Shane:

I first assume you are asking about a gravity counterweight.

1. elastic stretch for all dyamic start and stop and steady-state cases, dynamics include "what if" scenarios

2. thermal stretch for the design range

3. belt sag allowance during dynamic states

4. belt maintenance allowance for splice and repair - we recommend two full splice repairs

5. end clearances for alarm and avoidance of impact against structures

Fixed takeup travel is a little more complex to give a short response.

There are other considerations when evaluating extensive TUP travel that may need to be controlled such as the use of capstans. Capstans are use to boost the belt tension beyond the counterweight force for dynamic sag control.

Maybe you can refine the question to get a better insight. I am sure the above is not exhaustive. ■

Dear Mr.Shane,

I presume that it is related to VGTU only. We fix the take-up pulley at distance of 3m + 2/3 of take up travel ( 3% of belt length as take up travel)from belt top of carrying side.This will take care of all.

Regards.

A.Banerjee ■

It seems you are asking about a powereed takeup. I didnt realize that engineers have wandered into using VVfD's. What happened to hydraulics?

The travel definition requires you provide the dead band details and means of control. We select the normal full load running plus about 10 % as a start point. However, this also depends if you wish the takup force to hold for a 24 hour cycle or less. The temperature extremes must be considered, if using a steel cord belt, or even fabric if you know its expansion properties with teimperature.

I think you need to give more detail to allow a concise recital that addresses your query. ■

Another note.

Eddy current winches are a bad idea. I am aware of their application in the coal operation in OZ. RSA have also applied them. They are an accident waiting to happen as has happened in the VIctoria coal fields.

Eddy current drives can lose torqwue control for various reasons. What happens when you can't hold the tension during a necessary tensioning cycle? I understand from discussions with the engineers, a number of years ago, many conveyors were damaged by this event. Most conveyors do not benefit from powered takeups. It is a myth that the belt rating or safety is improved by their application. Quite the opposite! If you want to know more we can talk. ■

An eddy current clutch requires DC flux to transmit torque. What happens when you lose flux? So the designers hooked up a battery backup and its controller and fault sensors. Suds Law still prevails.

The clutch is used to provide variable speed and torque fitted with some controller and logic such as load cell and idea of constant pull (couterweight) regardless of belt response or some derivative of this. They are relatively cheap. Consume lots of power and heat. They have low efficiency at lower speed..... ■

Their pilot bearing is the weak link. They have an inner and outer rotor. The inner rotor is supported by the outer with a center pilot bearing that cannot be inspected except by removal and examination. SOmetimes the pilot bearing fails and wa la many new parts. Its kind of like the fluid traction coupling and its central bearing failure introducing impeller to runner vanes. ■

Dear Mr Banerjee..

I take issue with your 3% of belt length for take up travel. Assuming you mean 3% of pulley centres, then for a 12kM long overland the take up length would be 360m!!

We have such a conveyor here that is 11.8km long, has a horizontal curve and has a take up travel of 25m and has been operating for many many years.

My old Goodyear blue book gives 1.5% +.65m for fabric and .25% + 1 splice for steelcord.

Regards

LSL Tekpro ■

Dear Mr. LSL Tekpro/Graham,

I am sorry that I did not mention the type of fabric. It is true for NN belting.Belt manufacturer nomally offer you 1% permanent elongation + 1.5 % Elastic. But in actual feild it is 3% in totality.In catalouge you will find 1.5 % only.But no-body is taking into consideration of the same.

So for 12Km, I will not suggest you to go in for NN belting. You have to go in for steel cord belting & travel will be of 0.25%to 0.5%.

Regards.

A.Banerjee ■