BABBITT MATERIAL By Seminar Links

Introduction
Babbitt metal, also called white metal, is a soft, white
non-ferrous alloy used to provide a bearing surface.
It has properties that help reduce friction which make it a
good material to use in a plain bearing

HISTORY
• Babbitt was first created by Isaac Babbitt.
• Born July 26, 1799 in Taunton, Massachusetts, Babbitt was well known as an
inventor by trade.
• In 1839, he received a patent for a white metal alloy that showed excellent
bearing properties.
• The original formula for Babbitt's bearing metal was
• 89.3% tin
• 7.1% antimony
• 3.6% copper
• The formula is still marketed today by some manufacturers as ASTM B-23
Grade 2 Babbitt or as "Genuine Babbitt".
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PROPERTIES
• While Babbitt metal is soft and can be easily damaged when
treated improperly, and seems at first sight an unlikely candidate
for a bearing surface, its appearance is deceptive.
• The structure of the alloy is made up of small hard crystals
dispersed in a matrix of softer alloy.
• As the bearing wears the harder crystal is exposed, with the
matrix eroding somewhat to provide a path for the lubricant
between the high spots that provide the actual bearing surface

HOW BABBITT WORKS ?
• In order for any bearing to work, it must create a situation where there
is a low coefficient of friction.
• The lower the amount of friction on the rotating shaft, the easier it
turns.
• In the case of Babbitt bearings, this low coefficient of friction is
accomplished by two means.
• First, the bearing material itself (the Babbitt) has a relatively low
coefficient of friction.
• This means, even without lubrication, Babbitt bearings will have much
less friction than if a shaft was turning in other metals such as steel or
cast iron.
• However, with the addition of simple lubrication, Babbitt bearings can
have amazingly low coefficients of friction - even lower than that of ball
bearings.

Cont..
• In order to achieve this low level of friction, bearings must be properly
lubricated.
• Under ideal conditions, the motion of the rotating shaft over the babbitt
surface will draw in whatever oil may be present, which builds up a thin
film according to the laws governing the flow of fluids.
• As an example of how this works, when the shaft is still and not rotating,
the entire load of the shaft is making contact with the bearing surface.
• Ideally, at this point, there will be oil in the bearing, which will be
surrounding the shaft on either side of the contact point.

Cont..
• As the shaft begins to turn, oil from around the bearing will be
pulled under the rotating shaft until there is a wedged-shaped film
of oil completely around the shaft.
• If conditions are right and adequate lubrication is present, the
shaft will actually be floating on a thin film of oil and will not
come in contact with the bearing material, resulting in an
extremely low coefficient of friction.

Fluid Film Lubrication

Fluid Film Lubrication
• If there is not enough oil to create this film of oil, or if once
formed it breaks down due to insufficient speed, poor oil viscosity,
insufficient oil or excessive load, there is usually enough oil
present to wet the surfaces and prevent high friction coefficients.
• In this situation, it is not uncommon for the bearing to get warmer
than one would like but this will usually not cause great problems.

TYPES OF BABBITT
• The term "Babbitt" is commonly used to describe any kind of
"white metal" bearing material no matter the actual composition.
• Babbitt metals can generally be broken into two major families:
• TIN BASED
• LEAD BASED
• Tin based Babbitt is the best choice for high speed or hard to
lubricate bearings
• While, lead based works best with low speed or heavy load
bearings.

SELECTING A TYPE OF BABBITT
• To determine which bearing material would be best for your
application, the following are suggested guidelines:
Babbitt Classification LIMITS
Surface Speeds
(# of Ft/min)
LOAD
(Lbs/sq.in.)
MIN. MAX. MIN. MAX.
Tin-Based Babbitts 1,000 2,400 0 2,000
Lead Based Babbitts 100 1,000 0 500

CALCULATE SURFACE SPEED
• Surface speed of the shaft is defined as the number of feet travelled per minute
by the shaft circumferentially.
• To calculate this value for your shaft, use the following formula:
Surface Speed = Pi x D x RPM / 12
Where:
Pi = 3.1416
D = Diameter of the shaft in inches
RPM = Revolutions Per Minute
Example: Determine the surface speed of a 2-inch shaft going 1500 RPM.
3.1416 x 2 x 1500 /12 = 785 ft/min

CALCULATE BEARING LOAD
• The Load the bearing is required to carry is 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.
• For most old wood working machines, the load on the bearings is
not a major concern as the weight to surface area ratio is usually
great enough to not be an issue.
• Load comes more into play when you are using extremely heavy
shafting over long stretches, such as in line-shaft applications
where there is a lot of weight hanging on a couple of small
bearings.

Cont..
Even though load will probably not bear into the decision making on the type of
babbitt on most woodworking machines, it is still a good idea to calculate this value
to be sure.
Bearing Load = W / ID x L
Where:
W = Total weight in lbs carried by bearing (includes shafts, pulleys, cutter heads,
etc.)
ID = Inside diameter of bearing in inches
L = Length of Bearing in inches
Example: Determine the load on a bearing of a 2 inch inside diameter bearing, 4
inches long and carrying a weight of 100 lbs.
100 / 2 x 4 = 12.5 lbs/sq in

LEAD BASED BABBITT
• Generally, these compositions range from 10 to 15% antimony, up to 10%
tin and the remaining amounts being lead.
• Compared to tin babbitts, lead-base materials are less costly and
because they are softer than the tin based Babbitts, they have less
tendency to score a shaft.
• However, lead based Babbitt does not hold up well on high speed shafts
or under great loads.
• Lead based Babbitt will work fine for most light duty and low speed
applications such as a band saw arbor.
• For high speed arbors over 1000 RPM, tin based Babbitt is preferred.

TIN BASED BABBITT
• These materials are composed of 80 to 90% tin, with about 3 to 8%
copper and 4 to 14% antimony added.
• An increase in the copper or antimony increases hardness and tensile
strength and decreases ductility.
• Increasing the percentage of these hardening alloys above this range
decreases both cracking resistance and fatigue strength.
• Tin Based Babbitt is the best choice for high-speed applications (such
as jointers and planers) and hard to lubricate bearings.

TIN BASED BABBITT
• In reality, probably overkill for band saw bearings but sure would
not hurt to be safe than sorry.
• While the higher tin content does make this Babbitt more
expensive, when you consider the cost of time and labor for
pouring bearings, probably money well spent.
• Cost for tin based products is much higher than the lead based.
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RECYCLING BABBITT
• Many people who pour babbitt bearings are interested in reclaiming old
babbitt from worn bearings and re-using the material on new bearings.
• Because there is rarely enough babbitt left in the old shells to complete
a new pour, to save money, some people will be tempted to mix the old
metal with new. This is not advisable.
• Very seldom will somebody know the exact composition of their old
babbitt, much less if it is even a tin based or lead based product.
• Inevitably, when somebody tries to mix old and new Babbitt, they end up
mixing a lead alloy with tin-based babbitt.

RECYCLING BABBITT
• Mixing these two causes the low melting 63Sn/37Pb eutectic to be formed.
• This babbitt will selectively melt out of the lining and leave a “sponge” like
bearing. The 63/37 melts at 361°F and the Grade 2 babbitt does not completely
melt until 669°F.
• A premature bearing failure is the result.
• Users should not mix unknown babbitts and all pots, mixers, and ladles should be
free of lead. Even if the babbitt is a known tin-based babbitt, no more than 30%
of a pour should be recycled alloy.
• A larger amount can cause excessive dross to be trapped in the casting.

ASTM B-23 Babbitt Specifications
• The American Society for Testing and Materials (ASTM) was created in
1898 in order to standardize many materials used by engineers for
various purposes.
• This assures that products manufactured by different companies
adhere to the same standards in composition.
• Among the many standards ASTM has, different grades of Babbitt are
included.
• As such, many manufacturers of Babbitt will often provide a ASTM
Grade for different brands of Babbitt, allowing consumers to compare
one product to another knowing that its composition is similar.

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