Characterization of the granular-to-fluid state process during mixing by power evolution in a planetary concrete mixer

Cazacliu, Bogdan; Legrand, Jack

doi:10.1016/j.ces.2008.06.001

Cited by 34 publications

(21 citation statements)

References 19 publications

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“…This has been first studied during the early 1960s in concrete manufacturing [8]. For instance, during the mixing of powders and liquids, the torque measurement provides enough information to decide whether the operation should be stopped to get the wanted product [9]. Bagster and Bridgewater investigated the force needed to move dry particles with a blade at lab scale [10], using dimensional analysis [11].…”

Section: Introductionmentioning

confidence: 99%

Rheology of cohesive powders in a pilot scale planetary blender

et al. 2017

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a b s t r a c tPowder agitation experiments in a bladed planetary mixer have been performed with the objective of establishing correlations based on dimensionless numbers. Powders of different kind have been studied: free flowing (semolina) and cohesive (lactose, talc and milled sand). Mixtures of free flowing and cohesive powders have also been studied to get a more complete range of powders of different properties. It has been observed that the gyration motion plays an important role in the power consumption of cohesive powders. The relation between a modified power number (N pM = P/ρ b u ch 3 d s 2 ) and a modified Froude number (Fr M = u ch 2 /gd s ) used in several previous publications is adapted and shown to depend on powder cohesion. These dimensionless numbers are built on the basis of a characteristic speed u ch , a characteristic length d s , the bulk density ρ b and the power consumption P. The filling ratio f is also taken in account. For a free flowing powder, of cohesion smaller than 0.3 kPa, N pM = a(f)·F rM −1 while for a more cohesive powder, of cohesion higher than 0.6 kPa the correlation N pM =6·F rM b(f) is more appropriate. For both equations, a and b are powder-dependent parameters. Their linear dependency on the filling ratio of the blender has been established.

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Section: Introductionmentioning

confidence: 99%

Rheology of cohesive powders in a pilot scale planetary blender

et al. 2017

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“…This paper focuses on twin-shaft concrete mixers and the concrete mixing machine design and optimization, which are topics of great significance for achieving high-quality production standards with reduction of costs and waste. For this reason, scientific research is often focused on the mixing phases modeling [16][17][18][19], in order to study the influence of the various design and production parameters on the entire mixing process and to find the best way to improve the concrete quality [20][21][22][23][24][25][26] and reduce…”

Section: Introductionmentioning

confidence: 99%

Twin-Shaft Mixers’ Mechanical Behavior Numerical Simulations of the Mix and Phases

et al. 2019

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In this paper, the mechanical behavior of concrete twin-shaft mixers is analyzed in terms of power consumption and exchanged forces between the mixture and the mixing organs during the mixing cycle. The mixing cycle is divided into two macro phases, named transient and regime phase, where the behavior of the mixture is modeled in two different ways. A force estimation and power consumption prediction model are presented for both the studied phases and they are validated by experimental campaigns. From the application of this model to different machines and by varying different design parameters, the optimization of the power consumption of the concrete twin-shaft mixers is analyzed. Results of this work can be used to increase productivity and profitability of concrete mixers and reduce energy waste in the industries which involve mixing processes.Machines 2019, 7, 39 2 of 13 phenomena such as power consumption, wear [27][28][29][30] and friction among mixing components and mixtures [31] and to predict the useful life of the mechanical mixing organs [32,33].Concrete mixers can work by exploiting different geometrical configurations based on the positions of the mixing shafts and on the machine kinematics [34].In this paper, the study and optimization of a twin-shaft horizontal mixer are presented and discussed. The aim of the paper is to present a model to study the mechanical behavior of twin-shaft mixers, based on the prediction of the exchanged forces between the mixture and the mixing organs and the power consumption when design parameters vary in a realistic production range. The presented model is based on the soil mechanics and foundations theory differently from the models proposed in the state of the art.The evaluation of power consumption is done in the transient and regime phases of the mixing procedure, and the model is validated by means of experimental tests in a real production plant. Then it is applied to different machine models and sizes to define optimal design parameters.The main studied design parameters influenced by the optimization process are the mixing blades and arms size and shape, the radius and length of the tank, the shaft spacing, the processed concrete volume, and the filling level.

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“…The agglomerates are destroyed by impact and shear energy provided by the mixing equipment, thus, promoting fines and aggregates dispersion, as well as, the homogenization of the solid particles between them and with water [1][2][3][4][5][6]. The efforts related to the mixing process can be assessed by special rheometers capable to withstand and measure the high levels of torque generated during mixing of highly concentrated suspensions (like mortars and concretes) [1][2][3][4], or by mixers equipped adequately to quantify the energy consumption [5][6][7] during the process, also allowing for the identification of the moment that the material starts to behave like a fluid [2,8], the fluidity point. This point can be determined in the mixing curve as the moment in which the torque levels start to stabilize and the first derivative of the curve tends to zero asymptotically, Figure 1 [2].…”

Section: Introductionmentioning

confidence: 99%

Influence of the addition sequence of PVA-fibers and water on mixing and rheological behavior of mortars

França

Cardoso

Pileggi

2016

Rev. IBRACON Estrut. Mater.

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The mixing process of fiber-containing cementitious suspensions is a crucial factor to obtaining a good dispersion of fibers and guarantee adequate mechanical performance of the hardened products. The addition of fibers into the suspension causes reduction of the fluidity of the system due to factors inherent to the fibers, the matrix and their interaction. During mixing, these interactions make dispersion and homogenization processes more difficult due to the formation of fibers - particles agglomerates. Conventional techniques to assess workability of mortars are inadequate to evaluate the rheological behavior of fiber-reinforced systems, in which parameters like viscosity and yield stress are not completely taken into account. Therefore, this work employs rotational rheometry to evaluate the influence of fiber and water addition sequences on mixing and rheological behavior of mortars containing Polyvinyl Alcohol (PVA) fibers. Constant test parameters were: mixing time of 317s; impeller velocity 126.5 rpm; water flow 128g/s. A constant mix design was used with a water content of 16%wt, and a 0.2%vol of fibers were added to the reference composition. Four mixing sequences were studied: S1 and S2 are based on the addition of fibers at different stages of the mixing process; while in S3 and S4 not only the fibers are added at different stages, but also the water addition is performed in two steps (25% first and 75% latter).Results showed that it is possible to optimize the mixing step of fiber-containing systems by changing the moment of fiber addition into the mixture. The introduction of fibers after mixing the dry mortar with water, when it already had achieved its fluidity point, demanded a lower mixing effort and produced a more flowable material.

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Characterization of the granular-to-fluid state process during mixing by power evolution in a planetary concrete mixer

Cited by 34 publications

References 19 publications

Rheology of cohesive powders in a pilot scale planetary blender

Rheology of cohesive powders in a pilot scale planetary blender

Twin-Shaft Mixers’ Mechanical Behavior Numerical Simulations of the Mix and Phases

Influence of the addition sequence of PVA-fibers and water on mixing and rheological behavior of mortars

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