Long fibre injection

Long-fibre Injection moulding compounds improved surface treatment/coupling agents use of high-performance fibres in forms more suitable for injection moulded thermoplastics. 

Long-fibre injection moulding Linear low density (polyethylene)... 

One limitation of epoxide moulding compositions is their short shelf life (typically 1-3 months), which necessitates strict stock control. The compounds may be compression, transfer or injection moulded, although compression moulding is preferred for long-fibre grades. 

These long fibres give better product performance although injection moulding machine modifications may be necessary to prevent fibre damage and reduce undesirable fibre orientation effects in the mould. 

Processing of LFRT or LFT - long fibre (reinforced) thermoplastics injection, composite insert moulding, compression moulding, extrusion-compression. 

Mass production parts bumpers, soundproofing shields, cross-pieces, inserts for dashboards, seat frames, containers, welding helmets, ventilator housings, base of lawn-mowers, taping of pipes, pipelines, tanks, long fibre reinforced injected parts. 

Opinions vary as to the optimnm point to add a dry strength resin, and indeed this can differ from one paper machine to another. It will also to some extent depend upon the specific objectives for nse. The most commonly nsed point of addition is to the thick stock, after the last refining has been carried ont. Strazdins [13] reported a laboratory study on a European secondary fibre fnmish, where the benefits of resin addition to the long fibre fraction were demonstrated. Good mixing is essential to obtain the best performance from the product, so addition to a weU-stirred chest or the down leg of the thick stock level box is ideal. If the dilnte resin is added to a pipeline, optimum mixing will be achieved if a mnltipoint injection system is nsed. 

A further development is resin transfer moulding (RTM), in which long fibre reinforcement fabrics are cut to shape as preforms and placed in the mould cavity, before the resin is injected. This is potentially a slow process and one alternative is for the preforms to be made rapidly by spraying short fibres onto a suitably shaped pattern coated with an adhesive or binder. 

Polymers vary widely in their processing characteristics, and it is important to ensure that the design developed can be produced economically and efficient from the chosen material. The most obvious differences in processing behaviour are between thermoplastics and long-fibre composites, but fiiere are also significant variations within each class of materials. To take an extreme example, PTFE has such a high melt viscosity that it cannot be injection-moulded, but has to be formed from powder by... 

Fibre-reinforced NR composites are manufactured by various processes, the most common being extrusion, injection moulding and compression moulding (Figure 9.6). To fabricate glass-reinforced NR composites with unidirectional long fibres, extrusion is not used because this process can only result in short fibre-reinforced polypropylene composites (a few millimetres at most). 

Hine PJ, Davidson N, Duckett RA, Ward IM (1995) Measuring the fibre orientation and modelling the elastic properties of injection-molded long-fibre-reinforced nylon. Compos Sci Technol 53 125-131... 

It is possible to perform injection moulding with very high speeds, (i.e., with common cycle times of 10-30 s). A recent process called foiled FibrePur technology (FFT), which is a plastic-foil finishing technique in RIM based on long-fibre reinforced PU which produces fully finished painted parts in a single-step process [8, 9]. 

The method by which the compound will be moulded or shaped naturally dictates the form of reinforcement. In thermoplastic compounds (which will be predominantly injection moulded), short-length fibre or particulate reinforcement is used, but there has been important development of so-called long -fibre compounds, with a higher ratio of reinforcement to resin matrix and a longer... 

As a result, technology has been developed to enable the use of long fibres (around 2 mm) in a thermoplastic resin matrix. These are produced, not by classical physical mixing, but by a process analogous to the pultrusion process with thermosetting resin matrices, with internal lubrication additives to counteract the chopping effect of injection moulding. Similar effects have been measured with other fibres, such as aramid and carbon, and with other matrices, such as polypropylene and poly(phenylene sulphide). 

Hawley, R. and Jones, R. (2005), In-line compounding of long-fibre thermoplastics for injection molding , Journal of Thermoplastic Composite Materials, 18, 459 64. DOI 10.1177/0892705705054413. 

It was proved that the long fibres assure to the composites a higher resistance that the short ones, and are characterised by specific fracture properties. The microstructure and fracture mechanical behaviour of injection-moulded longer glass fibres reinforced polypropylene (Verton, aspect ratio 320) were studied as a function of the fibre volume fraction and compared to that of a shorter... 

Brake pedal for 1989 Ferrari, injection moulded in long fibre reinforced nylon (courtesy ICI). 

The same materials can be used as in long-fibre reinforced polymer matrix composites. Short-fibre reinforced polymers are useful in many applications where unreinforced polymers are not sufficient. The design of injection moulded components made of short-fibre reinforced polymers is complicated by the fact that the orientation of the fibre is determined by the fluid flow (see section 9.1.1) and can be irregular within the material. 

Thermoplastic resins are generally reinforced with short fibres (for use with injection moulding and not considered in this book), with long fibres (thermoplastic sheet compound, Chapter 5) or with glass mat (i.e. glass mat thermoplastics or GMT). Polypropylene is the resin most used as the matrix for GMT and the reinforcement is usually a random mat, primarily chopped strand but it may be continuous filament or needled mat. 

Metten, M., Cremer, M. Injection Moulding of Long-Fibre-Reinforced Thermoplastics Process Parameters Influence Fibre Length, Kunststoffe International (2000) 1, p. 35-37... 

Steinbichler, G., Egger, R, Pichler, M. Injection Moulding Long Fibres Fibre Damage and Effect of Fibre Length on the Properties of LFT, Kunststoffe International (2000) 3, p. 7-9... 

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