Install a deflector or collector hood to direct the flow to a common discharge point or spoon. This could also be made adjustable with a hydraulic cylinder and a signal from the VSD to position the hood correctly for the given speed.

It is usually better to regulate the feed to the conveyor than to try and regulate the conveyor itself. ■

Originally Posted by Gary Blenkhorn

Install a deflector or collector hood to direct the flow to a common discharge point or spoon. This could also be made adjustable with a hydraulic cylinder and a signal from the VSD to position the hood correctly for the given speed.

It is usually better to regulate the feed to the conveyor than to try and regulate the conveyor itself.

The key issue is the speed variation. You can design a deflector that could accommodate speed variations, you can design transfers providing if there is enough height that can accommodate without a deflector the lower speeds with the deflector set up for the higher speed regulation. Each application has to be looked at on its merit. What you need to avoid and only use as a last resort is some form of mechanical actuation of the deflector as this does not resolve the issues in the lower sections of the transfer and the actuation becomes a reliability and operational problem

Cheers

Colin Benjamin

Gulf conveyor Systems P/L

www.conveyorsystemstechnology.com ■

Hi there..

I have found that the most simple solution to the chute configuration is to use a dead-box to collect material from whatever trajectory profile is thrown at it.

Works on all but extremely sticky stuff, like clay or wet ash etc.

I first noticed this when over many years, one of my conveyors was speeded up for higher capacity requirement, and later speeded up again.

Fortunatley, the dead box I put in 25 years ago was big enough to cope with all this, and the original chute is still working fine.

Personally, I would never use a (dare I say) "intelligent" adjusting baffle in the trajectory. It is fraught with practical problems.

As they say in Sweden "Why make it easy, when you can make it complicated"

Fortunately, here in South Africa, we have it the other way round!

Cheers

Taggart LSL Tekpro ■

Col & Graham

Glad you guys corrected me on the "smart" chute. I had never attempted it before but thought it might be something to try. Good to know that it will cause problems. Thanks. ■

Indeed.. fear not, Gary..

You will be surprised how many have thought that a controllable baffle would be a good thing.. I even have a client right now that want's me to develop one, for use on good old coal!

Cheers

Taggart LSL Tekpro ■

Originally Posted by Graham Spriggs

Indeed.. fear not, Gary..

You will be surprised how many have thought that a controllable baffle would be a good thing.. I even have a client right now that want's me to develop one, for use on good old coal!

Cheers

Taggart LSL Tekpro

Graham,

For free flowing materials you do have a South African solution in the WEBA style of cascade chute which conceptually can tolerate some variations in belt speeds and I have applied this to designs successfully. If however you have any water content that can cause material aggregation or the material is cohesive/adhesive in nature then there are serious limits to what you can do so I would avoid it wherever possible. Varying belt speeds to maintain a constant material depth on the belt can have some significant plant throughput advantages when you have a long overland belt in the system and in such cases I would suggest a feeder belt arrangement as this could serve the dual purpose of giving additional protection to the overland.

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

Hi Colin..

I know we have the WEBA chute here in South Africa.

I should know, I have been called in to replace some of them with normal well designed chutes.

As for varying moisture content, I obviously take that into account too.

As for chutes with baffles, I am currently working on some here. These bafffles have holes worn in them, so I am going to replace them normal low wear chutes, properly modelled on my computer (and then checked using Rocky). My computer model also gives the calculated wear in kW for each part of the chute. It gives scary results with baffles and spoons. Vastly improved values with dead boxes of course.

As for varying the speed of the belts, yes.. provided of course the conveyor is generally over a kilometre long and can benefit from varying the speed. Then as I mentioned before, catch the trajectory in a suitably sized (and suitably positioned [v. important]) dead box.

For high speed major overlands with coal, where fines creation is a no-no, I use "super tubes". But I have found that I have had to tune the speed of the conveyor to the chutes, and not vice-verca. I use a secondary chute for the belt scrapings and the varying trajectory, during starting and stopping.

Cheers

Taggart LSL Tekpro ■

Hello,

Conveyor is always designed to operate satisfactorily while running at single speed for conveyor load empty to full design capacity. Then using speed variation in proportion to actual operating capacity implies we are compelling the conveyor to run at full cross section or nearly full cross section on belt. If one feels there is meaningful gain (some what less wear due to lower speed, etc.), then one can opt for it while inviting other resulting complexities and problems such as:

- Material discharge trajectory and resulting complexities of chute at transfer point (conveyor to conveyor / equipment). The optimum performance chute for varying speed is practically very difficult. The optimum performance implies proper magnitude of speed for material landing on belt. If conveyor is discharging on ground or in hopper, then this issue would not be there.

- Interlocking between feeder discharge setting and appropriate command from there to conveyor drive to run at so and so speed. If hopper on feeder becomes empty somewhat frequently, then it would require automatic safety control to avoid frequent physical exercise for belt conveyor (or conveyor system) to accelerate and decelerate.

- Simpler option would be to have selection of prefixed 2 - 3 discharge setting of feeder and corresponding 2 - 3 speed for conveyor. No change in conveyor speed, so long opting for next setting.

One can compare gain versus extra cost of equipment, extra liability for maintenance and upkeep, equipment degradation due to unsettled speed etc., and then decide accordingly.

Ishwar G. Mulani

Author of Book : Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book : Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Originally Posted by Graham Spriggs

Hi Colin..

I know we have the WEBA chute here in South Africa.

I should know, I have been called in to replace some of them with normal well designed chutes.

As for varying moisture content, I obviously take that into account too.

Cheers

Taggart LSL Tekpro

Hi Graham,

I recently downloaded a paper that is in the Technical Papers section of the Forum and my colleague Peter Donecker than added some comments and gave a link so you could download his paper. You should look this up and read it. I am well aware of the limitations of the cascade chute but they work for free flowing abrasive ores. They did not extend the patent to OZ so there are ways the concept can be significantly improved.

Having said that the way way we approach the challenge of cohesive/adhesive ores is empirical and very accurate. I have done enough work now to be extremely confident of our approach and contrary to you I know that it is impossible to accurately flow model such ores using DEM regardless of it's sophistication. The outcomes we are achieving with abrasive ores that are also cohesive/adhesive in nature is now getting us a lot of support. We are fine tuning our work but already we are able to design transfers regardless of ore type and size without impact idlers, without hard faced skirt systems, that do not block regardless of ore type and ore variation, have the capacity in excess of the delivery belt and where we can absolutely minimise wear within the transfer. Loading onto the receiving belt is also by implication very central with no spillage. It is all about flow control and understanding the flow mechanisms and despite the enormous research done over the last 20 years looking at computational solutions the complexity is such that it will light years before an accurate mathematical model will ever be created.

Cheers

Colin Benjamin

Gulf Conveyor systems Pty Ltd

www.conveyorsystemstechnology.com ■

Interesting, Colin..

We never use impact idlers unless the client insists, we limit impact of lumps onto the belt (not on an idler roll) by correctly configuring the chute, and are successfully loading iron ore from a HUGE gyratory crusher onto a 3m wide belt, using an impact area that we developed in-house.

We also load at a comparable speed to that of the belt.

We have designed literally hundreds of chutes, of all types , for all varieties of material and PSD's, and have had tremendous success thanks to the flow model that I developed from first principles. It covers chutes, super-tubes, hoods and spoons, dead-boxes, combinations thereof etc etc..

So..it can't be rocket science, as it didn't take that long to develop the model, unless I am ahead of my time.. which I very much doubt!

Cheers

Taggart LSL Tekpro ■

Hi Graham,

What you are doing is interesting, what belt and material speeds? Drop or dead boxes limit the system capacity unless the belt speeds are low. We are generally working with belt speeds of over 4 m/s and as high as 5.5 m/s, and have had drop heights of up to 17 meters. So we are achieving these controls while at the same time also controlling wear. Depending on the application and variability of the ore properties it is possible to achieve a zero maintenance outcome that could stretch to 2 years. Like you state it is about flow control but our solution has not been that simply achieved

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

Back in the days when VSD was a gleam in an electrician's eye it was sometimes possible to jettison two different material flows using pole switching and a longitudinal trouser leg chute. ■

Originally Posted by johngateley

Back in the days when VSD was a gleam in an electrician's eye it was sometimes possible to jettison two different material flows using pole switching and a longitudinal trouser leg chute.

Hi John..

What did you do with the dribbles, when you were using the longer trajectory?

Cheers

LSL Tekpro ■

Originally Posted by Graham Spriggs

Hi John..

What did you do with the dribbles, when you were using the longer trajectory?

Cheers

LSL Tekpro

Hi,

This application was small tonnage and the higher speed was, of course, the lesser throughput. Dribblings were completely ignored (left on the low speed receiving belt) until the low speed was required and the high speed dribblings were discharged into a skip before running proper began. Tioxide waste were the products and the copperas and salts disposal system was quite suited to the ignoring scenario. This waste was taken off site by trucks and the waste separation scheme was not as strict as it might be today. There was a wetland sanctuary next to the plant and the priority was to remove roughly sorted waste. Because the copperas was more toxic, and plentiful, the fewer salts left on the belt wouldn't do much damage.

Nowadays a movable side deflector could be built into the trouser leg to accommodate larger throughput but I would still try stop-start on the low speed conveyor if I could get away with it. ■

If you are working with standard conveyors that are not too long then your speeds are relatively slow. Normal head design should be specified so that the discharge does not impact the head . A properly designed head collects material from the scrapers all the way to the front so standard chute liners should do the job. If you are working with large tonnages and or high conveyor speeds then this is not the same story. Add a little extra steel in the head and take advantage of your material speed if you can. Conveyor suppliers like rock boxes because they reduce the overall amount of steel required in the head and that means $$$$ in their pockets. If you are changing direction drastically or abruptly with little to no headroom rock boxes can become a very good option. To date I have never had to use a deflector plate, not to say I am against it.

Under the circumstances I agree with Mr Muliani. Use the full speed design conditions and make this your base case for the head design and spend a little extra in steel to ensure you don't impact on the head.

Liam ■

Once the belt speed exceeds 2-2.5 m/s a rock box will constrain the system capacity i.e. the belt capacity will be greater than the chute capacity so it is not logical to use rock boxes when conveying materials at higher speeds. If the material being conveyed is cohesive or adhesive in anyway then rock boxes will build-up in an uncontrolled manner such that blockages could occur or worse, the chute does not protect the belt from severe impact. Rock boxes by design create ore on ore impact so if you are concerned about material degradation such as conveying iron ore pellets then you should not use them. Finally rock boxes because they create ore on ore impact are very dusty. Now I am not saying they are not useful and that there are not applications but in Australia you rarely see a rock box chute used for all the above reasons, simply there are better solutions.

In respect to variable speed drives there is no doubt you have more flexibility with a rock box but why would you vary a belt speed if the speed limit of a rock box is about 2.5 m/s unless it was a feeder belt. In this case there are alternatives to rock boxes given the low speed of the feed belt. Alternatively to a rock box and in order to maintain flexibility but at the same time increase system capacity you can look at a cascade chute. This is essentially a series of carefully designed rock ledges. This design also has limitations when handling cohesive or adhesive ores (it will block due to uncontrolled build-up) and while the ore on ore impact is not as bad it will still cause some material degradation and dust.

You are right in that you always design a system for the higher speed and then work out what to do at the lower speed but I do not agree that rock boxes are such a universal solution although they are relatively simple to design and inexpensive to build.

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■