An Overview of Melt Pressure Measurement Technologies in Polymer Processing

Dynisco

10.09.2025

An Overview of Melt Pressure Measurement Technologies in Polymer Processing

Pressure is a key parameter in polymer processing, influencing dimensional stability, throughput efficiency, and equipment safety. Whether the process involves extrusion, molding, or compounding, precise melt pressure monitoring ensures product quality and operational reliability.

At Dynisco, we have over six decades of expertise in melt pressure sensing. From early mechanical gauges to modern digital sensors, our innovations have shaped the way processors monitor this critical variable. This article outlines the key melt pressure measurement technologies available today, including traditional strain-gauge sensors, mercury-free options, and fill-free capacitance-based designs.

From Analog Gauges to Electronic Strain-Gauge Transducers

Historical Evolution

• Mechanical pressure gauges and hydraulic transducers were standard on early extrusion lines.

• These tools offered basic safety feedback but lacked the precision and digital outputs needed for modern automation.

The Strain-Gauge Breakthrough

• Strain-gauge melt pressure transducers introduced electronic signal output.

• They use a diaphragm and fill fluid to transmit melt pressure to a strain gauge.

• This enabled closed-loop process control, marking a significant step toward automation.

This foundational design remains central to many current pressure sensors.

Moving Beyond Mercury: Alternative Fill Fluids

While mercury has been favored for its thermal stability and pressure fidelity, evolving health and environmental regulations have prompted the development of safer alternatives. Dynisco offers several non-mercury fill options:

Fill Fluid Alternatives

• HTF (High Temperature Fluid): A sustainable, mercury-free fill with stability up to 350°C. Ideal for general polymer extrusion.

• NaK (Sodium-Potassium Alloy): Suited for high-temperature applications (up to ~530°C), including PEEK and fluoropolymer processing.

• Food-Grade Oil: FDA-approved for food and medical extrusion, ensuring regulatory compliance without contamination risk.

These fills allow processors to align sensor choice with process temperature, compliance requirements, and environmental priorities.

Fill-Free Capacitance Sensors: The Vertex® Innovation

Some applications demand a fluid-free solution. The Vertex® Series eliminates fill fluids entirely by employing capacitance-based technology.

Vertex Benefits

• No contamination risk: Ideal for sensitive applications in food and medical sectors.

• High accuracy: ±0.25% full scale.

• Rapid response: Critical for detecting transient pressure variations.

• Sustainability: Longer lifespan, no hazardous materials, and less sensor waste.

Vertex sensors represent a leap forward in combining safety, performance, and environmental stewardship.

Dynisco Sensor Families: Purpose-Built for Diverse Needs

Dynisco organizes its melt pressure solutions into specialized sensor families, each engineered for specific use cases:

• SPX Series: Versatile strain-gauge sensors with configurable fill options (HTF, NaK, oil, mercury). Designed for durability and digital integration.

• Vertex®: Capacitance-based, fill-free sensors optimized for high-purity, high-safety applications.

• PTX/MDX (BenchMark™): Economical strain-gauge models offering dependable accuracy for standard extrusion lines.

• ECHO: Budget-friendly sensors for non-critical applications requiring basic performance.

• Guardian Options: Safety-enhanced versions that trigger alarms or shut down processes when pressure thresholds are exceeded.

These sensor families enable processors to balance accuracy, regulatory compliance, durability, and budget constraints.

Application-Specific Use Cases

Melt pressure measurement technologies are widely deployed across polymer sectors:

• Blown Film Extrusion: SPX or ECHO sensors ensure uniform gauge and pressure stability.

• Medical Extrusion: Vertex or food-grade oil sensors provide contamination-free pressure monitoring.

• High-Temperature Polymers: NaK-filled SPX sensors deliver stable readings under extreme thermal loads.

• Food Packaging: Oil-filled sensors meet FDA standards while ensuring extrusion quality.

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