Non - Contact Wall Thickness Gauge

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

Extrusion is a continuous manufacturing process for producing hoses, pipes, tubes, and cables. Molten or semi-molten materials—plastics (PVC, polyethylene, polypropylene), elastomers, or metals—are forced through a die to form uniform, long profiles. Accurate control of wall thickness (or insulation/sheath thickness in cables) 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 2–20 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 (or conductor in cables). The system measures the time-of-flight (TOF) between these echoes, and wall thickness

S is calculated as: S = (v × t) / 2

where v is the ultrasonic velocity in the material (approximately 2,300 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, medical tubing, or multi-layer power cables—additional echoes from layer interfaces allow individual layer thicknesses to be resolved, often to below 0.05 mm.