Low speed chain drives are an expensive option but please read on:

The kiln builder wanted to keep repairs simple hence the V belt drive.

What is the actual size of the coal feeding the kiln?

what type of coal?

lignite? subbituminous? bituminous? anthracite? Is the coal plus thirty mesh pulverised with a hammermill?

Are you using a multiple pulley size power system to increase coal delivey rate through the gear box or an automatic transmission?

An auger will convey material as fast as the material will allow it to do so and it is obvious that one of two things is possibly happening.

First:

What is the speed of the electric motor delivering motive power to the gearbox?

Is it possible you have lost a phase if it is three phase powered?

What is the final drive speed of the auger feeding the kiln?

Is combustion air being fed through the auger tube?

Are you inspecting the belt drive of the auger to maintain proper belt tension?

Are trip settings on the electrical service to the electric motor/gearbox/auger too low?

Are the belts the proper size belts for the v belt pullies?

Do you have a v belt tensioning gauge? if not purchase one from the local snap on tool dealer in your area or a good tool supply house.

Is your belt drive set up with a spring belt tensioner forcing tension on the belt?

Do you know how to properly tension a v-belt drive with a single sheave or multiple sheaves?

If your auger has a multiple belt sheave do you make sure that the replacement belts are all the same batch number/lot number when replacing them?

Is the v belt pulley or belt sheave in the case of a multiple belt set up very worn ? check this by taking a new belt and putting it in the groove or grooves and inspect the pulley to see if the belt carcass is below the top edge of the pulley as this will effect the gripping power of the pulley and the belts and remember that the belt is only gripping one half of the pulley at any time so if the V belt is riding below the top of the pulley groove you have worn V belt pullies.

If the belt adjuster has a threaded rod or pair of threaded rods for adjustment are they equal in length when the tension is applied and are there two nuts, one for adjusting and the second for locking the threaded rod in place?, and are the tie down bolts tightened and secured with nylon lock nuts? -these bolts are the ones that are vertical in the mounting frame that hold the tray holding the electric motor in place.

Second:

Belt drives no matter the number of v belts on the sheave pulley or pulleys can only stretch so much and if stretched to far will bind on all the driving components increasing amperage and straining the drive components by increasing pressure on one side of the pulley and bearings.

The manufacturer of the kiln has set up the coal feed delivery system to deliver the coal at a set rate to the kiln and it should not be overloaded.

Third:

Consult the kiln builder and ask if it would be prudent to change the gearbox as it may be on the verge of catastrophic

failure, while you are talking to them ask about installing an auger with narrower pitch flighting/ribbon to allow for smoother delivery of the coal to the rotary kiln at the low power setting of the gear box drive. ■

Can you use a transmission chain drive at 60 rev/min driver speed - YES

This may help you.

http://www.renold.com/Renold/web/sit...nSelector.asp

Would I use a belt drive at 60 rev/min driver speed - NO.

In my view belt drives are for high speed (between motor and gearbox), chain drives are for low speed (between gearbox and driven machine) ■

The problem is we do not know the drive configuration as an electric motor could(and probably is) driving the auger through a smaller pulley at the electric motor to an oversize pulley reducing/ reduction pulleys so the the point is mute.

This is done on commercial clothes driers allowing full RPM at the electric motor and reducing drum speed to a very low number revolutions per minute via the oversized pulley on the drum shaft.

This is also done with grain augers and hay bale elevators using the same type of drive utilising a gas engine directing rotary power through a gear box on the gas engine to a driven pulley or electric motor using a small diameter pulley driving a larger diameter pulley to reduce the revolutions per minute at the auger or elevator to a humanly managable speed. ■

There is a distinct lack of detail in the problem.

But considering what we do know -

The machine is described as a screw conveyor - so it's not likely to be rotating at high speed

The material is coal - so if it's fine or lumpy again, it's not likely to be rotating at high speed

It feeds to a cement kiln - so it's a heavy duty industrial application (24Hr/day?) unsuited to the lightweight high speed grain augers used on farms

It would be unusual (but not impossible) to have a single reduction belt drive from the motor to the shaft of the screw conveyor. However the angle of wrap on the driving pulley would be very small.

Maybe we'll get more information and so have to make less assumptions. ■

A lot of the old home size coal stokers have belt drives for the fans which are in the tubes and chain drives for the augers.

Using the commercial clothes dryer as an example they run for hundreds of hours with out belt changes using the B size belt

Hopefully he will be able tell us more. ■

The drive arrangement to a screw is a staightforward mechanical design feature. Direct Vee belt drives to the screw shaft is usually only undertaken by relatively high speed grain augers and the like, with a 1500 or 1000 rpm motor and a maximum of 4:1 pulley reduction. The use of an inverter to vary the speed invariably reduces the operating speed and usually the power available, so is not a good option for a heavy duty industrial application. Belts can be used to drive from the motor to a reduction box instead of a chain, and this provides an easy maintenance and speed change facility. In such cases it is good practice to initial fit a 2:1 Vee belt drive to allow an option for a speed increase or reduction ratio.

For the application concerned, it may be interesting to understand why the starting torque is excessive on start-up after a 'breakdown', when presumably it will start OK on normal start-up. Perhaps the loaded condition settles to a denser condition or there is a 'caked' residue layer causing high 'tip drag'. Crews will run well at speeds in excess of 60 rpm to deliver 7.5 Te/hr but wear will be increased. I would ask an experienced screw designer to examine the specification and design features. A little investment in consultancy is much better than taking advice without understanding the background, and should lead to a more reliable operation - perhaps even eliminating the 'breakdowns' if due to screw overloading. ■

Sound advice.. ■