Lubricating oil chroma and test method

December 03, 2023

Lubricating oil chroma and test method

The color of the oil can reflect its degree of refinement and stability. Refined Base Oil, the oxides and sulfides in the oil are clean, and the color is lighter.

01. Chroma overview

Often can reflect its degree of refinement and stability. For the base oil, the higher the degree of refining, the cleaner the oxide and sulfide removal of its hydrocarbons, and the lighter the color.

However, even if the refining conditions are the same, the color and transparency of the base oil produced by different oil sources and classes of crude oil may not be the same.

02. Test method

There are two methods for determining the color of lubricating oil, direct observation method and international measurement standards laboratory test method, but generally use the latter.

Direct observation methods include ASTM D1500 method, ASTM Union method and Sayman colorimetric method.

1) ASTMD1500 Chroma (ASTMD1500)

Use the ASTMD1500 colorimeter to determine the color of yellow and even dark oil. The sample oil is correctly compared with the standard color plate under a certain light source. The results are 0.5, 1,1.5, 2,2.5, 3.... 8 represents it. The smaller the number, the lighter the oil color, the larger the number, the darker the oil color. When the oil color is more than 8.0, it must be diluted with kerosene and then determined. The volume ratio of kerosene to dark oil is 85:15. The measured number shall be followed by the word "Dil", or the word "D" (Dilution or dilution). If the color is lighter than 1.0, or between 0.5 and 1.0, it is expressed as L1.0 (meaning less 1.0), and so on. However, if the color is below 0.5, it should be determined by Sayman colorimeter, which is more accurate.

2) ASTM Union chroma

Using an ASTM Union colorimeter, compare oil samples with standard splatters under a light source as 1,1 1/2, 2, 21/2.... Indicates. This method has been replaced by ASTM D1500. Because ASTM D1500 color grading is more uniform and ideal, and ASTM Union is not, it is eliminated.

3) Sayer colorimeter (ASTMD156)

There are two glass tubes in a Sayboltchromometer. One glass tube is hollow and can hold glass slides of standard colors, while the other glass tube holds oil samples. Adjust the height of the oil in the tube, so that the color of the two tubes is a certain number to indicate its color. The shallowest is represented by "+30" and the deepest by "-16". The depth of the color of the oil can often determine whether its quality is uniform or whether it is contaminated with dirt.

03. The meaning of color

After the use of additives in the base oil, the color will also change, and the color as an indicator of the level of refinement of the oil has lost its original significance. As a result, most lubricants have no indicators of color or chroma.

For the oil in use or storage and transportation process, the oxidation, deterioration and contamination can be roughly estimated by comparing the previous determination results of its color. If the color becomes darker, in addition to the possibility of being contaminated by dark oil, it indicates that the oil is oxidized and deteriorated, because the gum has a strong coloring power, and the heavy aromatic liquid has a darker color; If the color becomes milky, there is water or air bubbles in the oil.

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