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Paving Principles and Control Methods
How a Screed Works
8
P-32+ and P-32 Operator’s Manual P/ N: 1001547-01
Always check mat depth in several locations before making any elevation corrections. The surface being paved
may have wheel ruts, dips and ridges that gives an untrue indication of overall mat depth. Check several spots
to get an average (Figure 15). If an elevation change is made, wait 3 tow arm lengths for full correction. Too
many set point changes and stabbing causes raise and lower changes that produces an uneven mat surface.
Figure 15: Checking Mat Thickness
The screed has four main forces acting on it at all times, whether paving in manual or with automatics
(Figure 16). A change in any one of the forces causes the screed to rise or fall, changing the mat depth. The
key to smoother paving is to keep these forces as constant as possible. The following sections review these
forces and the factors that have an effect on paving.
Figure 16: Forces Affecting the Screed
Tow Point Force (P)
The tow point force (P) is the resistance to forward travel (Figure 17).
Figure 17: Tow Point Force ( P)
Avoid cranking while in Auto mode and keep the left and right rotation the same.
T
ow Point
(Force P)
Reaction of Material
Under Screed
(Force R)
Head of
Material
(Force M)
Weight of Screed
(Force W)
R
W
M
P
Vibration and Tamp
er
Tow Point
(Fo rce "P")
P
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