Monday 02 June, 2014
Powders can be considered as a type of granular material, but have the defining characteristic of consisting of relatively fine particles. This difference is a fundamental and important one that results in individual powders exhibiting far greater variability in bulk density than products containing larger granules. This is especially true of fine powders. Under consolidation, fine particles may pack closely together and become solid-like in terms of their flow properties. Conversely, a fluidised powder sample will contain significant amounts of air, have a low bulk density, and flow like a liquid. The ability of powders to transition between these states complicates powder handling.
For many industries, powder handling is a routine, potentially troublesome aspect of operation. Food ingredients exemplify the broad range of powders that require consistent transport, from fine flours and milk powder through to more free- flowing materials such as salt and granulated sugar. Similarly in the pharmaceutical sector many active ingredients and excipients are handled in powder form. Generally speaking it is finer powders from both industries that are especially problematic. This is because with finer powders, cohesive forces, the forces of attraction between one particle and another, are large relative to the effect of gravity. This tends to inhibit powder flow. Adhesive forces, between fine powders and the processing surface may also be relatively high.
Experience is critical when it comes to powder handling since the associated science, though helpful, is not yet completely reliable. Guttridge has over five decades of experience in this area and in the last few years has invested considerable resource in powder testing to augment this skill base. The in-house material testing capability that we offer quantifies the cohesivity of a powder sample and provides data on which to base the design of a hopper, or the choice of construction material. Expert interpretation of this data, alongside practical knowledge, enables our engineers to design right first time solutions that fully meet customer requirements: a screw conveyor with the optimal flight angle, for example, or a hopper with a robustly specified half angle and outlet.
Equally importantly, Guttridge has a wide range of equipment to choose from when it comes to identifying an optimal powder handling solution including screw feeders, screw elevators and bulk bag discharge equipment. Screw conveyors are especially useful for powders and provide a fully enclosed solution for food and pharmaceutical applications. For hygienic transport these are supplied in stainless steel equipment, to ensure maximum corrosion resistance. Polished surfaces and crevice-free welding are also an option to reduce powder adherence to an absolute minimum. These features ease the removal of residual material between runs, to eliminate the risk of contamination.
With a foundation of 50 years of experience, Guttridge is a flourishing company, globally respected for delivering well-engineered, reliable materials handling solutions that continue to anticipate dramatically changing industrial needs.
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