ASTM D6184-17 Standard Test Method for Separation of Oil from Lubricating Grease (Conical Sieving Method)

The standard "ASTM D6184-17 Standard test method for oil separation from lubricating grease (conical sieving method)" developed by the American Society for Testing and Materials (ASTM) describes a test method for determining the tendency of lubricating grease to separate oil at high temperature. This test method shall be conducted at 30 degrees for 100 hours unless other conditions are required by the grease specification.

This test method can be used on any grease having a worked penetration greater than 220 mm⁄10 (NLGI consistency number 3 or softer) (ASTM D217-21 Standard test methods for conical penetration of lubricating grease). However, no precision data are available for greases having a penetration greater than 340 mm⁄10 (NLGI consistency number 1 softer).

For the purposes of this standard, the following terms and definitions apply:

• Lubricating grease refers to the semi-liquid to solid product formed by dispersing a thickener in a liquid lubricant. The dispersion of the thickener creates a two-phase system and immobilizes the liquid lubricant by surface tension and other physical forces. Other ingredients that impart special properties are often included.
• Oil separation refers to the emergence of a liquid fraction from an otherwise homogeneous lubricating composition.
• Thickener, in a lubricating grease, refers to a substance consisting of finely divided particles dispersed in a liquid lubricant to form the structure of the product. The thickener may be insoluble or at most slightly soluble fibers (such as various metallic soaps) or plates or spheres (such as some non-soap thickeners) in the liquid lubricant. The general requirements are that the solid particles be extremely small, uniformly distributed, and capable of forming a relatively stable, gel-like structure with the liquid lubricant.

In performing the test, the weighed sample is placed on a cone-shaped, wire-cloth screen, suspended in a beaker, and then heated under static conditions for the specified time and temperature. Unless otherwise required by the grease specification, the sample is tested at standard conditions of 30 degrees plus/minus 0,25 degrees for 100 hours plus/minus 0,5 hours. The separated oil is weighed and reported as a percentage of the mass of the initial test sample.

When lubricating grease separates from oil, the remaining material may change its consistency, which may adversely affect the ability of the product to function as designed. Test results obtained by this procedure are not intended to predict the oil separation tendencies of grease under dynamic service conditions. This test method is used for specification and quality control purposes.

The test results obtained by this test method are intended to relate to oil separation occurring in 16 kg grease buckets during storage. It is not intended to predict the oil separation tendencies of grease under dynamic service conditions.

The assembled test apparatus used in these tests consists of a cone-shaped sieve made of 60 mesh (wire mesh), corrosion-resistant wire mesh, a 200 mL tall beaker without a spout, and a tight-fitting lid with a hook in the center. The construction details and dimensions are shown in the standard. The conical sieve shall be constructed of No. 437 medium-heavy-pore stainless steel, Monel, or nickel wire mesh as defined in the table in “ASTM E92-60 Specification for Industrial Wire Mesh and Screens (Square Aperture Series)” and shall be manufactured to the dimensions and requirements shown in the figure. In the past, stapled or wire-bonded sieves have been used instead of silver-soldered construction. Such sieves are not suitable for this test method.

In these tests, an oven that can maintain a temperature of 100 degrees plus/minus 0,5 degrees and a scale with a capacity of at least 250 grams and a precision of at least 0,01 grams are used.

The sample is examined for any signs of inhomogeneity, such as oil separation, phase changes, or gross contamination. If any abnormal conditions are found, a new sample is taken. The sample sent for analysis should be at least sufficient for repeated testing. Although the mass of the test grease is determined, the sieve is filled by volume rather than by mass. Each test requires a quantity sufficient to fill the sieve to approximately the same level as indicated in the figure (approximately 10 mL). Approximately the same volume is used for each test, regardless of the grease density, with the mass varying from approximately 8 to 12 g.

In preparing the test, the sieve, beaker and lid are carefully cleaned by wiping them with a suitable solvent. The sieve is allowed to air dry. The use of an ultrasonic solvent bath has been found to be useful in cleaning the sieve. The sieve should be examined to ensure that it is clean and free from any deposits that may affect the passage of oil. It should be free from any sieve irregularities such as tears, dents, wrinkles or widened or reduced openings.

Unless otherwise stated, the test is conducted at standard conditions of 30 degrees plus/minus 0,25 degrees for 100 hours plus/minus 0,5 hours.

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