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What is a Melt Pressure Transmitter? Complete Guide on Uses, Principles, and Installation
In high-temperature melt processing industries such as plastics, rubber, metals, and glass, the melt pressure transmitter is one of the key instruments ensuring product quality and production safety. It is designed for extreme high-temperature and high-pressure environments, accurately measuring pressure variations within the melt and converting them into standard electrical signals for control systems. This helps operators stabilize process parameters, avoiding equipment damage or product quality fluctuations.
This article details the functions, working principles, major applications, and practical installation, operation, and maintenance tips for melt pressure transmitters, helping professionals choose and operate them correctly.
Main Uses of Melt Pressure Transmitters
The primary function of a melt pressure transmitter is to measure the pressure of molten material under high temperature (typically above 400°C) and high pressure, converting the physical pressure signal into standard industrial signals (4–20 mA or 0–10 V) for PLC, DCS, or dedicated controllers.
It mainly addresses the following critical issues:
Monitor pressure at the extruder screw front or die to prevent overpressure causing rupture or underpressure causing voids
Assess melt flow resistance and check if screens/filters are blocked
Provide feedback for closed-loop control (e.g., automatic screw or pump speed adjustment)
Ensure product quality consistency (e.g., uniform film thickness or pipe wall thickness)
Typical industry applications include:
Plastic extrusion (PE, PP, PVC, PET, etc.)
Rubber extrusion and molding
Blown film, cast film, and sheet production lines
Textile fiber spinning and composite material processing
Some metal die-casting and glass melt processes
Working Principle and Structural Features
Melt pressure transmitters typically use strain or diaphragm sensors, transferring high-temperature melt pressure through an isolation structure to the sensor chip in a normal temperature zone to prevent direct heat damage to electronic components.
Basic working process:
High-temperature melt pressure acts on a hard alloy or stainless steel isolation diaphragm (temperature resistant up to 538°C)
The diaphragm’s tiny deformation is transmitted via a rigid rod or capillary filled with silicone oil to the strain gauge/bridge
Strain gauge resistance changes generate an mV-level signal
Internal amplification and compensation circuits convert it into a 4–20 mA standard signal output
Common structural types include:
Rigid rod: suitable for short-distance, fast-response applications
Flexible capillary: keeps sensor electronics away from high-temperature zones, ideal for extreme heat
Many models also include overload protection diaphragms and high-temperature anti-stick coatings for long-term reliable operation.
Proper Installation Tips
Installation quality directly affects measurement accuracy and service life. Key steps recognized in the industry:
1. Installation Location
Preferably at the melt pump outlet, in front of the die, or before/after filters, avoiding dead zones and stagnant material areas
Avoid direct impact zones of the screw to prevent particle wear on the diaphragm
Recommended: middle to rear barrel or die connection of the extruder
2. Base Machining and Welding
High-demand environments may require custom curved bases matching pipe inner diameter
For ordinary cases, ensure tapered sealing surfaces are precise, welds are firm, and stress concentrations are avoided
Drill holes away from welds and bends
3. Sensor Installation and Sealing
Check thread and taper fit with a special gauge before installation
Apply high-temperature anti-seize compound (copper or nickel-based) evenly on threads
Torque control within recommended range (typically 40–60 N·m depending on model)
For flexible capillary types, secure the capillary to prevent excessive bending
4. Power-Up, Commissioning, and Thermal Tightening
Connect circuitry at room temperature, adjust zero to display 0
Pressure test system (air/water) to check for leaks
Heat to process temperature and perform thermal tightening (zero often drifts 0–0.3 MPa per 100°C)
Readjust zero to ensure accurate high-temperature measurement
Daily Maintenance and Operating Notes
Keep clean: regularly wipe the housing to prevent carbonized melt residue
Check seals: inspect for leaks at base and sensor connection
Use insulation and heat tracing in low temperatures to prevent crystallization blocking measurement ports
Periodic calibration: recommended every 6–12 months for zero and span
Avoid overpressure: install safety burst disks or pressure relief valves
Conclusion
Melt pressure transmitters are indispensable “eyes” in modern extrusion and molding production lines, converting high-temperature, high-pressure melt pressure into controllable signals for process optimization, quality stability, and equipment protection. Correct selection, proper installation, and careful maintenance are key to ensuring long-term high-precision operation.
If you are planning or optimizing plastic/rubber production lines, consider upgrading your melt pressure measurement system — a small pressure transmitter can significantly improve quality and reduce costs.
