Bulk solids handling and processing Technical Publications and Papers

AJAX Equipment

Milton Works, Mule Street, Bolton, UK, BL2 2AR
Tel: (0)1204 386723      Fax: (0)1204 363706
Email info@ajax.co.uk


Ajax Powder Technology Publications

Ajax Equipment, as a service to industry, have prepared a series of papers dealing with various aspects of powder handling problems and techniques based upon their experience. These papers explain and develop the current theories and practices of various aspects of solids handling, powder behavior and testing. A selection of related documents, with which the company has been connected, are also listed for reference. Additionally, information is also available on powder testing devices, wall friction, particle attrition, static and continuous mixing, de-aeration, compacting, heating and cooling of powders and varied associated topics.

1 Regimes of Flow in Storage Hoppers
2 Storage and Feeding of Particulate Solids
3 Interfacing Hoppers with Screw Feeders
4 Developments in Hopper Flow Systems
5 Converting Core Flow Hoppers to Mass Flow
6 Entrainment Patterns of Screw Feeders
7 De-aeration of Powders
8 Developments in Screw Feeders
9 Powder Testing for Flow

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1. 'Regimes of Flow in Storage Hoppers'

Fundamental to the consideration of any bulk storage situation is an understanding of the flow patterns that develop when bulk materials are filling into, or emptying from, hoppers. Structural aspects are affected by how the material exerts pressure on the container. Performance features, such as the size of outlet required, the maximum and minimum residence time of the material in store for given discharge sequences, the prospects of segregation and whether some material will remain static from the first hopper fill until the final emptying of all the contents, all depend upon the form of flow pattern which takes place. This paper identifies the differing types of flow patterns developed in hopper of differing geometry and sets out the key selection criteria according to the nature of the bulk material to ensure that the material leaves the storage hoppers at predictable and controlled rates of flow and in an acceptable condition.

2. 'Storage and Feeding of Particulate Solids'

The storage and feeding of solids is a requirement basic for the efficient operation of a wide spectrum of industries. Despite advances in powder technology many forms of problems arise in this activity. The root of these difficulties is that bulk materials experience a wide range of complex rheological properties. The multitudinous duties and environmental conditions that need to be accommodated compound this inherent difficulty. This publication outlines the varied forms of problem encountered and includes key graphs and multiple diagrams to provide an excellent introduction and awareness primer for anyone concerned with solids storage and feeding applications.

3. 'Interfacing Hoppers with Screw Feeders'

Helical screws are commonly used to extract bulk materials from hoppers as they offer great flexibility and allow large and extended hopper outlets to be employed, thereby yielding more favourable hopper shapes for flow reliability and greater storage capacity. The effects of screw specifications on the hopper outlet section and the consequent influences on the flow pattern generated within the hopper are considered in terms of hopper design, flow rates, site needs, feeder overpressures, power needs and good storage and handling practices.

4. 'Developments in Hopper Flow Systems'

Jenike laid the foundation for modern bulk storage technology, but the complexity of the field allows massive scope for further invention and development. From a structured analysis of various approaches to stimulating flow in hoppers, this paper focuses on geometric aspects of gravity flow channels. Inserts and hopper shapes of differing forms are described, which generate mass flow at lower wall angles with standard designs and secure reliable flow through smaller outlet sizes. A device using vibration to accelerate de-aeration of fluidised powders and promote reliable flow is shown. The number of variables is immense such that the subject is far from closed.

5. 'Converting Core Flow Hoppers to Mass Flow'

Core flow is the predominate feature of many bulk solids hopper discharge patterns and this creates problems that affect the nature, properties and constitution of the bulk materials, as well as imposing stresses and pressures on both the hopper and its contents. Techniques are discussed to promote flow and modify the flow regime and alter wall friction in order to develop mass flow. These principles apply to both existing and new hoppers.

6. 'Entrainment Patterns of Screw Feeders'

Helical screws are commonly used to extract bulk solids from the outlet slots of hoppers and accurately meter the contents to many process type applications. The manner in which material flows into the screw affects the flow characteristics of the hopper, residence periods of the contents in various locations, segregation, attrition and the torque requirements of the screw. Regimes of motion of the solids in various sections of the equipment are outlined. This quantitative analysis of screw mechanics enables predictions to be made based on material factors and screw dimensions. Consequential factors are discussed relevant to design and applications.

7. 'De-aeration of Powders'

Fine particulate powders in a fluid condition cause many difficulties. Their searching potential is problematical on seals and gaskets and their rapid flow rate through the smallest of orifices can be considerable and uncontrollable. The 'flooding' or 'flushing' of material through conveying equipment and into the final receiving vessel can also present problems, ranging from inconvenient spillage onto floors, to destructive, and potentially fatal, equipment failure.

8. 'Developments in Screw Feeders'

This paper reviews optimum specifications for efficient screw feeder design and development. It includes consideration of the flow related properties of and characteristics of the bulk powder(s) being handled, Mass and Non Mass Flow, wall friction and flow properties and geometrical features of hopper construction.

9. 'Powder Testing for Flow'

Loose solids are stored, handled and processed in prodigious quantities and diverse manners throughout industries. This paper considers the many factors that influence behaviour of such materials, from the intrinsic nature of the basic properties of material composition and ambient conditions to the operational circumstances of the equipment in use. To understand the requirements for reliable performance of powders, it is necessary predict the behaviour of the material and incorporate these into equipment design characteristics.

FURTHER INFORMATION: We can supply copies of the above, however, due to high demand we have regrettably introduced a preparation and postage charge of 25.00 (GBP) per publication. To request copies or discuss the content of any of our publications please contact: Ajax Equipment Limited, Mule Street, BOLTON UK BL2 2AR Tel: +44(0) 1204 386723 Fax: +44(0) 1204 363706 E-mail: techinfo@ajax.co.uk

See Also User Guide to Segregation and Design Selection and Application of Screw Feeders

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