In practical applications, it is very important to use an appropriate amount of grease. Typically, the bearing interior space should be filled about one-third to one-half with grease. Less grease can cause insufficient bearing lubrication, and too much grease can cause eddy currents. Both of these conditions can lead to excessive heat generation causing the temperature to rise. As the temperature of the grease increases, the viscosity decreases and the grease becomes thinner. This will weaken the lubrication effect, but also increase the loss of grease in the bearing, and may also cause the separation of the grease components, resulting in the failure of the grease. Bearing torque increases as the grease fails. Torque can also increase due to the drag created by the grease when too much grease creates eddy currents. For best results, it is best to have enough space in the housing to allow excess grease to escape from the bearing. However, it is equally important that the bearings are filled with grease. If there are large gaps between bearing sizes, the grease should be sealed to prevent the grease from flowing out of the bearing area. Filling the housing with grease should only be considered in low speed applications. When sealing measures are insufficient to keep out contaminants or moisture, this lubrication method prevents the ingress of foreign impurities. It is advisable to completely fill the housing with grease to protect the bearing surfaces when the equipment is not in operation. Before the next run, remove excess grease and restore proper amount. Equipment that uses grease should have grease fill and vent holes on opposite ends of the top of the housing. There should be a drain plug at the bottom of the bearing seat to drain the aged grease from the bearing. Bearings should be lubricated regularly to prevent bearing damage. However, the time interval for lubrication is difficult to determine. If you do not have the corresponding experience, please consult your lubricant supplier. Timken offers a variety of lubricants that help bearings and related components operate efficiently in harsh industrial work environments. High-temperature, wear-resistant and water-repellent additives provide better bearing protection in harsh environments. Timken also offers a range of single- and multi-point lubricators to simplify grease filling. Grease Application Methods In general, greases are easier to use than oils in industrial bearing lubrication applications. Most bearings, after being initially greased, require periodic relubrication in order to operate efficiently. Grease should be filled into the bearing so that it enters between the rolling elements and the raceways. For tapered roller bearings, forcing the grease from the large end face into the small end face of the bearing ensures even distribution of the lubricant. For small and medium-sized bearings, it is easier to fill with lubricant by hand (fig. 14). In workshops that require frequent re-greasing of bearings, a mechanical grease filling machine is appropriate to squeeze the grease into the bearings (Figure 15). Either way, apply a small amount of grease to the outside of the rolling elements after the grease has filled the inner area of u200bu200bthe bearing. For any application, the two main considerations in determining its relubrication cycle are operating temperature and sealing effectiveness. Obviously, leaking seals will result in frequent relubrication. Efforts should be made to maintain the seal at peak performance. Whenever the grease level in the bearing falls below the required grease level, grease should be added immediately. When the lubricating performance decreases due to contamination, high temperature, moisture, oxidation or other factors, the grease should be replaced. For additional information on the appropriate cycle for adding lubricants, consult the equipment manufacturer or your Timken representative. Figure 14. Grease can be easily filled by hand. Figure 15. Mechanical Grease Filler. Greases vary in consistency from semi-fluid greases that are not necessarily thicker than viscous oils to solid greases that are almost as hard as cork. Consistency can be measured with a needle viscometer, using a standard weight cone sunk into the grease. Penetration is the distance the cone penetrates (measured in tenths of a millimeter over a specified period of time). The National Lubricating Grease Institute (NLGI) classifies grease consistency as follows: Table 30. NLGI Classification The consistency of grease is not set in stone, when grease is sheared or processed, it usually becomes soft (thin). In the lab, the process is done by pushing a perforated plate up and down through a closed can of grease. This machining is not comparable to the severe shearing action that occurs in ball bearings, and does not necessarily correlate with actual performance.