Control OD Variation in Plastic Tubing Extrusion

Plastic tubing extrusion involves melting polymer resin and forcing it through a die to form a continuous tube. Internal air pressure is introduced to support the tube's bore and control the outside diameter as it cools in a sizing tank or water trough. Precise regulation of that internal air pressure is critical—MicroAir controllers maintain the set pressure with hysteresis-free accuracy to ensure consistent wall thickness and OD.

Key extrusion process parameters include melt temperature, screw speed, haul-off speed, cooling rate, die design, and internal air pressure. Internal air pressure is particularly influential in controlling outside diameter (OD) variation. MicroAir ultra-low pressure regulators allow extrusion engineers to set and hold air pressure values as low as below 1 inch of water, providing fine-grained control over tube dimensions.

MicroAir regulators are available in pressure ranges from 0–2 inches of water up to 0–5 psi, covering ultra-low and low pressure needs. The specific range is selected based on tubing type and application. Multi-range configurations are available, and OLC offers a range change service for units already in the field, ensuring flexibility as production requirements evolve.

Yes. MicroAir IV series regulators accept 0–10V analog input for direct PLC integration, enabling closed-loop automated diameter control. MicroAir II series units accept Air Up/Air Down contact closure signals from O.D. diameter gauges or external controllers. Manual models offer standalone 30-turn knob control for operators who prefer direct adjustment without automation.

MicroAir IV series regulators respond in less than 0.1 second—typically around 20 milliseconds—for a 50% full-scale pressure step. This high-speed response is achieved through a precision voice-coil linear motor with viscostatic damping. It makes the MicroAir IV ideal for bump and taper tubing applications where the air pressure must switch rapidly between two preset values.

Yes. Multi-channel MicroAir units (dual, 3-channel, and 4-channel models) provide independent pressure control for each lumen in multi-lumen tubing. Each channel can be configured with a different pressure range and its own display and output option, allowing separate and simultaneous OD control for each lumen cavity throughout the extrusion process.