Chopped glass fiber random mats or preforms are commonly used to make reinforced polyester parts. A preform generally consists of approximately 90 to 95% chopped fiberglass strands bonded together with approximately 5 to 10% resin binder. These preforms are then placed in a mold located within a compression press and resin paste is applied to mold the part into the final desired shape.
Preforms are formed into substantially the exact shape of the desired part using a preform screen of perforated material the exact shape of the male mold. The preform screen is mounted over a fan inlet which draws air through the preform screen to capture chopped glass fibers on the screen and hold them in place while a binder emulsion is sprayed onto the fibers and cured to hold the fibers in the proper shape during compression molding of the part.
The current system used to deliver chopped fiberglass strands to the preform screen includes a stationary chopper driven by an electric motor to chop a series of continuous fiberglass strands, called glass roving, into lengths for example of one-half inch to four inches. The cut glass fibers drop through a feed funnel into an air stream from a stationary blower which blows the glass fibers toward the preform screen through a flexible delivery tube that is moved manually relative to the preform screen.
While this chopper delivery system has been used effectively for many years, a major disadvantage is that the stationary chopper blower unit must be mounted several feet from the preform screen to accommodate the size and shape of the preform. The greater the distance between the chopper blower unit and the preform screen, the longer the distance the chopped glass fibers must be carried through the air to the screen. As this distance increases, a certain amount of the fiberglass strands fall out of the air stream and are lost. Also, with a longer flexible tube, the greater the risk that the tube will bend or kink, causing the fiberglass strands to clump up and drop out by gravity or causing the tube itself to clog up.