Babbitt

Alloys of tin are very important. Soft solder, type metal, fusible metal, pewter, bronze, bell metal. Babbitt metal. White metal, die casting alloy, and phosphor bronze are some of the... 

Babbitt alloys Babbitt compositions Babbit-type alloys BAB dye... 

Cast babbitts Cast film Cast film process Casting... 

The principal types of scrap are battery plates and paste, drosses, skimmings, and industrial scrap such as solders, babbitts, cable sheathing, etc. 

AHoy scrap containing tin is handled by secondary smelters as part of their production of primary metals and alloys lead refineries accept solder, tin drosses, babbitt, and type metal. This type of scrap is remelted, impurities such as iron, copper, antimony, and zinc are removed, and the scrap is returned to the market as binary or ternary alloy. The dross obtained by cleaning up the scrap metal is returned to the primary refining process. 

Several ASTM methods are available for the determination of tin in tin-containing alloys such as solder, babbitt, and bronze (18). 

The term babbitt iacludes high tin ahoys (substantiahy lead-free) containing >80 wt % tin, and high lead ahoys containing >70 wt % lead and <12 wt % tin. Both have the characteristic stmcture of hard compounds ia a soft matrix, and although they contain the same or similar types of compounds, they differ ia composition and properties of the matrix. 

The lead-base babbitts ate based upon the lead—antimony—tin system, and, like the tin-base, have a stmcture of hard crystals ia a relatively soft matrix. The lead-base ahoys ate, however, mote prone to segregation, have a lower thermal conductivity than the tin-base babbitts, and ate employed genetahy as an iaexpensive substitute for the tin-base ahoys. Properly lined, however, they function satisfactorily as beatings under moderate conditions of load and speed. 

Both types of babbitt ate easily cast and can be bonded rigidly to cast iron, steel, and bton2e backiags. They perform satisfactorily when lubricated against a soft steel shaft, and occasional corrosion problems with lead babbitt can be corrected by increasing the tin content or shifting to high tin babbitt. 

Babbitt ahoys ate suitable for hundreds of types of iastahations involving the movement of machinery, eg, the main, crankshaft, connecting tod big end, camshaft, and journal bearings associated with marine propulsion, tailtoad and automotive transportation, compressors, motors, generators, blowers, fans, rolling-mill equipment, etc. 

Arsenic added ia amounts of 0.1—3% improves the properties of lead-base babbitt alloys used for beatings (see Bearing materials). Arsenic (up to 0.75%), has been added to type metal to increase hardness and castabiUty (21). Addition of arsenic (0.1%) produces a desirable fine-grain effect in electrotype metal without appreciably affecting the hardness or ductihty. Arsenic (0.5—2%) improves the sphericity of lead ammunition. Automotive body solder of the composition 92% Pb, 5.0% Sb, and 2.5% Sn, contains 0.50% arsenic (see Solders and brazing alloys). 

Babbitt Metals. High lead and tin alloys patented by Isaac Babbitt ki 1839 offer a superior combination of compatibiUty, conformabiUty, and... 

Tin babbitts are based on the tin—antimony—copper system and commonly contain about 3—8% copper and 5—8% antimony. Within a soft, sohd-solution matrix of antimony in tin are dispersed small hard particles of the intermetaUic copper—tin, Cu Sn [12019-69-1] (13). 

Despite their higher cost, tin babbitts are often preferred over lead for their excellent corrosion resistance, easy bonding, and less tendency for segregation. SAE 12 (ASTM Grade 2) is widely used in both automotive and industrial bearings (13) ASTM Grade 3 and SAE 11 also find extensive industrial use. 

Babbitt appHcation methods vary greatiy. Most high performance bearings in automotive engines use plated lead babbitt of 10% tin and about 3% copper as covered by SAE 19 and SAE 190 specifications (6). 

For high, fatigue strength in automotive bearings, a very thin layer of babbitt is desirable so that much of the load is taken on a stronger backing material. Relative improvement in fatigue resistance was found to be as follows with tin babbitt (14) ... 

SAE 780 tin, silicon, and copper alloy, and SAE 770 using tin, copper, and nickel are aluminum alloys which have been widely used in medium- and heavy-duty diesels (6). With siUcon and cadmium incorporated for improved compatibiUty, both SAE 781 and 782 are used as an 0.5 mm to 3.0 mm overlay on a steel backing with a thin electroplated babbitt overlay. Traditional 6% tin—aluminum is also used as the SAE 780 alloy with an overlay. Eleven percent siUcon alloys are used for highly loaded diesel bearings in Europe. 

Aluminum babbitt has been a U.S. alternative (6,20). On cooling this molten material, 8% lead separates from the aluminum as globules at the surface for improved antiscoring properties. More recendy, a sintered lead—alurninum containing 8.5% lead, 4% siUcon, 1.5% tin, and 0.5% copper has been developed for automotive use. 

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