GB2046850A

GB2046850A - Diffusion barrier layer for multi-layer plain bearings with cast-on babbit metal

Info

Publication number: GB2046850A
Application number: GB8002184A
Authority: GB
Original assignee: HOHENZOLLERN HUETTENVERWALT
Current assignee: HOHENZOLLERN HUETTENVERWALT
Priority date: 1979-01-24
Filing date: 1980-01-23
Publication date: 1980-11-19
Also published as: DE2902682A1

Abstract

A plain bearing of the kind including a high-strength supporting bush, such as of steel, a resistant intermediate layer of bearing metal, particularly of lead bronze or aluminium- tin, and a bearing layer of babbit metal has a galvanically applied thin layer of iron between the intermediate layer and the layer of babbit metal to prevent the formation of a brittle intermetallic phase at the boundary face of the intermediate layer and the layer of babbit metal. Preferably the bearing includes a galvanically deposited layer of nickel or copper between the iron layer and the intermediate layer.

Description

SPECIFICATION Diffusion barrier layer for multi-layer plain bearings with cast-on babbit metal Heavy-duty plain bearings have along been constructed as multi-layer compound plain bearings because the demands which are made on a heavily loaded plain bearing are of a very complex nature and cannot be satisfied with a single material. Thus a satisfactory combination of partially contradictory properties such as carrying capacity, fatigue resistance, adaptability and dirt embedding capacity must be achieved. An additional demand on the bearing material consists in that, in the event of the bearing running very hot, the mounted shaft must not be damaged to the point where it becomes useless.

With regard to adaptability, which is understood to mean the snug fitting of the bearing seat against the shaft, and with regard to the embedding capacity for particles of dirt and metal particles contained in the lubricant, the tin- or lead-based alloys known as babbit metals occupy an outstanding position among bearing materials. Also the compatibility of the babbit metals with the shaft, even with an unhardened steel shaft, is better than with all other metallic bearing materials.

The disadvantage of the comparatively soft babbit metals lies in their low loading capacity, particularly in their low resistance to fatigue. In order to bring about an improvement here, efforts are made to produce multi-layer plain bearings with as thin a layer of babbit metal as possible because experience has shown that the fatigue resistance of such a layer is the greater the thinner this is.

In intermediate-layer bearings which consist of a strong supporting bush, for example of steel and a layer of babbit metal generally cast on by the centrifugal casting process, the layer of babbit metal cannot be made as thin as desired, however. In the event of a local wear of the babbit-metal layer, the shaft must be prevented from coming into contact with the steel supporting bush, which could lead to a total damage. This risk of local rubbing through of a thin layer of babbit metal exists, in particular, in large bearings because when the babbit metal is cast on the steel supporting bush, a distortion in shape may occur which leads to the fact that the thickness of the layer cast on is unequal after machining and very thin places occur in the layer of babbit metal.

In order to be able to make the layer of babbit metal sufficiently thin despite this distortion in shape, three-layer bearings have been developed wherein an intermediate layer of an aluminium- or copper-based resistant bearing metal, particularly a layer of lead bronze of of aluminium-tin lies between the steel supporting bush and the layer of babbit metal. In the event of wear of the layer of babbit metal the shaft continues to run on the intermediate layer of bearing metal (lead bronze or aluminium-tin) which has satisfactory sliding properties. This is generally withstood by the shaft without damage until the next bearing inspection. The covering layer of babbit metal can therefore be reduced to about 0.2 mm in such three-layer bearings.

One problem in the production and use of babbit-metal three-layer bearings, however, consists in that lead bronze or aluminium tin form a brittle intermetallic phase at the boundary face with the babbit metal during the casting of the babbit metal. Such a phase may also form, however, by slow diffusion processes during the operation of the plain bearing, when the operating temperatures can rise to 120"C.

Hitherto, no reliable means have been found of preventing the formation of such a brittle intermetallic phase between the bearing metal of the intermediate layer with a high copper content and the babbit metal. Copper forms, particularly with tin, brittle phases of the composition Cu3Sn and Cu6Sn5, but also with the cadmium which is contained in some babbit metals and which forms the phases Cu4Cd3 and Cu5Cd8.

With lead bronze there is also the risk that with babbit metals containing cadmium, a lead-tin-cadmium eutectic which melts already at about 1 50 C may form.

The same applies to babbit metal on aluminium-tin. Here the brittle intermetallic phase AlSb forms very quickly with the antimony contained in all babbit metals.

It is known that a certain remedy against the formation of brittle intermetallic layers is achieved by a layer of nickel deposited galvanically on the lead bronze or on the aluminium tin before the casting of the babbit metal.

Then it is true that no intensive formation of intermetallic phases takes place during the casting itself, but when such bearings are used at operating temperatures of only 80 or more, in the course of a prolonged time such phases form which can lead to a separation of the layer of babbit metal.

According to the invention, it has been found that in the three-layer bearings of the kind referred to, an excellent bonding of the babbit metal layer, which is also insensitive to heat, is achieved if a thin layer of iron is deposited galvanically on the intermediate layer of bearing metal, that is to say in particular on the lead bronze or on the aluminium-tin. A thickness of the layer of iron of only a few micrometres, for example 3, is sufficient. The bonding of the babbit metal then has the same or even a better quality than with direct casting on the supporting bush. The lead bronze can be cast on the metal supporting bush. The aluminium-tin can be rolled onto the metal supporting bush.

In order to improve the adhesion of the galvanically deposited iron on the lead bronze it is advisable first to nickel-plate or copperplate the lead bronze galvanically. The layer of nickel or copper likewise only needs to be a few micrometres thick.

Also with aluminium-tin a layer of iron deposited after previous nickel-plating leads to a firmer and more durable bonding of the babbit metal which also withstands the effect of the operating heat of the plain bearing.

If the layer of iron applied galvanically to the lead bronze or to the aluminium-tin is thin, for example only about 3 micrometres thick, there is no risk that on local wear of the babbit-metal layer the shaft will be damaged as is the case with two-layer bearings of steel and babbit metal. The extremely thin layer of iron is worn through by the shaft in a very short time and the latter then runs on the nickel layer and, after that is worn, on the lead bronze.

The excellent diffusion blocking effect of the iron layer with respect to the alloying elements contained in babbit metals was shown impressively by a diffusion experiment at 1 70 C. Even after a diffusion time of 500 hours, the bonding strength of the babbit metal was not reduced. The extremely high temperature of 1 70 C does not occur under operational conditions but this temperature is used by some motor manufacturers as a testing temperature to find the temperature resistance of multi-layer plain bearings.

Claims

1. A plain bearing including a highstrength supporting bush, particularly of steel, a resistant intermediate layer of bearing metal present thereon, particularly of lead bronze or aluminium-tin, and a layer of babbit metal cast on this, and including a galvanically applied thin layer of iron between the intermediate layer and the babbit metal.

2. A bearing as claimed in Claim 1, including a thin layer of nickel deposited galvanically between the iron layer and the intermediate layer.

3. A bearing as claimed in Claim 1, including a thin layer of copper deposited galvanically between the iron layer and the intermediate layer.

4. A bearing as claimed in Claim 1, substantially as herein before described.