| At present,China is in the period of rapid development of urbanization,and the improvement of urban construction level puts higher demands on the quality of buildings.The quality of the concrete directly effects whether the building quality is qualified.Mixing is a key process in concrete production.The forced twin-shaft mixer is the main equipment used in the current concrete.This type of mixer has the advantages of stable structure,high production efficiency and good mixing quality.However,the forced twinshaft mixer also has the disadvantages of high noise,high energy consumption,and easy wear of the flow parts.The concrete mixing process is very complicated.The research on the structural optimization of the twin-shaft mixer and the wear mechanism of the mixing process is not deep enough.It is urgent to carry out the basic theoretical research on the structure and wear mechanism of the mixer.In this paper,the blade of the twin-shaft mixer is regarded as research object,and the optimization analysis and simulation research of its installation angle are carried out.The main contents include the following aspects:1.Research and analysis of the relevant theory of the twin-shaft mixer.From the aspect of stirring medium,the physical properties of the concrete material are analyzed.From the aspect of the stirring mechanism,the convection confluence of the material,and the influence of the stirring blade installation angle on the material movement are analyzed.The study found that there has not only chemical but also physical interaction in the process of mixing.The properties of materials are different at different mixing moments,and the macroscopic physical properties of concrete of different magnitudes are also different.At the beginning of the mixing,the hydration is not complete,and the material inside the mixer is more in line with the discrete particle properties.When stirred to a uniform state,a homogeneous concrete fluid state is formed,the material properties of which conform to the non-Newton Bingham fluid.2.Based on DEM for contact model analysis,the contact parameters were calibrated by the “virtual experiment” of slumping degree,and the discrete element software EDEM was used to simulate and analyze the mixing characteristics of concrete at different angles of blades(30°,35°,40°,45°,50°).The research shows that the mixing quality decreases with the increase of the installation angle within 30~50°,and the corresponding energy consumption also decreases.3.Based on the fluid simulation software Fluent,the flow velocity and turbulent distribution of homogeneous concrete fluid materials under different blade installation angles were studied.The study found that the convective motion of 30° and 35° is very significant,and the siege motion at 45°is optimal.Overall,the flow field at the 35° mounting angle is optimal.The simulation results are basically consistent with the EDEM discrete element analysis results.4.Research on blade wear and its life prediction.Based on the wire wear rate formula of abrasive wear,combined with the pressure and velocity gradient distribution of the blade surface simulated by CFD,the maximum theoretical line wear rate of the blade is calculated and the theoretical service life of the blade is predicted.Finally,based on the results of uniformity,energy consumption and wear rate,the curve equation is fitted and the three-index performance evaluation function is constructed.The results showed that the optimal blade installation angle is 31.8° and the optimal interval is 30~34°.In summary,this paper studies the mixing characteristics and blade wear of the twin-shaft concrete mixer under different blade installation angles,which provides a theoretical reference for the optimization of the mixer blade structure and the wear of the flow parts,and also provides a technical support for related equipment research. |
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