Oils and greases form a hugely important function in almost every part of our lives. Using the correct specification for the machine and application is important. Just as one cannot mix a gear oil with engine oil, some greases made with different thickeners, also known as soaps, cannot be mixed. They are non-compatible.
All professionals understand the importance of scheduled maintenance in keeping machinery in the best condition. All want to do the right thing, so getting the right grease for the right equipment is imperative.
Changing from one type of oil to another is relatively straightforward. The use of a flushing medium helps. However, this is not so easy with greases. Greases are used when oils are impossible, where a sump cannot be used. So often in difficult to reach places.
All lubricants, oil, and grease are made up of base oil and additives. Different types of soaps are used to make a liquid into a semi-solid. Lithium is currently used the most, but others have different properties.
Both lithium and calcium soaps could be used with clay-based grease, but neither works very well. The compatibility problem has grown significantly more challenging in modern times due to the use of complex soaps, polyurea, calcium sulfonate, and even more exotic thickeners.
Grease mixture compatibility is usually divided into the following categories:
- Compatible means that the mixture’s characteristics are comparable to those of the different oils.
- Incompatible – The mixture’s features are very different from the individual greases.
- Borderline – Depending on the application, the mixture’s characteristics may not be suitable.
Some grease criteria, which further compounds the problem, are based exclusively on grease performance and pay almost no attention to the grease composition. Serious defects may occur if greases with various thickener types that meet the specification’s performance requirements mix while being used.
Further testing to ascertain the effect on other performance characteristics of the goods may be necessary once it is established that two greases are compatible in the three areas above. Any test intended to measure grease performance can be applied to a mixture of greases to ascertain the impact on that parameter when the greases are mixed.
To ensure that the attributes essential to the product’s proper operation in service are covered, the tests undertaken should be agreed upon by the user and the grease supplier. It is crucial to discuss what additional measures might be performed to assess grease compatibility if research has shown that the various grease compatibility tables are unreliable. According to ASTM D6185, a “Standard Practice for Evaluating Compatibility of Binary Mixtures of Lubricating Grease,” the planned greases are mixed in proportions of 25 to 75, 50 to 50, and 75 to 25. Changes in the mixtures’ dropping points, shear stability, and storage stabilities are assessed. These final two parameters measure the changes in the cone penetration value.
Although the consistency with which greases may be tested for compatibility has substantially increased thanks to this standard, it is worth mentioning that the three evaluation tests are static. Although the grease is mechanically worked before testing, this isn’t critical. A typical ball-bearing spinning at 1,750 revolutions per minute in three days of operation will experience almost 30 million mixing and working events. In contrast to the static reaction shown in cone penetration or dropping point studies, this combination will be subjected to constant dynamic forces. This will significantly impact its performance and potential degradation.
Methods to Reduce Mixing Effects
In a plant setting, it can be challenging to avoid combining greases. Still, several procedures can be done to reduce the effects and likelihood of mixing incompatible greases.
Step 1: Offer Plain Direction
The right product to use on each piece of equipment and the location should be explained to every employee who applies grease to machinery. This covers any workers at the institution, such as staff members and independent contractors. To avoid confusion, if possible, use labels and color codes.
Step 2: Include pricing in the specification for the grease
When purchasing or refurbishing equipment. Specify the grease that has to be used so that there is consistency within the plant.
Step 3: Consolidate lubricants
Decide on the bare minimum of greases needed to satisfy the specifications of the equipment being used. Don’t keep different products on hand out of convenience or brand loyalty. This raises the possibility of mixing. So consolidate.
Step 4: Examine Potential Combinations
Be aware that mistakes can happen. Be prepared by simulating grease mixing and functioning and checking dynamic characteristics. This will enable you to determine whether the incorrect grease has been accidentally introduced into a machine or whether consolidation is needed to transition to a more suitable product. To ensure long life and dependable operation, real effort needs to be exercised to follow correct procedures.
Set up Standard Operating Procedures (SOPs) and keep them. It will keep the operation running smoothly, as should all businesses involving grease.
