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Title: Roller compaction : mechanical properties of primary particles, pre-compacted body and ribbon
Author: Al-Asady, Riyadh Bakir Hasan
ISNI:       0000 0004 5993 3956
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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Roller compaction is a continuous dry granulation process in which the primary powder is compressed at high pressure by two counter rotating rollers to produce a ribbon. It is common that the ribbon is then crushed to produce granules. Although considerable research has been carried out, more understanding of the process is necessary to optimize the efficiency and to improve product quality. During the compaction process the particles exhibit different behaviours such as rearrangement, elastic and plastic deformation in addition to the fracture. The existence and the limit of each of these behaviours depends mainly on the mechanical properties of the powder and on the applied compaction parameters. The mechanical behaviour of the particles could therefore affect the bonding of the particles to each other. This study investigates the mechanical properties and specifically the hardness of the material which was measured throughout different stages of the process. The measurements covered different scales of hardness which represents different material properties. Nano-indentation hardness was used to indicate the plastic deformation of the single particle of the primary powder and it was measured for different materials with a wide range of mechanical properties. Then the hardness was linked to the properties of the ribbon. Such a relationship is useful to predict the product quality whilst only using few particles. From the results, the optimum hardness range that produces a good quality ribbon was suggested. Furthermore, indentation of the pre-compacted body was used as a novel approach to indicate the progress of the compaction process as the powder is grabbed by the two rotating rollers. The hardness was measured for what this study called a "pre-compacted body" which is the powder/compact in the space between the rollers before the minimum gap. This approach was used to determine the nip angle and how different process parameters such as roller speed, roller gap and applied hydraulic pressure affect the nip angle and other ribbon properties including ribbon temperature. The suggested new approach is easy to carry out. The measurement uses the actual data resulting from the process without any assumptions. Finally, micro indentation hardness of the ribbon was used to indicate the strength of the bonding between the primary particles and it was linked to the granule size distribution resulting from crushing of the ribbon. The findings from this study can be used by various industries to improve the quality of the product by choosing more appropriate formulation and process parameters. However, some industries need to use specific materials which could be hard to granulate; therefore, they do not have the option to choose the formulation. For these difficult materials, novel roller geometry was designed. The use of the new roller showed a significant improvement in the granulation process and product quality in comparison to the standard roller.
Supervisor: Salman, Agba ; Hounslow, Michael Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available