4. Summary of Test Methods
4.1 For unworked penetration, the sample is brought to 25°C (77°F) in a worker cup or other suitable container. The cone assembly of the penetrometer is released and allowed to drop freely into the grease for 5 s. Three determinations are made and averaged to give the reported result.
4.2 For worked penetration, the sample is brought to 25°C (77°F) and placed in the worker cup. The sample is subjected to 60 double strokes in the grease worker. The penetration is determined immediately by releasing the cone assembly from the penetrometer and allowing the cone to drop freely into the grease for 5 s. Three determinations are made and averaged to give the reported result.
4.3 For prolonged worked penetration, the sample is placed in the worker cup and subjected to a predetermined number of double strokes in the grease worker. Following completion of the prolonged working, the grease and worker assembly are brought to 25°C (77°F) and the grease is worked an additional 60 double strokes in the grease worker. The penetration is determined immediately by releasing the cone assembly from the penetrometer and allowing the cone to drop freely into the grease for 5 s. Three determinations are made and averaged to give the reported result.
4.4 For block penetration, a cube of the grease is prepared by slicing off a thin layer using the grease cutter. The cube of grease is brought to 25°C (77°F) and placed on the penetrometer table with the prepared face upward. The penetration is determined by releasing the cone assembly from the penetrometer and allowing the cone to drop freely into the grease for 5 s. Three determinations are made and averaged to give the reported result.
5. Significance and Use
5.1 These cone penetration tests not only evaluate the consistency of lubricating greases over the full range of NLGI numbers from 000 to 6, but also evaluate the consistency of stiff greases having penetration numbers less than 85. In contrast, Test Method D 937 is aimed at petrolatums and Test Method D 1403 uses less precise one-quarter and one-half scale equipment intended for use when the sample quantity is limited.
5.2 Cone penetration test results provide one measure of the consistency of a grease. Worked penetration results are required to determine to which NLGI consistency grade a grease belongs. Undisturbed penetration results provide a means of evaluating the effect of storage conditions on grease consistency.
5.3 Although no correlation has been developed between cone penetration results and field service, the cone penetrations obtained by the four procedures are widely used for specification purposes, such as in users' material specifications and suppliers' manufacturing specifications.
