LFT processing technology

The fiber length of LFT varies with the processing technology. Impact properties are particularly dependent on fiber length, so the compression molding process is significantly better than injection molding in terms of mechanical properties. Generally, fibers that are on average about 5 to 20 mm long in a part are considered long fibers.

In the initial LFT production, resin plus LFT-G long fiber pellets are usually used to complete the final product through an injection molding process. Since the fiber length of LFT-G long fiber pellets is limited, the final LFT product performance Still limited, in recent years, the LFT-D-ILC process technology has become the representative processing technology for LFT products.
LFT-D-ILC is called in-line compression molding technology for long fiber reinforced thermoplastic materials. In this process, an in-line compounding system is integrated into the molding process, and the matrix particles and additives are fed into a combination of gravimetric dosing units that ensure proper mixing according to the mechanical performance requirements of the part. Typically, colorants, antioxidants, heat stabilizers, and cross-linking agents will provide a suitable formulation. The molten compound passes through a die directly into the opening of the compounding extruder (twin screw). This is where the glass roving is added.

To reduce roving interaction, the spools are placed on specially designed roving creels. Each roving is individually guided through a special plastic tube, avoiding friction and electrostatic repulsion. Each roving is monitored by a sensor.

Rovings are fed through a tube into a preheating device, and they are spread on heated iron rods. The temperature should not be higher to prevent the glass fibers from being damaged. Through a specially designed interface, the fibers form an oriented alignment in the molten polymer as they enter the compounding extruder.

The compounder is a co-rotating, crossover and self-cleaning device, with pumping taking place at 26D (26 x diameter), vacuum assisted or atmospheric pressure. Additives can be added at site 14D using a side feeder. The extrusion pressure is approximately 40-60 bar (4-6 MPa), depending on the melt flow index (MFI) of the polymer.

The compounding extruder continuously supplies the plasticized material, and at the molding temperature, a slot die extrudes the bulk molding material onto a fully automated conveyor belt. The conveyor belt is covered with a heating channel to prevent the surface temperature of the extruded bulk molding material from dropping. When the bulk molding material is grasped by the processing robot, the heating channel is opened.