Amorphous and nanocrystalline cores are usually made by wound tapes or ribbons. Considering the high initial permeability and low coercivity, it can replace ferrite, permalloy or silicon steel. The manufacturing process of nanocrystalline and amorphous at Shanghai Xianyu Electronics is similar, introduced as below.
The alloys are produced as thin ribbons directly from a melt. The hot molten metal with a temperature of around 1300°C is compressed on a cooling roller that rotates at high speed (100 km/h). When the liquid metal is rapidly quenched, the amorphous structure freezes up to a certain extent. In the manufacturing process, the high cooling speed of about 106 K/s prevents the formation of crystals and the amorphous structure is kept for a wide temperature range. For nanocrystalline ribbons, the process is similar, except that some other material was introduced. The typical thickness of nanocrystalline and amorphous ribbons are 0.18~0.35mm.
The process after is tape wound. For small cores, we usually wound the cores by automatic machine, while for big cores, wound them manually. One important factor is that the weight and dimensions should be kept in spec. limits. It’s easy to manage that for toroidal or round cores. But for special shape cores, such as rectangular or oval cores, we should carefully calculate the loop length in advance. After wound, we’ll braze the end of the tape by the current spark.
After that, we’ll put the cores in the oven. We’ll keep the oven for a special temperature range and time period. In this process, if the parameters are not set properly, the final cores cannot achieve required performance.
Epoxy Resin Harden
For some big cores, we should make them strong enough, even without cases. So, the epoxy resin harden process is required. For small core, usually this step is skipped.
Then, we’ll put the bare inside plastic box, aluminum box, steel box and so on. For DC immune CT cores, we should put the amorphous rings and nanocrystalline rings together. For common mode choke cores, we usually assemble the rib plate and bottom plate.
Epoxy Resin Coating
Epoxy resin coating is suitable for some cores, especially small ones. But the process is not environment-friendly. So, this process is strictly limited by authorities in China during recent years.
Crepe Paper Wrapping
For some cores, crepe paper wrapping is a better choice. In that case, no need to make the plastic box mold.
For split amorphous cores, or split nanocrystalline cores, the process of cutting is very important. The material consumed by cutting should be considered in advance. So, the loop after tape wound is a little longer than that on the drawing. After cutting and grinding, we get exactly what we need.
When the cores are ready, we’ll test them to make sure the AL value is as required.
Packing and Shipment
As most of our products are exported, the finished cores should be packed properly. Foam and wooden cases are usually required.