Industrial coatings applied to substrates like metal, plastic, glass and composite protect various products from corrosion and damage to extend lifespan. Commercial coatings are also routinely applied to wood, metal and concrete structures to protect against mechanical, chemical and environmental degradation while improving aesthetics.
To ensure quality, manufacturers that utilize or formulate coatings rely on various methods of testing to determine resistance to friction, peel, wear and scratches.
Without the necessary adhesive strength or durability, it is possible for a coating to bubble, flake, peel or otherwise fail prematurely. Depending on the application, this can cause costly warranty issues as well as safety issues that can compromise the manufacturer’s reputation and market share.
As an example, for several years a popular minivan struggled with paint blistering and bubbling in the heat, direct sun and exposure to road salt in northern regions.
“Paint and primer would start to flake off some vehicles in a matter of just a few months, leading to rust spots and an undesirable finish. The auto manufacturer could have avoided damage to their reputation and financial loss from warranty claims with more thorough coating testing using the proper measurement equipment,” said John Bogart, Managing Director of Kett US, a manufacturer of a full range of testing instruments for adhesion, peel and wear measurement.
To create reliable coatings or products that utilize them, engineers and quality assurance teams require reliable test instruments to verify that the necessary properties and industry standards are met, particularly for high-value or high-volume applications.
Although desktop and inline process analyzers are available, the challenge is that conventional coating test equipment typically offers a limited range of functions. Consequently, multiple instruments are often required. There are also other issues with traditional testing methods that make them inconsistent, laborious and time-consuming.
As a result, some industry suppliers now provide a wide range of coating measurement equipment that performs like a “Swiss army knife” with multi-functional testing capabilities that allow greater flexibility and productivity. These desktop, online and inline testing solutions are cost-effective analytical tools that can quickly determine a wide range of critical coating properties.
All-in-One Desktop Units
When various coating properties need to be tested, a desktop all-in-one unit like Kett’s 14FW offers a significant amount of flexibility in a single machine with assorted jig attachments for specific tests. The device tests and measures multiple coating properties including friction, wear, peel and scratch resistance.
The all-in-one unit provides exceptional flexibility to test coatings. By changing the jig attachment, the contact mode in friction and wear testing can be modified and scratch intensity and peeling resistance tests can be performed. By presetting the speed of table movement, stroke length and stroke count, the tester can provide testing under various conditions.
The unit can also measure scratch resistance. This is expressed based on the size of the scratch made by a conical scratch test pin while a predetermined vertical load is applied. A pencil scratch intensity test can also be performed.
According to Bogart, conventional testing equipment utilizes substantial “force” that can damage the substrate material so ten tests or more may need to be conducted and averaged.
Since the H14FW unit utilizes much less force, it is more subtle and can be used to compare coatings on various substrates or items that are challenging to coat.
“The unit can detect very slight nuances in coating formulation batches. This allows manufacturers to confidently make critical coating decisions involving considerable capital, knowing they are making the best choice and proceeding correctly,” said Bogart.
Continuous Coating Testing
The industry has developed benchtop instruments that enable the real-time testing of changes in frictional resistance due to wear when this is required. As an example, Kett’s H40 Friction and Wear Tester uses a balance arm that crosses the feed table at right angles in forward and backward motions to measure frictional forces with very high accuracy.
The unit, which is equipped with a load converter containing a probe integrated into a holder, continuously measures changes in frictional resistance due to wear. The stroke count at which a coating peels or its surface condition changes, is determined from an increase or decrease in the frictional resistance of the balance arm as it moves back and forth.
For greater precision, manufacturers can set the stroke length of the reciprocating balance arm from 1 to 100mm and automatically stop it when the desired travel distance is reached. The frictional resistance between the coating and the balance arm can be measured very precisely, from 0 to 9.8N.
Quality assurance technicians can use a variety of measurement jigs including those for point contact measurement (i.e.-scratch test pin and ball indenter), plane contact (i.e.-flat indenter) and line contact (i.e.-blade holder).
With optional software, various measurements from static friction coefficient measurement to wear measurement can also be performed.
Although coatings are generally measured dry, testing a wet coating is possible with an addition that enables heating a sample to maintain the coating in liquid form.
Measuring Coating Thickness
To ensure consistent quality, OEMs also need to determine that a coating is evenly applied at the appropriate thickness.
“Applying too little of a coating risks poor product protection and aesthetics and applying too much wastes money,” said Bogart.
To simplify quality control, instant gauges like Kett’s model LZ990 allow users to measure coating thickness with a simple, non-destructive test. As a quality check that can improve product consistency with great precision, the device displays thickness in either mils (.001 inch) or microns (.001mm) to the thousandth decimal place.
Inline Composition Analyzers
In high-value applications, manufacturers may also want to analyze the composition of specialized coatings. Advanced composition analyzers utilize Near-infrared Reflectance (NIR) to provide accurate measurement of coatings without sampling, physical contact or degradation. These units are available in desktop, online and inline models.
“With NIR, the surface of the coating, whether solid or liquid, is measured and light is absorbed by the chemical components. The detected absorbance is converted into component values,” explained Bogart.
NIR devices can also be used to analyze moisture, film thickness and coat weight, which can simplify the process for users by allowing them to measure multiple properties with just one instrument and software.
Since measurement is instant, the instrument eliminates the need to take samples to a laboratory and put production on hold. With pinpoint accuracy, any employee can achieve consistent test results with minimal risk of error, allowing specialized technical staff to focus on other areas of the manufacturing process.
Ensuring essential coating properties are achieved is vital to performance in a wide range applications and products, so effective measurement is crucial to maintain quality. Manufacturers that take advantage of the most accurate instruments to measure all necessary coating characteristics can assure product quality, as well as protect the company’s brand and reputation.