-key has to be maintained, i.e. the key location on the shaft has to be deeper. Do not forget to specify a radius for the tool if not the stress can be so high that the shaft will be destroyed.

Ask for calculations and not only for opinions!

It might be helpful to know why the coupling failed.

I have seen this process done before at an old local professional metal shop foundry. Normally this is a two part process: First, the shaft is molten metal powder coated in accordance with this type of process standards and, second, the shaft is turned to precision tolerances using a metal lathe. So, in reality the end finished tolerances really depend on the lathe turning tolerances which, if done in accordance to procedures can be finished to any desired standards. This is not a particularly difficult process, but the shop must be properly equipped and documented (experienced) to turn out excellent results. The machine to do this type of process must be a dedicated piece of equipment for this type of procedure since in reality, a turning of the shaft while the plasma powder head runs along at predetermined so the molten metal is properly deposited. I believe that, on a do it yourself basis, you would have to do the whole procedure on a precision lathe, using the moving carnage for both mounting the plasma head and final precision turning and finishing the shaft to tolerances. The advantage of using a lathe is that, once you have the motor mounted between the turning ends, you would only remove it after both operations are finished and and done. Since this is a fairly large motor , the whole set up is not a straight forward operation as it would be for smaller motors. All in all, what this amounts to is, that you should seek outside pro expertise for a proper to-tolerance reconstruction.

My cousin used this process to restore model T crankshaft rod and main bearing journals. It required meticulous attention to detail and a specialized follower system on the lathe. The finished part was determined to be superior to the original, based on performance record.

At the other end of the spectrum, was a friend that repaired his drag racer transmissions by using two gear clusters, one with a bad first and another with a bad second. He would slice and bevel the hubs and while mounted on a shaft, stick weld them. His firebird was a runner!

PTAW is normally used for surface treatment not for shaft repairs....

Here's an interesting paper that takes a real close look at what PTAW does to the parent metal.

http://www.mdpi.com/1996-1944/8/2/424/htm

You haven't mentioned why a bit of porosity should matter. Just a coupling on there.