Jet Milling Services



What is Jet Milling?

In the broadest terms, jet milling converts the potential energy of compressed gas into high-velocity kinetic energy within the mill’s grinding chamber. This causes particles to collide and fracture into smaller sizes — a process known as comminution.
Comminution generally results in particles ranging in size from 1 to 10 microns, which is referred to as micronization.

Some applications require ultrafine particles sized from 1- to 100-nanometers. In some cases, nanonization can be achieved on certain jet mills by increasing both the power to the mill and the time the material spends in the mill’s grinding chamber.

Other products require particles larger than 10 microns. Attaining this particle size range is accomplished by either reducing power to the jet mill or increasing the raw material feed rate.

The Popularity of Jet Milling Across Industries

Jet milling is one of the most important services provided by toll processors, and in high demand within major industries including:

Jet milling is central to applications in these markets because particle size reduction significantly increases the available surface area per particle of material.

As a result, behavioral changes occur in the material, including how it interacts with other materials, with living systems, etc. That means manufacturers may be able to use far less of a high-value, potent, or environmentally adverse ingredient in formulations.

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Circular and Fluid Bed Jet Mills Explained

Two types of mills are used to control fine particle size during jet milling. The expense of the technology and expertise required to operate it can dissuade manufacturers from pursuing the process in-house, leading to key partnerships with trusted toll processors.

Circular Jet Mills

Diagram of circular jet mill (top view)

Circular jet mills are also referred to as spiral jet mills. The mill design is intentionally simple to maximize outcomes:

  • The disc-shaped grinding chamber has several points for gas injection
  • The milled material, air, and compressed gas exit the mill from the center of the grinding chamber
  • The resulting particles are separated from the gas by way of a cyclone or filtering process

Fluid Bed Jet Mills

Diagram of fluid bed jet mill with classifier

Unlike a circular jet mill, fluid bed jet mills have built-in classifiers that can be precisely adjusted to the target particle size and shape. As such, the mill design and functionality is also somewhat more complex:

  • Material enters the vertical grinding chamber from the top
  • Compressed grinding gas is fed into the grinding chamber from the bottom to establish particle circulation streams
  • Right-sized particles are identified and removed by the built-in centrifugal classifier, and the balance is recirculated through the milling process until they reach the correct size

Jet Milling Gasses

Despite dissimilarities between circular jet mills and fluid jet mills, the compressed gasses used in either machine are the same. 

Jets of air or steam are created by gas compressed to a gauge pressure of 50 to 120 pounds per square inch (PSIG). Commercially compressed air is the most commonly used gas, but it’s not the only choice:

  • Superheated steam (392-980°F) is compressed to 100-220 PSIG and used to process non-heat sensitive raw materials
  • Nitrogen is an inert gas that can protect materials from fire and/or oxidation
  • Argon is an inert gas with characteristics similar to nitrogen, but it is more expensive
  • Helium is used to achieve higher-velocity particle impact

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The Benefits of Particle Size Reduction

Jet mills provide exceptional versatility in particle size reduction. Nanonization and micronization deal in infinitely small particles — typically a fraction of the width of a human hair — or, larger particles in excess of 10 microns can all typically be achieved in the jet milling process.

However, versatility isn’t the only benefit to manufacturers; jet mill particle size reduction also provides:

  • Consistently low grinding temperatures allow for the processing of materials that are heat sensitive or have low melting points
  • Streamlined production cycles that combine grinding and collection processes to maximize time and processed material collection
  • Virtually no cross-contamination risk because there are no mechanical mill components and related wear, and GMP-certified toll processors manage equipment cleaning, product changeovers, and cleanroom environments to exacting standards
  • Increased surface area and particle size uniformity to promote even distribution and enhanced product performance

What Materials Can Be Jet Milled?

Like any process, the quality of jet milling outcomes is highly dependent upon the characteristics of the materials used.

Ideal Jet Milling Materials

Materials that respond well to jet milling are:

  • Abrasive
  • Brittle
  • Dense
  • Hard
  • Friable (easy to crumble)
  • Temperature-sensitive (requires expert toll processor guidance and specific feeds)
In some cases, jet milling may be used to homogeneously blend some powders since two or more streams of material can be fed into a mill at one time.

Problematic Jet Milling Materials

Materials that inhibit the jet milling process typically have one or more of the following traits:

  • Difficult to accelerate
  • Easily deformed
  • Elastic
  • Light and fluffy
  • Shock absorbent
  • Wet

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Partners in Particle Size Reduction

Toll processors undoubtedly provide value to customers across all types of milling methods. However, toll processing partners with jet milling expertise can add another layer of efficiencies and capabilities, including:

  • Process modifications that are proven and logical from the jet milling perspective, improve grinding outcomes, and streamline the overall project
  • Streamline processing that combines grinding and particle classification
  • Applied knowledge of in-house material scientists and engineers to gather required data for raw feed trials and pilot runs often without the need for physical testing
  • In-house sample testing and particle size analysis that aids in the collection, verification, and use of data guide materials selection, grinding specifications, and consistent jet milling repeatability

Having the capacity to drill into detailed information adds value to a jet milling partnership — and typically brings about desired high-quality results faster.

Critical Information for a Successful Collaboration

Further, a toll processor with a proven track record in a breadth of milling services is going to stay alongside manufacturers to help them achieve their goals.

  • Information-sharing is essential. In addition to requiring Safety Data Sheets (SDS) on each material to be milled, a toll processing partner will ask specific questions to enhance the collaboration and overall jet milling process, such as:
  • What is the particle size of the feed material?
  • What is the target particle size of the product?
  • Is the material a combustible powder?
  • Is the material abrasive?
  • How will the product be collected and returned or forward to the next process step?

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jet_milling_content_coverThere are many advantages to partnering with a toll processor that specializes in jet milling. Take this information with you in our free eBook, Jet Milling Services Fundamentals: A Manufacturer’s Guide. 

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