BS/EN 60424-4-2016 pdf download.Ferrite cores Guidelines on the limits of surface irregularities Part 4 : Ring-cores.
This part of IEC 60424 gives guidance on allowable limits of surface irregularities applicable to ring-cores in accordance with the relevant generic specification defined in IEC 60424-1.
This standard is considered as a sectional specification useful In the negotiations between ferrite core manufacturers and customers about surface irregularities.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
Void.
3 Limits of surface irregularities
3.1 Uncoated ring-cores
3.1.1 General
Generally, uncoated ring-cores are smoothed (for example: by tumbling) to remove any significant flash and to add radius to edges that would otherwise be sharp due to tooling angles. Tooling angles exist where the compaction punches meet the interior of the die mold, where a sharp angle in the edge of the piece that is formed is unavoidable. This is also the location inside the ferrite tool set where flashing may occur. The purpose of removing flash and rounding edges is to allow uncoated ring cores to be wound with insulated wire, using typical production winding processes, without damage to the wire.
3.1.2 Chips and ragged edges
Figure 1 shows examples of chips and ragged edges location on ring-cores.
— Ragged edges as defined in IEC 60424-1 are allowed.
— Chips shall not exceed 25 % of the wall thickness either in length or in width, up to a maximum of 2 mm.
— The maximum number of chips shall not exceed 3 on one core edge and a total of 5 on all edges.
3.2 Coated ring-cores
3.2.1 General
Coated ring-cores are generally smoothed (e.g. by tumbling) before the coating process. A variety of materials are used to provide dielectric protection by coating the surfaces of the ring cores to form a barrier. These include epoxies, polyurethanes, nylons, and paraxylylenes.
3.2.2 Coating features
A rough coating surface is acceptable provided that
1) dimensional specirications are met, and
2) the coating does not exhibit sharp features that would damage insulated wire that is applied using typical winding processes.
Excess dirt or ferrite debris on the surface or in the window of coated ring-cores is not acceptable.
Partial coating exposing bare core is unacceptable. Chips In a layer or layers of coating, exposing other coating, but not the bare core, are acceptable if they do not create sharp edges, and if the voltage breakdown limit is met.
Pin holes in the surface of coated ring cores are acceptable, provided that they meet the relevant voltage breakdown specification. Air bubbles under the coating are not acceptable.
Sharp flashing arising from the method of applying coating is not acceptable.
Paraxylylene coatings may show varying appearance, ranging from transparent to milky white, within individual production batches, and from batch to batch, This is acceptable, provided that the relevant voltage breakdown specification is met.
3.2.3 Coating performance
Coated ring-cores shall withstand the relevant voltage breakdown specifications. Coated ring- cores shall meet their relevant inductance, loss and other electrical performance limits. Manufacturers may publish modified limits for certain coated ring-cores, compared with the same cores not coated, due to characteristic changes resulting from mechanical stress of coating.
3.3 Area and length reference for visual Inspection
Irregularities such as chips, cracks and pull-out should be compared to five simple geometries
which are shown in Table 1,
Such a table should be used as a reference for evaluation by operators either at the outgoing stage (core manufacturers) or at the incoming Inspection (customers).
Other methods than visual inspection can be used, such as computerized optical detection.
NOTE The minimum area and length considered are respectIvely 0.5 mm2 and 1 mm.
Recommended resolutions are as follows:
a) for area
— 0,5 mm² up to 5 mm²
— lmm²from5mm²tolOmm²
— 2,5 mm² from 10 mm² to 20 mm²
— 5 mm² from 20 mm² to 50 mm²
b) for length
— 1 mm from 1 mm to 5 mm
— 2.5mmfrom5mmtol0mm.BS/EN 60424-4-2016 pdf download.