Method of compounding resin and fiber
Molding material consisting of resin coated reinforcing fiber strands in a molten mass of resin is prepared at a molding site for controlled supply to a molding machine. Continuous strands of fiber from supply spools are entrained with pressurized, molten resin flowing through a coating device and coated with the resin. The movement of the fiber and resin through the coating die may be controlled so as to accurately and predictably produce any desired quantity the molding material, i.e. the coating apparatus may be operated in a discontinuous manner to provide any predetermined quantity of molding material to a receiving device. The receiving device may be the feed screw for an injection molding machine or simply a plate movable to and from a compression molding machine. The fiber strands may be cut into predetermined lengths by a cutting device positioned downstream of the aforesaid coating device.
1. A process for preparing fiber reinforced resin for use in molding machines comprising:
threading at least one fiber strand through a passage having an outlet;
introducing into the passage a thermoplastic resin in a molten, pressurized state, so that the thermoplastic resin coats and entrains the at least one fiber strand within the passage such that the at least one fiber strand is pulled by the resin along with the resin as the resin flows out of the passage through the outlet.
2. The process of claim 1 further comprising a step of selecting a particular diameter of the passage of predetermined size larger in cross-sectional area than a cross-sectional area of the fiber strand such that a resin- flow annular space of predetermined cross-sectional area is defined between the fiber strand and the passage through which molten resin may pass with the fiber strand, the particular diameter of the passage being selected to obtain a desired ratio of resin coating to fiber strand.
3. The process of claim 1 further comprising a step of running the process in a discontinuous manner to produce a desired quantity of fiber reinforced resin.
4. The process of claim 1 wherein the introducing step comprises introducing resin into the passage at a sufficient pressure such that the at least one resin coated fiber strand exits the outlet at velocities between 80 and 250 feet per minute.
5. The process of claim 1 wherein the introducing step comprises introducing the thermoplastic resin into the passage at pressures between 12,000 psi and 14,000 psi.
6. The process of claim 1 wherein the introducing step comprises introducing resin into the passage such that the fiber strand comprises between 20 to 60 percent by weight of a fiber reinforced resin mixture flowing through the outlet.
7. The process of claim 1 wherein the introducing step comprises introducing the thermoplastic resin into the passage at pressures between 4,000 psi and 40,000 psi.
8. The process of claim 1 wherein the introducing step comprises introducing the thermoplastic resin into the passage at pressures greater than 4,000 psi.