US2264252A - Lead alloy bearing metal - Google Patents

Description

Patented Nov. 25, 1941 LEAD ALLOY BEARING METAL Robert J. Shoemaker, Chicago, Ill.

No Drawing. Application May 23, 1941, Serial No. 395,539

2 Claims.

This invention relates in general to lead alloys hardened in varying degree and having characteristics making them suitable for bearings and containing an inhibitor to prevent or reduce certain deleterious results obtained from the known bearing alloys. The instant application is a continuation in part of my co-pending application Serial No. 347,149, filed July 24, 1940.

A principal object of the invention is the provision of a bearing alloy which will resist the corrosive action of the oils used in lubricating bearings, such as the bearings used in railway service generally, automobiles, Diesel engines, and the like.

Another important object of the invention is the provision of a bearing alloy which will resist the destructive effects of oxidation products which generally result from the use of lubricating oils.

It is well-known that lubricating oils frequently contain naphthenic or other acids, such as free fatty acids which are used in the oils in order to increase the film strength and/or the viscosity of the oil. These fatty acids (for example, lard oil) have been. found to dissolve a lead-base bearing metal, and in this connection it may be noted that cadmium silver, cadmium nickel and lead bronze bearing alloys generally used in the machine bearing field are likewise attacked by fatty acids. It is a further object of the instant invention to provide a bearing metal which will overcome these deleterious results.

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description, which discloses a preferred embodiment thereof.

It is also well-known that oil exerts a corrosive effect upon a bearing by dissolving the lining metal and thereby increasing the clearance between the axle or driven part and the bearing, causing not merely high running temperatures but bearing failures, and it has been found that by using the alloys of the present invention for bearings, these difliculties are almost if not entirely overcome.

In the application hereinbefore referred to, as. in this application, the primary hardening agent is calcium, and it is used in amounts sufficient so that a number of calcium-lead crystals PbaCa are produced, which give the alloy its capacity for withstanding wear and resisting impact necessary to make the alloy useable for certain types of bearings. That is, the calcium is used in such quantity that a portion of it goes into solid solution with the lead, while another portion forms the before-mentioned calcium-lead crystals.

It has been found that tin, in addition to being a secondary hardener, is a valuable inhibitor not merely of oil corrosion, but resists the deleterious efiect of naphthenic acids, sulphur and its allied compounds and free fatty acids, when used in amounts over 2.2%. Accordingly, thisinvention contemplates the use of tin in amounts of 2.2% or over in a dual capacity as a secondary hardener and an inhibitor of oil corrosion. However, it has been found that while additions of tin up to 10% increase the resistance of the lining to oil corrosion, the tin, particularly in the higher percentages, has a tendency to cause segregation of the calcium, and reduces the fatigue resistance of the alloy, as evidenced by flaking of the lining in service. It has been found that the use of tin in amounts above 3% also tends to reduce the hardness and tensile strength of the alloy, particularly when used in amounts above 5%. Furthermore, a tin content above 5% reduces the solubility of the calcium in the matrix or background to such an extent that not over 0.06% of calcium remains in the lining at the journal surface, whereas, with an alloy having a tin content of less than 2.2%, the calcium in the matrix is 0.10%.

The segregation of calcium is particularly pronounced in the case of bearings lined by a centrifugal process. The rotational effect causes more or less segregation of calcium even in alloys having a low tin content. This segregation is more pronounced as the tin content of the alloy is increased. The difliculties afore-mentioned are overcome by the inclusion in the alloy of cadmium in varying amounts.

The inclusion of cadmium in the alloy not only results in strengthening the matrix, but leaves a higher calcium content in-the lining. Furthermore, the cadmium reduces the tendency ofv the metal to annealing effects, i. e., permanent softening of the metal caused by the high temperatures developed in service.

Extensive tests have clearly established that an alloy containing approximately 0.50% calcium, 5% tin, balance substantially all lead, is highly oil corrosive resistant, and in this respect superior to the same alloy but with only 2.0% tin. However, this increase of tin content causes segregation of the calcium. This difilculty will be overcome by reducing the tin content to approximately 3% and by adding approximately 1% cadmium. The resultant alloy is practically as corrosive resistant as the 5% tin alloy without the cadmium, and at'the same time there will be considerable less segregation of calcium.

Furthermore, a cadmium content around 1% increases the annealing hardness'of the alloy. An alloy containing 0.50% calcium, 3% tin and balance substantially all lead, cast in blocks and allowed to age-harden, has a hardness of about 19 degrees Brinell. However, when these blocks have been heated for one hour at 400 degrees -mobiles, Diesel engines, and the like.

When approximately 1% of cadmium is added to the abovemixture, the hardness after exposure for one hour at 400 degrees F. will recover to about 16 degrees Brinell after age hardening in Percent Calcium 0.6 Tin 3.0 Cadmium 1.0 Lead. Balance These preferred quantities may be varied as follows:

Per cent Calcium L 0.05to 2.0 Tin 2.2 to'10.0

Cadmium 0.5 to 5.0 Lead Balance The alloy referred todiifers from the bearing alloy described and claimed in United States patents to Robert J. Shoemaker, Nos. 1,745,721; 1,808,793 and 1,916,496, in which lithium, and/or becomes too brittle, the melting point is reduced,

and the hardness of the alloy is correspondingly decreased. Where a higher degree of hardness is desired, in addition to the tin, calcium and cadmium an auxiliary hardener such as mercury is added, and in such a case. a preferred formula is as follows, percentages being by weight of the alloy, taking into account, so far as possible, oxidation and other compounding losses:

Percent Calcium. 0.075

A Tin 5.0

Mercury 0.25 Lea Balance potassium are variously'employed as hardening agents, since it has been found that those ingredients might impart a deleterious corrosive eifect'to the alloy, particularly when used in thin bearing linings, where the alloy may be only inchto inch thick, as in bearings for auto- It has also been found that potassium and lithium are rather unstable and dross off readily on remelts.

The instant invention contemplates, if desired, not merely the use of as high as 2.0 calcium, but the avoidance of the use of lithium, and/or potassium, if found desirable, without the loss ofthe desirable characteristics usually imparted to alloys thereby, in addition to any desired inhibitor. However, its use in quantities above 2.0% is not desirable, as will be hereinafter more fully pointed out.

The alloy further differs in its characteristics from the lead alloy intended particularly for cable coverings, pipes, and like articles described and claimed in United States patent to Robert J. Shoemaker, No. 1,813,324, patented July '7, 1931, in which such small quantities of tin are used as to render the alloy therein described valueless as an inhibitor of oil corrosion. Furthermore, tin is used in said patent solely as a secondary hardener and in amounts not exceeding 2.0%, preferably 1.0%.

The present invention also contemplates, where a higher degree of hardness is desired, the use of auxiliary hardeners, in addition to calcium and cadmium such as mercury. However, as mercury is poisonous and to some: extent dangerous if used in large quantities for the purpose of enhancing the hardness of the alloy, the present invention contemplates the use of other auxiliary hardeners in place of all or part of the mercury, to wit: silver, barium, strontium, copper, manganese, magnesium in quantities to be indicated.

If the calcium is used in quantities above 2.0%. the alloy when melted will be too viscous. If the tin is used in quantities above 10.0%, the alloy These preferred quantities may be varied follows:

Per cent Calcium 0.05to 2.0 Tin 2.2 to 10.0 Mercury 0.1 to 1.0 Lead Balance If the mercury is used in quantities above 1.0% y

it will volatilize.

Another preferred formula in compounding this alloy, where a higher degree of hardness is desired, is as follows:

Per cent Calcium 0.5 Tin 3.0

Mercury- 0.45 Cadmium 1.0

Lead Balance These preferred quantities may be varied as follows:

, Per cent Calcium. 0.05 to 2.0 Tin 2.2 to10.0 Mercury 0.1 to 1.0 Cadmium 0.5 to 5.0 Lead Balance The alloy of the preferred formula will have a hardness of 24 degrees Brinell, a tensile strength of 12,000 pounds, a compressive strength of 18,000 pounds per square inch and an elongation of 9 to 12% in two inches.

The use of aluminum is optional in any of the alloys herein described, but its inclusion is desirable if the alloy is to be remelted. It is an anti-drossing agent preventing oxidation of the calcium. A preferred formula in which aluminum is employed is as follows:

Per cent Calcium 0.08

Tin 4.5

Aluminum 0.05 Lead Balance These preferred quantities may be varied as follows:

These preferred quantifies may be varied as follows:

Another preferred formula in whichaluminum is employed is as follows, percentages being by weight of the alloy, taking into account, so far as possible, oxidation and other compounding losses:

Per cent Calcium 0.075 Tin 5.0 Mercury- 0.25 Aluminum 0.05 Lead Balance The use of mercury in excess of 1.0% will add considerably to the. hardness of the alloy. For

example, the hardness of the alloy made in accordance with the preferred formula given above, is about 20 degree on the Brinell scale with the metal at 700 degrees F. The hardness may be increased to 25 degrees by using mercury up to 1.0%; but the employment of mercury in this quantity is likely to result in the production of poisonous fumes in the compounding or handling of the molten alloy. To avoid this, where a higher degree of hardness is desired, it is Possible to employ, in the place of the mercury (or in ad-- dition to mercury in quantities from 0.1% to 1.0%) any of the following metals in the quantities indicated:

Per cent Silver 0.5 to 2.0 Barium 0.02 to 0.1 Strontium 0.02 to 2.0 Copper 0.05 to 1.0 Manganese 0.05 to 0.5 Magnesium 0.01 to 0.15

Another formula in compounding this alloy is as follows:

7 Per cent Calcium 0.08 Tin 4.5

Lead Balance and where a higher degree of hardness is desired, any of the following in the amount specified:

and any of the following in the amount specified:

Per cent Silver 1.0 Barium 0.05 Strontium 0.25 Copper 0.25 Manganese 0.25 Magnesium 0.05

A method of compounding alloys in accordance with the invention as follows: The lead is melted and heated to a temperature of approximately 1500 degrees F. under a covering of calcium chloride or other suitable flux. The aluminum is introduced, preferably as an alloy consisting of 50% aluminum and 50% tin by weight. Since the amount of aluminum is very small, the tin introduced in this way is practically negligible.

'The calcium is introduced as metallic calcium or as an alloy consisting preferably of approximately 5% calcium and lead by weight. The cadmium and any of the auxiliary hardeners if employed, may be introduced at this state, either as the pure metal or in the form of a tin or other desired alloy. The melt is then allowed to cool to a temperature just above the melting point of lead, say to 700 degrees F., and the calcium-chloride covering is skimmed off; or the bath can be allowed to solidify and then remelted to about 700 degrees F., whereupon, in either case, the cadmium, tin and mercury are added.

- While the application earlier herein referred to and 01 which this application is a continuation-in-part contemplates the inhibition of oil corrosion by superimposing by electrolytic or other deposition a coating or film of tin or other oil corrosion resistant metal or metal alloy on the bearing surface of th lining portion of the hearing, no claim is made herein to such deposition,

as the subject matter thereof is embodied in a separate application. It will be understood how ever, that such coating or film may advantageously be deposited on any of the alloys herein described, to facilitate the initial running in of the lining.

It. is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the recited formulae without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the formulae hereinbefore described being merely a preferred embodiment