Ultrasonic Wall Thickness Gauge

Ultrasonic Wall Thickness Measurement in Hose, Pipe and Tube Extrusion Processes

Extrusion is a continuous manufacturing process for producing hoses, pipes and tubes. Molten or semi-molten materials — plastics (PVC, polyethylene, polypropylene), or elastomers - are forced through a die to form uniform, long profiles. Accurate control of wall thickness is essential. Variations lead to structural weaknesses, pressure failures, electrical breakdowns, leaks, or excess material consumption, increasing scrap and costs.

Ultrasonic wall thickness gauging provides a non-destructive, real-time, inline measurement solution using the pulse-echo principle. A high-frequency transducer (typically 2 to 20 MHz) emits acoustic pulses into the extruded product, usually with water from the post-extruder cooling bath acting as the coupling medium. The waves reflect from the outer surface and the inner surface. The system measures the time-of-flight (TOF) between these echoes.

Wall thickness S is calculated as: S = (v × t) / 2

where v is the ultrasonic velocity in the material (approximately 2300 m/s for many thermoplastics, depending on formulation and temperature) and t is the round-trip transit time. In multilayer structures - common in barrier hoses, fuel lines and medical tubing — additional echoes from layer interfaces allow individual layer thicknesses to be resolved, often to below 0.05 mm.