Injection moulding sprue

Polythene at 170°C is used to injection mould a disc with a diameter of 120 mm and thickness 3 mm. A sprue gate is used to feed the material into the centre of the disc. If the... 

This process uses the plasticising and heat advantages of the injection unit to impart good flow properties to the rubber mix. It also offers the advantages of the flexibility of the transfer layout without the sprue and runners of the balanced runner system required by injection moulding. The space used by runners in other systems can be profitably used by more mould cavities. 

Even yet experts say that the best combs are saw-cut from flat uniform pieces of bone (and such combs remain on sale in more-expensive shops). Combs can be cut in the same way from plastic sheet, achieving comparable quality, but the stock must be prepared suitably and the work as a whole is more costly than the commercial method of making plastic combs in large numbers—injection moulding using materials such as nylon or polypropylene from the moulding process, after removal of the sprues, fully finished, saleable products (teeth included) can be obtained in a few seconds. 

The sprue-plane is called the xy-plane. Results measured on four different TMA samples taken from an injection moulded sample, crystallinity 44 %wt.)... 

In extensional flows, the velocity increases (fibre melt spinning) or decreases (radial flow from the sprue in an injection mould) along the streamlines, but there is no velocity gradient in the perpendicular direction. Figure 5.5 shows fibre melt spinning where the velocity increases with distance x from the spinneret, as the result of a tensile stress along the fibre. The tensile strain rate 6x is defined by... 

A sp>ecial injection mould has been designed such that samples could be cooled at a known cooling rate and imder a known pressure (Brucato et al., 2002, Brucato et al., 2000, La Carrubba, 2001). This heated mould consists of a conical cavity (the sprue), which is located in the fixed platen of the injection molding machine, coupled to a "diaphragm". The front of the cavity is sealed with a high tensile, high thermal conductivity copp>er-beryllium... 

In RIM, as in injection moulding, whether thermoplastic or thermoset, there is a transition zone between the nozzle (mix head) and the mould. In injection moulding, this transition zone includes the sprue/runner/gate system, and, in special cases, can also include a static mixer. The analogy to RIM is very apt. The transition zone for the RIM process also includes a sprue/runner/gate system, as well as an after mixer. One function of the RIM transition zone is to convert the mixing head liquid stream from a turbulent state to one which is in a laminar flow mode. If this does not occur, air traps (i.e. large subsurface voids in the finished part) can become a problem. 

The acetal spring is manufactured by injection moulding. A two-impression tool is used. Although hot runners are often used for acetal, the extra tooling cost is not warrented in this case, and the approximately 20% sprue scrap is re-used. 

Fig. 7.6. Tensile deformation in constrained flow (a) tapering section of extrusion die (b) calendering and (c) injection moulding fed from a sprue gate as the liquid expands radially into the mould, elongational stresses are set up in the direction of the tangent (after Cogswell).

Figure 15-17 Feed system (a) typical shot consisting of moldings with sprue, nmner, and gates attached (b) section through feed portion of mold. (From Pye, R. G. W. Injection Mould Design, 4th ed., Longman, London, 1989. Reprinted by permission of Addison Wesley Longman Ltd.)...

Example 5.4 Eight polypropylene mouldings, each weighing 10 g are to be moulded using the runner layout shown in Fig. 5.19. If the injection time is 2 seconds and the melt temperature is 210°C, calculate the pressure at each cavity if the injection pressure at the sprue is 80 MN/m. The density of the pwlypropylene is 909 kg/m3 and the volume of the sprue is 5000 mm. Assume that the flow is isothermal and ignore the pressure losses at comers. 

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