Mechanisms and quality control in mixing solids | Applications and equipment for grinding materials

Several mechanisms are used in mixing solids, such as powders, namely convection, diffusion and shear. In convection mixing, masses or groups of particles move from one location to another. In diffusion mixing, individual particles are distributed over a surface that develops within the mixing. In shear mixing, groups of particles are mixed by the formation of sliding surfaces within the mass of the mixing.

The importance of quality control in the mixing process of powders is that it helps to see and understand if there is unwanted segregation of the powder mixture, as in mixing powders. When particles with significantly different densities are mixed, it can be observed that the denser particles tend to settle to the bottom of the mixture. Moreover, fine particles may separate from the larger particles when they are set in motion. By carrying out quality control, any segregation issues in powder mixing can be identified and addressed, allowing homogeneous mixing to be achieved.

At Delft Solids Solutions, we have different types of mixing equipment available for mixing powders, including diffusion mixers, convection mixers and high-speed mixers. Having different types of mixing equipment allows us to mix a wide range of powder materials, such as mixing powders, from free-flowing powders to highly cohesive materials, in different mixing volumes. Our high-shear mixers are especially suitable for mixing lumpy and agglomerating materials that do not mix effectively in a diffusion mixer. We can also evaluate the homogeneity of the mixing process through sampling and analytical techniques such as particle size analysis and segregation analysis.

With our expertise in powder technology and our wide range of services, we can support you in developing and optimising your mixing processes using mixing powders.

What are the applications of material grinding? 

Material grinding has several applications in powder processing, such as powder milling. The main purpose of grinding is to produce smaller particles, either because of their larger surface area or because of their shape, size and number. The final product usually consists of a mixture of particles with a wide variety of sizes and shapes. Grinding of materials can be carried out using different equipment.

For grinding materials, we use different mixing principles in our test area. Our ultracentrifugal mill is effective for reducing soft to medium-hard and fibrous solids. The grinding process takes place by impact and abrasion effects through a fast-rotating rotor mill with sieve screens. These sieve screens can be replaced to change the particle size. This grinding method ensures fast and gentle particle reduction. The range of particle size that can be achieved is about 40-50 micrometres. The centrifugal mill can be used for various applications, such as grinding food, chemicals, minerals and more.

To achieve even smaller particle sizes, the principle of ball milling is used. This is a type of grinding equipment that works on the basis of impact and friction. The particles are reduced by the impact of the balls on the surface of the particles. The ball mill can reduce the particle size to about 10 micrometres. This method is particularly effective for relatively small sample sizes.

For grinding special materials, such as heat-sensitive materials and materials that are difficult to grind, cryogenic grinding can be applied. Cryogenic grinding is the process of cooling a material and then reducing it to a smaller particle size. This is applied, for example, when grinding cocoa nibs. By cooling the material with dry ice or liquid nitrogen, the cocoa nibs can be easily ground into powder.

When grinding materials, particle size analysis can be used to confirm the effectiveness of the grinding process by measuring the particle size distribution and checking whether the desired size has been achieved.