Particle Size Analysis with the New Mikro Air Jet Sieve

The Mikro Air Jet Sieve™ MAJSx is a highly accurate and reliable particle size analyzer designed for identifying the particle size distribution of dry powder ranging from 20 µm / # 635 (mesh) to 4,750 µm / # 4 (mesh). It is designed for use in the chemical, mineral, pharmaceutical, and food industries. An on-board computer enables the operator to flow through the process. This video briefly discusses how particle size analysis is conducted.

Sieving Principle

The Mikro Air Jet Sieve™ MAJSx utilizes test sieve screens and the pneumatic sieving principle to enhance the accuracy and reproducibility of particle size analysis. Use of this method has become a preferred standard for such tasks as quality assurance of incoming raw materials, process control, and the verification of final product specifications. While under negative pressure, a positive upward air flow is emitted from the rotating slit wand, continuously dispersing particles across the surface of a test sieve screen. The particles finer then the opening of the test sieve screen will pass through and are carried away from the sample, leaving the coarse particles larger than the sieve opening retained on the test sieve screen.

Precise determination of particle size within the range of 20 to 4,750 µm can quickly be determined. This unique rotating wand method also reduces, and in many cases, eliminates the need for tapping or brushing, enhancing the analysis reproducibility. The overall system is designed for cleaner operation and requires less counter space than other types of analytical equipment.

Operating Parameters

Four key operating parameters need to be consistent to produce repeatable and reliable results.

Sieving Time – Excessive sieving time can lead to particle degradation due to attrition. In most dry powder applications, Hosokawa recommends a sieving time cycle of two minutes. This provides ample time for the particles of the entire sample to pass through the sieve screen or be retained.

Sieving Vacuum Pressure – Hosokawa recommends a sieving pressure between 8-16 inches of water column during a sieve analysis. If the pressure is too low, the air velocity passing through the rotating wand may not evenly disperse the entire sample. If the pressure is too high, the air velocity could generate enough force to further grind material as the sample repeatedly impacts the sieve screen and sieve cover.

Sample Volume – In most air jet sieve particle size analysis devices, a sample between 10 grams to 100 grams is recommended, depending on the density of the material being tested. Samples larger than 100 grams can blind the test sieve screen and affect the analysis results.

Test Sieve Screen Quality – The integrity of a test sieve screen is critical in any particle size analysis. Hosokawa only provides test sieve screens that are 99% accurate. Those with any damage such as holes, tears, scratches, waves, or other imperfections are not recommended. Sieve screens should be re-certified as recommended by the manufacturer on a routine basis.