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Conveyers
Figure 6-11.Wash and screen plant.

Equipment Operator Advanced - Advanced construction equipmet operators manual
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Figure 6-10.-Conveyer. rubber stripping of the wipers adjusted to just make contact  with  the  face  of  the  belt.  This  adjustment removes rocks from the belt, thus preventing rocks from entering between the pulley face and inside face of the belt. Three  factors  affect  the  efficiency  of  conveyer operation. These factors are as follows: speed, loading, and  incline. 1. Speed.  Most conveyers operate at a speed of approximately 300 feet per minute and have a capacity of  approximately  300  tons  of  material  per  hour.  A reduction  in  speed  obviously  reduces  the  conveyer capacity, and an increase in speed theoretically increases the capacity. An increase in conveyer speed may also increase wear on the conveyer belt due to increased slippage of the material at the loading point. An increase in speed also increases the throw of the material at the discharge end of the conveyer. In some cases, it may be necessary to fit the end of the conveyer with a box or bangboard so the material from the belt falls properly. 2. Loading. Proper loading of a belt conveyer is mandatory for efficent operation. This includes placing the load in a position centered on the conveyer belt. A good practice is to load a conveyer in such a manner that allows the material to strike the belt in the direction of travel. When material is to be delivered from a spout or belt to another belt from one side, a transfer box or bangboard  should  be  provided  to  facilitate  proper delivery on the belt. Loading a conveyer belt on one side causes it to run to the opposite side of the support rollers which results in excessive belt wear. 3. Incline. Portable  conveyers  can  be  adjusted  to operate at the various inclines required to meet job conditions. The maximum incline is determined by the material carried on the conveyer and varies from 12 degrees for washed gravel to 20 degrees for loose earth. When the maximum angle is exceeded, slippage may occur. WASH PLANT In many types of construction operations, it is not necessary  to  have  washed  clean  aggregates  in  the finished product; however, some types of operations require clean aggregates free of objectionable material. The  wash  and  screen  plant  (fig.  6-11)  consists  of  a scrubber,  a  vibrating  screen,  and  a  screw  (sand) dehydrator (fig. 6-12). In operation the raw material is fed   into   a   scrubber   designed   to   break   loose   all deleterious  material.  The  scrubbed  aggregate  and  wash water are cast upon a triple deck vibrating screen for size separation. The materials retained on the decks of the screen are sent by individual chutes to their respective conveyers for further disposition. The wash water and sand are carried through the third deck into the well of the sand dehydrator, where the undesirable products are removed from the sand by the abrasive washing action of the spiral conveyer and carried out into a flume by means of the overflow water. The clean sand is carried up and out of the water and discharged into a stockpiling conveyer. The capacity of the washing and screening plant is based on the percent of sand in the deposit; for example, each single screw washer can handle a certain amount of material. The screen is also a factor to consider when figuring the capacity of this plant. It is necessary to have enough  screening  area  to  handle  each  gradation  of material desired. 6-11







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