Dear Shri Kayem,

In case of ROM coal, you can think about using inclination up to 8 degrees at loading point. The plus minus decision is subjective to coal size, belt width, belt speed and specific application.

Regards,

Ishwar G Mulani.

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

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Dear Kayem,

We meet again.

There are conventional conveyor installations with transport angles of 26 degrees. This is not to say it is often practiced.

Transfer point granular dynamic stability and gained within the skirtboard region is essential. Most crusher broken ores form interlocking that you can obserb in the stockpile such as 37 degrees with the large lumps toward the outer surface. A number of criteria must be met:

1. friction between belt and ore does is not exceeded during starting and stopping.

2. some spillage will occur on large incline angles greater than 14 degrees: a) due to random shapes that approach cubics with rounded edges, and b) trailing load angle exceeds the stable surcharge angle - incline angle plus trailing load angle

3. degree of moisture may allow more or less inclination when transporting smaller particle groups

4. dynamic internal friction angle is not exceeded

5. dynamic agitation does not unstabilize ore such as low tension, sag and idler alignment

6. safety isssues with rock catapulting from belt due to anglular momentum increase from rolling and spinnning

7. ore stream is sufficient to maintain rock interlocking such as crossection not falling below 35% and there are no large boulders that cannot be interlocked -- can be helped by reducing center roll length.

8. rule of thumb - is a dangerous propsition when safety is considered. A novice can obuse the knowledge by assuming the simple answer is the only fact required Having said that a rule of thumb is to take the surcharge angle as the dynamic limit and then reduce it for the transverse surcharge in combination with the incline angle (some say the cube of the cos(surcharge), and reduce it for acceleration and deceleration reduction in the apparent surcharge, and reduction for cubicity on trailing angle of pile if lumps are ndangerous to life, limb and pursuit of log life.

The above must be less than the internal friction between ore and belt.

Its a start.

Lawrence Nordell

www.conveyor-dynamics.com ■

omission:

I did not dwell on the transfer point stability which is strongly dependent on the chute design. DEM is the only way to quantify the ore dynamics at the transfer. DEM can, as I am sure you have read many times on this forum, quantify the issues of:

1. rock shapes - rocks are not spheres, some processed minerals become spheres and many fruits and vegetables

2. rock size distribution for better incterlocking

3. internal ore apparent friction coefficient - wet or dry

4. friction between ore and belt - wet or dry

5. incline angle at transfer noting that many belts are loaded far beyond the 8 degree critieria Mr. Mulani sugests.

6. belt speed - what is the limit as a function of chute design, ore factors and incliniation angle ???

7. flow dynamic vectors at point of contact on belt from chute exit.

DEM is the formulae for success. Less than DEM is to be ignorant of the arab proverb -- "he who doesnt know and doesnt ask".

Lawrence Nordell

wwww.conveyor-dynamics.com ■

It seems as though my writing habits are getting worse such as the misspellings, (obserb, anglular,...) grammatical aberations and the like.

Dr. Wohlbier has not responded to my request to apply the spell checker or is it my lack of using the tools available?

Anybody out there??

LKN ■

Dear Mr. Kayem,

For the conveyor parameters you have indicated,ideally horizontal feeding would have been preferred.I suspect that you are constrained to load at an incline -may be because of layout limitation.

Our experience for similar installation is to feed at as low an angle as possible-but never exceeding 8 degree.

Regards,

diptasmallick ■

Dear Shri Kayem,

I appreciate Mr. Nordell’s detailed reply. Meanwhile, I add following information to my reply for benefit of general readers.

Firstly, it is better to be clear what we imply by ROM coal. The ROM coal as understood in India and possibly in UK, is un-sized black coal of (-)250 mm to (-)400 mm size.

Now, in case of applied engineering (contract implementation), there needs to be consensus between buyer and seller. The buyer (their designers) do not want to take risk and seller (their designers) do not want to get blamed. Therefore, the general consensus as prevailing in India amongst A class buyers and A class suppliers is to have inclination somewhere around 8 to 9 degree at loading point, for this case. Generally, people do not indulge in contractual complications (if it so arises).

However, I do not intend to say that, do not use inclination more than 8 degrees.

Foe example, the maximum conveying inclination for ROM coal, as mentioned by M/s Dunlop is 18 degrees (for conveying route and not loading point). However, in India, people restrict the conveyor inclination upto 13 deg / 14 deg for ROM coal, so that there would not be roll back whether conveyor is partially loaded or fully loaded and so on. A-class buyers insist that material should not roll back in any situation, as it may injure somebody and the designer may have to answer.

You have about 150 coal based medium and mega power stations and may be coal mining at 3 digit places in India. So, if you wish to opt for more inclination at loading point, get the feedback from various places.

I prefer to give information on somewhat safer side so that somebody does not land up in difficulty (because many times precise data is not mentioned, nor I have seen your coal or the site etc.).

I once again clarify that inclination more than 8 degrees may be possible, but the information given by me is for an acceptable situation in business circle.

Regards,

Ishwar G Mulani.

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

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Safety is the central issue with +/- 400 mm ROM coal lumps ( 60 kg projectiles). As David states, roll back may occur at a slope much over 10 degrees.

Belts can be safely loaded at 20 degree slopes with ROM lump provided you have the ability to set the chute design. The difficulty is maintaining stability when the ore trailing edge has cubic or rounded lumps that are not interlocked with smaller material.

Idler agitation can cause motion which leads to rotation, spin, momentum, and catapulting. This can be overcome with a cage or mess installled over the conveyor or a light cover belt is draped on top of the charge.

Here is the US, certain groups have set their own standards and prescribe 22 degrees as their limit in coal and quarryes. Longer skirt zones are used. However this is not ROM.

So it becomes a choice to satisfy: a) extreme caution, b) fit for purpose, c) most economic with special operating practices as is used for highly sloped conveyors in tunnels.

Gaining first hand observation and operator affidavits of working installations is surely the best way set your criteria.

Lawrence Nordell

www.conveyor-dynamics.com ■