Common crushing method
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The process of deforming a material under the action of an external force and splitting it into finer particles is called breaking. The broken objects are biological cells and solid materials, and the breaking of solid materials is called crushing. When crushing, the external forces of the material mainly include several types such as splitting force, impact force, compression force, shear force and grinding force. In the process of crushing, there are often several forces combined, and rarely is the force of a simple method. For example, the impact force, compression force and splitting force are mainly used in coarse crushing, and shear force and grinding force are the main functions in fine crushing. force.
When the material particles are subjected to an external force, stress is generated inside, and when the stress exceeds the attraction between the molecules, the splitting of the particles occurs. The specific process is as follows: the protruding part of the material is firstly subjected to external stress to generate local stress, and the local temperature rise causes the material to expand and crack. As the external force increases, the resulting stress concentrates on the crack, and the crack rapidly elongates and spreads, causing the material to break.
The pulverization effect of the solid material is often expressed by the degree of pulverization, and the ratio of the average diameter of the particles before the pulverization of the material to the average diameter of the pulverized particles is the degree of pulverization.
When measuring the crushing effect, the degree of crushing is an important indicator for checking the crushing operation.
Second, the crushing method
1. Method for pulverizing solid materials
(1) Open pulverization and cyclic pulverization: the material is only passed through the pulverizing equipment once, and the product is called open pulverization. If the obtained product contains particles that do not meet the required fineness, the coarse particles are separated by sieving and returned to the equipment for pulverization. Call the cycle to smash.
(2) Dry pulverization and wet pulverization: The pulverization carried out after drying the material is called dry pulverization, and the pulverization operation by adding an appropriate amount of liquid to the material is called wet pulverization.
(3) Separate pulverization and mixed pulverization: pulverization of only one raw material is called smashing alone. The powder obtained by pulverization alone is easily agglomerated. The simultaneous pulverization of a plurality of raw materials is called mixing and pulverization. Mixed comminution reduces the re-agglomeration of the powder.
(4) Low-temperature pulverization: A pulverization method for cooling a material before pulverization or during pulverization is called low-temperature pulverization. It can be used as a medium-temperature low-temperature pulverization method using frozen raw materials, pulverizer interlayer refrigeration, adding dry ice or liquid nitrogen.
(5) Fine powder pulverization: Cell-level pulverization of raw materials is called pulverization of fine powder. After the material is pulverized by an ultrafine pulverizer, the particle diameter is about 5, and if it is a plant, more than 95% of the cells are broken.
(6) Nano-crushing: The material is pulverized into ultrafine particles having a diameter of 1 to 100, and the pulverization is called nano pulverization. After the nano-pulverization, the physical and chemical properties of the materials change correspondingly, and some special pharmacological activities will be produced. Therefore, its application in preparation has yet to be further studied.
2. Method for breaking biological cells
The methods of pulverizing biological cells mainly include mechanical methods, chemical methods, and enzymatic methods.
The method of mechanically exerting various forms of force on cells to cause cell wall breakage is called mechanical method, and the method of lysing cells by chemical reagents or enzymes to dissolve cell walls is called non-mechanical method. At present, mechanical methods are widely used for cell disruption in production.
Third, common crushing machinery
1. Grinding machinery for solid materials
(1) cutting machine
Before extracting the traditional Chinese medicine extract, it is necessary to pulverize the Chinese medicinal material into granules of a certain size. In order to avoid leaching of macromolecular compounds which are easily gelatinized, such as polysaccharides, the Chinese medicinal materials are cut into small pieces or sliced ​​by a cutting machine. Less pulverized into fine powder particles. According to the cutting machine movement mode, it can be divided into two types of reciprocating and rotary cutting machines.
The cutter of the reciprocating cutting machine is connected to the crankshaft. When the motor pulley rotates, the crankshaft 5 drives the connecting rod 4 and the cutter 1 to reciprocate up and down. The Chinese herbal medicine is produced and conveyed by the conveyor belt 7, and is pressed and fed at the cutter bed 2 The cutting length and the cutting length are adjusted by the six conveying speeds of the conveying belt.
(2) Chinese herbal medicine grinder
In addition to cutting or slicing, depending on the requirements of use, it is sometimes necessary to pulverize Chinese herbal medicine into coarse powder or fine powder. For example, the precious Chinese herbal medicine is finely pulverized and directly made into a proprietary Chinese medicine. In the industry, a universal pulverizer is commonly used for coarse crushing of Chinese herbal medicines, and a micro pulverizer is used for fine pulverization of Chinese herbal medicines.
The Chinese herbal medicine pulverizer generally belongs to the impact crusher and consists of three parts: the main machine, the auxiliary machine and the electric control box. The main machine is composed of a hopper, a casing, a movable sprocket, a fixed sprocket, a centrifugal grading device, and a sieve screen is installed in the main machine for grading the particles. The steel bar fixed on the toothed disc is called steel tooth, and the toothed disc is fixed on the rotating shaft and driven by the electric motor through the pulley. The auxiliary machine is composed of a cyclone and a pulsed dust collector to collect and pulverize the obtained particles and prevent the dust from flying. When the motor is started, the high-speed relative movement between the movable toothed disc and the fixed toothed disc, the material is crushed by the combined action of the impact of the teeth on the toothed disc, the friction and the impact of the materials on each other. The particle size after pulverization can be arbitrarily adjusted between 10 mesh and 200 mesh.
When the universal pulverizer is in operation, the cap should be closed first, and the machine should be idling. After the rotation is stable, the material to be pulverized should be added. Otherwise, the added materials are blocked between the steel teeth, increasing the starting load of the motor and damaging the machine equipment.
(3) Micropulverizer
Usually the micro-grinder belongs to the hammer mill, as shown in Figure 9-4. The micro-grinder consists of three parts: the main machine, the auxiliary machine and the electric control box. The rotor or the suspension hammer is suspended by a hinge on the rotor in the main body, and a grille and a lining plate are installed in the pulverizer chamber, and the grille controls the granularity of the product. The material enters the crushing chamber from the hopper through the screw conveying rod, and is subjected to the action of hammering, cutting and lining impact of the high-speed rotating hammer, and is crushed. The pulverized material is discharged through the sieve hole at the bottom, and the coarse particles are intercepted by the grille. It is again sent to the crushing chamber for crushing. Qualified pellets enter the cyclone under negative pressure wind transport and are collected into storage containers via a bag filter.
(4) Ball mill
The ball mill is a finely divided device made of stainless steel or ceramic material with a certain number of steel balls or porcelain balls. When the tank rotates, due to the friction between the spheres and between the sphere and the tank wall, the spheres rise to a certain height with the tank wall and then fall down in a parabolic manner, thereby causing impact and grinding on the material and making the material height. Smash.
Ball mills are often used for fine grinding of materials and can be used for aseptic comminution because they can be comminuted under sealed conditions.
2. Breaking of microbial cells
The microbial cell wall is very tough and can withstand a certain high pressure without breaking. When the product of interest is in the cell, an efficient method must be used to disrupt the cell, allowing the desired product to be released from the cell for extraction.
At present, the production mainly uses mechanical crushing to break the cells, and the equipment used mainly includes a high pressure homogenizer and a bead mill.
(1) High pressure homogenizer
The key components of the high-pressure homogenizer are the high-pressure pump and the crushing valve. The high-pressure pump usually uses a plunger reciprocating pump, and its structure is the same as that of a general piston pump. The crushing valve is mounted on the discharge line of the plunger pump and is generally composed of a valve stem, a valve seat and an impact ring.
The working principle of the high-pressure homogenizer is: when the material enters the homogenizing valve at high pressure and low speed, the flow valve seat and the narrow gap of the column valve enter the low-pressure zone. According to Bernoulli's law: the pressure energy is converted into kinetic energy, and the huge kinetic energy increases the flow rate. At 300-500 m/s, the pressure rapidly drops to a saturated vapor pressure, and bubbles form in the material, causing cavitation. Under a huge pressure drop, the material is depressurized, expanded, and exploded. Under the action of huge kinetic energy, the material particles produce strong shearing effect through the narrow gap of the valve member. At the same time, the huge kinetic energy can be shot at a speed of 300-500 m/s (100 MPa up to 500-1000 m/s). The impact of the impact ring produces a powerful impact, under the influence of various factors, the biological cells are broken into pieces.
The liquid temperature rises rapidly due to the release of a large amount of heat during cell disruption. In order to protect the equipment while avoiding the loss of biological activity of the heat-sensitive target product, a cooling jacket is designed in the high-pressure homogenizer, and the coolant can be removed to prevent the high-pressure homogenizer from operating at a stable temperature. Therefore, before using the high-pressure homogenizer, the coolant must be passed through and then turned on.
(2) Bead mill
The crushing chamber of the bead mill is composed of a jacket, and the coolant in the jacket can remove the heat generated when the cells are broken. The crushing chamber is provided with lead-free glass beads of about 1 mm in diameter or beads of other materials. When the motor is started, the glass beads move in various forms as the paddle rotates, causing impact and shear effects between the beads and the cells, breaking the cells and releasing the contents. A bead liquid separator is provided at the outlet of the cell homogenate to retain the beads, so that the bead liquid can be separated and broken continuously. Bead mill is a cell crusher with high crushing rate and is often used in the production of biopharmaceuticals.