A self-propelled spreader is shown in figure 16-31.This machine moves forward and makes possible auniform and continuous application of cover aggregate,because it is capable of keeping up with the asphaltdistribute. The spreader is self-powered and has areceiving hopper in the rear.Aggregate trucks arehitched to the spreader, dump their loads into the hopper,and are pulled by the spreader. Belt conveyors carry theaggregate to the front of the machine where it is droppedinto the spreading hopper (fig. 16-32). Aggregate flowsover a spread roll onto a screen that permits initialplacement of larger particles on the asphalt, followed byfine aggregate on top.Calibration and adjustments for all types ofaggregate spreaders should be made according to themanufacturer’s instruction and operating manual. Hereare some additional checks that should be made toensure good results:1. A tachometer, used as an aid in maintaininguniform spreader-box speed, is most helpful.2. Distribution rates are closely controlled bymeasuring off the length that each truckload ofaggregate should cover.3. A quick check on the rate of application ofaggregate can be made by laying a 1-square-meter(yard) section of cloth or building paper on the pavement(or by supporting a shallow l-square-yard box above theasphalt with nails or screws) and by passing over it withthe spreader. The cloth, paper, or box is then carefullyFigre 16-31.-Self-propelled aggregate spreader.Figure 16-32.—Flow of aggregate through a self-propelled aggregate spreader.16-27
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