The direct on-line blending process of long glass fiber reinforced thermoplastics was compared with GMT and LFT-G processes. The direct on-line blending process of long glass fiber reinforced thermoplastics has the characteristics of low processing cost, simple forming process and optimizing material properties, so it has broad application prospects in automobile manufacturing industry.

Market expedite

Since the 1990s, the market share of long-fiber Reinforced Thermoplastic (LFT) in the automotive industry has been increasing because of its small proportion, high rigidity, good chemical resistance and good chemical resistance. It has the advantages of damping property, high vibration resistance and fatigue strength. In the field of long fiber reinforced thermoplastic, semi-finished pressing technology is used. The first step of the process is to process semi-finished products of long glass fiber reinforced thermoplastic sheets or rod-shaped granules, namely glass-Mat Reinforced Thermoplastics (LFT-GMT) and long-fiber Reinforced Thermoplastic Granules (LFT-G). Then they are plasticized into parts by pressing process. This molding process has now become a commonly used technology in the field of long fiber reinforced thermoplastic.

Later, due to the pressure of increasing cost in the automotive industry, the direct processing technology of long-fiber-Thermoplastic-Direct-In-Line-Compounding (LFT-D-ILC or LFT-D) was born in 1996. In this kind of processing technology, without the production steps of semi-finished products, parts are directly produced by matching raw materials, namely thermoplastics and reinforced fibers, through programmed control processing machinery. This is also a direct processing technology fundamentally different from the semi-finished products processing technology.

Superiority

Comparison of different LFT materials

The different LFT materials are compared in the table. It can be seen that compared with GMT and LFT-G, LFT-D processing technology has great cost advantages, which is the result of the direct forming of semi-finished products and parts. In addition, LFT-D also has processing advantages, among which the great advantage is the free choice of glass fibers and polymer matrix materials, which means that commercialized raw materials on the market can be well selected, of course, the final choice is also limited by the market price of materials at that time.

Using LFT-D processing technology to process waste recycling components directly can bring double advantages of economy and ecology. The whole process includes the processing of scrap parts (cut and separated from metal fittings) and the use of scrap materials. The diameter of the material recovered by chopping is 12 to 50mm. The recycled material is first melted in a special single screw recycling extruder and then directly fed into a twin screw device (ZSG). At the same time, there are long fibers added to increase the rigidity of the components. For the recycled material with a size of 8 to 12mm, it can be directly fed into the polymer mixer.

It should be noted that for LFT-D processing, unlike GMT and LFT-G, the quality of products is mainly determined by the performance of semi-finished products. In fact, the operator who has a deep understanding of material properties is the dominant factor that plays a role in processing control, especially in the processing of recycled materials.

Equipment technology

Using the direct processing equipment of long glass fiber reinforced thermoplastics, reinforcing fibers can be added to the melted polymer as a continuous roving, and then the continuous fibers can be split into glass fibers and impregnated, diffused and homogenized in the polymer. The resulting long glass fibers are then molded into components.

Here, we introduce the long glass fiber reinforced thermoplastic direct processing equipment. The front end of the device is a twin screw extruder that plasticized the matrix polymer. The extruder has high shear effect and has high melting ability. The extruded polymer melt passes through a specially developed slot die in the form of a polymer film and is transferred to the second stage, the so-called "twin screw device unit (ZSG)". Here, the preheated continuous fiber tow is joined with the transferred matrix. The ZSG device is specially designed and manufactured by Leistritz Company. Its length-diameter ratio is 13. It is ventilated by an air or vacuum controlled ventilation system. The homogenized mixture of thermoplastic matrix and glass fibre flows out of the slot die and is transported through a PAL conveyor, and then cut into final parts by a chopper cutter. In addition to the above devices and workstations, the equipment also has a weighting and weighting feeding station for mixing thermoplastic and recycled materials. The workstation can weigh and quantitatively add additives such as pigments, antioxidants, thermal stabilizers and glass fiber/matrix coupling agents according to the formula.

With this equipment, the total extrusion volume of long glass fiber reinforced polypropylene (PP) can reach 500-600 kg/h at screw speed up to 500 r/min. However, whether this yield can be achieved depends on the content of glass fiber in the extrudate.

Factors affecting material properties

Based on the study of the bonding between polypropylene and glass fibre, the factors affecting the properties of long fiber reinforced plastics are drawn. Three main factors affecting the properties of materials are obtained: glass fibre, resin coupling agent between fibre and matrix resin coated on the surface of fibre, and matrix resin.

Factors affecting the properties of long glass fiber reinforced plastics

1. Glass fiber

Glass fiber reinforced