This may help

http://www.c-kit.com/secure/conveyor...i1-paper03.htm ■

So far, only through Discrete Element Analysis. It provides the 3-D path of all particles as they leave the belt and strike the chute or stockpile. As you may know the trajectory is highly dependent on:

1. belt speed

2. idler trough angle

3. transition path geometry, slope and length

4. elevated head or discharge pulley

5. belt tension if discharge pulley is elevated above or below belt path

6. discharge pulley diameter

7. moisture content of product -cohesive and adhesive properties

8. product size distribution

9. belt width

This probably does not list all. ■

10. tonnage

11. material bulk density ■

Hi Chirag...

Also note that for very slow speeds, (like with belt feeders) the trajectory is not so much dictated by the belt speed, but by the speed the material gains while sliding off the end of the pulley.

On larger discharge pulleys, this effect is quite significant, and the material can land a long way from where you think it should.

Regards

LSL Tekpro ■

I don't think any of the published methods adequately cover the full range of possibilities.

Choose your method, look at the result and see if it looks realistic. To help, get out and look at some real machines and see how the material discharges. ■

Dear Lyle,

As Graham has said, at low speed the sluffing over the pulley is not considered by all static analysis methods.

Only DEM can analyze material acceleration as it flows downward and forward before it reaches the discharge pulley centerline. This is highly dependent on the approach angle to the discharge point. DEM takes all this into account including the fanning out in the tranverse direction.

We published this effect at BELTCONV 12, in South Africa and India Bombay BSH conference about 2 years ago.

Attachments

traject beltcon12 (PDF)

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A second note not referenced is the height and shape of the discharge crossection as it flows forward, sideways and down or upward as it leaves the pulley. ■

Yes, on a weekly basis. We design chutes for many clients with many products from powder to 1000mm bolders, coal to copper, not only in chutes, mills, crusher, bins, bunkers, rock ladders, movement of material in high speed belts and in horizontal curves. If its a rock or 100,000 going places, we can simulate it.

Flow stream dynamics, wear on belts and liners, degradation of products, dust generation, will the flow center or cause the belt to shift off center. Maybe some posting will be of interest. I said before I would post so tomorrow I will try and make a thread. ■

DEM would appear to be to be the "high tech" way to go.

My only concern would be that -

"As you may know the trajectory is highly dependent on:

7. moisture content of product -cohesive and adhesive properties

8. product size distribution"

and these factors can vary considerably in the same application which thus leads to variability in the output of any modelling process. So you use various factors, get various results that you end up combining into an overall max and min discharge trajectory.

There is also the matter of cost.

How much to model the discharge per head pulley?

How much to buy the modelling software ■

Dear Shri Chirag,

The trajectory subject is a complex issue, as a comprehensive solution. Because when the material is falling it is subjected to wind resistance in its direction of motion, which changes as the material moves forward. An article by Z. Korzen Poland, provides mathematical solution for the path of the trajectory, but it involves many inputs. Again, if you are deciding the material trajectory in open yard, then it will be subjected to horizontal winds. In such situation, the material path would be accordingly.

If you decide the trajectory for usual material in a chute then use the conventional methods. If you have got a very specialised problem of material trajectory, then consult the people with its know-how.

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 25871916 ■

"As you may know the trajectory is highly dependent on:

7. moisture content of product -cohesive and adhesive properties

8. product size distribution"

and these factors can vary considerably in the same application which thus leads to variability in the output of any modelling process. So you use various factors, get various results that you end up combining into an overall max and min discharge trajectory.

Automating Trajectories is a bit like predicting where your cat goes on an evening. The 2 photos attached show predominately wet pebbles(5-10mm) and predominately wet grits (3mm). It's the same chute taken 15mins apart and with the same belt speed. OK its a very low tonnage but it describes the effect of particle size on wet Kimberlite. Different materials will show a different trend and if dry would show a totally different configuration.

Attachments

wet grits (JPG)

wet pebbles (JPG)

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Dave,

Yes, the problem is evident and dependent on the attachment of particles to belt and to each other.

Cohesion and Adhesion properties can be included in the DEM analysis. The only restriction is the size of the model. A million particles, no problem, 10 million maybe a little time and cost constraint, 100 million tomorrow. ■

Of course if you get carried away with your belt speed you end up with a trajectory like this ..... (OK, it's grain).

Attachments

trajectory (JPG)

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There are a few points that i should add to my last post.

• The material is not hydroscopic
• Belt speed is quite low approx 1.5m/s
• The water includes a flocculent

I also should have included the attached photo of the mixed wet material being discharged at high speed. Approx 6m/s. I could not get a side on shot since this was discharging over the edge of a dump.

A point of interest away from the topic is that when the mine increased the belt speed they also cured belt high speed narrow belt tracking problem in an unusual way.

Take a close look at the head pulley.... The belt is NOT running off... the pulley is approx 150mm narrower than the belt making it the weirdest crown in history. The conveyor is of course a tail drive.

Attachments

wet trajectory (JPG)

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