Jet milling uses compressed air or gas to impact fine particles, reducing them in size to produce powders. It is used in industries such as plastics, pharmaceuticals, and explosives. Jet milling equipment can be expensive, but it offers advantages over other methods. Challenges include controlling particle size and energy efficiency. The method is growing in popularity due to its ability to produce materials with particle sizes ranging from 1 to 10 microns and its avoidance of product contamination and heating effects.
Jet milling is a process that uses highly compressed air or other gases, usually in a swirling motion, to impact fine particles against each other in a chamber. This gradually reduces them in size, resulting in powders with particle sizes just a micron in diameter or 50-100 times smaller than the width of a human hair. Fluid energy milling is another common term for the process, and is often employed in the propellant and explosives making industries, with some systems capable of grinding rocket propellant fuel down to a particle size of two microns at a rate of 500 pounds (227 kilograms) per hour.
Milling machines using jet milling processes are also widely used to create polymer powders for the plastics industry, adhesives, cosmetics, paint and ink compounds, pharmaceuticals and more. Due to the fine nature of size control and the variety of output products produced, jet milling equipment can be expensive. Commercial units sold in India can be set to produce 22 pounds (10 kilograms) to 1,587 pounds (720 kilograms) per hour.
The basic function of a jet milling machine is pretty easy to understand. A feed funnel is used to pour raw material into a compressed gas intake tube which channels it into a cylindrical grinding chamber. The compressed air or gas in the chamber is accelerated into a vortex, with centrifugal force pushing smaller particles to the center when impacts occur and larger ones to the perimeter. When the particles reach a preselected size, they are removed from the vortex center through an outlet tube.
The benefits of jet milling are broad, covering advanced material processing in a wide variety of industries, from metallurgy to synthetic chemicals and food processing. There are, however, also challenges to overcome in controlling the particle size and energy efficiency of jet milling machines. The particle size output can affect everything from the taste of a chocolate that contains jet mill products, to drug absorption, toner quality for printing, the life of ceramic-edged tools, and more.
However, the grinding of materials by jet milling continues to grow in industry, as it is the primary method for producing materials with particle sizes ranging from 1 to 10 microns. It also offers advantages over ball or hammer mills as it results in zero product contamination and the heating effect of the products ground in typical ball and hammer mills is avoided. The Joules Thompson cooling effect of the air exiting a jet mill keeps the product at approximately 200° Fahrenheit (93° Celsius), which is the same temperature as that of the internal grinding chamber.
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