Bearing Retainer

Bearing Retainer keep the balls evenly spaced around the raceway preventing ball to ball contact and thus allowing higher speeds. They also help to retain grease around the balls and raceways. For greater accuracy and to prevent any additional friction, it is important that the bearing retainer is not allowed too much radial movement. To achieve this, the bearing retainer is guided by either the balls or one of the rings. Ball bearing cages are guided by one of the available surfaces between the inner and outer rings. There are inner land riding retainers where the retainer’s bore slides, or is guided by, the O.D. of the inner ring, Outer land riding retainers where the O.D. of the retainer slides, or is guided by, the bore of the outer ring, and ball riding retainers where the retainers touch neither ring and is totally guided by the balls. See the sections below for information on how each cage type is guided.

Metal crown/ribbon

Bearing RetainerThis standard bearing retainer is manufactured from carbon steel for chrome bearings and AISI304 or AISI430 grade stainless steel for stainless bearings. These were often made from brass which also offered a high temperature capability but this is much less common due  to higher cost of brass and advances in steel technology.

For higher temperatures, stainless steel is usually recommended. The crown cage and ribbon cage perform the same function but the crown cage is used primarily on smaller miniature bearings and thin-section bearings where space is more limited. Steel cages  are preferredBearing Retainer  for arduous operating conditions and where high levels of vibration are experienced.
• Good for low to medium speeds
• Can withstand higher temperatures according to the type of steel (see “Bearing Material” section)
• Crown type – inner ring guided
• Ribbon type – mainly ball guided

 

Nylon crown (TW)

Bearing RetainerThis moulded synthetic bearing retainer has better sliding characterisitics than the steel cage and produces fewer fluctuations in running torque. It can increase maximum speeds by up to 60 percent so is generally used in high speed applications and has good low noise properties. This bearing retainer is not suitable for low temperature applications as it loses elasticity below about 35°C. In vacuum applications, it may become brittle.
• High speed and low noise
• Max temperature range approx -35 to +110°C
• Ball guided

Phenolic crown (TP == THA or THB)

Bearing RetainerThis bearing retainer is also used for high speed  applications. Phenolic resin machined one-piece snap in crown type. These retainers have high rigidity and emergency running characteristics. Can be vacuum impregnated with oil. These are used in high speed deep groove ball bearings. “A” designation is for outer ring guided, and “B” designation is for inner ring guided. Generally more expensive, it does have advantages over the synthetic type such as absorbency allowing it to be vacuum impregnated with oil for long life application.
• Good oil retention.
• Can operate well with marginal lubrication
• Max temperature approx 140°C
• Inner ring guided

Full complement (F/B)

Bearing Retainer A full complement (or full ball) bearing contains extra balls and has no bearingretainer. It is used for its greater radial load capacity although axial load capacity is very small. These bearings can only be used at low speeds and bearing torque is increased due to ball to ball friction. An exception is a hybrid full complement bearing(ceramic balls) which can be used for very high speeds. Improved steel and hardening techniques have increased the load capacities of bearings with cages and the full complement bearing is much less common now.
• Higher radial load capacity
• Low speed only (except with ceramic balls)
• Low axial load
• Increased bearing torque

Special Materials for Ball Bearing Cages:

Phenolic Resin – Retainers are manufactured from linen and or paper based phenolic materials because of their ability to absorb oil lubricants. During bearing operation the lubricants are wicked or forced out of the retainers due to G-forces, which provides extra lubricant to the rolling and sliding elements. The phenolic materials are manufactured from linen or paper sheets that are coated with a phenyl formaldehyde resin which are rolled into tubes under high heat, tension, and pressure.

Phenolic tubes for ball bearing retainers should be formed with less tension and pressure than the tubes manufactured for structural end use. This is done to assure that the paper and linen fibers are not completely filled with the resin, leaving virgin paper or linen available to absorb and act as a reservoir for oil lubricants. The retainers are then machined from the tubes.

Vacuum Impregnation – Prior to assembly into the bearing, the retainers are meticulously cleaned and placed into a vacuum chamber along with a container of the oil lubricant. A hard vacuum is drawn and the chamber is heated to approximately 1,200°F. The vacuum and heat draws out any air and moisture from the retainers and degasses the oil. While maintaining a vacuum the retainers are covered with the degassed oil. The container is then introduced to atmospheric pressure, which forces the oil into the virgin paper or linen materials. The retainers are then assembled into bearings. Some customers will request that the bearings must be subjected to low centrifugal forces to remove excess surface oil.

Cages, or retainers, can also be manufactured from sacrificial solid lubricants:  Ball bearing retainers manufactured from Teflon, PGM or Salox M are extremely expensive and are used only in very specialized expensive equipment. Normally they are used in hard vacuum and outer space type applications. Both PGM and Teflon retainers have been used extensively in slow speed torque sensitive applications such as flow meters.

Materials for TxA, TxB, TxHB, and TxHA:

TNH = Synthetic. Good Running and Torque. 1-Piece Molded Medium Speeds. Temp Range -30°C TO 80°C
T9NH = Synthetic Molded Glass Fiber Reinforced. Higher Speed than “TNH”. More Strength. Temp Range -30°C TO 120°C plus.
THB = Linen Based Phenolic
T1HB =  Paper Based Phenolic (for starting torque better than linen)
T3HB = Vespol SP3 (hard vacuum applications)
T4HB = Torlon 4301. 12% Graphite, 3% PTFE
T7HB = Torlon 4203
T8HB = Pure PTFE (used with ceramic bearings in highly corrosive environments)
T9HB = PA 6.6 WITH 25% Glass Fibers

Properly Designed Ball Bearing Retainers:

Definitions: For two piece steel ribbon retainers, Tabs (ears) are the protrusions on the male half of a ribbon retainer that is clinched over the female half to hold them together.

Ball Pocket: The part of the retainer that surrounds and positions the ball. The diametrical clearance between the ball and the ball pockets can be as small as 0.0035” in miniature and instrument bearings and can be upwards of 0.010” in larger bearings.

Slot: For crown type retainers, the slot is the opening that the ball passes thru (during bearing assembly) prior to entering the ball pocket.

Properly designed retainers will have the ball touch the ball pocket exactly on the pitch circle of the balls. Should contact be made above or below the pitch circle, you could statically experience retainer hang-up and dynamically experience running torque spikes.

The only time that the surface finish becomes an issue regarding retainers is when you have a land-riding retainer. The surface of the retainer that is touching the land should be ground.  Retainers should be properly de-burred.

Coined ball pocket:  In metallic crown ball bearing retainers: An oversized ball is drawn through the blank ball pocket to form a spherical surface for the balls to contact. The retainer is then hardened so the retainer can be snapped into the bearing without permanently deforming the ears.

Coined ball pocket in a metallic crown ball bearing retainer

Loose Clinch (Crimp):  Ribbon retainers should be loosely clinched so that the balls can orient the two rettainer halves.  The loose clinch provides for less noise as well as lower runner and starting torque.

Loose Clinch (crimp) of a Ribbon Ball Bearing Retainer

Ball Bearing Retainer Performance Problems

Hooping:  Is the phenomena when the retainer wobbles like a hula-hoop causing torque spikes in the rotating assembly. The retainer should track in a true circumferential plane concentric with the pitch diameter of the balls.

Hang-up (Wind-up):  When an axial load is applied to static bearings, that have the axis of their shaft in a horizontal mode, the balls fall downward to a position where they are unequally spaced prior to the load being applied. When the axial load is applied it squeezes the balls between the inner and outer raceways. Now that the balls are held securely in unequally spaced positions they cause the retainer to bind. This binding is called “retainer hang-up.” Once bearing rotation commences the retainer is stressed and some of the balls may skid causing damage that will initiate premature bearing failure.