SECTION VII
Screed System
pre-heated, asphalt does not stick to the metal as the first
strike-off and smoothing begins.
The flat screed bottom can be bent at its midpoint so that
the single plane becomes two connected planes which
can be adjusted into a slight V-shape or into a slight
inverted-V (^) shape.
Such adjustment produces a
positive (^) or a negative (V) crowning contour on the mat
for the specified water drainage requirement. The contour
adjustment linkage is called the crown adjustment. (See
Figure 9)
Floating Screed Assembly
Figure 1
SCREED PRINCIPAL
The screed is a free floating attachment to the paver
which strikes-off and smooths the fresh asphalt after it is
spread by the screws. It is attached to the tractor unit by
means of two pull arms which are free to pivot at the pull
points located close to the forward end of the tractor.
(See Figure 1).
The height of the two pull-points for the screed, and the
angle of the screed bottom in relation to the pull arms, are
the factors which control the amount of asphalt deposited
on a roadway. The handwheels at the ends of the screed
which change the angle of "screed bottom to pull arm,"
are the operator's means of making adjustments of
asphalt deposit (mat thickness) whenever necessary.
Cut-away View - L.H. Screed Lift Cylinder
Figure 3
RAISING AND LOWERING SCREED
The raising and lowering of the screed is accomplished
by two double acting hydraulic cylinders connected to the
screed by cable and pulley arrangement (See Figure 3).
Cylinder movement is controlled by a toggle switch on the
console which operates a hydraulic system flow control
valve.
When the engine is at full throttle and the console
toggle switch is moved to UP, the screed will be raised to
Cross-section thru Screed and Material
its maximum elevation. When the switch is moved to
Figure 2
DOWN the screed will slowly descend to the ground. The
The screed is equipped with electric vibrators which
rate of descent is limited by a flow valve so that the
help to obtain the initial compaction of the fresh mat. It is
screed will not sustain damage and personnel in the area
also equipped with a heater which is capable of bringing
will not be endangered.
the temperature of the screed up to the temperature of
When the toggle switch i. in the central position the
the asphalt supply prior to paving start-up. When the
existing screed elevation is held by a hydraulic holding
screed is
valve.
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