BS 9: Mixing of Bulk Solids
BS 9:
Mixing of Bulk Solids Part 1: Review of Powder - Powder Mixing SUMMARY 1. INTRODUCTION 1.1 What is Powder Mixing ? 1.2 What is Cohesivity ? 1.3 State of the Art on Wet Cohesive Mixing 2. MIXING OF WET COHESIVE MATERIALS 2.1 Cohesionless Mixing 2.2 Quality of Mixing 2.2.1 Physical Phenomena 2.2.2 Statistical Phenomena 2.3 Random Mixing Quality 2.3.1 Statistical Analysis 2.3.2 Real Mixing Systems 2.4 Non-Random Mixing Quality 2.5 Ordered and Interactive Mixes 2.6 Buslik Homogeneity 2.6.1 Examples of Buslik Homogeneity 2.7 Indices for Continuous Mixers 2.8 Measurement of Powder Mixing Quality by Sampling 3. COHESION OF POWDERS 3.1 Powder Yield Loci 3.1.1 Coulomb-Mohr Yield Criterion 3.1.2 Yield locus and cohesion 3.2 Jenike flowability and cohesiveness of powders 3.2.1 Direct Shear Testers - Translational Displacement 3.2.2 Direct Shear Testers - Rotational Displacement 3.3 Direct Measurement of Cohesion 3.3.1 AJAX Equipment (Bolton) Ltd. - Warren Spring Laboratory - Cohesion Tester 3.3.2 Cylindrical Mould Testers 3.3.3 Cohesiveness from Bulk Powder Densities 3.3.4 Measurement of tensile strength 4. THE INFLUENCE OF INTERPARTICULATE BONDING AND MOISTURE ON MIXING 4.1 Interparticulate Bonds 4.1.1 van der Waals Forces 4.1.2 Electrostatic/Coulombic Forces 4.1.3 Ratio of van der Waals and Coulombic Forces 4.1.4 Contact Frictional Forces 4.2 Forces due to Moisture 4.2.1 Adsorbed moisture layers 4.2.2 Mobile Liquid Bonding by Liquid Bridges 4.2.3 Static Cohesive Forces 4.3 Effect of Moisture on Cohesiveness and Tensile Strength 4.4 The Influence of Particle Size Distribution on Cohesion 5. MIXING EQUIPMENT 5.1 Categorisation of Cohesive and Non-Cohesive Mixers 5.2 Categorisation of Mixers by Mixing Mechanisms 5.3 Categorisation of Mixer by Mixer Geometry and Operation 5.4 Mixer Selection by Powder Characteristics 6. CONCLUDING REMARKS 7. NOMENCLATURE 8. REFERENCES 9. APPENDIX A 10. APPENDIX B | Volume BSH 9: Part 1 State-of-the-Art Review This part considers the intention of this review on the mixing of wet cohesive solids is to provide an appraisal of the current information available in the scientific, engineering and commercial literature on the assessment of the mixing quality in wet cohesive powders, together with the methods and the equipment commercially available to attain and maintain a specific degree of mixing or non-segregation in wet cohesive powdered systems. Cohesion in powdered materials may be due to either the range of moisture present within powdered systems or due to the interactive forces between particles. This report is therefore divided into three main parts. The first part highlights the mixing of wet cohesive materials in terms of the quality of mixing that can be achieved in both cohesionless and cohesive powders. In the assessment of the mixing quality of, and the degree of mixing in, cohesive powders emphasis has been placed on non-random mixing quality rather than random mixing quality, the statistical parameter which is generally used to describe segregating non-cohesive mixtures. The second part of the review (Sections 3 and 4) appraises the numerous techniques, instrumentation and limitations of measurement which are applicable for the measurement of bulk powder flow characteristics and which can possibly be used to predict the degree of mixing in wet cohesive powders. The final part of this review categorises mixers in terms of cohesive and non-cohesive mixers, mixing mechanisms, and mixer geometry and operation to propose ultimately various selection trees, based on the bulk powder characteristics of cohesive materials. In Appendix A there are listed names and addresses of a number of mixer manufacturers which can provide mixers suitable for the mixing of wet cohesive materials. Selection of the types of mixers suitable for cohesive mixing is based on a survey, published in SH Volume 9 Part 1, of commercially-available mixers used in powder-liquid mixing. It is planned that this part will contain the following features:
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