The complexity of Mixing Powders

The blending of powders has been used an industrial process for many years, primarily to homogenise materials in large quantities. As technology has improved the number of applications for this production method has increased. Practical experience with a variety of different types of machine has enabled the development of specific equipment, designed to produce reliable results, taking into account scale-up and mixing behaviours. This has expanded the number of uses which now include; improving the quality of a product, fusing materials, altering the functional properties, and many others. This degree of specialism requires a high level of knowledge; built up from data accumulated over many trials, in order to select the optimal equipment and process.

Material properties

Mixing powders can be a complex matter due to the varying properties of the materials involved. Many powders have cohesive properties, especially when friction builds up a static charge; others can agglomerate when there are humid conditions or storage temperatures rise. If there is a difference in particle size there is a natural tendency for the smaller grains to sink to the bottom of the mix, this is also influenced by density, shape and resilience. The aim of the operation is to produce a homogenous product using the minimum amount of energy and time, which both add costs.

Types of mixing

The two main styles of mixing are convective and cohesive; during the convective process the materials are distributed across each other in a sequence of motions; with each cycle the distribution becomes more random. Used for free-flowing and coarse components, a stage is reached when the combination is in its most random state, after which separation might begin to occur as the particles begin to segregate. Convective mixing is required when dealing with fine powders, where the inter-particle forces are liable to produce clumping. Here much stronger forces are required than with convective mixers and impact and shearing motions are involved.

Pooled resources

Powder mixing is used by a wide range of companies that are either equipped to carry out the process in-house or who will use a specialist company to carry out the work for them. The choice to use an external contractor might depend on experiments with new materials, trial runs of a new product, or if their own machinery cannot cope with a bulk order, or is otherwise tied up. Due to the complexity of the mixing processes it is quite usual for the powder mixing company and the company placing the order to pool experience in order to achieve the desired result. This collaboration often occurs during trials, or when trials are being up-scaled to full production runs.

The mixing of powders is used across a number of different industries that include food, pharmaceuticals, chemical preparations and additives. Although simple in theory, achieving the correct result can require patience and ingenuity.