Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/388231
www.machinerylubrication.com | September - October 2014 | 21 Through comparison with the depos- ited fresh grease spectra, the process provides quick and reliable information on whether greases have been mixed together or a completely different type of grease has been used. The process can also determine whether the grease contains a base oil that is synthetic or mineral oil based. For base oils that are mineral oil based, FTIR establishes whether oxida- tion has taken place because of a lack of relubrication or because of damage caused by high temperatures. If the grease contains high-pressure addi- tives, additive deterioration may be detected. A fresh grease comparison can also prove whether there is too much water. Karl Fischer Titration Too much water in grease may cause corrosion and bearing damage. In places with high relative movement, cavitation can occur. If too much water is present or water penetrates continu- ously, relubrication must be performed more frequently. If the grease cannot withstand water, it may become soft or watery, and the quality will decrease. Just as with oil, the amount of water in a grease sample is calculated using the Karl Fischer (KF) method. It requires that water is "driven out" of the sample. With oil, the water from the sealed sample is steamed away by heating it to temperatures of up to 140 degrees C. However, it is much more difficult to boil water out of grease. In this case, the water must be extracted slowly at a temperature of 120 degrees C. The water is channeled into a titration vessel using a hollow needle and nitrogen. An electrochemical reaction then takes place with a special KF solu- tion. Once the transition point of the titration cur ve has been reached, the exact water content can be stated in parts per million. If a grease contains too much water, it is important to find the origin and eliminate it. The Karl Fischer method provides quantita- tive information about water content. The elements investigated by atomic emission spectroscopy help to distinguish between conden- sate and tap water. If the used grease sample is unlike the fresh grease sample and is polluted with sodium, calcium, potassium or magnesium, this points to "hard" water, which may have pene- trated the grease during high-pressure cleaning. If these minerals are not present, it may be "soft" rain or condensed water. If water was not removed effectively during the production of the grease, it may be found in the fresh grease sample. An analysis of fresh and used grease will clarify this matter. ML Karl Fischer titrator (Ref. Hanna Instruments)