Introduction
ONEhalf20 Melt Pressure Transducers are a measuring
instruments that are subject to damage if mishandled, improperly
installed or dropped.
Melt
Pressure Transducer Diaphragm
The
ONEhalf20 Melt Pressure Transducer is a sealed system.
The sensing diaphragm is the most important component of the transducer. The
standard diaphragm is of a one piece construction, machined from
type 15-5PH stainless steel, with a proprietary coating designed
to increase durability. It has a nominal thickness of 0.0050 inches.
If the sensing diaphragm becomes damaged in any way i.e.: dented,
gouged or deformed, the transducer will no longer provide accurate
readings and should be returned to
ONEhalf20 for repair and/or replacement. See the
repair and re-calibration information in the Technical section of
our website for further details.
The
Melt Pressure Transducer Mounting Hole
A poorly prepared
or machined transducer mounting hole is one of the main causes of
damage to the transducer. Extruder barrel wear should be monitored
periodically. As the extruder barrel wears, the transducer diaphragm
will move closer and closer to the barrel bore until it is flush
with the sidewalls. Once the diaphragm is flush with the extruder
barrel, it will wear at the same rate as the extruder barrel. To
alleviate this problem, ONEhalf20
recommends that the transducer be recessed 0.0175" from the
barrel bore. A copper spacer can be manufactured or purchased (to
seal on the 45 degree seating surface) that will act as a separator
backing off the transducer diaphragm from the inside barrel bore.
If the transducer diaphragm protrudes into the extruder barrel,
it is subject to unnecessary rapid wear and is subject to permanent
damage by a passing screw flight.
Preparing
and Gaging of the Melt Pressure Transducer
Mounting Hole
The mounting hole
should be cleaned and gagged prior to the installation of a new
transducer or when replacing an existing transducer. A
ONEhalf20 Cleaning Tool Kit is available from
ONEhalf20 to permit cleaning of the mounting hole.
The kit also includes a gage plug to check the integrity of the
mounting hole.
Melt Pressure Transducer Mounting Hole Threads
The transducer mounting
threads should be 1/2-20UNF-2B. See the mounting hole dimensional
drawing in the Technical section of our website for further details.
The mounting hole should be cleaned and inspected prior to the installation
or reinstallation of a transducer. The use of a high temperature
anti-seize compound will help in prevent galling and will allow
easy removal of the transducer. Copper graphite anti-seize compounds
are recommended.
Melt
Pressure Transducer Mounting Torque
ONEhalf20 Melt Pressure Transducers are capable of
being installed at a mounting torque of up to 500 inch/pounds without
damage or zero shifts; an adequate seal is generally achieved with
a mounting torque of 100-200 inch/pounds. This can be accomplished
by first installing finger tight and then tightening the transducer
a quarter turn with a wrench. Excessive mounting torque will cause
seizing and make the transducer difficult to remove.
Melt
Pressure Transducer Operating Temperatures
The
ONEhalf20 Melt Pressure Transducer diaphragm is capable
of operating at temperatures up to 750ºF. The transducer electronics
are capable of operating at temperatures of up to 150ºF. It
is important that the electronic housing not be exposed to temperatures
above 150ºF.
Melt
Pressure Transducer Affects of Cold Starts
One of the most common
causes of Melt Pressure Transducer diaphragm damage is cold starts.
A ONEhalf20 combined
temperature and pressure transducer can be used to insure that the
extruder barrel is up to temperature prior to the rotation of the
extruder screw.
Melt
Pressure Transducer Removal or Replacement
The transducer should
only be removed or replaced while the machine is at operating temperature
and the polymer is liquid. Removing the transducer from a cold extruder
will cause diaphragm damage due to polymer adhesion. A transducer
should never be installed into a mounting hole where there is the
presence of solid polymer. If the diaphragm is forced against a
solid, the transducer can easily be overloaded and left with a very
high zero offset, often too high to be rezeroed.
Cleaning the Melt Pressure Transducer Diaphragm
If the transducer is removed warm
from the machine, the diaphragm can be easily be cleaned with
a soft cloth. If there is solid polymer present, a fluidized bed
cleaning system can be used. Never use a wire brush, knife, or
torch to clean the tip of a transducer.
Melt
Pressure Transducer from ONEhalf20
FOLLOWING THE ABOVE WILL PROVIDE
YEARS OF TROUBLE FREE PERFORMANCE
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