title = "Coating Thickness Measurement Methods"

content = """
Measuring coating thickness accurately is fundamental to ensuring protective and functional coatings meet specification at Ridgecrest Metalworks. Different measurement methods apply to different coating and substrate combinations, and selecting the correct instrument prevents measurement error.

Magnetic induction gauges measure non-magnetic coatings (paint, powder coat, zinc, aluminum) on ferrous (steel, iron) substrates. A probe placed on the coated surface generates a magnetic field; the instrument measures field strength, which varies with the distance between the probe and the ferrous substrate (i.e., the coating thickness). These gauges are fast, non-destructive, and accurate to ±1–3 µm for calibrated instruments. They are the most common instruments on the production floor for painted and powder-coated steel components.

Eddy current gauges measure non-conductive coatings (anodize, paint, powder coat) on non-ferrous conductive substrates (aluminum, copper, brass). The probe induces eddy currents in the substrate; coating thickness changes the impedance. These gauges are used for anodize thickness on aluminum and paint on aluminum structures.

Ultrasonic thickness gauges measure coating thickness through ultrasonic pulse-echo. A pulse is sent into the coating and reflected from the substrate interface; the time of flight gives thickness. Ultrasonic gauges can measure coatings on non-metallic substrates and can measure multiple coating layers individually if acoustic impedance differences exist.

Coulometric (chemical stripping) measurement dissolves the coating in a defined area using electrolytic stripping; coating thickness is calculated from the charge required. This destructive method is used for electroplating thickness verification when calibration confirmation or audit testing is required.

Cross-section metallographic measurement is the most direct and accurate method: a sample is cut, mounted in resin, polished, and examined under a calibrated optical microscope. Coating layers are measured directly from the image. This is used for quality audits, dispute resolution, and qualifying new processes.

At Ridgecrest, measurement frequency for painted parts is defined in the painting process specification — typically minimum five measurement points (four corners and center) per part for large areas, and minimum three readings per part for small components. All readings must fall within the specified minimum and maximum DFT range. Results are recorded on the inspection traveller. Gauges are calibrated on a substrate representative of the actual part (same material and geometry) using certified foil standards.
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version = "0.0.1"
