Material Selection

[MickHutton]

Hi, I am hoping to gain some assistance on a Metallurgical topic. We are currently having issues with a gearbox shaft sleeve (Ø75OD, Ø63ID) which is currently 4142H. The problem is that the tube is subject to an abrasive environment (U/G coal mining) with coal shearing about its OD. Problems have arisen with the tube cracking on its abraded surface, causing oil to weep through the tube. (The oil is low pressure). In an effort to combat this, we changed material to an 8620 which was carburised on the necessary surface, but found the same issue occurred. There are no other loadings on the tube, apart from vibration. Would there be a better material to try in its place? I am thinking that the carburisation may have changed the structure to a martensitic one, causing it to become too brittle, and the 4142H mah be too brittle to begin with, being oil quenched. Am I heading down the correct path? Is there another material that you could suggest that could withstand the harsh environment described? Any assistance you can give is gratefully accepted. Many thanks, Mick.

 

[dbooker630]

What are the print requirements and heat treat notes for the 4142 and/ or the 8620 material? Need surface hardness, heat treat recipe, any post-HT processing (RP, straightening, phosphating, plating, etc.)

 

[gr2vessels]

Mick,
could be there a case of external stress corrosion cracking associated with the coal? The hardness of the tube would work against your interests, particularly with the erosion accelerating the cracking. Can you weld overlay the sleeve with some corrosion resistant alloy? It may just do the trick...
cheers,
gr2vessels

 

[redpicker]

MickHutton,

You will have to determine the cause of the cracking to solve this. If they resulted from fatigue, I'd expect the carburized part to have been an improvement. If, as gr2v mentioned, they result from corrosion, a carburized surface might just make it worse. If they result from the material just being too brittle, perhaps just lowering the hardness would solve the problem.

My point is that without knowing the cause of the cracking, you are just throwing darts in the dark.

I do have to ask are the dimensions you gave (75 OD and 63 ID) milimeters, inches, or furlongs?

rp

 

[MickHutton]

Guys- Thanks for all your replies.

dbooker630- I am not too sure of the heat treatment specs at this stage- will try to find more info.

gr2vessels- Thanks for the insight. It has given me the most sensible cause thus far- I will look into it. The only reason I did not go down that path initially was I was under the belief that the part needeed to be under some sort of tensile force for SCC to occur. I will, nevertheless look more closely at this.

redpicker- The dims I supplied were mm. Sorry for the ambiguity.

Thanks to all for the help. I will soldier on...

 

[macmil]

have you thought of using a coated sleeve, similar to gland water shaft sleeves on pumps ? The ones I sell ( disclosure !!! ) have a Rockwell 63 c coating, .030" or .060" thick on a (usually) carbon steel base. They work very well in pumps .