Bearings « Dr.
Mel's Technical Notes Page 1 of 9
Technical information for Dr. Mel Giberson
Archive for the ‘Bearings’ Category
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.
Posted in Bearings | Tagged Babbitt, porosity | 1 Comment »
Bearing Repair and Refurbishing
December 2, 2010
Here is a photo I snapped in the shop this morning. It is a TRI Transmission & Bearing pad that
has been sent back for refurbishing. The surface is rough because the babbitt has been puddled.
The next process will be machining the surface to the proper diameter.
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Bearings « Dr. Mel's Technical Notes Page 2 of 9
(http://turboresearch.files.wordpress.com/2010/12/babbitt-bearing-repair.png)
The puddling process is a manual operation that takes some time. You can see the babbitt is laid
down in rows. After machining the bore, porosity will be revealed. More babbitt will be laid
down to fill the voids and the machining will be repeated.
Posted in Bearings | Tagged bearing, pad, repair | 2 Comments »
WARNING: Cracks Found in Westinghouse
Cast Steel Bearings
November 9, 2010
3 Case studies with solutions…read more
(http://www.turboresearch.com/technotes/TechNote_2010-05.pdf?
title=Cracked+Westinghouse+Bearings)
Posted in Bearings | Tagged bearings, cracks, Westinghouse | Leave a Comment »
Solving Ring-Oiled Bearing Problems
November 2, 2010
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Bearings « Dr. Mel's Technical Notes Page 3 of 9
In recent years, TRI has encountered and resolved a number of problems with ring-oiled bearings
for fans, motors, and pumps. Oiling rings damage the journal surfaces and a lack of good
lubrication can lead to excessive wear and eventually complete bearing failure. Many cost effective
improvements can be implemented for this class of bearings given the technology that is available
today…read more (http://www.turboresearch.com/technotes/TechNote_2009_04.pdf)
(http://www.turboresearch.com/technotes/TechNote_2009_04.pdf)
Alignment problems of ring oiled bearings can cause damage and oil leaks
Posted in Bearings | Tagged bearing, lubrication | Leave a Comment »
Tin-Copper Bondline Embrittlement
and Debonding Phenomena
October 28, 2010
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Bearings « Dr. Mel's Technical Notes Page 4 of 9
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… (http://www.turboresearch.com/engineering/casestudy.asp?id=23)
Posted in Bearings | Tagged Babbitt, bearings, bonding | Leave a Comment »
Common Problems of Extension Shafts, Oil Pumps and
Steady Rest Bearings
October 26, 2010
The extension shafts of Westinghouse large steam turbine-generators are used to drive main oil
pumps, support a thrust bearing, hold a mechanical overspeed bolt, and/or to power a fluid drive
and boiler feed pump. The design and maintenance of these extension shafts have been the sources
of many problems over the years. TRI Transmission & Bearing Corp. has designed and installed
proven solutions to these problems…read more
(http://www.turboresearch.com/technotes/TechNote20051203.pdf)
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Bearings « Dr. Mel's Technical Notes Page 5 of 9
(http://www.turboresearch.com/technotes/TechNote20051203.pdf)
New TRI Extension Shaft and Steady Rest Bearing for Westinghouse Steam Turbine-Generators
Posted in Bearings | Tagged bearings, shafts | Leave a Comment »
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 (http://www.turboresearch.com/bearings/tilt_pad_bearings.asp)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.
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Bearings « Dr. Mel's Technical Notes Page 6 of 9
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
(http://www.turboresearch.com/bearings/bearing-repair.asp) and Babbitted Bearing Repair
(http://www.turboresearch.com/bearings/bearing-repair.asp), please contact an engineer
(http://www.turboresearch.com/contactus.asp) at TRI Transmission & Bearing Corp
(http://www.turboresearch.com).
Posted in Bearings | Tagged Babbitt | 1 Comment »
Lube Oil Systems
October 19, 2010
Many bearing failures are due to poorly construction lube oil systems. TRI has built or redesigned
many lube oil systems. Read more…
(http://www.turboresearch.com/technotes/TechNote20031001.pdf)
(http://www.turboresearch.com/technotes/TechNote20031001.pdf)
A damaged bearing caused by a faulty lube oil system
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Bearings « Dr. Mel's Technical Notes Page 7 of 9
Posted in Bearings | Tagged lubrication | Leave a Comment »
Scraped Babbitt Bearings Conform to Journal
October 11, 2010
(http://turboresearch.files.wordpress.com/2010/10/scraped-journal-bearing.png)A 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.
(http://turboresearch.files.wordpress.com/2010/10/elliptical-bore-bearing.png)
TRI repairs babbitted bearings. We can centrifugally cast Babbitt or puddle the bore. We have
many years of experience in machining to tight tolerances.
Posted in Bearings | Tagged Babbitt, journal bearing, machined, oil wedge, repair, scraped,
vibration control | Leave a Comment »
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Bearings « Dr. Mel's Technical Notes Page 8 of 9
Making Rotor & Bearing Alignment Moves Easily
October 5, 2010
A large number of bearings for steam turbines have “alignment pads” mounted on the outside of
the bearing housing that seat against the bore of a pedestal or standard. Almost all of these
alignment pads have only shims that move the pads in or out on the bearing, and these are used to
make the bearing go up or down, or to the left or right. As a standard part of the alignment of a
string of turbine rotors, the shims are changed and then the alignment blocks are “scraped in” by
hand. This takes days to do, sometimes as much as a week.
TRI bearings use “alignment pads” with two types of shim packs: Type 1. standard radial shim
pack that moves the alignment pad in or out, Type 2. two tangential shim packs, one pack on each
side of the alignment pad. The use of both types of shim packs permits precise movement of the
bearing housing in any direction according to a table of changes while maintaining full contact of
the alignment pads on the pedestal bore without any hand scraping.
This feature adds cost, but it has shortened outages by several calendar days. We are told “they
pay for themselves before the turbine is on line.”
(http://www.turboresearch.com/bearings/bearings.asp)
TRI Bearings reduce the time to make rotor alignment moves
Posted in Bearings | Tagged alignment, bearing, saddle blocks | Leave a Comment »
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