Tractor Unit (Power Unit)The tractor unit provides moving power for thepaver wheels or tracks and for all powered machineryon the paver. The tractor unit includes the receivinghopper, feed conveyor, flow control gates, distributingaugers (or spreading screws), power plant (engine),transmissions, dual controls, and operator’s seat.The tractor unit power plant (engine) propels thepaver, pulls the screed (leveling) unit, and providespower to the other components through transmissions.Hot mix is deposited in the hopper and is then carriedby the feed conveyor through the flow control gates tothe distributing augers (spreading screws). The augersdistribute the mix evenly across the full width of thepaver, thus providing uniform placement of the mix ontothe roadway surface. These operations are controlledby the paver operator by means of dual controls withineasy reach of the operator’s seat. Figure 16-40 showsthe operating controls of one type of finisher used in theNCF.To ensure the paver functions properly, you shouldinspect the paver before commencement of paving.Below are some of the compments you should check.PAVER TIRES OR TRACKS.— When the paveris equipped with pneumatic tires, tire condition and airpressure must be checked. It is particularly importantfor the pressure to be the same in the tires on both sidesof the paver.When the paver moves on tracks(crawlers), the tracks should be checked to be certainthey are snug but not tight, and the drive sprocketsshould be checked for excessive wear. Low tire pressureor loose tracks can cause unnecessary movement of thepaver, which is transmitted to the screed unit, resultingin an uneven pavement surface. There should be nobuildup of material on the tires or on the tracks.GOVERNORS.— The governor on the enginemust also be checked to be sure that there is no periodicsurge in the engine rpm.When the governor is notworking properly, there can be a lag in power when theengine is loaded (strained). Such a lag causes temporaryfailure of the vibrators or tamping bars in the screed unit,resulting in a stretch of pavement that is less dense orFigure 16-40.-Operating controls, Barber-Greene model SA-35 finisher.16-36
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