Direct Pin Sensor Placement and Dynamic Viscosity Control in Micro-Moulds
Direct pin pressure sensing in micro-moulds compensates for melt viscosity drift by dynamically adjusting injection speed to hold precise shear rates.
Piezoelectric Pin Sensor
Meaning
A high-precision contact transducer measures the dynamic pressure of the polymer melt inside a mold cavity by detecting the mechanical force exerted on an ejector or dummy pin. Molding engineers deploy the piezoelectric pin sensor in high-volume production lines to acquire realtime cavity pressure curves during each injection cycle. This method avoids placing a sensor directly in contact with the plastic surface, preventing cosmetic marks on the molded part.
Mechanical Action
As the polymer melt fills the cavity, it presses against the head of the ejector pin. This force is transmitted down the shaft of the pin to the piezoelectric pin sensor located behind it in the ejector plate. The compression of the quartz elements in the sensor generates an electric charge proportional to the force, which the machine controller interprets as cavity pressure.
Positioning Impact
Selecting the correct pin is essential for accurate data collection. Placing the piezoelectric pin sensor at the end of the flow path ensures that the controller can verify complete cavity filling. If the sensor is placed too close to the gate, it fails to detect short shots.
The pin must also move freely in its bore to prevent frictional losses from distorting the pressure reading.
Process Optimization
The feedback from these devices is used to automate sorting gates for defective parts. When a cycle fails to reach the required peak pressure, the machine rejects that specific part immediately.