IEC 61631 pdf – Test method for the mechanical strength of cores made of magnetic oxides
4.2 Testing device The testing device shall be a mechanical testing machine capable of applying a force to the loading wedge high enough to break the test core. The machine shall be capable of applying the force at a constant loading rate. The machine shall be equipped with a device for recording the peak load applied to the test core. The accuracy of the machine shall be 1 % of the indicated load. The force calibration of the machine shall be checked in accordance with ISO 7500-2.
4.3 Humidity measuring device A humidity measuring device, such as, but not limited to, an aspirated psychrometer or whirling psychrometer that is capable of measuring relative humidity to an accuracy of ±2 % shall be used.
5 Test cores General
5.1 The test cores shall be selected as agreed between the parties concerned. They may be machined to the specified dimensions, because any machined surface plays an important role in the mechanical strength (see the Introduction).
5.2 Number of test cores For material development, characterization or quality checking, the minimum number of test cores shall be five pieces. For statistical evaluation of strength data (for example, Weibull parameters), the minimum number shall be thirty. For comparison of data for different materials, it is important that the number of specimens is high enough to obtain results with sufficient statistical confidence. Since the confidence limits, in general, depend on the number of test results and their dispersion, the number of test specimens should be decided on the basis of statistical considerations.
5.3 Precautions The prepared test cores should be handled with care to avoid introduction of additional damage. Test cores should be kept separately at all times, and should be wrapped individually for transport.
6.1 Test conditions The test shall be carried out at an ambient temperature between 15 °C and 35 °C. The temperature shall not vary by more than 3 °C during the course of a test series. The relative humidity shall be between 45 % and 85 % and shall not vary by more than 10 % during the course of a test series.
6.2 Test procedures General
6.2.1 The test core shall be arranged in the test apparatus in accordance with 184.108.40.206, 220.127.116.11, 18.104.22.168, 22.214.171.124, 6.2.3, 126.96.36.199.2, 188.8.131.52.3 or 184.108.40.206.4 as applicable (see Figure 1 to Figure 8). For standard dimensions of E-cores and their support for strength test see Annex A.
The E test and W test can be used for material-related purposes, while the M test and T test can be used for process-related purposes. The test of I-cores is only recommended for flat- shaped test cores such as antenna rods. The test method of stretching, shearing and pressure is only applicable to ring-cores. A preloading force of 5 N to 25 N shall be applied because the upper and lower faces of the test cores are never absolutely parallel. The test force shall then be applied at a loading rate of between 5 mm/min and 20 mm/min until the test core fractures. The load at the instant of fracture shall be recorded. The fractured fragments shall be identified and preserved for later fractographic examination.
6.2.2 Test of E-cores Dimensions
220.127.116.11 The specifications and dimensions of E-cores are according to IEC 63093-8.
18.104.22.168 E test For test core sizes equal to or larger than E13, the test core shall be placed on roller bars as shown in Figure 1. For test core sizes less than E13, the test core shall be placed on a flat support as shown in Figure 1. The load shall be applied through the loading wedge, and the load at the instant of fracture recorded.
22.214.171.124 W test For test core sizes equal to or larger than E13, the test core shall be placed on roller bars as shown in Figure 2. For test core sizes less than E13, the test core shall be placed on a flat support as shown in Figure 2. The load shall be applied through the loading wedge, and the load at the instant of fracture recorded.