Long fiber reinforced thermoplastics (LFRTs) are being used in injection molding applications that demand a high level of mechanical property performance. While LFRT technology is capable of excellent strength, stiffness, and impact properties, how these materials are processed plays a major role in determining how much of that performance ends up in the part.
In order to successfully mold LFRTs, it is important to have a basic understanding of what makes them unique.
Understanding the differences between LFRTs and conventional reinforced thermoplastics drives the equipment, design, and processing decisions that maximize the benefits and potential of LFRTs.
The difference between LFRTs and conventional chopped, short glass fiber reinforced compounds lies in the length of the fibers. In LFRTs, the length of the fiber is the same as the length of the pellet. This is due to the fact that most LFRTs are produced via a pultrusion process, rather than shear-intensive compounding. In LFRT manufacturing, continuous strands of glass-fiber rovings are pulled through a die, where they are coated and impregnated with thermoplastic resin. This continuous rod of reinforced plastic is then chopped or pelletized, typically to lengths of 10-12 mm. In contrast, conventional short glass compounds incorporate chopped fibers 3-4 mm long that have been further reduced to typically less than 2 mm in a shear-intensive extruder.
The length of the fiber encased in the LFRT pellet contributes to the improved mechanical properties of LFRTs. Impact resistance, or toughness, is increased while maintaining stiffness. As long as the fibers remain long throughout the molding process, they create an “internal skeleton,” providing the mechanical performance for which they are noted. However, a poor molding process can convert a long fiber product into a short fiber material. If the length of the fiber is compromised in the molding process, the level of performance that is possible and desired may not be achieved.
In order to maintain fiber length throughout the molding of LFRTs, there are three important areas to consider: the injection molding machine, part and tool design, and processing conditions.
The article comes from China injection mold manufacturer - Mold Best Assurance Company Limited, website is www.mbamoldanddesign.com
