Coating inspection Instruments
A correct paint- or coating thickness is an important parameter in the surface treatment industry. The performance of a coating system is based upon correct application of this system following the paint manufacturers specification sheet. Each layer from primer to topcoat and individual intermediate layers are exactly specified with a minimum and maximum coating thickness. Often both a dry and wet film thickness is specified.
|Too low dry film thickness can lead to:||Too high film thickness causes problems like:|
Adhesion is the tendency of dissimilar particles and/or surfaces to cling to one another. The adhesive strength of paint and coatings are of crucial importance to enable the material to meet the basic functions of protection and decoration.
Adhesion testing in the paint and coating industries is necessary to ensure the paint or coating will adhere properly to the substrates to which they are applied. Adhesion testing after the coating process will quantify the strength of the bond between substrate and coating, or between different coating layers or the cohesive strength of materials.
Appearance is the common situation where surface influences meet visual differences in perception of gloss and color. The impact of different gloss levels does have a great influence on a product as well on its color. The surface quality of a coated surface is often assessed by measuring gloss. Poorly applied coatings or cured paints will show a variety of gloss levels.
|Gloss terms are divided in two different groups:||Focus on reflected image is further divided in:||Focus on surface is related to:|
A clean and well prepared surface is crucial for a successful coating performance.
The pre-treatment process of an industrial coating job often consumes more time and budget than the actual paint application itself.
There are various methods and systems to prepare a surface prior to the coating application. Depending on the project and job specifications one could choose for hand cleaning like brushing, grinding or using needle hammers. Often grit blasting is utilised or shot blasting in automatic line for example. If no anchor pattern is required or already in place (ultra) high pressure water jetting, chemical cleaning or a simple wash down might be the solution.
Temperature, humidity and related climatic parameters are important to many industrial processes and the application of paint and coatings is no exception to that rule. Measuring and controlling climatic parameters such as relative humidity, air-temperature, dewpoint and moisture is vital to a successful application of high-end coating systems. Incorrect climatic conditions during pre-treatment and application often lead to premature failing of coatings systems.
Physical properties of paint and coatings play an important role in the quality control. Depending on the application a coating is supposed to be extremely hard and rigid such as for example the coating on the hull of an ice-breaker. Automotive coatings however require a certain flexibility since the thin sheet metal of a car body is not fully rigid and a slamming hood should not cause the paint to break. Coil coated steel that is to be formed into products such as white goods or cladding should have excellent forming properties.
Several empirical tests
There are a number of different empirical tests that are used to deform test panels and so assess the deformation resistance or flexibility. Coatings that fail such a test will crack and/or detach from the substrate. Also there is quite some overlap between different test systems and their results. Many tests provide information about similar parameters such as elasticity / forming resistance, adhesion, hardness, brittleness, stress resistance etc..
Although some tests overlap there is no cross-reference for their results.
More information can be found in the section hardness/scratch resistance
Commonly used tests
Common tests used in the paint and coatings industry are:
Coatings applied can have irregularities due to different circumstances. Surface uncleanness, paint differences and dust or air bubbles enclosed can cause pinholes, thin spots, cracks etc. To prevent an early breakdown of the coating system causing corrosion underneath, tests has to be made to find the weak spots and action can be taken before problems occur over time. For these kind of tests High Voltage Holiday Detectors provide an accurate way for locating faults in non-conductive coatings and linings and detection of pinholes, flaws, inclusions, thin spots and bubbles in a coating.