Disc granulator: efficient granule forming technology

Introduction

Granulation is also called rolling forming, concentrates moistened by water. When the concentrate is moistened to the maximum molecular binding moisture, capillary water is formed in the material layer. Due to the action of capillary force, the particles around the water droplets are pulled toward the center of the water droplets. To form the cue ball, through the action of rolling and rubbing in the granulator, a layer of particles will stick to the surface of the cue ball, causing the cue ball to grow and become denser to achieve the required particles.

Working principle and characteristics of disc granulator

• Working principle: When the diameter, rotation speed, and inclination angle of the disk are constant, small balls with different diameters will have different trajectories in the disk. When a small ball moves in the disk, it is subject to centrifugal force, gravity, and friction. Different diameters The movement of particles in the disk. When the ball leaves the edge of the disk and begins to fall, at this time, due to the different friction forces experienced by the balls of different diameters, the breakaway angles are different.
• The larger the ball diameter, the greater the breakaway angle, that is, The smaller the height of the ball rises. Therefore, during the rolling forming process, the balls segregate according to the particle size. The concentrate added to the granulator and the formed balls follow the parabola and are close to the irregular spiral.
• Rotation, as the ball rolls and grows, the descending part of the parabola approaches the left side of the disk according to the size of the ball diameter, while the rising part leaves the disk along the direction of the vertical line of the disk according to the size of the ball diameter (i.e. the big ball (above), this regularity of the material causes the material and pellets to be polarized according to particle size, so that pellets of different diameters roll down at different positions in the disc, and the smallest particles move along the edge of the disc and enter the lower part of the disc first , above which are larger spherules, and the outermost layer is the spherules with the largest diameter;
• Working characteristics: The material can form regular motion. Larger pellets and smaller particles can run along their own different orbits. Therefore, the cue ball can segregate according to its size. Only the largest cue ball can finally be produced. Throw it out from the granulator.

The relationship between the inclination angle, rotation speed and materials of the granulator

• When the inclination angle of the granulator is constant, if the rotation speed is too small and lower than the actual working speed, the material will not rise to the apex of the vertical diameter of the disc, resulting in “empty material” in the cue ball formation area. If the rotation speed is too high than the actual working speed
• When the rotation speed is high, all the materials in the disk will be thrown to the edge of the disk, resulting in “empty material” in the center of the disk. It cannot be classified according to particle size. Only a suitable disk speed can make the material roll along the working surface of the granulator, and disk granulation is achieved.
• The speed of the machine varies with the inclination angle of the disc working surface and the properties of the material. It is usually 1.0-2.0 m/s.
• Generally, if the friction angle of the material is large, the speed can be selected smaller. On the contrary, the speed can be selected larger (1.6 -2.0 m/s), at the same time, the rotation speed is related to the inclination angle.
• The larger the inclination angle, in order to make the material rise to the specified height, a larger rotation speed is required. If the rotation speed is constant, the optimal inclination angle will be certain. The inclination angle of the granulator Generally it is 45-50°.
• The friction angle of the material mainly refers to the friction between the material and the lower surface of the disc, which is related to the properties of the material itself, such as viscosity, particle size and humidity.

Raw material properties

• Cohesiveness of raw materials: Raw materials with high cohesiveness are easy to granulate, such as sulfur concentrates, copper concentrates, etc., while oxide ores and gold concentrates are difficult to granulate; if you want to improve the pelletization of raw materials, Additives can also be used to increase the adhesion of raw materials.Particle size of raw materials:
• The particle size of raw materials varies greatly, and segregation is easy to occur, making it difficult to granulate; the particle size of raw materials should be as small as possible, and the shape should be multi-angular and irregular to make granulation easier.
• Specific gravity of raw materials: The specific gravity of each component in the mixture is too different, which is not conducive to granulation.

Effect of raw material moisture content on particle quality

• The moisture content of the raw material is suitable, so it is easy to form a cue ball, and the cue ball grows up easily; the raw material moisture is low, and the ball forming speed is slow; the raw material moisture content is high, and it is easy to stick together, and the resulting particles are larger in size.
• The humidity of raw materials has a great influence on pelletizing. If dry materials are used to pelletize, the mineral dust will fly, the working conditions are poor, the formation of particles is very slow, and the structure is fragile.
• If materials with insufficient moisture are used to pelletize, the particles will also be very fragile. It is difficult to grow up. If the material with too much moisture is used to make balls, the cue ball will be easily bonded and deformed, resulting in uneven particle size.
• At the same time, over-wet materials and over-wet cue balls will easily stick to the granulator and cause granulation problems. It is difficult to operate the machine. Over-wet raw materials will inevitably form over-wet particles. Such over-wet particles have very little strength and are easily squeezed and deformed during transportation.
• Since the granulator requires a very narrow humidity range of the raw materials, In production, the humidity of the materials sent for granulation is required to be slightly lower than the optimal humidity after granulation.

The form and position of adding water to the granulator

• In the general process, before the material enters the granulator, the moisture is controlled under the appropriate granulation moisture, and then a small amount of supplementary water is added during the granulation process, because this operation can control the appropriate particle moisture and can adjusting the size of the particles can also change the water supply method and strengthen the granulation process.
• When adding water, one principle must be followed, which not only makes it easy to form an appropriate number of cue balls, but also allows the cue balls to grow quickly and become compact.
• To meet this requirement, generally use The operation method of “dropping water into balls, growing mist, and compacting without water” means that most of the water droplets are added to the material in the “balling area”. At this time, around the water droplets, due to the action of capillary force, the bulk material can be easily The cue ball is quickly formed, and another small amount of water is added to the cue ball in the “long ball area” in the form of spray, causing the cue ball to grow rapidly.
• On the surface of the cue ball in the “tight area”, due to rolling and During the rubbing process, water is squeezed out from the inside of the cue ball, causing the surface of the cue ball to become too wet. Therefore, it is forbidden to add water to prevent the particle strength from being reduced and the cue ball from being bonded;

The influence of feeding position and feeding amount on granulation

During the granulation process, the position of adding materials must also comply with the principle of adding water. The raw materials must be added to the “ball-forming area” and the “long ball area” respectively, and it is prohibited to add materials in the “tight area”; it can be obtained from production practice The amount of material required to form the cue ball is less than the cue ball, so most of the material must be discharged into the “long ball area”, while only a small part of the material must be discharged into the “ball forming area”. Generally, the feeding of the granulator is from the disc feeding through the material tube to form a material flow, which is added slightly to the lower right side of the granulator (the granulator rotates clockwise), which can basically ensure the balling area and long balls. There is material in all areas. In addition, the disc granulator adopts belt feeding, so that the material can fall loosely into the granulator, and the effect is better.