Bearings work under the principle of minimizing the friction between two surfaces of relative turning motion and
transfer of the load seamlessly. Bearings are in every application that has a turning mechanism.
A perfect bearing leads to a perfect mechanism. Mechanisms like gear units, ventilators, pump systems, bench housings, door systems, various industrial electronics, washing machines, vacuum cleaners, agricultural machineries, heavy duty machineries, wind turbines, etc. all have bearings in them.
Components of Bearings
CagesThe cage retains the rolling elements in correct relative position and prevents contact during rotation. Cages are not a part of force transfer. There are various types of cages as listed below:
Pressed Steel Cage (J): The standard material that is used in cages is DC04-DC01-DC03. The operating temperature is up to 150 Celsius (302 F) degrees. Steel cages comprise 2 parts that are riveted to each other during production.
Polyamid 6.6 Plastic Cage (TN): The operating temperature is up to 115 Celsius (239 F) degrees. The material that is used for this cage is P6.6. The technical description of an ORS bearing with a TN cage is A4H.
Glass Fibre Reinforced Polyamide 6.6 Plastic Cage (TN1): The operating temperature is up to 150 Celsius (302 F) degrees. The material that is used for this cage is P6.6. The technical description of an ORS bearing with a TN1 cage is A3HG5.
Glass Fibre Reinforced Polyamide 6.6 Plastic Cage (TH1): The operating temperature is up to 170 Celsius (338 F) degrees. The material that is used for this cage is P4.6. The technical description of an ORS bearing with a TH1 cage is Stanyl.
Solid Brass Cage (M): This type of cage is mostly used in heavy load environments. The production of such cages is difficult and expensive.
Steel and brass cages are produced by a series of pressing operations of the corresponding material and solid brass cages are produced by processing brass material or plastic injection. Polyamid 6.6 plastic cages, glass fibre reinforced Polyamid 6.6, and Polyamid 4.6 are preferred over other cages in most of the recent applications because of their light weight, and the sliding and noise absorbing properties. Additionally, phenolic cages are produces based on customer requirements and the type of applications for which they are going to be used.
Sealing of BearingsSeals prevent the lubricant from escaping from the bearing and contaminants from entering the bearing.
Shields (ZZ): Produced out of sheet metal based TS 275 – DIN EN 10202 material standard. Shields do not have contact with the inner ring, which allows higher limiting speeds compared to seals.
Seals (2RS): Seals are composed of two parts; polymers such as NBR, ACM, FKM, NDNN, and HNBR, and a steel stiffening ring. Since seals run on the inner ring, they prevent lubricants escaping and contaminants entering the bearing; however, they are not likely to work on higher speed limits. For sealed bearings with higher speed limits, light contact and no-contact seals could be produced. Depending on the application for which they are going to be used, seal lip design might be different (RSR, RS1, RDD, etc.).
Operating temperature of polymer based seals are as shown below:
NBR: -30 °C / +105 °C (can operate up to +120 °C for short running times)
NDNN: -40 °C / +130 °C (can operate up to +150 °C for short running times)
HNBR: -40 °C / +150 °C (can operate up to +170 °C for short running times)
ACM: -20 °C / +150 °C (can operate up to +170 °C for short running times)
FKM: -30 °C / +200 °C (can operate up to +230 °C for short running times)
Rolling ElementsRolling elements take part in force transfer and are the main determinants in bearing categorization. Balls are in spherical shape and with their lower friction compared to other rolling elements, they are preferred in high speed applications. Ceramic is also used as the ball material other than steel. Balls ensure that there is always a point contact with the raceways. On the other hand, rollers ensure line contact with the rolling surface and have conical, cylindrical, spherical, and needle roller types. In order to minimize the force distribution at the contact points, they have crown profile at the outer surface. Load capacities are higher in roller bearings due to having a line contact and force distribution.
Lubrication and GreaseIn order to avoid metal-to-metal contact of the rolling elements and the raceways, therefore avoiding wear and premature fatigue, bearings must be lubricated appropriately. Proper selection of the lubricant, the method of lubrication, etc. are essential at this point. Greases, oils, and solid lubricant for some special cases are used for bearing lubrication. Lubrication minimizes the contact of the rolling element with the raceways, and therefore the wear and the rusting. Moreover, lubricants have cooling, sealing, and load carrying properties as well. Forming of a thin load carrying lubricant film depends on the bearing load, speed limit, lubricant viscosity, and the size of the bearing.
In selection of the right lubricant theoretical calculations (micro and macro geometries of the contact points, lubrication at the time of rolling contact, etc.) as well as experimental calculations should be considered (especially if high pressure EP additive containing lubricants pose a chemical reaction.
Greases are mineral or syntetic oils that are thickened by additives. Greasing the bearings is the most widely used form of bearing lubrication. There are a variety of greases differentiated based on load, operating temperature, speed, ambient conditions, etc. Understanding all operating and ambient conditions is essential to determine the appropriate grease for the application. The amount of grease in the bearing is about 20 - 30 percent, but subject to change based on customer requirements. For example, less grease is used in high speed applications. Mostly, grease added to the bearing during production covers the whole lifetime of the bearing, making them greased-for-life.
Oil lubrication is preferred over greases for higher speed-higher operating temperature applications. To ensure low friction, faster cooling, and noise and vibration minimization, oil lubricants are used. Oil bath, splash, drip, circulation, and mist and jet lubrication methods are widely used forms of oil lubrication.
PackagingAs for packaging, conservation oil and VCI are used to prevent rusting. Single box, single nylon, bulk, special design, etc. packaging is tailored based on customer requirements and the type of handling.