Archive for December, 2014

Understanding the Numbering System for Bearings

Friday, December 26th, 2014

For roller bearings, although the boundary dimensions have become internationally standardized and accepted by the ISO (ISO is a French acronym which is translated into English as the International Organization for Standardization), the standardization of bearing numbers has not. Manufacturers in different countries are continuing to use their own bearing numbers.

As a guide, the ISO dimensional system specifies the following dimensions for rolling bearings: bore diameter, “d”, outside diameter, “D”, width, “B”, (or height, “T”) and chamber dimension, “r”, and provides for the diameter to range from a bore size of 0.6 mm to an outside diameter of 2500 mm.

For this tutorial on bearing numbers, the information comes from NSK. Numbers and letters are used to form symbols to designate a variety of types and sized of bearings. Typically, you will see four to five numbers, potentially accompanied by one or two letters.

In a series of numbers, the first will be the type symbol, indicating the engineering style, or features such as a single or double row, deep or angular type, tapered or spherical.

Next, the width series symbol and diameter series symbol are combined and called the dimensional series symbol. This also tells us how large of a load the bearing will be able to hold.

For radial bearings, the outside diameter increases with the diameter series symbols 7, 8, 9, 0, 1, 2, 3, 4. Width series symbols include 0, 1, 2, 3, 4, 5, and 6, and are combined with the respective diameter series symbols. Width series symbols become wider to match the respective diameter series symbol.

The bore number is found last, relating to 1/5 of the bore diameter dimension for bores 20mm or greater. For instance, a bore diameter of 30mm then has the symbol 06.

There are many countless combinations. Therefore, many options for people designing machinery and/or parts.

Bearings may have the same IDOD (inside dimensions and outside dimensions) but designed internally for various applications. For example: Three different bearings, the last three digits of their numbers indicating that they all measure IDOD at 25x52mm, may be used for different applications, as follows:

Bearing number 1205: We can tell by the first digit that this bearing self-aligns to accommodate radial and axial loads

Bearing number 3205: The first number, 3, tell us this is a double-row ball bearing more suited for heavy duty industries such as materials handling.

Bearing number 6205: The first number, 6, indicates this is a radial ball bearing, which is one of the most popular and versatile.

Each of these bearings have the same boundary dimensions and fit along the same sized shaft.

NSK offers a great tool for determining the bearing indications and numbers on tapered roller bearing, miniature ball bearings, auxiliary and dimensional bearing symbols, which can be downloaded as a .pdf here.

Fundamentals of Bearings

Friday, December 19th, 2014

Wondering what those nifty little (sometimes very big) suckers do for us? Let’s take a closer look at the fundamentals of bearings.

For those of you who run equipment, it’s highly important that you fully understand the bearings you’re working with.

To begin, there are two types of bearings – sliding and rolling. The majority of bearings used, however, are rolling bearings, which were developed to help eliminate sliding friction.

Sliding friction is when one object continually slides against another object. Sliding friction can be nearly eliminated in some applications, with smooth machined or cast metal bearing elements that slide against equally smooth surfaces that are separated by a thing layer of lubricant.

Roller bearings, believed by the majority to be the better way to eliminate sliding friction, use rolling elements between the moving surfaces. Consisting of four major parts, roller bearings have an inner ring, outer ring, and cage containing the rolling elements in the center.

Roller bearings can be classified as radial bearings or thrust bearings, depending on the internal design. These bearings are named for their uses – a radial bearing will carry a radial load, which is a pressing force at right angles to the shaft. Whereas, a thrust bearing will support a thrust load, which is a pushing force against the bearing parallel to the shaft.

Those bearings having a contact angle of 45 degrees or smaller are considered radial bearings, and their ratings are typically provided as radial load. Bearings with a contact angle greater than 45 degrees are considered thrust bearings and are rated as such.

There are two basic families of rolling element bearings – those based on the ball of the rolling element and those based on the roller. Ball bearings have small areas of contact with the raceway. They are limited in load carrying, but have low friction and run smoothly. Roller bearings have much larger contact areas, making them more suitable for heavy loads.

Likely the most versatile and popular bearing is the deep groove ball bearing. It can carry axial and radial loads, is suitable for light load and high speed applications.

Also popular is the spherical roller bearing, which is able to carry both very high radial and axial loads in either direction, and accepts both dynamic and static misalignment. The range of bearing widths and sections make it an extremely versatile bearing.

The correct amount of lubrication is critical for the performance of the rolling bearing. Many factors need to be taken into account when determining what that amount is. Be certain to find or determine the correct lubricant and application for your roller bearings. They will thank you in longevity and performance.

For a great introduction to the many types of bearings we did not cover today, watch this video from SKF.

Keep Away from Counterfeit Bearings

Friday, December 12th, 2014

Counterfeit products are an issue for all branded bearing manufacturers – existing in all geographical markets, industrial segments and for all types and sizes of bearings.

Difficult to identify, counterfeits are labeled and marketed with another company’s brand illegally, and put in packaging which appears identical to genuine packaging used by the actual brand owner.

Counterfeit bearings are sold to customers who are unsuspecting, at around the same price as genuine products. There is money to be made in this market, making it prevalent and dangerous.

It is a big deal that counterfeits exist and are being sold to customers unbeknownst to them, because people are being cheated, and the risks can be serious. Counterfeits can cause machinery breakdowns and even injuries if used.

Sometimes “the eye test” is not enough to ensure your safety against counterfeit bearings. They can be difficult to identify, yet made of substandard materials, making them less reliable.

The best way to protect yourself from counterfeit bearings is to always purchase through an Authorized channel. If possible, do the research on the front end. Self-education is your best defense against counterfeits.

Some companies have made it easy for people to check if you are working with an authorized channel, such as NSK, who offers this toll-free number 1.800.675-4898 on their website. They have partnered with the World Bearing Association and its efforts to protect against counterfeiting.

SKF also offers assistance with counterfeits. On their website, they offer – “If you believe that you have accidentally purchased a counterfeit, or would like to anonymously inform us of activity in this area, contact SKF at genuine@skf.com.”

It is important to engage the premium brand manufacturer concerned with counterfeits of their products.

In the words of Mike Schmidt, “there exists a major difference between trying to avoid the purchase of counterfeit products and actually avoiding the purchase of counterfeit products.”

Remember, safety first.

Bearing Damage Analysis

Friday, December 5th, 2014

Today, we’re going to take you through the process of analyzing damaged tapered roller bearings. In other words, we’ll answer – what went wrong?

Tapered roller bearings have many applications, such as: agriculture, construction, and mining equipment, axle systems, gear box, engine motors, and reducers.

Stress can cause extensive damage to bearings if:

  1. They have inadequate or contaminated lubricant
  2. They were damaged or dropped during installation
  3. They were adjusted or installed improperly

First, let’s look at the bruising effect. Debris from other parts, inadequate sealing, or contaminated lubricant can leave small bruises or indentations along the raceway. This reduces the lifespan of the bearing, and is why ensuring cleanliness during installation is vital.

Another common cause of damage is moisture or water exposure. This moisture may enter the bearing during installation, or could be the result of fluctuating temperatures which forces the steel to sweat.

This moisture rusts or etches away at the bearing’s material creating dark lines around the raceway. We call this an “etching” effect. Chunks of the raceway material may be torn off by rollers during operation if the etched bearings continue to be used.

If during installation the bearing is dropped, be sure to inspect it for damage or cage deformation. A bent bearing cage is good reason to scrap it. The cage could also be damaged by compression during installation, which causes skewing and deformation.

It is also important to use the right tools when installing the bearing. A tool that is harder than the bearing’s material can cause deformation in the raceway that will result in spalling under the stress of operation. No hardened drifts, center punches, or brass bars.

Inadequate lubrication can cause heat or welding damage, typically showing up near the large end of the cone or the larger ends of the roller components, as these sections undergo sliding contact.

Peeling or micro-spalling is also due to inadequate lubrication and allows for rapid wearing away of the raceway material.

Excessive preload during adjustment can sometimes cause rapid spalling as well, allowing large chunks of material to be torn from the raceway and rollers due to the extreme heat.

Misalignment damage can be caused when excessive endplay is exercised. This will result in one-sided deep spalling along the raceway or cone.

The various causes of bearing damage all have one thing in common – human error. That’s why taking extra precaution, and slowing down when installing bearings is paramount.

For more information, watch this bearing damage analysis video by The Timken Company.