Conveyor systems

However, such mixer—settler methods are continuous only by virtue of repeating a sequence of similar stages to achieve a given degree of extraction. More fully continuous methods of extraction were designed as tower systems and later as screw conveyor systems as effective methods of soHds transport became reHable. 

In the screw conveyor process, solutions of poly(vinyl acetate) and catalyst are mixed in a high intensity mixer and continuously introduced to a screw-type saponification and conveyor system (270). Downstream details are similar to those found in the belt process. 

The objects are conveyed through the beds by an overhead conveyor system. Fluid beds are used because of the high heat-transfer rate and uniform temperature. See Reindl, Fluid Bed Technology, American Society for Metals, Cincinnati, Sept. 23, 1981 Fennell, Jnd. Heat., 48, 9, 36 (September 1981). 

Crushed Stone and Aggregate In-pit crushing is increasingly being used to reduce the rock to a size that can be handled by a conveyor system. In quarries with a long, steep haul, conveyors may be more economic than trucks. The primaiy crusher is located near the quariy face, where it can be suppRed by shovels, front-end loaders or trucks. The crusher may be fully mobile or semimobile. It can be of any type listed below. The choices depend on individual quariy economics, and are described by Faiilkner [Quairy Management and Products, 7 6), 159-168 (1980)]. 

Initial cost of a conveyor system is usually related to life ejqjectancy as well as to the flow rate chosen. There is a great temptation to overdesign, which should be resisted. The first really longdistance belt conveyor was designed and fabricated to extremely hi standards of quality. After 35 years it was still in operation with almost all its original components. Had this operation been planned for only... 

Comparative costs for conveyor systems can be based only on studies of specific problems. For example, belt-conveyor idlers are available in a range of quahties that may make the best unit cost three times as much as the cheapest. Bearing quahty, steel thickness, and diameter of rolls all affect cost, as does design for easy maintenance and repair. Therefore, it is necessary to make cost comparisons on the basis of a specific study for each conveyor application. 

While successbil and economical system designs can be devised by experienced process engineers, the competent technical aid available from equipment supphers has led to a growing trend toward the purchase of complete systems, even on small jobs, rather than iu-plaut assembly from components on the basis of in-house designs. An idea of the change in capital investment for typical pneumatic-conveyor systems as a function of increasing transfer rates is given in Table 21-12. 

Slide Conveyors Simple gravity slides and spiral chutes, while not technically conveyors, are widelv used with conveyor systems or as separate units for lowering materials from one floor to another. They are low in cost and require httle floor space if slopes are held at fairly steep angles. However, they must be used only after a careful study... 

Because of the steep pitch required, slides are limited in application. They are most commonly used to bridge the gap between roller-conveyor systems on two floors, because the roller conveyor can take the container off the slide rapidly and ehminate or reduce the chance for collisions. Slides may also be used when containers can be chuted from an upper floor to a manually loaded carrier. The use of several rollers at the feed point is recommended for easy dehveiy to the sloping section. If the drop is short and containers light, a roller cleanout will prevent backup of containers on the slide. The slope of gravity slides is a function of container weight, size, and friction characteristics and should be selected with care to be sure that containers do not move either too swiftly or not at all. Slides usually use flat steel sheet. 

Personnel Hazards The following case history illustrates how vacuum can be harmful and dangerous to personnel. A plant superintendent was checkiug an open nozzle on a glass-lined reactor on which there was a vacuum pump pulling vacuum, when suddenly his arm was sucked into the nozzle, up to his shoulder. He could not remove his arm until help arrived to release the vacuum on the vessel. He was injured painfully, though not seriously. The injury could have been veiy serious if help had not been nearby. Personnel hazards can also result from vacuum conveyor systems for solids handling. 

Consider a conveyor system, requiring an average torque of 100% during pick-up. The motor data are as follows ... 

The conveyor belt is one of the most efficient devices available for moving goods over short distances. Billions of tons of minerals, foodstuffs and consumer goods are handled in this way every year. Figure 28.1 shows the essentials of a typical conveyor system. The following data are typical of the largest conveyors, which are used for handling coal, iron ore and other heavy minerals. 

Fig. 28.1. Schematic of a typical conveyor system. Because the belt tends to sag between the support rollers it must be kept under a constant tension T. This is done by hanging a large weight on the tension drum. The drive is supplied by coupling a large electric motor to the shaft of the drive drum via a suitable gearbox and overload clutch.

These fires are caused by heat produced by, for example, inadequate lubrication, poorly controlled cutting or grinding operations, of maladjustment of power drives and conveyors. Friction can be created by two moving parts, or by one moving and one stationary part, as can be found in a conveyor system. 

Polyurethanes are manufactured by the mixing of various resins, isocyanates and catalysts to produce an exothermic reaction, which liberates the foaming agent and causes the mix to expand. They are made in large block molds as a batch process or are continuously foamed onto a paper or polythene substrate on a conveyor system. 

The loading on each roll is generated by the belt, wire mesh, and/or transported product. The amount and distribution of the load varies depending on the wrap of the carried load. Wrap refers to the angular distance around the roll that touches the belt, wire mesh, or product. In most conveyor systems, the load is relatively uniform and is in a downward direction. In this case, the traditional vertical, horizontal, and axial mounting positions are acceptable. 

A baghouse system consists of the following pneumatic-conveyor system, filter media, a back-flush cleaning system, and a fan or blower to provide airflow. 

As in any other pneumatic-conveyor system, special attention must be given to the piping or ductwork used to convey the dust-laden air or gas. The inside surfaces must be smooth and free of protmsions that affect the flow pattern. All bends should be gradual and provide a laminar-flow path for the gas. 

Wheels and tires are one of the major uses of cast polyurethane elastomers. We commonly see these on fork lift trucks and shopping carts, where their excellent abrasion resistance, resistance to oil, and good elasticity are valued. In industrial settings we find polyurethane covers on rollers used for paper, steel, and textile conveyor systems. In such applications, their excellent cut and abrasion resistance help prolong their useful life. If used in hot and humid conditions, polyether-based polyurethanes are preferred. 

Conveyor systems are applied in a number of areas in the rubber industry. The types used can range from simple canvas belt conveyors used for haul-off from conventional extruders, to systems used for transport and cooling of profile products, both in and emerging from continuous vulcanisation units. The latter types have to be resistant to the temperatures used in such systems and are variously constructed from glass fibre-reinforced polytetrafluoroethylene or a silicone rubber covered belt. 

Other areas of use of conveyor systems are for transport of rubbers and chemicals to mixers, for carrying product from various sources to further processing and packaging. 

Heat Treatment Heat treatment can be divided into two types, treatment of fluidizable solids and treatment of large, usually metallic objects in a fluid bed. The former is generally accomplished in multicompartment units to conserve heat (Fig. 17-28). The heat treatment of large metallic objects is accomplishecTin long, narrow heated beds. The objects are conveyed through the beds by an overhead conveyor system. Fluid beds are used because of the high heat-transfer rate and uniform temperature. See Reindl, Fluid Bed Technology, American Society for Metals, Cincinnati, Sept. 23, 1981 Fennell, Ind. Heat., 48, 9, 36 (September 1981). 

Design of the overhead conveyor system for the caustic bath should be tested to demonstrate satisfactory reliability. 

The COINS process uses an overhead conveyor system that collects metal parts containing explosive energetics components (fuzes and bursters) into baskets that are moved through a tank containing a caustic bath that hydrolyzes the energetic materials in the metal parts. No propellant is sent to the COINS. 

The most significant worker safety issue will probably be maintenance of the conveyor system through the caustic bath of the COINS. 

In the earlier ACW I Committee s report on the Eco Logic design, the most significant worker safety issue was expected to be maintenance of the COINS conveyor system by personnel in DPE suits (NRC, 1999). The conveyor system was to operate immersed in a hot caustic solution. The ACW II Committee s Demo II report noted the COINS process had been changed to provide for an overhead chain conveyor system to move the immersed baskets in the caustic bath (NRC, 2001b). The committee remains concerned that the COINS will require significant maintenance by personnel in DPE suits and finds that efforts to minimize maintenance should continue. 

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