Surface Profile Gauge

What Does Surface Profile Gauge Mean?

A surface profile gauge is a type of profile gauge that measures the surface roughness of an object, usually to facilitate substrate preparation and the application of a protective coating. This tool records the roughness or cross-sectional shape that may be observed on a surface.

The surface profile gauge consists of a set of steel or plastic pins that are set tightly against one another in a frame that keeps them on the same plane while allowing them to move independently and perpendicular to the frame. When the pins are pressed against an object, they conform to the topography of the object's surface. By looking at the gauge, the technician can determine the height or depth of surface irregularities. The gauge can also be used to draw the profile on another surface.

The proper use of a surface profile gauge can improve a coating's overall performance and is a determining factor for how adhesion, coverage and overall volume of coatings are used. If there is an instance where the surface profile is too large, then the amount of coating needed increases. There is also the possibility that the peaks will remain uncoated, thus reducing the effectiveness of the coating and increasing the chances of future corrosion. Alternatively, when the surface profile is too small it results in insufficient coating adhesion, which leads to premature coating failure.

The profile height of a surface should be accurately measured to ensure that the correct surface preparation has been performed and to optimize coating usage performance. This parameter is essential as it determines the adhesion, coverage and overall volume of coating used.

Corrosionpedia Explains Surface Profile Gauge

Substrate Surfaces are Rarely Smooth and Uniform

Surfaces that may seem flat and uniform are not in fact, perfectly flat. Even machined surfaces that are put through surface finishing processes are not perfectly uniform. When viewed under magnification, most surfaces would be viewed as a series of peaks and valleys rather than just as a perfectly flat plane. The degree of surface smoothness depends on the deviation between the relative heights of peaks and valleys. The higher the difference, the rougher the surface, and vice versa.

The Value of a Surface Profile Gauge

A major reason for measuring the uniformity of surfaces is to ensure the proper application of coatings. The surface uniformity of an object affects both the coverage and the volume of the coating being applied and its overall adhesion to the surface.

For example, prior to applying a coating to a steel surface, the surface might be cleaned and/or intentionally roughened to create an anchor pattern using blast cleaning. After cleaning, there is a risk that the high points on the surface may not be sufficiently covered by the subsequent coating, resulting in unprotected spots that later corrode or rust. On the other hand, if the profile value is too low then the coating may not properly adhere to the surface, which may cause the coating to prematurely peel away.

Surface profile gauges provide a quantitative measurement of the uniformity on a surface, thus defining its relative smoothness or roughness with a numerical value.