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ples were determined.
2. Experimental setup
2.1. Part
A box-shaped part that consists of some details such as ribs, holes, large flat surface, conical surface and rounded edge was adopted, in order to observe the effects of runner systems on its dimensions and shape. The main dimensions of the part are 112 · 78 · 36 mm and the thickness of the walls is 2 mm. The drawing and the general view of the part are presented in Fig. 1.
2.2. Mould
In order to examine and to precisely compare the effects of HRS and CRS, it is necessary to perform the experiments at the same conditions. Thus, a two-cavity mould which can be used with both HRS and CRS
was designed and produced. The diameter of the nozzles was determined as 1.9 mm. Six resistances of 400 W for heating the nozzles and manifold, and four thermocouples for controlling the melt temperature were fitted to the mould. The determination of gate location was carried out by utilizing the Mold Flow analysis software for both HRS and CRS, as shown in Fig. 1. For each mould cavity, four cooling channels with parallel connec- tion were generated. The core and cavity halves of the mould are assumed to have the same temperature to minimize warpage. After completion of the experiments with HRS, the mould was modified for CRS by assem- bling some appropriate components such as sprue pulling pin and plugs for nozzle nests. Thus, the possibility of doing all experiments with both runner systems on the same mould and comparison of the results precisely were provided.
2.3. Injection machine and materials
An injection moulding machine having a clamping force of 80 tonnes and a shot capacity of 170 g. was used for the experiments. In the exper- iments, acrylonitrile butadiene styrene (ABS) and polypropylene (PP) polymers were used. ABS is an amorphous polymer produced by GE Plas- tics, and PP is a semi-crystalline polymer produced by Petkim A.S. Of some major specifications, the process temperature range is 220–280 °C
for ABS and 170–260 °C for PP, and the melt flow index is 3.7 g/10 min
for ABS and 6 g/10 min for PP. The detailed specifications of these poly- mers are listed in Table 1.
3. Determination of optimal moulding area
The experimental study was carried out in a wide range of temperatures recommended by the manufacturer of the material. Within this range, both melting point and decom- position limit of the material were taken into consideration. The value of packing pressure was determined to be half of the injection pressure, and the other parameters (i.e., mould temperature, injection velocity and cycle time) were kept constant during all experiments for both runner sys- tems. The process conditions adopted in the experiments are presented in Table 2.
Injection moulding processes were performed at three stages. In the first stage, achievable minimum and maxi- mum values of injection pressure were determined by heat- ing the material on the injection moulding machine to a minimum temperature at which it can be injected. Then, the same procedure was repeated for mean and maximum process temperatures. In order to determine optimal pro- cess area for HRS in comparison with CRS, moulding area diagrams (MAD) were drawn on the bases of the data obtained from the experiments. Produced samples relating to various MAD regions are shown in Fig. 2. The MADs for ABS and PP polymers are shown in Figs. 3 and 4. The lower and upper limits of the process variables used in the MADs were determined so that there would neither be a flash formation nor short shot in the injected part as well as no chemical degradation. The regions that are located to the left of and under the closed areas on these diagrams represent the short shot in the injected part at low pressure and low temperature (i.e., top in Fig. 2). The regions that are located to the right of and above the closed areas represent the flash formation in the injected part at high pressure and high temperature (i.e., middle in Fig. 2). The closed areas represent the appropriate