Bearing lubricants

Lubrication is a very important factor for the proper functioning of any machine tools and spindle bearing is no exception. Lubrication is necessary to protect the different parts from wear and tear. Different types of materials are used for lubricating the bearings. To enhance the service of bearings, you must choose the right type of lubricants.

Types of Lubricants:

• Oils
• Greases
• Dry lubricants

Function of Lubricants
Despite having different types of lubricants for spindle bearings, their function is almost same. All lubricants provide some common services.

• Lubricants apply a thin elasto hydrodynamic layer that reduces contact between the rolling parts.
• They protect certain spindle bearing components from oxidation.
• They help in minimizing the effect of contamination.
• They enable spindles to run faster, cooler and longer.
• They allow a significant increment in the operating speed of the spindles.
• They enable the spindles to run at the same speed and help in reducing the operating temperature.

Oil Lubrication
Different types of oils are used for bearing lubrication. In industrial applications, petroleum based oils are the most common in use. A general misconception about oil lubrication is that more is better. Too much oil isn't good for the health of bearings. To produce the perfect elasto hydrodynamic (EHD) film between the layers of rolling elements of bearing, an adequate amount of oil is required at the specific temperature and operating speed. Any excess amount of oil will be responsible for increased bearing temperature.

Lubrication Systems
Lubricating the spindle bearings require certain oil introducing mechanism. Here are given three basic ways of it:

• Air-oil mist: This method is very simple, inexpensive and reliable. A fog of oil droplets is created in an air stream delivered to the bearing. It features adjustable air pressure and oil delivery rate.
  
  
• Air-oil injection: This method delivers a controlled microscopic oil stream to the bearing, featuring adjustable oil and air delivery rate. They demand slightly increased cost set up. They provide a longer bearing life.
  
  
• Oil-injection: This method needs high cost for set up, but they ensure maximum bearing life. In it high pressure oil is directly fed to the bearings. But generally it is not used in machine tools.

Grease Lubrication
Grease lubrication in bearings is very common and simpler. It is a permanent greasing solution and require minimal maintenance and is inexpensive. The grease is injected between the balls and races. Grease is actually oil mixed with a thickener. Thickener is an inert substance added just to hold the oil like sponge.

Limitation of Greasing
However there are certain limitations on grease limitation. Almost all greases are rated to operate up to the temperature of 300°F. Those grease which can tolerate high speeds have ester oil base and barium complex as thickener.

• The spindles packed with grease are unable to run above dN values of 850,000 for continuous operation.
  
  
• When the operating speed increases the operating temperature increases too and it started to break down the grease.
  
  
• Excess of grease application is not good for bearings because it can create heat due to churning which can cause grease to deteriorate.