CLUTCH GP 1229222 - Caterpillar

There are several different types of screed available for use with the AP-1200. The comments that follow are, therefore, of a general nature.The screed is essentially a flat plate that rides on the asphalt mix to form the mix, finish it and provide the initial compaction. A tow arm at each end of the screed connects the screed to the tractor.Heaters that burn diesel fuel supplied from the tractor are used to heat the screed before the paving operation is started. An unheated screed will cause tearing of the mat. After the paving operation is started, the asphalt will keep the screed warm so the heaters are turned off.Adjustable vibrators mounted on the screed provide the initial compaction of the asphalt mix. The vibrators move the screed up and down, causing the weight of the screed to compact the asphalt. The vibrator speed must be adjusted to match varying asphalt mix characteristics and/or changing travel speeds.The screed is designed to allow the front to be crowned slightly more than the rear, if needed for proper flow of the asphalt mix. The crown of the mat placed by the screed is determined by the crown set in the rear of the screed.A mat thickness control is mounted on each end of the screed. The control raises and lowers the rear of the screed in relation to the front of the screed, causing the screed to ride lower or higher over the asphalt mix, thus placing a thinner or thicker mat.The tow arms connect the screed to the tractor at two points called the tow points. When the grade control system or slope control system is used, the tow point is moved up or down by the tow point cylinder to control thickness of the mat. When neither control system is used, the tow point is pinned in place.