Bearing FAQs

2019-08-26

We have assembled a wide variety of frequently asked questions (FAQs) about bearings (e.g. ball bearings, roller bearings, plain bearings, linear bearings) and bearing related products (and bearing services too). Just refer to the question you’re interested in below and you will be taken to a remarkably succinct, straight-forward, and accurate answer:

Q1: Can bearings be refurbished?

Yes, but it depends… Generally speaking, for small bearings it is uneconomical to attempt to refurbish a bearing product. However, for larger size bearings (6 inch bore and above) there potentially could be economic gains. In particular, bearings such as slewing rings, cylindrical roller bearings, and spherical roller bearings are candidates for refurbishing. But beyond the accumulated wear there are many other factors involved in this financial decision including maintenance cycles, lubrication, MTBF, environmental considerations and more.

Q2: What’s The Difference Between Bearing Seals And Shields?

Seals and shields are both in place to keep contaminants out of a bearing. In order of effectiveness, the enclosures that are offered are as follows: metal shields, rubber non-contact seals, Teflon non-contact seals, and rubber contact seals. Not surprisingly, as the sealing performance is increased, the torque required to turn the bearing will also increase due to the increased friction caused by the seal/shield. The application’s condition and life requirements are important to know to determine the best shield or seal choice.

Q3: What Are ABEC Ratings?

The ABEC scale is an industry accepted standard for the tolerances of a ball bearing. It was developed by the Annular Bearing Engineering Committee (ABEC) of the American Bearing Manufacturers Association (ABMA). There are five classes, going from widest tolerances to tightest: 1, 3, 5, 7, and 9. Higher ABEC classes provide better precision, efficiency, and greater speed capabilities, but do not necessarily mean that the bearing can spin faster. Additionally, the ABEC rating does not specify many other critical factors, such as smoothness of the rolling contact surfaces, ball precision, and material quality.

Q4: Does A Higher ABEC Rating Mean A Quieter Bearing?

While there may be a loose correlation between ABEC precision ratings and noise, higher ABEC ratings to not always mean a quieter bearing. ABEC ratings do not specify many other critical factors, such as smoothness of the rolling contact surfaces, ball precision, and material quality all which may affect noise.

Another major factor affecting noise performance is the lubricant type. For very quiet running, the selection of a quiet grease is very important. Handling, installation and correct preloading will also ensure the quietest possible operation.

Q5: What Are ABEC And ISO Precision Level Equivalencies?

ABEC precision levels, ABEC-1, ABEC-3, ABEC-5, ABEC-7, and ABEC-9 are the equivalent to ISO precision levels P0, P6, P5, P4, and P2 respectively.

Q6: What Are Precision vs. High-Precision Ball Bearings?

“Precision” and “high-precision” are generic bearing terms; however, there is no official definition for either in the bearing industry.Generally speaking, “precision” ball bearings comply with ABEC-1 and ABEC-3 tolerances while “high-precision” ball bearings comply with ABEC-5, ABEC-7, or ABEC-9 tolerances.

Some general purpose ball bearings intentionally do not comply with the ABEC precision tolerance specifications and are not graded or rated as such.

Q7: Bearing Shelf Life – What Is The Shelf Life Of A Bearing?

The most important factor for determining the shelf life of a “properly stored” bearing is the lubrication.  Greases and oils dohave shelf lives (expiration dates).

Otherwise, providing the bearing is stored poperly (typically in its original factory packaging), the potential effects of contamination and oxidation will be minimal and not significantly effect shelf life.

Q8: What Is A “Torque Tube” Bearing Or A “Thinex” Bearing?

“Torque Tube” bearings and “Thinex” bearings are generic industry names for “Thin Section Ball Bearings”.  While not required, Torque Tube bearings often have an extended inner ring to provide a stronger and stiffer bearing (minimizing torque) than its thinness would allow otherwise.

Generally, Thinex ball bearings are thinner given the same outside diameter than Torque Tube ball bearings (the term Thinex may have been derived from “thinest”); however, there is no standard definition for either in the bearing industry.

Whether called Torque Tube or Thinex ball bearings, Thin Section Ball Bearings are often used as specialized Instrument Ball Bearings where low friction and high accuracy are required, where space is at a premium, and where load support is less important than shaft location.

Q9: What are “Super Precision”, “Super High Precision”, versus “Ultra Precision” bearings?

Some factories promote bearings as “Super Precision (MM),” “Super High Precision (MMV),” and “Ultra Precision (MMX)” bearings. These are all just factory defined terms to used describe ABEC-7 through ABEC-9 (ISO-P4 through ISO-P2) tolerances with one of them being a compromise between the two specifications.

More specifically, bearings called Super Precision (MM) are typically manufactured to ABEC-7 (ISO-P4) tolerances. Ultra Precision (MMX) bearings are usually manufactured to ABEC-9 (ISO P-2) tolerances. However, so-called Super High Precision (MMV) bearings are manufactured partly to ABEC-7 tolerances, but also partly to tolerances defined by ABEC-9 specifications. Super High Precision bearings operate with performance levels and running accuracy meeting ABEC-9 specifications; however, their remaining features meet ABEC-7 specifications and consequently are less expensive compared to fully ABEC-9 compliant (Ultra Precision) bearings.

For more about official bearing tolerances and their definition by the ABMA and ANSI, please see our white paper entitled, “Bearing Tolerances and Precision Levels.”

Q10: What bearing grease is the “best?”

The answer is, “it really depends.” The selection of the best bearing lubricant (whether grease or oil) will depend on the application conditions. With a wide variety of greases and oils available, solutions are available for most applications; however, there is no perfect grease whether natural, synthetic, micro-filtered or otherwise.
Every grease has strengths and weaknesses in its performance and consequential monetary costs. For example, high temperature greases typically can’t handle high loads very well. “Quiet” greases may break down at high temperatures. Additives have benefits but some drawbacks too. So there is no single best grease for bearings; it really comes down to the application and what characteristics are most important (and which are less).

Q11: Will a stainless steel bearing protect against rust?

“Somewhat”… Stainless steel is not rust proof, it is “corrosion resistant” and will rust in corrosive environments over time. However, stainless steel will corrode at a much slower rate than chrome alloy steel. But it is not a simple as that.

There are various types of stainless steels each with different corrosion resistance properties. For example a special steel called SV30 is far more corrosion resistent than 440C stainless steel.

Q12: How fast can a bearing rotate?

The speed capability of a bearing will depend on its size, the type and amount of lubrication used, the bearing and cage materials, precision levels and tolerances, and for how long the the maximum speed is required (among other factors).

Q13: How is bearing material hardness measured?

There are several standard scales for measuring a material’s hardness including Rockwell, Brinell, Vickers, and Shore. For bearings, the Rockwell scale is predominantly used. However, even within the Rockwell Hardness Test, there are several different scales used to specify the hardness of different materials. Typically, the Rockwell “C Scale” is used for measuring the hardness of bearing materials since bearings are usually made from very hard materials.

Q14: What is a Spherical Bearing?

A “spherical bearing”, as the name implies, is a bearing that is composed of a raceways that are rounded (spherical) on the inside axially (in addition to the normal radial curvature of course). However, there are many different types of spherical bearings including:

  • Spherical ball bearings (a.k.a. double-row, self-aligning ball bearings)
  • Spherical roller bearings (a.k.a. double-row, self-aligning roller bearings)
  • Spherical plain bearings (a.k.a. ball busings)
  • Rod ends (a.k.a. spherical rod end bearings)

The one thing they all have in common besides spherical raceways is that they all are designed to accomodate shaft misalignment.

Q15: What are flanged ball bearings?

Many ball bearings have flanges as options to their configurations. The flange is designed to aid in mounting and positioning.  This is especially true for miniature and instrument bearings but applies to other ball bearing types. 

Flanges are also used with bearings on external housings used to mount a bearing unit. A mounted bearing unit acts as a system to position the bearing securely for reliable operation. 

Q16: What is an Axial Needle Bearing or Axial Needle Roller Bearing?

“Axial Needle Bearing” and “Axial Needle Roller Bearing” are just two variations of a type of bearing that the bearing industry typically calls “Roller Thrust Bearings” or “Cylindrical Roller Thrust Bearings.” In all of these cases, the bearing is designed to support high axial loads (i.e. loads parallel to the shaft) as compared to radial ball bearings. 

Generally, roller thrust bearings (a.k.a. Axial Needle Bearings or Axial Needle Roller Bearings) consist of two washers (raceways) and rolling elements which, in this case, are rollers (cylindrical rolling elements) as opposed to thrust ball bearings which use balls as their rolling elements.  While ball thrust bearings sometimes use groves in the raceways, typically roller thrust bearings use retainers (cages) to ensure proper spacing and orientation. 

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