Milling is a very old discipline originated in milling agricultural products to flour. Despite the enormous literature on size reduction, milling is a unit operation which has no sound underlying theory comparable to those existing for other unit operations. The design of milling equipment for a given application is based on accumulated experiences of the manufactures. It is not for lack of either interest or investigation that a quantitative theory of milling does not exist. In contrast, the number of references in the literature dealing with milling is overwhelming. This led to the belief that milling is an art which only could be learned by years of experience. From the perspective of process control this is an undesirable situation. This situation is specifically undesirable in the pharmaceutical industry where product control is critical.
Jet milling is a process of using highly compressed air or other gasses, usually in a vortex motion, to impact fine particles against each other in a chamber. This gradually reduces them in size, resulting in powders that have particle size dimensions as small as one micron across, or 50-100 times smaller than the width of a human hair. Fluid energy milling is another common term for the process, and it is often employed in the propellant and explosives creation industries, with some systems able to grind rocket propellant fuel down to a two micron particle size at a rate of 500 pounds (227 kilograms) per hour.
The benefits of jet milling
The benefits of jet milling are broad, covering advanced materials processing
across a range of industries from metallurgy to synthetic chemicals and food
processing. There are, however, also challenges to be overcome in the control of
particle size and energy efficiency of jet milling machines. Output particle
size can affect everything from how a chocolate tastes that contains jet milling
products, to drug absorption, toner quality for printing, the durability of
tools with ceramic edges, and more. As the professional manufacturer of complete
sets of mining machinery, such as ore processing plant, Henan
Hongxing is always doing the best in products and service. ball
Jet Milling is a concept of feeding of the powder particles into a flat circular milling chamber and subjecting the same tangentially with pressurized air or nitrogen through a venturi. The powder inside the milling chamber by number of angular holes in a ring and placed around the periphery of the chamber.
The heat sensitive and low melting point materials are easily micronized. The micronization takes place due to the collision between the incoming particles and the particles, which are alread, accelerated into the spiral path. The larger particles of the product get retained at the periphery of the chamber by centrifugal force and the smaller particles exit with the exhaust air from the central portion of the chamber.
The basic function of a jet milling machine is rather easy to understand. A feed funnel is used to pour unprocessed material into a compressed intake gas tube that channels it into a cylindrical grinding chamber. The air or compressed gas in the chamber is accelerated into a vortex, with centrifugal force driving smaller particles to the center as impacts occur, and larger ones to the perimeter. As the particles reach a chosen size, they are removed from the center of the vortex through an exit pipe.
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