Hello all.

We are looking at arc spray to repair crankshafts but since this is new to us we have some apprehension about the ability of the coating to stay adhered with the normal flexing you might see in service.

Has anyone done any type of testing to crankshafts to test the coatings ability to stay on under these type of stresses - short of in engine dyno testing?

I am familiar with the standard tuning fork type testing done with cranks (imparts bending forces) but wonder if this is enough to test the coatings.

Thanks

Hi jdew1920

to the Surface Engineering Forum.

Sorry, can't help much here.

What is the "tuning fork type testing" ? is it a fatigue test?

Not too sure about testing methods but can help to put your mind at rest regarding the application.

This application has been carried out for at least 3 decades, if not longer. It has been used on everything from motorbike engines through to large commercial diesel engines. Although less common in many parts of the world now as it is often cheaper to buy new (particularly for cars/van etc), it is still widely used in less developed countries and when new replacement parts are not easily available (old tractors / trucks etc.).

In my opinion, if you stick to the tried and tested procedure, you should not experience issues. The correct procedure will include a rough cut, degrease, grit blast, bond coat and then top coat. When you try to cut corners by missing out a process (blasting is commonly not done or people will skip the bond coat) then you are POSSIBLY going to get problems.

Hi jdew1920

A few older posts concerning crankshafts may be of interest:

http://www.gordonengland.co.uk/sef/diama...t-410.html
http://www.gordonengland.co.uk/cgi-bin/b...s/398.html
http://www.gordonengland.co.uk/cgi-bin/b...10025.html
http://www.gordonengland.co.uk/cgi-bin/b.../3132.html

I generally concur with Stuart, but not all crankshafts are the same. Be wary if you are repairing the higher performance crankshafts and those with induction hardened or nitrided journals.

Quote:we have some apprehension about the ability of the coating to stay adhered with the normal flexing you might see in service.

A well applied coating should not have problems in this respect. If you have concerns about under-cutting/modifying original surface treatments, possible negative effects on strength and fatigue I can certainly appreciate concerns for testing.

In addition to Stuart's comments, finishing of the coating and sealing are other important factors to the "correct procedure"

Dear Jdew1920,
I have been repairing crankshafts by arc spray method for about a decade now. We have tested crankshafts in one of the rigs specially designed by Mumbai Muncipal corporation workshop before putting crankshaft in to service. How ever mostly we carry out repair for hard to get Vintage cars. My Last work was for a 1939 ford car. This car is running well.
But one has to have a very close control of parameters and total supervision while coating, machining and grinding
Best of luck
Vijay Deshpande

Thank you all for the replies.

So it seems that main challenge with crankshafts may be hardened shafts where preparing the surface to promote good bonding may be the issue.

It seems that if you can achieve a good bond strength than you should be in good shape?

Vijay - could you provide any additional information on this test rig?

Thanks

Hi jdew1920

Quote:So it seems that main challenge with crankshafts may be hardened shafts where preparing the surface to promote good bonding may be the issue.

Yes, but also you need to consider effects regarding fatigue strength on some crankshafts, particularly around the fillet areas.