ASTM D6393/D6393M Standard Test Method for Bulk Solids Characterization by Carr Indices

Get Certified ASTM D6393 Testing for Reliable Bulk Solids Flow Data

Powders and granular materials that have poor flow can bridge, rathole, and segregate inside a hopper or storage bin. Thus, unverified flow characteristics can lead to blocked feeders, inconsistent dosing, and unplanned downtime after a material reaches full-scale handling equipment. ASTM D6393 provides engineers with a standardized method to measure Carr Indices, supporting broader grain flow and bulk density characterization work across the materials handling industry. The test results enable manufacturers to make decisions during hopper design, material selection, and process control for powders and granular products.

The scope of ASTM D6393 includes:

• Material type: Free-flowing and moderately cohesive powders and granular materials up to 2.0 mm (1/16 in.) in size.
• Purpose: Measurement of ten Carr Indices, made up of eight direct measurements and two calculations, that describe the bulk properties of a powder or granular material.
• Properties evaluated: Angle of repose, angle of fall, angle of difference, loose bulk density, packed bulk density, compressibility, cohesion, uniformity, angle of spatula, and dispersibility. 
• Testing method: A technician prepares a representative bulk solid sample and performs the eight Carr Index measurements using the specified apparatus, while an analyst calculates two remaining values from the measured results.
• Results: Observed and calculated values follow the significant-digit and rounding guidance of Practice D6026, with SI and inch-pound units treated as separate standard systems that must not be combined.
• Test limitations: The procedures do not account for material variation, purpose of the data, and a user’s specific objectives, and the material must pour through a 6.0 to 8.0 mm (1/4 to 5/16 in.) funnel outlet while aerated for the method to apply.
• Use conditions: An analyst evaluates the ten Carr Index values with experience to rank a material’s bulk handling behavior for a specific application.
• Applications: Hopper and bin design, material handling equipment selection, and process control for powders and granular materials.

What are the Uses of ASTM D6393 Testing?

ASTM D6393 testing provides manufacturers with a standard method to describe how a powder or granular material behaves once moved through storage and handling equipment. Engineers then use the ten Carr Index values to compare materials and anticipate flow-related issues before they reach production. This test method:

• Measures eight Carr Index properties directly from a single bulk solid sample.
• Calculates angle of difference and compressibility from the measured values.
• Provides data for characterizing bulk-solid properties.
• Supports comparison of bulk-handling behavior for a specific application.
• Provides separate density, angle, cohesion, uniformity, and dispersibility measurements.

Which Materials Can Be Tested Under ASTM D6393?

ASTM D6393 applies to free-flowing and moderately cohesive powders and granular materials up to 2.0 mm (1/16 in.) in size that can pour through a 6.0 to 8.0 mm (1/4 to 5/16 in.) funnel outlet in an aerated state. A technician obtains a representative bulk solid sample and prepares the portions required for the applicable Carr Index measurements before the analyst calculates the corresponding values. 

Why is ASTM D6393 Important?

ASTM D6393 gives industries that handle bulk powders and granular materials a standardized method to detect and compare flow-related risks before a material reaches full-scale processing equipment. A material with poor flow characteristics may bridge or rathole inside a hopper, disrupting feed rates and causing unplanned downtime. Consequently, the results from this test method help engineers select materials, design handling equipment, and support consistent processing across a production line.

ASTM D6393 Testing Process and Data Collection

A technician first obtains a representative sample of the powder or granular material and prepares the portions required for the individual Carr Index measurements. Next, the technician performs the eight measured Carr Index tests using the specified apparatus. After that, the analyst calculates the angle of difference and compressibility from the measured values. Once all ten values are complete, an engineer reviews the full Carr Index profile, alongside practical experience, to provide a relative ranking of the material’s bulk handling behavior for the specific application.

Common Challenges and Troubleshooting in ASTM D6393 Testing

Accurate ASTM D6393 results require competent personnel, suitable equipment, and consistent execution of the specified measurement procedures. Variation in sample handling or measurement technique can affect the results used to characterize the bulk properties of powders and granular materials. Technicians follow the specified procedures carefully and use suitable apparatus for each Carr Index measurement to maintain consistent testing conditions. Analysts apply the same calculation and rounding practices to the measured values, so that results are comparable across samples.

• Angle of repose, angle of fall, angle of difference, and angle of spatula appear in degrees.
• Loose bulk density and packed bulk density appear in SI units as grams per cubic centimeter (g/cm³), or in inch-pound units as pounds per cubic foot (lb/ft³).
• Compressibility, cohesion, and dispersibility appear as percentages.
• Uniformity appears as a dimensionless ratio derived from the material’s particle size distribution.
• Engineers can combine the measurements with practical experience to provide relative rankings of bulk-handling behavior for a specific application.

Link to ASTM D6393