contains slightly less material than the immediatelyadjacent area. After rolling, you can see that an areashows up as a transverse ripple in the pavement. Apower lag can also interfere with the smooth andconsistent operation of the electronic screed controls.HOPPERS, FLOW GATES, AND AUGERS.—The hopper, the slats on the feed conveyor, the flowgates, and the augers should be checked for excessivewear and observed to be certain they are operatingproperly. Necessary adjustments should be made toensure that these components are functioning asdesigned and are able to deliver a smooth flow ofmixture from the hopper to the roadway. This includesadjustments to any automatic feed controls.The speed of the conveyor and the opening of thecontrol gates at the back of the hopper should beadjusted, so just enough mixture is being delivered toFigure 16-41.-Tamping bar.the augers to keep the augers operating about 85 percentof the time.‘This allows a uniform quantity of mix to bemaintained in front of the screed.When additional mixis required to allow an increase in the thickness beingplaced, the flow control gates should be adjusted.Augers should be kept about three-quarters full ofmixture during paver operations.Screed UnitIn operation, the screed is pulled along behind thetractor unit. The long screed pull-arms are pivoted thatpermits the screed to have a floating action, as it travelsalong the road. As the tractor unit pulls the screed intothe mix, the screed seeks the level that allows the pathof the screed to be parallel to the direction of pull. Atthis level, all of the forces, acting on the screed, are inbalance, as the paver moves down the road. The screedplate irons the surface of the mixture, leaving the matthickness at a depth that conforms with job specification.Mat thickness and crown shape are regulated by screedcontrols.Tamping bars (fig. 16-41) or vibratoryattachments then compact the mat slightly in preparationfor rolling. Figure 16-42 shows the workings of ascreed.Attaining proper mat thickness is a matter ofbalancing the forces, as shown in figure 16-42, with oneanother.1. To maintain forward motion of the screed, forceP must be greater than force H.2. To increase the thickness of the mat, tilt thescreed plate so that more material is crowded under thescreed plate.The screed will rise until the finishedsurface is again in a plane parallel to the direction of pull.Figure 16-42.-Forces acting on the screed.16-37
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