Low-pressure casting

Anionic polymerization of nylon-based polymer systems to produce finished parts directly from monomers or prepolymers can be carried out by several processes e.g., reaction injection molding, low-pressure casting, resin transfer molding, rotational casting. 

In low-pressure casting, static or dynamic mixers are employed and the pumping systems are set up to compensate for polymerization shrinkage by packing the mold with additional material. Thus, a solid part can be produced. 

In many instances, one wishes to produce solid parts so as to maximize the toughness of the product. In some cases, the economics of the busines will not permit the high cost and process sophistication of reaction injection molding equipment. Low-pressure casting is then the process of choice. Casting machine prices are usually 20 to 50% of those of RIM machines. They are typically smaller and simpler machines. They use static or dynamic mixers rather than impingement mix heads. 

In almost all other respects, the low-pressure casting process is the same as the RIM process for nylon systems. 

Permanent mould or multi use a mould, mould that is used for gravity and low-pressure casting, pressure die-casting, or centrifugal casting typically the moulds are metallic... 

The most common material used in cylinder construction is cast iron for the larger, low-pressure cylinders and steel for the smaller, high pressure cylinders. In some cases, nodular or ductile iron can be used in lieu of cast iron. For hydrocarbon service, steel is most desirable, although not universally available. 

The process interaction in cast plastic products is mainly involved with the curing processes and with mold filling problems. Voids and porous sections are a frequent problem with castings because the mold filling is done at atmospheric pressure, or low pressure, and if the product has thin sections to fill, the flow may be a problem. 

Cast Iron and Ductile Iron Cast iron and ductile iron provide more metal for less cost than steel in piping systems and are widely used in low-pressure services in which internal and external corrosion... 

Expls which may be cast at temp of low pressure-steam in shells, bombs, etc consist of suspension of EDNA > 40% in molten TNT) 15) R.N. Jones ... 

The conventional method of loading most bursting expls is by casting, but if melting of the expl cannot be achieved at the temp of low-pressure steam(ca 95°), the Amer practice is to use press-loading. Some countries cast -loaded expls with mp higher than 95-100° for example, PA(mp ca 120°) was cast-loaded in Japan and called Shimose... 

Fig. 6.18 TEM image from a mixture of a PS-PI diblock (M = 82kgnior, /PS = 0.81) with 80% PS homopolymer (M = 580kgmol 1) (Koizumi et al. 19946). The film was cast from a good solvent for both blocks under low pressure (rapid evaporation). Clustering of PI micelles is evident.

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