Reference Story: Example of an application for soft magnetic technology

Again and again we hear from processors of electrical steel, e.g. producers of laminations or manufacturers of electric motors, generators and transformer, of the challenge they are faced with when testing the hysteresis loss of electrical steel prior to and during production. For, as a result of the individual stages of processing and annealing, there are substantial changes to the electromagnetic properties of the material which may no longer meet the specified requirements.

A concrete example:

A customer presented the quality manager in a company engaged in the production of punched parts with stators in which the watt loss test of individual items in one and the same batch showed deviations of up to 100%. The only control documentation available to this quality manager was a certificate from his steel supplier.

The aim:

It was our aim to make it possible for this company to test the hysteresis loss in three stages so that they could react accordingly:

Control 1) On delivery of the steel stripes, quality control of each coil at goods reception.

Aim: To improve quality together with the supplier or to search for a new supplier.

Control 2) Test individual laminations after the punching process.

Aim: Optimization of the annealing process.

Control 3) After packaging (also including measurement of loss of eddy current).

Aim: To control the production process. To develop the punching of packages as a favourably-priced mode of production and to have control over the more complex annealing of the ring cores.

The solution:

The MPG 100 D measuring instrument was chosen so that individual measuring tasks, including steel strips, laminations and ring cores, can be carried out with one single device.
For testing all the coils it receives this company uses one strip coil into which strips (28 mm x 300 mm) are inserted which are cut lengthwise and crosswise from the coil. The hysteresis and the resulting losses are measured. The data for the samples of each material grade are recorded and documented only once by the MPG Expert Software. Also each required measuring process is only entered once and can be called up for any identical measurements at a later date. A calibration based on the results of an Epstein measurement already carried out or on Epstein data provided by the supplier can now be carried out to establish quickly whether all the coils delivered are of an acceptable quality.

In our example the electrical steel is annealed by the steel supplier, cold- formed once again and then delivered as a semi-finished product, since, in the company concerned, the final annealing process takes place after punching. During punching and the subsequent annealing process there are changes in the electromagnetic properties of the steel: there is a significant improvement in the material properties compared with the original strip. With the punched part sensor punched parts in a wide variety of shapes can now be tested for hysteresis loss, thereby ensuring that only high quality punchings are packaged.

Nowadays production is being changed over to packaging of punched parts and annealing of the packages, thereby increasing the risk of hysteresis loss through inadequate annealing. This is because, due to scaling, the development of the temperature in the package and the resulting formation of the insulation between the layers of steel are no longer always guaranteed. Since, on the one hand, the company in question wished to make increased use of this favourably-priced production process, yet, on the other hand, did not wish to supply its customers with inferior quality, the only solution could be 100% final testing.
This is made possible by the ring sensor. By means of a pluggable cable ring with a primary and secondary coil an electromagnetic field is created in the ring core through the primary coil. The strength of this magnetic field is then measured with the secondary coil. With a suitable instrument equipped with several slots and enabling automated measurement it is possible to measure large quantities of almost any size.
The company concerned can now guarantee quality to its customers. Any changes in the electrical steel supplied or in the production process which lead to an improvement in quality can now be tested and specifically controlled.

Your situation?

The application described above which is based on the production of punched parts can also be implemented by manufacturers of electric motors, generators and transformers and by other processors of electrical steel and semi-finished products. Explain your situation to us. Our specialists would be pleased to have the opportunity to discuss your special case with you.

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