Liquid injection moulding

Catalysts are essential components in the liquid injection moulding (LIM) or reaction injection moulding (RIM) processes. Prepolymer systems for solid polyurethane elastomers usually do not require catalysts, and if long-term hydrolytic stability is required in the final polymer their use is undesirable. 

Reaction Injection Moulding (Liquid Injection Moulding)... 

RTV silicones face strong competition from moulded silicone gaskets used by US manufacturers, and European manufacturers have preferred to use moulded rubber gaskets in most applications. Furthermore, many applications are developing for liquid injection-moulded gaskets that that can be injected and cured into preformed grooves in an assembled component. Up until now, this has only been possible with silicones, but Freudenberg NOK G.P. has announced a family of non-silicone liquid elastomers ... 

Resin transfer moulding (RTM), is a prominent type of liquid injection moulding, defined as a closed moulding process of composite preparation in which catalyzed resin is transferred into an enclosed mold cavity to impregnate a pre-positioned fibrous reinforcement (preform), as presented in the Figure 13.1 [1],... 

Because of the particular material properties of LSR in comparison to other materials which are capable of being injected, a special processing technology is required. This technology is known by its abbreviation LIM, which stands for liquid injection moulding. 

Polymers owe much of their attractiveness to their ease of processing. In many important teclmiques, such as injection moulding, fibre spinning and film fonnation, polymers are processed in the melt, so that their flow behaviour is of paramount importance. Because of the viscoelastic properties of polymers, their flow behaviour is much more complex than that of Newtonian liquids for which the viscosity is the only essential parameter. In polymer melts, the recoverable shear compliance, which relates to the elastic forces, is used in addition to the viscosity in the description of flow [48]. 

Because of their low viscosity the liquid cyclic aliphatic resins find use in injection moulding and extrusion techniques, as used for glass-reinforced laminates. They are also very useful diluents for the standard glycidyl ether resins. 

The early 1980s saw considerable interest in a new form of silicone materials, namely the liquid silicone mbbers. These may be considered as a development from the addition-cured RTV silicone rubbers but with a better pot life and improved physical properties, including heat stability similar to that of conventional peroxide-cured elastomers. The ability to process such liquid raw materials leads to a number of economic benefits such as lower production costs, increased ouput and reduced capital investment compared with more conventional rubbers. Liquid silicone rubbers are low-viscosity materials which range from a flow consistency to a paste consistency. They are usually supplied as a two-pack system which requires simple blending before use. The materials cure rapidly above 110°C and when injection moulded at high temperatures (200-250°C) cure times as low as a few seconds are possible for small parts. Because of the rapid mould filling, scorch is rarely a problem and, furthermore, post-curing is usually unnecessary. 

It will be seen that a polymer of molecular weight A/, may be processed either as a liquid (by injection moulding, extruding, etc.) or as a rubber (by vacuum forming, sheet blowing, warm forging). In the case of the polymer... 

The beneficial effects are demonstrated of heterogeneous secondary pyrolysis reactions on the liquid products of PU pyrolysis. Pyrolysis volatiles are passed through a packed bed of carbonaceous solids that promote the secondary reactions. Activated carbon and reaction injection moulded PU (RIM) char were found to be suitable bed materials. The long-term object was to develop marketable solid products by pyrolysis of wastes, so obtaining high char yields. In addition to affecting the liquid products, RIM char also increased the total char... 

Plasticisers are compatible and miscible with their host polymer causing them to swell and allowing them to be used for coating, moulding, spraying (when used as a suspension in a liquid solvent) or calendering, extrusion and injection moulding (when used as a polymer melt). 

Injection moulding of silicone and polyurethane rubbers differs, because the material mixed and injected is usually liquid. 

To facilitate and accelerate folding and crystallization of polymer chains, internal plasticizers are often added to PET to serve as crystallation promoters. Such additives are usually based on poly(ether ester)s. These plasticizers are liquids that are typically added at levels of 2-4 wt%. They reduce cycle time in injection moulding operations by increasing the rate of crystalline formation. They also plasticize the resin and act as processing aids by virtue of their lubricating action in the melt. On a molecular level, these plasticizers reduce the intermolecular... 

Low-pressure injection moulding, RIM, RRIM for liquid polyamide ... 

Now let s summarize the data on the viscosity of PVC plastisols. First, as concerning injection moulding (filling of thin moulds), both the plastisols (those showing and those not showing thyxotropic phenomena) may be considered as non-linear liquids with no characteristic times provided that the filling time is much larger than the characteristic time of the medium. 

Polystyrene is an inexpensive transparent plastic which is often used in industry for the fabrication of parts by injection moulding. However, the tougher acrylic plastics are preferable for the construction of laboratory apparatus. Polystyrene is soluble in many organic liquids and, if strain free, may be solvent-bonded by the use of chlorinated hydrocarbons, benzene, or toluene. Special impact-resistant grades are available which are less susceptible to solvents and thus a little harder to solvent-bond than the conventional material. Polystyrene also may be welded. 

Reaction injection moulding is associated with polyurethanes and is different entirely from moulding techniques used commonly for thermoplastics in that the starting materials usually are liquids at room temperature. As the name implies, a chemical reaction takes place in the course of moulding and complex polyurethane items can be made in one step from mixtures comprising polyol, polyisocyanate, and a suitable promoter of the reaction. 

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