Surface roughness refers to the specific depth and contour of ridges on a surface. Why is it important to test surface roughness? Since there is no such thing as “zero” surface roughness (in other words a completely flat surface), every project will have a level of surface roughness that needs to be measured. Not paying attention to the exact level of surface roughness can have a significant impact on the overall quality of a product. For example, surface roughness may affect:
- How a surface looks?
- How a surface functions?
- How well coating adheres to the surface?
Consider the importance of surface roughness in the production of car parts. Car engines have parts that constantly rub together or parts that need to fit together precisely. A surface that is too rough or not rough enough can cause parts to wear out too early or cause unwanted gaps that affect the functionality of the engine.
You can also use a surface roughness measurement to detect abnormalities and defects in a product. Surface roughness measurements can therefore be relevant during production and during the quality control phase.
Each project must be measured for surface roughness, and if the parts need to match with larger parts, the required surface roughness will probably be specified in a plan from the very beginning.
How is Surface Roughness Testing conducted?
Measurement of Surface Roughness
A measurement of surface roughness looks at the height, depth, and at gaps between protrusions. Each different material and even material types have ideal surface roughness features. For example, different types of steel maintain different surface roughness levels.
Surface roughness can be represented by the variable ‘Ra’. The larger the number Ra, the rougher the surface. Ra is often used as a way for manufacturers to demonstrate how different processing techniques will affect surface roughness. What RA captures is the mean roughness (the arithmetic mean value of the degree of deviation above and below the surface that is considered flat).
Another way to measure surface roughness is ‘Rz’, the maximum height of a surface’s profile. There is also an ‘Rq’, which is the root mean square deviation of a profile. Before you worry too much about calculating numbers, know that these variables can be derived using tools.
One can measure surface roughness using a “contact type” method (with the end of a probe tip profiler) or a “non-contact type” method (with light measurement). Stylusprofil builders physically touch the surface and use a diamond tip and stabilizer to move along the surface in a straight line. When the Stylus encounters a ridge, the line reflects the deviation, and the Ra value is calculated based on the degree of deviation from the straight line. Of course, not every material can allow such direct contact, and direct contact is not always the easiest, fastest or most precise way to measure surface roughness.
One of the most popular types of non-contact methodology is optical profiling, which captures millions of data points by measuring wavelengths of light reflected from a surface. This requires the use of an optical profiling machine, many of which can be configured according to different project sizes and measurement needs.
Regardless of whether your project guarantees contact or non-contact measurement, it is crucial that surface roughness measurements are taken consistently, accurately and precisely every time. Incorrect measurements can result in failed coating applications, inconsistent product output, poor performance quality, and poor durability.
Kalkancı Surface Roughness Testing
Surface Roughness Testing, another component of our Quality Control process, is one of the most important processes that determine the performance, life and quality of our products. Our products are tested with the most reliable and accurate controls; undergoing qualitative and quantitative evaluation.
Here at KALKANCI we prefer “Liquid Penetrant Examination” (also sometimes referred to as the Liquid Penetrant Test) because it is one of the most sensitive and non-intrusive examination methods to detect surface errors. If we were to list our reasons for our preference;
- It is a highly sensitive method,
- It is an extremely simple test to apply,
- It is relatively inexpensive compared to many other methods,
- It can be applied to many different substances,
- All surface controls are fast because they enable single process controls.