PLease state the CEMA edition you are working with and I will advise the necessary page(s). All CEMA design manuals, from the first edition in 1966, have the needed formulae. ■

If you know the steady-state tension Tc, at some point along the belt loop, and Ta is the accelereation or deceleration tension leading up to the reference point Tc, then you solve for Ta:

a) mass of belt to Tc ,

b) idlers rotating mass referenced at belt line to Tc, and

c)material on belt leading to Tc then:

Ta = m x a; where m denotes the total mass of points a,b;c above from the gravity take-up and a is the rate of acceleration or deceleration (-a) in the proper units. ■

Good morning Emerson..

Interesting question this one, as the theory normally does not very accurately match what happens in practice for decelleration.

A typical example is a 1km flat overland conveyor we did where the client insisted on a brake being fitted (from his decelleration calculations).

I maintained that from extrapolated values of the friction factor that I had calculated from actual coasing tests during various times during my sheltered life, that a brake would not be required if I simply reduced the counterweight mass a little bit.

When we commissioned the conveyor, the brake was faulty and had to be removed and sent away for repair.

So I reduced the counterweight mass a little bit, and the conveyor was fine.

(The client however would not accept the conveyor without a working brake though, and as you know, the customer is always right....)

Regards

LSL Tekpro ■

Dear Mr. Emerson,

It is difficult to explain the exact procedure for calculation of various tensions during deceleration. However, simple rule is that backward forces minus forward forces = mass x deceleration. Here, forward and backward forces are with reference to the direction of belt velocity. The mass is the segment of belt being analysed with reference to the prevailing forces.

You have to know this calculation procedure by studying the appropriate literature of your choice.

The formula and method are based on unquestionable proven rules. If the input data into the formula are erroneous, the result will be erroneous and mismatching to the observed values. Therefore, it is equally important that the designer should use right values of inputs in the formula. In this context, the appropriate literature also helps the designer to derive the right values (from engineering requirement).

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 ■

Hi there again Emerson..

Actually, to answer your actual question, a very simple and nice method to calculate the tension distribution during decelleration of a conveyor is as given in Section 6 of the old Goodyear blue book "Handbook of conveyor and elevator belting"

Just remember though, you don't use the same low running friction factor for the coasting condition, as the increased belt sag increases this factor by anywhere around 50%.

Hence the wide discrepancies in calculated values and measured ones, and hence the reason why I was able to vary the loaded belt coasting time of a conveyor by adjusting the counterweight mass.

Good luck

LSL Tekpro ■

Khalid

You need practical values so you can calculate the coasting times.

Its not only just calculating the tensions.

LSL Tekpro ■