The primary functions of the machine are listed below.
- Receiving the asphalt
- Delivering the asphalt
- Metering the asphalt
- Spreading the asphalt
- Towing the screed
- Constant forward speed
- Constant supply of material to the hopper
- Uniform distribution of material to the screed
The machine performs three major functions. Each function is critical to overall performance of the paver. The quality of the mat depends on the three functions that are listed below.
Material Handling - Material that is deposited in the hopper is moved by the drag conveyor and the auger conveyor into position for the strike-off by the screed.
Mat Laydown - The thickness of the mat and the smoothness of the mat are established during screed strike off. The screed also compacts the mix.
Forward Movement - Because the screed does not operate without a machine, the machine controls the paving speed.
The primary functions of the screed are listed below.
- Controlling the width of the mat
- Controlling the depth of the mat
- Providing the initial finish
- Providing the initial compaction
- Providing the profile of the mat
To achieve proper control of the screed, the operator must understand the forces which affect the floating action and the self-leveling action. The floating action and the self-leveling action are the mechanical basis of the control systems that have been developed. These control systems increase the quality of the pavement.
The paver tows the screed with the leveling arms. A change in the angle of attack will cause a change in mat thickness. This controls the mat thickness. The material is pulled under the leading edge of the screed and compressed by the screed which produces a uniformly compacted mat.
If the base is level, the tow points will be level. The path of the screed will also be level. A level mat will be produced if no other forces affect the screed.
The machine typically travels over a wavy base. The screed follows the path of the tow points. The screed fills in the low spots. The screed levels the high spots. The mat will become more level with each pass of the paver over the base.
The self-leveling effect of the screed depends on the length of the high spots and the length of the low spots. If the distance between the high spots and the low spots is short, the screed will flatten the profile. If the distance between the high spots and the low spots is long, the screed will reproduce the same pattern.