Babbitt metal or bearing metal is any of several
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
s used for the
bearing surface
A bearing surface in mechanical engineering is the area of contact between two objects. It usually is used in reference to bolted joints and bearings, but can be applied to a wide variety of engineering applications.
On a screw the bearing area ...
in a
plain bearing
A plain bearing, or more commonly sliding contact bearing and slide bearing (in railroading sometimes called a solid bearing, journal bearing, or friction bearing), is the simplest type of bearing, comprising just a bearing surface and no rolli ...
.
The original Babbitt alloy was invented in 1839 by
Isaac Babbitt Isaac Babbitt (July 26, 1799 in Taunton, Massachusetts – May 26, 1862 in Somerville, Massachusetts) was an American inventor. In 1839, he invented a bearing made of a low-friction tin-based metal alloy, Babbitt metal, that is used extensively ...
in
Taunton,
Massachusetts, United States. He disclosed one of his alloy recipes but kept others as
trade secrets.
[Isaac Babbitt]
"Mode of making boxes for axles and gudgeons,"
U.S. patent no. 1,252 (issued: July 17, 1839). Babbitt did not patent his alloy, although he does state its formulation: "The inner parts of the boxes are to be lined with any of the harder kinds of composition known under the names of britannia metal or pewter, of which block tin is the basis. An excellent compound for this purpose I have prepared by taking about 50 parts of tin, five of antimony, and one of copper, but I do not intend to confine myself to this particular composition." Other formulations were developed later.
[.] Like other terms whose
eponymous origin is long since deemphasized (such as ''
diesel engine'' or ''
eustachian tube
In anatomy, the Eustachian tube, also known as the auditory tube or pharyngotympanic tube, is a tube that links the nasopharynx to the middle ear, of which it is also a part. In adult humans, the Eustachian tube is approximately long and in d ...
''), the term ''babbitt metal'' is frequently styled in lowercase.
[American Heritage Dictionary, 4th ed, headword ''babbitt metal''.] It is preferred over the term "
white metal", because the latter term may refer to various bearing alloys,
lead- or
tin-based alloys, or zinc die-casting metal.
Babbitt metal is most commonly used as a thin surface layer in a complex, multi-metal assembly, but its original use was as a
cast
Cast may refer to:
Music
* Cast (band), an English alternative rock band
* Cast (Mexican band), a progressive Mexican rock band
* The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis
* ''Cast'', a 2012 album by Trespassers William
...
-
in-place
In computer science, an in-place algorithm is an algorithm which transforms input using no auxiliary data structure. However, a small amount of extra storage space is allowed for auxiliary variables. The input is usually overwritten by the outpu ...
bulk bearing material. Babbitt metal is characterized by its resistance to
galling
Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. Galling is cau ...
. Babbitt metal is soft and easily damaged, which suggests that it might be unsuitable for a
bearing surface. However, its structure is made up of small hard
crystals dispersed in a softer metal, which makes it a
metal matrix composite
In materials science, a metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic (such as alumina or silicon carb ...
. As the bearing wears, the softer metal erodes somewhat, creating paths for lubricant between the hard high spots that provide the actual bearing surface. When tin is used as the softer metal, friction causes the tin to melt and function as a lubricant, protecting the bearing from wear when other lubricants are absent.
Internal combustion engines use Babbitt metal which is primarily tin-based because it can withstand cyclic loading.
Traditional Babbitt bearings
In the traditional style of a babbitt metal bearing, a
cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
pillow block is assembled as a loose fit around the shaft, with the shaft in its approximate final position. The inner face of the cast iron pillow block is often drilled to form a
key
Key or The Key may refer to:
Common meanings
* Key (cryptography), a piece of information that controls the operation of a cryptography algorithm
* Key (lock), device used to control access to places or facilities restricted by a lock
* Key (ma ...
to locate the bearing metal as it is cast into place. The shaft is coated with
soot
Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed ...
as a
release agent
A release agent (also mold release agent, release coating, or mold release coating) is a chemical used to prevent other materials from bonding to surfaces. It can provide a solution in processes involving mold release, die-cast release, plastic re ...
, the ends of the bearing are packed with
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay parti ...
, and molten metal is poured into the cavity around the shaft, initially half filling the pillow block. The bearing is stripped, and the metal trimmed back to the top surface of the pillow block. Hardened babbitt metal is
soft enough to be cut with a
knife
A knife ( : knives; from Old Norse 'knife, dirk') is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidence ...
or sharp
chisel
A chisel is a tool with a characteristically shaped cutting edge (such that wood chisels have lent part of their name to a particular Grind#Typical grinds, grind) of blade on its end, for carving or cutting a hard material such as wood, Rock (g ...
.
A
steel shim
Shim may refer to:
* Shim (spacer), a thin and often tapered or wedged piece of material
** CPU shim, a spacer for a computer heat sink
** Shim (fencing), a device used in the sport fencing
** Shim (lock pick), a tool used to bypass padlocks
* Sh ...
is inserted to protect the face of the lower bearing and to space the cap of the pillow block away from the shaft. After resealing the ends with clay, more metal is then poured to fill the cap of the pillow block through the hole in the top of the pillow block cap which will eventually be a lubrication hole.
The two halves of the bearing are then split at the shim, the
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
holes cleared of metal and oil ways are cut into the surface of the new bearing. The shaft is smeared with
engineer's blue
Engineer's blue (also known as scraping blue, Prussian blue, or simply bluing) is a highly pigmented paste used to assist in the mating of two or more components.
History
Joseph Whitworth popularized the first practical method of making accurat ...
and rotated in the bearing. When the bearing is disassembled the blue fills the hollows and is rubbed off the high spots. The high spots are scraped down, and the process repeated, until a uniform and evenly distributed pattern of blue shows when the shaft is removed. The bearing is then cleaned and lubricated, and shimmed up such that the shaft is held firmly but not binding in the bearing. The bearing is then "run in" by being run heavily lubricated at low load and revolution, completing the process of exposing the hard bearing surface. After final adjustment of the shimming, a very reliable and high
load
Load or LOAD may refer to:
Aeronautics and transportation
*Load factor (aeronautics), the ratio of the lift of an aircraft to its weight
*Passenger load factor, the ratio of revenue passenger miles to available seat miles of a particular transpo ...
capability bearing results.
Before the advent of low cost
electric motors, power was distributed through factories from a central engine via
overhead shafts running in hundreds of Babbitt bearings.
The expression a "run bearing" also derives from this style of bearing, since failure of lubrication will lead to
heat build-up due to
friction in the bearing, eventually leading to the bearing metal liquefying and running out of the pillow block.
Modern Babbitt bearings
Until the mid-1950s, poured Babbitt bearings were common in automotive applications. The Babbitt was poured into the block or caps using a form. Tin-based Babbitts were used as they could stand up to the impact loads found on the
connecting rod
A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaf ...
s and
crankshaft. The poured Babbitt bearings were kept thin. The rods and caps would have shims that could be peeled off as the Babbitt wore. Ford was known to use two .002" on each cap and Babbitt that was 86%
tin, 7%
copper, 7%
antimony (see the KRW catalogs for the Model T). Steel shims were used as the
brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...
shims used today tend to compress over time contributing to shorter bearing life. The poured Babbitt bearings commonly get over 50,000 miles of use before needing replacement. Poured Babbitt bearings are also known to fail gracefully, allowing the car to be driven for extended periods of time. The failed bearing is not likely to damage the crankshaft.
In more modern practice, the crankshaft and connecting rod big end bearings in a modern
automobile engine
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gene ...
are made of a replaceable steel shell, keyed to the bearing caps. The inner surface of the steel shell is plated with a coating of
bronze
Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids such ...
, which is in turn coated with a thin layer of Babbitt metal as the bearing surface.
The process of laying down this layer of white metal is known as Babbitting.
Alternative bearings
In many applications,
rolling-element bearings, such as
ball
A ball is a round object (usually spherical, but can sometimes be ovoid) with several uses. It is used in ball games, where the play of the game follows the state of the ball as it is hit, kicked or thrown by players. Balls can also be used fo ...
or
roller bearing
In mechanical engineering, a rolling-element bearing, also known as a rolling bearing, is a bearing which carries a load by placing rolling elements (such as balls or rollers) between two concentric, grooved rings called races. The relative m ...
s, have replaced Babbitt bearings. Though such bearings can offer a lower
coefficient of friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
*Dry friction is a force that opposes the relative lateral motion of t ...
than plain bearings, their key advantage is that they can operate reliably without a continuous pressurized supply of lubricant. Ball and roller bearings can also be used in configurations that are required to carry both
radial and
axial
Axial may refer to:
* one of the anatomical directions describing relationships in an animal body
* In geometry:
:* a geometric term of location
:* an axis of rotation
* In chemistry, referring to an axial bond
* a type of modal frame, in music
* ...
thrusts. However, rolling-element bearings lack the beneficial damping and shock-load capability provided by fluid-film bearings, such as the Babbitt.
Babbitt alloys
The science of bearing Babbitt selection
The engineering of a bearing's Babbitt lining is usually completed during the design of the machine. In selecting the proper type of Babbitt for a particular job there are a number of factors to take into consideration, the most important of which are as follows:
# Surface speed of the shaft
# Load that the bearing is required to carry
There is no doubt that if a bearing is to be highly loaded in relation to its size, a high tin alloy is desirable; whereas for much slower speed work and less heavily loaded bearings, a lead-Based Babbitt may be employed, and is far more economical.
1. Surface speed of the shaft: (The number of
feet
The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...
traveled per minute by the shaft circumferentially.)
Formula: (Pi x D x RPM) / 12 = S
Example: Determine the surface of a 2
inch diameter shaft going 1,400
revolutions per minute (RPM)
(Pi x D x RPM) / 12 = (3.1416 x 2 x 1,400) / 12 = 733.04 Ft/min
Where: Pi = 3.1416, D = Diameter of shaft, S = Surface speed of the shaft
2. Load bearing is required to carry: (the weight which is being exerted through the combined weights of the shaft and any other direct weights on the shaft and measured in
pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied t ...
.)
Formula: W / (I.D x L.O.B.) = L
Example: Determine the load on a bearing of a 2-inch I.D bearing, 5 inches long and carrying a weight of 3,100 lbs
W / (I.D x L.O.B.) = 3,100 / (2 x 5) = 310 Lbs/sq.in
Where: W = Total weight carried by bearing, I.D = Inside diameter of bearing, L.O.B = Length of Bearing, L = Load bearing required to carry
Babbitt bearing selection
While not subject to precise calculations, the following considerations must also be taken into account:
* Continuity of service
* Bonding characteristics
* Cooling facilities
* Lubrication
* Cleanliness
* Maintenance schedule for the bearing in use
* For example, a bearing in continuous use in a harsh environment without regular maintenance will require different Babbitt and lubrication than a bearing in intermittent use in a clean, light duty environment. This so-called art is really the condensation of the experience of the technician and the experience of the bearing being rebuilt.
If the bearing has performed well in use over many years, the bearing needs simply to be rebuilt to its original specification and formulation. In this case the technician's greatest concerns are:
# Bearing shell surface preparation
# Bonding characteristics of the tinning compound and the Babbitt layer and,
# Load bearing surface preparation and finish
Eco-Babbitt
Eco-Babbitt is an alloy of 90% Sn, 7% Zn, 3% Cu that is not technically a Babbitt metal. See
Solder alloys for more information on Eco-Babbitt.
References
Bibliography
* .
*
External links
*
*
{{DEFAULTSORT:Babbitt Metal
American inventions
Engine technology
Lead alloys
Tin alloys
fr:Régule