Earlier respondents have already given useful suggestions / hints.

The general practice is to first try to design the belt conveyor by considering synthetic fabric belt. In the event, if take-up stroke is unmanageable or one does not find synthetic fabric belt of suitable tensile strength, then opt for steel cord belt.

Finally, it is the price comparison and economy, which matters, when both the types of belts are suitable.

The synthetic belt and steel cord belts have their specific characteristics and advantages / disadvantages. These should be studies for technical suitability of the belt.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Dear Mr. Rajesh Mendiratta,

Although all of the above respondants have given useful information, I would like to add that you should also consider the following fabric belt alternatives:

(1) Polyester/nylon reduced ply carcass;

(2) Single ply straight warp; and

(3) Two-ply straight warp.

Any of the above fabric carcass choices will provide less stretch than your nylon/nylon option. You can choose different strength ratings, depending on the ply strength and the number of plies.

Of course, if your application requires a high tensile belt, steel cord belts are a viable option.

Regards, ■

Some additional points:

1. Fabric belt single flight lengths have exceeded ................. 5 km

2. Fabric belts consume more power ... up to twice steel cord creating obvious limits in use for overland applications especially when including operating costs.

3. At higher tensile ratings and narrow widths, idler trough conformance can be a problem

4. Typical cross-over in fabric belt strength to steel cord is about ST-1000 N/mm. Also note, steel cord strength, used for overland applications have a safety factor ~ SF= 5-5.5:1. Fabric is usually 8-10:1. Thus, breaking strength alone is not the only measure.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

Conventional theories regarding the "crossover zone" from textile reinforced belts to steel cord belts seem to be undergoing a fairly rapid redefinition. Let us try and see why -

The oft cited application advantages of a steel cord belt (over textile belts) include -

1. Higher tensile range

2. Lower stretch

3. Greater impact absorption due to higher rubber content

4. Greater longitudinal flexibility

5. Higher transverse flexibility

6. Higher splice reliability

What do these mean to the user ? To my mind the corresponding potentials lie in -

1. Combining series conveyors to a single flight eliminating transfer points. But this angle is traditional and does not address the current query

2. With elongation between 1/8th to 1/16th of equivalent textile belts, the steel cord belt is the only choice in installations where plant layout inhibit adequate take-up allowances

3. Some of the coal carrying conveyors in India - including conveyors in a few of the most technologically advanced thermal power plants have exploded the 'crossover' theory by adding years to their belt life in conveyors as short as 40 - 50 m (C to C) and with ratings as low as ST 400.

Their problem was impact damage and steel cord belts solved this. Mind you, some of these belts were not with the conventional cord configuration as prescribed in DIN / AS et al.

4. Enhanced dynamic flex fatigue resistance has encouraged users to convert existing textile belts to equivalent steel cord belts in relatively short installations : 200 - 400 m long.

The textile carcass is susceptible to fail before an equivalent steel cord carcass does - all other factors remaining unaltered. This is understood to be because the textile belt has a multi-ply carcass, the consolidation of which 'decays' with every flex around the system pulleys. A steel cord 'carcass', on the other hand, is not similarly affected (as long as adequate transition distance and curve radii are taken care of), and therefore lasts longer than a equivalent textile carcass.

Forward thinking users therefore, opt for a steel cord belt with greater cover thickness to realise a longer dynamic life out of their investment on this product. If the carcass lasts, it is really the cover thickness (within limits !) that govern the useful life of a belt.

5. With a superior transverse flexibility, steel cord belts provide the option of a deep troughing application : 40 to 45 degree troughing in a steel cord belt is not uncommon while not too many textile belt installations venture beyond a 35 degree troughing. The reason is that, with a distinct weft, a textile belt - on a deep troughing system - would tend to create pressure on the wing idlers adding to idle power consumption and - at times - even faster back cover wear.

With a higher troughing angle, the user now has the option of actually opting for a narrower belt width without having to increase the belt speed and yet, maintain the same throughput as with a wider belt on a flatter troughing angle. The lump size, of course, remains a probable constraint in certain cases.

Option to use a narrower belt width can - for new installations - be translated to a narrower conveyor system ! Imagine the cost savings ....

6. The cost of an unplanned shutdown - due to a sudden splice failure - is the conveyor maintenance manager's nightmare. The distinct advantage of a steel cord belt in this respect alone, is often a compelling arguement in its favour - conveyor length, strength notwithstanding.

Yes, the price remains a deterrent ; but only if viewed in isolation. Look at the return on investment - say in cost per MT conveyed over XX years - and the choice, with few exceptions, is usually the same : STEEL.

Kayem ■