Page 357 - Plastics Engineering

340 Processing of Plastics

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London (1995).
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Questions

4.1 In a particular extruder screw the channel depth is 2.4 mm, the screw diameter is 50 mm,
the screw speed is 100 rev/min, the flight angle is 17' 42' and the pressure varies linearly over
the screw length of lo00 mm from zero at entry to 20 MN/m* at the die entry. Estimate
(a) the drag flow
(b) the pressure flow
(c) the total flow.
The plastic has a viscosity of 200 Ns/mz. Calculate also the shear rate in the metering zone.
4.2 Find the operating point for the above extruder when it is combined with a die of length
40 mm and diameter 3 mm. What would be the effect on pressure and output if a plastic with
viscosity 400 Ns/mZ was used.
4.3 A single screw extruder has the following dimensions:
screw length = 500 mm
screw diameter = 25 mm
flight angle = 17'42'
channel depth = 2 mm
channel width = 22 mm
If the extruder is coupled to a die which is used to produce two laces for subsequent granulation,
calculate the output from the extrudeddie combination when the screw speed is 100 rev/min. Each
of the holes in the lace die is 1.5 mm diameter and 10 mm long and the viscosity of the melt
may be taken as 400 Ns/mz.
4.4 An extruder is coupled to a die, the output of which is given by (KP/q) where P is the
pressure drop across the die, q is the viscosity of the plastic and K is a constant. What are
the optimum values of screw helix angle and channel depth to give maximum output from the
extruder.
4.5 A circular plate of diameter 0.5 m is to be moulded using a sprue gate in its centre. If the
melt pressure is 50 MN/mz and the pressure loss coefficient is 0.6 estimate the clamping force
required.
4.6 The container shown at the top of p. 341 is injection moulded using a gate at point A. If
the injection pressure at the nozzle is 140 MN/mz and the pressure loss coefficient, m, is 0.5,
estimate (i) the flow ratio and (ii) the clamping force needed.
4.7 Compare the efficiencies of the runners shown on p. 341.
4.8 A calender having rolls of diameter 0.3 m produces plastic sheet 1 m wide at the rate of
2000 kghour. If the roll speed is 5 revlminute and the nip between the rolls is 4.5 mm, estimate