Anyone who has worked on lactose powder sieving in the pharmaceutical industry has likely encountered a typical issue:
A powder labeled as 50 μm ends up showing a distribution concentrated in the 80–150 μm range after sieving.

Many people’s first reaction is “abnormal particle size,” but from an engineering perspective, the more common cause is actually:
Powder agglomeration, which leads to distorted sieving results.

Based on frontline sieving engineering experience, this article systematically analyzes the challenges and solutions of lactose powder sieving from six dimensions: What / Why / Who / When / Where / How.

Ⅰ. What | What is a small negative-pressure airflow sieve?

A small negative-pressure airflow sieve is a fine sieving device based on aerodynamic principles. Its core logic is:
Using airflow to disperse particles before sieving, rather than relying on mechanical vibration.

Key technical features include:
Applicable particle size range: ≥10 μm
Single sieving time: 2–3 minutes
Sieving method: Air jet + negative-pressure suction
Adjustable parameters: Sieving time, negative pressure, nozzle airflow velocity (all digitally controlled)

The device uses airflow to break apart agglomerated particles, allowing the powder to participate in sieving in a “single-particle state,” thereby obtaining a true particle size distribution.

Ⅱ. Why | Why must lactose powder use an airflow sieve?

1. Lactose powder is naturally prone to agglomeration
Lactose powder is a typical hygroscopic material. When environmental humidity ≥60%, liquid bridges easily form on particle surfaces, causing micron-scale particles to stick together.

2. Traditional vibrating screens cannot solve agglomeration
The core function of vibrating screens is “classification,” not “dispersion.”

For fine powders in the 10–100 μm range:

Vibration energy is insufficient to break agglomerates

“Pseudo-coarse particles” are easily formed during sieving

Typical manifestation:
Labeled 50 μm powder → sieving result shifts to 80–150 μm

Data fluctuation range: ±10% or even higher

3. Airflow sieving enables “true particle size restoration”
The airflow sieve generates shear forces through high-speed airflow to break agglomerates, and uses a negative-pressure system to carry fine particles through the mesh for precise classification.

Actual engineering data comparison:

Sieving method	Particle size deviation	Data repeatability
Vibrating screen	±10%–15%	Poor
Airflow sieve	±3%–5%	High consistency

Conclusion:
The airflow sieve solves the “particle dispersion problem,” not just the sieving problem.

Ⅲ. Who | Who must use an airflow sieve?

The following scenarios are recommended to prioritize airflow sieving:

Pharmaceutical QC laboratories (particle size testing and release)

Process engineers (verification of sieving parameters)

Quality management personnel (batch consistency control)

Applicable material characteristics:

Particle size range: 10–100 μm

Hygroscopic and prone to agglomeration

High requirements for sieving repeatability (e.g., GMP environments)

Ⅳ. When | When must it be used?

It is recommended to use an airflow sieve in the following four situations:

1. Particle size testing (release level)
When error must be controlled within ±5%, traditional vibrating screens are difficult to meet the requirement.

2. Obvious powder agglomeration
Manifestations include:

Forms clumps when squeezed by hand

Frequent mesh clogging

3. Large batch-to-batch data fluctuations
If repeated sieving deviation of the same material exceeds 10%, it indicates that agglomeration has not been resolved.

4. GMP audit or validation stage
It is necessary to ensure that sieving results have:

Repeatability

Traceability

Standardized operation records

Ⅴ. Where | Which industries is it suitable for?

In addition to the pharmaceutical industry, small negative-pressure airflow sieves are widely used in:

Food industry: milk powder, starch, food additives

Fine chemicals: pigments, coating powders

New materials: powder coatings, functional powders

Common characteristics:
Fine powders (10–100 μm) + prone to agglomeration + high-precision sieving requirements

Ⅵ. How | How to select and use?

1. Key parameters for equipment selection

(1) Mesh aperture selection
Recommended principle: mesh size = target particle size × (1.1–1.2)

(2) Negative pressure range
Recommended range: -2 kPa to -10 kPa
Note: Stability of negative pressure is more important than the absolute value

(3) Nozzle airflow adjustment capability
Recommended features:

Multi-level adjustment (≥3 levels)

Continuous adjustment is preferred

2. Standard operating procedure

Typical steps:

Connect to a vacuum cleaner or negative-pressure system

Set sieving time (2–3 minutes)

Adjust negative pressure and nozzle airflow

Start the sieving process

Collect undersize material and record data

3. Common problems and solutions

Problem 1: Excessive negative pressure
Consequences:

Fine powder is directly sucked away

Particle size results become smaller

Solution:
Gradually increase from low negative pressure to find a stable range

Problem 2: High environmental humidity
When humidity >60%, agglomeration significantly increases

Solution:
Control environmental humidity at 40%–55%

Problem 3: Misuse of vibrating screens for precision analysis
Consequences:

Poor data repeatability

Deviation can exceed 15%

Solution:
Prioritize airflow sieving for precision analysis scenarios

Ⅶ. Engineering practice summary

From an engineering perspective, the core issue of lactose powder sieving is not “insufficient sieving efficiency,” but:
Agglomeration masking the true particle size distribution.

The small negative-pressure airflow sieve achieves the following key values through airflow dispersion:

Eliminates agglomeration effects

Improves sieving accuracy (error controlled within ±3%–5%)

Shortens testing time (2–3 minutes per test)

Meets GMP consistency requirements

Ⅷ. Real case reference

A pharmaceutical company’s lactose powder sieving test data:

Using vibrating screen:
Deviation between two tests: about 12%

After switching to airflow sieve:
Data deviation: stabilized within ±3%
Single test time: reduced from 10 minutes to 3 minutes

Conclusion:

Stability of sieving results improved by approximately 70%

Testing efficiency improved by about 3 times

Ⅸ. Conclusion

For agglomeration-prone fine powders such as lactose powder:
The essence of sieving is not “classification,” but “disperse first, then classify.”

The core value of the small negative-pressure airflow sieve lies in:
Restoring the true particle state and improving data reliability at the source.

If further equipment selection or parameter matching is required, the following information can be provided for engineering evaluation:

Particle size range (μm)

Throughput (kg/h or testing frequency)

Whether it is used for quality inspection (GMP requirements)

Based on specific working conditions, targeted sieving solutions and parameter recommendations can be provided.