Mat forming apparatus

A mat forming apparatus comprising an air temperature and humidity control chamber, a supply-air plenum, a first fan having an inlet connected to the temperature and humidity control chamber and an outlet connected to the supply-air plenum, a chopper room connected to the supply-air plenum, strand choppers in the chopper room, a forming hood beneath the choppers for receiving chopped strands from the choppers, an endless conveyor chain beneath the forming hood for collecting the chopped strands, forming them into a mat, and transferring the mat away from the forming hood for further processing, a chopped strand collecting chamber for collecting chopped strands which happen to pass through the conveyor chain, a suction chamber disposed beneath an upper flight of the conveyor chain and having an inlet communicating with the forming hood through the conveyor chain and an outlet communicating with the chopped strand collecting chamber, nozzle-forming downstream convergent baffle plates in the inlet of the suction chamber, a second fan having an inlet connected to the chopped strand collecting chamber and an outlet connected to the temperature and humidity control chamber, each of said first and second fans having blades which are movable to change the pitch thereof, mechanism for moving the blades to change the pitch thereof, and an actuator for operating said mechanism, a static pressure sensor associated with the forming hood for sensing the static pressure therein, and a fan blade pitch controller operatively connected to the static pressure sensor and to the actuators of each of said fans for controlling the pitch of the fan blades in accordance with the static pressure in the forming hood.