Conveyors and Elevators

Lengths of screw conveyors usually are limited to less than about 150 ft when the conveying distance is greater than this, a belt or some other kind of machine should be chosen. The limitation of length is due to structural strength of the shaft and coupling. It is expressed in terms of the maximum torque that is allowable. Data for torque and power of screw conveyors are given in Table 5.4 and are applied to selection of a conveyor in Example 5.3. 

Size and Power Requirement of a Pneumatic Transfer Line 

A pneumatic transfer line has 300 ft of straight pipe, two long radius elbows, and a lift of 50 ft. A two-stage cyclone is at the receiving end. Solid with a density of 1251b/cuft is transferred at the rate of 10 tons/hr and the free air is at 5000 ft/min. Inlet condition is 27psia and 100°F. Investigate the relation between line diameter and power requirement. 

On a first pass, the effect of pressure loss on the density of the air will be neglected. 

Assume air and solid velocities equal. Elbow radius = 122). Elbow equivalent length, 

The angle of repose is a measure of the incline at which conveyors such as screws or belts can carry the material. The tangent of the angle of repose is the coefficient of sliding friction. This property is a factor in the power needed to transfer the material by pushing or dragging as in pneumatic, screw, flight, and Redler equipment. 

Allowable loadings as a percentage of the vertical cross section depend on the kind of material being processed examples are shown in Table 5.4. 

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Belt Conveying Troughing and Betum Idlers, CEMA Standard502-1980, Conveyor Equipment Manufacturers Association, Rockville, Md., 1980. Conveyor and Elevator Handbook, 3rd ed.. Rubber Manufacturers Association, Washington, D.C., 1988. 

Magnetic pulley, conveyors, and elevators, rotary cooler, screening, crusher-mixer Particulates (dust) Exhaust system, cyclone, and baghouse... 

The classifier described above works very well with coarse particles where exact splits are not needed. Typical applications are in connection with ball or rod mills for reduction to particle sizes between 8- and 20-mesh. These classifiers have high capacities they lift coarse solids for return to the mill, so that auxiliary conveyors and elevators are not required. There are other types of classifier that must be usual for close separations with fine particles. One such device is the centrifugal classifier its action bears a strong resemblance to that of the crossflow classifier, but the settling is greatly accelerated by the substitution of centrifugal force for gravitational force. 

Closing Comments. Most kinds of conveyors and elevators are obtainable from several manufacturers, each of whom builds equipment to individual standards of sturdiness, materials of construction, mechanical details, performance, and price. These differences may be decisive in individual cases. Accordingly, a selection usually must be made from a manufacturer s catalog, and ultimately with the advice of the manufacturer. 

The kiln, 220 feet long and 15 feet in diameter, is equipped with a four stage preheater similar in layout to the Genstar plant. Whole tires are fed, one at a time, into the riser duct just above the kiln feed housing through a trap door and isolation chamber. Tires are handled using a conveyor and elevator system that picks up one tire at a time. 

Mechanical Conveyors and Elevators 76 Properties of Materials Handled 76 Screw Conveyors 76... 

Classification of Equipment.—Equipment for the mechanical handling of materials may be classified as the carriers which carry the material in a limited but continuous stream (endless conveyors and elevators), and the hoists, trucks and railways which carry more concentrated, and frequently more compact, loads more or less intermittently. This classification will be adhered to so far as practical to simplify a logical selection of handling equipment for the industrial establishment and consideration of equipment will parallel the passage of the material, commencing with its delivery. 

Classification.—The classification and terminology for conveying and elevating equipment has grown quite confused and as conveyors are frequently installed at an inclination so that they elevate as well as convey, it is well to classify such material handling equipment as carries a continuous, or approximately so, load under the one head of conveyors and elevators, to distinguish them sharply from other material handling equipment which handle more intermittent loads. 

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