Aluminum sliding bearing alloy

Details Aluminum sliding bearing alloy Aluminum sliding bearing alloy

2000-06-28

2001-12-11

Wyszomierski, George (Department: 1742)

Metal treatment

Stock

Aluminum base

C148S551000, C164S454000, C164S455000

Reexamination Certificate

active

06328823

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention concerns a method for manufacturing a cast product comprising an aluminum friction bearing alloy having portions of zinc, copper, magnesium, silicon and lead, as well as the product itself. A friction bearing alloy of this kind is e.g. Alzn4.5CuMgSiPb which the applicant has been producing for some time under the trade name KS 961. This friction bearing alloy is distinguished by its high stability under load. It has not been possible up to now to increase the lead content to a satisfactory degree for improving the emergency running properties, i.e. to increase resistance to scuffing, since with lead contents of more than 1 mass %, phase separation occurs in the liquid melt in the form of a precipitation of a liquid lead phase. This separation for higher lead content of the aluminum alloy friction bearing prevents formation of finely distributed lead precipitates. It has not been previously possible to produce a superior quality friction bearing material of this kind. EP 0 440 275 A1 proposes a continuous casting method for an aluminum alloy which can comprise one or more of the following components: 1 to 50 mass % lead, 3 to 50 mass % bismuth and 15 to 50 mass % indium and additionally one or more of the components: 0.1 to 20 mass % silicon, 0.1 to 20 mass % tin, 0.1 to 10 mass % zinc, 0.1 to 5 mass % magnesium, 0.1 to 5 mass % copper, 0.05 to 3 weights iron, 0.05 to 3 mass % manganese, 0.05 to 3 mass % nickel and 0.01 to 0.3 mass % titanium, wherein the billet is chilled with direct cooling water at a rate of 700 K/s. This procedure is intended to prevent formation of large-volume minority phase precipitates during the time period between arrival at the segregation temperature and solidification of the matrix metal. It has, however, turned out that direct water cooling of the solidifying billet is associated with large temporal and spatial fluctuations in the cooling rate, leading to inhomogeneities in the cast product. Process stability required for series production cannot be achieved in a reproducible fashion. Moreover, due to the very high cooling rate, there is the considerable danger that cracks are formed in the cast product.
It is therefore the underlying purpose of the present invention to improve the emergency running properties of the above-mentioned aluminum alloy friction bearing.
SUMMARY OF THE INVENTION
This object is achieved in accordance with the invention by a continuous casting method and with a continuously cast product made from aluminum friction bearing alloy having the features claimed.
The aluminum alloy friction bearing is preferably cast vertically
The cooling rate of less than 100 K/s is achieved in that the alloy or the solidifying billet is not cooled by direct chilling of the billet but by directing cooling agent onto the chilled casting mold.
In accordance with the invention, it has been determined for the first time that aluminum alloy friction bearings of the mentioned type comprising an increased lead content of 1.9 to 4.5 mass %, in particular from 2 to 4.5, from 2 to 4, from 2.5 to 4, or from 2.5 to 3.5 mass %, can be produced using the above-mentioned processing method with satisfactory quality with respect to the cast structure. The cooling rate of continuous casting is preferably between 20 and 50 K/s. The withdrawal rate of the billet is preferably between 1.5 and 2.5 mm/s.
The inventive friction bearing alloy is advantageously characterized in that 90% of the drop-shaped lead precipitates have dimensions of less than 10 &mgr;m.
It has turned out that with a lead content of more than 2.5 mass % somewhat larger lead balls of a diameter of up to approximately 20 &mgr;m are sometimes produced. These have, however, no negative effects on the strength of the friction bearing material.
Only with lead contents of approximately 3.5 mass % and more, are larger lead balls, having sizes up to a maximum of 50 &mgr;m, more frequently produced. It has, however, generally turned out that with lead contents of up to 4 mass %, and in any event, of up to 3.5 mass %, the cast structure does not show any significant stability loss.


REFERENCES:
patent: 4170469 (1979-10-01), Mori
patent: 4996025 (1991-02-01), Pratt et al.
patent: 5053286 (1991-10-01), Pratt
patent: 5453244 (1995-09-01), Tamaka et al.
patent: 5846347 (1998-12-01), Tanaka et al.
patent: W 1271. 40b 18 (1951-09-01), None
patent: 28 09 866 (1979-02-01), None
patent: 43 17 989 (1993-12-01), None
patent: 0 440 275 (1991-08-01), None
patent: WO 87 04 377 (1987-07-01), None

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