Conveyor belts

Tunnel dryers are shown in Fig. 3.15a. Wet material on trays or a conveyor belt is passed through a tunnel, and drying takes place by hot air. The airflow can be countercurrent, cocurrent, or a mixture of both. This method is usually used when the product is not free flowing. 

No contact with the material, no moving parts to wear out or corrode Unaffected by changes in the tension or stiffness of the conveyor belt Direct readout and adaptabiUty to modem controls... 

In the spunbond process (Fig. 10), an aspiratory is used to draw the fibers in spinning and directiy deposit them as a web of continuous, randomly oriented filaments onto a moving conveyor belt. In the meltblown process (Fig. 11), high velocity air is used to draw the extmded melt into fine-denier fibers that are laid down in a continuous web on a collector dmm. 

In the spunbond process, the fiber is spun similarly to conventional melt spinning, but the fibers are attenuated by air drag appHed at a distance from the spinneret. This allows a reasonably high level of filament orientation to be developed. The fibers are directly deposited onto a moving conveyor belt as a web of continuous randomly oriented filaments. As with meltblown webs, the fibers are usually thermal bonded or needled (53). 

The high speed continuous filament process (69) was first used for manufacturing in 1974, and this enabled the yam production rates to be raised from 150 to 380 m /min. This system uses a pair of net conveyor belts to protect and transport an overfed warp of yams through washing and drying. 

Transportation. For short distances from the mine, transportation (qv) is by tmck or conveyor belt. Rail transportation is generally used for greater distances. Slurry pipelines (qv) ate being considered as an alternative. Rail transport over hundreds of kilometers results in loss of surface material in uncovered cats and a tendency to overheat in bottom-dumping tail cats owing to air infiltration around the cracks (31). Proper sealing and covets permit shipping over hundreds of kilometers. 

Dry soHds, such as as-rnined ore, emshed ore, and dried concentrates, are transported using tmeks, rail cars, ore passes, conveyor belts (see Conveying), or slurry pipelines (qv) as dictated by the logistics, distances involved, and capacity. Within the mill, conveyor belts are more common, but for fine particles, tailings, and coal, slurry transportation is more typical. 

Magnetic pulleys are available ia diameters from 152 to 1524 mm and ia widths that match the conveyor belt width. The material burden on the belt, belt speed, and type of tramp iron expected to be encountered are all considerations ia magnetic pulley selections. 

Selection. The magnetic pulley width should match that of the belt. The face width is normally 51 mm wider than the belt width up to 1067 mm wide, and 76 mm on widths ia excess of 1219 mm. The speed of operation of the conveyor belt should be determined by calculating the maximum capacity to be handled. Using this iaformation, the diameter of the pulley required to handle the capacity can be determined (Table 2). The operating belt speed must be acceptable for the diameter selected. If the recommended belt speed is exceeded, the pulley diameter that can handle the belt speed must be used. 

Automatic discharging suspended magnets can be operated transversely (Fig. 2) or parallel to conveyor flow (Fig. 3b and 3c). Because the tramp iron must be attracted from a buried location and turned 90° from the movement of the conveyor belt, a larger and stronger magnet is required for a transverse installation. In some instances, the material handling layout, or desired operation location, dictates the use of the transversely mounted magnet. 

Fig. 2. Self-cleaning suspended magnetic separator over conveyor mn (cross-belt), where A = conveyor belt width B = distance to magnetic belt.

Fig. 3. Suspended magnets, where A = conveyor belt width B = suspension height C = overall height D = distance to magnet centerline and E = location of lift point, (a) Manually cleaned over conveyor mn system, (b) manually cleaned over head pulley, and (c) self-cleaning separator over head...

Draglines are equipped with a 71-m bucket at the end of a 111-m boom and can be employed to dig both a portion of the overburden, which is free-cast into the mining pit, and the tar sand, which is piled in windrows behind the machine. Bucket-wheel reclaimers, similar to bucket-wheel excavators, load the tar sand from the windrows onto conveyor belts which transfer it to the plant. 

Textiles are among the most ubiquitous materials ia society. They provide shelter and protection from the environment ia the form of apparel, as weU as comfort and decoration ia the form of household textiles such as sheets, upholstery, carpeting, drapery, and wall coveting, and they serve a variety of iadustrial functions, eg, as tire reinforcement, tenting, filter media, conveyor belts, iasulation, and reinforcement media ia various composite materials. 

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