Dear Shri S K Bose,

You have asked for allowable inclination for belt conveyor which is conveying coal of 100% (-) 50 mm, of which 70% is (-) 25mm. The standard information on the permissible inclination is as below:

- As per IS 8730:1997, material serial number 120 is close to size you have mentioned, where allowable inclination is 18 degree. This is bituminous mined coal, unclassified. If you refer to this IS you will find the permissible inclination greatly varies for anthracite and bituminous coal and also with respect to sizes.

- If you refer Dunlop, they have listed six variants of coal (anthracite and bituminous), where permissible inclination is ranging from 16 degree to 24 degree.

Please note that the coal permissible inclination precise value will depend upon the surface texture of coal granules and their shape. So, exact value for particular case can only be decided by the buyer, miners or the people who are concerned with this coal.

One thing is that you do not have big size lumps, so if the conveyor is kept reasonably loaded then possibly, you may not have problem. However, what inclination are you using at loading point? Keep the belt tight, i.e. sag value should be somewhere around 1% as per DIN or ISO so that material receives the least disturbance / agitation during conveying. The least disturbance / agitation improves the allowable inclination.

Generally, inclination should be kept below 10 degree at loading point. The material velocity at loading point shall be kept close to the belt velocity in such situation.

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 ■

What is reasonably loaded?

Your belt width, and speed specifications are poor choices.

1. As specified you have a belt loaded to about 14% of its capacity

2. A high degree of rollback is likely with the material bed depth of 38 mm

3. Idler trough angle agitation will tend to initiate rollback with such a light x-sectional loading

You have not stated the reason for such a wide belt for the piddling stream of coal. Is it because of an extreme lift that requires an unusually high belt strength that will not trough?

You have not stated the trough ange. A higher trough angle is beltter on steep inclines for two reasons:

1) load containment is superior if there is rollback

2) higher wing roll projection of belt makes it stiffer ann therefore less idler agitation will occur all else beigh equal

As a rule ,you should strive for about a 50% X-sectional loading if possible to aboate rollback. THis rule yields a 700mm belt width running at 1.0 m/s.

As Mr. Mulani has said there are conditions where incline angle in coal have been successful at 24-26 degrees. Contol of rolllback requires a constant stream of coal. Breaks in the stream intiates rollback because of the higher included rollback angle between belt incline and stream trailing angle of surcharge. This trailing angle will become the equilibrium angle of repose.l The equilibrium angle is made up of three components:

1) belt incline angle

2) belt x-sectional surcharge angle as per convention

3) trailing stream surcharge angle

When these three combine to a resultant anlge that exceeds the stability angle of product rollback will ocurr.

These above conditions neglect the potential for loss of product to belt adhesion.

In a nutshell, you have not provided enough information about product or conveyor to offer a recommendation.

We now commence our December holiday and wish you good cheer. ■

Dear Mr. Bose,

There is always chance of rolling as the percentage of lump is also high. But in JINDAL STEEL, Raighar, I have seen all conveyor having 18 deg inclination. But they experience also rolling back of material.In RSP, I approved one coal conveyor with 21 deg. The result I do not know.I suggest that you must use rough top belt for such type of application which will reduce rolling back of materials.

Regards.

A.Banerjee ■

Hello Mr Bose..

To answer your question:

No.. do not do it like that

Regards

LSL Tekpro ■

Dear Mr. Graham,

In INDIA, due to constrain in layout we have to go in for 18 deg conveyor inclination.Simply you cannot say "no, do not do it".Please suggest how to reduce the roll back.

Regards.

A.Banerjee ■

Dear Mr Banerjee..

I did not know that INDIA was so small that you cannot get your conveyors in properly.

I still maintain that one must stick to the rules and never go at 19 degrees on a 1000mm wide conventional conveyor with only 60t/h of material on it.

If you cannot get it in then obviously put in an aero conveyor.

Regards

LSL Tekpro ■

Dear Mr. Graham,

Tata Steel wants to set up Ferrochrome plant at Richard Bay, South Africa.WE ARE THE CONSULTANT FOR THAT PROJECT. Due to space constrain, we are using Steep angle conveyor. Land is very costly there. You are well aware of that.So plant area cannot be compared with country.

Best Regards.

A.Banerjee ■

Dear Mr. Bose and Mr. A. Banerjee:

If roll-back and spillage are concerns due to the requirement for steep angle conveying, the problem can be easily resolved by using an Imperial Multi-Fold Belt System or a Belt-On-Belt System (Hewitt-Robbins Loop Belt System, Continental HAC System, or Dos Santos International Snake Belt System).

These system contain and compress the material so that high angle conveying is possible. The Multi-Fold System permits very steep angles with one belt that folds on itself (two hinge points). The Belt-On-Belt Systems permit vertical conveying, which is useful in tunneling projects and self-unloading ships. Both system types allow for easy belt cleaning as the belts are flat at the discharge and tail pulleys.

Regards, ■

S.K.Bose,

At the Great Lakes Plant of US Steel, formerly National Steel we installed a Continental HAC conveyor (sandwich belt) for exactly the same reason - limited space. This conveyor will lift vertically, but we run it slightly inclined, perhaps 80 degrees.

It is regularly used for Taconite pellets (round), limestone and steelmaking slag. We feed about 2000 tons per day of taconite up the belt, in batches, not continuously. It works quite well considering the typical level of maintenance in a steel mill.

A belt like this would eliminate your concern about roll back.

H. Crosmun ■

Dear Mr Crosmun.. and Mr Bose..

Do you not maybe think that the added complication of a sandwich HAC belt system to get to 19 degrees is rather like using a sledge hammer to crack a nut?

As I mentioned previously, the obvious solution to me is the Aero Conveyor.

It is enclosed and therefore has no spillage at all, has no carry idlers, the belt rides on a smooth cushion of air, it can go up inclines at least 5 degrees steeper than conventional conveyors. It is roughly the same price as a conventional conveyor too.

Due to the semi-circular trough under the belt, the material gathers at the lowest point at the belt's centre-line, which greatly assists prevention of roll-back of lumps as well.

I have used Aero Conveyors on coal with very great success.

To get the material started I loaded at less angle and put in a concave curve to a steep angle.

Many told me this could not be done on an Aero Conveyor, and they must be straight.

To me there is no such thing as cannot be done as long as I have checked it out, so I went ahead and did it, with excellent results.

Regards

LSL Tekpro ■

More food for thought:

PWH ala PHB now a part of Krupp, and Steven-Adamson now Metso developed the high angle incline, up to 26 degrees and in some cases more, many years before. THis was accomplished by placing a blanket belt, light or lead weighted (SA) which is similar to Joe's HAC snake or not.

These were installed in USA ports and in the coal pits in Germany.

A old piece of fabric belt is laid atop the material, if not too lumpy. The top or blanket belt is recirculated over the top like the HAC. No hold down idlers were used. You do need retrn idlers with head and tail (w/ fixed TUP) pulleys. No drive is required. ■

Lost my thought. These were developed many years before Joseph A. Dos Santos HAC concept was introduced. ■

THIS IS REALLY A VERY INFORMATIVE DISCUSSION,I WILL ALSO APPRECIATE THE EXPOSURE OF MR. BANERJEE IN THIS FIELD.

IN INDIA SOME CONSULTANT DESIGN/SUGGEST THE LAYOUTS AND LEAVE EVERY THING TO POOR SUPPLIERS.

ANIL ■

Dear Mr. Anil,

Mr.Bose has written that there is space restriction & that is why he wants to use 18 Deg. conveyor inclination. He is well aware of the application of steep angle conveyor & others type also.

So we should give solution to him considering the same only.

As regards the suppliers.Mr. Anil, please note the following:

JINDAL STEEL,Raighar approached to us to get remidial measure from spillage due to 18 Deg. inclination (Design done by others not by us.).We suggested the following:

-Use back skirt as it was not there.

-use rough top belt

-increase little higher speed

With this they get good result.

So consultant like us is always with poor supplier.

Regards.

A.Banerjee ■

I have come in late on this discussion and there are many suggestions but the reality is the tonnage is not high and the angle while likely to cause roll back, not excessively steep. In such instances the simplest and cheapest solution is to use a conveyor belt with cleats molded to the top cover. Manufacturers such as Andrew Yule in India are aware of this constrauction and can supply it. Rather than a sandwich or other construction of HAC belt, my alternate would be a pipe or tube conveyor. ■

I must agree with Graham.

From both a cost and risk point of view, the Areo Conveyor is best suited to resolve this difficult configuration. Attempts should still be made to increase the belt fill for better adhesion.

Since the conveyor will have empty sections after a stop, you should also consider the accelleration curve for starting especially if it is not a continuous operation unit.

Engicon Systems (Pty) Ltd

Tel +27-11-789-2102

Fax +27-11-789-9664 ■

Dear Mr.Bose,

All belt manufacterer like Phoenix Yule,MRF, Northland can supply rough top belt. It is ordinary belt having small cleats( very low height) through out the length of belt in a zig-zag pattern.This is very usefull for such installation.

Regards.

A.Banerjee ■

Take care that the material conveyed has no soil or clay like caking tendency. If you do the cohesive material will stick inbetween cleats and continue to build up and plate the return belt zone and idlers with unwanted product. You will also realize that belt cleaners do not work on this style of belt.

If you product is not clay like, and is made of dry or wet granular material of sizes larger than 0.5 mm, then it may be for you.

If you have a product size distribution of this later category, and mainly non-round, angular, < 50mm in size, with a good interlocking granular structure, then you can incline it beyond your needs without cleats. ■

This message has been changed due to non contribution to the forum ■

Dear Mr.Nordall,

Mr Bose has specified that he wants to handle coal of -25mm 70% & +25-50mm of 30%.The material is not clay ,rather dry.The capacity is 60 t/hr.So for cleaning we can use rotary brush or we can provide belt beater arrangement like what we give for steep angle conveyor.

I request you to write in line with the specific requirement only.

Regards.

A.Banerjee ■

A 19 degree incline at a conventional conveyor is irresponsibly risky. No one knows the safety factor against slide back even in sysems of more modest incline. It is a gamble and slide back can occur anytime when conditions are adverse.

A well engineered sandwich-belt conveyor not only acheives the incline safely but the safety factor against slide back is set and well known. The writer is inventor of the HAC and the DSI Snake. We market the DSI Snake because it derives its material hugging pressure naturally by radial pressure due to tension. The tension exists and alternating curves are engineered to exploit the tension inducing the desired pressure to develop the material's internal friction. The DSI Snake uses all conventional conveyor equipment including smooth surfaced belts that can be continuously scraped. There are no external pressing rolls.

Check it out on our web page and let me know if we can help you.

Joe Dos Santos ■