ASTM B214-22

Sieve Analysis of Metal Powders: A Guide to ASTM B214-22

1. Introduction

In modern manufacturing, materials science, and powder metallurgy, the physical characteristics of metal powders dictate the quality and performance of the final product. From traditional press-and-sinter processes to state-of-the-art additive manufacturing (such as Laser Powder Bed Fusion and Electron Beam Melting), metal powders serve as the foundational feedstock. To ensure structural integrity, predictable densification, and smooth flowability during automated processing, engineers must meticulously evaluate the Particle Size Distribution (PSD) of these raw materials.

Sieve analysis remains one of the most reliable, cost-effective, and widely adopted industrial methodologies for measuring the PSD of coarse-to-fine particulate materials. ASTM B214-22, titled Standard Test Method for Sieve Analysis of Metal Powders, is the premier consensus standard that governs this evaluation. Developed and maintained by ASTM International’s Committee B09 on Metal Powders and Metal Powder Products, this standard outlines the precise apparatus, procedures, and conditions required to generate accurate, reproducible, and verifiable PSD data.

2. What Is This Standard?

ASTM B214-22 specifies the dry sieve analysis method for metal powders. The primary objective of a sieve analysis (often referred to as a gradation test) is to separate a representative granular sample into discrete size fractions by shaking it through a nested stack of wire-cloth screens. The mass of the powder retained on each individual screen is weighed and calculated as a mass percentage of the total starting sample.

The designation “ASTM B214-22” identifies the standard, with the suffix “-22” representing the revision year (2022). Sieve analysis is based on mechanical agitation, utilizing a specialized shaker that subjects the powder sample to a specific combination of horizontal, circular, and vertical tapping motions. By standardizing the equipment, the runtime, the screen specifications, and the sample size, ASTM B214-22 minimizes operator-induced variability and provides a reliable benchmark for global material trading, verification, and quality control.

3. Scope and Purpose

The technical scope of ASTM B214-22 encompasses the dry sieve analysis of metal powders, utilizing standardized wire-cloth test sieves with nominal opening sizes ranging from 45 micrometres (µm) up to 850 micrometres (µm). This is roughly equivalent to a range between U.S. Standard Sieve No. 325 and No. 20.

While some mechanical separation techniques can evaluate coarser aggregates or finer emulsions, dry sieve testing is physically constrained. Particles below 45 µm (retained or passed through a No. 325 mesh) are highly susceptible to electrostatic interactions, van der Waals forces, and ambient relative humidity. These micro-forces cause fine particles to agglomerate, cling to the sieve frames, or clog the mesh openings, a phenomenon known as sieve blinding. Therefore, for powders dominated by particles finer than 45 µm, alternative standards—such as ASTM B822 (which utilizes light scattering or laser diffraction) or ASTM B923 (which utilizes gas pycnometry)—are recommended.

The primary purpose of ASTM B214-22 is to verify that a powder shipment or batch conforms to predefined dimensional specifications. It is used as a critical quality gate for:

• Evaluating incoming feedstock consistency before compounding or manufacturing.
• Conducting in-process quality monitoring of powder manufacturing (such as atomization or milling).
• Establishing contractual agreements and compliance documentation between powder suppliers and end-users.
• Tracking changes in particle size distribution of recycled powders in metal 3D printing.

4. Key Requirements

To perform a compliant ASTM B214-22 test, laboratory technicians must utilize specific apparatuses and follow strict operational guidelines. The core requirements include:

Sieves

The test sieves must strictly conform to ASTM E11, the Specification for Woven Wire Test Sieve Cloth and Test Sieves. Standard dimensions dictate that the sieve frames must be 203 mm (8 inches) in diameter and feature depths of either 25 mm (1 inch) or 50 mm (2 inches). The wire cloth is typically composed of high-durability materials such as brass, bronze, or stainless steel.

Mechanical Sieve Shaker

A manual hand-shaking process is not compliant under this standard for obtaining formal results. The procedure relies on a mechanical sieve shaker capable of imparting a horizontal circular motion coupled with a vertical tapping frequency. This specific “rotary and tap” mechanism (historically modeled on the Tyler Ro-Tap shaker) operates within standard parameters:

• Rotational speed: 270 to 300 rotations per minute (RPM).
• Tapping rate: 140 to 160 taps per minute.

This dual-action movement ensures that metal particles continuously shift over the mesh surface while the vertical tapping dislodges wedged particles, keeping the mesh openings clear.

Analytical Balance

The standard demands a high-precision analytical balance with a minimum capacity of 150 grams and a sensitivity (readability) of 0.01 grams. The balance must be calibrated in accordance with the laboratory’s ISO/IEC 17025 quality management guidelines.

5. Industries and Applications

Sieve analysis is implemented across a diverse array of advanced engineering and production sectors:

6. Testing Methods or Technical Requirements

A compliant ASTM B214-22 test is executed through a sequence of steps, prioritizing material representative sampling and equipment accuracy.

Step 1: Representative Sampling

The validity of the entire analysis hinges on the starting sample. Technicians should obtain the test portion in strict accordance with ASTM B215 (Standard Practices for Sampling Metal Powders). This typically involves using a mechanical riffle splitter or rotary sample splitter to reduce a bulk batch of metal powder to a manageable laboratory size without inducing size segregation.

Step 2: Determining Test Sample Mass Based on Apparent Density

ASTM B214-22 specifies that the starting weight of the test portion must be adjusted based on the apparent density of the metal powder under investigation. Excessive sample mass can overload the screens, preventing fine particles from reaching the lower sieves.

• For powders with an apparent density ≥ 1.5 g/cm³: Weigh a test portion of 90 to 110 grams (nominally targeted at 100 grams).
• For powders with an apparent density < 1.5 g/cm³: Weigh a test portion of 40 to 60 grams (nominally targeted at 50 grams).

The apparent density of the material must be pre-determined using recognized funnels or meters, such as the Hall Flowmeter (ASTM B212), Scott Volumeter (ASTM B329), Carney Funnel (ASTM B417), or Arnold Meter (ASTM B703).

Step 3: Sieve Nest Assembly

Select the standard set of sieves required for the specific powder classification. Arrange the clean, validated sieves in a vertical stack. The coarsest sieve (largest opening) is positioned at the very top, with progressively finer sieves nested below it. A tight-fitting collection pan is placed beneath the finest sieve at the bottom of the stack to catch any sub-sieve particles.

Step 4: Mechanical Sieving Procedure

1. Pour the prepared test portion carefully onto the top sieve, taking care to avoid releasing airborne dust or losing material.
2. Place the sieve cover securely over the top sieve.
3. Mount the nested stack into the mechanical shaker.
4. Clamp the sieve hold-down bar firmly to secure the nest within the shaker cradle.
5. Set the mechanical or digital timer for a duration of exactly 15 minutes.
6. Initiate the shaker and verify that the rotational and tapping systems are operating concurrently without abnormal friction or vibration.

Step 5: Recovering and Weighing Fractions

Upon completion of the 15-minute cycle, the machine is stopped, and the sieves are disassembled. Starting with the top sieve, the technician must carefully transfer the retained material to the analytical balance pan.

• Gently tap the side of the sieve frame with a soft tool (such as a rubber mallet or nylon brush handle) to release any particles caught on the underside. Never use wire brushes, metal scrapers, or high-pressure air, as these will permanently deform the calibrated mesh wires.
• Weigh the recovered fraction of powder retained on each screen to the nearest 0.1 grams, recording the mass for each mesh size.
• Finally, weigh the fine powder collected in the bottom pan.

Step 6: Calculations and Mass Balance Check

To verify the physical validity of the test, the sum of the weights of all individual fractions (including the pan) must be compared to the original starting sample weight. A material loss of greater than 1% (or more stringently, 0.5% in high-integrity aerospace environments) invalidates the test, requiring the procedure to be repeated with a fresh sample.

Calculate the mass percentage retained on each sieve using the formula:

Percentage Retained (%) = (Mass of Powder Retained on Sieve / Total Starting Mass) × 100

7. Compliance Considerations

For laboratories maintaining ISO 9001, AS9100, or NADCAP accreditations, compliance with ASTM B214-22 requires rigorous documentation and equipment validation. Key compliance points include:

Sieve Calibration and Certification

Test sieves do not remain accurate indefinitely. Repeated impact from dense metal powders causes the fine wire cloth to stretch, wire spacing to drift, and micro-tears to occur. Under ASTM E11, sieves can be certified at three distinct tier levels:

• Compliance Sieves: Supplied with a basic statistical certificate based on manufacturing tolerances.
• Inspection Sieves: Subjected to optical measurement of a statistically relevant sample of wire apertures, offering a higher confidence interval.
• Calibration Sieves: Checked using ultra-precision automated optical scanners that measure a large portion of the screen openings, ensuring the highest level of repeatability.

Accredited laboratories must establish a routine calibration schedule for their sieves, often utilizing standard reference materials (such as calibrated glass beads) or sending the sieves to accredited calibration bodies.

Shaker Verification

The mechanical shaker’s RPM and tap frequency must be checked annually using digital tachometers or strobe lights to ensure the device remains within the mandated 270–300 RPM and 140–160 taps-per-minute ranges.

Environmental Controls

Because humidity significantly influences dry sieving, the laboratory’s climate must be controlled. Relative humidity should ideally be maintained between 30% and 50%. Low humidity can exacerbate static electricity, while high humidity can cause powder clumping and block the sieve openings.

8. Benefits of Implementing This Standard

Adhering to ASTM B214-22 provides substantial operational and economic advantages to manufacturers and sourcing managers:

• Global Standardization: It ensures that a powder characterized in Europe, Asia, or North America will yield comparable results, streamlining international supply chains.
• Predictable Manufacturing: By verifying the particle size distribution, engineers can prevent printing defects in additive manufacturing (such as pore formation or layer lamination issues).
• Cost Optimization: Sieve analysis is an incredibly inexpensive method compared to laser diffraction or scanning electron microscopy (SEM). It allows rapid, routine checking of massive powder volumes with minimal training.
• Defect Isolation: Sieve testing physically segregates the powder by size. These isolated fractions can then be subjected to further chemical or morphological analysis to discover contamination or oxidation.

9. Common Challenges and Best Practices

While the mechanical process of dry sieve analysis is straightforward, technicians often encounter physical obstacles that can distort the data.

Sieve Blinding (Mesh Clogging)

Near-size particles (particles that are almost exactly the same diameter as the sieve openings) tend to wedge themselves into the wire mesh. This blocks the path for other particles.

Best Practice: Periodically clean the sieves using an ultrasonic cleaner bath specifically designed for laboratory sieves. Never use high-pressure air or stiff metal wire brushes, which stretch and damage the delicate woven wire cloth.

Electrostatic Accumulation

High-purity, non-conductive, or extremely fine metal powders (such as titanium or aluminum) can build up heavy electrostatic charges during the 15-minute mechanical shaking cycle. This causes particles to adhere to the metal sieve walls and the underside of the mesh.

Best Practice: Ensure that the mechanical sieve shaker is properly grounded. When permitted by internal quality specifications, a tiny, standardized quantity of an anti-static flow agent (such as fumed silica) can be blended into the powder sample before testing.

Sampling and Segregation Error

Pouring powder directly from a large storage drum into the test container will cause larger particles to roll to the outside, while finer particles concentrate in the center. This segregation skews the test results.

Best Practice: Always use a rotary sample splitter or a standard chute riffler according to ASTM B215. Never scoop sample portions directly from the top of a drum.

10. Related Standards and Certifications

ASTM B214-22 operates within an ecosystem of complementary standards:

• ASTM E11: The fundamental governing specification for the manufacture and verification of wire-cloth sieves.
• ASTM B215: The standard practices for extracting representative sample portions from industrial-sized batches of metal powders.
• ASTM B822: Standard Test Method for Particle Size Distribution of Metal Powders and Related Compounds by Light Scattering (essential for sub-45 µm powder sizing).
• ISO 4497: The International Organization for Standardization equivalent, which covers the dry sieve analysis of metallic powders.
• MPIF Standard 05: Published by the Metal Powder Industries Federation, this standard is technically equivalent to ASTM B214 and is widely cited in the North American powder metallurgy industry.

Frequently Asked Questions

What is the minimum particle size that can be tested under ASTM B214-22?

The standard covers dry sieve analysis down to 45 micrometres (µm), which corresponds to the U.S. Standard No. 325 sieve mesh. Particles finer than 45 µm are difficult to dry sieve reliably due to agglomeration and mesh blinding.

Can I perform ASTM B214-22 with any type of sieve shaker?

No. The precision and reproducibility of the standard are based on a mechanical shaker that provides both a horizontal circular motion (270 to 300 RPM) and a vertical tapping action (140 to 160 taps per minute). While other shaker designs exist, they have not been verified under this standard to yield equivalent precision.

How do I determine the correct sample weight for testing?

The sample size is determined based on the apparent density of the metal powder. If the powder’s apparent density is 1.5 g/cm³ or greater, you must use a test portion of 90 to 110 grams (target 100g). If the density is less than 1.5 g/cm³, use a test portion of 40 to 60 grams (target 50g).

What are the rotational speed and tapping rate requirements for the shaker?

The shaker must operate at a rotational speed of 270 to 300 RPM and a tapping rate of 140 to 160 taps per minute to meet standard verification requirements.

How is the test validated if some powder is lost during the shaking process?

To validate the test, the technician must sum the weights of all individual sieve fractions, including the powder caught in the bottom pan. The total recovered mass must be within 1% (or more stringently, 0.5% in high-integrity fields) of the initial sample weight. If the loss exceeds this, the test is invalid.

What is the standard shaking time for ASTM B214-22?

The mechanical sieve shaker must be operated for exactly 15 minutes. This duration has been proven to provide complete particle segregation while minimizing wear on the sieve wires and sample degradation.

12. Conclusion

In the highly precise world of powder metallurgy, additive manufacturing, and thermal spray coating, raw material quality assurance is paramount. ASTM B214-22 remains one of the most accessible, reliable, and standard-setting methodologies to determine the particle size distribution of metal powders. By outlining strict requirements for density-based sample sizing, calibrated E11 sieves, and dual-action mechanical shakers, this standard protects manufacturers from material defects and facilitates seamless global trade in industrial powders. Implementing ASTM B214-22 in your laboratory is an essential step toward achieving robust quality management and maintaining high manufacturing standards.