Bearing Cage and Separator Materials
It is important when considering ceramic and hybrid bearings to define the correct material for use as a separator or cage. Whether it is metal, plastic or composite each has its own advantages and disadvantages depending on whether the application requires it to be nonmagnetic, lightweight or vacuum compatible the selection of the correct material is important.
Available as either machined or moulded, Nylon/polyamide represents a low cost, light weight cage option that is suitable for applications below 100oC.
Nylon/polyamide however, does not represent a good choice of cage in a vacuum application as the material will ‘out-gas’ and contaminate the environment.
But due to there light weight and insulating properties make them a suitable choice for hybrid electrical or high speed applications.
Polyether ether ketone, more commonly known as PEEK is preferable material for use in clean and ultra-high vacuum environments as it has low particle generation and will not out-gas in a vacuum. It is temperature resistant to approximately 150°C but is incompatible with acids and corrosive solutions. It can be used with both fully ceramic and hybrid bearings.
Chemically resistant, insulating and non-magnetic PTFE is widely used polymer throughout a number of industries. Due to the strong covalent bonding of the fluorine and carbon PTFE has strong chemical resistance and is completely hydrophobic.
However, PTFE does not have a high load bearing capacity and isn’t suitable for high temperature applications. PTFE can be used in both full ceramic and hybrid bearings.
A standard choice for many applications with high temperature, vacuum or clean requirements metal cages can take many forms. The use of 52100 steel or stainless steel cages is common in many hybrid bearings as it matches the material used for the races and provides a low cost option that will survive many applications. More exotic alloys can be used in special circumstances the use of beryllium copper in non-magnetic applications is possible but these would no longer be a low cost option. Need less to say carbon steels are not the ideal choice for non-magnetic or electrical application due to their conductive behaviours. Metal cages are prevalent in hybrid bearings more unusual in ceramic bearings.
Full compliment (no cage) negates all the issues with using an additional material for a cage therefore making it a possibility for applications including ultra clean, vacuum, high temperature, nonmagnetic, corrosive and electrical. But principle function of a cage or separator is to ensure the balls do not contact one another, without it the rolling elements will eventually contact at such a time the opposing rotational directions cause high contact stress the consequent abrasion will cause residue wear to the elements and races resulting in increased torque and reduced fatigue life.
Full compliment bearings are suitable for radial loading applications only.
Brass cages can be both crown ball pocket and riveted type, they offer a very durable heavy duty solution particularly at elevated running temperatures. A brass cage is not typically suitable for high speed use and is more often found in larger bearing assemblies.
Phenolic cages are light weight and strong making them ideal for high speed applications, they can be supplied in crown, ball pocket and two part riveted with additional options for metal backing and metal reinforcing.
Phenolic produced by impregnating textile with a thermo setting resin. The resulting component when machined to required sizes offers a very low coefficient of friction, the material is also able to absorb lubricants and maintain dimensional rigidity while offering a high strength to weight ratio.
Speciality Cage Materials
Bearing cages can also be produced in speciality materials specifically to suit applications ceramic, Vespel®, Meldin® moly disulfide impregnated PEEK, aluminium, Delrin® and graphite are examples that
can be considered.
Spacer Slugs, Toroids & Spacer Balls
These options replace the cage with a separator which floats between each of the balls. The materials used would be the same materials listed for cages.
These options are most suited to applications which have low torque and low speed for slow moving oscillating applications.
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