The extend-a-mat screeds are equipped with strike-off plates (1) .
The strike-off plates limit the amount of material that reaches the screed plates. On the extenders, the strike-off plates also function as moldboards. On the main screed, the strike-off plate is a narrow strip that is attached to the bottom edge of the moldboard.
The strike-off plates are equipped with two adjustment screws (2). These screws allow the operator to make fine adjustments to the position of the strike-off plates in order to accommodate different mix consistencies.
Note: The adjustment screws for the right extender plate are shown in Illustration 2. The left extender plate and main screed plates are similar.
The strike-off plates are adjusted at the factory so that the bottom of the shield is approximately 26.7 mm (1.05 inch) higher than the bottom of the screed plate. The factory setting can be used to pave with mixes of average consistency. The plates should be raised when the mix is sandy. The plates should be lowered when the mix is coarse.
Center of Main Screed
The center of the main screed can be raised or lowered in order to provide a ten percent positive or to provide a three percent negative crown. The screed is equipped with a power crown control mechanism.
The power crown control uses electric motor (3) in order to turn two adjustment screws (4). One adjustment screw is at the front and one adjustment screw is at the rear of the main screed frames. A chain connects the front and rear adjustment screws. The crown switch is located at the right screed operator station. The crown switch controls the electric motor.
Scale (5) near the crown control mechanism indicates the approximate crown which has been applied to the main screed.
Scale (5) should only be used for reference. The mat should be checked for the actual crown. Fine tuning may be required to obtain the desired crown.
Right Side of Screed
Fine adjustments can be made to the mat thickness on the right side of the screed by using right thickness control screw (6). The left side of the screed is equipped with a thickness control screw which can be used to fine tune the mat thickness on the left side of the screed.
Thickness control screws (6) can be used to null the screed before the start of operation. In order to null the screed, the screed should be lowered onto a flat surface which is the same thickness as the desired mat thickness. The tow point switches should be used to center the tow point cylinders. The thickness control screws should then be rotated until the controls turn easily for approximately one half of a turn. In this slack area of the controls, the screed is in the null position.
During operation, thickness control screws (6) can be used to make minor changes in the angle of attack. This provides fine control of the mat thickness.
Thickness control screws (6) are equipped with positive locking mechanism (7). This mechanism locks the screw in place while the screed is paving.
Thickness control screws (6) on the extend-a-mat screed are available with the following one of four different Acme thread configurations: clockwise standard thread, counterclockwise standard thread, clockwise course thread and counterclockwise course thread. When the thickness control screw has the clockwise standard thread configuration, clockwise rotation of the screw increases the angle of attack. Therefore, the mat thickness increases. Also, the counterclockwise rotation decreases the angle of attack.
Scale (8) can be used as a reference to indicate the approximate change in the angle of attack.
The screed extenders are attached to the main screed through a triangular support configuration. This structure provides the extenders with torsional resistance and rigidity.
The extenders can be used to vary paving width. The extenders can also be raised, lowered, and tilted in relation to the main screed. The screed width switches at the main screed operator stations and the screed width switches at the extender operator stations are used to extend and retract the extenders. A single hydraulic cylinder at each extender serves as the actuator to move the extender. Scale (9) indicates the distance that the extender has been extended. Each extender is equipped with a fixed walkway. The walkways allow the operator to move between operator control stations without walking on the mat.
Right Side of Main Screed
The extenders can be raised 64 ± 6 mm (2.5 ± 0.25 inch) above the main screed. Also, the extenders can be lowered 25 ± 6 mm (1 ± 0.25 inch) below the main screed. The extend-a-mat screeds are equipped with a power extender height control mechanism.
The power extender height control uses electric motor (10) to turn an adjustment screw that raises and lowers the extender as a unit. The main screed operator stations are equipped with the extender height control switches that operate the electric motors. Extender height scale (11) shows the amount of adjustment in 6 mm (0.25 inch) increments.
At the initial setup the extenders should be set a distance of 6 mm (0.25 inch) higher than the main screed.
The outboard edges of the extenders can be lowered in order to provide a maximum positive slope of 10 percent (76 mm (3 inch) below horizontal). Electric motor (13) is used to pivot each extender. Slope scale (14) indicates the percent slope.
Note: The extender height scale and slope scale should be used for reference only. The mat should be measured in order to determine the actual position of the extender. Fine adjustments to the position of the extender may be necessary in order to obtain the desired shape of the mat.
The screed is equipped with one spring-loaded end gate, outboard of either extender. The end gates prevent material from flowing around the screed. Also, the end gates create the longitudinal joint during paving.
Two spring-loaded jacks (15) control the height of each end gate. When a jack is rotated clockwise the following occurs: the corresponding side of the end gate lowers, the spring force decreases and the available vertical travel increases. When a jack is rotated counterclockwise, the corresponding side of the end gate rises, the spring force increases, and the available vertical travel decreases. Guide bolts (17) allow the end gate to travel vertically and follow the profile of the surface that is being paved. springs (16) keep the gate in contact with the surface.
The springs should always be adjusted in order to provide sufficient movement that will allow the end plate to follow the profile of the surface that is being paved. If the springs are not properly adjusted, the screed may ride on the end gate. As a result, there will be increased wear on the end gate and possible quality problems with the mat.
When the initial lift is laid, the end gate should be adjusted in order to allow the end gate to ride on the grade. When a longitudinal joint is to be matched, the end gate should be adjusted in order to allow the end gate to ride on the adjacent mat.
Each extender and the main screed are equipped with flat screed plate (18). Curved nose bar (19) is installed at the front of each screed plate. Two checks can be made on the screed plates that checks thickness and flatness. As a general rule a screed plate should be replaced if the plate is less than 3.175 mm (0.125 inch) thick.
The screed plates should be flat to within 0.76 mm (0.030 inch) at the following areas: along the front edge, along the rear edge and diagonally. If a screed plate is not flat along the front edge, rear edge, or diagonally, adjustment screws (20) can be used to adjust the front and rear edge.
Note: The screed should be in the null position with no crown before any flatness checks are made.