The Advantages Of Vibratory Grinding

Rob Yake, grinding mill product manager, SWECO | Mar 21, 2023

Particle size reduction or grinding is a basic part of many important industries – organic and inorganic chemicals, minerals, ceramics, paints, printing inks, pharmaceuticals, and many more. These and other industries depend heavily on grinding as one of the basic steps in their processing. Grinding is an old art and there are numerous grinding methods and machines.Grinding of particles can take place in a wet or dry process, depending upon the nature of the material and the principle of the machine. A vibratory mill can be applied equally well to wet or dry grinding. However, mechanization of both methods requires significantly different designs. Traditional wet grinding is accomplished in a vibratory mill having a diameter-to-height ratio of one-to-one. Traditional dry grinding is accomplished in a mill having a diameter-to height-ratio of two-to-one.

Many traditional grinding mills can grind to minus 10 microns, but their inability to furnish a product in the lower micron range with a narrow particle size distribution makes them inadequate for many modern industrial processes. The vibratory grinding mill is capable of grinding to one micron or lower on average with a very narrow particle size distribution. Additionally, it grinds and disperses with great speed and efficiency utilizing less energy input than other conventional mills.

Vibratory grinding mills use a three-dimensional motion to produce the vibratory action required to grind a variety of materials. It is this high-frequency motion that enables vibratory mills to perform fine grinding to a particle size of a half-micron or less with consistent results.

There are a few forms of grinding action that a vibratory mill can perform, but the main one is impact. Impact is the fracturing of the particles when the media collide with each other. With this type of mill, it is best that the material is friable. Thus, any material that can be broken by impact can be ground in a vibratory grinding mill.

For dry grinding, a typical starting size for the material is ¼ inch (6,350 microns). Vibratory mills can typically reduce the material size down to as low as 30 microns. Powders below 30 microns tend to coat the media, form a cake on the bottom of the chamber, and stick to the cover and chamber walls, which prevent the grinding process. For this reason, vibratory dry grinding should be limited to 30 microns. However, for wet grinding, the solid particles are in a solution allowing a vibratory mill to grind the material more consistently and evenly. The material typically starts at 300 microns and can be reduced to as low as 0.2 microns.

Whether the grinding is performed in a dry or wet mill, the size reduction relies on a fluidized bed of grinding media that is activated by the grinding chamber motion. It is the media that is actually doing the work.

Since it is the media that is performing the work, choosing the correct media is extremely important. Media comes in many different shapes, sizes, and materials. The media of choice for most grinding applications in a vibratory mill is that of a sintered alumina cylinder. During vibration, cylindrical media tends to align itself in layers or sheets with each piece of media sitting side by side. This media will sit in the grinding chamber forming what is known as a packed cylindrical bed. The media action produces face-to-face, line-to-line and point-to-point contacts. This results in the larger particles being preferentially ground resulting in a very narrow particle distribution.

During grinding, each individual piece of cylindrical media slowly rotates on its own axis against the others. This provides a small amount of shear force that is effective in dispersion of agglomerates and brings wetting agents in contact with the particles breaking surface tension. In addition, the rotation results in even wear on the surface of the media which prevents facets from forming.

Vibratory grinding is not the answer to all grinding solutions. But if your process requirements include a fine particle size, narrow particle size distribution, fast and efficient grinding, low energy input, and easy installation and maintenance, then vibratory grinding may be your best option.

Rob Yake is the grinding mill product manager at SWECO. He has more than 35 years of experience with bulk solids processing equipment.

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