Laminated cores based on electrical steel (silicon steel) are used for transformers or rotors and stators of electrical motors. The base material of the cores is coated with an insulation varnish to increase the electrical resistance, the eddy current resistance and also to protect them against corrosion. The coating process is done in a continuous process before cutting and punching of the single parts of the core. The thickness of the insulation layer is very important for the quality of the core. In the past e.g. paper was used which results in a bad stacking factor and limited the maximum temperature of the core. Nowadays, mainly coatings related to the AISI classes C3, C5 and C6 are used. The benefits of any manual or automatic coating process control highly depend on the measurement accuracy of the layer thickness gauge. The paper concentrates on information about the MESACON´s F2800 layer thickness measurement system, improvement of customers coating process, benefits and customers experience.

Key words: silicon steel, electrical steel, insulation coating, process improvement

A highly constant coating over the whole width and length of the material to be produces is required. In case upper or lower limits of the coatings are exceeded the stacking factor or the resistance are influenced. Such over-coating as well as weakness in the electrical resistance of the coating can be drastically reduced by using MESACON´s F2800 layer thickness measurement system. Former measurement systems, even based on the same general measurement principle, were not able to measure the full production program with a reliable accuracy. MESACON´s task was to design the new F2800EL based on the already existing F2800 system with the capability to measure the full production program in a silicon steel coating line.


Measurement Principle Basic System Design

MESACON´s F2800 is a layer thickness measuring gauge based on the beta backscattering principle. The isotope source emits a constant beta ray beam that is backscattered by the surface layer material. The backscattered radiation results in a current due to the ionization process inside the high stable ionization chamber. This current is amplified to an adequate signal for further data processing. Considering a determined calibration curve of the measured layer, the corresponding value for the layer thickness is calculated.

To avoid any influence of different kinds of base material the F2800 system is equipped with a base measurement system.


F2800EL configuration


MESACON F2800 paint / varnish measurement system was developed into a insulation layer thickness measurement system F2800EL with the capability to measure reliable these very thin layers down to less than 0.5µm for the full production portfolio of the customer. By replacing systems even based on the same principle from other suppliers the customers reached the possibility to minimize the used amount of insulation coating.

Author: Dipl. Ing. Detlef Jährling




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