Belt Conveyors

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Edition 12/08/98

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THE BELT CONVEYORS Knowledge & Adjustment

Continuous Professional Training Course of Mr. Marc des Rieux

des RIEUX SASau capital de 40 000 uro Quartier St.Ruff 26000 VALENCE Tel. 0475.569.215 Fax 0475.781.494

n SIRET : 398 454 389 00014 APE : 742 RC ROMANS 26 :94 B 431 Existance declaration n Training Enterprise 82 26 000610 26






1.1) The function 1.2) The means 1.3) The main element 1.4) The objective II) MASTERING THE TRAJECTORY OF A CONVEYOR BELT

2.1) The elements of the conveyor 2.2) Interaction of the forces 2.3) The transported material 2.4) The elements to be neutralized 2.5) Factor that can perturb the trajectory of the belts. a) The deformation of the belt. b) The deformation of the drum. c) The deformation of the support. d) Variation of the tension. 2.6) Other factors that can perturb the trajectory of the belt. a) The problems related to the presence of inlet chutes. b) The problems related to the overflows of materials. III) TERMINOLOGY OF THE MATERIALS

3.1) Longitudinal view. 3.2) Transversal view. 3.3) Particular cases. 3.4) Other elements that serve to define a conveyor. IV) THE TRANSPORTED MATERIALS

4.1) Restraints due to materials. 4.2) Other imperatives imposed by the materials. 4.3) Calculation of a belt. 4.4) The outputs. 4.5) Influence of the materials on the belt. V) THE ELEMENTS THAT CONSTITUTE THE CONVEYOR

5.1) The belts 5.2) The coatings 5.3) The frame 5.4) The gearbox group 5.5) System of tension


5.6) The drums 5.6.1) Minimum diameter of the drums. 5.6.2) The forms of the drums. 5.6.3) The materials and surfaces of drums. 5.6.4) Zones of influence for the drums. 5.7) The supports 5.7.1) The supports of the slippage surface. a) The used materials. 5.7.2) The contact supports per bearing. a) Belts auto centering. b) Coating of the rollers. c) Parasite forces. VI) VII) TRANSITION LENGTH CONVEX CURVE






1.1) The function: It is about realizing a handling of material, in bulk in a continuous manner. 1.2) The means: The conveyors and the elevators with conveyor belt Commonly called: The belt conveyors. 1.3) The main element: It is about well considering the belt like "main element" when we define the means that must realize the handling compare to the material to transport. The frames, motors and other elements, which constitute the transporters, must be considered as being in service for the belt and therefore, they will be defined compare to the belt. 1.4) The objective: Making the use of the belt " accurate and durable". For that, define its characteristics according to its use, the transported materials.. Choosing and adapting the materials that surround the belt in accordance with this one. Attention: It is very frequent to find installations for which the above rule has not been applied. These situations often end up to " dead-ends ", which turn out sometimes very onerous.



MASTERING THE TRAJECTORY OF A CONVEYOR BELT Mastering the trajectory of a belt,* It is to arrange the forces of the turning elements of the conveyor in the same direction; For that it is a must to determine the tolerance values of the forms and the positions of these elements. * It is to balance the right forces of tension / left of the belt according to the axis of the conveyor. For that it is necessary to determine and to appreciate the importance of the parasite forces.

2.1) The elements of the conveyor: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. The transported material The belt (belt, or carpet) The drive drum [+ its stressing drum] The drum of jetty [+ its stressing drum] The drums of the pouring trolleys The tension drum [+ its deviation drums] The tail drum (tail or discharge) The deviation drums The sliding supports or with rollers, return belt. The roller supports, return belt. The accessories: flanks, scrapers The annexes: feeding chutes(s)

* The frame must be considered that when it begets a variation of the position of one or of the turning elements. 2.2) Reminder: All those elements, the ones that compose the conveyor, generate or support forces. It is enough for one element to have a variable force so that the other elements see their forces fluctuate. Therefore the elements of the conveyor are " variables parameters". That state "unstable" leads to an " uncertain trajectory " of the belt, depending of the fact that those elements implicate forces of different directions. So, the conveyors are complicated machines, as far as physics is concerned. Mastering the trajectory of a belt, it is neutralize a maximum of variable then bring the conveyor to the state of a simple machine, it means to tension towards a system of forces of the same direction. That notion of physics finds its mechanical expression "at the near tolerance". It is about considering here the tolerances of forms and positions of the elements of the mechanical system that the conveyor represents. The value that is affected for each tolerance can only fixed in accordance with a minimum general tolerance of good functioning and of the number of interactive elements acting together (covered influence zones).


2.3) The quantity: The quantity of the transported material remains by force a variable parameter, it goes from 0 % to 100%. 2.4) The elements to neutralize: All the elements that have a movement of "revolution" must present "together" forces of one and same direction, They are drums and rollers, when they are included in same zone of influence. All the couples of elements "in friction" must be decomposed in surfaces "pairs" and present a symmetry of forces to the axis of the conveyor ; they are the couples belt/sole slipping, belt/ drum, belt/roller, material/belt, scraper/belt, mud flap /belt. All the elements that have a movement of revolution "with a related movement" must keep a constant of direction of forces; they are tension drums, the drums of the pouring trolleys, the drums are reserved from the belt. 2.5) Factors that can perturb the trajectory of the belts: It is matter of considering the modification of the state of an element, such as its occasional or permanent consecutive putting out of shape: - to an excessive effort, - to a moderated and repeated effort (it is "fatigue"), - or due to a report or a retreat of material. We then consider the revolution of the state of one or several conveyor. We find, for illustrating that situation: a) The deformations of the belt under an important load of product, asymmetric to the axis of the conveyor. In the case of slipping supports, that asymmetry of load is expressed by an asymmetry of friction resulting from the difference of the applied vertical force applied by the material on the belt by the material on the belt and which begets an unbalance of the pull forces. In case of roller supports, that asymmetry of load is expressed by an arrow of the belts between the supports, superior on one side compare to the other, then a resistance at the advance of the asymmetric belt. That resistant unbalanced factor is worsened by the crumbling of the materials pile on the belt, more important on one side then on the other and according to the cohesion of the material ( internal friction ) presenting a difference of resistance to compression, more or less important, at the passage of each support, that factor creates a supplementary unbalance of the pull forces. In the case of transition lengths that are too short and convex curves badly calculated, we notice, at term of (# 1), a permanent deformation of the sides of the belt; that modification brings a bigger sensitivity of the belt to the parasite forces (# 2). That deformation can be, on top of that, asymmetric which creates an imbalance of pull forces, that situation is worsened by a big sensitivity of the belt to the parasite forces, like previously.#1 at term = after some hours with several months of work, according to the excess importance, in number and in value. #2 parasite forces = forces that are acting in different directions to the normal forces of the conveyor.


In the case of a ratio "material width/total belt width" bending toward 0 %, with as worsening factor the materials of high densities, the conveyors of long distance between the head and the tail drums, the ascending conveyors, the conveyors of concave curve, the belts whose carcass structure lacks duitage , the belts functioning on drums which are too much convex. b) The deformation of the drums under the applied loads, or for the addition of material in an asymmetric way, or the retreat of material, at the axis of the conveyor can lead to belt drifts: In the case of excessive loads for the drum, this one bends in a way that its outline, for the part under the belt support, describes, in longitudinal (transversal view compare to the belt), a " concave curve ". In the case of material plugging on the ferrule whose thickness, even very weak, does not present any symmetry to the conveyor axis. What we commonly call " spuds " is not considered in the worsening factors as far as the direct belt drifts are concerned. The presence of those spuds finally lead to a localized deformation, longitudinal of the carcass, that observation leads us to the belt drifts due to the deformation of this one. In the case of wear in shape of "diabolo toy", more or less centered, more or less excessive. This type of deformation is the developer of abnormalities of the belt trajectory, it is matter of permanent oscillations, of weak amplitudes; in that case it is interesting to look for the real causes of those drifts on top of the r