INJECTION SPEED

Foamed plastic articles may be produced with good results using normal screw-type injection moulding machines (see Fig. 4.43(a)). However, the limitations on shot size, injection speed and platen area imposed by conventional... 

For the slit-shaped cavity with a unidirectional flow, presented in Fig. 6.79, derive an expression for the pressure at the gate during mold Ailing for a constant injection speed. Assume a volumetric flow rate Q and an isothermal flow of a shear thinning polymer with a power law model. 

Figure 8.42 Comparison between theoretical predictions with experimental measurements of mold filling pressure requnements as a function of injection speed [28],... 

For flash vaporization injection, the effect of injection speed, choice of solvent, and injector temperature greatly affect the solvent peak width. Injection of a low-boiling solvent at high injector temperatures can cause the entire expansion volume of the liner to be exceeded by the expanded solvent. It must be remembered that 1 pi of liquid solvent injected at 250°C at 10 psig head pressure is converted to some 200-1000 pi of gas. Thus, as the injection volume increases, the injection rate should be adjusted so as not to exceed the expansion volume available in the port liner. Generally, nonpolar solvents perform best in the direct flash mode. The injection rate should follow the following formula [26] ... 

Tracer injection position center of the pipe and wall ring of the pipe. (The injection speed of the tracer is set to the average velocity as the injection region.)... 

Proper machine cycle settings are also important for energy savings. The injection speed control system (available on new machines as an option or as a retrofit on old machines) optimizes the speeds available for specific time intervals. The injection high volume pump is available for a fixed time period and is then dropped out of the system. This time period should coincide with... 

To increase shot size upsizing the plasticator can be made. A number of items have to be considered for the upsizing process, such as barrel wall thickness, resultant screw L/D, injection speed reduction, screw drive torque, and injection pressure drop. Before considering the upsizing process, one has to determine whether the output can be met properly using the decreased pressure and speeds that occur. The pressure and speeds will decrease directly proportional to the difference in the barrel ID projected areas. If this poses no problems, the L/D and structural integrity of the barrel have to be considered before proceeding. 

Heat Deflection <0.178 mm Injection speed hold time Increasing hold rime decreases Heat Deflection (HOT). Decreasing speed decreases HDT. 

Foil quality at center >2.5 Injection speed increasing speed decreases foil quality at center. Worst condition (=1) results in washing away of the foil in a 3.175 mm. to 3.429 mm. diameter at center. 

Foil quality at edges >2.5 Melt temperature, injection speed, hold pressure Increasing any of these parameters increases foil quality at edges. The most effective is melt temperature, then injection speed, then hold pressure. 

Parabola at 20.32 mm. 11.58 mm to 11.84 mm. Melt temperature, hold pressure, hold time, and injection speed Increasing mell temperature or decreasing injection speed linearly increases this dimension. Dependence on hold time and hold pressure is quadratic however, in the range of these parameters the team is most interested in (due to other criteria), increasing hold pressure or hold time increases this dimension. 

Parabola at 10.16 mm. 13.18 mm to 13.44 mm. Melt temperature, hold pressure, hold time, and injection speed Injection speed and hold time are most effective with decreasing speed or increasing hold time increasing this dimension. Melt temperature and hold pressure has less of an effect with increasing temperature or decreasing hold pressure increasing parabola height at 10.16 mm. 

Parabola at center 13.87 mm to 13.97 mm. Melt temp., hold pressure, hold time, and injection speed Same trends as above (for parabola at 10.16 mm.) with, in this case, hold time having the biggest effect, followed by injection speed and hold pressure melt temperature has the least effect. 

Parabola Constant 193.92 mm to 195.92 mm. Hold time, hold pressure, injection speed Increasing injection speed or hold pressure increases parabola constant increasing hold time decreases it. 

In creating a process window for the combination of material, machine and heater used in this study, the first consideration was the moldability, which was dictated by the maximum injection pressure and the maximum clamp force. No changes in melt and mold temperature, injection velocity, or gate size could remedy this situation. Thus, an injection molding machine with higher injection speeds, pressures and clamp force was required to mold thin-walled syndiotactic polystyrene. 

---