Blog 2018 05 | Purvis Industries

BEARING LUBRICATION FAILURE

Article by: Dan Whitehouse

Bearing failure due to lubrication is a very common occurrence. About 50% of bearing failure is related to lubrication. Below is a section of an article from www.machinerylubrication.com that details eight failure mechanisms.  (Full article can be read here.)

When in doubt, it does not hurt to ask when lubrication comes into play.

1. Unsuitable Lubricant - First, you must choose the correct lubrication for the application. Fundamental properties, such as the viscosity, additive package and consistency (for grease), should be carefully selected based on the bearing type, speed factor and operating conditions. If these factors are not thoroughly considered and an unsuitable lubricant is applied, the lubricant may become overly stressed or be insufficient for the machine's lubrication needs. In either situation, the bearing will likely undergo premature wear and failure.

2. Lack of Lubricant - For greased bearing applications, the correct regreasing volume and frequency must be established to ensure the bearing load zones are lubricated properly. Too much time between regreasing intervals or applying too little grease will cause excessive boundary and bearing wear.

3. Excess Lubricant - More grease is not always better. When too much grease is added to a bearing in a medium to high-speed applications, the temperature will rise from the churning, and the machine must work harder to overcome the fluid friction. As the temperature rises for the excessive grease charge, the viscosity will drop and other adverse effects will ensue.

4. Hot Running Conditions - A bearing running at a higher than expected temperature can be either a root cause or a symptom. If the bearing is exposed to an external environment that is exceptionally hot, this would indicate a root cause.

5. Solid Contamination - Solid contaminants can enter a system in a number of ways, including through a new lubricant, ingested from a headspace port or hatch, via defective seals, etc. The type of solid contaminants can vary depending on the source, but typical airborne dust/dirt will consist primarily of sillica and alumina.

6. Moisture Contamination -Similar to solid contaminants, moisture can enter a system in many different ways, including through headspace entry point, seals, or new oil. WHen the headspace is humid, thermal cycles can cause moisture to escape the air, sweat onto surfaces, and find its way into the oil through gravity. Moisture may exist in a lubricant as dissolved, emulsified or free water. Emulsified water has the most destructive potential in oil.

7. Mixed Lubricant -Topping up (if oil) or regreasing (if grease) a bearing with the wrong lubricant can drastically change the physical and chemical properties of the resulting lubricant mixture. Not only can factors like the wrong viscosity impact lubrication, but additives can also react negatively with each other, impeding their functionality.

8. Other Contaminants - Depending on the machine type, bearings maybe introduced to other processed chemicals, blow-by contaminants, glycol, etc. Based on the type of contaminant, the lubricant can change chemically or physically, resulting in lubrication failure.