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D562-10 – Standard Test Method Technical Guide
📐 Scope, Apparatus, and Terminology
This test method covers the measurement of Krebs Unit (KU) viscosity for evaluating the consistency of paints and related coatings using a Stormer-Type viscometer. The method defines consistency strictly as the load in grams required to produce a rotational frequency of 200 r/min. Krebs Units (KU) are a specialized scale derived directly from this load, established specifically for paints typically applied by brush or roller.
The specified apparatus includes a Stormer viscometer equipped with a paddle-type rotor. The test container must be 500 mL (1 pt) with an 85 mm (3⅜ in.) diameter. Temperature is controlled using an ASTM Stormer Viscosity Thermometer (49C) covering a range from 20 °C to 70 °C, or equivalent devices providing comparable accuracy. A stopwatch with 0.2 s resolution and a comprehensive set of weights ranging from 5 g to 1000 g complete the required equipment.
⚙️ Test Procedure and Calibration
The procedure strictly determines the load necessary to maintain a constant rotational frequency of 200 r/min for the offset paddle rotor fully immersed in the paint sample. The stroboscopic timer attachment, while optional, provides direct 200 r/min readings and significantly enhances the overall speed and accuracy of the measurement.
Calibration is performed using standard oils of known absolute viscosity in poise (P). The standard explicitly requires the use of two oils differing by a minimum of 5 P. The verified normal operational range for the instrument is effectively covered by oils having viscosities of 4 P (70 KU), 10 P (85 KU), and 14 P (95 KU). Users must establish appropriate safety, health, and environmental practices prior to performing this test.
📊 Key Measured Properties and Specifications
The fundamental outputs of this test method are consistency (measured in grams) and its derived value, Krebs Units (KU). The following tables provide the critical calibration benchmarks and apparatus specifications mandated by ASTM D562.
| 🟦 Standard Oil Viscosity (Poise) | 📏 Corresponding Krebs Unit (KU) | 🎯 Typical Application Range |
|---|---|---|
| 4 P | 70 KU | Low Viscosity Coatings |
| 10 P | 85 KU | Mid-Range Trade Sales Paints |
| 14 P | 95 KU | High Viscosity / Heavy Paste |
| ⚡ Apparatus Component | 📐 Specification per ASTM D562 |
|---|---|
| Test Container | 500 mL (1 pt), 85 mm (3⅜ in.) diameter |
| Thermometer | ASTM 49C, Range 20 °C to 70 °C |
| Weights Set | Range covering 5 g to 1000 g |
| Timer Resolution | Stopwatch measuring to 0.2 s |
💡 Calibration Tip: While the standard requires a minimum of two oils differing by 5 P for verification, utilizing all three benchmark oils (4P, 10P, and 14P) to construct a full calibration curve ensures your Stormer viscometer maintains accuracy across the entire 70 KU to 95 KU operational envelope.
⚠️ Safety and Compliance Note: As per Section 1.3, this test method does not purport to address all safety concerns. Users must establish comprehensive safety, health, and environmental practices. Note that this standard is approved for use by U.S. Department of Defense agencies; ensure compliance with all applicable regulatory limitations.
❓ Frequently Asked Questions
🔍 What does the Krebs Unit (KU) specifically measure?
KU measures the consistency of paints typically applied by brush or roller. It is a direct function of the load (in grams) required to rotate a paddle rotor at a standard speed of 200 r/min in the Stormer viscometer, providing a practical scale for quality control in the coatings industry.
💡 Why is the 200 r/min rotational speed a critical benchmark?
This specific speed is the defined standard rotational frequency for the test. Achieving 200 r/min allows the load to be read directly on the instrument scale and converted into Krebs Units. The optional stroboscopic timer attachment specifically facilitates the accurate detection of this exact rotational speed.
⚡ Why is the container size strictly specified as 500 mL (85 mm diameter)?
The container dimensions ensure standardized shear geometry around the paddle rotor. Any significant deviation from this size would alter the hydrodynamic flow patterns within the paint sample during rotation, compromising the reproducibility and accuracy of the KU measurement.
📌 Are digital thermometers acceptable as alternatives to the ASTM 49C thermometer?
Yes. The standard specifies that temperature measuring devices such as thermocouples or platinum resistance thermometers may be used, provided they offer equivalent or better accuracy and fully cover the required temperature range of 20 °C to 70 °C. The standard allows for a variety of traceable sensors beyond liquid-in-glass instruments.