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THE BELT CONVEYORS Knowledge & Adjustment

Continuous Professional Training Course of Mr. Marc des Rieux

des RIEUX SAS au 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

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BELTS CONVEYORS

SUMMARY

I)

DEFINITION

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

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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)

TRANSITION LENGTH

VII)

CONVEX CURVE

VIII) CONCAVE CURVE IX)

ADJUSTMENT OF A CONVEYOR BELT.

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THE BELT CONVEYORS

I)

DEFINITION

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.

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II)

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).

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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.

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∗ 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 replacement of the defective drum. However there exists a particular case or the wear in "diabolo shape" of a drum is a worsening factor; that concerns the succession of three drums having wrapping angles close to 90°/180°/90°, in that case, the belt is alternatively drifted from right to left and conversely from a drum to another; once arrived at an extreme amplitude, the movement goes opposite again and so on. In that case, it is evident that the change of drums is a must ; a wear presenting a bend of 5/10 mm is already significant, the first drum to be damaged is always one of the two drums of 90° of wrapping angle. The change of drums does not make exemption to searching and find a solution to the main problem, which allowed the beginning of the wear process for the drums. c) The deformation of the roller supports and the state of the rollers properly called or the one of the soles and sliding skates truly bring disorders on the trajectory of the belts. The first handicap in the understanding of the drifts begotten by these elements is determined in the multitude of the elements to consider and the accumulative total of defaults for each element, knowing that certain defaults of the "supports" will be more or less active according to the variation of other parameters like the material load on the belt, the vibration of one sieve, the wind. In annex, there is a list for the main changes of the state of the supports. d) The variation of the tension existing in the belts is a worsening factor for the situations of precarious balance. In fact, if the existing tension, during the observed moment for a belt drift, cannot be the real cause, the direct cause of the drift, in the case of symmetry of the forces to the conveyor axis (in value and direction), it allows, by its simple variation, the ascendancy of the parasite forces, pre-existent, origin of the system unbalance. That observation values as much for variations toward superior forces as for the inferior forces to the initial values.

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∗ The conveyors ascending or descendant, of strong output, of long length, are more exposed to beget those variations of tension at the ends of the (conveyor) length. ∗ The conveyors equipped of pouring trolley present also important annoyances, especially if they are equipped of breaks placed at the head of the frame. For that type of material we should be afraid of the sagging of the belt between two supports at the foot of the concave curve (having the raising toward the drum at the top of the trolley) at a stopping moment, when the section of the belt preceding the rise toward the top of the trolley if fully loaded; therefore the material is poured out on the internal side of the return belt, then goes to pollute the extremity drum and this begets the drifting of the belt. 2.6) Other factors that can perturb the trajectory of the belt: All the forces related to the passage of the material on the conveyor are sources of belt drifting. It is specified at the beginning of the text that the variation of output of the material is a variable factor that is inescapable whose effects must be limited by element that are sufficiently proportioned. In this chapter "other factors" we have to consider the perturbations related to the parasite forces that are generated by the handling of the material. We find, for illustrating that situation: a) The problems that are related to the presence of inlet chutes and/ or feeding hoppers, at the capacity banks, which beget "frictions" asymmetric to the axis of the conveyor in the case of badly studied materials. The belt drifts are due: ∗ To the differences of the material flow, then of pressure in the hoppers or feeding chutes. ∗ To the differences of the material flow between the capacity banks. ∗ To the differences of pressure on the belt, generated by a granulometry segregation during the passage of chutes, in the case of feeding under an axis of different direction at the reception conveyor axis. Here it is matter of affecting the responsibility of belt drifting to the bad design of the chutes. ∗ To the incorrect material centering by the chutes. The 4 articles, here above, have in common, as factor of belt drift, a very important gap of the total forces on the right side of the conveyor axis compare to the ones on the left side. For solving this type of problem, either we delete the cause by working on the geometry of the chutes, or we make the parasite forces insignificant compare the main forces by over sizing the elements of the conveyor, starting with the belt. These two solutions are not always easy to implement. b) The problems that are related to the overflows of materials. These overflows pollute the return belt, They are transported up to the drums and they drift the belt. They are due: ∗ To the rebounds in the zone of putting the material in speed, either because the material arrives so quickly (with too much energy) on the receiver belt, or because the speed of the receiver belt is very important compare to the speed of arrival of the material. The worsening factors are the conveyors that are strongly sloping, the rolling materials, the raised belts (rafters, battens), in this last case, the raised ones play like the whip of a kid who is striking his top (toy).

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∗ To the lengths of transition that are too long. It is matter of considering the time of material heap compare to the time that the belt takes to cover the distance from the last trough support (trough of the current length) to the drum of jetty. The worsening factors depend on the weak cohesion of the materials, of the rolling materials. ∗ To the under-speeds of the belt, consecutive to a too much important output of material (absorbed power superior to the installed available power). In the same kind of default there is lateness of feeding output; In this case it is matter of problem of chute or/ and of speed related to material/ belt. ∗ There exists a case of overflow that is very particular on the sloping conveyors which is due to the excessive presence of water in the material during the transport. The water builds up and piles up between the belt and the material until this one is lifted when the quantity of water has reached a sufficient value, and the whole thing slips towards the tail of the conveyor.

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III)

TERMINOLOGY OF THE MATERIALS

Types and outlines of the conveyors: 3.1) Longitudinal View: The conveyor is:

- straight horizontal - straight upward of x° (or x %) of slope - straight descendant of x° (or x %) of slope - straight vertical = elevator - straight + 1 bend "concave" - straight + 1 bend "convex" - straight + 2 bends "concave and convex" - with multiple sections (straight, concave, convex, curved in the plan)

For all the conveyors, it is a must to know the total elevation height, the slopes and the radius of the curves. An ascendant conveyor consumes energy. A descendant conveyor can produce energy.

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Elevation height Upward Straight conveyor

Descendant Vertical Elevator Belt width

Belt width

Conveyor length conveyor with bend Conveyor length Concave curve conveyor with double bend

convex

Elevation convex curve

Concave With multiple curves in the plan Top view

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3.2) Transversal view: The shape of the support(s) The belt moves on a support (or on supports) " flat " The belt moves on a support (or on supports) " V " at 20°, 25°, 30° The belt moves on a support (or on supports) " trough " at 20°, 25°, 30°, 45° The belt moves on a support (or on supports) " deep trough " at 60°, 90° The troughs are regular (standard), deep or large. The nature of the support(s) The support(s) is (are) constituted by a slipping sole, by slides. The support(s) is (are) constituted by rollers, by garland rollers It is a must to use a form and a type of support that is adapted to the belt. Notably the slipping soles corresponding to belts of internal face without coating. The weak coefficient of fabrics friction, associated to the relief of these ones, enable its functioning. Not retaining this rule has often as consequence destroying first the gearboxes, then the belt by a suction disc effect. We should make sure as well we do not use V or trough shapes for carcass belts, which is steep in grid. The preceding paragraph puts in evidence the distinction that is done between the shape and the nature of the supports.

Outline: support form

flat

In V for x°

In regular trough with 3 rollers of x°

In special trough

Type of support Turning supports Rollers

Supports with slipping surface

Sole

Sole

Bar or skate

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3.3) Particular cases: The measurers and weighers (weighbridges) Their function: measure a quantity, a mass of material either in continuous movement, or in intermittent movement. They require a particular care as far as the homogeneity of the belt is concerned. The junctions must have a minimum effect on the weighing devices, for the measures. measure and weigher

Materials forbidden for commercial

The extractors: Their function: extract directly the material under a hopper or silo. There is then no free space between the two materials, the belt make therefore the bottom of the hopper or of the silo. The nature of the material, the section, the height of the column in support on the belt, the speed are determining for the choice of the components of the transporter. The drainage doors represent often traps in those materials. It is must, in principle, to give privilege to an important door opening height for a reduced speed of the belt advance. To define this type of application, there are particular calculations.

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3.4) Other elements that serve to define a conveyor: The conveyors are defined as well by their width and their length. For the width, it is about the width of the belt in millimeters. The conveyor length is given in millimeter or meters. This measurement is not enough to know the length of the belt. In certain cases the width of the belt can be equal or superior to the conveyor length. Developed length, without end, of a belt (∅ t1 +∅ t2)
+ (2 x conveyor length) = length without end 2 buying length = length without end + junction It is the manufacturer of the belt who, himself, must precise the necessary over-length for the junctions. He also must precise the number of belt reels to be delivered for the big conveyor lengths, which determines the number of junctions.

Drum 2

Drum 1 Conveyor

Developped length = (∅t1 x π x α1)+( Rc x 2 x π x αc)+(∅t 2 x π x α2)+(∅t3 etc. jusqu'à t9) + 360° 360° 360° EA1 + EA2 etc. up to EA9. In the case of an utilization "big cold", consider the retreat according to te nature of the carcass and ∆t temperature. Length. s real end = Lengths calculated end x ∆t. (t°u - t° 20° C) ∆t = coefficient of expansion per ° C per m. linear t°u = utilization temperature (even at stop)

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Direction of movement : The movement direction of a belt is defined by the direction of the material movement. We say that: - the belt is pulled when the drive drum is at the head. - the belt is pushed when the drive drum is at tail (tail). - the belt has double direction, then it is pulled and pushed alternately. In that case, a particular care is brought in the choice and the assembly of all the elements that compose the transporter (see paragraph belt, drums, supports). During the calculation of the conveyor, we have to " necessarily " proceed according to the two possibilities belt "pulled" et "pushed"; that concerns notably the values to apply to the tension systems and to be determined according to the radius of the concave curves. The conveyors that are equipped of pouring trolley present often abnormalities of functioning having as origin partial calculations.

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IV) THE TRANSPORTED MATERIALS (compare to the belt) 4.1) Restraints due to the material To determine a belt it is a must to know well, of course, the restraints that will be imposed to it. The transported materials will have on the belt some influences : PHYSICAL } CHEMICAL } or THERMAL }

a combination of all 3

The physical influences are: The load, the abrasion, the punching, the cut, the fouling. The chemical influences are: The range of the materials is so large that it is always careful to make tests. A aggressive material for a belt will make its mechanical resistances drop down. The thermal influences: Are as destructive for low temperatures under 0° C (of the order of -10°C, -20°C, -30°C an more); as for temperatures above 20° C (of the order of +70° C to +250°/+400° C and above). WE HAVE TO RETAIN OBSOLUMENT THAT ALL TECHNICAL CHARACTERISTICS, THE MECHANICAL RÉSISTANCES OF THE BELTS ARE GIVE ON DOCUMENTATION

FOR A USE AT "20° C"

4.2) Other imperatives imposed by the materials: We also have to consider supplementary factors when we determine a conveyor belt compare to the transported materials. We mean sanitary restraints, material fragility, the weight of the daily work, weekly work, incident frequencies (starting in full load), industrial risks (cost of production stop), manufacturing standards. The objective being to move a material from a point A to a point B, we have to know the quantities in volume and in mass, for a peak output and for an average output, the distance and the height of elevation (or the difference in height) of the transport.

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.3) Calculation of a belt The standard to know: NF H 95-203 (ISO 5048) Determination of a conveyor belt. Calculation of the forces, output and section. 4.4) The outputs in "Volume", in "Mass" The transported quantity is expressed by the output which is very often given in tons / hour. In that case we should not forget, especially, to calculate the output in m³/ hour because before all a belt transports a "volume". For that, we have to know the density of the material when this one is in movement : It is the apparent density. This density may be very different from the "Physical" density, considering the presence of air in the pile: material of heterogeneous shapes and granulometry, material that emulsifies. Not respecting that rule has always got as consequences to see the material overflowing from the belt and making the installation dirty, which has got as second consequence to provoke the dysfunction of the belt In that case, it will be useless to talk about belt adjustment. To adorn this problem, we can often increase the output by increasing the speed or / and the linear capacity which mean by increasing the trough value. But pay attention when modifying these parameters you can also make some new constraints to occur (abrasion, patination during start etc.).

Tobacco leaves Density : 0.08

Zin ore Density : 5.5

1 masse unity Ratio between these 2 example densities: 68.75

1 mass unity

-

A belt, as all the " containers " carries before all : A VOLUME The outputs are often given in tone/hour: t/h Always, we have to take care of calculating the output in cubic meter / hour: m3/h for that we have to know the Density of the material in movement. when the density reduces, the volume increases, when the density increases, the volume reduces.

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4.5) Influence of materials on the trajectory of the belt : In a belt drift due to a material that is badly centered, the amplitude of that drift is very uncertain; because many factors intervene, it is difficult to have a situation that is foreseeable of equilibrium (centered) for the belt trajectory and that this one is satisfying for the minimum outputs to the maximum one. By experience, despite the real report of a material that is badly centered on the belt, it turns out that a neutral position of the turning elements and a sufficient pre-tension of the belt reduce, even supersede, the belt drift. But pay attention, by modifying these parameters you can also make new restraints appear.

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V) THE ELEMENTS THAT CONSTITUTE THE TRANSPORTER : 5.1) The belts: Description: The belts are composed of carcass and coating(s) The types of carcass: There are "mono-pleat " carcass and "multi-pleats " carcass with an inter-pleats rubber assuring the liaison of the pleats. In the case of thick inter-pleats the rubber serves in addition to the protection against shocks and punching. For information, There are belts without carcasses. The polyester (E), the polyamide (P), the cotton (C), the metal (S), the glass (G). Other materials: the Kevlar, the polyethylene, Nomex (aromatic polyamide) The carcass constitution: The chain and grid cables are of the same material. The chain and grid cables are in different material. The grid cables are in mono-filament of big diameter (stiff). The weavings are straight, of SOLIDWOVEN type, with superposed chain and grid (steel carcass), with cable, then without grid (steel carcass). There are carcasses with pleats of different natures (example: Round Baller agricultural machine). Abbreviations: E = polyester P = polyamide Lengthening due to rupture: E = 15 % P = 23 % Lengthening of service of: E = 1,5 % (under 10% of load of rupture) The metal, the glass has a lengthening of service of 0,25 %. Certain references of belt with metal carcass have a lengthening of service 0,6 to 0,8 %. The nature and the number of pleats have a direct influence on the diameters of the drums. The inter-pleats are of the same material like the coatings, or of different materials. They also contribute to the protection of the carcass; inter-pleats strong thickness will be more resistant against punching but will necessitate bigger drums; (see standard NF T 47-103). Standards of fabrics in resistance against rupture for lengthening N/mm : 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630. We must consider these values at the junction in accordance to the type of junction.

THE CARCASS ENDURES THE TENSIONS AND THE CHOCS

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5.2) The coatings: THE COATINGS PROTECT THE CARCASS The used materials: The natural rubber = NR, the SBR, NBR, IIR, EPM, NCR, CR, PVC, PU, silicone, Teflon, leather, felt, PE, PP For information, there belts without coating. The coatings protect the carcasses against abrasion, punching, heat, cold, all sorts of chemical products, fire, static electricity. They have a function of capacity in the case of rafters, battens and buckets, sides. They have a function of drive with the relief of bee nest type. A function of guidance with the trapezoid guides.

Calculation of tension for a belt and for its counterweight of tension: (annex file)

THE CHOICE OF A BELT MAKES NUMEROUS PARAMETERS INTERVENE. IT IS THEN VERY IMPORTANT TO CLASS IN DECREASING ORDER THE CHOICE CRITERIA FOR EACH APPLICATION. TO RECLASS THIS HIÉRARCHY AS THE EXPERIENCE ON THE FIELD GOES ALONG BY A MATERIALS’ FOLLOW-UP.

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THE BELT CONVEYORS Interaction of the components: It is matter of determining the influences of all the components of a handling by belt conveyor, as well on the resistant forces, the absorbed powers as the utilization constraints that are specific to each component. 5.3) The frame It is by definition the skeleton of the transporter and supports the whole of the elements that compose the transporter including the bulk (materials) to handle. Its first quality is to be stable in the time, as well in its form as in its dimensions. It must neither fold, nor subside under the load. It is desirable that it is not sensitive to its environment; for example to the vibrations of a sieve, to the heat of an oven, to the wind blows, etc. 5.4 ) The gear box group No matter the used energy or the model of material, the power* expressed in kW will be retained and if it is equipped of a system of progressive start. Do not neglect the systems of breaks which can have a "power" widely superior to the motorization, it is the case of the descendant transporters. ∗ From Installed Power: we have to know the efficiency of the group of command up to the drum shaft. This efficiency is in general of 0,9 for the coaxial gear boxes, it can go down up to 0,45 for the gear boxes with wheels and screws. The efforts of traction on the belt will be: - maximums in DIRECT start (and superior to the ones of the stabilized movement regime) - rising with an equipment "PROGRESSIVE" (and will not overpass the ones of the stabilized movement régime.)

That information will be determining to evaluate the coefficient of security for the resistance against belt rupture. Knowing that that resistance against rupture is defined compare to the motor power and to the speed we also have to know the "Speed" given to the belt and expressed in meter/second (m/s).If this one is fixed or variable, we are supposed to know the minimal and maximal values. The frequency of starts under load is to be considered as well. Note: For a "given power" and a "given output" : - the more we increase the speed of the belt the more the necessary resistance against rupture reduces. - the more we reduce the speed of the belt the more the necessary resistance against rupture increases. (see § calculation).

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5.5 ) Tension systems: They are classed in two categories. • The tensions whose run is "invariable in service" irrespective of the jolts of load applied on the belt. They are for example the screw tensions. • The tensions whose course is "variable in service " in accordance with the applied loads. They are for example the counterweight tensions. The function of a "system of tension" is to apply a defined force (calculated) and of a direction that is opposed to the forces resisting the traction of the drive drum. When we apply a force of traction on any material, we provoke its lengthening according to its nature and its size (section). The mechanical characteristics of the material under traction as well as other values will allow to determine the necessary course of the tension. The tension system is not used to adjust the belt, but practically it is true that in numerous cases the " tension system " totalizes these two functions. Manage the trajectory of the belt by an action on the geometric position of the tension drum often underlines the absence of the research of the defaults which are the origin of the problem. The tension can partially serve to catch up the over-length of the soft belt side. On the big conveyor lengths it is preferable to realize a pre-tension by the good care of your vulcanizer. Calculation of a tension: (see calculation of a belt Paragraph 6.3.3)

AFNOR NF H 95-203

In the practice, very numerous belts function "over-tensioned". A good principle wants that we apply a tension that is equal to the 2/3 of the nominal value (value issued by calculation) and only in case of "slipping" we increase "if necessary" and progressively that tension after having, of course, eliminated the causes of slipping and without over passing the nominal tension; otherwise we should look for the error! Example: Scraper, flanks in excessive pressure, belts and drums that are wet or have fat, the same for certain dusts (case of the calculation with as conditions "clean environment"), unreliable drive drum, without rubber coating, wrongly assembled, belt in friction with the belt. Particular case: For the belts with double direction it is often necessary to tension them "to the maximum of the calculated value" in order to assure them a good guidance (only by the drums) by reducing (or canceling) in this case the effects due to a load which is incorrectly shared out. In certain cases from elsewhere, we will use a type of belt superior to the calculated value. Example: calculated type 250 N/mm, recommended type 315 N/mm even 400 N/mm. Precautions: On the transporters with counterweight tension notably, we often find a succession of drums that are close to one an other: the more the length of the drums is important, the less the uncertainty on their geometrical position will have influence on the trajectory of the belt.

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Run Run = 50 mm 100 mm Belt : F = 0.5

Belt : F = 0.5 Anchorage = 0.5 t Angle : superior to 5° = drum Angle : inferior to 5° = roller

F=1t at the hook -% of the efficiency ( 1%)

Anchorage = 0.5 t P = Spacing f = curve

Limits prescribed by the standard H95-203 #6.3.3 Æ F = 0,5 at 2 % of P Value of the wrapping angle on the rollers Æ 2.α  2. tangent line α = 2. f ½P Example For a spacing of 3000 mm Æ ½ P = 3000 = 1500 m 2 for a curve of 1% Æ f = 1 % of P = 30 mm the wrapping angle on the roller = 2 α α = tang. α = f = 30 = 0,02  1° 8' 26" meaning 2 α  2° 16' 52" ½ P 1500 Measurement of the tension of a belt in accordance with the spacing of the rollers and of the belt curve, Measurement of its curve in accordance with the tension and with the spacing, Measurement of the spacing in accordance with the tension and with the curve: Prescriptive reference: NF H 95-203 #6.3.3 (correspondence ISO: 5048) Calculation of the Tension T = P²x m x g 8xf

Calculation of the curve Calculation of the Spacing f = P²x m x g P=⌦ Tx8xf 8xT mxg

T : the tension applied on the belt "at the measurement place" = value in N P : spacing between two consecutive belts supports = value in m m : mass " at the measurement place " = value in Kg/m linear either the mass of the belt alone / or belt + material / or belt + material + impact energy (feeding) 8 : factor in the expression of a parabola f : belt curve mesured at ½ supports spacing = value in m (Pay attention on frequent errors of conversion of the measurement unities)

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5.6 ) THE DRUMS

Standards ISO 3, 1536, 251, 583, 7590. NF T 47-103, T 47-004, T 47-111

It is prudent to distinguish the drums and the rollers, their uses are different. - For the drums we have the high loads of geometric qualities with tighter tolerances. - For rollers we have weak loads with medium geometric tolerances. Wrapping angle of the belt

180° and

Drums domain

Near another

Far from another

Rollers domain

The name of the drums that correspond to the location that they occupy on the frame ; the order of the goes from the drum that supports the strongest load to the weakest. The standard class them in three categories: A, B, C A Drive drum A Motor drum (it is a drive drum whose gear box is integrated in the ferrule of the drum.). A Head drum, drums for the pouring trolleys B or A Tale drum (for dismissal) B or A Tension drum or counterweight drum C Stressing drum C Deviation drum C Bend drum

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You will notice by yourself that this hierarchy goes from the drum to the strongest load towards the on with the weakest load is strongly respected in the technical manuals from the belt manufacturers. In fact, they indicate the diameters of rising values according to the above bill of materials. The technical documentations always indicates the minimum diameters recommended compare to a belt reference which is well precise; that value is not forcibly suitable for two belts of the same type, meaning of the same resistance to rupture to the lengthening that is given in (N/mm) That minimum diameter corresponds for a use at 100% of the load capacity of the belt in reference. In certain case, it is possible to reduce that minimum diameter when we are sure that the belt will always be used with half load, as well in transported product as in traction force, but pay attention to the temperature and fatigue factors (this one depends on the frequency of a flexion of the belt around a drum).

1: head drum 2: tale drum 3: tension or stressing drum 4: constraint drum 5: deviation or inflexion drum

Pulled Head drum = Drive drum

Pushed Tail drum = Drive drum Drive drum on return belt

internal face pulling

carrying face pulling

run c : Tension run

Counterweight tension Bolt

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5.6.2) The forms of drums : NF T 47-004 In principle, a drum is a cylindrical form with a well centered axis. But, in order to obtain an effect of centering of the belts, a convex form is given to the ferrule. Actually, a convex drum enables to resist to the parasites forces which are superior to the cylindrical drum. The general rule is to keep a cylindrical form for 1/3 of the width of the belt in the middle of the drum (maximum 40% of the length of the drum), the adjacent parts, right and left having a form of a cone trunk. The standard AFNOR NF T 47-004 indicates: ∅ d = ∅ D - 1 % for belt carcasses That have an lengthening und load of reference, at 10 % of the rupture, of 0,8 % to 1,6 %. Example : the carcasses in polyester (E) The carcasses with weak lengthening in metal, glass, Polyamide, the convex is invalid ∅d= ∅D-0% Note: The width of the belt does not intervene at all in the value of the convex.

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Form of the drums called convex according to NF T 47-004 ∅d= or

∅ D x 0,99 ∅D-1%

value given for the carcasses whose lengthening under load of reference* is between 0, 8 % and 1, 6 % of lengthening.

* The lengthening under load of reference is an lengthening which is measured under a tension (a load) that is equal to 10 % of the tension (the load) of rupture, for example the belts with polyester carcass (E).

Length of the Drum Width of the Drum = B

In maximum 40% of the length of the drum

The belts with metal carcass, glass, Kevlar ® are excluded from this standard. Their lengthening under load of reference is of 0,25 %. The drums must be cylindrical. In the case of small diameter of the drum and of big width of the belt, the slope resulting from the difference of the diameters D and d is practically void, then without effect of " guidance ". In this case of big width (1200, 2000 mm and +) a multi- convex can be utilized. This method comes to consider that our belt is equivalent to a number "x" of belts. We can also increase the guidance efficiency of a convex form by increasing the friction coefficient (of adhesion) belt/drum by realizing a rubber coating. Particular case: The drums " squirrel cage ". These drums have their ferrule made of metallic barrettes, straight, arched (convex) or not, set on the circumference of the flasks with a spacing which is more or less tight. At the origin this type of drum was utilized on dirty installations to avoid plugging of the transported material on the drums. It would have, as it seems to us, been more convenient to improve the cleanness of the transporter (except in particular case: the elevators). The followers of this type of drum have the conviction to obtain a better drive for the belt. No scientific calculation with equal use has proved it. The elements to retain in order to determine the transmission factor:

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The factor of transmission corresponds to the drive capacity for the belt by the drum. It depends : - on the coefficient of adhesion belt/drum; which changes depending on the nature and the state of the present materials. - on the contact surface belt/drum; this one is equal to the width of the belt by the length of the wrapping angle on the drum, if this surface is full, and it is reduced from the surface of grooves or empties, if the surface of the drum is structured. - On the tension force that is applied to the belt; this one is measured near the drum (see NF H 95 203, # 6.3.3). Save a polygonal effect of the barrettes of the squirrel cage (then a certain increase of the "tension" factor), the other factor are widely unfavorable. The results " pull force " is then not more favorable with the drums of the squirrel cage type. In practice, we have often noticed that the belts turning on the transporters with drums of "squirrel cage" type were over-tensioned. In the cases of normal tensions, the belt ware presenting, internal face, important and significant traces for slippage on the drive drum . 5.6.3) The materials and surfaces of the drums: The main role of the drums is to lead the belt, to tension it, to enable it to change direction. High loads correspond to those functions! It is then evident to manufacture the drums in steel sheet of strong thickness. Their handicap is to have a coefficient of medium adhesion; on the other hand, when an object passes between the belt and the drum it is the belt which suffers (punching by the internal face) if that object is hard, if the object (material) is soft or of fine granulometry it will form “potatoes” or a dandruff of material which will drift the belt and will also deform the belt carcass. Facing those problems, it is very effective to garnish the drums with rubber, either with smooth surface*, or with structured surface (grooves). The most common quality is the natural rubber. According to the chemical restraints, thermal (hot or cold) or sanitary other qualities of coating are used. *smooth surface coating: this is justified only when we can guarantee a real cleanness of both surfaces in contact (belt and drum), which is practically a rare case; the we have to prefer the structured surface!

The hardness of the rubbers which is expressed in Shore A, for a drum coating, depends on the resistance to rupture at the lengthening of the belt, on its rate of utilization and of the category of the drum (A,B,C). In general, we use rubbers of 45-50 Sh for the types up to 400 N/mm, above that we pass to the rubbers of 65-70 Sh. There again, the width of the belt is not to be retain as criteria of choice for the hardness of the rubber. As well the thickness of the coating follows the rules which are similar to the preceding paragraph. It goes from 2 mm to 8 mm, even 12, 15, 20 mm. A weak thickness of drum coating, of medium hardness (45-50 Shore), foreseen for an installation that have a belt of strong resistance to the rupture, risk of getting stuck by " delaminating ". We notice the same phenomenon with the rubbers of weak elasticity. (see table on the following page)

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Table of hardness and thickness of the rubbers of drum coating, in accordance with the resistance to the rupture of the belt and its rate of utilization (% of the RMBT): ÎResistance to the rupture / rate of utilization at 100% RMBT -/-