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The Important Steps In The Production Of Diamond Powder – Crushing And Shaping

June 03,2023

The crushing and shaping process of diamond plays an important role in the production of micro powder, and directly affects the shape of micro powder particles and the content of target particle size. Different crushing methods will result in different crushing effects. A scientific and reasonable crushing and shaping process can not only quickly crush coarse-grained (conventional particle size 100-500 microns) diamond raw materials intodiamond micropowderparticles with a particle size range of about 0-80 microns, but also optimize the particle shape to make the micropowder product particles more rounded and regular, reducing or even completely eliminating particles that affect the final quality of micropowder, such as long strips, thin sheets, needle rods, etc. Maximize the proportion of marketable target granularity output.

In the production of micro powder, the crushing method can be divided into dry method and wet method. Different crushing and shaping methods are used, and their working principles and process parameters are also different.

▲ Diamond ball mill

1. Process control points for ball mill dry grinding method

Taking the horizontal ball mill dry grinding method as an example, the main process control points are the ball mill speed, ball material ratio, filling coefficient, steel ball ratio, etc. In actual production, flexible control is required based on different raw materials and the purpose of crushing and shaping.

(1) The reasonable speed of the ball mill is an important condition for unleashing its production capacity, provided that the cylinder diameter of the ball mill is the same. The higher the rotational speed, the greater the centrifugal force generated, and the higher the distance that the steel ball is driven to rise along the cylinder wall. The diamond raw material is crushed by the collision and impact of the steel ball when it falls. The stronger the collision and impact of the steel ball when it falls, the higher the crushing efficiency. However, when the rotational speed of the cylinder reaches a certain critical value and the centrifugal force is greater than the weight of the steel ball itself, the steel ball cannot detach from the cylinder and rotate with the cylinder. At this point, the ball mill loses its crushing effect, which means that the ball mill has not done any work. On the contrary, when the speed of the ball mill is low, the distance that the steel ball is driven to rise along the cylinder wall is shorter. At this time, the steel ball mainly acts on the diamond raw material through compression and friction, which has a better shaping effect on the protrusions on the surface of the diamond particles and does not damage the overall structure of the particles. But when the speed of the ball mill is too low, the ball and material cannot be lifted to a certain height before sliding down, which has little effect on the diamond raw material and cannot achieve the purpose of effectively crushing the material. It is generally believed that the suitable working speed for ball mills is 75% -88% of the theoretical critical speed.

(2) The appropriate ball to material ratio and loading coefficient are crucial in the crushing and shaping process. If the ball to material ratio and loading coefficient are too high or too low, they will affect the production efficiency and product quality of the ball mill. If the ball to material ratio is too high or the filling coefficient is too low, the feeding amount of a single machine is restricted. If the ball to material ratio is too low or the filling coefficient is too high, the crushing and shaping time needs to be correspondingly extended or even cannot achieve the desired effect. When the speed of the ball mill is appropriate, the corresponding filling coefficient φ= 0.4~0.54, for a ball mill with a given speed, the ball loading amount should be certain. Excessive or insufficient ball loading will reduce the production efficiency of the equipment. Practice has shown that for the crushing of diamond raw materials, a loading coefficient of 0.45 is generally better. The ratio of balls to materials should be 4:1. After the loading coefficient is determined, the ball loading amount can be calculated using the following equation, G=3.77 φ D ² In the L formula, G is the weight of the ball (ton): φ Is the filling coefficient( φ= 0.4~0.5); D is the diameter of the cylinder (m); L is the length of the cylinder (m).

(3) In order to effectively crush diamonds, the diameter and ratio of steel balls should be determined. After determining the loading coefficient and ball loading amount of the ball mill, steel balls with different diameters should also be selected in proportion to obtain better particle shape and faster crushing and shaping efficiency. Generally speaking, the crushing effect of large steel balls is good, while the shaping effect of small steel balls is good. The contradiction between efficiency and quality can be effectively resolved through a steel ball ratio scheme with different diameters. The maximum diameter of the filled steel ball is calculated using the following formula, where d ball is the maximum diameter of the steel ball (mm); D feed is the maximum size of the feed particle size (mm); D discharge is the final product particle size (µ m).

It should be pointed out that the selection of the size of the steel ball inside the cylinder solely based on calculation is not enough, and it must also be determined through experiments according to specific production conditions. It is generally believed that when the inner diameter of the cylinder is 150mm and the particle size of the raw material is between 50/60 and 80/100, the weight ratio of the steel ball should be 10% with a diameter of 20-25mm, 60% with a diameter of 15-18mm, and 30% with a diameter of 10-12mm.

2. Segmented fragmentation

In the production process of micro powder, wet crushing has a better effect than dry crushing. Because when the dry crushing method reaches a certain fineness, it is easy to cause wall sticking, which reduces the crushing effect; Wet crushing, where the raw materials always exist in the form of slurry, makes it easy to increase the proportion of fine particles.

In order to control the particle size ratio, segmented crushing should be used when producing more fine-grained micro powders, especially wet segmented crushing is better. This can not only avoid excessive crushing of the material, but also achieve segmentation according to strength during the crushing process. This is because the first diamond to be crushed is low strength and poor quality diamond, followed by high strength and good quality diamond.

3. Airflow crushing

Another crushing method is the airflow crusher, which uses compressed air as the working medium. Compressed air is sprayed at high speed into the crushing chamber through a special supersonic nozzle. The airflow carries the material at high speed, causing strong collisions, friction, and shear between the materials, thus achieving the purpose of crushing. When the force acting on a particle exceeds its destructive stress, fragmentation occurs. High speed impact and collision cause particle volume fragmentation, while shear and grinding effects cause surface fragmentation of particles. This crushing method is very advantageous for the production of diamond powder, as it can produce ideal particle shapes. The biggest advantage of an airflow crusher is that it is not limited by mechanical linear velocity and can generate high airflow velocity. Especially, a supersonic airflow crusher can generate a flow velocity several times that of sound speed, thus generating huge kinetic energy, making it easier to obtain ultrafine powders in the micron and submicron scales.