Meaning
Transducers positioned behind cavity ejector pins convert mechanical force exerted on ejector pins into electrical measurement signals. An indirect force sensor detects internal cavity pressure through physical transmission across intervening tool components without contacting polymer melt. The installation protects sensitive piezo elements from extreme cavity temperatures and corrosive resin gases.
Scope includes sub-ejector pin mountings and tool plate force washers, stopping at flush-mounted direct cavity transducers. Toolmakers select indirect configurations to avoid leaving sensor marks on aesthetic plastic surfaces.
Mechanical Transmission
Pushrods and ejector pins transmit cavity pressure directly to the sensor baseplate during injection. An indirect force sensor measures compressive force, which software converts to equivalent cavity pressure using pin surface area calculations. Friction along the ejector pin channel absorbs a portion of the transmitted force, introducing slight signal attenuation.
Machine operators adjust calibration values to compensate for mechanical resistance within the pin assembly.
Signal Calibration
Pin geometry and friction coefficients influence voltage output during process monitoring runs. An indirect force sensor requires empirical calibration using known cavity pressures or reference transducers. Software algorithms scale measured force against pin area to yield cavity pressure readings.
Variations in pin lubrication or thermal expansion alter calibration accuracy over long production cycles.
Maintenance Requirement
Polymer debris and grease accumulation inside ejector pin holes degrade force transmission over time. An indirect force sensor requires routine tool inspection and pin cleaning to maintain baseline signal accuracy.
