Definition
An electrolytic thickness gauge is an instrument that accurately measures the thickness of the overlay on a metallic or non-metallic matrix through the principle of electrochemical dissolution. It is a non-destructive or micro-destructive testing equipment widely used to evaluate the thickness of surface treatment layers such as electroplating, coating, and anodized film to ensure that the product meets process specifications and quality standards.
Principle
Electrolytic thickness gauges work based on Faraday's laws of electrolysis. When measuring, the instrument places the electrolytic cell on the surface of the overlay to be tested, and the electrolyte comes into contact with the overlay through a specific pore size. Under constant current, the overlay is electrolytically dissolved as an anode. When the overlay is completely dissolved and the substrate is exposed, the electrode potential undergoes a mutation, and the instrument determines the end point of dissolution by detecting the point of abrupt change in this potential. The average thickness of the overlay can be calculated based on the amount of electricity consumed by the electrolysis process (the product of current and time), combined with the electrochemical equivalent, density and dissolution area of the overlay material. Its basic relationship can be expressed as:
δ = (K * Q) / (ρ * A)
Among them, δ represents the thickness of the overlay, K is the constant related to the electrochemical equivalent of the material, Q is the amount of electricity consumed during the electrolysis process, ρ is the density of the overlay material, and A is the dissolved area of the electrolysis.
Measurement method
Measurements usually follow a standardized operating procedure. First, the appropriate electrolyte and measurement parameters need to be selected according to the properties of the overlay and substrate material. Place the measuring head of the instrument against the surface of the specimen to ensure that the cell is sealed. After starting the measurement, the electrolysis process is carried out automatically, and the instrument monitors the potential change in real time. When a potential transition is detected, the instrument automatically stops the electrolysis and calculates the displayed thickness value. To improve the reliability of the results, multiple points are usually selected on the same specimen for measurement, and the average value is taken as the final result. This method is suitable for measuring most metal coatings and partially converted films.
Influencing factors
Measurement accuracy is influenced by various factors. The composition and concentration of the electrolyte must match the material to be tested, and improper formulation may lead to abnormal dissolution rates or difficulty in determining the endpoint. Fluctuations in ambient temperature can affect the conductivity and reaction rate of the electrolyte. The uniformity of the overlay material, porosity, and roughness of the substrate surface may cause local dissolution rate differences. The contact pressure, centering and electrolytic cell tightness of the measuring head and the specimen surface during operation will also directly affect the constancy of the dissolved area and the repeatability of the measurement. In addition, the current control accuracy and potential detection sensitivity of the instrument itself are the basis for ensuring accurate measurement.
Application
Electrolytic thickness gauges are widely used in industrial quality control and research and development. In the electrical and electronic industry, it is used to measure the thickness of the gold plating layer of printed circuit boards and the silver plating layer of lead frames. In automobile manufacturing, it is used to monitor the thickness of the chrome plating layer of the piston ring and the galvanized layer of the fastener. It is commonly used in the aerospace sector to inspect thermal barrier coatings or anti-corrosion coatings on engine components. In the general hardware and decoration industry, it is used to evaluate the thickness of precious metal plating for sanitary ware, jewelry and other products. This technology provides direct data support for production process adjustment, cost control and product reliability evaluation.
Selection
When selecting instruments, it is necessary to comprehensively consider technical parameters and application requirements. The measurement range should cover the expected thickness of the coating to be measured, and the resolution should meet the requirements of process control accuracy. The instrument should support the material combination to be tested (e.g., the coating-substrate system) and be equipped with the appropriate electrolyte and measurement procedure. In terms of ease of operation, you can pay attention to the degree of automation, user-friendliness and data management functions. For complex shaped workpieces, the fit and contact mode of the measuring head need to be considered. Instrument calibration traceability, long-term stability, and ease of maintenance are also important considerations. It is recommended to conduct measurement verification in combination with specific samples to evaluate the applicability of the instrument under actual working conditions.