Among them,the diamond crushing and shaping process plays an important role in the production of micro powder,and directly affects the shape of the micro powder particles and the content of the target particle size.Different crushing methods will produce different crushing effects.The scientific and reasonable crushing and shaping process can not only quickly crush coarse-grained diamond raw materials(conventional particle size100-500 microns)into diamond powder particles with a particle size range of approximately(0-80 microns),but also optimize the particle shape.,making the particles of micro powder products more round and regular,reducing or even completely eliminating long strips,flakes,needles and rod-shaped particles that affect the final quality of micro powder.Maximize the proportion of marketable target particle size 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.
1.Process control points of dry grinding method of ball mill
Taking the horizontal ball mill dry grinding method as an example,the main process control points are ball mill speed,ball-to-material ratio,filling coefficient,steel ball ratio,etc.In actual production,they can be flexibly controlled according to different raw materials and the purpose of crushing and shaping.
1.Ball mill speed
The reasonable speed of the ball mill is an important condition for exerting its production capacity.When the diameter of the ball mill’s barrel is the same.The higher the rotational speed,the greater the centrifugal force generated,and the higher the distance the steel ball is driven to rise along the cylinder wall.The diamond raw material is crushed through the collision and impact of the falling steel ball.The stronger the collision and impact of the falling steel ball,the higher the crushing efficiency.However,when the cylinder speed reaches a certain critical value and the centrifugal force is greater than the steel ball’s own weight,the steel ball cannot break away from the cylinder and rotates with the cylinder.At this time,the ball mill loses its crushing function,which means that the ball mill does no work.On the contrary,when the speed of the ball mill is low,the distance 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 by squeezing and friction,and the better the effect of shaping the protruding parts on the surface of the diamond particles is.,without destroying the overall structure of the particles.However,when the speed of the ball mill is too low,the balls and materials cannot be raised to a certain height before sliding down,which has little effect on the diamond raw materials and cannot achieve the purpose of effectively crushing the materials.
It is generally believed that the suitable working speed of the ball mill is 75%-88%of the theoretical critical speed.
2.Filling coefficient,ball to material ratio
In the crushing and shaping process,the appropriate ball-to-material ratio and filling coefficient are crucial.If the ball-to-material ratio and filling 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 capacity of a single machine will be restricted.If the ball-to-material ratio is too low or the filling factor is too high,the crushing and shaping time needs to be extended accordingly and even the ideal effect cannot be achieved.
When the ball mill speed is appropriate,the corresponding filling coefficientφ=0.4~0.54.For a ball mill with a given speed,the ball loading amount should be certain.Too much or too few balls will reduce the production efficiency of the equipment.
Practice has proved that for the crushing of diamond raw materials,the loading coefficient is generally 0.45.The ratio of ball to material is 4:1.
2.Segmented crushing
In the production process of micro powder,wet crushing is more effective than dry crushing.Because when dry crushing reaches a certain fineness,wall sticking is easy to occur,reducing the crushing effect;with wet crushing,the raw materials always exist in the form of slurry,and it is easy to increase the proportion of fine particle size.
In order to control the particle size ratio,when more fine-grained micro powder needs to be produced,segmented crushing should be used,especially wet segmented crushing is better.This can not only avoid excessive crushing of materials,but also achieve segmentation according to strength during the crushing process.This is because the diamonds with low strength and poor quality are broken first,and the diamonds with high strength and good quality are broken later.
3.Air flow crushing
Another crushing method is the airflow pulverizer crushing method.The airflow pulverizer uses compressed air as the working medium.The compressed air is sprayed into the crushing chamber at high speed through a special supersonic nozzle.The airflow carries the material in high-speed movement,causing the material to move between them.Produce strong collision,friction and shear to achieve the purpose of crushing.Fragmentation occurs when the force acting on the particle is greater than its failure stress.High-speed impact collision causes volumetric fragmentation of particles,while shearing and grinding effects cause surface fragmentation of particles.This crushing method is very beneficial to the production of diamond powder because it can produce ideal particle shapes.The biggest advantage of the airflow pulverizer is that it is not limited by the mechanical linear speed and can produce very high airflow speeds.In particular,the supersonic airflow pulverizer can produce a flow rate several times the speed of sound,so it can generate huge kinetic energy and it is easier to obtain micron-level particles.and submicron ultrafine powders.