WO2019112479A1 - Magnetic separator - Google Patents

Abstract

The invention relates to the field of powder metallurgy, specifically to devices for separating the waste resulting from the production of NdFeB permanent magnets. The technical result consists in increasing the selectivity of separating the waste resulting from the production of NdFeB magnets during magnetic separation. The technical result is achieved as follows: A magnetic separator includes a feeder and receivers for products to be separated, a chute, and a magnet system that is an endless conveyor belt having permanent magnets mounted thereon; the chute wraps around the magnet system in the direction of travel of the system and, in its lower portion, diverges downward from the magnet system; the permanent magnets are fastened to the conveyor belt by like poles, and pole tips are mounted on the opposite poles of the magnets.

Description

 Magnetic separator

Technical field

 The invention relates to the field of powder metallurgy, namely, devices for separating waste production of permanent magnets NdFeB.

 The level of technology

 Currently, NdFeB permanent magnets are the most popular among the rest (cast, ferrite, etc.), because they have the highest magnetic parameters.

 These magnets contain up to 40% of scarce rare-earth metals and cobalt, therefore their production wastes (magnets are rejected in appearance, geometric dimensions and magnetic parameters) are reused to reduce costs.

 Since NdFeB permanent magnets are manufactured by powder metallurgy technology, the waste is demagnetized, crushed to particles with a size of 0.8-1.0 mm and injected into the processing chain during the grinding operation with powder of fresh magnetic materials.

However, the magnetic material NdFeB very actively interacts with the surrounding air, therefore oxygen gradually accumulates in it, which destroys the main magnetic phase Nd ₂ Fei ₄ B to form neodymium oxide NdO. At the same time, its main magnetic parameters are reduced (residual induction of Br and coercive force Hsv) and its magnetic susceptibility increases c.

The increase in the magnetic susceptibility of the material NdFeB (c = 0.05) during its oxidation is associated with the release of iron in it (c = 1100) in the process of destruction of the main magnetic phase Nd ₂ Fei ₄ B. As a result, with the formation of 1 mass. % NdO simultaneously forms about 2 mass. % Fe, which increases the magnetic susceptibility of the material by almost 22 units.

 This fact makes it possible to separate particles of a material containing NdO above the permissible value (0.3 mass%) by the magnetic separation method, since the force acting in a magnetic field on a particle of a substance is proportional to its magnetic susceptibility (Tikhonov, ON Magnetic, electric and special methods of enrichment / O.N.Tikhonov, E.E.Andreev, V.B. Kuskov, M.V.Nikitin.- SPb: SPSU, 2016.- 70 p.).

 At the moment, there are various types of separators with adjustable values of the magnetic field in the separation zone, which are used as separators-analyzers [Karmazin, V. V. Magnetic and electric enrichment methods / V. V. Karmazin, V. I. Karmazin - M .: Nedra, 1988.- 304 p.]. A common drawback of these devices is low productivity, operation only in a periodic mode and low separation selectivity.

 In this case, the separation selectivity (Cp) is the ratio of the magnetic susceptibilities of the separated materials:

 Cp = g 1 / g2, (1)

 where gΐ-magnetic susceptibility of less magnetic fraction;

 at 2, the magnetic susceptibility of the more magnetic fraction.

The closest in technical essence is a gravity magnetic separator, which includes a chute and a magnetic system located under it (US 4659457, published September 30, 85. Gravitymagnetic ore separators and methods). The magnetic system is an endless ribbon with permanent magnets mounted on it. However, it is used in this invention for transportation the magnetic fraction along the gutter and is structurally capable only of separating the magnetic fraction from the nonmagnetic one.

Therefore, magnetic separators are used in the separation of NdFeB materials, only to isolate the main highly coercive (c = 0.05), low-coercive low-magnetic (c> 1000) and non-magnetic fraction (c <KG ³ ). In this case, the selectivity of the separation process is about 5 x 10 ⁵ .

 DISCLOSURE OF INVENTION

 The technical result is to increase the selectivity of the separation of waste production of NdFeB magnets during magnetic separation.

 The technical result is achieved as follows.

 The magnetic separator includes a feeder and receivers of separation products, a chute and a magnetic system, which is an endless conveyor belt with permanent magnets installed on it, the chute bends around the magnetic system in the direction of its movement and deviates from the bottom in the bottom part, and the permanent magnets are fixed on the conveyor belt poles of the same name, and on their opposite poles are mounted pole pieces.

 Brief Description of the Drawings

The device of the invention is shown in FIG. 1. Magnetic separator operates as follows. The powder of the separated material 2, through the hopper 1 enters the feeder 3, in which it is captured by the magnetic field of the magnet 4 and under its influence moves after the magnet along a non-magnetic chute 7. The motion of the magnet is provided by a conveyor belt 6, on which it is rigidly fixed. Pole tip 5 is used to create a uniform magnetic field in the working area on the surface of the chute.

 The implementation of the invention

 In the lower part of the separator (during the return stroke of the conveyor belt), the chute deviates downward from the line of pole pieces. As a result, the gap between the permanent magnets and the particles of the material begins to increase and the magnetic field acting on the particles of the material begins to weaken. Falling particles of separated material are collected in receivers 8.

 The main elements of the proposed utility model, determining its essential features and providing the necessary technical result, are:

 - permanent magnets mounted on a conveyor belt of the same poles and having pole tips at opposite poles.

 - chute, which goes around the magnetic system and deviates from it downwards in the lower part.

 Permanent magnets 4 in this design provide not only the transportation of magnetic material along the chute, but also form the working zones of the magnetic separator, which moves in space according to the law defined by the shape of the chute.

 During the reverse course of the particles of the material (in the lower part of the separator) they are influenced by two forces: magnetic force and gravity.

 The specific magnetic force (magnetic acceleration) f, acting per unit mass of the particle in the air (Fig. 1) is equal to:

f = m ₀ c ₄ H gradH, (2)

 where mo is the magnetic constant;

c ₄ - magnetic susceptibility of a particle of a substance; H is the magnetic field strength;

 gradH is the gradient of the magnetic field strength in the direction from the source of the magnetic field B (in this case, the pole tip).

 If the specific magnetic force (magnetic acceleration) is higher than the gravitational acceleration g, then the particle will be pressed against the surface of the trench. If on the contrary, the particle will fall down.

 In this case, as can be seen from formula (2), the point of incidence of a particle of a material does not depend on its mass, but is determined only by the ratio of the parameters of the magnetic field created by the permanent magnet and the magnetic susceptibility of the material particle. As a result of this, particles with lower magnetic susceptibility will fall first (in a magnetic field with a higher intensity).

 To increase the selectivity of the magnetic separator, it is necessary that the difference in the magnetic parameters of the permanent magnets forming the magnetic system be minimal, since, basically, it will determine the selectivity of the separation process in the proposed utility model.

 Pole tips 5, made of magnetic material, are necessary to create a uniform working zone of magnetic separation. The best options will be to create with their help a working zone across the gutter with a width comparable to the average particle size of the material to be separated. Currently, there are various designs of pole tips, which ensure the uniformity of the magnetic field at a level of 0.001%, for example, in the working volumes of medical tomographs.

The installation of all permanent magnets on the conveyor belt of the separator with the same poles is necessary to prevent the particles of the material to be magnetised against each other. In contrast from other magnetic materials, the waste of permanent magnets NdFeB are particles having a magnetic texture. Like any rare earth magnet, they can be magnetized only along the direction of the texture.

 Getting into the magnetic field, even if not magnetized, the particles unfold a texture along the magnetic induction line, in this case vertically (figure 2). In this case, the polarity is formed in them strictly in accordance with the polarity of the permanent magnets forming the magnetic system, and, like any magnets placed in parallel and with the poles in one direction, they start repelling each other. In reality, the material particles stand in one line across the gutter (Figure 2) at some distance from each other.

 The non-magnetic chute 7 serves not only to transport the material to be divided, but also by its downward deflection sets the law for changing the magnetic field strength (H gradH) in the working zone of the magnetic separator, which in this device is always on the surface of the chute and moves along it.

 In Fig. 1, chute 7 is depicted rejected at the bottom of the separator at an angle g, however, its shape can be any (parabola, hyperbola, etc.), depending on the magnetic susceptibility range of the fraction to be separated from the material to be divided. .

The design of the feeder can be any of the known, which are used for the dosed supply of the material to be separated. The feed rate of the material is chosen empirically, based on specific requirements. With an increase in the feed rate of the material, there will be a decrease in the selectivity of separation and an increase in the productivity of the separator, with a decrease in the feed rate material - increasing the selectivity of separation and reducing the performance of the separator.

 Similarly affects the speed of the conveyor belt, which is also chosen empirically depending on the specific requirements for performance and selectivity.

 Example:

 For magnetic separation, thermally demagnetized waste of permanent NdFeB magnets in the form of powders with a particle size of 0.755 - 1.0 mm with an average NdO content of 0.52 wt. %, which can not be reused in the production of magnets due to the high content of NdO (more than 0.3 wt.%).

 The magnetic separator manufactured by the NPO Magneton JSC according to the proposed option contained a non-magnetic brass trough 20 mm wide. At the bottom of the magnetic separator, the chute was deflected at an angle of 15 °. At the same time, the magnetic field strength on its surface fell (in a deviated section with a length of 80 mm) from 180 kA / m to 20 kA / m.

 Permanent magnets with geometrical dimensions 10 x 10 x 20 of NdFeB material were attached to the conveyor belt according to FIG. 1. The gap between the magnets was 10 mm. The size of the 20 mm magnets was located across the conveyor belt. The number of magnets placed on the tape was 25 pieces.

 Pole tips were made of steel STU and were equilateral triangular prisms, the upper (facing the chute) angle of which was dulled by a facet 0.5 mm.

The length of the conveyor belt was 50 cm. The speed of movement of the conveyor belt was 0.48 m / s and was provided with an electric drive with a power of 50 W. The outlet of the feeder was a slit with dimensions of 1.2 x 15 mm, placed the largest size across the separator chute.

 As receivers separated products used 10 containers, which were under the working area of the separator according to figure 1. In the process of magnetic separation of 0.5 kg of material, the entire divided material turned out to be distributed over 10 containers, the numbering of which was carried out in figure 1 from left to right.

 Overall dimensions of the magnetic separator 200 x 250 x 400 mm. Weight 4.4 kg. The capacity of the magnetic separator for the material to be divided was 18.6 g / min, which corresponds to the annual productivity with a 2-shift operation of 4.5 tons / year.

 The results of magnetic separation are shown in table 1.

Table 1 - Results of magnetic separation

As can be seen from the obtained results, the use of the utility model allows to increase the selectivity of the separation of waste from the production of permanent magnets NdFeB to 0.24 - 0.82 depending on the content of NdO in them.

Claims

 Claim Magnetic separator including a feeder and receivers of separation products, a chute and a magnetic system representing an endless conveyor belt with permanent magnets installed on it, characterized in that in order to increase the selectivity of the separation of materials, the chute bends around the magnetic system in its direction of movement and in the lower part deviates from it downwards, and the permanent magnets are fixed on the conveyor belt with like poles, and pole tips are mounted on their opposite poles.