Journal rebuilding

[shantanu]

Hi All,

Any experience in repairing /restoring journals of steel mill rolls where wear is cased due to metal to metal fatigue - or is this not a thermal spray application at all?

To be precise, wear us caused due to metal fatigue between the roll journal and the inner race of the bearing...

Regards

Shantanu

[Stephen Booth]

There are many type of steel rollers, and bearings used to support them.

I suppose this is a back up roller?

The roll you are describing requires the bearing inner race to slip on the surface of the roll, and for that to work, the tolerance between the roll, and the bearing must be accurate. You can control the roll diameter, and the roll surface, but for this really to work well, you need to control the bearing installation and maintenance.

Strongly suggest you cooperate with SKF or similar to get them to join you to the customer, and cooperate with the customer.

Coatings that work well are HVOF ground and polished, or a good arc spray cored wire with 55HRC hardness, and ground smooth.

[shantanu]

Hi Stephen

Thanks for your response

If you guys had to chose between a pure Moly coat applied using combustion wire / ARC and a cored wire coating, what would be your pick for the application ?

Regards

Shantanu

[Stephen Booth]

Hi Shantanu, Go for the MOLY

Good question, I think the Moly coating applied properly using WIRE FLAME SPRAY would be the best solution.

First one or two passes use standard parameters to achieve good bonding and build up, thereafter use excess oxygen to get the hardness.

Grinding to proper Ra and Rz will be critical

[Met.Eng.]

Hi Stephen,

I have heard that metco not recommended molybden with in Arc Spray system. Have you ever try to coat moly with arc spray? And what aboud the surface after grinding ?

And you saied " you can try a good arc spray cored with 55 Hrc" can you say which wire is it?
We try with Metco 8222 CrC core wire next year. The coating ground is not smooth after grinding. Can you give some advice which wires can we choose

[Stephen Booth]

Hi Metallurgy Eng

Yes, you are correct , and I have edited my reply above to add clarification, that Wire Flame Spray is best for Moly. Arc Spray Moly coatings are fine, but they are not oxidized, and will not achieve the hardness.

There are several makers of the cored wires that all have various features and advantages. Our company has a few like W 662.1 , similar to SM 8222 and TAFA 95MXC

[shantanu]

Hi Shantanu, Go for the MOLY

Good question, I think the Moly coating applied properly using WIRE FLAME SPRAY would be the best solution.

First one or two passes use standard parameters to achieve good bonding and build up, thereafter use excess oxygen to get the hardness.

Grinding to proper Ra and Rz will be critical

Hi Stephen

Hope alls well

Refer to your reply above; when you mean excess oxygen, to want percentage would you increase the flow / pressure from the normal spraying parameter? As this would be a moly coating using std flame spray with high thickness- say 1-2 mm including grinding allowance, I'm afraid that too hard a coating would become brittle. Le me know what would be the max allowed increase in O2 flow from normal to get increased hardness....

Regards

Shantanu

[loriolo]

Hi Shantanu
I agree with Stephen and as I worked for many years, setting spray parameters on friction linings production, and I obtained hardness since HRc 61 and more, you can use the same flowmeter settings, and increase the O2 pressure about 3,5 bar, as result you must have on molybdenum wire an acute finish like a needle. .