Report on Failed Extruder Screw
May 7th, 1996
Prosyma Research Ltd report to Weltonhurst Ltd
S F Bush
Introduction
In mid 1995 the extruder screw on a major blow moulding machine fractured in the feed zone, more or less under the hopper.
The machine had been run continuously over the previous 12-15 months with a single scheduled break of 14 days. The screw speed is normally 62 rpm with a maximum power available from the motor of around 65 kW. Set barrel temperatures appear to be as follows:
| Zone | Feed | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| Set temp | 50 | 180 | 185 | 190 | 200-210 |
From inspection of the machine, zone 1 appears to apply about 3-4 turns from the feed hopper. The barrel has cooling water and electric heating for temperature control, but there is no screw heating/cooling system. The materials being processed consist of standard MDPE/HDPE blow moulding grades with varying proportions of recyclate. The recyclate usually consists of chopped product which has failed a visual inspection test in the factory.