**2.2 3D surface roughness parameters and characteristics of blasting surface**

The complex information about a surface is possible to gain by three-dimensional, therefore spatial, measuring of the surface profile. Spatial 3D surface characteristics allow, compared with flat 2D characteristics, to evaluate and define a surface more detail.

Spatial measuring and evaluation of a surface 3D, brings very valuable and practically usable information about relations between geometrical characteristics of a surface and its functional properties. Fast development of measuring technique and control software will nowadays allow implementing advantages of 3D evaluation for a surface texture. Spatial measuring of a surface micro-geometry in comparison with 2D evaluation of a single profile assures more objective presentation of the whole surface with notably bigger statistical meaning of obtained characteristics. Individual spatial surface roughness parameters of a texture are calculated from considerably bigger amount of data.

Data for spatial evaluation of the surface texture are possible to obtain either by a contact measurement (scanning of a set of normally parallel profiles) or by the optical technique. Optical devices use scanning ray, which monitors a surface similarly as a contact scanner or defined viewing field of a microscope.

Nowadays a variety of devices are available (contact and optical) using which it is possible to measure also a surface texture. Differences in measurement are given by various principles of scanning systems, varied precision of measurement, and also interaction of devices and controlled surface. Difference in results is also affected by the methodology of verification of devices properties and their calibration.

ISO 25178 norm is an norm for spatial texture of 3D surface. Measuring and elaboration of notably bigger amount of data, which describe a spatial surface profile, bring a huge amount of information for a real presentation of the controlled surface.

Practical result of implementation of the norm is not only a contribution for the selection of suitable surface roughness parameters of surface structure evaluation, but also a preparation of measuring and analyzing devices of a quantitative control of surface structure. Advantages of spatial evaluation show that they are progressive metrological methods. Not only increasing requirements on precision and quality of existing production technologies, but also the development of new materials and technological methods will undoubtedly contribute for their wider practical utilization.

A 3D study of blasted surfaces of different types of blasting abrasives (shot and grit types) in a contact way is shown in **Figure 8**.

The creation of a 3D surface texture by the contact method was realized using the Surftest SJ – 301 stylus profilometer, Mitutoyo, Japan. The measured research area was 4 × 4 mm. The resulting spatial image of the surface is then created in such a way that the profile curves and their data in the parallel direction at a defined scanning distance are recorded by the scanning tip of the profilometer and subsequently joined by the software. The method is applicable if the workplace has only a 2D roughness meter. The disadvantage of the method is its time-consuming compared to contactless evaluation.

3D imaging of blasted surfaces was performed by the non-contact method with a confocal laser microscope Olympus LEXT OLS 3000, **Figure 9**. The measured research area was 1.25 × 1 mm, the profile height is presented on the Z axis.

It is a highly accurate 3D measurement in real time and a reliable evaluation of profiles, which is based on the illumination of the sample with a laser beam,

**Figure 8.** *3D imaging blasted surfaces by contact method. (a) 3D surface blasted by steel shot, (b) 3D surface blasted by steel grit, and (c) 3D surface blasted by brown corundum.*

which is focused on one point. This eliminates noise caused by unwanted light, resulting in better image quality.

The performed measurements show that noncontact method is sensitive enough for imaging blasted surfaces. Compared with the contact method, the contactless method is less time-consuming, but the device itself is more expensive compared with the conventional roughness tester.

At a mutual visual comparing of assessed surfaces, **Figures 8** and **9**, a difference is visible in a character of surfaces blasted by various blasting materials. At such types an uneven surface is reached, resulting by an incidental fall of particles blasting abrasives. A surface blasted by a sharp blasting abrasives—steel and corundum grit does not show such uniformity as at blasting by round particles—steel shot. Notches are on the surface in a various orientation, intersected mutually and a notable part of holes and juts is sharp. From utilized sharp blasting materials, the most segmented surface was detected at the surface blasted by a steel grit. At blasting by round blasting abrasives—a steel shot, more uniformed surface modification was achieved, which is created by intersected round juts.

By realized measurements and 3D visualization of blasted surfaces a presumption was proved that abrasive particles make after the fall in a base material their prints which are dependent on their shape and size, by which a detection of surface complexity was achieved—thus its various segmentation. The particle shape of blasting abrasives (round or angular) has thus a notable effect in the process of blasting and is one of the attributes for an achieved microgeometry of blasted surface and further characteristics as well.

**Figure 9.**

*3D imaging of blasted surfaces by the non-contact method. (a) 3D surface blasted by steel shot, (b) 3D surface blasted by steel grit, and (c) 3D surface blasted by brown corundum.*
