Material handling systems range from simple pallet rack and shelving projects, to complex conveyor belt and Automated Storage ND Retrieval Systems (AS/RSI). A more fundamental way of grouping the methods used for the bulk handling of materials, especially from the standpoint of the mechanics involved, is to consider the three main groups as: 1 . Continuous methods, 2. Semi-continuous, or many small batches, methods, and 3. Batch methods. Further division of the methods can be according to the means by which the material is moved. The following means can be used: 1. Carriers, 2. Pushers, 3. Eiders, 4. Fluid suspension, 5. Rails, 6. Road 7. Hoists and cranes, 8. Fluid borne. Different systems can be used for bulk transport of materials as shown in Table 1 . Group Section System 1 . Continuous A. Carriers (I) belt conveyors (it) other continuously moving conveyors B. Pushers (I) open chain conveyors closed chain conveyors (ill) screw conveyors and feeders C. Guiders (I) chutes (it) shaker conveyors (iii) vibratory conveyors D. Fluid suspensions (I) open flumes (it) suction pipe hydraulic (iii) pressure pipe hydraulic (v) suction pneumatic (v) pressure pneumatic 2.
Semi-continuous other conveyors (ill) monorails (iv) bucket elevators v) aerial replays (I) chain conveyors (iv) roller conveyors 3. Batches A. Rail (I) rope-hauled (it) locomotive-hauled B. Road (I) trucks special vehicles C. Hoists and Cranes (I) cranes hoists and lifts (iii) cablecast D. Fluid borne (I) boat airplane 2. Belt conveyors 2. 1. Definition A conveyor belt is a continuously moving strip made of an endless strap stretched between two drums as in Fig 1. Figure 1 This very simple feature is suitable only for very short distances and low outputs.
To deal with longer distances it is necessary to support the top “strand” of the conveyor t regular intervals to reduce endue sagging, and to reduce the spillage of material which may occur if the belt does not run truly, while maintaining a high carrying capacity. These two requirements are met by “thorough idlers”, which consist of three separate rollers to support the belt and also bend it into a trough shape. The two outer and smaller, rollers are tilted upwards at an angle of 250-300, as in Fig. 2. Figure 2 The lower strand of the belt does not require support at as close spacing as the top strand, and it can be allowed to remain flat. . 2 Angle of wrap 2. 2. Angle of wrap 2. 2. 1. 1 Angle of wrap for an open belt The driving drum relies on the friction between drum and belt to provide the drive to the belt. The lower strand tension depends on the belt being sufficiently tight all along its length for some tension to be remaining at the point Just after the belt leaves the driving drum. The angles of wrap for an open belt are given by (Fig. 3): Figure 3 2. 2. 1. 2 Angle of wrap for a crossed belt Figure 4 The angles of wrap for a crossed belt drive may be determined by: 2. 3 Tensions ratio 2. 3. 1 Tensions ratio for a flat belt
Let consider a differential element of belt. The forces acting on the differential element are: TTL is the belt tension in tight side (N), TO is the belt tension in loose side (N), 0 is the angle of wrap of belt on pulley (radar), 0 is the coefficient of friction between belt and pulley dry is the normal force (N), OR is the frictional force between belt and pulley that always opposes the tendency to move (N). Figure 5 Setting up an arbitrary x and y for the element of belt such as the y direction coincide with the direction of normal force and considering the differential element in equilibrium yields,
For small angles and dropping out differentials of second order, Taking the moment about the pulley center yields, Combining (1) and (2) gives, 2. 3. 2 Tensions ratio for a V-belt Normal force and frictional forces in a V-pulley are shown in Figure 6 is the frictional force that is caused by the normal force which rectangular components are and , but not alone. As a result, on Figure 6, the resultant of the frictional force is (+) = but not Figure 6 The resultant component of the normal force in Y direction is Setting up an arbitrary y direction for the belt element in figure 4. Such as it incises with the direction of normal force and considering the differential element in equilibrium yields, Since in the limit for small angles and dropping out differentials of the second order, Figure 7 Combining (3) and (4) yields, The tensions ratio for V-pulley drive is then given by For , we recover the tensions ratio of a flat pulley. For a long conveyor with a large hauling duty TTL requires to be large, and so the biggest value of TTL possible can be obtained by increase a snub pulley or by using more than one driving drum. 2. 4 Effective belt tension – Maximum belt tension The resultant component of TTL
Effective belt tension. The effective belt tension, or the Setting up an arbitrary y dire( head 0 can be calculated from the total power required coincides with the direction o conveyor as follows Where is the effective belt tension in N Since in the limit for small an, Maximum belt tension. The maximum tension can be e effective belt tension as follows Or or Where is the non-slip ratio. The value of is assumed to conveyor belting on a steel drum, 0. 35 for rubber on la a layer of rubber), the corresponding values for p. V. C b respectively. 2. 5 Belt stress – Maximum permissible belt stress
The maximum tension in tight side of belt for a bare p on the allowable stress of the belt material. The calculi tension can be used to find the belt stress as follows Where is belt stress in ink/m per ply of belting material Taking the moment about the is the width of the belt in m, is the number of plies. The calculated maximum stress can then be compare stress for any particular type of belting. 2. 6 Major components of a belt conveyor Major components of a conveyor belt are the belt, the c drive, the belt cleaner, the take-up… The tensions ratio for V-pulley) 2. 6. 1 Belt For , we recover the tensions 1 2. 1. 1 Types of belts Different belts used to for conveying bulk materials ma For e long conveyor with a Ian Rubber belt. The so-called rubber belt is used almost u cotton duck “carcass” which provides the strength necessary to transmit the pull and give body to the belt so that it can carry the load. Several plies can be bounded together such as the top and bottom are protected by rubber covers. The number of plies depends on the pull to which the belt is to be subjected. If the distance the material is to be conveyed is too large, reducing the pull may enable to use a single envenom instead of two in tandem.
The top, or carrying side, is protected by a heavier thickness of high-grade rubber, which resists the impact of the load. The bottom cover protects the belt from damage by impact against the idlers, prevents impregnation of dirt, and takes, or transmits, the driving traction. Stitched canvas belts, usually impregnated with oil or gum, are applied for the lighter duty of handling packages. Blast belts are of duck impregnated and cemented with blast gum. Flat steel belts, often sliding on hardwood decks, are used sometimes for special conditions. High-Temperature Belts.
Rubber belts will withstand temperature up to about 1220 C. This limit is increased to about 1490 C with synthetic-rubber belts. Woven wire belts are used where higher temperatures are involved. 2. 6. 1. 2 Belt design The belt width is determined by the capacity, the weight of the material, and the size of lumps. The width of the belt depends also on the maximum size of lumps in the material and whether it has been screened or is a mixture of lumps and fines. The belt thickness, or number of plies, depends on the pull to which the belt will be subjected, and the cover thickness depends on the severity of service. 6. 2 Carrying and return idlers The spacing between idlers depends on the weight of the material, since, if the idlers are so widely spaced that the sag between idlers becomes excessive, power is wasted, the belt wear increases, and if the conveyor is inclined there is a slippage of material due to impact at carrying idler. 2. 6. 3 Drive A high-speed motor, which costs less and occupies less space, is preferable to a slow- speed motor, and so there must be a speed reduction gearing between the motor and head shaft. The total power required at the driving drum is given by
From the above formula, we can see that for a given maximum belt tension the power which can be transmitted to the belt depends on the arc of contact 0, and the coefficient of friction 0 at the head pulley. For a fixed maximum tension, we secure a lower slack side tension TO by lagging or snubbing, to increase the of the drive without increasing Tama We can increase the coefficient of Fri. 0. 25 for rubber on steel to 0. 35 for rubber on rubber by lagging (with a lay rubber) the head pulley. The limit with a single pulley is reached when we pulley and snub for maximum arc of contact (see figure 9).
Figure 9 But we may increase the arc of contact by using dual pulleys, preferably the motor drive head pulley as a driver (see Figure 10) Figure 10 For a fixed maximum tension, we can secure a lower slack side tension TO b or snubbing, to increase the capacity of the drive without increasing Tama 2. 7 Carrying capacity of belt conveyors The carrying capacity of a belt conveyor is the mass of the load conveyed pee time or mass flow and can be expressed as Where Cap is the carrying capacity of the belt in keg/s a is the average cross-sectional area of the material conveyed by belts in is the speed of conveyor belt in m/s. Is the bulk density in keg/mm 2. 7. 1 Average cross sectional area of material The average cross sectional area of material conveyed by belt depends on t of material. Blocky materials such as broken rock, coal or ore can be piled o belt and the value of the average cross-sectional area is high as shown in If value of the cross-sectional area in this case of high loading is given by Where W is the width of the belt in m. Figure 11 The average cross-sectional area for smooth material such as sand or grain tends to run out over the belt (Fig. 12) is given by Figure 12 2. 7. Sulk density The value of the bulk density d relates to the density of broken material including air spaces, and not to the solid relative density. 2. 7. 3 speed For small conveyor the speed is kept to about 1 m/s, but for carefully aligned conveyors speed up to 3 m/s can be used. 2. 8 Power required by a belt The power required by a belt can be divided into three components: 1 Power required to drive the empty belt, Pee. 2. Power to convey the material, Pm. 3. Power to raise the material, Pr. The total power required at the driving drum of the conveyor (or at the belt), is then given by
The value of Pr is subtracted when the material is being lowered as this helps to run the belt, and the power requirement for this is thus negative. The drive must have sufficient reserve power not only to pull through possible overloads, as in starting up, but also to overcome the frictional resistance in the gearing at the trailhead, and is given by Where is the motor power in W, is the efficiency of the drive. 2. 8. 1 Power required to drive the empty belt The power required to drive the empty belt depends on the total force to move the empty belt that is given by: Fee = total weight on idlers x friction coefficient.