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  • Flow field analysis of materials in a polyurethane foaming machine mixer
    来源:http://motokone.com发布时间: 2018-05-18 09:20 Author: Polyurethane foam machine Source: http: //motokone.com Published: 2018-05-18 09:20
    Abstract: Using AN SYS, the flow field of the material in the mixer is analyzed, and the shear stress is obtained based on the velocity field. The results show that the material has a low speed zone in the longitudinal groove, and training is set up. When a hub is used, the longitudinal groove should not be too deep. The boundary between the hub edge and the longitudinal groove should be a circular arc; there is a circulating flow in the cross section and the direction, which is conducive to the full mixing of the material.
    With the development of the polyurethane industry, polyurethane foaming machines are widely used. The machine is mainly composed of a storage device, a metering device, a mixer and a control system. Among them, the mixer is the core component and the heart expansion of the foaming machine], Its performance directly affects the mixing effect of the material and the foaming quality. Due to the complicated state of the material flow in the mixer, the current design of the agitating mixer is based on experience only, so studying its structure and parameters to improve the performance of the foaming machine and its products The quality of the material is significant. Taking the stirring hub as the research object and the finite element analysis software ANSYS as the platform, the flow field of the fluid in the mixer is analyzed to determine the speed, pressure distribution and shear stress of the material in the flow channel, and the experimental results. Basically match, provide basis for mixer design.
    Flow field analysis of materials in a polyurethane foaming machine mixer

    Flow field analysis of materials in a polyurethane foaming machine mixer
    1 mixer structure and working principle
    The structure of the agitating mixer is shown in Figure 1. It is mainly composed of a stirring cavity sleeve, a stirring hub and a hub driving device. The stirring hub and the stirring cavity sleeve form an annular mixing chamber. During operation, the A and B components are respectively composed of two metering pumps. It is pumped into the mixing chamber through the component feed ports 3 and 6. The hub 5 rotates at high speed under the action of the drive motor 1. The mixing chamber sleeve is stationary. As the hub rotates, the material is cut and stretched in the mixer to achieve Mixing [2 3].
    2.1 Geometric Model
    Figure 2 is the geometric model of the stirring hub. The hub is a rectangular screw with longitudinal grooves, with a diameter of 30 mm, a root diameter of 25 mm, a groove width of 3 mm, and a spiral groove depth of 1.0 to 3.0 mm. Figure 3 is a three-dimensional flow channel. Geometric model, which is obtained by subtracting the stirring hub from the stirring cavity sleeve using the pre-processing function of the ANS YS software [Use.
    Since the time that the fluid passes through the flow path is relatively short compared to the time to start gelation, the conversion rate can be regarded as zero (the reaction heat is negligible); given that the viscosity of the reaction liquid is not high (4 to 6 Pa0s for 25 field inches), friction occurs The temperature change caused by heat can be ignored. From the viscosity model formula, the viscosity can be assumed to be constant. To simplify the calculation, make the following assumptions:
    (1) Unfold the stirring hub and the mixing chamber sleeve into two planes, ignoring the curved surface effect between the barrel and the hub.
    (2) There is no slippage on the wall of the runner.
    (3) The dynamic viscosity of the material is 4 Pa0s, and the density is 1.2X 103kg / m3.
    3 result analysis
    3.1 Velocity diagram of spiral groove
    It can be seen from Figure 5 that under the action of the drag speed, there is a low speed zone in the cross section of the spiral groove. The size of this area is related to the drag speed and the depth of the spiral groove: the greater the drag speed, the smaller the depth of the spiral groove. , The smaller the area; the velocity contour is arc-shaped at the junction of the hub and the longitudinal groove. Therefore, the longitudinal groove should not be too deep, and the arc transition should be at the junction of the hub and the longitudinal groove.
    3.2 Cross-section velocity profile
    It can be seen from Fig. 6 that there is a low-speed zone at the center of the cross section of the spiral groove and the sides of the bottom, but it has no effect on production capacity. As can be seen from Fig. 7, there is a significant backflow phenomenon in the cross-section velocity, which makes the material in the flow channel. Overturning, which is beneficial to the full mixing of materials.
    Figure 6 shows the pressure distribution at cross sections B, C, and D when the depth of the spiral groove is 3 mm, 1 mm, and 2 mm. It can be seen that when the depth of the spiral groove is 3 mm, the pressure and fluctuation are small, and the material flows smoothly; When the depth of the spiral groove is 1 mm and 2 mm, the pressure and fluctuation increase sharply, which increases the pressure of the metering pump and the difficulty of the shaft dynamic seal.
    3.4 Effect of rotational speed on shear stress
    As shown in Figure 9, the shear stress is proportional to the speed of the hub. The greater the speed, the greater the shear stress the material is subjected to, and the more fully mixed it is.
    3.5 Shear stress distribution in the depth direction of the spiral groove
    As shown in FIG. 10, the shear stress remains basically unchanged when the spiral groove is within 0.5 mm from the stirring cavity sleeve, and the shear stress increases with the distance from the spiral groove to the cavity sleeve when the spiral groove distance is 0.5 to 0.7 mm. It decreases sharply. When it is larger than 0.7 mm, the shear stress continues to decrease with the increase of the distance between the spiral groove and the cavity sleeve, but the decrease is smaller than the former, which indicates that the closer the material to the cavity sleeve is, the more thorough the mixing.
    4 conclusion
    a. The material has a low speed zone in the longitudinal groove. When designing the hub, the longitudinal groove should not be too deep. The boundary between the hub edge and the longitudinal groove should be arc-shaped.
    b. There is a backflow phenomenon in the cross-section direction, which is conducive to the full mixing of materials.
    c. Pressure and pressure fluctuations increase with decreasing spiral groove depth.
    d. Shear stress is proportional to the speed of the hub, and the relationship with the distance from the spiral groove to the cavity sleeve is: the greater the distance, the smaller the shear stress.
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