Injection molding process conditions

Table 5.9 RRIM and injection molding processing conditions compared for large surface production parts...

The effects of a number of injection-molding process conditions (gate size, melt temperature, part thickness, mold temperature, ram forward time) on the maximum birefringence value of polystyrene are shown in Figs. 12-5-12-9. Examination of these plots shows that maximum orientation values occur for... 

Currently, use of PLA for injection molded articles is limited for commercial applications because PLA has a slow crystallization rate when compared with many other thermoplastics as well as standard injection molding cycle times. The overall crystallization rate and final crystallinity of PLA are controlled by the addition of physical nucleating agents as well as optimization of injection molding processing conditions [4]. 

Tianjin P(3HB-4HB) and Tianan PHBV can be molded via injection molding. The temperature profile in the injection molding barrel is different than conventional thermoplastics with the hottest temperature at the first zone and the coolest temperature at the nozzle. PHAs can be exposed to a temperature range between 160°C and 190°C. PHAs viscosity is too large for injection molding at temperatures below 160°C. PHAs can thermally decompose at temperatures above 190 C. PHAs also require a heated mold to enhance crystallinity. The injection molding parameters for P(3HB-4HB) are displayed in Table 4.4. Injection molding process conditions are similar for PHBV. 

The crystallinity and crystallite size of injection molded isotactic polypropylene was measured by wide angle X-ray diffraction(WAXD) and the distinct skin-core morphology was visible under a polarizing optical microscope. The results show that the crystal structures are dependent on the injection molding processing conditions. The crystallinity and crystallite size decreases with the distance from the gate. The skin layer thickness is thinner with the higher injection temperature. 

Keywords stress concentrator, injection molding, process conditions, and plastic parts. 

The effect of the injection molding process conditions (melt and mold temperatures, holding/packing pressure and injection velocity) over the adhesion resistance of two overmolded materials was studied. The materials used were a Thermoplastic Vulcanized Elastomer (TPV) (Santoprene 8211-55) and a Polypropylene (PP) (Moplen HP501H). The measurement of the adhesion resistance was done by Tensile Test and it was observed that the melt and mold temperature are the parameters that affect in greater degree the adhesion resistance. 

The thermal history as a result of such things as injection molding processing conditions, aging or other weathering, can in also affect the ability of the materials surface to withstand a scratch incident. 

Alabran, M. W., A Study of the Effects of Various Injection Molding Processing Conditions on Nano-... 

Rotational flow and pressure flow rate calculations for the screw geometry and process conditions are performed for the injection-molding process in the same manner as for an extrusion process. Since the plasticator of an injection-molding process is not a continuous process, the instantaneous rate must be calculated based on the time that the screw is actually rotating. The instantaneous rate is the rate that is compared to the calculated flow rates for the screw. The instantaneous specific rate is calculated as follows ... 

For the flow of polymer melts, the Reynolds number, Re = pUch/r], is usually 10 5, with the exception of the reaction injection molding process, RIM, where Re —> 1 — 100 at the gate. The geometric and dynamic conditions of the lubrication approximation, applied... 

The color formulator must learn as much as possible about the processing conditions the colorant system will encounter. Important conditions to determine are cycle times and process temperatures. Hot runner systems commonly used in today s injection molding processes may add temperature to the polymer melt and add to the time the polymer is under heat. Remember that the heat stability of any colorant and additive system is a function of both time and temperature. An excellent color match may be produced, but if the formulation cannot withstand the stress of processing without breaking down or changing shade, then effort and time have been wasted. 

One of the unique features of the optimal extrusion or injection molding process utilized for HIPS, when compared with other styrenics, is simplicity. HIPS has good thermal stability and resists degradation over a wide range of conditions. Since it is a nonpolar polymer, HIPS displays only a slight tendency to absorb water and the natural, uncolored polymer rarely requires drying prior to melt processing. 

Composite density can be expected to vary because of the uneven distribution of filler particles in the manufactured product. This is very typical of the injection molding process where filler is distributed in a complex pattern of flow. In glass reinforced polystyrene parts, manufactured by injection molding, the density varied between 0.9 and 1.4 g/cm depending on the process conditions and locations Ifom which the sample was taken. ... 

These functions must be performed automatically under conditions that ideally should result in a high quality and cost-effective part. Injection molding machines have two principal components to perform the cyclical steps in the injection molding process. These are the injection unit and the clamp unit (Figure 11.4). We now describe the operation of the various units of the injection molding machine... 

Determine the cycle time of an injection-molding process of polystyrene at the following conditions. How can you decrease flow time Cooling time Dead time ... 

This method makes it possible to compare quantitatively the adhesion strength results of a wide range of material combinations under real manufacturing conditions. The influence of material formulations and injection molding process parameters can now he investigated with a high level of... 

Pantani R, Coccorullo I, Speranza V, Titomanlio G (2005) ModeUng or morphology evolution in the injection molding process of thermoplastic polymers. Prog Polym Sci 30 1185-1122 Pantani R, Speranza V, Titomanlio G (2001a) Relevance of mold-induced thermal boundary conditions and cavity deformation in the simulation of injection molding. Polym Eng Sci 47 2022-2035... 

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