Lube-Tech


significant problem. However, in the case of other SAE J300 tests this is far from the case, as we shall see later.


For the sake of completeness, it is necessary to see how these Acceptance Limits are calculated. ASTM D3244 describes the process in detail and also gives a methodology for resolving disputes between a supplier and receiver who have both tested the same material and obtained differing results. However, in the case of a blender deciding whether they should or should not release product on a single test result the following equations apply.


For a maximum specification: Acceptance Limit = S - 0.594* R where S is the specification limit and R is the published reproducibility of the test method.


Similarly, for a minimum specification: Acceptance Limit = S + 0.594* R These equations are both for 95% confidence limits.


Using these equations, a table can be built to show both Specification and Acceptance Limits for SAE J300 kinematic viscosity – see Table 2.


As can be seen from Table 2, the difference between Specification and Acceptance Limits for kinematic viscosity tested by ASTM D445 is quite small due the extremely high precision associated with this test method. Unfortunately, the same cannot be said for the other tests referred to in the SAE J300 standard. These will now be examined in turn.


Low-Temperature Pumping Viscosity by ASTM D4684


Although the SAE J300 standard specifies that just one method (ASTM D4684) shall be used to determine this critical parameter there is a slight complication in that it allows 2 separate procedures and these have different published levels of precision. In this paper only the more recent Procedure A will be considered as this employs more modern cooling techniques, as well as removing the need


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.113 page 3


Table 2. ASTM D445 Kinematic Viscosity Acceptance Limits for unused engine oils – based on single test


for using methanol as a heat transfer medium with all its associated toxicity issues.


Procedure A has the additional advantage that the published precision data is not temperature dependent so the same figure can be used for any grade from 0W-xx to 15W-xx oils, which were the only grades used in the precision study.


Around the maximum specification limit of 60,000 mPa.s the published reproducibility is 14.6% of the mean result for unused oils. Using the expression quoted above: Acceptance Limit = S - 0.594* R


= 60000 – 0.594* 8760 = 54800 mPa.s


Therefore, the blender should not release the product if, when a single sample of the material is tested, a result for low-temperature pumping viscosity of greater than 54800 mPa.s is obtained.


For the record, the precision of Procedure B was not quite as good as Procedure A when 10W-xx and 15W-xx oils were evaluated and significantly worse when 5W-xx and 0W-xx oils were studied. This implies that anyone using this procedure on older test instruments should not release blends unless they are significantly further within the specification limits.


High-temperature high-shear-rate (HTHS) viscosity


Switching to the other high-temperature test, that of HTHS viscosity, there is a further complication in that there is more than one method allowed in the SAE J300 to determine this critical parameter and they do not share common levels of precision.


For this paper only ASTM D4683 which employs the commonly used Tapered Bearing Simulator Viscometer will be considered.


Table 3. Specification and Acceptance limits for HTHS viscosity by ASTM D4683 LUBE MAGAZINE NO.142 DECEMBER 2017 35


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