Conveyors operating conditions

The mechanical design of the idler roUs is a function of the particular service under which the conveyor operates. Minimum industrial standards for roU dimensions, bearings, and appHcation criteria for different service conditions have been estabHshed (14). Idler life is deterrnined by a combination of factors such as bearings, seals, shell thickness, load density, and the operating environment. 

Labor expense, almost a negligible factor with belt conveyors, may be arbitrarily set at cts. per inch of width of conveyor per hour, irrespective of the load handled. Incidental expenses for supplies to keep the equipment in good operating condition vary closely with the power requirements and may be taken at % ct. per horsepower per hour. 

The most common way to size a conveyor dryer is to base the sizing on previons experience. Most conveyor dryer mannfacturers and many prodncers who use conveyor dryers have a large database of field test data, which can be used to size conveyor dryers. Typically, the sizing parameter is prod-net retention time in the dryer, based on a given set of operating conditions. Table 18.1 shows some typical retention times for conveyor-dried products. 

The motive power is provided by the primary driver, which generates the gas (typically air) velocity required to transport material within a pneumatic-conveyor system. Therefore, the efficiency of the conveying system depends on the primary driver s operating condition. 

Many times the actual operating conditions fall far short of the ideal. That is especially true for conveyor chain that cannot be enclosed. The chain designer must consider conditions that may be hostile to the chain. 

These conveyors can be furnished in extremely heavy-duty versions with great strength and rigidity. This allows them to operate well under severe operating conditions. 

The conveyor and collector parts are thoroughly insulated to reduce heat losses in diying and other heating operations. Operating control is maintained usually by control of the exit-gas temperature, with the inlet-gas temperature varied to compensate for changing feed conditions. A constant solids feed rate must be maintained. 

The belt conveyor is almost universal in apphcation. It can travel for miles at speeds up to 5.08 m/s (1000 ft/min) and handle up to 4539 metric tons/h (5000 tons/h). It can also operate over short distances at speeds slow enough for manual picking, with a capacity of only a few Idlograms per hour. However, it is not normally apphcable to processing operations, except under unusual conditions. 

Vacuum systems are typically used when flows do not exceed 6800 kg/h (15,000 Ib/h), the equivalent conveyor length is less than 305 m (1000 ft), and several points are to be supplied from one source. They are widely used for finely divided materi s. Of special interest are vacuum systems designed for flows under 7.6 kg/min (1000 Ib/h), used to transfer materials short distances from storage bins or bulk containers to process units. This type of conveyor is widely used in plastics and other processing operations where the variety of conditions requires flexibility in choosing pickup devices, power sources, and receivers. Capital investment can be kept low, often in the range of 2000 to 7000. 

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