Posted on Wed, Jul 15th, 2015 in: Technology
Bearings that get damaged oftentimes need to be replaced, resulting in downtime which hurts your productivity and ultimately your bottom line. Having to spend time replacing a bearing that failed is much more time-consuming than simply keeping your bearings adequately lubricated on a regular basis. In fact, many leading bearing companies have stated that incorrect lubrication can account for over 30% of bearing failures, ranking it as the #1 potential "killer" to the life cycle of a bearing.
There are many bearing types, including: ball bearings, roller bearings, ball thrust bearings, roller thrust bearings, and tapered roller thrust bearings. This lack of lubrication adversely affects all of these bearings, causing them additional friction which will raise temperatures as well as damage the surface of everything they come in contact with. This is especially the case when bearings get worn out to the point where they physically break apart. This can be catastrophic, especially to industrial machines.
What is lubricant?
Lubricant provides a separating film between the bearing rolling elements, raceways, and cages to prevent metal-to-metal contact. In doing so, the lubricant is able to minimize the effects of surface contact, namely undesired friction that otherwise would produce excess heat, metal fatigue, and wear. Lubricant also prevents corrosion and contamination damage.
Bearing lubricants fall into three chief categories: greases, oils, and solid dry film lubricants, the latter of which are usually limited to moderate speed and very light loading conditions. The selection of a specific type of bearing lubricant is usually governed by operating conditions and limitations of a bearing system. Factors can include: the maximum and minimum allowable operating temperatures, the speed at which the bearing will operate, and the viscosity of the lubricant at operating temperature.
How do you know what lubricant is needed for your application?
It is very common for bearing suppliers and Original Equipment Manufacturers to specify the correct amount of lubricant you will need, sometimes even including for you the appropriate amount, grade, type, replenishment cycle, supply system, viscosity, and additives (if applicable). It is also common for manufacturers and distributors to make suggestions in the way of storage, shelf life, filtration, delivery and any other notable precautions you can take to keep your bearings in a healthy state.
No matter what, it is decidedly important that you select the appropriate lubricant for your bearings. An appropriate lubricant does the following: acts as a contaminant barrier, reduces friction and wear by providing an elastic film of sufficient thickness and strength to support the load and separate the balls from the raceways, minimizes cage wear by reducing sliding friction in cage pockets and land surfaces, prevents corrosion of the bearing rolling elements, and acts as a heat transfer agent.
Is it safe to mix either different additives or different grades of grease?
Grease is basically thick oil, with thickeners to make it stiff, and additives to reduce metal corrosion and wear. There are basically two types of additives for metal wear that one needs to consider: Lithium and Molybdenum Sulfide. These two additives are not compatible, so it is unwise to mix them.
Additionally, more often than not, mixing different grease grades in general can lead to disastrous consequences, meaning the bearings can seize and break. The compatibility of lubricants must be verified before mixing or else chemical differences within thickening agents, base oils, additives, and additional ingredients could cause a change in viscosity, causing the bearing breakage and would possibly necessitate bearing replacement.
How can I monitor my bearings for any signs of distress after lubrication?
A laser heat gun will work great for this; simply point it at your bearing and watch the temperature at maximum load. You want to make sure your heat does not reach more than 180 degrees Fahrenheit. This is the point where your oil will thin out and fail. This is even the case with oxidation inhibitors. We will have another blog in the near future that will outline how you can physically inspect your bearings and signs of wear you can look for.