Jet molding

Guss, m. casting, founding cast iron gate (of a mold) gutter pouring jet (of liquid) ... 

There is not too much orientation that is permanently added to material as it passes through the gate since the continued flow in the cavity basically tends to produce turbulence that destroys the orientation. The last material to pass through, however, does retain its orientation and the gate area in a molded product is usually highly oriented and could be weak. In the case of jetting, the result is a patch of highly oriented material somewhere on the molded product near where the first material entered the mold. 

Jetting Jetting is a condition that results when the mold design has no immediate impediment to flow and the plastics is ejected into a relatively large open volume. This jetted material becomes a weak point on the product and a surface blemish that is difficult to conceal. 

Uses. The most important commercial use for benzonitrile is the synthesis of benzoguanamine, which is a derivative of melamine and is used in protective coatings and molding resins (see Amino RESINS Cyanamides). Other uses for benzonitrile are as an additive in nickel-plating baths, for separating naphthalene and alkylnaphthalenes from nonaromatics by azeotropic distillation (qv), as a jet-fuel additive, in cotton bleaching baths, as a drying additive for acrylic fibers, and in the removal of titanium tetrachloride and vanadium oxychloride from silicon tetrachloride. 

In case of an accurate formulation of the problem, it is difficult to consider theoretically the process of molten thermoplastic drawing from a molding tool even under isothermic conditions. In the literature several approximate approaches have been suggested. For instance, it has been proposed 83 84), for analysis of a similar problem (isothermic swelling of a jet leaving the capillary without subsequent drawing), to cross-link the inner (in the capillary) and the outer (free jet outside the capillary)... 

The inner (flow in the capillary) and the outer (outside the capillary) solutions of the problem of polymer drawing from the molding tool were also cross-linked by the flow of elastic energy86) (the idea was borrowed from the above-mentioned Refs.8 4,85) but this flow was calculated already accurately with the use of the model given in Ref. 48), and the external extraction of the jet was calculated with regard to the possible flow. Analytical data have been compared to the experiment to reveal a satisfactory quantitative correspondence 86). 

When the mixture of monomers is cast in an open mold, the air bubbles formed at the jet nozzle in the mold usually have enough time to leave the material due to the low viscosity of the reactive liquid. When more viscous oligomers and prepolymers are used, particularly in the case of low-lifetime reactive mixtures, it may be necessary to use some simple procedures, for example, filling through a pipe immersed into the mold, to prevent the formation of air bubbles in the product. 

The so-called RIM-process (reactive injection molding) is a current realization of the reactive molding process. The heart of the process is the shock mixing of the reactive ingredients, which is achieved by collision of two jets injected at a pressure of 10 - 20 MPa. The reactive mixture is injected into the mold in a laminar flow regime the pressure at this stage does not exceed 0.1- 0.4 MPa.259 The practical development of this method relies on automatic control systems and modem high quality equipment. 

It was established experimentally that a jet-type of flow appears when the characteristic size of the stream is less than the minimal gap between the walls of the mold.277 This proves that the cause is related to the ratio between the size of the injection nozzle and the coefficient of swelling of the elastic liquid moving inside the mold rather than to the axial momentum of the moving liquid. This conclusion is also supported by evidence that highly filled polymers, which are less elastic than pure melts, form jet-like patterns at lower flow speeds. 

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