What is a Film thickness Gauge?

Coatings and platings are applied to materials to improve their functional performance and extend their life expectancy. The range of acceptable thickness for the coating must fall within the range that has been specified. 

The final product could fail too soon in the field because of corrosion, wear, or poor electrical contact in the case of electronics if the plating is too thin. Overly thick coatings can interfere with assembling complicated components, such as engine parts.

When applying a decorative coating, it is crucial to get the thickness just right so that the final product looks good; otherwise, the part will either need to be redone or thrown away.

Film thickness, paint thickness, or dry film thickness (DFT) gauge is a tool for determining the thickness of the surface coating and measuring dry film thickness on different substrates. Because of its impact on the coating process, quality, and cost, dry film thickness is arguably an essential measurement used in the coatings industry.

Dry film thickness measurements can be used to assess the expected life of a coating, the product's appearance and performance, and compliance with a variety of International Standards.

The Film thickness gauges that can measure the metal or non-metal substrate in a non-destructive manner are the ones that are used in most applications.

This tool is employed in the engineering and production processes that necessitate precise Film thickness measurements to meet government regulations or individual client needs.

You can measure the Film thickness in both states, wet and dry. But non-destructive Film thickness measurements are needed when the film or coating is dry.

In most cases, the substrate is a ferrous metal like steel or iron or a non-ferrous metal like aluminum or copper. When measuring the thickness of a coating, it is sometimes necessary to do it on a non-metal substrate such as wood, glass, or plastic. The thickness of the coating is generally determined in microns (one micron is one-thousandth of a millimeter).

Coating ThicknessGauge Working Principle

Materials and components are coated for different reasons, with a layer made from a different material. Independent of the actual cause, like protection or decoration, the measurement of the existing Film thickness of the applied material is crucial. coatings measurement typically fall into two category:

• Destructive Film thickness measurement
• Non-destructive Film thickness measurement

Destructive Methods

As the name implies, destructive methods typically destroy the component being measured during the process. This can be accomplished by microscopy (sample preparation) or couloscopy (coating removal via reverse electroplating) techniques.

Microscopy

Optical microscopy is a destructive technique for measuring Film thickness that reveals the edge of a coating under an optical microscope.

The sample needs to be cut into pieces, then mounted and polished to show the exposed edge of the hot-dip galvanized coating. The thickness of the coating can then be determined through the calibrated eyepiece of an optical microscope.

Due to the destructive nature of the method, it is generally suitable for inspecting a single specimen sample, resolving measurement disputes, or for research purposes. The operator's skill significantly impacts the accuracy of optical microscopy.

Couloscope (Reverse Electroplating)

The couloscope uses the coulometric method based on anodic dissolution (DIN EN ISO 2177) to measure the thickness of almost any metallic coating, including multi-layer coatings, on any substrate material. 

This involves reversing the electroplating process (de-plating) by dissolving a metal coating from its metallic or non-metallic substrate using an electrolyte and a controlled electric current. The mass of the metal to be removed directly determines how much current is needed for de-plating.

When the test current and area are both held constant, a clear relationship between the de-plating time and the Film thickness appears.

Measuring Film thickness with a couloscope offers a variety of benefits. It is possible to measure several coatings on any substrate; there is no need for sample preparation, the process is quick, and the findings are precise (less than 1 micrometer).

However, there are some restrictions imposed by the approach. The procedure is unable to measure coatings that are not metallic, and the sample must be depleted (it is destructive).

Non-destructive Methods (AFM)

Unlike the previous methods, which involved destroying the sample to measure the thickness of the coating, the following will aim to measure the thickness of the coating without damaging the sample.

Ultrasonic

When measuring the thickness of a substance, ultrasonic techniques work by inducing sound waves through the material. Wall thicknesses, such as those of oil or gas pipes (to detect corrosion on the internal diameters), are the most common application for these instruments; nevertheless, they can also be used to measure the thicknesses of coatings. When a sound wave introduces to the surface of a material, it moves through the material until it reaches the opposing side.

Any boundaries that the wave encounters, such as the boundary between a coating and substrate, result in the signal's reflection back to the probe that initially generated it. This is identified, and the thickness is calculated using the distance, speed, and time formula based on the speed of sound in the material. Ultrasonic methods are universally applicable for measuring almost any material.

β-Backscatter

The method operates based on the EN ISO 3543 measurement standards. The probe contains an isotope that, when activated, generates β -particles that can break through the coating surface and the substrate. A Geiger-Müller tube detects particles reflected 180 degrees from the coating and substrate. The measurement can be successfully done only when there is a difference of at least five atomic numbers between the coating and the substrate. The -backscatter has been used in the automotive sector to measure paint and lacquers on plastic components like bumpers and in the electronics business to measure coatings on ceramics.

Magnetic Induction

The magnetic Film thickness gauge is used primarily for Coatings on ferromagnetic substrates. An excitation current will produce a low-frequency magnetic field. Its strength depends on the distance between the probe and the base material. A measurement coil measures the generated magnetic field. The resulting measurement signal is translated into Film thickness values using a specific probe output function. Non-ferrous metal, organic plastic/paint coatings, or anodic films on electrically conductive non-ferrous metal substrates are typical applications. This method is suitable for coating measurement in a variety of industries, including architectural (anodizing), automotive (dry film thickness of paint), and aerospace (functional or protective coatings on lightweight substrates).

Eddy Current (phase-sensitive)

Eddy's current method uses the difference in phase between the excitation and detection signals to determine the Film thickness. This method is intriguing because it can assess dual coatings (paint on zinc, copper, or nickel) on ferromagnetic substrates, such as steel, and organic coatings on non-ferromagnetic substrates.

Why Is Film thickness Measurement Important?

Film thickness measurement is an excellent option for various businesses and stages of their production processes because it can be done on dry and wet coatings. Detecting coating problems promptly can result in a longer lifespan for the coated component and significant savings in long-term expenditures. Also, choosing the suitable Film thickness lets you find the right balance between aesthetics and protection of the coated part. Uneven thick coatings may result in undesirable textures and the possibility of paint cracking and then leading to failure.

What Is a Mil Film thickness?

In the U.S., the Film thickness is presented in mils (one mil equals 1/1000 of an inch). Other countries across the world express Film thickness in microns (1 micron = 1 millionth of a meter and 25.4 microns = . 001” inch or one mil). A mil is a thousandth of an inch. It is a typical manufacturing dimension. The mil is the standard measurement unit used when describing a product's thickness. For example, the thickness of a credit card iS ABOUT 30 mils (30 divided by 1,000 = .030).

Applications Of Film thickness Gauge

• PCBs

• Electroplating

• Connectors

• Semiconductor wafers

• Galvanized coatings

• Industrial and automotive paint and powder coating:

• Anodized layers

• Quality assurance in the painting process

• Quality assurance in anodizing aluminum coatings

• Quality assurance for rubber coatings of metal

• Car experts

• Aerospace

• Marine sector

• Commercial vessels

• Mega yachts sector

• Oil & Gas, for piping inspections

• Chemicals, to avoid corrosion

• Construction

• Electronics

• Aircraft, to check the paint coating consistency

• Nautical and maritime maintenance, including bulkheads, tanks, ship hulls, and other coated parts

• Maintenance inspections on bridges

Features

• easy to use

• compact and a very robust

• precise

• Fast measurement

• Accurate readings

• Rapid, semi-automatic operation

• Better operating efficiencies

• Reduced lacquer consumption

• Improved product quality

• Lower spoilage

• very durable and insensitive to harsh environmental conditions

Calibration of The Film thickness Gauge

It is essential to calibrate your Film thickness gauge to get the most accurate readings. Calibration adjustment configures the gauge to established thickness values to assure accuracy across various substrate kinds, forms, and surface finishes.

There are numerous ways to calibrate the Film thickness gauge. The gauge can be set up to meet National and International Standards or a particular application. But for optimal performance and to make full use of the gauge's 1% accuracy, it should be recalibrated based on the gauge’s internal calibration routines to meet the needs of the user's unique application.

A range of calibration options is available on Film thickness Gauge, including:

Zero Calibration

Zero calibration, often known as "Single Point Calibration," is an easy method for calibrating on smooth substrates. Place the probe on the uncoated metal substrate while following the calibration instructions displayed on the screen. Ensure that the probe has complete and total contact with the surface. The gauge is prepared to measure Film thickness after automatic calibration adjustment.

Smooth Calibration

Smooth Calibration is more accurate than the single point or zero methods because it uses calibration foil and an uncoated substrate to calibrate the gauge. Calibration foils also called "shims," are the easiest way to make a coating thickness standard based on the substrate's material, surface finish, or shape. Smooth Calibration is the best way for the calibration adjustment of the Film thickness gauge to achieve maximum accuracy.

Rough or 2 Point Calibration

Rough or 2 Point is the best approach to calibrate a gauge on a rough or blasted-profiled metal substrate or a substrate with significantly different magnetic or electrical properties. For this method of calibration, you need two foil values: one above and one below the target film thickness. It's easy to calibrate your Film thickness gauge by following the on-screen instructions.

Zero Offset Calibration

Zero Offset Calibration is a unique technique for measuring film thicknesses under ISO 19840. Since the roughened surface affects the readings, the calibration employs the smooth surface approach, and a correction value (zero offsets) is given to each reading during the calibration process; the offset value is determined by the original surface profile and is expressed in ISO 19840.

Questions

Why do I Need To Calibrate?

Coating and substrate parameters affect the accuracy of any physical measurement technique. These parameters include parts geometry, electrical conductivity, magnetizability, the density of the coating, measuring surface, etc. It is vital to recalibrate the measuring device whenever there is a change in the coating or substrate parameters.

What Does a Digital Film thickness Gauge Do?

As its name suggests, the digital coating gauge primarily measures film thickness. The primary purpose of the digital Film thickness gauge is to measure the Film thickness on metal substrates such as the film layer of the PCB board process, the Ni / Cr coating on the alloy, the paint coating on the metal, and so on. Digital Film thickness gauges come in two varieties: handheld and desktop. The handheld digital Film thickness gauge is most frequently used in practice because it is convenient to use and transport. There are three digital coating thickness gauge types based on the type: magnetic thickness gauge, eddy current thickness gauge, and fluorescent X-ray thickness gauge.

Can The Gauge Be Used On Materials other Than Steel?

Yes. Most uses of the gauges require them to be used on steel. Still, they can also be used on several other materials by either entering the known speed of sound in meters per second or calibrating the gauge with the general thickness of the material being tested. Typical examples are Aluminum, Copper, and Gray cast iron, Magnesium, Nickel, Stainless Steel, Tungsten, Monel, Inconel, Phosphor Bronze, and Brass.

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