Capillary Rheometer for Polymer Processing

What is the Capillary Rheometer for Polymer Processing?

A capillary rheometer forces molten polymer through a die at controlled piston speed and measures the pressure required, giving viscosity at shear rates that match extrusion and injection moulding. It is used where process-relevant viscosity, not elasticity, is the required output.

Overview

A heated barrel with a piston forces melt through a die of defined diameter and length, and a pressure transducer above the die records the pressure drop. Shear stress is calculated from pressure and die geometry, apparent shear rate from piston speed, and the ratio gives apparent viscosity. Because pressure is measured continuously, the instrument also records die swell, melt fracture onset and the pressure at which flow becomes unstable. Die sets with different length-to-diameter ratios allow the Bagley correction for entrance pressure loss, and multiple barrel diameters extend the shear rate range. Typical coverage is 1 to 10⁶ s⁻¹, which includes the conditions in a real extruder die, and the instrument tolerates filled, reinforced and recycled materials that would damage a rotational gap.

How does it work?

A rheometer applies a controlled deformation to a polymer sample and measures the resulting force or torque. Rotational instruments use parallel plates, cones or concentric cylinders and can work in steady shear, giving shear viscosity against shear rate, or in oscillation, giving storage and loss moduli against frequency. Capillary instruments force melt through a die of known diameter and length at a controlled piston speed, measuring pressure to calculate apparent shear viscosity at shear rates that reach those of real extrusion. Torque rheometers mix material in a heated chamber and record the torque needed to turn the rotors, which tracks gelation, fusion and degradation in a compounding context. The choice depends on the shear rate range, the sample form and whether elasticity or only viscosity is required.

What are the key features?

• Die sets with L/D ratios of 10, 20 and 30
• Pressure measurement at shear rates to 10⁶ s⁻¹
• Bagley and Rabinowitsch correction utilities
• Barrel diameters for extended shear rate range
• Detection of melt fracture and die swell
• Interchangeable dies in hardened or corrosion-resistant steel

What are the technical specifications?

A typical capillary rheometer for polymer processing configuration offers maximum pressure of Up to 1000 bar, barrel diameter of 9.55 / 12 / 15 mm, temperature range of Ambient to 400 °C, temperature accuracy of ±0.5 °C, piston speed of 0.001–20 mm/s and shear rate range of 1–10⁶ s⁻¹. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Capillary Rheometer for Polymer Processing is used in extrusion grade selection and process window definition, injection moulding fill simulation input, filled and reinforced compound viscosity and recycled polymer processability assessment. Across the wider Rheometers class, laboratories also deploy it for molecular weight and molecular weight distribution comparison, processing behaviour prediction for extrusion and moulding and filler and additive effect on melt viscosity.

Which standards and certifications apply?

Relevant standards and methods include ISO 3219, ISO 11443, ISO 6721-10, ASTM D3835, ASTM D4440, ASTM D2538 and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Sample preparation dominates repeatability: dry hygroscopic polymers, compression-mould discs of defined thickness for rotational testing, and ensure filled samples are homogeneous. Set the gap and check it with a zero-gap routine before each series, because a small gap error changes the calculated viscosity. In capillary work, verify piston speed and pressure transducer calibration, and apply the Bagley and Rabinowitsch corrections when true viscosity is required. Purge the oven with nitrogen for high-temperature or oxidation-sensitive polymers. Clean dies and plates thoroughly, since degraded residue changes the surface and the measured torque, and record temperature, geometry and gap with every result.

How do I select the right Capillary Rheometer for Polymer Processing?

Select a capillary rheometer when the viscosity range of interest lies above what a rotational instrument can reach, when samples contain abrasive fillers, or when die swell and melt fracture data are needed for die design. Specify the maximum pressure and temperature for your stiffest and hottest material, and confirm the die sets and barrel diameters required to cover the shear rate range.

How does it compare with other Rheometers variants?

Match the instrument to the shear rate range that governs your process. Rotational rheometers cover low shear rates and are the only option when viscoelastic data, yield stress or normal force are required, making them suitable for molecular weight comparisons and additive studies. Capillary rheometers reach the high shear rates of extrusion and injection moulding and are more tolerant of filled and highly viscous materials. Torque rheometers are used when the question concerns compounding behaviour, gelation or thermal stability under shear rather than a fundamental viscosity value. Inline instruments are selected for continuous process monitoring and never replace laboratory characterisation, because they see only one fixed measurement point.