Molybdenum Plasma-Sprayed Coating

hi,

i am not quite sure that moly-coating is a practical solution in your case; i may be wrong.

however, you might want to consider the following:

what kind of wear, abrassive? is it because of the dust from the mill?

what kind of lubrication are you using now?

surf. handness of gears? (if adhesive wear or pitting, then your gears are too soft...)

in a high dust factor environment, exposed gears will never achieve any acceptable life, even with the best surf. handness and/ or lubrication. besides, any lubricant will be contaminated and act as abbrassive paste.

i am assuming the gears are housed, so improve the sealing.

if dust contamination is not, or is only partly, the cause, check gear surf. hardness: many methods to improve it for large gears...

best of luck

Dear Sir,

I greatly appreciate your comments and would further appreciate suggestion with regards to improving surf. hardness or wear charateristic of larger size/type gears such as the ones I am working with. To answer your question, the gears are housed but not to the extent that you could call dustproofing hence my reason for going down the road of 'dry' surface conditioning. If you have any more suggestion on alternative method I would very definately appreciate your sharing them.

Many thanks,

Campbell

Hi,

your first goal should be to keep out the dust - especially the coarser fractions: these will act with any lubricant as as grinding or lapping paste.

No metal will survive this.

Oxides or carbides can survive for not too long lifetime.

So I would try hard to shield from the worst parts of the dust and blow out the rest as complete as possible. Then I would try to flame-spray mixtures of carbides as chromium and tungsten carbides.

RHABE

firstly, i suggest addressing the dust contamination. change the seals to something that allows nothing to enter the housing. i am sure you can find ready-made sealing solutions for the shaft entry positions (obviously, no other holes allowed). If you'd rather get creative and a bit ad-hoc, machine any labyrinth structure and pack it with grease, if speed permits: a rough solution that should keep the dust out.

then clean the housing, change the oil/ grease/ whatever lubricant you currently use and make sure that no more dust gets in (i.e. from sloppy maintenance). i advise you to do this regardless of any other remedy.

as far as surface hardness is concerned, first check with the gear manufacturer. it may well be that hardness is adequate (see my previous comment on adhessive wear and pitting). if you cannot discern between types of wear, then by all means get a local expert, i.e. from the nearest university, to evaluate. if adhessive wear and/ or pitting are identified, then hardening is indeed needed. the original gear manufacturer should do it, otherwise a specialised shop. depending on material, flame hardening is usually a good choice for large gears: gives good surf. hardness +core ductility. i advise against doing anything on site or by non-experts.

i suppose this is enough to get you started.

beware that long distance advice can be quite wrong, as i have no way of knowing what's really happening there. by all means, get an expert to LOOK at your application.

RHABE,

Once again many thanks for the input from your side, as might be apparent in my description and lack of gen on the processes, I am new to this particular field and have found myself somewhat neck deep. The getting hold of the Girth Gear Manufacturer is not really an option available to me as the mills and gears I am working with are ancient and no longer in production. I'm also having to look into building the gear teeth back up and re-machining them for new pinions as management is as most management are, very tight on budgets. There is a definite 'just make a plan' philosophy that I have to work in and around. I have already removed a sample of the Girth Gear teeth for Metallurgical Analysis in order to ascertain a welding and machining process so I will at least have data on hardness and composition for consideration in the hardening process to be applied . If you know of any other little tricks I'd hardly object to hearing about them.

Take care, Many thanks

Campbell

Besides all the good info you received, like tooth hardness etc. I would like to direct your attention to the dust problem once again.

An enclosure is a must, but that you have. What is also needed is small blower that receives its fresh air from outside of the plant, and pressurizes the gear enclosure. You need only a few inches of water column to keep pretty much all the dust out. A half hp motor or so would do.

Clean air of course is essential. You may even add a sponge filter of larger size (8 to 10 inch square) at the suction inlet that is changed periodically. It may require a long duct to reach the outside wall of the building, but it is necessary. 4 to 6 inches fresh air duct diameter would suffice.

We have done that with good results.

Regards

Floram

I work with industrial electronics and when we need to keep some thing dust free, we purge it with nitrogen. If the enclosure is relatively tight but not airtight you need a large nitrogen bottle, regulator/reducer, gauges, and 1/4" tubing to bulkhead fitting on enclosure. experiment with the flow you'll need to keep dust free. I use 0.5 cfm and go through one bottle a month, but it's well worth it.

Have you found a solution to your lubrication challenges? if you have , I would be keen to know how you have solved the problem