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Figure 16-38.-Two common types of asphalt finishers.
Screed Unit

Equipment Operator Basic - Beginning construction equipment operators manual
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Tractor Unit (Power Unit) The tractor unit provides moving power for the paver wheels or tracks and for all powered machinery on the paver. The tractor unit includes the receiving hopper,  feed  conveyor,  flow  control  gates,  distributing augers (or spreading screws), power plant (engine), transmissions,  dual  controls,  and  operator’s  seat. The  tractor  unit  power  plant  (engine)  propels  the paver, pulls the screed (leveling) unit, and provides power to the other components through transmissions. Hot mix is deposited in the hopper and is then carried by the feed conveyor through the flow control gates to the distributing augers (spreading screws). The augers distribute the mix evenly across the full width of the paver, thus providing uniform placement of the mix onto the roadway surface.   These  operations  are  controlled by the paver operator by means of dual controls within easy reach of the operator’s seat. Figure 16-40 shows the operating controls of one type of finisher used in the NCF. To  ensure  the  paver  functions  properly,  you  should inspect the paver before commencement of paving. Below  are  some  of  the  compments  you  should  check. PAVER TIRES OR TRACKS.— When the paver is  equipped  with  pneumatic  tires,  tire  condition  and  air pressure must be checked. It is particularly important for the pressure to be the same in the tires on both sides of  the  paver. When  the  paver  moves  on  tracks (crawlers),  the  tracks  should  be  checked  to  be  certain they are snug but not tight, and the drive sprockets should be checked for excessive wear. Low tire pressure or loose tracks can cause unnecessary movement of the paver, which is transmitted to the screed unit, resulting in an uneven pavement surface. There should be no buildup of material on the tires or on the tracks. GOVERNORS.—   The  governor  on  the  engine must also be checked to be sure that there is no periodic surge in the engine rpm. When the governor is not working properly, there can be a lag in power when the engine is loaded (strained). Such a lag causes temporary failure of the vibrators or tamping bars in the screed unit, resulting in a stretch of pavement that is less dense or Figure 16-40.-Operating controls, Barber-Greene model SA-35 finisher. 16-36







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