Dear Mr. Henk,

Regarding the troughing angle for belt conveyors, there are certain misconceptions such as deeper the troughing, superior is the idler and conveyor. The troughing angle and whether to use three equal roll or smaller roller at centre, depends upon the application which can broadly be classified as below :

- In plant conveyors for the length up to say 500 m

- Long distance conveyors where length happens to be in km

- Large belt width mine conveyors, such as shiftable conveyors or large belt width long distance conveyors.

Many times, in-plant conveyors happens to be up to 1600 mm belt width. These conveyors have small length ranging from 25 m to say 500 m and there are numerous junction houses. In such houses, transition distance is sometime constrained. The present day widely used troughing angle for such in-plant conveyors, equipped with synthetic fabric belt or steel cord belt are as below :

- In general, 30 degree trough for belt width up to 1000 mm.

- In general, 35 degree trough for belt width ranging from 1000 mm to 1600 mm.

The widespread use of aforesaid troughing angle is based on the experience in the industry such as transition distance which are manageable in such plants, the belt crease fluctuation frequency at idler kinks do not adversely affect the belt life, troughability of the belt, etc. The belt is troughed on carrying run but it could be flat or can have shallow trough on return run. The shorter length of conveyor increases the frequency of the crease creation and elimination in each cycle.

The deeper trough idlers will give better result for longer conveyors or when the belt widths are very wide.

The usual practice is to have three equal rollers for carrying run. This reduces the inventory. The widespread use of these idlers for average conveyors signifies that industries have found such idlers to be better in overall consideration. The use of smaller length central roller, has only one purpose that the load acting on all the three rollers is nearly equal. This type of idlers are used for very wide belts. For example, heavy class shiftable conveying system in India at Neyveli are equipped with such idlers. The idler lengths are decided by analysing the cross section so that load acting on rollers is nearly equal. Such idlers demand longer transition distance.

Above is the general answer and specific selection depends upon the application and other constrains etc. For example, grain conveyors often have deeper troughing because the grain conveyor belt has lighter carcass and thereby it is troughable even up to 45 degree troughing, without detrimental affect to the life. The troughability of the belt for a particular application is to be checked while designing.

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.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

CDI has developed a series of analysis procedures for selecting the belt construction that passes our criteria for desired idler spacing up to 6 m on carry and 12 m on return, with trough angles of 45 degrees and beyond, for belt width beyond 2000mm, belt speed beyond 8m/s, idler diameters to 194mm, idler offsets, horizontal and vertical curvatures, et al.

These features and other parameters are a part of optimizing long overland designs. ■

My stab at this matter:

Belt travel resistance is made up of the following:

1.) Bearing rolling resistance

2.) Bearing seal resistance

3.) Belt on roll imprint resistance

4.) Belt flex and shear resistance

5.) Material flex and shear resistance

1 is very small and directly related to the magnitude of the load.

2 and 3 benefit from a large roll diameter. The larger the diameter the better.

4 and 5 will suffer from increased troughing angle as the material load spreads the belt between idlers and is again squeezed at the idlers.

With this in mind the idler design is a compromize dictated by economics.

Joseph A. Dos Santos ■

Morning Henk..

Lets keep it simple..

The more rolls you have per idler, the less shaft deflection you have, and the more bearings you have.

Therefore, the more rolls you have per idler, the greater the idler spacing you can get.

So you have to determine for your application, which is the more economical.

For example, you can have:

three equal roll with series 25 shafts close spaced or...

three unequal roll with series 25 shafts medium spaced or ...

three equal roll with series 30 shafts long spaced or....

five roll with series 25 shafts long spaced.

Calculate each application on its specific criteria, especially for the surcharge angle and % loading, and if its a long one, on the power consumption too.

Generally use 35 degree 3 roll or 45 degree 5 roll

As the belt width increases, you will find that using the above considerations will dictate when you have to use the 5 roll configuration.

Regards

LSL Tekpro ■

Morning Neil

For the record, I have just finished the basic design of the new coal feed system up to the Eskom overland (to the power station which was approved on Monday) at 4000t/h, which is actually twice the 2000t/h you have in mind.

Be that as it may be very very very very very careful when using deep trough idlers on horizontal curves, especialy ones with tight radii..

The flatter the better where you tend to get belt lift off the wing rolls on the outside of the curve due to the resultant belt tension being towards the centre of the curve.

Virtually all my horizontal curves, as well as the roller coaster "Pretzel" on my dual carry conveyor, use 35 degree configurations and track extremely well for all conditions.

Super-elevation of the frames effectively gives about 40 degrees inside and 30 degrees outside the curves.

Cheers

LSL Tekpro ■