Bearing Materials: Choosing the Right Alloy to Meet Your Needs

Conventional hardened chromium bearings are not always the ideal solution.

Most rolling element bearings are manufactured using rings and rolling elements fabricated from AISI 52100 degassed chrome bearing steel.

While AISI 52100 chrome steel is exceptionally suited for many applications, there are other cases where special materials are required. Criteria for these scenarios may include:

  • Greater Corrosion Resistance
  • Higher Temperature Durability
  • Lower Temperature Durability
  • Grease Free Use
  • Lighter Weight

Applications common to these needs can be found in a variety of manufacturing processes and in military and medical equipment. For such sensitive applications, it is important to ensure the right materials are used for the job.

Below is a list of some materials that can deliver on higher demands that the popular AISI 52100 can’t match:

AISI 440C Stainless Steel

Think of AISI 440C as your general purpose stainless steel.

This martensitic stainless steel is used for inner and outer rings and ball bearings with applications in food processing machinery, cleaning equipment, LCD and semiconductor equipment, instrumentation applications and high temperature and high humidity environments.

AISI 440C offers:

  • Higher resistance to corrosion and chemicals versus 52100,
  • Durability in high temperatures:

               o   ZZ type (shielded) -40° F to +302° F
               o   2RS type (sealed) -22° F to +230° F

  • Precision to ABEC 1-3 standards. Higher ABEC class bearings available upon request
  • Available up to 60mm bore
  • Extended inner rings with set screw mounting

AISI 304 Stainless Steel

AISI 304 is used in highly corrosive and temperature-sensitive applications where even its 440C counterpart can’t survive. AISI 304 is resistant to acids including dry chlorine, chlorine gas, caustic soda, ammonium sulfate and others.

AISI 304 is an austenitic stainless steel used in LCD and semiconductor manufacturing equipment, metal plating equipment and other equipment used in environments where the bearings come into contact with acidic or alkaline chemicals.

AISI 304 is also used for retainers, metal shields and snap rings. Heat resistant grease is prepacked in sealed and shielded bearings. It is also suitable for food processing machinery and washdown environments.

Notable features of AISI 304 include:

  • Greater corrosion resistance than AISI 440C stainless steel ball bearings
  • Nonmagnetic
  • Lower load ratings due to softer material
  • Available up to 40mm bore

AISI 630 Stainless Steel

AISI 630 is a semi-austenitic and martensitic precipitation-hardening stainless steel. This metal boasts an improved corrosion resistance compared to AISI 440C and can be hardened by heat treatment and used for heavy-load and high-rotation applications not suitable for AISI 304 stainless steel ball bearings.

AISI 630 stainless steel ball bearings are suitable for LCD and semiconductor manufacturing equipment, metal plating equipment or film manufacturing equipment. 630 performs effectively in acidic or alkaline environments as well as applications requiring heat- and chemical-resistant fluorine grease pre-packed as standard lubricant.

Notable features of AISI 630 stainless steel include:

  • Corrosion resistance that is superior to AISI 440C stainless steel
  • Can be hardened by heat treatment
  • Supplied with silicon nitride ceramic balls (Si3N4)
  • Available up to 30mm bore

1T Titanium

1T Titanium is a nonferrous, unalloyed titanium metal. Because of its very high tensile strength and resilience to corrosion and temperatures, it is most commonly used for military applications, aircraft, spacecraft and medical devices.

1T Titanium can also be used in food processing, seawater related applications, etching equipment and low temperature environments.

Key features for 1T Titanium include:

  • Superior corrosion resistance using pure titanium class 2 inner and outer rings and silicon nitride ceramic balls and fluorine resin retainers. For use in extreme applications.
  • Tensile Strength, Ultimate: 34,800 psi
  • Tensile Strength, Yield: 24,700 – 45,000 psi
  • Heat capacity of 1004°F
  • Melting point of 3040°F
  • Excellent low temperature range
  • No allergen reactions when used in artificial joints
  • Lightweight

When considering what materials are best for your application, it’s necessary to know exactly what kinds of conditions your ball bearing will be subjected too.

This infographic by Emerson Bearing offers an effective and easy-to-read guide on which metals can work best in the most common critical applications.

Ceramic and Polymer Ball Bearings for Nonmagnetic Applications

Varieties in the metal for a ball bearing solution are important, but not every application is friendly to magnetic materials.

The magnetic properties in ball bearings will often interfere with the effectiveness of medical, military and aerospace machinery. Grease-free bearings can be required in some food processing applications and for use in hard to reach areas of machines, like cranes.

So what are the alternatives to AISI-certified metals or traditional lubrication.

TC2 Grease Free Bearings

TC2 grease free bearings are designed to be used where lubricants can’t be applied. This is accomplished by using a special coating on the retainer. These bearings can be used in applications including printing machinery, food applications, cleanroom environments and medical equipment.

The specifications are:

  • Inner and outer rings: AISI 440C
  • Retainer: AISI 304 + Special Coating
  • Balls: AISI 440C
  • Smooth rotation by low torque, except RS and 2RS types
  • Note: Load Ratings (N) and Allowable Rotation (rpm) are reduced

2C Full Ceramic Bearings

2C full ceramic bearings can be used in extremely corrosive environments due to ceramic inner and outer rings with a fluorine resin retainer. These same properties also ensure the bearings are nonmagnetic and do not need grease.

The main drawback of these bearings is the extremely brittle nature of the ceramic rings.

Detailed properties include:

  • Inner and Outer rings: Zirconia Ceramic (ZrO2)
  • Retainer: Fluorine Resin
  • Balls: Silicon Nitride Ceramic (Si3N4)
  • Completely nonmagnetic
  • Ceramics are extremely brittle and must be handled with care

Polymer Ball Bearings

Polymer ball bearings use thermoplastic inner and outer rings, which can be used without lubrication. Plastic ball bearings have an all-plastic race and plastic cage with a ball made of either plastic, glass, or stainless steel – each with their own advantages for certain environments.

Plastic balls are used for applications requiring low weight and noise. Glass balls are a nonmagnetic, non-metal option, but are quite brittle. Stainless steel provides the most durable and heat resistant option.

One of the greater advantages to polymer ball bearings, however, is their ability to self-lubricate. Lubricants for polymer ball bearings can include Teflon, Silicon, Graphite, and Moly. As the lubricants are spread over the ball, a film is developed that will self-lubricate the ball bearing.

Polymer ball bearings are the most cost effective compared to stainless steel and ceramic ball bearings.  This type of bearing is most often used in cleanrooms, food processing applications and textile and packaging equipment.

Properties are:

  • Self-lubricating
  • Non-magnetic
  • Corrosion resistant
  • Lightweight
  • Cost effective compared to stainless steel and ceramics
  • Options include balls made from 316 stainless steel, glass or plastic
  • Ideal for light loads and high speeds

Know your Ball Bearing Lubricants

Lubrication should receive particular attention for using specialty materials and their applications.

For example, ExxonMobil provides a selection of mobile equipment oils and greases. The Mobil Infinitec 152 high temperature grease for industrial applications can achieve an average life of 490 hours when subjected to temperatures of 350°F.

Bearings are typically supplied with heat resistant grease. The Mobil 1 Synthetic Grease can be most effective for stainless steel ball bearings that are under threat from extreme temperatures and corrosion, with its resistance to water washout.

Special high temperature or chemical resistant grease such as fluorinated grease is available upon request from Emerson Bearing.

Food applications require NSF H1 grade grease, due to the risk of food coming into contact with machinery. An H2 grade variant is strictly for applications where food contamination will not be possible. The H3 grade variant, which are soluble or edible oils, are used to clean food processing equipment.

See Emerson Bearing’s chart below for more examples of lubricating greases and their properties:

To find the right bearing, download the Nomenclature Guide to Common Bearing Types from Emerson Bearing.

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Emerson Bearing has sponsored this post.  It has no editorial input into this post.  All opinions are mine. –James Anderton

Written by

James Anderton

Jim Anderton is the Director of Content for Mr. Anderton was formerly editor of Canadian Metalworking Magazine and has contributed to a wide range of print and on-line publications, including Design Engineering, Canadian Plastics, Service Station and Garage Management, Autovision, and the National Post. He also brings prior industry experience in quality and part design for a Tier One automotive supplier.