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Table of Contents [Hide/Show] History Types of Babbitt    Selecting a Type of Babbitt       Calculate Surface Speed       Calculate Bearing Load    Lead Based Babbitt    Tin Based Babbitt Recycling Babbitt ASTM B-23 Babbitt Specifications

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History¶

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.

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 and 3.6% copper and that formula is still marketed today by some manufacturers as "Genuine Babbitt".

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.

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 or lead based. Tin based Babbitt is the best choice for high speed or hard to lubricate bearings whiel 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, use 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 traveled 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.

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¶

Lead Based Babbitt is the least expensive babbitt that you can buy. It is also the softest type of Babbitt. While this material would work fine for light duty and low speed applications such as a band saw arbor, for just a little more money, you can get a much better quality tin based material.

Within the category of the lead based babbitts, there are several types - such as a lead based coppered babbitt. While still classified as a lead based babbitt, this mid-grade Babbitt product, it is generally considered a better material than plain lead based babbitt because of the alloy mix.

Tin Based Babbitt¶

Tin Based Babbitt is the best choice for high-speed applications (such as jointers and planers) and hard to lubricate bearings. 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.

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. 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, allows consumers to compare one product to another knowing that its composition is similar.

While the number of grades detailed by ASTM has changed over the years with fewer grades being standard today than before 1959, here are the current standards for Babbitt metal by ASTM.

ASTM Babbitt Analysis Chart
ASTM B-23

Chemical Composition, %	Tin Base Babbitt Grades ALLOY NUMBER (GRADE)
	1	2	3	11
	UNS-L13910	UNS-L13890	UNS-L13840	UNS-L13870
Tin	90.0-92.0	88.0-90.0	83.0-85.0	86.0-89.0
Antimony	4.0-5.0	7.0-8.0	7.5-8.5	6.0-7.5
Lead	0.35	0.35	0.35	0.50
Copper	4.0-5.0	3.0-4.0	7.5-8.5	5.0-6.5
Iron	0.08	0.08	0.08	0.08
Arsenic	0.10	0.10	0.10	0.10
Bismuth	0.08	0.08	0.08	0.08
Zinc	0.005	0.005	0.005	0.005
Aluminum	0.005	0.005	0.005	0.005
Cadmium	0.05	0.05	0.05	0.05
Total named elements, min	99.80	99.80	99.80	99.80

Chemical Composition, %	Lead Base Babbitt  ALLOY NUMBER (GRADE)
	7	8	13	15
	UNS-L53585	UNS-L53565	UNS-L53346	UNS-L53620
Tin	9.3-10.7	4.5-5.5	5.5-6.5	0.8-1.2
Antimony	14.0-16.0	14.0-16.0	9.5-10.5	14.5-17.5
Lead	remainder*	remainder*	remainder*	remainder*
Copper	0.50	0.50	0.50	0.6
Iron	0.10	0.10	0.10	0.10
Arsenic	0.30-0.60	0.30-0.60	0.25	0.8-1.4
Bismuth	0.10	0.10	0.10	0.10
Zinc	0.005	0.005	0.005	0.005
Aluminum	0.005	0.005	0.005	0.005
Cadmium	0.05	0.05	0.05	0.05
Total named elements, min

All values not given as ranges are maximum unless shown otherwise.
Alloy Number 9 was discontinued and numbers 4,5,6,10,11,12,16, and 19 were discontinued in 1959.
A new number 11, similar to SAE Grade 11, was added in 1966.