gentle man explain me about...........

What are you trying to cut with the rotating blade?

Good evening Sundararavi.

Milo here.

I'm thinking that you are running some kind of ID fan that is being eroded by dust particles.

I'm thinking that you want to rebuild and rebalance the skeletonized fan to get it pulling the volumes of air that your process needs.

I'm also thinking that you want to hardface so that you don't have to do this evry week/ two weeks/ month or whatever.

If I'm correct, you really need to do a better job of pulling the particles out ahead of the fan, because at the velocities involved, and any frequency of particles getting through at all, that fan is going to be eaten alive. What are the rpms and diameter so that we can calculate the feet per minute at the "rotating equipment's OD?"

Next, if I'm correct, the frequency of needin gto do this is much more often that you would like. I believe that the hardest or Premium hardface coatings/claddings are n't necessarily going to pay for themselves with longer time between applications, although I could be wrong.

I would treat this as a volume removal/volume replacement function over time, and try to establish the optimum between cost of material, cost of application, and cost of downtime. The best decision will give you the most materials processed/produced in your plant (between shutdowns to rebuild the fan) for the lowest total cost.

In my experience as a very young pup, at a sintering plant with electrostaic precipitators and baghouses ahead of the fan, we were still metallizing the fan weekly (not weakly!)

Regardless of the hardness or expense of the metallizing applied, we shut down every tuesday for maintenance and the hardface guys came in and rebuilt the fan.

Iron based materials are cheapest, Austenitic manganese was I think what we settled on. We did not choose nickel, cobalt or any of the really exotic alloys because our operating temperatures were relativley low. (unless the baghouse caught on fire...) I'm pretty sure that they used an oxy acetylene process, although today there are a host of options including plasma arc, transfer arc, and many many more

Here are two standards which will give you some excellent background-

Specification for Surfacing Electrodes for Shielded Metal Arc Welding
Document Number: ANSI/AWS A5.13-2000
American Welding Society

Composite Surfacing Welding Rods and Electrodes
Document Number: ANSI/AWS A5.21-2001
American Welding Society

You should note that most companies that do this kind of work have their "preferred favorites" based on their economies and talent and equipment.

If you solve this first as engineering problem, "WHat are my minimum performance requirements?" and then look at the economics "Which of these choices will get me at least what I need for the best cost and least loss of operating time?" you will be successful in your quest.

milo "dont pay for nickel, tungsten or cobalt if you don't need tungsten or cobalt- you won't be recovering them as they are lost by impingement."

my dear milo,

thank you for you thoughtful reply. actually the fan is cement plant pre heater fan. actually what happened in that fan,once in 20 days of operation,a hole(about 3") created in the back plate of fan in a particular place(this was understood by us while vibration readings is increased from3.2mm/sec).that is at near to the hub .this due to the air with dust taking turning on that zone this phenonmena is 3 rd time.previously that particular zone(complete inlet area of back plate) was hard faced by tungston carbide electrode in chequered manner .even after we were not able to eliminate the problem.only benifit is the hole formation period is extend from 20 days to 35 days.it is very head ache to us.hence why i am asking any other superior methods available for wear resistance.pls note that inlet dust loading is un avoidable.and the material used for back plate is naxtra-70 rpm of rotor is 1440 and outlet dia of rotor is2.85 m

Devcon makes some wear resistant epoxies. http://www.devcon.com/products/products.cfm?brandid=1&catid=4

Take a look, they might be of some help to you. Good luck.

I think that you are decribing an eddy or vortex is being set upp, causing the perforation at the same spot. I am presuming that you rebalanced the fan.

I am not a design engineer, but perhaps baffles can be arranged such that this eddy or vortex can be avoided. provide some means ahead of the fan to provide a means of reducing the particle load.

In my life experience, I have found that whenever people wanted "harder" in actuality they wanted "stronger/ tougher" (Easy boys!) and that just going to the hardest material did not really solve the problem. It did make for some awesome failures, though!

The tungsten carbide gives you a respectable 30 days with a 5 day or ~15% safety margin. I'd plan on 1 maintenance day per month, if you cannot remove the root cause, which is the particulate loading impinging on the blade.

I was pretty sure I understood your application after looking at your prior postings.

milo

Hardness is not always the best material for wear.

Example; rock tumbler tubs were made first out of sheet metal , didn't last long.

Next, various welding rods , mild steel to cobalt was used ,it lengthened the time of

replacing or repairing the holes in the tub.

Now tubs are made out of neoprene rubber and they last and last.

Wouldn't cost too mach galvanizing or gluing a thin sheet on your problem area.

It just might work

That was part of the Devcon epoxy idea. They sell an epoxy called Flexane. Available in putty, or a liquid form. It has greatly reduced wear in tumblers and chutes in industrial applications.

dear sir,

the air with iron ore dust hitting the back plate with a velocity of 18 m/s. in this velocity is neoprine rubber withstand?.further it is not a flat area hub and shaft make it as a stepped zone. will the gluing of neoprene with backplate strong enough?

Devcon advises a primer before the application on the epoxy. The website gave more detailed information. They quoted a specific adhesion strength.

sorry sir,

baffle cannot be arranged since it reduces the inlet area and consequently volume reduces.further our design not permit to fixing any baffle on back plate and cone.additional dust collection equipment before fan inlet also not possible due to inreased pressure requirement(there is no cushion on fan pressure and also the fan is direct drive hence i cant increase speed to boost the pressure). we people supply the fan to our costomor.hence periodic maintanance not in our hand .if we suggested about periodic cleaning ones in 15 days which also not accepted by client. what they replied that,all data were given before placed the order.further there is no standby fan due to high investment cost hence shutdown of fan for cleaning not possible.now the equipment is under guarantee period .hence i need a permanant solution that ensure the stoppage of problem.

Well then prepare for legal issues, as the particulateloading will canibalize the fan in short order.

Permanant solution is removal of particulate in inbound airstream.

I have given you benefit of my actual experience, which agrees with your facts.

QUestion to have in mind before talking to customer: "whose engineering responsibility was it to anticipate the consequences of the normal particulate air quality in this application?"

milo