DEAR MR BANARJEE

Pipe conveyors in case they are reasonably loaded can negotiate 5-6 degree higher inclination due to following reason

1.0 When belt is in shape of Pipe it is very stiff, Idler agitation is much less

load containment is superior if there is rollback

2.0 Material fill inside the pipe ranges from 65 percent to 70 percent accordingly constant stream of material exists.

3.0 Equilibrium angle of repose which is component of pipe inclination, surcharge angle and trailing stream surcharge angle is more in pipe conveyor due to increase surcharge angle of material inside pipe cross section.

you can also note in case of pipe conveyor open portion of conveyor will always have

angle of inclination limited to conventional conveyor. In case of any roll back if there due to less loading of material cannot be noticed inside the pipe as there will not be any spillage .

A R SINGH ■

Dear Mr. Banerjee,

the Technical University of Magdeburg (Prof. Friedrich Krause) operated already years ago a test installation for vertical material transport in a pipe conveyor. Easy flowing materials like plastic granulates with particle sizes of around 2 mm were elevated a couple of metres in a pipe conveyor of around 200 mm diametre.

Special designed feeding area using forces of inertia to fix the product on the belt before the pipe is closed. Transport due to friction between product and belt + internal friction. Continuous or intermitting transport depending on the filling level of the pipe. Looked really impressiv.

Big problem preventing practical application: what happens in case of power failure? If the pipe stops before being emptied - the material runs back causing clogging of the pipe at the bottom.

Unfortunately, I do not have details any more. May be somebody in Magdeburg has further information.

Holger Lieberwirth ■

Dear Mr. Banerjee,

as mentioned Prof. Friedrich Krause of the Technical University of Magdeburg is certainly a competent partner for that topic. At the internet page http://www.ttz.uni-magdeburg.de/scri....idc?Nr=60502. I found his e-mail address as follows friedrich.krause@mb.uni-magdeburg.de.

Holger Lieberwirth ■

The mathematics is amazingly simple. If it is a pipe then the material cannot escape without bursting the pipe. Of course, if you think there is a hard way then, by all means, theorise away. ■

As Dr. Holger Lieberwirth hits to the heart of the problem, what happens when the power is cut? The pipe is not a pipe in that it cannot contain the hoop stress. The crossectional wall is dialated along the pipe longitudinal axis with the emphasis at the beginning of the elevation.

Restarting the belt with the bulge can produce an exaggerated resistance, multiples of the steady-state condition when the material is forced between the idler spans and can only occur with fine granular materials.

There are means that overcome this condition at a price.

DEM can give reasonable hoop loading against the pipe wall which can be translated into the expected distortion and resistance to starting. ■

Maximum static angle is the least of the material's internal friction angle and the friction angle between the material and belt surface. Material disturbance (due to accel at loading, sag, etc) lowers the angle, wedging (at 60% loading) mitigates the lowering. At incline before the internal friction angle the material will slide back and plug the cross section. The material must be plugged to not slide back. If loading corresponds to 60% fill at the belt speed then the material must move at only 60% speed and slide at 40% of the belt speed. The sliding will not be continuous and uniform, rather it will be a grip and rerlease, clugging type action, lots of wear and tear and material degrade. The material will bulge between idlers and be choked at the idlers, imagine the power required to push the material through the choke. Calculating the minimum swelling pressure to convey at any high angle is quite easy if the least friction (material internal friction or material to belt surface friction) is known. The minimum pressure will result in the material moving upward and it will not move upward until that minimum pressure is realized.

A pipe belt is not suited for high angle conveying and the material can never be purged.

A sandwich belt high angle coveyor is the answer always hugging the material as required to develop the internal friction regardless of the loading level. Check out the DSI Snake Sandwich Conveyor system at the DSI website.

Joseph A. Dos Santos ■

Dear sir

Pipe conveyor and sand witch conveyors are having its own merits and cannot replace each other and are to be provided where conventional conveyors use is not feasible

1.0 INCLINATION

Sand witch conveyor can take up to 90 degree elevation where as conveying by pipe conveyors are restricted to 4-5 degree higher than conventional conveyors. Pipe conveyors canot be used for higher inclination

2.0FINES TRANSPORTATION

Pipe conveyor can convey fines much more efficiently than any other type of conveyor . I am doubtful about fines like ash/cement feasible by sand witch conveyor

3.0MATERIAL DEGRADATION

In case of soft material , material degradation is not ruled out in sand witch conveyor as material is pressed between two belts and changing position of idlers from one position to other side of material also contributes to material degradation . In pipe conveyor if angle of inclination is properly selected degradation is not expected

4.0BIG LUMPS TRNSPORTATION

Pipe conveyor can be used up to maximum 1/3 of pipe dia only. For sand witch conveyors I am not sure up to what lump size transportation is feasible.

5.0Horrizontal Curves

Not feasible in sandwitch conveyor

6.0Material To Belt Friction

In sand witch conveyors speed of both belts should be same . speed variation of both belts may occur in case of uneven were of both drive pulleys. As separate motors are driving two belts even slight difference in revolutions of both motors may cause speed variation

In case of variation in speed one belt will rub against material and may degrade material and cause belt wear

sandwitch conveyor is very good conveyor for high angle applications for certain materials

A R SINGH ■

Mr. A. R. Singh

You have reaffirmed my point, a pipe conveyor is not a high angle conveyor and therefore one system is not in competition with the other since one is a high angle conveyor the other is not.

You have some misconceptions about our Sandwich Belt High-Angle Conveyors that need correction. I will make my points regarding the Dos Santos Systems, particularly the DSI Snake:

DSI Snakes can offer a cost advantage where conventional conveyors are feasible, say at slopes from underground (phenomenal savings in excavation costs), open pit slopes (phenomenal savings in excavation costs, better access to the ore body), to tall silos (phenomenal savings in steel structure), etc, etc, etc.

Ref. 1.0 Inclination: I agree

Ref. 2.0 Fines transportation: Fines are not a problem if there is internal friction. The problem is with materials that aerate and fluidize, like cement. Such materials have slide back problems at conventional conveyors as well and likely at pipe conveyor. at the pipe conveyors you can't see the back-sliding because it is contained and shielded from sight

Ref. 3.0 Material Degradation: This is the farthest thing from the truth. There is no material degradation in the sandwich. This has been amply demonstrated in controlled cases where this issue was in question and at many installations. Indeed preservation of chips quality is its most important selling feature in pulp and paper and great savings in pulp yield are documented

Ref. 4.0 Big Lumps Transportation: As with conventional conveyors, big belts can convey big lumps little belts cannot. Lump size criteria is related to belt width or, more specifically, depth of trough. 250 mm thru 300 mm minus materials are routinely conveyed at Dos Santos Sandwich belts of 1800mm thru 2200 mm belt width. Such units typically work with or displace conventional conveyors in the 1200mm thru 1500mm range. The lump size criteria is therefore compatible with that for conventional conveyors (b/5 for predominantly lumpy material)

Ref. 5.0 Horizontal Curves: I agree

Ref. 6.0 Material to belt friction: It is not possible to cause relative belt slip in a well designed system. Traction is developed at the material interface and at the substantial material free edges. Poor control of the pulley diameters or poor matching of motors will result in poor load sharing but not in belt slip. Indeed there are some units where only one belt is driven and the other follows (the writer does not recommend driving only one belt but for other reasons). Your fears of belt slip and material degradation are unfounded in a Dos Santos System.

I know that there have been and are sandwich systems that were poorly conceived and executed by unqualified people. That is a poor reflection on them not on the system and its foundation. In general Dos Santos Sandwich Belt Systems will handle any material that can be handled on conventional conveyors.

Joseph A. Dos Santos ■

Mr. Joseph A. Dos Santos

I may have some misconceptions about Sandwich Belt High-Angle Conveyors that that I would like to correct if convinced

A.0 I fully agree there should be cost advantages compared to conventional conveyors where substantial saving in RCC work and Steel structures can be done. However unfortunately we don’t have a single installation in India of sand witch conveyor that may be due to any of the reason

1.0 lack of awareness about these conveyors

2.0 or your cost may be too high that these conveyors are not viable

3.0In India more than 100 installations of high angle Flexowall type conveyors exists. Even though cleaning problem of side wall conveyor belt is faced at many installations but we do not have other alternate at same cost.

4.0Regarding under ground installations ,90 percent of these installations are in power plants below wagon tippler where (-)300 mm size coal is conveyed for these application sand witch conveyor is not feasible

5.0 For ash silos and cement silos these conveyors are not feasible

B.0 I am not convinced about material degradation

C.0 I not convinced Material belt friction by relative belt speed Due to following

1.0It is difficult to maintain same linier speed of two belts if driven by two different drives

2.0 Even if same linear speed is achieved it may be difficult to maintain same relative speed of two belts while negotiating convex/concave curves with two radius. In these types of conveyors belt while carrying the material at inclination is always in convex curve or concave curve one above and second below material guided by idlers , in this position both belts will be having different radius and may cause relative belt speed difference

Mr Santos pl explain how same speed is maintained to correct my misconcept.

A R SINGH ■

Mr. A. R. Singh

Firstly I realize that we have diverted the discussion and I don't know what are the rules of the forum in this regard. I invite the moderator to advise us.

A.0, 1.0, 2.0 No Snakes in India:

We have gotten many inquiries from India but all have been for relatively low conveying rates. The economics is greatly in favor of our system when the volumetric rates are high and the advantage increases dramatically as the rates increase, indeed we have coined the saying

"The Greater The Load

The Higher The Lift

The Better We Look".

This is further complicated by the high project costs associated with distance and duties. It will take a significant project to justify the first installation in India but, with working relationships established, subsequent projects may be easier to justify.

3.0 We have replaced many pocket belt (Flexowall type) installations. To date no pocket belt has replaced a Dos Santos Sandwich system

4.0 I cannot judge the feasibility for collecting from under a particular wagon tippler project but I can tell you that I have built Sandwich Belt units elevating from underground vaults. A particular unit comes to mind, located in Florida, USA, 2000 t/h coal.

5.0 I agree where such materials tend to fluidize

B.0 If you are not convinced then you need to learn more about the system beyond your mental rationalization. I can assure you that there is no material degradation and this is an attribute that we advertiste not defend.

C.0, 1.0 Similar to "B.0". You must realize that the traction between the belts, if sufficient (and I can assure you that it is sufficient), causes the two belts to behave as a single composite belt (same as if they were glued or stapled together) from just beyond the sandwich entrance until just before their separation at the head end. You say it is dificult to maintain same linear speed at both belts but the opposite is true. The linear speeds are the same, as they can't be otherwise, and the consequential problems are in load sharing not in speed matching.

2.0 The argument here is same as above, it is a matter of sufficient traction so that the composite belt behaves as one. Indeed if you extend your argument then each troughed belt at a convex curve will tear itself apart along longitudinal shear lines.

Mr. A. R. Singh, there are many Dos Santos units in operation to demonstrate the claims that I am making and these are explained in math and materials science if one just digs a little deeper. Unfortunately it is a failure of understanding, by others, that has led to other systems that are poorly conceived and poorly excecuted and consequently don't perform well.

Joseph A. Dos Santos, PE ■

There should be no concern for the two belts matching speeds. As working examples, beyond noted by Joe, there are the cable belts, TT-booster belts, and of course the many conventional HAC belt also developed by Mr. Dos Santos and marketed by Continental Conveyor.

CDI developed the Power Strip conveyor with two belts and have no problems with speed matching. ■

Dear Dos santos/Nordell

Thank you very much for convincing reply. Mr Dos Santos you mean to say both belt speed is same due to sufficient traction force between the two belt edges

A R SINGH ■

Mr. A. R. Singh,

Yes substantial traction is developed between the belts at the material free edges but traction is developed across the entire belt width including through the material sandwiched between them.

Joseph A. Dos Santos ■