Q4 A thin rectangular plastic part is to be manufactured by injection moulding using the runner layout shown in Fig. 24.

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Q4 A Thin Rectangular Plastic Part Is To Be Manufactured By Injection Moulding Using The Runner Layout Shown In Fig 24 1 (52.7 KiB) Viewed 46 times

Q4 A Thin Rectangular Plastic Part Is To Be Manufactured By Injection Moulding Using The Runner Layout Shown In Fig 24 2 (22.29 KiB) Viewed 46 times

Q4 A Thin Rectangular Plastic Part Is To Be Manufactured By Injection Moulding Using The Runner Layout Shown In Fig 24 3 (70.89 KiB) Viewed 46 times

Q4 A Thin Rectangular Plastic Part Is To Be Manufactured By Injection Moulding Using The Runner Layout Shown In Fig 24 4 (47.53 KiB) Viewed 46 times

Q4 A Thin Rectangular Plastic Part Is To Be Manufactured By Injection Moulding Using The Runner Layout Shown In Fig 24 5 (6.66 KiB) Viewed 46 times

Q4 A thin rectangular plastic part is to be manufactured by injection moulding using the runner layout shown in Fig. 24.1. The plastic material is polyethylene and its flow and thermal properties are given in Figs 24.2 & 24.3. a) Calculate the shot size and determine the injection time if the planned flow rate is to be 8,200 mm/s. The volume of the sprue may be ignored. [4 marks) b) If the plastic enters the runners from the sprue at 210°C, estimate the pressure loss that the melt will experience in flowing through the runner and gate system to the edge of the part. You may assume isothermal conditions. [8 marks) c) If it may be assumed that the melt has cooled to 170°C when it enters the cavity, estimate the pressure loss in fully filling the cavity at this melt temperature. Again you should assume isothermal conditions and entry effects may be ignored. Hence determine the minimum injection pressure (ignoring the sprue) required to fully form the part. [6 marks) d) If the part may be ejected from the mould when its centreline temperature reaches 80°C, use the information given in Fig. 23.3 to calculate the cooling time. Hence estimate the cycle time. The thermal diffusivity of the plastic is 1.1 x 107 m/s and the mould temperature is 35°C. 17 marks]
54mm Runner 6mm diameter 26mm 68mm Gate 2 mm wide 2.5 mm long 1 mm deep sprue Part 1.75 mm deep 102mm 25mm 48mm Figure Q4.1 - Injection Moulded Part -
106 Tensile Viscosity 105 170°C 104 Figure Q4.2 - Flow Curves for Polyethylene Viscosity (Ns/m2) 210°C 103 Shear Viscosity 102 10 1 10 103 104 102 Strain Rate (S-1)
1 0.8 Conduction ( Bi =a ) 0.6 0.5 0.4 Flat Sheet 0.3 Figure Q4.3 -Dimensionless Temperature Data for Two Geometries Temperature Gradient 0.2 Cylinder 0.1 0 0.2 0.8 0.4 0.6 Fourier Number
Q4(a) 1.35 x 10 mm, 1.64 s; (b) 2.93 x 10' Pa; (c) 52.66 MPa; (d) 5.26 s