The Effects of Over-Greasing a Bearing
What are the Effects of Over-Greasing a Bearing?
|Over 35% of all bearing failures are due to improper lubrication. These include:
Many people have been instructed to attach a grease gun to a bearing and keep pumping the lever until grease comes out somewhere. This is acceptable for hinge pins and other applications where old grease and contaminates need to be removed and not cause damage.
A typical manual grease gun can generate 15,000 psi of pressure which can damage seals, push grease into areas where it is not needed and cause other problems. Over-greasing is a common problem and can cause over heating that leads to reduced bearing life.
Remember that for every 10°C (18°F) rise in temperature over 65°C (150°F) will cut the service life of the bearing in half.
So how much grease does a bearing need?
A commonly used formula is to take the outside diameter of the bearing in inches and multiply it by the width in inches, then multiply that figure by 0.114. This will give you the amount of grease in ounces required for that bearing.
For example, a 3 inch outside diameter bearing that is ½ inch wide will require 0.17 ounces or 4.8 grams of grease.
Ok so what about re-greasing a bearing?
And how much grease per pump does my grease gun deliver?
To determine how much grease is delivered per pump, take a tared (previously weighed) pan and pump the lever 10 times allowing the grease to go onto the pan. Weigh the amount of grease in the pan and divide by 10, this will give you the average number of ounces or grams per pump of the lever.
The amount may vary from grease gun to grease gun and with the type and viscosity of grease used. It is a good idea to test each grease gun yearly and use a different grease gun for different greases. In other words, don’t continually switch greases in a grease gun as this can lead to contamination, possible compatibility issues, and misapplication. All grease guns should be clearly labeled with the grease type and manufacturer.
When and how much grease do you add?
On some of the modern equipment, the OEM will indicate how much, when, and the correct procedure to re-lubricate. The rest will require the use of measuring devises and/or your senses. These may include but not limited to temperature, noise, vibration, and grease discoloration. An increase in operating temperature, noise or vibration may indicate it is time to lubricate the bearing.
If the grease is visible, a discoloration may be from contamination, heat, or oxidation and lubrication is advised. Ideally the bearing will have an exit hole or plug for the old grease to pass through. Slowly pump fresh grease into the bearing while it is running to evenly distribute the grease and not over pressurize the seals. Stop when you see old grease coming from the exit and allow the bearing to run, a bearing will push out any excess grease it doesn’t need. If a bearing doesn’t have an exit hole, one can be drilled in the housing.
Always make sure the grease gun dispensing nozzle is clean and free of contaminates as well as the grease zert or fitting.
What to do when start using a different grease?
When changing to a different grease on a piece of equipment, it is important to try and purge out the old grease to help reduce compatibility issues. Slowly add some of the new grease until the old grease is starting to come out of the exit zone. Allow the equipment to run for an hour or two and repeat the process. Continue to repeat the process until all of the old grease has been purged. Temperature, noise, or vibration readings should be monitored to determine if the lubrication cycle needs to be adjusted.
These same techniques can be used with centralized systems, new settings may be required when changing grease.
As always, call or e-mail your SWEPCO agent if you have any questions.
Southwestern Petroleum Corporation®