Dear Sureshaji:

Without knowing the chute configuration it is difficult to determine if the problem is one of chute design or of the transported material. Also, you stated that you chutes are line, but not what they were lined with.

Three actions you may consider are the use of UHMW polyethylene as a lining material, the use of a vibrating device, or a chute redesign. Of course, there are other possibilities, including the use of a rubber chute, but you should have a service call from a reputable company that specializes in material transfer points.

Good luck. ■

Dear Shri Sureshaji,

As Mr. Dave Miller says, it is very difficult to comment on the reasons for chute blockage without knowing the chute layout. In general, blockage can be due to inadequate slope of the chute, coasting time difference and consequent filling-up of the chute.

I will like to mention that, the Indian iron-ore is mostly very abrasive and consequently if it is lumpy, UHMW polymer liners are found to be unsuitable.

In the existing set-up, one can also think of incorporating chute vibrators.

Regards,

Ishwar G Mulani.

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

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Adding to the previous comments.

Iron ore fines (<200 microns), with moisture present, can have a strong surface tension strength that inhibits flow.

The valley angle of chutes with wet fine iron ore should exceed 75 degrees. Further the chute should be designed to push the flow with a first-in-first-out philososphy.

Iron ore fines will quickly damage UHMW plastic due to impact. Flow surfaces, induced by gravity, with no impact, can successfully use UHMW. Its low coefficient of friction has design advantage over metal and ceramics.

Impact locations should be equipped to handle the abrasive ore by using +500 Brinnel metal. High impact locations should use +600 Brinnel with a high chrome and with sufficient mass (thickness) to give long life.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

Apart from the design and materials aspects referred to above, I would suggest that a water audit is often worthwhile in this circumstance.

This would involve listing and inspecting all sources of water into the process, such as dust suppression, belt cleaning, equipment cleaning, belt scraper returns. If you are at a minesite, this should also include consideration of the mining operations.

Intermittent water sources can be the hardest to track, but can have significant impact on a process. These are often associated with points in the circuit where water can accumulate. Examples are the mine floor, belts and bins.

If it is possible to maintain your moisture content below the lower sticky limit, and in particular to avoid brief excursions into the sticky range, then your problem may be reduced.

Best wishes ■

I am surprised that no body so far has recommended a venting system for the gravity feed chutes. Chutes not only have to have the proper slope but they also need venting to remove the displaced air. Without a vent line even a properly sloped chute will plug up.

Regards.

Amrit Agarwal (Tim)

PNEUMATIC CONVEYING CONSULTANTS

www.powderandbulk.com/pcc

polypcc@aol.com ■

Mr. Agarwal:

You need a vent if the flow stream is dry, slows and blocks the air stream and the product's free passage. If the dry flow stream does not block the air stream, you do not need nor do you want such a vent.

A proper chute design will maintain a coherent non-dialating (expanding) dry product flow stream. Air does not become entrained with the dry product stream and therefore does not need venting.

Entrapped air, in the dry product stream, causes excessive dust generation and makes the prediction of the flow volume iffy.

The questioner stated the product to be wet, with fines, implying it to be sticky. I doubt an air vent would do much in this condition. Signifcant air would not be entrapped.

Lawrence Nordell

Conveyor Dynamics, Inc.

website: www.conveyor-dynamics.com ■

Testing for Ore Rheology:

A word of caution on the "fundemental" testing suggested above. Such testing may give accurate insight to the flow properties. However, highly weathered and moist ores have unique properties that may not be accurately laboratory tested based on their moisture content.

Testing procedures require drying of the ore to measure its moisture content. Once moisture is removed, how do you add it back in measurable quantities to trend moisture verses flow behavior. Research carried out around the world in "red mud" (iron, nickel; bauxite) demonstrates that you cannot recombine percent moisture, in the laboratory, and observe the same rheological behavior that the mineral has achieved in geological time with the same test procedure.

Laboratory mixing is not able to reproduce the wetted strength of the in-situ mineral composition. This leaves us with the problem of how to quantify moisture and rheology. In some highly weathered minerals, the moisture cannot be driven back into the dried fine particle mass that gives the same result as the in-situ mineral by a test device such as the Jenike & Johanson shear cell tester.

Another approach is to mimic, by Discrete Element Modeling (DEM), the observed flow behavior and its problem areas. It is possible to model the existing chute geometry and introduce flow properties that induce pluggage similar to your observation in the same locations.

With this field calibration data, we can redesign the chute to properly flow given the same material properties. Usually, this is not a trail and error process. The model shows critical restrictions that likely lead to appropriate geometric changes which appropriately debottleneck the flow, predict wear patterns, analyze sensitivities to stronger particle-to-particle strengths, etc.

Contact us if this is of further interest.

Lawrence Nordell

Conveyor Dynamics, Inc.

email: nordell@conveyor-dynamics.com ■

I also suggest caution in assuming that the measurement of flow properties can provide a universal cure to this problem.

Build-up in chutes handling materials such as iron ore fines is not necessarily related to bulk ore properties in some simple way even if the ore could be re-constituted in the laboratory. It is common for segregation to occur, whereby the finer fractions of the ore are selectively deposited on the surfaces of the chute. A brief description of this process is the case of coal is given in:

Taylor, P.D. / Matchett, A.J. / Peace, J., Chemical Engineering Science, Jan 1987

In some cases, the particle size of the built-up cake can be extremely fine, reaching colloidal dimensions. It is hard and brittle.

It is possible to mimic such behaviour by physical modelling, but as in the case mentioned above, this needs to be matched carefully with field observations. ■

A Pipe/Chute mounted pneumatic piston vibrator should do the trick. You can learn more by visiting www.navco.org/pipe.html

- it talks about coal pipes, but works as well for any type of bulk material that is clogging a pipe, even one with with liners.

Call our Flow Solutions Hotline at 1-(800)231-0164 if you'd like to speak to someone about your particular problem.

Have a great day!

Tiffany

NAVCO

The Vibratory Flow Solutions Specialists ■

Caution is always the best policy when considering material flow through chutes particularly if the chutes are not flowing 'flush full'.

Some years ago I carried out trials dividing the coal flow from a feeder into two streams using a breeches chute (75 degrees inclination). The system was to have a coal flow of 5 T/hr with a 10:1 turndown. At 5 T/hr the coal flowed down the chutes lined with either polished stainless steel or UHMW polyethylene. However at 0.5 T/hr the coal stuck to both the stainless steel and UHMW !

It confirmed the experience of many years that with transfer chutes the problem was frequently not that the bulk flow of materials caused buildups, but that the dribbles and scrapings caused them.

Unfortunately when detailing chutes most consideration is given to the bulk flow, the dribbles are an afterthought but they can turn round and bite you. ■

Before getting into, too complicated matters, I suggest the use of a vibrator (free trial) and note the outcome. This will save you time and money.

We at Chamberland Engineering are vibration engineers and many times customers get complicated and it really is not necessary.

Give us the size and slope and we will suggest the proper vibrator for you to try.

David Chamberland

Chamberkand Engineering

vibrate@comcast.net ■

Dear Sureshaji,

We are solving the blocking, sticking and flow problems for 22 years and we have been succeeded in hard - to - solve problems. We are manufacturing Air Cannons to overcome these types of problems. Air Cannons are accepted as the best solution to problems of the material blocking.

Please check our Web Site at www.yunel.com and contact me via sales@yunel.com for more information.

Best Regards,

Ufuk YUNEL

(M.Sc. Mining Eng; M.B.A)

Sales Coordinator

YUNEL LTD., STI ■

Another caution:

Some here advise the use of vibrators. Most vibrators do not do the anticipated job due to lower than required frequency and higher than appropriate amplitude.

THose that advocate vibrators, should also note their experience with these two parameters and material physical properties they have solved.

We have had poor experience with most common vibrators. They exacerbate the problem: force fines compaction and consolidation which in turn increases ore fines shear strength and aggomeration. ■