Holding pressure time

FIGURE 5.18 Cavity pressure profile at different holding pressure times... 

The optimization of the holding pressure time using several cavity pressure curves (open nozzie) is iiiustrated in Figure 5.18. Only when the gate is sealed can assumptions of a minimum holding time be made. In the course of the cavity pressure, this can be seen through a difference of, for example, just 0.1 seconds more or less holding pressure time, which will lead to a slow decrease of the pressure curve and not an abrupt pressure drop. 

Injection pressure, holding pressure time 500 bar (LD)-1200 bar (HD). If holding pressure time ends before gate freezes, this leads to formation of sink marks or cavities, because of the high shrinkage. 

Injection pressures, holding pressure time 1000-1500 bar Select sufficiently long holding pressure time (similar to PE)... 

Recommended Values for Holding Pressure Time and Remaining Cooling Time... 

The cooling time consists of both the holding time and the residual cooling time. The holding pressure time and cooling time can be calculated as follows ... 

Residual cooling time Holding pressure time Injection time Plastication time... 

Changing the holding pressure or the holding pressure time has no effect on the size of the hollows. 

Table 1 gives the factors and factor levels selected in the main experiments. In our previous investigation, the two-way interactions of mold temperature and melt temperature, mold temperature and holding pressure time for samples with weldline, and interactions of mold temperature and holding pressure time, mold temperature and holding pressure time for the samples without weldline were selected. For the five factors and two two-way interactions. The L27(3 ) orthogonal arrays including two way interactions were used[6]. 

Fig 3(b) shows the factor effects on non-weld strength. Here, melt temperature is the most important factor. The increase of melt temperature causes the decrease of the strength for the reason of the thermal residual stress increasing. The increases of holding pressure and holding pressure time cause the compact construct of the part, and thereby the increase of the strength. 

Factors Mold temperature A/ °C Melt temperature B/ C Holding pressure time C/s Holding pressure D/MPa Injection pressure E/MPa... 

M elt temp erature - M old temp erature injection time holding pressure time - holding pres sure... 

Melt temperature Mold temperature injection time holding pressure time holding pressure... 

---