Mr. Quintal,

It is very well known that pocket belts are entirely unsuitable for handling sticky materials as the material will cake up in the pockets and will not completely discharge at the discharge point. This results in much material carry-back. The limited means of belt cleaning is by belt beaters, rolls that thump (impact) the back of the pockets attempting to dislodge the caked material. Even with many thumping rolls over a substantial distance the material cannot be completely discharged. Much better systems for elevating sticky materials are the Dos Santos Sandwich Belt high angle conveyors. These utilize smooth surfaced rubber belts that can be continuously scraped clean just like any conventional conveyor. Dos Santos Sandwich Belt systems have been used in many cases to replace pocket belt systems that were already in operation.

Joe Dos Santos ■

Hello,

Some general information is as below in context of application engineering.

For very long time (more than a century) the available options of elevating bulk material have been: 1) Inclined regular belt conveyor. 2) Bucket elevators.

Regarding belt conveyor, it has been suitable for practically any capacity and any lift. It only demands horizontal space length 4 times the elevating height (considering 14 - 15 degree inclination). Its reliability as equipment is excellent because: 1) It is open all around. 2) It is accessible from walkway. 3) Regular inspection by walking along conveyor and 4) Can be easily restored to work in case of sudden failure (chances for which are minimum due to openness and daily apparent inspections). In present day fashionable word it is user friendly.

As for bucket elevators, it has capacity limitation, roughly 300 cubic m/hr for centrifugal discharge elevator, and 500 cubic m/hr for super capacity elevator. For grain elevator the capacity range is somewhat more.

The super capacity elevator has double strand chain, getting them ‘matched’ and remaining so during operational wear, needs high class workmanship and restricted sources. These two strands are rigidly bolted together by steel buckets. Any anomaly in chain wear, etc. will result into unequalised load sharing, reduced life and failure. ‘Average’ manufacturers of bucket elevators are averse to such possibility for double strand chain, and apprehensive about risk. Well, such elevators are in use.

The bucket elevator reliability is less compared to belt conveyor because 1) Everything is enclosed. 2) Absence of easy visual inspection does not allow to notice developing weakness immediately, and can result into sudden failure sometimes. 3) It is not only elevating, but also scooping material. 4) Chain is contaminated by material and will lead to its wear and weakening when handling abrasive materials. 5) Repairing is less easy compared to belt conveyor. 6) For belt bucket elevator, aligned running of belt needs proper care during erection, particularly belt joint.

In spite of above, the bucket elevators (chain and belt) have very large space in market, and will remain so due to price, very large number of sources (for equipment as well as for spares) locally, nationally and internationally and its requirement for design know-how is comparatively simple.

The need to meet the modern demand (possibly since 25 / 30 years) for high capacity equipment to elevate materials; has resulted into development and availability of new equipment such as:

1) Sandwich conveyor as mentioned by Mr. Joseph A. DosSantos.

2) Cleated and flexible side wall belt conveyor for sharply inclined conveyor.

3) Pocket and flexible side wall belt elevator (S - shape), popularly known as Flexowell, Contiwell, etc. conveyor-elevator.

These new equipments are suitable for elevating bulk materials at very high capacity in thousands of cubic m/hr (as mentioned in their publications), as compared to few hundred cubic m/hr for bucket elevators.

Thus these equipment have their share of market, as a preferred equipment or when capacity makes them only choice. Functionally these act as elevators for bulk materials, and their grouping among bulk material elevators could express their function application more effectively. These can be also said as elevators with some advantage of conveyors.

I think, this analytical technical information will draw the attention of probable users, to the available option / equipment, as on now.

There are also other type of widely used and important conveying-elevating equipment such as chain conveyor (apron, bucket, drag, Redler / bulk-flow), screw conveyor, etc. These have specialised application and are not mentioned here, as these do not constitute alternative options in context of the subject here.

Regards,

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 ■

Dr. Mulani,

Thank you for your summary but I take exception to important aspects of your summary.

Your summary of the conventional conveyor inclines, 4 horizontal to 1 vertical may be a bit simplistic (and I know that you don't mean for this to be precise rules). I can cite many instances where the conveying angles are held to much lower values because of the failures experienced with the simplistic rules. More fundamentally, there are no theoretical, technical rationalizations at all for the conventional conveyor inclines, just rules of thumb with wide disagreement.

Apart from the angle issue the sandwich belt high angle conveyors are much more akin to conventional conveyors then they are to the pocket and sidewall belts. Sandwich belt high angle conveyors are the generalization and the conventional conveyors are a particular manifestation of the generalization. I made my case for this in my Y2K publication "Sandwich Belt High Angle Conveyors according to the Expanded Conveyor Technology". The sandwich belt high angle conveyor development did not create new equipment, it utilized the conventional conveyor equipment. It did not subject the equipment to new rules of their design rather it subjected the equipment to the same rules for which they were developed in the conventional conveyor technology, hence expansion of the technology. That is why the sandwich belt high angle conveyors have the same positive operating characteristics as conventional conveyors including smooth surfaced rubber belts that can be scraped clean and unlimited conveyor capacity (though it does require a wider belt than the conventional for the same rate).

I reject your categorizing the sandwich belt high angle conveyors with the pocket belts and sidewall belts. Before the Dos Santos Sandwich Belt high angle conveyors, indeed the pocket belts were the best high angle conveyors available, but they still suffered capacity limitations requiring multiple parallel units to achieve any high throughput rates. They could not be scraped clean. They required special belts that were tremendously expensive for any moderate to high capacity systems. The pocket belt cannot acheive the conveying rates of the Dos Santos Sandwich Belt high angle conveyors. In the 1980's an Illinois underground coal mine was operating vertical twin flexowall conveyors each 60" (1524mm) wide for a combined claimed capacity of 1200 STPH (1089 t/h). The mine needed to increase the design rate to 1500 STPH (1361 t/h). Schenk/ Flexowall could not acheive this with the system that was in place. A Dos Santos Sandwich belt system (a Continental HAC) of only 60" (1524mm) belt width was installed to replace the twin Flexowalls and did acheive the 1500 STPH (1361 t/h) design conveying rate. So you see, from a capacity standpoint the pocket belts don't come close to the Dos Santos Sandwich belts.

Having said all of the above I do respect your knowledge and expertise and appreciate the clarity that you typically bring to the discussion in this forum.

Joe Dos Santos ■

Dear Mr. Dos Santos:

Without interjecting which system is better, I would propose that you provide examples of your systems in the markets the Author asked about.

For example, I am aware of your system (or a very similar system) being used very successfully in a gypsum facility, in Florida. I believe that the customer has had great success with this type of belt.

I am not personally aware of a pocket belt being used in a gypsum facility. ■

Mr. Fernandez,

The original post asked about pocket belts handling sticky material. The only success I am aware of is in tunneling where the material can be sticky. In these cases their limited success is achieved with a long discharge section that is oriented over the outgoing surface conveyor and multiple belt beater rolls that attempt to thump the material out of the pockets onto the outgoing belt below. This needed alignment at discharge is also why the vertical twist was developed.

My objection to Dr. Mulani's categorization was more fundamental. The Dos Santos Sandwich Belt high angle conveyors are an extension of the conventional conveyor technology and therefore have the same positive characteristics. But more importantly, additionally our systems can convey at high angles to 90 degrees.

With regard to citing examples of applications in sticky materials there are many. Besides elevating gypsum there are many Dos Santos Sandwich Belt systems elevating municipal sludge and sludge and sawdust mix at composting systems. It cannot get much stickier than that.

Of course the very big point is that the Dos Santos Sandwich Belts have no capacity limitation. You need merely to pick the required belt width and speed. We are presently delivering a 4000 t/h coal elevating system that uses 2438mm (96") wide belts. This is the highest volumetric rate to date but is by no means the limit.

Joe Dos Santos ■

...how in Krishna's name did bucket elevators enter a thread concerned with the demerits of cleated sidewall conveyors?

Joe's machine is streets ahead in terms of capacity and cleanliness. Leave it there: enough said? ■

Hello,

Referring to my earlier reply in this thread, I add following information about the application characteristics of equipment:

In case of ‘Cleated belt steep angle conveyor’ and ‘Pocket-belt conveyor-elevator’, it is not possible to have external scraper. So, designer is to use the equipment considering this aspect. Such belt manufacturers’ leaflet / catalogue itself sometime mentions absence of external scraper and suggest to opt for equipment accordingly.

Thus if used for sticky material (or material having high moisture content and large proportion of fines or fine powder), will have some dropping of such material under return run, particularly in a zone near to head end.

The remedial measure could be to provide ‘Spillage conveyor’ under the return belt run zone near head end; in a manner similar to the spillage conveyor under the apron feeder, if one likes it. Needless to mention that such spillage conveyor discharges into common chute at head end. The effectiveness of such arrangement is subjective to the particular application and designer to decide accordingly. Some points / hints are as below:

- In case of S-conveyor having head end zone horizontal, the matter is simple.

- In case of steep angle conveyor made moderately inclined at head end; the matter is also simple.

- In case of steep angle inclined conveyor, designer has to see whether the flat belt spillage conveyor will be able to convey the material for the concerned inclination. Such dropping of fine material will have very thin layer on belt. In such situation, the material cohesion component will be dominant and permissible inclination will be more (compared to thick layer of material for regular conveying). Fine dust particles or very moist particles can remain stuck to surface which is more inclined compared to regular value of inclination. So issue to be decided by designer as per experience and exact nature of the material.

- As stated by others; some other remedial measures are also in use. I do not have first hand experience to comment about non-effectiveness / effectiveness of the said measures, but certainly due consideration needs to given to the views expressed by them.

Regards,

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 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 ■

What boils down is that for sticky materials conveyed at high angles a pocket belt conveyor requires extensive and complicated cleaning equipment which then itself requires a cleaning and debris collection system.

I worked on an extensive Flexowell installation at Krakatau Steel where each Flexowell deposited head end debris down onto a preceding conveyor. This caused a circulating load which surely restricted the design capacity according to yours truly. The Contractor, Ferrostal, vehemently denied this capacity reduction and I lost interest: until today!

Conveying sticky material is a dirty business which some relish and some, like me, do not relish. The thread starters quandary should have been 'What room is available and what tonnage is moved?' and that's all. Anybody who builds conveyors tails up will finish up with a high angle requirement, higher than necessary. It is often bad planning, poor layout and client ignorance. There are viable, and non viable remedies mentioned here, but that is what they are. As Designer said, quoting an Irish saying, "Well Sir, if I wanted to go there I wouldn't be starting from here." ■