T.L. Wong et aL. /Journal of Materials Processing Technology 63(1997)399-404 Table 3 Such a study was carried out by using the energy Twin-screw compounding conditions spectrum analysis system attached to the Joel JSM 820 SEM Die diameter(mm) 2.7. Whisker length measurements Screw length/dia, ratio Screw speed (r.p. m feed 200210220210 The whisker length distributions of the three A/W/P blends A 6 mm die was used for the alumina/ whisker/polymer blends which after compounding and after injection moulding were measured cannot be extruded from the 3mm die The procedures for carrying out the measurements were described as follows:()small pieces of samples were cut from Rectangular bars with size70×10×6mm3 injection the corresponding sprues, followed by ashing at 600C to moulded from the four types of A/W/P blends prepared using a remove the polymeric binders; (i)the ashed sample was Hitech WellTec Industrial Equipment Ltd, HK). The injection minutes with a Thermolyne magnetic stirrer; (in) a drop of moulding conditions are given in Table 4 and the injection lution was taken and spread onto a glass slide(in order to moulded rectangular bar with sprue is shown in Fig 3 avoid errors caused by sedimentation the drop of solution was taken while the solution was still being stirred) length of 800 whiskers per sample were measured by using ar optical image analysis system. Cumulative frequency of the 3. 1. Lubricant and mixing route During the MFI measurement, the a/P blends with N15 and cm E43 lubricant could not be extruded from the heated barrel at Fig. 3. The injection moulded rectangular bar the specified MFI testing conditions stated in Section 2.2 However, the A/P blend with the N34 lubricant had an average MFI value of 0. 17 g/10 mins. Clearly, the lubricant N34 2.5. Ceramic weight composition measurements provided better flow properties to the A/P blend and consequently was selected as the lubricant for subsequent The ceramic weight composition after injection moulding compounding and injection moulding. From Table 1, it is noted Sprues were cut from the as-moulded that N34 has the lowest molecular weight. Thus, it possesses a rectangular bars and some of these were used as samples for lower viscosity than the other two types of lubricant [111 this measurement. It was assumed that the ceramic wt at the Usually, for a given ceramic content, a lower binder viscosity sprue and that at the body of the rectangular bar were the same ill give a lower ceramic/polymer blend viscosity. Therefore Five sprues from each type of rectangular bars were ashed at there is no doubt that N34 provides better flow properties 600C in a Nabertherm Model L3/17S programable furnace to among the a/P blends remove the polymeric binders. The weight of the specimens Fig. 4 shows the SEM micrographs of the fracture surface of and after ashing were measured by a Ohaus ToP-pan the compression moulded bars prepared by mixing route I with 5, 15 and 30 vol SiC w respectively. Examination on the micrographs revealed that the whiskers were 2. 6. Iron content analysis homogeneously inside the moulded bars. The SiCwconcen- tration are low in some regions (as shown by the photographs SiCw is a very abrasive material, and can cause we on the left-hand-side of Figs. 4a-c), but are exceptionally high the barrels and of the compounder and the in some other regions(see photographs on the right-hand-side of moulding machine. A study of the composition of the Figs. 4a-c). However, for the compression moulded bars content in the compounded blends and the injection prepared by mixing route 2 a uniform bars can indicate the extent of wear in the barrels and Injection moulding conditions A/W/P bler Screw Length/dia, ratio Barrel temperature(feed-nozzle, C) 200-210200 200-210-200 200-210-200 ould Temperature (C) Cycle time(sTL. Wong et al. I Journal ofMaterials Processing Technology 63 (1997) 399-404 401 Table 3 Twin-screw compounding conditions Screw diameter (mm) 41.8 Die diameter (mm) 3* Screw length/dia. ratio 7 Screw speed (r.p.m.) 30 Barrel temperature (feed to die, 0c) 200-210-220-210 * A 6 mm die was used for the alumina/whisker/polymer blends which cannot be extruded from the 3mm die. Rectangular bars with size 70x IOx6 mm3 were injection moulded from the four types of A/W/P blends prepared using a reciprocating-screw machine (Cosmo TTI-220/80 Hitech, WellTec Industrial Equipment Ltd., HK). The injection moulding conditions are given in Table 4 and the injection moulded rectangular bar with sprue is shown in Fig. 3. c:."" Fig. 3. The injection moulded rectangular bar. 2.5. Ceramic weight composition measurements The ceramic weight composition after injection moulding was measured. Sprues were cut from the as-moulded rectangular bars and some of these were used as samples for this measurement. It was assumed that the ceramic wt% at the sprue and that at the body of the rectangular bar were the same. Five sprues from each type of rectangular bars were ashed at 600 °C in a Nabertherm Model L3117S programable furnace to remove the polymeric binders. The weight of the specimens before and after ashing were measured by a Ohaus Top-pan electronic balance. 2.6. Iron content analysis SiCw is a very abrasive material, and can cause wearing on the barrels and screws of the compounder and the injection moulding machine. A study of the composition of the iron (Fe) content in the compounded blends and the injection moulded bars can indicate the extent of wear in the barrels and screws. Such a study was carried out by using the energy dispersive spectrum analysis system attached to the Joel JSM 820 SEM. 2. 7. Whisker length measurements The whisker length distributions of the three A/WIP blends after compounding and after injection moulding were measured. The procedures for carrying out the measurements were described as follows: (i) small pieces of samples were cut from the corresponding sprues, followed by ashing at 600 °C to remove the polymeric binders; (ii) the ashed sample was dispersed in a beaker of alcohol by continuous stirring for 20 minutes with a Thermolyne magnetic stirrer; (iii) a drop of this solution was taken and spread onto a glass slide (in order to avoid errors caused by sedimentation the drop of solution was taken while the solution was still being stirred); and (iv) the length of 800 whiskers per sample were measured by using an optical image analysis system. Cumulative frequency of the whisker length were then plotted. 3. Results and Discussion 3.1. Lubricant and mixing route During the MFI measurement, the AlP blends with N15 and E43 lubricant could not be extruded from the heated barrel at the specified MFI testing conditions stated in Section 2.2. However, the AlP blend with the N34 lubricant had an average MFI value of 0.17 g/1O mins. Clearly, the lubricant N34 provided better flow properties to the A/P blend and consequently was selected as the lubricant for subsequent compounding and injection moulding. From Table 1, it is noted that N34 has the lowest molecular weight. Thus, it possesses a lower viscosity than the other two types of lubricant [11]. Usually, for a given ceramic content, a lower binder viscosity will give a lower ceramic/polymer blend viscosity. Therefore, there is no doubt that N34 provides better flow properties among the A/P blends. Fig. 4 shows the SEM micrographs of the fracture surface of the compression moulded bars prepared by mixing route 1 with 5, 15 and 30 vol% SiCw respectively. Examination on the micrographs revealed that the whiskers were not distributed homogeneously inside the moulded bars. The SiCw concen￾tration are low in some regions (as shown by the photographs on the left-hand-side of Figs. 4a-c), but are exceptionally high in some other regions (see photographs on the right-hand-side of Figs. 4a-c). However, for the compression moulded bars prepared by mixing route 2, a uniform dispersion of SiCw Table 4 Injection moulding conditions A/W/Pblend Screw diameter (mm) Screw Length/dia. ratio Barrel temperature (feed - nozzle, °C) Mould Temperature ("C) Injection pressure (MPa) Hold pressure (MPa) Hold time (s) Cycle Time (s) A152 33 18 200-210-200 20 90 90 5 20 5SC 33 18 200-210-200 20 100 100 5 20 15SC 33 18 200-210-200 20 130 130 5 20 30SC 33 18 200-210-200 20 130 130 5 20