Magnetic separator and permanent magnet

What is a magnetic separator?

Magnetic separator is one of the most widely used and versatile machines in the industry, which uses the magnetic difference between minerals for separation, improves ore grade, purifies solid and liquid materials, and recycles wastes.
Magnetic separators are widely used in mining, timber, kiln, chemistry, food and other industries. For mining industry, the magnetic separator is suitable for wet or dry magnetic separation of manganese ore, magnetite, pyrrhotite, roasted ore, ilmenite, hematite limonite and other materials with particle size less than 50 mm. It is also used for iron removal and waste treatment of coal, non-metallic ore, building materials and other materials.

Structure and working principle of magnetic separator

The magnetic separator (taking the wet permanent magnetic drum separator as an example) is mainly composed of cylinder, roller, brush roller, magnetic system, tank body and transmission part. The cylinder is welded by 2-3mm stainless steel plate, and the end cover is cast aluminum or workpiece, which is connected with the cylinder by stainless steel screws. The motor drives the cylinder, magnetic roller and brush roller to rotate through the reducer or the stepless speed regulating motor.

After the pulp flows into the tank body through the feeding box, the ore particles enter into the feeding area of the tank body in a loose state under the action of the water flow of the feeding spout pipe. Under the action of the magnetic field, the magnetic particles gather to form a “magnetic cluster” or “magnetic chain”. The “magnetic cluster” or “magnetic chain” moves to the magnetic pole under the action of the magnetic force in the pulp and is adsorbed on the cylinder. Because the polarity of the magnetic pole is alternately arranged along the rotation direction of the cylinder, and it is fixed when working, the phenomenon of magnetic stirring occurs when the magnetic pole is alternately rotated with the cylinder, and the gangue and other non-magnetic minerals mixed in the magnetic pole fall off during the overturning, and are finally absorbed on the surface of the cylinder It’s concentrate. The concentrate is transferred to the weakest part of the magnetic system edge with the cylinder, and is discharged into the concentrate tank under the action of the flushing water from the discharge pipe. The non-magnetic or weak magnetic minerals are left in the slurry and discharged out of the tank with the slurry, that is, tailings.

Classification of magnetic separators

Magnetic separators are classified according to different characteristics and standards.
According to the intensity of the magnetic field and the strength of the magnetic field force, it can be divided into three types:

• Low intensity magnetic separator: the magnetic field intensity of working gap is (0.6 ~ 1.6) × 105a / m, which is used to separate strong magnetic minerals;
• Medium magnetic field separator: the magnetic field intensity of working gap is (1.6 ~ 4.8) × 105a / m, which is used to separate medium magnetic minerals;
• High magnetic field magnetic separator: the magnetic field intensity of working gap is (4.8 ~ 20.8) × 105a / m, which is used to separate weak magnetic minerals.

According to the selected medium, it can be divided into:
Dry magnetic separator: it is mainly used to separate large and coarse strong magnetic ore and fine weak magnetic ore in air. At present, it is also used to separate fine-grained strong magnetic ores;
Wet magnetic separator: separation in water or magnetic fluid. It is mainly used to separate fine-grained strong magnetic ore and fine-grained weak magnetic ore.
In addition, it can also be classified according to the way in which the magnetic particles are selected, the movement direction of the feeding materials, the method of discharging the separation products from the separation zone, and the structural characteristics of the discharged magnetic products.

Magnetic circuit design and magnet of magnetic separator

The closed circuit through which the magnetic flux is concentrated is called magnetic circuit. The magnetic system of magnetic separator needs to produce a certain intensity of magnetic field, and most of the magnetic flux in the magnetic field can be concentrated through the separation space. The height, width, radius and number of poles of the magnetic system, the magnetic potential difference between the adjacent poles, the distance between the poles, the ratio of the width of the pole surface to the width of the pole gap, the shape of the pole and the end face of the pole, and the distance from the end face of the pole to the center of its arrangement all have great influence on the magnetic field characteristics.
The magnetic separator shown in the following figure is an example. The magnetic circuit part adopts five pole magnetic system. Each magnetic pole is bonded by ferrite and NdFeB permanent magnet block. It is fixed on the magnetic guide plate through the central hole of the magnetic block with screws. The magnetic guide plate is fixed on the shaft of the cylinder through the bracket. The magnetic system is fixed, and the cylinder can rotate. The polarity of the magnetic poles is arranged alternately along the circumference, and the polarity is the same along the axis. The drum is made of stainless steel non-magnetic material, which is sheathed outside the magnetic system. The non-magnetic material is used to prevent the magnetic line of force from entering the selective zone through the cylinder and forming a magnetic short circuit with the cylinder. Non magnetic materials should also be used at the position of the tank close to the magnetic system, and ordinary steel plate or hard plastic plate should be used for the rest.

For permanent magnet separator, permanent magnet is the most important component, the quality of permanent magnet determines its performance characteristics. The permanent magnet of magnetic separator is usually made into a certain size (for example, length × width × height = 85 × 65 × 21mm), so it is used to be called permanent magnet block or magnetic block for short. The permanent magnetic materials that can be used in the magnetic system of magnetic separator include permanent ferrite, alnico, fecrcoco, Mn Al Fe, SmCo permanent magnetic materials, and NdFeB permanent magnetic materials. At present, the main permanent magnet materials used in domestic magnetic separation equipment are permanent ferrite (strontium ferrite, barium ferrite), followed by NdFeB permanent magnet materials.
In the design of magnetic system, we need to choose which kind of permanent magnet material to use according to the specific situation of various aspects:

• Magnetic field strength: a constant magnetic field will be generated in the specified working space. The strength of the magnetic field determines what kind of permanent magnet materials need to be used. The magnetic properties of NdFeB permanent magnets are much higher than that of ferrite.
• The requirements for the stability of magnetic field, that is, the influence and adaptability of permanent magnet materials to environmental factors such as temperature, humidity, vibration and impact.
• Mechanical properties, such as toughness, flexibility and compressive strength of magnets;
• Price factor

Source: China Permanent Magnet Manufacturer – www.rizinia.com