Significance and Use
5.1 The test method can be used to evaluate the following:
5.1.1 Classification or Comparison of Powders—Both the measured PDq and calculated gas permeability can be used to classify powders relative to each other.
5.1.2 Sensitivity Analysis—The test can be used to evaluate the relative effects of a range of powder properties or environmental parameters, or both, such as (but not limited to) humidity, particle size and size distribution, particle shape and shape distribution, moisture content and temperature.
5.1.3 Quality Control—The test can be used to assess the PDq and gas permeability of a feedstock, intermediate or product against pre-determined acceptance criteria.
5.1.4 Process Design and Operation—The determined parameters can be used to quantify powder behavior in numerous processing environments. The ability of a powder to discharge consistently from a storage vessel, through pipes or down chutes is primarily dependent on its flow properties, interaction with the material of construction and the geometry of the equipment (1 and 2)3. However, design methodologies assume that there is a gas interchange between the top and bottom of the stored powder that allows consistent flow through the outlet. Gas permeability is a controlling factor in discharge rates (1 and 2). Powders with low gas permeability may exhibit reduced or intermittent/pulsatile flow, or both, that cannot be predicted from only considering shear and dynamic flow properties. This could lead to poor filling or discharge of cavities/bags/vessels and thus result in poor weight uniformity or slow discharge. Furthermore, a powder with low gas permeability may be more likely to have compromised compression properties in tableting operations due to increased entrained gas after the filling stage and a reduced ability to release this gas during compression.
Note 1: The quality of the result produced by this test method is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this test method are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors. Additional guidance on sampling of powders is given in Reference (3).
Practice D3740 was developed for agencies engaged in the testing and/or inspection of soil and rock. As such it is not totally applicable to agencies performing this test method. However, users of this test method should recognize that the framework of Practice D3740 is appropriate for evaluating the quality of an agency performing this practice. Currently there is no known qualifying national authority that inspects agencies that perform this test method.
Scope
1.1 This method covers the apparatus and procedures for quantifying the pressure drop and deriving the gas permeability of a powder bed with respect to consolidation stress or superficial gas velocity, or both, using the FT4 Powder Rheometer.
1.2 The parameters generated during this test are most commonly used to assist with the design and operation of powder processing and transport operations. They can also provide relative classification or comparison of the flow behavior of different powders, or different batches of the same powder, that are subjected to similar stress and flow regimes within their processing equipment.
1.3 The 50 mm apparatus described in this standard can be used to measure the properties of powders and other bulk solids with a maximum particle size of 6 mm. It is practicable to test powders that have a small proportion of particles of 6-10 mm, but it is recommended they represent no more than 5 % of the total mass in samples with a normal (Gaussian) size distribution.
1.4 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.
1.4.1 The procedures used to specify how data are collected/recorded or calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user's objectives; and it is common practice to increase or decrease significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.5 Units—The values stated in SI units are to be regarded as standard. No other units of measure are included in this standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
