Sytem and method for dewatering an acoustical tile basemat

A system and a method for dewatering an acoustical tile basemat comprising a continuously traveling wire， a device for depositing a dilute water slurry of solids including fiber and binder on the wire， a vacuum box below the wire for separating water from the solids deposited on the wire to form a basemat， a vacuum source， and a valve for cyclically connecting the vacuum source to the vacuum box at a cyclic rate that limits vacuum exposure to a length of the basemat newly arriving at the vacuum box to less than four inches per cycle. The problem is that vacuum removal of water from the wire supported mat is limited by a tendency for the mat to crack along lines transverse to the wire movement. When a vacuum box operating at a high vacuum relative to the water content of the mat， excessive shrinkage can occur locally in the direction of wire travel. The result can be a transverse crack developed across the mat that renders it defective for use as a finished tile. This is solved by the rate of vacuum modulation in relation to the conveying speed of the wire is high so that the mat is treated in small steps along the conveying length in a manner that may be compared to a jiggle or vibratory action. The modulated vacuum is less prone to produce cracking with the same vacuum level used in a traditional manner applied constantly to a vacuum box.