The magnetic core refers to a sintered magnetic metal oxide composed of various iron oxide mixtures. The magnetic core refers to a magnetic conductive material body disposed in the magnetic circuit of the inductor coil in order to increase the magnetic induction strength of the electromagnet. Magnetic cores are the most critical components in high-frequency electronic transformers that use soft magnetic materials and operate on the principle of electromagnetic induction. The main development direction of magnetic core materials is to reduce losses, widen the temperature range used and reduce costs. The main development direction of the magnetic core structure is how to form planar cores, chip cores and thin-film cores with the best shape and size (parameters for electromagnetic performance, heat dissipation, usage, and cost). Nowadays, all kinds of soft magnetic materials are constantly being improved and developed to compete with the market of high-frequency electronic transformers.
Core material classification 1, permalloy permalloy often refers to iron-nickel alloy, nickel content in the range of 30 to 90%. It is a very widely used soft magnetic alloy. Through appropriate processes, magnetic properties can be effectively controlled, such as an initial magnetic permeability exceeding 105, a maximum magnetic permeability exceeding 106, a coercive force as low as 2 ‰ Oersted, a rectangular coefficient close to 1 or close to 0, Permalloy with a face-centered cubic crystal structure has good plasticity, can be processed into 1μm ultra-thin tape and a variety of uses. Commonly used alloys are 1J50, 1J79, 1J85 and so on. The saturation magnetic induction of 1J50 is slightly lower than that of silicon steel, but its magnetic permeability is several times higher than that of silicon steel, and the iron loss is also 2 to 3 times lower than that of silicon steel. The transformer with higher frequency (400 to 8000 Hz) is manufactured, and the no-load current is small, so it is suitable for making small high-frequency transformers of 100 W or less. 1J79 has a good overall performance, suitable for high-frequency low-voltage transformers, leakage protection switch core, common-mode inductor core and current transformer core. The initial magnetic permeability of 1J85 can reach more than 100,000 105, which is suitable for low-frequency or high-frequency input and output transformers, common-mode inductors and high-precision current transformers for weak signals.
2. Silicon Steel Sheet Iron Core Silicon steel sheet is an alloy. A small amount of silicon (generally below 4.5%) formed in pure iron is called silicon steel. This type of core has the highest saturation magnetic induction value of 20000Gs; because of their good magnetoelectric properties, it is easy to mass-produce, the price is cheap, and the mechanical stress has little effect, and it is widely used in the power electronics industry. Such as power transformers, distribution transformers, current transformers and other iron cores. It is the most productive and used material in soft magnetic materials. It is also the most used material in magnetic materials for power transformers. Especially suitable for low frequency and high power. Commonly used are cold-rolled silicon steel sheet DG3, cold-rolled non-oriented electrical steel tape DW, cold-rolled oriented electrical steel tape DQ, suitable for all kinds of electronic systems, household appliances, medium and small power low frequency transformers and chokes, reactors , Inductor cores, these alloys have good toughness, can be punched, cut, and other processing, core lamination and winding type. However, the loss increases sharply at high frequencies, and the general frequency of use does not exceed 400 Hz. From an application perspective, the choice of silicon steel must consider two factors: magnetics and cost. For small motors, reactors and relays, pure iron or low-silicon steel sheets are available; for large motors, high-silicon hot-rolled silicon steel sheets, single-oriented or non-oriented cold-rolled silicon steel sheets are available; single-oriented cold-rolled silicon steels are often used for transformers. sheet. When used at industrial frequency, the thickness of commonly used strips is 0.2-0.35 millimeters; when used at 400Hz, a thickness of 0.1 millimeter is often preferred. The thinner the thickness, the higher the price.
3. Amorphous and Nanocrystalline alloys
Both silicon steel and permalloy soft magnetic materials are crystalline materials. The atoms are regularly arranged in three-dimensional space to form a periodic lattice structure. There are crystal grains, grain boundaries, dislocations, interstitial atoms, magnetic crystal anisotropy, etc. Defects are detrimental to soft magnetic properties. From the perspective of magnetic physics, amorphous structures with irregular atoms, periodicity, and grain boundaries are ideal for obtaining excellent soft magnetic properties. Amorphous metals and alloys are a new type of material developed in the 1970s. Its preparation technique is completely different from the traditional method. Instead, ultra-quick solidification technology with a cooling rate of approximately one million degrees per second is used. The molten steel and thin strip are formed in one pass, and the cold rolled metal strip is manufactured. Many intermediate processes have been reduced. This new process is known as a ** to the traditional metallurgical process. Due to the ultra-rapid solidification, the alloy is less ordered and crystallized at the time of solidification, and the resulting solid alloy is a long-range disordered structure. There is no crystal grain and grain boundary of the crystalline alloy, which is called an amorphous alloy and is called a metallurgical material. A school **. This amorphous alloy has many unique properties such as excellent magnetic properties, corrosion resistance, wear resistance, high strength, hardness and toughness, high resistivity and electromechanical coupling properties. Because of its excellent performance and simple process, it has become the focus of research and development in the material science community at home and abroad since the 1980s. At present, the United States, Japan, and Germany already have a perfect production scale, and a large number of amorphous alloy products gradually replace silicon steel and permalloy and ferrites in the market.
How to use the magnetic core The tighter the hole and the cable that passes through, the better;
The longer the magnetic ring, the better;
When harassing at the low-frequency end, it is recommended that the cable be circumscribed by 2-3 turns. When harassing at the high-frequency end, it is not possible to bypass (because of the presence of distributed capacitance), and use a longer magnetic ring.
The development of soft magnetic cores The application of soft magnetic materials in the industry began in the late 19th century. With the rise of power workers and telecommunication technologies, the use of low-carbon steel for motors and transformers has started, and fine iron powder, iron oxide, and fine iron wire have been used in the magnetic core of the inductor coil in telephone lines. By the early 20th century, silicon steel sheets were developed to replace low-carbon steels, which improved the efficiency of transformers and reduced losses. Until now, silicon steel sheets still rank first in soft magnetic materials for the power industry. In the 1920s, the rise of radio technology promoted the development of high-permeability magnetic materials, and Permalloy and Permalloy powder cores appeared. From the 40s to the 60s, it was a period of rapid development of science and technology. The inventions of radar, television broadcasting, and integrated circuits also required higher requirements for soft magnetic materials, resulting in the production of soft magnetic alloy ribbons and ferrite materials. . Into the 1970s, with the development of telecommunications, automation, and computer industries, a soft magnetic alloy for magnetic heads was developed. In addition to the traditional crystalline soft magnetic alloys, another type of material-amorphous soft magnetic alloys emerged. .
