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D5551-95 – Standard Test Method Technical Guide
This article provides an overview of ASTM D5551-95 (Reapproved 2019), a standard test method for determining the cloud point of oils used in the softening and stuffing of leather and in the manufacture of fat liquors and other compounds. Derived from Test Methods D97 and D2500, this standard is essential for quality assurance in the leather industry.
🛠️ Test Apparatus and Specifications
The test apparatus consists of a clear cylindrical glass test jar with a flat bottom, inside diameter of 30 to 33.5 mm, and height of 115 to 125 mm. A mark at 54 ± 3 mm above the inside bottom indicates the sample height. Thermometers must conform to ASTM Specification E1, with ranges specified for different applications.
| 🟦 Thermometer Type | 📏 Temperature Range | 🎯 ASTM Number | ⚡ IP Number |
|---|---|---|---|
| High Cloud and Pour | -38 to +50°C | 5C | 1C |
| Low Cloud and Pour | -80 to +20°C | 6C | 2C |
| Melting Point | +32 to +127°C | 61C | 63C |
⚠️ Important: Thermometers should be checked immediately prior to the test for accuracy within ±1°C (e.g., ice point) to ensure reliable readings.
The jacket, made of metal or glass, is watertight with a flat bottom, 115 mm depth, and 42 to 50 mm inside diameter. It must be supported vertically in the cooling bath with no more than 25 mm projecting out. A cork or felt disk, 6 mm thick, fits inside the jacket, and a gasket prevents the test jar from touching the jacket walls.
⚙️ Test Procedure and Cloud Point Determination
The cloud point is defined as the temperature, expressed in multiples of 1°C (2°F), at which a cloud or haze of wax crystals first appears at the bottom of the test jar when the oil is cooled under prescribed conditions. The sample is cooled in a bath maintained at prescribed temperatures, and observations are made to detect crystal formation.
💡 Tip: Maintain the cooling bath at the specified temperature consistently to avoid variations in cloud point readings due to inconsistent cooling rates.
The test method involves placing the oil sample in the test jar up to the marked line, inserting the thermometer with a cork, and placing the jar in the jacket within the cooling bath. The temperature is monitored, and the cloud point is recorded when wax crystals appear.
📊 Significance and Application
This test method is intended for quality assurance in the leather industry. The cloud point of oils used in softening and stuffing compounds indicates their low-temperature performance. Oils with appropriate cloud points ensure smooth application and prevent defects in leather treatment. The standard is under the jurisdiction of ASTM Committee D31 on Leather and Subcommittee D31.08 on Fats and Oils.
The values stated in SI units are regarded as standard, with inch-pound units in parentheses for information only. This test method addresses safety concerns as per user responsibility.
❓ Frequently Asked Questions
🔍 What is the cloud point of oil?
The cloud point is the temperature at which a haze or cloud of wax crystals appears in the oil under controlled cooling, indicating the start of crystallization.
💡 Why is cloud point important for leather oils?
It ensures the oil remains fluid at application temperatures, affecting the quality of leather softening and stuffing processes.
⚡ What equipment is needed for this test?
Equipment includes a test jar, thermometers conforming to ASTM E1, a jacket, cooling bath, cork disk, and gasket with specific dimensions.
📌 How is the cloud point test performed?
The oil sample is cooled in a controlled bath, and the temperature at which wax crystals first appear is recorded as the cloud point.