Greetings from the "Frozen Eastern Wilderness",

We need more information as we or at least I do. My not knowing if you have fluid drive couplers, chain drive from a reduction gearbox, hydraulic drive etc.

I am willing to assume that your drive has a reduction gearbox powered by a 480 to 600 volt 3 phase motor/60 cycle feed with a rubber coupler between the reduction gear box and the electric motor.

Assuming that the conveyor has a chain drive and a matched gear set for the other side to deliver poewer equally.

With my having experience with only Hewitt Robins and Continental drives I will take an educated guess that you have one of several possibilities.

1. Stress fracture and breakage of gear teeth.

2. Worn out bearings exerting more pressure against the better gear set.

3. Or the usual worn out components due to misalignment of individual parts of the installation when they were repaired last

4. Component age /end of usefull life.

5. Any piece of conveyor operating machinery will break down from use or overload of the conveyor.

6 . Are you running your machinery past its usefull life cycle resulting in higher operating costs to try and increase its life cycle?

How long the units have been in service or when they were last repaired? What is the conveyed tonnage? Are you conveying wet or dry product? Aree you maintaing an adequate house keeping program in regards to cleaning and shoveling out and around conveyor drive units and tail pulleys? etc- the big thing is that all the componenets have to be aligned and daily maintenanace must be done or they will not last very long in service. please tell us more.

There is no easy answer unless we know all the details:

Signed,

Curious in the "Frozen Eastern Wilderness"

"Excesior" "Veritas"

The safety traingle:

ALERT

AWARE ALIVE

Remove any part of the triangle and an accident or injury/fatality will occur.

Arab proverbs/sayings

"Not knowing what you don't know"

"When the dog barks the caravan moves"

"Disappontment is my dail bread, I thrive on it"-taken from "The Great Influenza" ■

Dear Angus,

As stated, more information would accelerate meaningful dialog.

Two points in the failure analysis tree:

1. Assume the manufacturer did his proper job of rating the gear breaking and endurance strengths and designed for proper lube at the inital stage of starting for all gear assys.

a) wound rotor stepping selection can hammer the gear set with the input stage taking the greatest impact - each subesquent stage has more elasticity or compliance to cushion the shock.

b) the initial step and final steps usually have the greatest impact torque differential that can exceed inifinite life cylces to failure.

c) are the steps binary stack or conventional? How many steps? Are they fixed timing, velocity ramp or dV/dT selected. Who designed the resistor bank? How long have they been in operation and are they freaquently restarted? Are they cast iron, stainless steel or CrAlFe? The point here is: the increase in heat and then restarting under load, can cause further torque differential due to the resistance increase in some steps which causes change( initial torque reduction) in avcritical step.

d) the last step has to bridge the last resistor to the impedance of the rotor circuit which may be more than 2% - if so, this will cause a significant torque spike that can be felt but not seen.

e) given the competence of your team and your resources I would not like to second guess without dialog what you have already studied and things that have been eliminated.

f) have you FFT'd and/or torque monitored the drive during starting? We have such equipment to measure to 1% error as do some in Australia. Data acquisition should be capable to 10 ms sampling rate for torque and 2 ms for FFT. THis would verify the wound rotor step design is culpable or not.

g) Have you taken vibration measurements on the reduced with FFT analysis?

h) how are the motors started - sequentially or together?

i) how is the reducer supported and who's couplings?

These comments are not exhaustive - just a probe into your investigation.

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2 Reducer Design flaws:

j) I have witnessed, a reducer manufacturer, in Australia, produce a product that had suspected flaws - Not Rio Tinto. The size range is similar. We did field measurements on torque suspecting dynamic shock wave impulses. No damaging shock waves were measured by two independent teams with different equipment. Conclusion was the reducer.

k) your reducer specifications are usually quite exhaustive - what about you Q/A for this manufacturer?

l) did you have a Reed Frequency Analysis performed on the reducer spiral bevel stage at the design phase?

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3. Other points:

m is Carl investigating?

n) are there flyweels?

o) unacceptable resonance: when we did Kennecott (11 x 1500 hp in 1987) a consultant stated our low and high speed flexible coupling selections would cause a destructive motor to reducer resonance. We stated this was not so with evidence of like-and-kind. Although we were correct per 18 years of operation, their point was correct, just off a bit in the details. THis argument was again raised during the design of 20 km Channar overland on the Flender-couplings- flywheel arrangements.

p) rolling mills are designed to take shock loads due to ingot/slab impact in the bite of the mill ( simialr to resistor step impulses) where torque amplification can exceed 2-3X anticipated values - here high speed Dac can guide you.

The above is a week end warrior response. If you wish more investigative dialogue, you have my details below. I anticipate visiting in Oz within the month of July.

FYO: We were awarded the +20 km single flight Curragh overland with BMCL. There are some new developments in its design. Is RT still pursuing the 40 km Brazil overland? Carl asked if our report could be efficiently updated.

Give John Wood and Carl Wilson my regards.

I wish you well. ■

Dear Mr. Nordell,

I do not consider my self a weekend warrior, I have been away from the business for a while but I have not forgotten that much.

Our conveyor belts were upgraded to Square D PLC operation in the late 1990's And I spent a considerable amount of time in my working life maintaining, repairing and rebuilding conveyor components in the mine where I worked.

I honestly feel that your terming me a "weekend warrior" is a slight.

I may not know all there is to know about conveyor belts but I feel the 22 years of working as a maintenance mechanic involving underground and surface mining machinery means something-at least to myself. I have not been able to finish my college education due to economic considerations and I hope to finish it some day.

lzaharis ■

Dear lzaharis,

Please accept my apology for the ambiguity. I was refering to myself. I meant no disrespect to you. ■