It is an extremely common problem and is caused by poor ore presentation at the transfer. You cannot fix no matter what anyone says with a re-designed skirt system, you must correct the ore flow in the transfer.

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

colin.benjamin@gcsm.com.au

www.conveyorsystemstechnology.com ■

Colin is partially correct. I highly depends on the pressure exerted by the flow stream that drives the rocks under the skrt edges. This can be mitigated in two ways:

1. Reduce the critical pressure through quantifyable pressure reduction techniques

2. Improve the skirt design with ways of minimizing the pressure concentration - as Designer says taper the surface outward and upward, there are many other tehniques including reducing the pressure field with designs other than the chute curvature.

Best to use ROCKY per our website: www.conveyor-dynamics.com . It can quantify the pressure on all surfaces such that your own experimentation leads to a proper design. ROCKY has some tutorials that can help. ■

Once again the only way there is sufficient pressure for material to get under the skirts is if the presentation of ore is poor. Re-designing the skirt system is an exercise in futility Larry. I have written a paper on this subject that I have distributed due to earlier posts (a long time ago) on this subject. As for running a DEM simulation, common sense will tell you what is wrong with the presentation if you look at the liner wear and deduce the flow pattern in the chute from this without going to this expense and doing it this way is far more accurate than any DEM programme.

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

Colin,

I have designed skirts that did protect the belt against rock forcing inself under the skirt bottom plane. So, I claim if one can make a skirt that does not show hard rock damage, in combination with proper chute design, then a redesign may be in order for the skirt that does damage the belt. Kennecott is a case in point. At last time I looked, the series of four belts, transported 10,000 t/h though 5 transfers with primary crushed copper ore, and no ill effect of the rock becoming entrapped by the skirts for the last 250 million tons. The chutes had no curved spoon arrangements. THis was before the days of DEM.

As far as the DEM side is concerned, it can do a far better job a quantifying pressure gradients and the pressure's potential for rock damage under the skirts than any pencil pusher. The pressure at the skirt can be quantified. It will likely lead, even the less skilled designers to come up with a reasonable plan to redesign the skirt in question. For those who wish to evaluate the potential of such a enlightened path, I suggest you take a look at ROCKY on our website: www.conveyor-dynamics.com ■

Larry,

All of us have designed skirt systems that protect the belts, not the point. If the loading from the transfer is the root cause you cannot design a skirt system that will address the issue unless you adjust the material flow onto the belt. As far as reference to pencil pushers as distinct I guess to those who use computors as the basis of their chutes designs, you continue to exaggerate how far DEM has developed. While we are looking at yours and other DEM software you have not even taken the time to interact on the successes we have had and continue to have using our design techniques. We are publishing further material shortly must send you a copy

Cheers

Col Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

Dear Tom,

Please send to my email information and photos. If we can help, I will promptly respond. ■

Dear All,

I have come across this,problem at several locations.

For Fixed Chutes,the best method is to go in for a Skirt system flaring to wards the direction of the flow.

An effective inspection system and repair to ensure that the gap between the skirt rubber holding plate and the belt is kept to the minimum so that pieces does not get trapped.Damage of impact idler increases the problem.

There is no permanant solution,other than effective inspection and repair.

In case of discharge chute, like that of Stacker cum Reclaimer,feeding chute to reclaimer, this problem is very frequent and the belt damage is controlled by

an efficient inspection and repair only.

Rgds,

Narayanan Nalinakshan. ■

Originally Posted by Tom Christophersen

Thanks everyone for all the feedback.

I tried to upload some photos but I'm having some technical issues. The only other potential cause of damage that has been suggested is the belt being over-tensioned and running on the skirts (personally I haven't seen this happen, and am not yet convinced it is a problem). This leads me to another question; what tension should these belts be set at after a change-out, in relation to the running tension (these are all head pulley driven, with a fixed take-up at the tail pulley)?

Looking at the inside of the skirt boards, it's fairly obvious that there is pressure against them. I think the feed is definitely the issue here.

Apart from Feed, I think there is problem of counter weight which is leading the belt to run in over tension condition. Also, kindly check the skirts and adjust the tension of skirts accordingly (if they are of adjustable type). ■

[/B]

Originally Posted by nordell

Colin is partially correct. I highly depends on the pressure exerted by the flow stream that drives the rocks under the skrt edges. This can be mitigated in two ways:

1. Reduce the critical pressure through quantifyable pressure reduction techniques

2. Improve the skirt design with ways of minimizing the pressure concentration - as Designer says taper the surface outward and upward, there are many other tehniques including reducing the pressure field with designs other than the chute curvature.

Best to use ROCKY per our website: www.conveyor-dynamics.com . It can quantify the pressure on all surfaces such that your own experimentation leads to a proper design. ROCKY has some tutorials that can help.

Hi Larry, Your are correct in that pressure has to be reduced at the skirt point of contact and this can be accommodated with a slight divergent skirt wings but also with a folded out bottom section, horizontal outward facing, to allow only gravity forces on the minimal quantity of product at the skirt point of contact. A seal, rubber or other, can then be added in a generally horizontal orientation, on top of the folded out section of the skirt, to just contact the belting to control any possible spillage due to the inclination of the belt conveyor. There is formed a basic void formed between the folded out section of the shirt bottom and the top of product that tends to 'walk out under the skirt'. The chute system also should be curved such as to introduce the product load to the belt at the same speed as the belt which reduces the tendency to eddy and drag turbulence against the skirt walls which is the most common cause of damage wear at the skirt contact with the belt. If done right, no skirting is required as I have used this process since 1964 in hard pink (+300mpa) granite rock production of aggregate and the belting has lasted more than 20 years at 300 t/h on a 750mm belt. ■