Study on reasonable speed of agitator
At present, the self-falling and forced mixers widely used in various countries have been used for more than 50 years. The speed is the basic parameter of the mixer, but the research on the speed science and system is not in-depth. On the basis of theoretical analysis, the author has done a lot of experimental research on the determination of the speed of mixer. This paper will focus on this issue.
The speed of mixer is the basic parameter to ensure the normal operation of mixer. It must meet the performance requirements of mixing quality and mixing efficiency. Mixing quality is to produce fresh concrete that meets the requirements of Chinese standards. Mixing efficiency is to shorten the mixing time to improve the productivity and utilization of equipment and reduce production costs on the premise of meeting the quality of mixing.
Concrete is an important building material. To ensure the quality of fresh concrete is the basic requirement for the performance of mixer. Concrete quality is evaluated by its macro and micro homogeneity. The macro homogeneity is measured by the relative error of mortar density in mixtures M (less than 0.8%) and coarse aggregate quality G (less than 5%). The micro homogeneity is measured by the average value of concrete strength R, standard deviation_and deviation coefficient CV, and the more R value is. The higher, the smaller_and CV values, the better the concrete quality. Therefore, the mixer should work efficiently and economically on the premise that the quality of fresh concrete meets the requirements of Chinese standards, which is the criterion for determining the reasonable speed of mixer.
At present, the mixers used in various countries are divided into two main types according to their working principles: the self-falling type which uses gravity to work and the compulsory type which forces the material to move according to the predetermined trajectory. The principle of self-falling stirring is that when the stirring drum rotates, the fixed blade installed in the drum drives each component material up to 0.7 times the diameter of the drum, and the material falls down by means of gravity.
Material distributed in different parts of the drum, because of its different particles, different falling time, falling point and rolling distance, so that materials interpenetrate, mix and mix with each other, to achieve uniform diffusion, its working principle is seen. The main working part of the forced mixer is a disc with several mixing blades distributed along the radial direction. When the disc rotates, when the blades at different angles and positions pass through the material layer, the inertia force, friction force and viscous resistance of the material are overcome, and the circular, radial and vertical motion of the material is forced, thus the stirring effect is produced.
The choice of speed is related to the type of agitator. Because of the different working principle, the rotational speed of the self-falling mixer must be different from that of the compulsory mixer with the same capacity. In addition, because of the difference of working process, the rotational speed of the mixer with the same type and different structure must be different.