Dear Andres,

There is no relation of belt tension with take-up travel. I think it should be read as take -up weight. But from the replies of other I under stand you want a relation between belt elongation & tension.

Belt manufacturer restrict the elongation within 3% ( !% permanet & 2% elastic for NN belt). Based on belt rating they select the carcass thickness & it is their propitory thing cannnot disclose. So I cannot help you in this regards.

A.Banerjee ■

Dear all,

I feel the belt elongation depends on conveyor profile, belt carcass, site conditions, load on the conveyor, starting/stopping per hour, drive pulley lagging , type of drive etc.,

The conveyor belt having soft start or VVVF drives may not elongate much comapred to conventional DOL start conveyors. The Drive pulley having ceramic lagging may elongate more than that of the conveyor belts having rubber lagged drive pulleys.

Request your opinions.

Thanks & regards, ■

If you used BELTSTAT you would know take-up travel is dependent on:

1. Belt Tension and Elastic Modulus do contribute

2. Starting and stopping range of tensions for all governing conditions including friction change between summer and winter operations and with type of starting and stopping controls

3. Know belt sag contribution dependent on beltline geometry during stopping - could be many times tension travel and in opposite direction - only accurately predictable with dynamic analysis and how belt is tuned to minimize overall travel penalty.

4. Thermal travel (not predictable with many fabric belts)

5. Permanent elongation (differs with type of tensile member and weave construction)

6. Splice and repair belt lengths (more repair with fabric belts)

7. Clearances to steel on both ends of travel

8. No simple formulae - can use textbook guesses for short in-plant conveyors such as:

steel cord TUP travel = .0025 x pulley centers (could be way off depending on above details)

polyester fabric TUP travel = .020 x pulley centers ( could be way off if permanent elangation is removed before final splice is made permament. Then multiplier is closer to .012 x pulley centers. ■

Forgot to add another point:

9. Partial loading case when starting and stopping - may not apply same loading and weather extremes to worst variation of load distribution to define total travel allowance.

10. Types of brake action and variations in levels of braking for overland and downhill systems such as controlled versus uncontrolled brake action. ■

Dear Mr. Andre,

There are two aspects one is the take-up travel length and second is the actual travel of take-up pulley during the conveyor operation (steady state, starting and braking).

As for the take-up travel length, generally its value is specified in the standards you are following. I am not repeating the value of these here. These travel lengths, are based on the consideration that it will take care of the belt length variation that will occur during erection / vulcanizing (the final vulcanized joint will not create the exact belt length under applicable tension condition), and belt stretch during use and consequent frequency of re-vulcanising of the belt. One can take somewhat less take-up travel length, but it will need revulcanising of belt at shorter interval, to eliminate the belt stretch arising due to stretch (permanent elongation).

Regarding take-up travel, at any point of time (day), one has to work out the tension diagram area. Then find out the average tension in the entire belt which is equal to tension diagram area divided by belt length. The difference in the average tension say during starting minus during steady state will create the stretch in the belt during this situation. Use the modulus of elasticity equation to find out the belt length increase attributed to aforesaid changes in tension. The take-up pulley travel will be half of the aforesaid stretch of the belt during these two situations. This stretch of belt is called elastic elongation.

Belt modulus elasticity data will be available from belt manufacturer.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: parimul@pn2.vsnl.net.in ■