Jet Mill Drill Machine: Precision Particle Size Reduction Explained

What Is a Jet Mill Drill Machine?

Jet mill drill machines, often shortened to jet milling machines, is a milling machine that is used to reduce particle size (i.e. granulometry) using a high-speed jet of compressed air. Jet mill drill machines can be configured to produce particles below a designated size while continuing to drill particles beyond that size, which leads to a resulting product with narrow size distribution.

These bulk solid particles can have distinct attributes, such as pharmaceuticals, metal powders or minerals, and foodstuff. Compared with other drilling and milling equipment, or more particularly the impact mills, jet mill drill machines have uniquely no moving parts as the energy is provided by a gas dispersed at high speed in a milling chamber wherein coarse particles are introduced as well. The mechanism of the jet mill drill machine revolves around the impact among the particles themselves or against the milling chamber wall.
 

How Does Jet Mill Drill Machine Work?

The working principle of a jet milling machine can be explained in several parts. Let’s start with the velocity impact. How a jet milling machine goes about reducing the size of a particle is through high-velocity impact in between those particles, and the interaction between the chamber wall and the particles. The energy (typically air) supplied to the jet milling machine at high speed enables multiple high-speed impacts to take place, leading to an exceptionally strong communication of the feed particles.

The energy or gas that we mentioned above refers to air, steam, or inert gases, with the air being the most prevalent and largely available gas. It is however not the cheapest option and also requires a substantial amount of energy. The air pressure is typically 3.5-8.5 bar g. Another gas is steam, which is relatively less expensive than air energy provided that the factory is deployed with efficient boilers. But steam is typically only used as energy when it does not interact with the material (e.g., heat). The pressure is typically 7-15 bar g at 200-520 degrees Celsius in this case. The last alternative is inert gases, which are generally referred to as nitrogen or argon that can be used in specialized applications.
 

Designs of Jet Mill Drill Machine

The Jet milling machine can come in different designs. We'll introduce two of the common ones in this section.
 

Fluidized Bed Jet Milling Machine

This type of milling machine is coupled with a cylindrical, vertical chamber wherein the particles are introduced at the center of the chamber and the gas is input from the bottom as energy to produce impact. The exhaust output is released from the top of the chamber, and the outlet is coupled with a classifier which enables the selection of particles; particles above a designated size need to be recycled back to the chamber of milling machines, and particles below a target size will leave the mill. The particles are fluidized as the gas is input at the bottom of the chamber, creating circulation streams.
 

Jet Milling Machine without Air Classifier

The design of this type of jet milling machine is relatively simpler. As the name implies, it does not have an air classifier like the fluidized counterpart. The working principle of this type of milling machine involves feeding materials into a grinding chamber resembling a disc where the gas is input at several points. The middle of the grinding chamber acts as an exit for the material milled and the air. 

Other key components inside these jet milling machines include the feeding system as well. The feeding system of the milling chamber of the jet milling machine serves as an airlock to prevent the air from escaping as well as the inlet of material. Then, the separation of solids will be undergone. A large volume of gas will leave the jet milling machine alongside the mill particles. The particles of interest will have to be separated from the gas. This is typically accomplished using a cyclone or a filter, or a combination of both.
 

The Limitations of Jet Mill Drill Machine

Jet milling machines are appealing to some because of the following benefits:

● As aforementioned, jet milling machines have no move parts unlike other equipment of the larger family. So they are not susceptible to mechanical wear or breakages that could have an adverse impact on the final products.
● Jet milling machines enable a narrow particle size distribution, commonly abbreviated as PSD.
● Jet milling machines enable output of very fine particle size, potentially ranging from 1 to 10 microns for certain materials.
 

The Disadvantages of Jet Mill Drill Machine

Mill drilling machines incorporate a unique working principle of gas injection as an energy source (e.g., air, steam, inert gases like argon and nitrogen). But it is also because of the unique technology that it is faced with certain limitations: 

● Jet milling machines require high amounts of energy to compress the gas, meaning that they are more of a niche kind of machinery to accommodate certain specialized products. This makes the process more competitive than it needs to be. 
● As mentioned previously, jet mill drilling machines require a separation system that separates the desired particles from the dispersed gas. This is an essential part of the process that allows milling to be performed, which in turn incur additional costs and require more footprint.