The magnetic properties of ferromagnetic materials are usually expressed in the form of characteristic curves, the most common of which is to reflect the relationship between the magnetic induction of ferromagnetic materials and the strength of external magnetic fields. Starting magnetization curve The initial magnetization curve is a curve obtained when the external magnetic field H monotonically increases, as shown in Fig. 4-5-12(a). The common point curve of the initial magnetization curve of the ferromagnetic material consists of a steep section and a flat section. The steep segment corresponds to the case of easy magnetization, and the flat segment corresponds to the case where magnetization is difficult. According to the relationship of B=μH When the magnetic field strength H reciprocates in both positive and negative directions, the magnetization process of the material undergoes a cyclic process, as shown in Fig. 4-5-13. The closed curve is called a hysteresis loop. If the material is saturated at both ends of the magnetization curve, the resulting return line is called the hysteresis loop. If the material is saturated at both ends of the magnetization curve, the resulting loop is called the saturation hysteresis loop or the main hysteresis loop. 3. Normal magnetization curve The circulation range of the magnetic field H is gradually reduced, and the trajectory of the top end of a series of hysteresis loops is the normal magnetization curve, as shown in Fig. 4-5-14. This curve can be reproduced to illustrate the magnetic properties of the material. The shape of the normal magnetization curve and the initial magnetization curve are very similar. From the above three Magnetic materials are commonly used as magnetic conductors, permanent magnets, and special magnetic components. Different uses require different magnetic properties of the material. Magnetic materials are generally classified into two broad categories based on the basic magnetic property parameters of the material: soft magnetic materials and hard magnetic materials. The basic characteristics of soft magnetic materials are high magnetic permeability and low coercive force. The basic feature of hard magnetic materials is the ability to generate large magnetic fields in the workspace. Its coercive force is very large [H e ≈ 104 ~ 106 A / m]. Usually, the coercive force is used as the basis for judging the magnetic hardness of the material. Hard magnetic materials are mainly used on the magnetic source of magnetic separation equipment to generate a magnetic field. The basic parameters of the magnetic characteristics of the sign permanent magnet are its residual magnetic induction Br, coercive force He and maximum magnetic energy product (BH)max. There are two major types of hard magnetic materials; alloys and ceramic magnets (or ferrite magnets). Compared with the ferrite magnet and the alloy magnet, the residual magnetic induction Br is much lower, but the coercive force He is several times higher, which will affect the size and shape of the magnetic system magnetic pole of the magnetic separator. Ferrites are inexpensive and have a wide range of raw materials, and are often used in weak magnetic field magnetic separators. Permanent magnet materials containing rare earth elements have much higher magnetic properties than ferrites and common alloy magnets, and have been used as magnetic source materials for permanent magnet magnetic separators. Table 4-5-4 shows the characteristics of several permanent magnets. The magnetic material used for the permanent magnet is a hard magnetic material, and has a high residual magnetic inductance Br and a large coercive force He, which both determine a large magnetic energy product (BH)max per unit volume. The residual magnetic induction Br value characterizes the ability to provide magnetic induction for permanent magnets, and the coercivity He value characterizes the ability to maintain magnetic induction without attenuation. The magnetic field energy W of the permanent magnet in the air gap of the magnetizer is proportional to the product of the magnetic induction and magnetic field strength at the operating point of the demagnetization curve. For example, for the operating point d, the point magnetic energy product is equal to Bd Hd (as shown in Figure 4-5-15). From the demagnetization curve, BH=0 at two points B= Br and H=He, at point D The magnetic energy BDHD has a maximum value [BH)max. The greater the magnetic energy product of the material, the greater the magnetic induction produced in the air gap with the greatest energy. The magnetic energy of the unit body h accumulation air gap Wmax = BDHD / 20 From the economic point of view, the optimal working point of the permanent magnet should be the same as the point where the magnetic energy product is the largest. Aluminum Electric Wheelchairs,Wheelchair Aluminum,Cheapest Folding Electric Wheelchair,Aluminum Folding Wheelchairs Ningbo Baichen Medical Devices CO.,ltd , https://www.bcscooter.com
curve. The magnetic properties of the material are not only related to magnetic field strength, temperature and mechanical stress, but also to the magnetization process. Getting Before the curve, the material sample should be pre-demagnetized so that the magnetic domains in the sample are not magnetized, and the material is in a demagnetized state with a magnetization equal to zero. When the material is magnetized, it can be divided into the following curve. The slope of the line connecting the point A and the O point on the curve tanα
The saturation magnetic induction, residual magnetic induction, coercive force and relative magnetic permeability of the material can be known, which are magnetic property parameters of the magnetic material. The hysteresis loop is long and narrow, and the enclosed area is small. The soft magnetic materials used in the magnetic separator are engineering pure iron, magnetic conductive stainless steel and low carbon steel. Generally, the strong magnetic separator uses engineering pure iron as the core, yoke and magnetic pole; the magnetic stainless steel is used as the induction magnetic medium; the medium magnetic field or the weak magnetic field magnetic selection equipment uses low carbon steel.
Table 4-5-4 Characteristics of permanent magnets
In various magnetic material, iron is the most important representative of a ferromagnetic material, cobalt, nickel, gadolinium, dysprosium, yttrium, also ferromagnetic. Conventional multi-ferromagnetic material is an alloy of iron and other metals or nonmetals, and some iron oxides.