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D2639 – Standard Test Method Technical Guide
📐 Scope, Terminology, and Units of Measurement
Standard D2639/D2639M – 24 covers the determination of the plastic behavior of coal using a constant-torque Gieseler plastometer. This test method provides a relative measure of plastic behavior and yields semiquantitative values critical for evaluating coals and blends used in carbonization processes. The standard explicitly requires that values stated in SI units or inch-pound units be regarded separately as standard; to ensure conformance, each system must be used independently.
⚠️ Mandated Unit Separation: Per Section 1.2, the values in SI and inch-pound units are not exact equivalents. They must not be combined. Furthermore, the term “mass” applies to measurements in both kilograms and pounds as specified in Section 1.3.
Key terminology governing the test includes DDPM (dial divisions per minute, where one full 360° stirrer rotation equals 100 divisions), Initial Softening Temperature (the temperature at which the DDPM first reaches a reading equal to or greater than 1.0), Breaking (free spinning behavior resulting from a molten ball of coal around the stirrer base), and Jamming (swelling of coal into the retort tube).
| 🔍 Term | 📖 Definition (Section 3) | 📌 Practical Impact |
|---|---|---|
| DDPM | Stirrer rotation rate in dial divisions per minute. One rotation = 100 DD. | Primary unit of fluidity measurement. |
| Initial Softening | Temperature where DDPM first reaches ≥ 1.0. | Marks the onset of thermoplasticity. |
| Breaking | Free spinning behavior caused by a molten coal ball. | Obscures reporting of true maximum fluidity. |
| Jamming | Swelling up of coal into the retort tube. | May produce erratic stirrer movement. |
⚙️ Recording Protocol and Procedural Terminology
The standard mandates a strict data recording protocol to harmonize results between historical manual plastometers and modern automated systems. The DDPM shall be recorded at the end of each sequential minute interval (e.g., 00:01:00, 00:02:00, 00:03:00). This recording must commence at the initial furnace temperature of 300 °C and continue without interruption until the solidification temperature is reached. The standard also references complementary practices for sample collection (D2234/D2234M) and sample preparation (D2013/D2013M).
💡 Temporal Alignment Requirement: To ensure inter-laboratory reproducibility of the fluidity curve, modern instruments must timestamp their readings to match the end of each sequential 60-second interval, exactly replicating the historical manual timing method.
📊 Measured Properties and Fluidity Curve Analysis
The plastic properties derived from the Gieseler plastometer allow for the construction of a comprehensive fluidity curve plotting DDPM against temperature. The key output points used for coking coal classification include the initial softening temperature, the temperature of maximum fluidity, the maximum fluidity value (peak DDPM), and the solidification temperature. The width of the plastic range and the maximum fluidity are the most commonly reported parameters.
| ⚡ Measured Property | 🟦 Definition Criteria | 📏 Typical Significance |
|---|---|---|
| Initial Softening | DDPM first reaches 1.0 | Defines the start of the plastic range. |
| Maximum Fluidity | Highest DDPM recorded during the test | Correlates with coking pressure and coke structure. |
| Solidification | Stirrer stops; DDPM returns to 0 | Defines the end of the plastic range. |
✅ International Standardization: This test method was developed in accordance with internationally recognized principles on standardization established by the World Trade Organization Technical Barriers to Trade (TBT) Committee, ensuring global applicability of the Gieseler fluidity data.
❓ Frequently Asked Questions
🔍 How is DDPM specifically defined in D2639/D2639M – 24?
DDPM stands for Dial Divisions per Minute. It represents the stirrer rotation rate measured by the accumulated rotations (full or partial) of the stirrer, recorded over sequential 1-minute periods and based upon 100 dial divisions for each complete 360-degree rotation.
💡 What is the exact definition of the Initial Softening Temperature?
Per Section 3.1.3, the Initial Softening Temperature is the temperature at which the DDPM first reaches a reading equal to or greater than 1.0.
⚡ What is the difference between “breaking” and “jamming”?
Breaking is the free spinning behavior of the stirrer resulting from a molten ball of coal forming around the stirrer base. Jamming is the swelling up of coal into the retort tube during the test. Both phenomena can make the reporting of true maximum fluidity difficult.
📌 When must DDPM readings be recorded?
The standard specifies that total accumulated stirrer rotations shall be recorded at the end of each sequential minute interval (e.g., 00:01:00, 00:02:00) beginning when the furnace regains the initial temperature of 300 °C and ending precisely at the solidification temperature.