Paving Principles and Control Methods
How a Screed Works
7
P-32+ and P-32 Operator’s Manual P/ N: 1001547-01
Figure 12: Screed Determines Mat Thickness
Because the screed floats, it does not immediately react to a change in the tow point. It needs a certain amount
of time or distance to make a correction in the mat thickness (Figure 13).
If the tow point is changed by a unit of one, the paver must move one tow arm length before the screed
corrects 63% of the elevation.
After 2 tow arm lengths 83% of the correction is made and 3 tow arm lengths would account for 95% .
It takes 6 tow arm lengths to achieve 100% of the elevation change.
Considering that 95% of the change takes place after 3 tow arm lengths, this can be used in practical
applications to qualify for full correction.
Figure 13: Tow Arm Travel
The same is true when making elevation changes with the manual thickness cranks (Figure 14).
Figure 14: Manually Changing Mat Thickness
Tow Point Path
Tow Point Path
1 Tow Arm
Length Travel
2 Tow Arm
Lengths Travel
3 Tow Arm
Lengths Travel
4 Tow Arm
Lengths Travel
5 Tow Arm
Lengths Travel
6 Tow Arm
Lengths Travel
63%
87%
95%
98%99%100%
Elevation
Change to
Tow Point Path
Tow Po int Path
Tow Po int Path
1 Tow Arm Leng th Travel2 Tow Arm Leng ths Travel
3 Tow Arm Leng ths Travel4 Tow Arm Leng ths Travel5 Tow Arm Leng ths Travel6 Tow Arm Leng ths Travel
63%
95%
98%
99%
100%
Change in Screed
A ngle of Attack
fro m Cran k
87%