Filling flat mould

Filling a Two-dimensional Flat Mould Through a Point Gate (Runner) 105... 

Third, the rheological properties of plastisols during isothermal filling of thin moulds (the applicability of isothermal injection into thin flat moulds will be referred to below) at some medium range y (corresponding to the flow with qx) and considerations of dimensions suggest that the filling time for a flat mould, tm, as a function of pressure may be represented as ... 

Equation (4.23) holds true when H/q0 > e1/s. The existance of 5+, which minimizes the filling time for radial forming cavity, is conditioned by the same physical (hydrodynamical) reasons as in the case of a flat moulding. 

Fig. 11a, b. Kinetic identification of the first stage of filling a flat mould through a round (point) runner a flow is purely radial during some limited time interval, flow front is approximately circular b the radius of free boundary becomes equal to half-width of the forming cavity R(t) = B/2... 

At this stage, one has to take into account the volume compressibility of the material, since upon feed-up the hold-on time of material under pressure is determined by compressibility and slow viscous flow. If the pressure of injection PQ is sufficiently high, then at this stage a liquid may be considered to be Newtonian with viscosity q ,. Keeping this in mind, we may state that the calculation given below will be applicable to various plastisols (of types I and II) with the only difference that for plastisol I q = const, while for plastisol II q = q. For the sake of simplicity, the analysis will be performed for the case of a flat mould filled through a slit runner (Fig. 10 a). 

One such process is the TAP process, the basic patent being held by Dow. It was developed in Japan by Asahi in conjuction with Toshiba. Foam expansion after mould filling is made possible by use of retractable mould cores. Because of the difficulty of allowing expansion in more than one direction this process has been largely limited to the production of flat products. Efficient gas sealing systems are also vital and the process needs close control. For this reason it has not been widely used in either Europe or North America. 

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