Angle of Repose ISO 4324

Testing Surface Active Agents - Powders and Granules - Measurement of the Angle of Repose

Introduction

The angle of repose is a crucial parameter in determining the flowability and storage properties of powders and granules, particularly in industries that handle surface-active agents such as detergents and washing powders. The angle of repose is especially important for understanding the behavior of these materials in storage containers like silos, where flow characteristics can significantly impact handling and processing efficiency. ISO 4324 provides a standardized method for measuring the angle of repose, ensuring consistency and reliability in the assessment of these materials.

Scope and Field of Application

ISO 4324 specifies a conventional method for determining the angle of repose of surface-active agents in powder or granular form, as well as washing powders that are free from agglomerates. This standard is also applicable to other powders and granules with similar properties. The angle of repose is defined as the base angle of the cone formed by a material when it is allowed to flow freely through a funnel onto a flat surface.

References

The standard refers to ISO 554, which specifies standard atmospheres for conditioning and testing, and ISO 607, which outlines methods for sample division of surface-active agents and detergents.

Definition

For the purposes of ISO 4324, the angle of repose is defined as the angle formed between the horizontal surface and the slope of the cone created by the material under specified conditions.

Principle

The principle behind this test is to determine the angle of repose by allowing a given volume of powder or granules to flow through a specially designed funnel onto a flat, level plate. The angle formed by the material’s pile with the horizontal surface is then measured. This angle gives insights into the material's flow characteristics, which are crucial for understanding its storage and handling properties.

Apparatus

The apparatus required for this test consists of several key components:

  1. Glass Funnel: A glass funnel with an internal stem diameter of 10 mm.

  2. Agitator: An agitator with two rods placed opposite each other along the funnel’s interior wall. These rods extend into the stem and can be turned using a handle to ensure consistent flow of the material.

  3. Base-plate: A rigid base-plate with a polished surface or engraved concentric circles ranging from 10 to 100 mm in diameter, coaxial with the funnel’s axis.

  4. Transparent Plastic Vessel: A vessel with a minimum diameter of 100 mm and height of 25 mm, placed 75 mm below the funnel. The vessel’s rough interior surface helps in collecting the material.

  5. Graduated Measuring Cylinder: A 250 ml measuring cylinder that complies with ISO 4788 standards.

Sampling

The sample must be prepared and stored according to ISO 607 to ensure consistency and accuracy in the test results. If the sample forms agglomerates after storage, it can still be tested if it regains a fluid state after inverting the storage container.

Procedure

  1. Preparation of Sample and Test Portion: Take a 150 ml sample using the graduated measuring cylinder. Ensure the sample is free-flowing, especially if it has been stored for an extended period.

  2. Determination: The test should be carried out in a standard atmosphere as defined by ISO 554. Place the test portion in the funnel, block the stem, and allow the material to flow freely onto the base plate while gently agitating it with the agitator. After the flow stops, measure the height of the resulting powder cone.

Expression of Results

The angle of repose (ϕ) is calculated using data generated from the test.

Multiple tests should be performed (5 or more)and the arithmetic average of these results is taken as the final angle of repose.

Precision and Accuracy

ISO 4324 provides guidelines on the repeatability and reproducibility of the test.

Test Report

The test report should include all necessary details for identifying the sample, reference to the ISO 4324 standard, test results, test conditions, and any deviations from the standard procedure that might have influenced the results.

Conclusion

ISO 4324 provides a standardized and reliable method for determining the angle of repose of powders and granules, particularly surface-active agents. This measurement is vital for understanding the flow characteristics of these materials, which is essential for their handling, processing, and storage in industrial settings.