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Paving Principles and Control Methods
How a Screed Works
10
P-32+ and P-32 Operator’s Manual P/ N: 1001547-01
The most common factor affecting force (M), the head of material, is incorrectly adjusting the Automatic Feeder
Controls.
These systems, whether of the “hanging paddle” type or the sonic sensor type, should be adjusted to operate
the auger/ conveyor assemblies 95% to 100% of the time. On/ off operation of the auger system causes
fluctuation in the head of material.
The highest quality mat generally results when a constant head of material is maintained across the entire width
of the screed and the material almost covers the auger shaft. If the volume of paving material is too high, there
is resistance to the travel of the screed. This causes the screed to rise and can result in ripples, auger shadows
and long waves. I t also results in increased auger wear (Figure 20).
Figure 20: Head of Material Affects Mat
Reaction of Material Under Screed (R)
Ideally, every truck load of material delivered to the paver would be exactly like every other load, with no
variation. However, as a practical matter, changes in mix characteristics such as mix temperature, density,
gradation, A.C. Content, segregation, etc., affects the internal stresses developed within the mix, which in turn
affects the resistance of the mix to flow under the screed, also known as the reaction of material under screed
Head of
Material
Too High
Screed Rises
Due To
Increased
Resistance
Correct
Head of
Material
Correct Depth
of Mat
Maintained
Head of
Material
Too Low
Screed Settles
Due To
Decreased
Resistance
Indicates Centerline
of Auger
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