Grease is a semi-solid lubricant that is useful in a variety of situations where traditional lubricants (e.g., oil, dry lubricants) do not provide the necessary performance. However, just because grease can function like oil in many respects does not mean that the two substances are interchangeable. There are some major differences between grease and oil that will help you better understand where to use grease when it comes to your hydraulic equipment. It is also important to understand the key properties of grease to help you decide what type is most appropriate for your system.
Purpose of Hydraulic Grease
Grease primarily serves as a specialized type of lubricant that works where other lubricants would fail. It is known for being thick and messy, but good at staying in place and quite resistant to moisture. However, in addition to its lubrication properties, grease can serve other purposes simultaneously. For example, grease acts as a sealant, keeping contaminants out of sensitive components and keeping lubricants in where they belong. It can also help seals continue doing their job despite the fact that they may be in the process of deteriorating. Because it stays in place so well, it is often used with pins and bushings that are exposed to the environment rather than enclosed within the equipment.
Grease also works very well with solid lubricants, such as graphite or molybdenum disulfide, because it is able to hold those particles in suspension (i.e., they do not sink to the bottom of the grease). This is in contrast to oils, in which these solid lubricants would merely settle at the bottom. This dry lubricant feature can be especially useful in applications that involve extremely high pressures or high temperatures.
Because of its thickness, grease is much easier to keep in place than oil and requires simpler, less expensive devices to retain it in a functioning system. Also, unlike oil, the fluid levels of grease do not have to be carefully monitored in order for proper lubrication to be achieved. Even a small amount of grease can often provide a thick enough film layer to prevent potentially damaging metal-to-metal surface interaction.
Where is Grease Used?
There are some components that simply cannot be accessed for frequent lubrication or are sealed for life (e.g., gearboxes, electrical motors). These components can maintain their lubricity for extended periods of time (and in some cases, throughout their useful life) by using high-quality grease instead of oil.
Another area where grease is commonly used in place of oil is in extreme operating conditions. These operating conditions can include high pressures, high temperatures, shock loads, and extremely large loads.
There are certain pieces of equipment that are only used intermittently or must be stored for extended periods of time between uses. That can lead to serious lubrication issues if an attempt is made to use more traditional oil, which must reach a certain temperature to be distributed correctly. Grease, on the other hand, forms an instant lubricating film which means equipment can be run immediately and without potential issues related to dry starting.
One of the more interesting uses of grease involves extremely worn components. Over time, clearances can be worn until they are larger than intended, which can cause some serious lubrication issues unless grease is used. Grease can maintain a thicker film in enlarged clearances and further extend the life of the parts involved.
What is Grease Made from?
Grease is a combination of three component types: an oil, a thickener, and various additives. The oil (either synthetic or mineral) is what provides the necessary lubricity and makes up between 70% to 90% of the grease. A thickener is also included and can make up anywhere from 3% to 30% of the grease. Most thickeners are made from a type of simple or complex metal soap, but there are some thickeners that are not soap-based. The thickener, as the name implies, is what gives bulk to the grease. Additives are then included to either enhance desirable properties or reduce undesirable ones.
What Kind of Properties Does Hydraulic Grease Have?
In order for grease to do its job, there are certain key properties that it needs to have. And while its primary purpose is lubrication, these properties are very different from the properties of lubricating oil. For example, grease is much thicker than oil, making high-viscosity one of its desirable properties. This thickness means that the grease will stay where it is supposed to be and can form a thick film to prevent metal-to-metal surface interaction between parts such as shafts and bearings.
Grease has a dropping point, which refers to the temperature at which it will become a liquid. As the temperature increases, the grease will begin to soften. Because one of the key benefits of grease is its ability to stay in place and behave as a semisolid material, the dropping point of grease is very important when considering a particular type of grease for an application. The dropping point should be considered in regard to expected operating temperatures.
There are other ways that grease can react to temperature. The pour point of the oil used in the grease serves as a very good lower limit for its operating temperature range. And even before temperatures reach the dropping point of grease, grease can be negatively impacted by heat. Because of its thickness, grease cannot dissipate heat like an oil can. When it does overheat, the grease can form a thick crust and, depending on the oils used in the grease, can even burn. Additionally, if temperatures drop too low, it behaves as a hard grease.
Another important property of grease is its ability to resist water, or withstand the effects of water. When used correctly, grease can essentially act as a seal to prevent the ingression of water and moisture. Water may have an effect on its ability to maintain lubricity, but exposure to water does not seriously compromise its performance.
Pros and Cons of Hydraulic Grease
Grease acts as a good lubricant where the use of oil is not recommended or is simply not feasible. It is not, however, a replacement for the use of oil. Unlike oil, grease cannot conduct heat away from sensitive components, so packing a planetary gearbox with grease instead of using an appropriate type of gear oil would be a serious mistake. Also, grease is good at keeping water out of certain joints and clearances while still providing lubrication, but the use of too much grease can force components out of place and lead to premature wear. And while grease can typically handle extreme temperatures fairly well, it does have its limits. Lubricating oil can be flushed and replaced fairly easily, but the same is definitely not true for grease. In fact, grease that has been contaminated with abrasive particles is extremely difficult to clean out and replace. And, like oil, grease will age over time and gradually lose key properties and additives.
What Are Grease Points?
Areas that use grease (and need regular replenishment of that grease) are known as grease points or lube points. If you do not already know where they are, a quick check of your equipment’s manuals will help you track them down. Most of them are easy to access, but not all. These grease points need to be checked on a regular basis to ensure that there is enough grease present to do its job. Grease is replenished using a grease gun that allows you to control how much grease goes in and prevents the grease from being contaminated before it is applied (although the nozzle will still need to be wiped down with a clean cloth before the application of the grease begins).
Conclusion
If you are running machinery or equipment of any size, then chances are you have grease points that need to be maintained. Grease is a special-purpose semi-solid lubricant that works well where other approaches to lubrication fail. When the proper type of grease is used and the grease points are inspected on a regular basis, it supports the efficient and trouble-free operation of your equipment. When neglected, however, grease points and grease can be the source of all manner of problems.
MAC Hydraulics
At MAC Hydraulics, we service your entire hydraulic system — and that includes both internal and external grease points. We know that most technicians dread dealing with grease — it is messy, often smelly, and seems extremely imprecise compared to checking and changing oil fluid levels. However, our highly skilled hydraulic technicians can help you with all aspects of maintaining the grease in your system, from selecting the most appropriate type of grease (based on operating characteristics such as temperature, pressure, moisture levels, and loads), inspecting all of the grease points, and maintaining those grease points at the correct levels. We also offer a 24/7 emergency onsite repair service in addition to our comprehensive maintenance plans. Contact our experienced team MAC Hydraulics today to find out how we can assist you in keeping your machinery running at peak performance!
