Page History: Babbitt - What is Babbitt?

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Table of Contents [Hide/Show] History Types of Babbitt    Lead Based Babbitt    Tin Based Babbitt ASTM B-23 Babbitt Specifications Recycling Babbitt

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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. To determine which bearing material would be best for your application, use the following 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. One type of lead based babbitt that is still commonly available through McMaster Carr is their Stonewall brand. Composition is 80.25 percent lead, 14.75 percent antimony and 5 percent tin. 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 material. Probably best to shy away from for most machinery applications. Pouring Temperature is 650 degrees F. Prices vary buy expect to pay around $4.50 per pound.

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. An example composition of this type would be approximately 74.5 lead, 14.75 percent antimony, 10 percent tin, 0.25 percent copper and 0.5 percent arsenic. With twice as much tin as plain lead based Babbitt, as well as some copper and arsenic, this Babbitt is stronger and more suited for heavy loads. Still only recommended for low speed applications - not what you would want to use on a jointer or planer head but probably plenty adequate for a band saw with wheels only turning in the 400-500 RPM range. Prices vary but expect to pay around $6.00 per pound. For no more than it cost, this Babbitt would nearly always be preferred over plain lead based. Pouring Temperature is 700 degrees F.

Tin Based Babbitt¶

Tin Based Babbitt is the best choice for high-speed applications (such as jointers and planers) and hard to lubricate bearings. Composition is approximately 89% tin, 7.5% antimony, and 3.5% copper. 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 at approximately $16.50 per pound. Pouring Temperature is 725 degrees F.

ASTM B-23 Babbitt Specifications¶

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.

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 or even if it is a tin based or lead based product. When people try this, very often they will mix a lead alloy with new 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. A user 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.