Grease selection for centralised lubrication systems
In order to enhance operational efficiency and reap the benefits of automation, there has been an increase in the adoption of centralised or automatic lubrication systems. This shift has been observed across industrial sectors and heavy-duty machinery.
A centralised lubrication system is a piece of complex machinery that addresses several lubrication requirements, including the volume and frequency of grease application, grease points such as grease for roller bearings, diameter, and distance to grease points. A centralised lubrication system can range from a single port lubricator to more complex machinery incorporating time-frames and alarms that deliver grease to multiple grease points.
Using a centralised lubrication system effectively can boost employee productivity and operational efficiency. However, like any other system, it must be periodically maintained to make the most of your investment. Selecting a grease that meets the requirements of the machine is an important aspect of an effective centralised lubrication system and eases the operation and maintenance of the system.
This blog covers 4 tests to help you select grease for a Centralised Lubrication System.
Grease selection
It is important to know how the ingredients in the grease interact with the Centralised Lubrication System. Grease is composed of 3 parts:
- Base oil
- Additives
- Thickener
The base oil constitutes between 75% - 95% of the grease. A mineral, synthetic, semi-synthetic, or vegetable oil is used as a base oil in grease, which provides viscosity and film thickness to the grease. Additives are utilised to impart new properties or to eliminate or enhance existing properties of the grease as per requirements. Thickeners act as the vessel through which the properties of base oil and additives are delivered.
Here are 4 tests that help you ascertain the compatibility of the selected grease with the centralised lubrication system.
1. Apparent viscosity test
The viscosity of a lubricant is the most important factor in determining its compatibility with the Central Lubrication System. To determine the required base oil velocity, one must define the optimal viscosity requirements for each component to be lubricated. After determining the required base oil viscosity, a list of greases that satisfy the viscosity requirement can be shortlisted for further testing of their apparent viscosity. Apparent viscosity is the collective viscosity imparted by the base oil, additives, and thickener.
2. Cone penetration test
The cone penetration test determines the consistency of the grease. The estimated operating temperature and speed factor serve as a general starting point. The type of thickener, the type of base oil, and the base oil viscosity are additional factors that can affect the required consistency.
A cone penetration test uses a weighted cone to penetrate a block of grease and test the grease consistency according to 4 standards:
- Undisturbed
- Worked
- Prolonged worked
- Blocked
Undisturbed greases are preferred in Central Lubrication Systems as the grease may lay dormant in storage until required. Grease is subject to storage requirements both in supply lines and while it is in a drum or another storage container. It is necessary to include vertical paths, time taken by grease to enter the supply line, and exposure to temperature in the supply line before choosing a grease.
3. Structural stability test
This test judges the structural stability of the grease under operating conditions. Different applications in industries have different stability requirements due to different operating conditions, e.g hot working environments require high-temperature greases. The structural stability test uses a penetrometer to determine the structural stability of the grease. A standard roll stability device works the grease for two hours at a temperature of 20 to 35 degrees C. The grease is then subjected to a second penetrometer test. The difference between the two tests is used to calculate the lubricant’s effectiveness in low shear stability.
4. Ventability test
The ventability test determines the supply-line diameter required for a specific grease in the Central Lubrication System. It will decide whether grease valves and injectors work correctly in a centralised lubrication system. The test pressurises grease to 1,800 psi in a 25-foot coil. After the grease stabilises at 1,800 psi, a relief valve is opened, and the pressure gauge is monitored after 30 seconds. This reading, combined with a supply-line reference, gives you the required diameter for a specific grease.
Conclusion:
These 4 tests give you all the required information to select a suitable grease for a central lubrication system. The central lubrication system’s overall budget should also include the cost of replacing the chosen grease. Ideally, the Central Lubrication System should be designed according to the grease's nature and not vice-versa.
Castrol is the global leader in liquid engineering. We provide a comprehensive range of cutting oils for all industrial sectors that address every requirement. Our lubricants improve Central Lubricating System operations and maintenance processes while prolonging the machine's life.