Posts Tagged ‘Babbitt’

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Bearing Repair Process

July 27, 2016

Electric generation companies make their money when it is hot outside. Consequently, they keep their machines running or available in the summer. Maintenance usually happens in the spring or fall…when the temperature is moderate.

Consequently, we have had some time at TRI to work on our web site. We undertook a big job to redesign it with a layout that will work devices of all size. We want it to look good on your desktop as well as your smart phone.

Our initial job is complete, but now we are adding more content for our customers.

Our latest addition is the Bearing Repair page. This page does more then just tell potential customers that TRI Transmission and Bearing Corp. repairs bearings. It is a bullet list of the steps bearings get when they come in the door. The list has been published so our customers understand what goes into a bearing repair.

When a bearing is sent to TRI during the summer, it usually means a machine is in an unscheduled outage. Unscheduled outages are expensive so it is critical that the repairs be done ASAP. When TRI goes to an expedited schedule, we work on the bearing repair 24 hours a day, 7 days a week. It’s important to us that the customer knows exactly what we are doing and how far along we are in the process.

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Minimizing Porosity in Rebabbitted Bearings

February 29, 2012

There are various ways to rebabbitt a bearing that has been in service previously, among them are centrifugal casting, static casting, and hand welding. Each one has advantages and disadvantages. The choice used depends, in part, on the material composition of the bearing backing material.

Some of the most difficult applications to rebabbitt are cast iron fan bearings that have water jackets. Essentially, these bearings have two walls to consider, an outside wall and an inside wall.

There are various concerns with these bearings.

Read the rest of this entry ?

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Tin-Copper Bondline Embrittlement and Debonding Phenomena

October 28, 2010

A simple literature review, or search on the Internet for “intermetallic compounds” would lead one to believe that this represents the state of the art in material science.  While the study of many new compounds is on the leading edge of technology, the intermetallic nature of copper and tin in an alloy form has been studied for more than 5000 years.  Without the aid of high tech tools, the Chinese developed the beta bronze alloy form of tin and copper some 1400 years ago.  This was the first metal that could be intentionally heat treated to provide a wide range of mechanical properties.  In more recent research, much attention has been paid to the formation of Cu6Sn5 and Cu3Sn intermetallic compound layers, and their effect on solder joints in electronic assembly.  Unfortunately, little, or no attention has been paid to the identical reaction that occurs when bonding a tin based Babbitt to a copper alloy backing material typical of many fluid film bearings used in industry today.

My first direct exposure to the resultant phenomenon of the formation of these compounds came about 10 years ago.  During the dis-assembly of a high speed gas compressor, the thrust pads were removed from the unit for inspection.  In this particular bearing, the pads were designed with ASTM-B23 Grade 2 Babbitt bonded to a copper alloy containing approximately 2% chrome for increased mechanical strength.  In this application, the high sliding velocity present in the oil lubricated thrust bearing would have yielded unacceptably high bearing temperatures if conventional steel backing material had been used.  The copper alloy backing material was used due to its high thermal conductivity to provide improved bearing performance.  In this instance, following successful dimensional checks, and ultrasonic inspection of the Babbitt bond, the pads were returned to the compressor deck to be re-installed in the machine.  During the installation process, one of the pads was inadvertently dropped from a height of about three inches on to a steel workbench.  As a result of this minor impact, the Babbitt completely separated from the copper alloy backing material.  This was indeed somewhat disturbing that the Babbitt could fall off of an otherwise acceptable part that was ready for installation in a very expensive machine that operates in excess of 10,000 RPM.

Read more…

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Babbitt

October 21, 2010

Babbitt was first created by Isaac Babbitt in the early 19th century.  Babbitt is a relatively soft metal that is used principally as a liner for oil-lubricated sliding bearings, both journal bearings and thrust bearings.   There are two characteristics that make Babbitt an extremely useful material for sliding bearing applications.  The first is “lubricity”, or the ability to slide surface to surface without galling, generally in the presence of a lubrication such as a mineral oil.  The second is embedability, that is, the characteristic whereby hard particulate matter in lube oil embeds in the layer of Babbitt and thereby minimizing scratching or other damage to the surface of the journal or thrust runner.

There are many combinations of constituents that are used in manufacturing Babbitt.  The first distinction is whether the Babbitt is “tin-based” or “lead-based”.  When tin was difficult to obtain during WW 2, some equipment manufacturers added portions of lead to the Babbitt used in bearings in order to stretch the supply of tin. Many of these bearings failed because lead made the tin-lead Babbitt brittle. This experience was a good justification for using only tin-based Babbitt for rotating equipment where ductility and endurance are always important.

Two widely used Babbitt compositions are known as ASTM B23 Grades 2 and 3.  There are other grades, however, for rotating machinery, Grades 2 and 3 are very common.  Grade 3 has higher strength than Grade 2, but Grade 2 is easier for Mechanical Technicians to use in the refurbishment of existing bearings, and for this reason, it is more commonly used. Other compositions may be used.  TRI typically uses a proprietary Babbitt material that has a unique combination of constituents and special methods of manufacture, with the result of significantly higher strength at higher temperatures.

One of the most important issues that affects the success of the performance of a bearing is the attachment of the Babbitt layer to the backing of the bearing. Carbon Steel is an excellent backing material.  The surface of the steel can be machined and then tinned, avoiding the use of mechanical Babbitt anchors, or dovetails.  Suitable tinning compounds are readily available in the commercial market.

Babbitt thickness is also an important factor in the ability of oil-lubricated babbitted bearings to take abusive pounding.  Thinner layers can survive higher levels of pounding forces, yet thin layers cannot permit large particulate matter to embed without damage to journal or runner surfaces.  Consequently, a compromise is required, usually in the range between 0.030 inches to 0.125 inches, depending upon the application and cleanliness of the lube oil.

Copper based backing materials that are not properly coated before tinning can be expected to develop a brittle coating at the boundary between the tin-based Babbitt and the copper-based backing material.  This phenomenon is called “copper-tin embrittlement and debonding”, and was discovered several years ago by another well-known Babbitt bearing manufacturer. This phenomenon can cause Babbitt layers of bearings with copper-based backing materials to fall off in the storeroom even if they have never been used.  They can also fall off in service, which obviously can damage a machine.  With proper surface preparation and coating, a copper-based backing can have a tin-based Babbitt layer attached, and this bearing can be expected to have excellent performance and service life.

For more information about Babbitt, Babbitted Bearings and Babbitted Bearing Repair, please contact an engineer at TRI Transmission & Bearing Corp.

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Scraped Babbitt Bearings Conform to Journal

October 11, 2010

A machine journal bearing creates a proper oil wedgeA Babbitt bearing bore that has been “scraped” will conform to the shaft journal it supports. A scraped bearing will not create a converging oil wedge which is necessary for proper vibration and temperature control. TRI highly recommends bearings that are machined to tight tolerances. For better performance, an elliptical bore will produce a secondary wedge film above the journal that will help to retrain the vibratory motion of the journal.

Journal bearing with a machine elliptical bore

TRI repairs babbitted bearings. We can centrifugally cast Babbitt or puddle the bore. We have many years of experience in machining to tight tolerances.