In steel manufacturing processes, surfaces and their properties are as important as the bulk properties of the material. The surface topography has an effect on a wide range of application properties, such as friction, wear, bonding behaviour of paints and coatings, visual appearance, corrosion resistance, fatigue behaviour, sealing capacity, electrical and thermal contact resistance, etc.

To enhance the effect of these properties it is often desirable to induce a pattern into the surface. When a pattern is made into a surface the end product is known as textured steel. Textured steel will have surface properties designed to improve its application performance. CEMMNT partner, Taylor Hobson, provides state-of-the-art metrology tools such as the Talysurf CCI to characterize the complex structures that are increasingly being produced within the textured steel industry.

• Measure all surface types, independent of material, reflectivity or texture
• Ultra High resolution allows operators to visualize small features within large structures (0.01 nm Z resolution over full 100 µm Z scan range)
• Large measured areal bandwidth of information with 1 million data points (X - Y area from 330 µm to 6.6 mm)
• informative easy-to-use 3-dimensional analysis software
• Fast (10 - 20 seconds) component set-up and measurement time

The Talysurf CCI is quickly becoming an instrument of choice for quality control of textured steel. This instrument can be used to characterise electrical steels, enamelling steels, hot and cold rolled steels, metallic coatings, tube and plate steels and other metallurgy applications. A general advantage of the Talysurf CCI is that all measurements are fast, operator friendly, non-contact and 3-dimensional, with high data density and quantitative numerical results. Results can be offered and displayed in the form of surface texture parameters, 3-dimensional pictures, extracted profiles, heights and depths of structures, hole volumes, grain sizes, localized flatness, cell diameters and sizes plus many more numerical expressions to describe the most complex of surface types.

*Talysurf CCI 6000 non-contact 3D measuring system

Surface Texture is Complex

Surface characteristics can be complex with roughness, waviness and form often existing in combination. Along with the manufactured surface there is an inherent structure to the material. Very few surfaces are molecularly smooth. In metals, grain areas will produce surface irregularities that are extremely fine compared with the texture generated by the manufacturing process. There are many texture parameters available to describe these complex surface features and characteristics. Care must be taken when selecting a parameter; e.g., amplitude parameters such as Sa (Sa is the 3 dimensional equivalent of Ra) can be applied to both a sinusoidal and stepped shaped surface but still offer a similar Sa value. Sa would therefore be useless in describing the difference between two such surface types (see figure 1). However, parameters that are correctly applied can prove useful in describing the differences between many surface types. Parameters can be used to relate surface appearance (optical), surface resistance and conductivity (shielding), surface energy (cleanliness, hygiene), heat transfer (flux control), barrier (corrosion performance, permeation control), surface topography (friction, forming behaviour, touch), adhesion, compatibility with additional coating layers (paints, glues) and other characteristics.

Just as surface parameters can be used to describe an existing surface, they can also be used to specify a new surface, i.e., define the particular texture characteristics required for the desired performance.

pyright©2005 • Taylor Hobson Precision • Textured Steel_2/05 

*High accuracy surface metrology is crucial to controlling textured steel surface characteristics and performance

Talysurf CCI and Textured Steel

Designers often find it difficult to describe a surface through traditional 2-dimensional profiling techniques. When shapes become very complex in nature it would be a great benefit to describe and view the surfaces 3-dimensionally. The Talysurf CCI is the latest non-contact, 3-dimensional metrology tool from Taylor Hobson. This instrument offers extremely low noise and highly repeatable 3D (areal) measurements. With very high data density the 3D graphic measurement results offer an excellent representation of a surface. All numerical results can be described using the new Field [S (surface) and V (volume)] and Feature type parameters from ISO 25178 part 2 which defines the new set of areal surface texture parameters, which are now recommended to describe 3-dimensional surface texture.

Coherence Correlation Interferometry

Areal measurements by the Talysurf CCI instrument are produced using coherence correlation interferometry (CCI). This new measurement technique not only provides high resolution (0.01 nm Z resolution) but also high sensitivity to a variety of surfaces. The unique scanning mechanism of the TalySurf CCI enables sub nanometre resolution imaging of millimetre and micrometre scale features. The Talysurf CCI is therefore suitable for the measurement of both highly reflective and low reflective surface types. Textured steel, other metals, ceramics, coatings, polymers and inks can all be measured. With a measurement array of more than 1 million data points in X and Y it makes possible high graphical visualization and reliable calculation of area, volume, height and lateral distances as well as surface texture.

With designers developing and specifying ever more complex surfaces, manufacturers will face increasingly tighter tolerances and a greater need for inspection equipment to control the manufacturing process. The Talysurf CCI can provide the accurate surface metrology that is required for the most demanding applications.

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