Cavity filling time

The cavity filling time tf for the circular disk cavity of radius is givmi by... 

In order to study the filling phase, the melt front advancement was analyzed with the objective to verify that the cavity fill time selected was the appropriate election for the dimensions of the mold components. Figure 4 shows the melt front advancement in the impact test specimen and the impact modified test specimen, for both materials. 

Thus for any plastic where the Power Law constants are known, the clamping force can be calculated for a given radius, R, cavity depth, H, and fill time, /. 

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. 

Therefore, if it turns out to be possible to vary the dimensions of a forming cavity until Eq. (4.38) be fulfilled, it will have to be done, since it leads to minimization of filling time (and the process as a whole) and hence to enchanced productivity of the injection moulding of plastisols. 

Sample balancing problem. Let us consider the multi-cavity injection molding process shown in Fig. 6.54. To achieve equal part quality, the filling time for all cavities must be balanced. For the case in question, we need to balance the cavities by solving for the runner radius R2. For a balanced runner system, the flow rates into all cavities must match. For a given flow rate Q, length L, and radius R, solve for the pressures at the runner system junctures. Assume an isothermal flow of a non-Newtonian shear thinning polymer. Compute the radius R2 for a part molded of polystyrene with a consistency index (m) of 2.8 x 104 Pa-s" and a power law index (n) of 0.28. Use values of L = 10 cm, R = 3 mm, and Q = 20 cm3/s. 

The general features of the parabolic flow law expressed by Eq. 4.36 have been widely confirmed [12]. However, the flow process itself is more complicated than that implied above. The irregular pore space of most granular materials may better be thought of as a bundle of nonuniform capillaries, all interconnected to one another. Near the advancing solvent front the liquid is pulled into the smaller pores because of the lower rc and thus r. The large pores are left dry until more liquid arrives from the rear, at which time the cavities fill one by one from smaller to larger, but by then the semidry front has moved on. Thus the level of liquid saturation of the porous bed decreases continuously as one advances toward the front. 

Once the process has been optimized, plastic conditions should be recorded such as fill time, peak pressure at fill, cavity pressure,184 melt temperature, mold temperature, melt flow rates, and gate seal time. Record all basic machines setpoints on the setup sheet such as the transfer time (fill time) and weight, overall cycle time, and total shot weight, part weight, % runner, etc. 

The evolution of classical fields in the cavities filled in with media whose dielectric properties vary in time was considered, for example, as far back as in... 

This distribution possesses the photon-number variance ct = sinh2(2ooo f). Similar formulas for the amount of photons created in a cavity filled with a medium with a time-dependent dielectric permeability (and stationary boundaries) have been found [222], The quadrature variances change in time as (now... 

A numerical analysis of cavity filling was developed to evaluate and optimize the use of reactive fluids in RIM. This method, which has been previously described in detail O), employs the marker and cell method for treating transient fluid flows in conjunction with finite difference solutions of the conversion and temperature fields in the pre-polymer and the mold wall. The time-temperature-conversion-vlscoslty correlations shown earlier for epoxy + AEP were then used in the mold filling simulation. 

The most reliable method for filling cavities has been to use a filling gun operating on an injector principle. A method gaining popularity uses compressed air in the hopper. Of the two approaches, the injector method provides a lower capital cost, smaller air requirement, and lower material unit cost, whereas compressed air provides a significant shorter fill time. 

In these investigations it had already been found that in the final state a coacer-vate wets the walls of the enclosing membrane and thus a parietal coacervate is produced which surrounds a central cavity filled with equilibrium liquid. Because of the comparatively large thickness of the celloidin membranes (diffusion processes slow), it lasts a considerable time before this final state is reached. 

Short shot n. In injection molding, failure to fill all cavities of the mold completely, caused by too low melt temperature, too low injection pressure, insufficient plasti-cation time, too constricted gates, too viscous resin, inadequate venting of cavities, etc. Short shots are often made deliberately when testing a new multicavity mold to reveal the pattern of runner flow and the sequence of cavity filling. 

Injection time, the maximum time for which injection can occur, is the setting on a timer. When this time is set for the transfer technique (transfer from fill to pack), it determines the time in which the cavity fills. However, if other transfer techniques are used, the time setting is merely a safety or default value. Thus, if transfer does not occur by the other technique, the machine switches to pack or second stage at the set time. When time is set for the transfer technique, injection time is incremented until the entire shot size is injected into the mold and the plastication begins immediately. When other transfer techniques are used, injection time is set 1 to 2 seconds higher than the time required for injection. 

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