Online Waviness Measurement
AMEPA online measurements of the surface area profile provide fundamental advantages for the customer:
Visualization for the waviness measurement is structured in the same way as the roughness measurement. In addition to the waviness values for Wsa and Wa 0.8, the roughness values Ra, Rz, RPc, and other values can also be calculated and displayed. The WMS system provides versatile visualization options for the data.
The exemplary screenshot indicates the online Ra, Rz, RPc, and Wsa results over the coil length with the last microscopic image. Repeated warnings and alarm signals are displayed as soon as the waviness or roughness degree moves outside the tolerance determined for the customer-specific limits. The operator can immediately implement the necessary corrections without much loss of time.
The good correlation of the determined parameters of the WMS waviness measuring system with values for waviness and roughness as measured in the laboratory is illustrated in the figures above.
The individual microscopic images are taken in an overlapping manner to achieve the measuring length of 30 or 50 mm, which is required for the waviness measurement. The stitching algorithm determines the alignment and specifies the displacement of the individual images, so they can be combined to form a long image strip.
The laser line that is obtained and extends over all images can be detected and evaluated to determine the waviness and roughness parameters.
When the ripple on a steel sheet metal is located above the specified limits, the steel user will generally not accept the annealed and galvanized product for high value-added applications. Subsequent processing steps, especially painting, can lead to poor quality and product downgrading. This means that direct online measurement is always required in order to fully assess the surface area quality along the entire coil.
In principle, surface topography refers to the horizontal and vertical information regarding the height alteration of the surface area and can be divided into (micro-) roughness and rippling.
Unlike roughness, which in the case of steel only comprises the height variations with a horizontal spacing or a wavelength of up to 0.8 mm or 2.5 mm, rippling in steel refers to structural components with longer wavelengths. Rippling generally means the shape deviation of a surface area in the wavelength range above the roughness, which leads to clearly visible distortions in the reflection of a high-gloss painted surface.
The Waviness Measurement System is based on the SRM Surface Roughness Measurement System, which works based on a line projection – a two-dimensional laser triangulation method. The online roughness measurement and waviness measurement, based on this principle, was patented by the Centre for Research in Metallurgy (CRM, Liège).