1 Principle of airflow analysis:
1.1 Principle of airflow boundary layer: flat plate operation During translational motion or rotation of a rotary body, the surface of the moving body drives a layer of air to flow due to friction, and due to the viscosity and friction between air molecules, the inner layer of air drives the outer layer of air, layer by layer, forming an airflow layer on the surface of the moving body. . The airflow velocity in this airflow layer changes drastically (that is, the velocity gradient is large) and forms a certain distribution. This airflow layer is called the boundary layer.
1.1.1 Thickness distribution of the boundary layer: Within a certain range, the farther away from the formation point, the thicker the thickness of the boundary layer.
1.1.2 Velocity distribution of the boundary layer: the closer it is to the moving body, the greater the speed and is close to the surface speed of the moving body; the farther away from the surface of the moving body, the velocity The smaller.
1.1.3 Distribution of pressure difference in the boundary layer: In addition to the tangential inertia force (formed by viscosity and friction), the boundary layer also has normal inertial force. (Centrifugal force) creates a radial pressure difference in the boundary layer. The radial pressure at any point in the thickness direction of the boundary layer is proportional to the square of the velocity at that point (it is also proportional to the mass of the boundary layer at that point, which is also the separation principle of fibers and impurities). Therefore, the surface speed of the near-rotary body is the fastest, and the radial pressure is proportional to the square of the velocity at that point. The radial pressure is also the largest. As the thickness of the boundary layer increases, the speed decreases, the radial pressure in the layer decreases, and the radial pressure in the outer layer is equal to zero.
1.1.4 Principle of fiber and impurity separation: Since the boundary layer has velocity distribution, fibers and impurities always tend to tangential to the streamline in the airflow layer; due to the boundary layer With radial pressure distribution, fibers and impurities tend to be in the normal direction of streamlines in the airflow layer; due to the different mass and density of fibers and impurities, the different terminal velocities of fibers and impurities, and the velocity distribution in the boundary layer, they have air resistance. and other influences, giving fiber and impurities a chance to separate. In the outer layer of the boundary layer, there are more impurities than fibers, while in the inner layer, there are more fibers than impurities. Therefore, different cutting depths and cutting directions can be given to the boundary layer to achieve the purpose of adjusting waste, removing impurities and preserving fiber.
1.1.5 Air flow around the boundary layer: Under normal pressure, no matter how much air flow is taken away by the boundary layer, there will inevitably be an equal amount of air flow to replenish it.
1.1.6 Advantages and Disadvantages of Air Boundary Layer: Using the principle of air flow boundary layer, giving different cutting depths and cutting directions to the boundary layer can eliminate impurities and lint , the purpose of adjusting waste, removing impurities and protecting fiber, this is the advantageous side of the airflow boundary layer; the disadvantage is that changes in the speed, pressure, etc. of the airflow boundary layer cause interference to the movement of the fibers that have been fully separated. This makes it difficult to control fibers and causes a series of problems.
1.2 Basic principles of pipeline fluid flow:
1.2.1 Continuity equation: According to the law of immortal mass, when fluid flows in a closed pipe (because the resistance of the pipe is far lower than atmospheric pressure, the compression can be ignored), every time the fluid flows through the pipe per unit time The fluid mass across the cross-section is a constant. That is: V1F1=V2F2.
1.2.2 Law of conservation of energy: When fluid flows in a closed pipe, it follows the law of energy conservation and transformation. Ignoring the influence of factors such as pipeline resistance, the total pressure P = dynamic pressure P1 + static pressure P2. The direction of dynamic pressure is tangential, while static pressure has no direction and is transmitted to any point. In order to facilitate the study of the problem, the above principles can be approximately used for the analysis of airflow at the bottom of large and small leaks.
2 Symptoms of abnormal air flow in carding machine and control of air flow:
2.1 Symptoms of abnormal air flow:
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①. The carding machine has a lot of flying dust, poor cleaning, and abnormal life.
②. The low-pressure cover of the licker-in roller has the phenomenon of blowing air outward, which causes the cotton roller to be wound.
③. Abnormal cotton waste in the litter area, white waste at the bottom of small leaks, accumulated fiber or hanging flowers at the entrance, internal mesh paste plugging or hanging long fibers.
④. The bottom of the large leakage blows wind and flowers outward, causing the wallboard flowers to increase.
⑤. Fibers rotate in the triangular area, and fibers accumulate at the entrance of the large leakage bottom.
⑥. Airflow leaks out of each suction port.
2.2 The principles of air flow control of carding machines are: reasonable removal of impurities and waste, uniform and stable air flow control and prevention of key parts (especially several Triangular area) The thickness of the boundary layer and the direction of the supplementary air flow have an impact on the fiber movement and the structure of the cotton web.
2.3 Methods and means of controlling air flow
2.3.1 Control the amount of air flow generated. The boundary layer produced by the high-speed rotation of the cylinder is the main cause of air flow, followed by the licker-in. Therefore, reasonable cylinder and licker-in speeds are crucial to stable air flow. With the continuous emergence and improvement of new card clothing, we have increased the technological means of exchanging density for speed, and exchanging density and sharpness for carding degree. For example, if we consider reducing the speed of the licker-in, but are worried about insufficient combing, we can use dense or thin teeth on the licker-in to achieve this goal.
2.3.2 Reasonably distribute the airflow at each point (especially the triangle area). Make use of the process spacing at the cover plate, drain bottom, etc. to distribute the air flow reasonably.
2.3.3 Due to the increased rotation speed of the cylinder, lick-in roller and doffer, high-yield carding machines must make reasonable use of low-pressure covers, cotton mesh cleaners, dust and impurity exhaust, etc. Negative pressure suction portDivert and relieve airflow in high-pressure areas.
2.3.4 The fixed carding plate can alleviate, disperse and induce airflow, which is beneficial to the control of airflow.
2.3.5 Reasonable air flow supplementation. Reasonable air flow helps stabilize pressure, stabilize waste, support cotton webs and automatic cleaning functions.
3 Summary:
The air flow control of the carding machine is a vital task . Only by carefully understanding it in principle, observing it carefully on site, and exploring it in practice can we achieve better results.
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