Machines now run at higher speeds and higher temperatures than in the past. The high quality of lubricating oil is therefore essential. This can be ensured by viscosity measurement.
Lubricants and lubricating oils have many different uses. Lubricating oils extend the working life of machines by reducing the friction and corrosion and preventing premature wear. Lubricants are responsible for good heat dissipation, which means they conduct the produced heat out of the system. They also prevent solids and liquids entering sealing points and therefore reduce the repair and maintenance costs. Paper machines, for example, increasingly use circulating oil lubrication systems in order to take care of parts which are under a high level of thermal or mechanical stress.
Lubricants and their properties
The composition of a lubricant – its “formulation” – consists of base oils and additives. The formulation determines the characteristics of the lubricant, both in terms of performance and working life.
The lubrication of machines usually requires a high volume of lubricant and a lot of work on the seals. The manufacturers of lubricating oil try to ensure that the lubricating oil remains as long as possible in the system in order to avoid maintenance costs, production stops and downtimes.
The build-up of pressure from outside the oil creates a lubricating film inside the oil which is responsible for the “smooth running” of the mechanical parts. This lubricating film is greatly affected by the viscosity and temperature.
Viscosity and temperature
As the viscosity of lubricating oil changes over time this is an important parameter for determining the oil’s quality. The viscosity of lubricating oil is increased by soot, lead, coolant, metal particles, high temperatures, dust and silicates.
The Viscosity Index (VI) indicates how much the viscosity of lubricating oil changes due to the affects of temperature. A low value means a pronounced change in viscosity when there are temperature fluctuations. A lubricating oil with these properties is highly viscous at low temperatures and very fluid at high temperatures. In comparison to fresh oil, a used lubricating oil has a low Viscosity Index.
If the viscosity of lubricating oil changes significantly this indicates possible problems in the machine. Although viscosity measurement cannot identify the problem it can reveal the problem and prevent damage or technical failure.
Viscosity and density
The viscosity is one of the most important parameters for the evaluation of lubricants. By simultaneously measuring the viscosity and density it is possible to detect different influencing parameters such as oil thinning by coolants. With the SVM™ 3001 Stabinger Viscometer™ from Anton Paar both parameters are measured in one measuring cycle. The kinematic viscosity and Viscosity Index are determined to monitor the quality of lubricating oil. SVM™ 3001 meets the requirements of DIN 51659-2 – a test method to determine the kinematic viscosity of used lubricating oils.