Swarf or other material to be dewatered is delivered to the extruder feed hopper. It accumulates until a pre- determined level is reached, at which time a load sensor signals the extruder PLC, initiating the dewatering cycle described below.
While in the forward compression cycle (see next page), the top of the ram box seals the bottom of the feed hopper. Upon commencement of a new cycle, the hydraulically powered ram fully retracts. As the ram face passes beneath the hopper, the hopper bottom is exposed, allowing a new batch to drop into the charging chamber (see above). Once the ram has fully retracted, the control system initiates the next forward cycle of ram movement.
The extruder discharge plenum, which was wide open during the previous forward compression cycle to permit discharge of dewatered solids, now partially closes. Its separate hydraulic motive system accumulator remains charged, maintaining pressure on the plenum in this position until additional solids are compressed, dewatered and ready for discharge.
As the compression cycle begins, the ram face passes the forward edge of the feed hopper. The top surface of the ram box seals the feed hopper bottom. During the forward movement of the ram, newly charged wet material is pressed with progressively increasing force into previously compressed partially dewatered material that is restricted in its forward movement by the partially closed discharge plenum.
Liquid (effluent) extraction occurs as the ram pressure increases in programmed steps, causing liquids and a minor amount of very fine particulates to be expelled through small perforations in the walls, roof and floor of the dewatering chamber. Usefully, these perforations have an outwardly tapered self-relieving design which acts to prevent blinding and impairment of liquid extraction. Expelled effluent is collected in a pan positioned beneath the extruder. This flow may be directed to a pump box for delivery to a holding tank or other disposition.
As each programmed level of ram pressure is reached, the forward movement of the ram is halted temporarily to permit full evacuation of liquid from the innermost section of the dewatering chamber. This patented, time interval controlled compression technique is the key to producing a uniformly dry solids discharge product.
As the ram nears the end of its forward travel, pressure within the dewatering chamber reaches the maximum desired level for effective liquid expulsion. Pressure sensors acting in concert with the extruder control system cause the discharge plenum to open fully, permitting ejection of a dewatered solids cake into a container. Control of the plenum opening is modulated by pressure sensing from within the dewatering chamber. The cycle is complete. The ram box retracts and a new cycle begins.