Mold-cavity pressure

In order to judge performance capabilities that exist within the controlled variabilities, there must be a reference to measure performance against. As an example, the injection mold cavity pressure profile is a parameter that is easily influenced by variations in the materials. Related to this parameter are four groups of variables that when put together influences the profile (1) melt viscosity and fill rate, (2) boost time, (3) pack and hold pressures, and (4) recovery of plastica-tor. TTius material variations may be directly related to the cavity pressure variation. Details on EQUIPMENT/PROCESSING VARIABLE are in Chapter 8. 

Fig. 7 Effect of mold cavity pressurization on the bubble dissolution time, based on experimental data presented by Spence. (From Ref l)...

Figure 10.9. Topical pressure profiles during injection molding. and stand respectively for nozzle and mold cavity pressure. Stages are 1 - dead time, 2 - filling, 3 - packing, 4 - cooling, 5 - ejection.

Plastic temperature, °C Plastic viscosity, Pa s Injection pressure, bar Injection time, s Mold cavity pressure, bar Gates... 

It is important to set the pressure to the proper level. If the holding pressiue is too low, or if the holding pressure period is too short, this would result in the production of a defective molding. The ideal curve for the mold cavity pressure is shown in Figure 7-6. 

It is especially important for the transition Irom injection- to holding-pressiue phase to occur at the precise moment. Figure 7-7 shows a few examples of wrong mold cavity pressure curves. If transition occurs too early, a pressure drop results. This entails the risk that it will be impossible to completely fill the cavity. If transition occurs too late, a pressure spike occurs. In the long run, such pressure spikes can result in damage to mold and machine. 

Figure 7-7 Wrong mold cavity pressure curves...

CM is the most common method of forming TS plastics. Until the advent of injection molding, it was the most important of plastic processes. CM is the compressing of a material into a desired shape by application of heat and pressure to the material in a mold cavity. Pressure is usually at 7 to 14 MPa (1000 to 2000 psi). Some TSs may require pressures down to 345 kPa (50 psi) or even just contact (zero pressure). The majority of TS compounds are heated to about 150 to 200°C (302 to 392°F) for optimum cure but can go as high as 650°C (1200°F). 

FIGURE 5.14 Quick Connectors for the mold cavity pressure and mold wall temperature... 

The input for the neural network developed in this work is not limited to the residual wall thickness of part, it can be other specificatiorr, such as wato- paretrate length. The outputs of the network can also include other processing parameters, such as the mold terrrperatrrre and mold cavity pressure. 

---