US1804883A - Alloy metal for bearings - Google Patents

Description

Patented May 12, 1931 UNITED STATES WAL'IHER MATHISIUS MARTIN W.

NEUFELD, or nnnnm-cnmor'rnunune,

- GERMANY ALLOY miru. ron BEARINGS 17o Drawing. Application filed February 24, 1927,

affected in other directions. By the employment of high percentages, such as about 1 per cent., of the different alloy'constituents, either the fluidity of the alloy or its resistance to oxidation is disadvantageously affected or its brittleness is increased to an extent which prevents its practical use as a bearing metal. It has not been found possible to raise the hardness of the metal as commercially used above 30 or at the most above 35 Brinell (ball pressure) units.

Applicants have discovered that by the addition of a number of different alloying constituents of the alkali metals and the metals of the alkaline earths, each of which is added in only small quantities, the ball pressure hardness can be extended up to 38-41 Brinell units. The alloy constituents may be used in the following proportions:

0.5% Ca 0.1% Mg 0.5% Na 0.04% A1 0.1% Ba Rest lead This specific example constitutes the sub ject matter of our German Patent 441,071, issued Feb. 21, 1927. I

Each of these constituents in thepercentage stated is of some influence on the Brinell hardness of the alloy, so that if the amount of one or another of these constituents is con- 4 siderably reduced, or if one of them is omitted, the Brinell hardness is reduced by 4 or 5 units. This alloy has a stationary point in the cooling curve which is strongly marked at 320 C. On heating to 450 C. it is very fluid and easil poured, and is not injured by heating up to 00 or 800 C. It is not brittle and is especially suited for use as a bearing metal- We have now, since making the invention -set forth in the German patent, discovered of the alloy at high temperatures.

Serial No. 170,735, and in Germany Kay 17, 19%.

that-the hardening eflect is further increased if the content of the alloy metal of the Na group is increased to between 0.6 and 0.65%.

If the Na content is raised above this upper limit, the specific hardening action of this element is essentially decreased, and the further increase of the Na content has also the drawback of producing a tendency of the alloy to corrode.

The increase of the Na content from 0.5 0.65% has, however, a very large effect on the hardening action, so that the alloy constituent barium may be omitted without reducing the'range of hardening given in the above-mentioned alloy.

Experience has also shown that definite rules must be observed as regards the ratios of the alloy constituents MgCa and Mg Al, in order to obtain a good result. vThese {ulesare found by experience to be as folows:

The Mg contentshould be about 4th to 5th of the calcium content and the Al content about half that the Mg content. I

In alloys made according to these rules, it is ,75 found that an 'Al content, which, if possible, should not be below 0.05%, exerts an extreme protection" against the tendency to oxidition t is practically proved that an alloy having a con- 30 stitution in accordance with the above-mentioned rules, with a content of 0.05% Al. can be maintained in the liquid condition for about 15 minutes at a temperature of- 800 C. without any practical waste by burning of 5 the hardening constituents. The maintenance of the alloy under these extreme conditions is probably due to a complete thin (sintered) covering of slag formed on the upper surface of the liquid metal which prevents the further entrance of oxygen or oxidizing air. Only after a long exposure to the oxidizing air at high temperature so that the waste by burning has reduced the Al content below 0.035% a rapidly increasing oxidation occurs by which all the hardening alloy Constituents are more or less burnt out of the metal.

The higher the Al content is raised, within practical limits, the greater is this protecting action of the Al, so that it is possible, 100

for example, to expose the unprotected surface of an alloy containing about .0.1%

of Al to the oxidizing action of atmospheric air at 800 C. for an hour without any diminution of the ball pressure hardness of the cast alloy.

WVith the above-mentioned rules respecting the numerical relations to be maintained between the alloy constituents AlMg and Mg-Ca it has been proved that lead-magnesium alloys with higher content in Mg have high hardening characteristics for a short time after melting and pouring, but that the alloys, in consequence of crystallization, tend to deteriorate and for that reason even with contents of Mg in which there is no substantial deterioration of the alloy, a decrease of the ball pressure hardness is observed in the course 0 time.

Practical experience has, on the other hand, shown that by maintaining the above-mentionednumerical relations between the three alloy constituents AlMg andCa, no reduction of the. ball pressure hardness occurs during a very long time.

This result may be explained by the fact that during the addition of Al to a magnesium-lead alloy, in consequence of the small afiinity of Al to lead, also on account of the relatively small content of Al and M there is a combination between Mg and l corresponding to the type Mg Al which is soluble in an excess oflead and has a hardening efiect on the latter.

imilarly, with the presence at the same time of Mg and Ca, a ternary combination between MgCa-.-lead is formed which is also soluble in an excess of lead, has a hardening action, and does-not show the tendency to qefteriorate produced by a Mg content by itse From these experimenta results and also from the rules founded upon them, it is found that the Al content of an alloy of thiskind should not be below 0.1% and correspondingly then the Mg content should not exceed 0.2%, which corresponds to a mini- .mum Ca content of 0.70.8%.

The manufacture of an alloy with 0.1% of Al presents considerable difliculties.

It has been known for a long time that lead with considerable excess of Al melted with it and strongly agitated is capable of dissolving up to 0.07% of Al. Such a content of Al can only be obtained if uneconomically large excesses of A1 are melted with the lead. In an economical alloy process, relatively high contents of Al shouligl be possible without the use of an excess of In carrying outthe alloying process in this known manner, the content does not essentially exceed 0.04%. j

It is possible by long continued melting at high temperature to raise this alloy content above the limits of about 0.08% if the Al is added in the form of a previous mixture of Al-Mg or Al-Ca. But this method of carrylng out the alloy process does not afford an economically satisfactory result. If, on the other hand, in carrying out the alloy process, that is by immersing the Al in a large lead bath, it is possible within the same apparatus to introduce metallic Mg or metallic o9. into the lead with the alloying Al, and in this way the lead takes up the Al in a very surprising and satisfactory manner. In this way in a few minutes by the use of moderate alloy temperatures, for example 500 (3., an Al content of 0.2% and more can be easily obtained. This very surprising result may be due to the fact that the heating of the metal at the moment of immersion produces a strong exothermic chemical combination Al-Mg or Al -Ga by which the temperature of the lead alloy is so greatly increased locally that the Al is easily and quickly absorbed in the lead bat-h.

From the above-mentioned considerations it is found advisable to change the alloy contents to the following: 7

(Mill-0.65% Na 0.75l.-% Ca 0.20-0.25% Mg Such an alloy has the previously mentioned important properties with respect to covering of wood charcoal or the like. .The

alloys can be exposed for a longer time at the casting temperature to the air without oxidation. It may also be recast as often as may be required without altering its properties,'an'd it is also insensitive to overheating. In consequence ofthe absence of oxidation, the percentage content in the alkali metals and metals of the alkaline earths can bemore exactly proportioned in the manufacture than formerly, since there is no considerable waste by burmng to be taken into account. This fact economizes the use of the hardening metals and ensures a much greater reliability in the compositionof the alloy.

The waste formed in the manufacture and use, in casting and also in the factory operations, can always be used again, if necessary v no after the adjustment to the right composi- 1 tion.

In the above-mentioned alloys a casting small quantities of bismuth, copper or tin, or two or more of these metals so that the castin temperature can be reduced to about 500 This effect occurs with anaddition of Bi of about 0.1% Cu of about 0.1% Sn of about 0.1%

If more than one of these metals is used, the total content should not exceed 0.1%. We claim q 1. A bearing metal consisting of lead hardened by alkali metals andmetals of the alkaline earths, containing 0.60-0.65 per cent. Na; 0.75-1. per cent. Ca; 0.20-0.25 per cent. Mg; 0.10 per cent. Al, the Pb constituting the main bulk of the alloy.

2. A lead alloy containing about 0.6% to 0.65% sodium, about 0.7% to 1.0% calcium, magnesium equal to about one-fourth to onefifth of the calcium content, aluminum equal to about half the magnesium content, lead constituting the main bulk of the alloy.

3. A lead allo containing about 0.6% to 0.65% sodium, about 0.7% to 1.0% calcium magnesium equal to about one-fourth to onefifth of the calcium content, aluminum equal to about half the magnesium content, about 0.1% of at least one of the metals bismuth, copper and tin, and lead constituting the main bulk of the alloy.

In testimony whereof we have signed our names to this specification.

PROF. ALTHER MATHESIUS. DR.-'ING. MARTIN W. NEUFELD.