Multi-layer Film Thickness Measurement

Paint and Coating Layer Thickness is a Critical Measurement

Coating layer thickness is a critical output parameter for paint and coating application processes.   Insufficient thickness of a primer layer can result in delamination or disbonding.  Insufficient thickness of a basecoat or color layer can negatively impact color, while insufficient thickness of other layers such as clearcoat can affect appearance.  Excessive thickness can result in material waste, sagging, solvent popping, or in the case of plastic car bumpers with crash avoidance sensors, interference in the operation of the sensor for certain metallic paint coatings.

High resolution ultrasonic thickness gauges perform thickness measurements of one or multiple layers of paint and coatings on virtually any substrate type.  Substrates include automotive steel and aluminum body panels, plastic bumper and trim components, wood, composite materials such as carbon fiber and SMC (Sheet Molded Composites), and glass.
 

Figure 1 Pulse Echo Layer Thickness Gauge (PELT) by BYK-Gardner

Principal of Operation

High resolution ultrasonic thickness gauges such as the BYK-µPELT series of gauges, are in essence acoustic microscopes, providing a one-dimensional cross-sectional image through a point on a surface.  Whereas an optical microscope discriminates layer boundaries via the differences in optical properties of the coating or paint layers being measured, an acoustic microscope senses the differences in mechanical or acoustic properties of the coating or paint materials.
 

An ultrasonic thickness gauge functions by sending an extremely short ultrasonic pulse into the top coating layer.  At the interface between each pair of coating layers, a portion of the ultrasonic pulse will be reflected back to the sensor. The remaining portion of the ultrasonic signal will continue to propagate through the subsequent layers.  Each time the ultrasonic signal crosses the interface between a pair of layers having differing mechanical or acoustic properties, an echo will be generated. The interval of time between echoes is proportional to the thickness of each coating.
 

Figure 2 Micrograph cross section of a 4-layer filmbuild on steel with PELT waveform output side by side.

Measurement Applications

• Multiple layers of coatings on automotive steel and aluminum body panels.
• Automotive plastic bumpers and other automotive trim components. 
• Primer and topcoat systems for construction equipment, railroad locomotives and rolling stock, and high-speed railway equipment.  
• Wind turbine blade coatings, shipping container anti-corrosion and topcoat coatings, and marine coatings.
• Paint coatings and lacquers on wood such as cabinetry, furniture, musical instruments, and flooring.
• Laminate coatings and layers. 

Figure 3 Intermodal shipping container.

Figure 4 Wind turbine blade

Figure 5 PELT measurement on aluminum wheel.