Dear Shri A K Bhatnagar,

It is difficult to describe here all the points for reducing maximum belt tension. In general these can be as follows:

1) Use rubber lagged drive pulleys with herringbone grooves.

2) Include measures to reduce conveying friction coefficient (of frictional forces) of conveyor.

3) Softer starting process, as can be permitted / economical

4) Softer braking process as can be permitted / economical

5) Multiple drives spread among resistances.

6) More pitch of idlers, up to certain level (i.e. to reduce total rotating mass).

7) Reduction in belt weight as could be possible.

8) Higher the belt speed lesser will be the belt tension. To be used appropriately.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Dear Mr. Bhatnagar:

A good question, but how, where, when and with whom are you going to apply this knowledge? Many of the answers posted here are rubber rheology related. The answers to most of these questions form a part of our and some belt manufacturers' intellectual properties.

Will we be seeing this in your, to be published, specifications?

Counting the ways to reduce belt tension in a long distance overland belt conveyor, of steel cord manufacture, may, as you suggest, not produce the most economic Net Present Value.

Here are a number of key factors:

A. BELT DESIGN & CONSTRUCTION

1. Belt Covers - a) ideal thickness for longest life yet thinnest covers by minimizing belt mass based on best belt tranfer chute design, and b) minimized pulley cover for steel cord diameter selection. c) best rolling resistance properties for the temperature range and temperature frequency optimizied for the installation location such as your warmer climate.

2. Belt Splice Design - minimize belt strength or service factor and therefore mass by providing best splice dynamic fatigue strength which is controlled by splice design and core gum performance under fatgue conditions.

3. Belt Straight Running Construction - control of manufacturing errors and steel cord alignment that induce added lateral drag from snake action.

4. Belt Straight Running Installation - minimize idler installation errors by placing roll set normal to belt axis and close to theoretical vertical plane while maximizing or optimizing horizontal and vertical radii within economic practical limits to minimze pressure on idler rolls.

5. Belt Speed Optimization - selecting highest belt speed to minimize belt mass and width while not increasing rolling resistance.

6. Belt Flexure and Trampling Loss Optimization - selecting the best combination of takeup tension, idler spacing, belt speed and material crossectional loading that, in total, minimizes belt tension due to bet sag and material aggitation.

B. IDLER DESIGN

7. Optimize Idler Spacing - to reduce idler drag while optimizing this with effect of larger spacing that will increase rolling resistance and propensity to induce belt flap which should be minimized as per point

8. Optimum Trough Angle - in association idler spacing and belt speed the ideal trough angle is minimized to spred the idler presssure that minimzes belt power but maximizes width and speed, and to be integrated witb points 5, 6 and 8.

9. Idler Diameter & Tolerance - largest ecomonic practical design diameter which minimizes local indention pressure, and controls manufacturers TIR tolerance to the best practice that minimizies belt flap vibration without compromising economics.

10. Idler Drag Optimization - belt seal and lubricant that minimizes drag but not life and in conjunction with point 8.

11. Idler Installation Tolerances - idler pressure and belt tension are increased by poor installation of idler sets where the rolls are not set to the theorectical belt line such as aerodynamic vernacular of yaw, roll, and pitch (as oposed to spacing pitch).

WIND & SUN PROTECTION

12. Sun Protection by Hood Covers- wind protection if high lateral winds increase idler side pressure and thereby belt viscoelastic drag, and controlling rubber compound to optimize fillers that otherwise reduce rolling efficiency or drag due to the rubber compound.

DRIVE and TAKE-UP TYPE & PLACEMENT

13. Optimizing Drive Placement - that minimizes overall belt tension such as: dual head drive with power ratio of 2:1 vs single drive or 1:1 ratio ; head and tail drives with idealized power ratio, but may otherwise be impractical associated with standard drive components, safety and maintenance issues.

14. Takeup Type, Size & Placement - gravity takeup will almost always yield a minimum belt tension (may not be practical for other reasons), optimized mass that minimizes belt tension (too low and you get higher belt trampling losses and belt flexural losses as noted in point 6), placement to control starting and stopping dynamics and associated takeup reuqirements.

I am sure there is more. Others will submit. I must go to work.

Please see our website below and publications for an introduction to the above points.

Looking forward to the publication of these factors in your latest technical novel.

Lawrence Nordell

Conveyor Dynamcis, Inc.

1111 West Holly Street

Bellingham, Washington 98225

USA

ph: 360-671-2200

fx: 360-671-8450

email: nordell@conveyor-dynamics.com

website: www.conveoyr-dynamics.com ■

Second Wind:

As Mr Mulani pointed out some of the other attributes that need attention. I elborate on the 6.7:1 Belt Safety Factor composed of three considerations that can yield further reduction in belt mass construction and consequent tension reduction:

1. General Dynamic Splice Fatigue: based on superior core gum rubber and steel cord fatigue strength technology the strength can be enhanced by more than 20% (of the 64% allowance of the dynamic splice strength) or will allow a reduction in the needed steel cord breaking strength by more than 9%( per DIN 22101 splice dynamic strength from 64% to 55%).

2. Elongation & Degradation Strength: proper splice field construction, belt alignmentand stress increase at pulley with belt transition design, pulley selection and bending stress in the steel cords, age and rubber age inhibitors, vertical and horizontal curve stresses on cords, can collectively lead to another 7% reduction in strength (per DIN 22101 degradation allowance from 1.0 to 0.5.

3. Dynamics of Starting & Stopping: proper regulation of starting and stopping dynamics can further reduce the belt strength by 3% depending on the basis (per DIN 22101 dynamic allowance from 0.4 to 0.2 on the 6.7:1 basis).

These points yield a possible total reduction of 19% with a 6.7:1 basis. The net Belt Safety Factor is reduced to 5.4:1. The steel cord strength, cord diameter weight, savings in core gum, and reduction in overall weigh is significant.

Lawrence Nordell

Conveyor Dynamic, Inc. ■