Oil separation

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The oil separation is a method for determining the oil loss of lubricating greases .

background

As a rule, lubricating greases consist of 80% lubricating oil, approx. 5–10% of thickener and approx. 10–15% of additives. The thickener is made on the basis of a metal soap (e.g. lithium or calcium complex soaps) and works like a sponge: In its "pores" it stores the lubricating oil and the additives. These must not escape during storage, but should only be released while moving at the lubrication point. If the oil escapes during storage, this process is also known as bleeding.

The determination of the oil loss is described in the DIN standard 51817 "Testing of lubricants - Determination of oil separation from lubricating greases under static conditions".

Measurement

To determine the oil separation, a certain amount of the grease to be tested is poured into a conical container, free of air bubbles, the bottom of which consists of a wire screen bottom with a mesh size of 63 μm. The sieve is then weighed together with the fat and placed on an oil container, the tare weight of which is known. A metal weight (brass or stainless steel) is placed centrally on the sample surface in order to increase the pressure within the fat sample. In the case of very soft lubricating greases (e.g. wheel flange or soft lubricating greases), a weight can be dispensed with. At a constant test temperature (40 ° C and 120 ° C) and a test duration of 18 hours (DIN short test) or 168 hours (DIN normal test), part of the oil separates from the thickener and runs off through the sieve and drips from the tip of the cone into the collecting container. After the test period has expired, the amount of oil separated is weighed out and the result is given in percent relative to the weight of the fat:

With:

  • M = oil separation, in percent (% (m / m))
  • A = amount of separated oil, in grams (g)
  • E = weight, in grams (g)

Interpretation of the measurement result

The higher the oil separation, the more oil can float up in the time from filling to use by the end user, or it can separate in the container in so-called oil pockets. The oil required for lubrication is no longer available; As a result, a used lubricating grease is used up faster or, in the worst case, is unusable for the planned use. How big the oil separation may be is determined by the manufacturer depending on the application.

Problem ingredients

With some lubricating greases, the solid lubricants or thickening systems contained in them can pass through the mesh of the wire screen base during the test and thus falsify the measurement result.

Norms

There are two main standards used in industry to measure oil separation:

  • DIN 51817: 2014-08 - Standard from the "Testing of Lubricating Fats" working committee in the Mineral Oil and Fuel Standardization (FAM) committee of the Material Testing Standards Committee (NMP) at DIN
  • IP 212: 2011 - Standard of the Institute of Petroleum (IP)

Both standards are technically equivalent; However, there are differences in the following points:

  • Short test duration: 18 hours according to the DIN standard or 42 hours according to the IP standard
  • Test temperature: between 40 ° C and 120 ° C according to the DIN standard or 40 ° C according to the IP standard
  • precision

See also

Web links

  • OELCHECK ; Free accessible wiki for lubricant and oil analysis, commercial analysis offer.

Individual evidence

  1. ↑ a b DIN 51817 - 2014-08 - Beuth.de. Retrieved March 18, 2019 .
  2. ↑ a b c d e f g Totten, George E., Westbrook, Steven R., Shah, Rajesh J .: Fuels and Lubricants Handbook: Technology, Properties, Performance, and Testing . ASTM International, West Conshohocken, PA 2003, ISBN 978-0-8031-4551-1 .
  3. ↑ a b c d e f g Standard DIN 51817: 2014-08 `` Testing of lubricants - Determination of oil separation from lubricating greases under static conditions ''