3. Apply a coating of Dykem Blue on the gauge blanking plug over the whole area below the threads.
Screw the plug into the extruder until it bottoms out on the 45°face. Remove the plug and inspect
– only the 45°face should have had any blueing removed. If there is evidence that blueing has been
removed from other surfaces, this may mean that the port has not been cleaned correctly or the
port has not been machined properly.
4. Having ensured that the port is now fit for purpose, remove the plastic protective cap from the
transducer threads and screw this into the extruder port. If the threads on the port are clean, it
should be possible to screw the transducer in by hand until it bottoms out on the 45°face. Now
using a torque wrench with a 7/8” crow foot, torque the transducer into the extruder to 20ft.lbs
maximum.
Note: Exceeding the recommended mounting torque could result in damage to the body of the transducer
and internal tubes, thus rendering the transducer useless.
5. Next, remove the protective rubber gasket from the electrical termination head, connect the
appropriate cable assembly to the transducer and the installation is now complete. Now, the
transducer must be calibrated through the measuring instrument as follows:
6. Without running the extruder screw, apply temperature to the extruder until the desired settings
are achieved. Upon reaching temperature, allow 20 minutes for the temperature to stabilize
around the transducer and then adjust the zero on your pressure indicator/signal conditioner and
then check and adjust the calibration at 80% of the full range i.e., on a transducer with a range of
1,500 psi the cal figure will be 1,200 psi. If there are large adjustments to be made, it may be
necessary to repeat the calibration procedure once more. Calibration is now complete and the
extruder may now be started following your standard operating procedures.
Note: Under no circumstances, must the extruder be run until all zones have reached the desired polymer
extrusion temperature, as another primary cause of transducer failure is cold starts. Not only will a cold
start damage the transducer but this can also result in severe damage to the extruder.
EXTRUDER START UP AND SHUT DOWN
On many extruders, manual controls are provided for starting/stopping the extruder drive by means of
delivering an analog signal to the drive circuitry. It has been found that if the extruder drive is subject to a
fast start or closure by cranking up the control potentiometer, this will in effect produce a very fast
pressure peak that is almost impossible to detect, unless the melt pressure transducer is connected to an
instrument such as a UV recorder. However, this fast rising pressure peak is sufficient to destroy the
pressure transducer strain gage assembly and it is therefore recommended that fast starts are avoided.
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