Ensure that you only carry out the procedure using the
necessary safety equipment. The
safety equipment required is as follows:
These are in addition to the usual good practice of wearing
overalls and protective shoes/boots. Ensure that other
personnel, including operatives, are clear of the machine
during the procedure. Pay special attention to the rear
side of the machine and any personnel working on adjacent
machines. Make them aware of your intentions to carry
out the process.
Equipment
required for the process is a follows:
- Pyrometer
fitted with 'needle' type probe suitable for immersion
in the melt. Do not use a surface contact type of thermocouple
probe.
The
best practice process is as follows and for accuracy,
should be carried out after at least moulding 10 cycles
Wear
all safety equipment.
Set the machine to 'HAND' operation.
Withdraw the injection unit as far as possible so that
the nozzle is clear of the back of the fixed platen.
Adjust the injection speed and injection pressure to low
values for safety.
Place a piece of cardboard on the bed of the machine under
the nozzle.
Operate 'SCREW ROTATE' to create a charge of melt at the
front of the barrel.
Ensure that the nozzle guard is closed and operate the
'INJECT' or 'SCREW FORWARD' control - the machine will
purge a shot of melt onto the cardboard.
Plunge the needle probe into the centre of the purged
melt and move the probe around within the melt for some
seconds, whilst watching the read-out on the instrument.
When the temperature indicated has stabilised at a constant
figure, this is the true melt temperature. Record the
temperature on a note pad.
Remove the needle probe as soon as the temperature has
been recorded to avoid the melt freezing onto the probe.
Remove the purging with the cardboard and dispose of it
into a metal bin. Clean the probe immediately, removing
all traces of melt from it so that it is ready for the
next usage.
Finally compare the temperature measured in this way with
the indications from the machine controllers - differences
of more than 10°C are not uncommon. Variations greater
than this may indicate a fault on the machine instruments
or the thermocouples, or may be the result of long residence
times. If the latter, adjust set values until desired
melt temperature is achieved.
Plastic.IT
2005
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