US1975114A - Manufacture of springs - Google Patents

Description

Patented Oct. 2, 1934 I UNITED STATES 1,975,114. I MANUFACTURE-F. sramae Georg Masing, Berlin,- and Otto Dali Berlin- 'Charlottenburg, Germany.

No Drawing. Application, October 22,1931,

Serial No. 1926 570,505. In Germany May 8 Claims. (0 1. 148-32) 1 ing a small proportion of phosphorus, tin, zinc,

iron, cobalt, aluminum or the like; all as more fully hereinafter set forth and as claimed.

In a prior and copending application, Serial No. 191,263, filed May 13, 1927, of whichthe present application is a continuation in part, we have described various alloys of copper and beryllium and methods of heat treating the same. The present application is directed to methods of manufacturing springs from these alloys and to 2 the springs as articles.

The use of springs in scientific and technical instruments of high grade, such as scales, is considered bad practice in many cases. Steel springs are desirable mechanically but are subject to corrosion with resultant deterioration in accurac,

and performance. Various alloys of less corrodible properties have been suggested, and some are used. It is, however, generally found to be the case that the alloys having the best mechanical properties for springs have the least resistance to corrosion and vice versa. Corrosion resistant alloys in spring form are generally subject to fatigue. Plated steel springs, with a coating of corrosion resistant metal such as gold or chromium are not satisfactory in practice for high grade instruments.

We have found that copper-beryllium alloys containing a major proportion of copper have certain properties which fit them especially for use in making springs for scientific and commercial instruments as well as for all technical purposes in which resistance to corrosion, permanence and lack of fatigue are primary requisites. These alloys can be softened to permit mechanical working and many of them may be readily hardened to a hardness corresponding to that of good steel. In order to illustrate the adaptability of these alloys for the purpose in question, their properties and methods of production will be briefly described.

Copper-beryllium alloys may be produced by melting the two metals together in well known manner. The beryllium is conveniently added in the form of a so-called pre-alloy rich in beryllium and produced by electrolytic processes, for

example. Other metals may be added. The alloys may also be produced by simultaneous reduction of their metal salts or of their ores.

The beryllium alloys important in the present invention have a beryllium content ranging from about 0.3 up to 12 per cent. These alloys can be roughly divided into two ranges, according to their characteristics, (1) alloys from which a so-called beta modification separates from a melt and (2) alloys where the beta modification does not separate from-a melt. It may be said that the,beta modification separates upon solidification of alloys having, roughly, a beryllium content of from 5 to l2 per cent, while alloys having a lower content do not show such a sepa- 7 ration. The lower limit of the existence of the beta modification, however, is altered by the presence of other alloying materials. Thus, in some instances, the beta modification has been found to exist in compositions representing a beryllium content of as low as 3 per cent, when other materials were also present. These other materials have an action auxiliary to that of beryllium; they reinforce the action of beryllium and in their presence relatively small amounts of beryllium suflice.

We have found that these copper-beryllium alloys may be hardened to the extent necessary for making good springs by a two-step process comprising heating at an elevated temperature for some time, followed by quenching and agehardening of tempering ata lower temperature for a time sufiicient to improve their properties. But each heating stage is severally useful with these alloys under some circumstances.

7 Alloys having a beryllium content too low to permit the existence of the beta modification, that is a beryllium content roughly, below 5 per cent, are advantageously hardened by heat treating at temperatures above a certain transition point, which appears to lie at approximately 580 to 600 C. followed by ageing o age-hardening below this temperature. For example, the

alloy may be first heated at any convenient temperature between the transition point and the 0 melting point, that is advantageously above 600 0., followed by cooling. Small pieces cool with sufficient rapidity in the air while large pieces should be quenched. This may be followed by a prolonged heating at temperatures below the transition point, such as from 150 to 500 C.

This heating is continued for a time sufficient to improve the properties of the alloys or, for example, to bring a spring to the desired degree of hardness. At the lower temperatures several days may be required for this treatment, while at 300 0., two hours may be sufilcient. "In a specific example of such a heat treatment, a spring containing 97 per cent copper and 3 per cent beryllium and having an initial hardness of about 125 Brinell, after heat treatment was found to have a hardness of about 360 Brinell.

Throughout the range of the existence of the beta modification the heat treatment required to produce the maximum hardness in a spring, for example, comprises merely the first step of the above described process, namely a heating to temperatures above the transition point followed by quenching, although it is advantageous, even in this case, to follow with an ageing. The second step, namely heating below the transition point may be employed to obtain the metal in a relatively soft and mechanically workable condition suitable for fabrication. In one particular case a copper-beryllium alloy containing 6.7 per cent of beryllium was found to have a hardness of 490 in the chilled casting. Upon a prolonged heat treatment at temperatures below 580 C., the hardness of this alloy was reduced to about 240 Brinell. While in this condition the alloy was mechanically worked, being finally drawn into the form of a wire. A spiral spring was then fashioned and bent into final shape. The spring was then heated somewhat above 600 C. and quenched. The final hardness was found to be 730 Brinell.

The above described heat treatments can be applied to both cast and to mechanically worked alloys. In the case of cast alloysthe heat treatment at the higher temperatures may usually be obviated, the cooling in the casting taking the place of this treatment. A chilled casting may be merely reheated between 150 and 300 C.

For the production of alloys having intermediate properties between the extremely hard'and the malleable types there are two methods available. The first method consists in a heat treatment at intermediate temperatures, for example between 450 and 600 C. The second method consists of a prolonged heat treatment at somewhat lower temperatures. This latter represents merely the second step of. the stated two-step process. I

The first effect of a prolonged heating at temperatures below the transition point is to harden the alloy, but this is followed by the production of high ductility and toughness as well as high tensile strength, since the heating may be interrupted at any point, it is possible in this way to produce articles having, within wide limits, almost any desired properties. Definite values of hardness, ductility, toughness and strength may be produced. The production of such definite values becomes important when springs are being produced for certain technical purposes. ,Somewhat similar results to the above may be obtained by heating the alloy above 600 C. followed by a slow cooling. This method is not as conveniently controlled, however.

In one particular example of the above heat treatment, a copper-beryllium spring, with a beryllium content of 2.5 per cent was heated at 500 C. for some time. found to possess a notched bar toughness of about 15 meter-kilograms per square centimeter and a tensile strength of 75 kilograms per square millimeter. This same spring, after being treated by the two-step process, namely by heating above 600 C. and then at temperatures in the neighborhood of 450 C. gave a notched bar test tough- The spring was then ness of only 1 meter-kilogram per square centimeter and was found to have a tensile strength of 140 kilograms per square millimeter. It has been found that advantageous results with the single heating at the lowtemperatures are only obtained when the beryllium content of the alloy amounts to at least 1 per cent.

The effect of added metals upon the properties of the alloys and upon the heat treatments re quired is very striking. The addition of up to 1 per cent of phosphorus has been found to permit a considerable reduction in the amount of beryllium metal required to produce an alloy having certain improved characteristics. The time required for heat treatment is reduced by the presence of phosphorus. Other metals such as tin, aluminum, silver, zinc, iron and magnesium may be simultaneously present in the alloy' and supplement the action of beryllium in the production of improved properties.

Inone particular example of heat hardening, as carried out with a spring containing 0.25 per cent of phosphorus and about 1.5 per cent of beryllium, the spring was heated above the transition point, that is, at about 800 C., and was then quickly cooled. After cooling its hardness was found to be only Brinell. Upon subsequently tempering by heating for an hour at 350 'C., the hardness was found to have increased to 210 Brinell.

In comparison with the above, when a copperberyllium alloy of the same beryllium content but free from phosphorus is treated in the same manner, the hardness, on cooling from 800 C. is found to be about 74 Brinell and, upon heating for as long as '7 hours at 350 C., the hardness increases only about 20 Brinell. The beneficial eflects of the phosphorus addition is evident.

The beryllium content can be reduced without detriment when addition metals, such as aluminum, tin, silver and magnesium, are present in the alloy. Alloys of this type contain up to about 2.5 percent of beryllium, a somewhat larger per cent of one of these other metals and a major proportion of copper; 5 to 10 per cent of addition metal for example, produces desirable results.

We have found that the addition of metals other than copper and beryllium permits the reduction of the beryllium content to a fraction of the amount required when only copper and beryllium are employed. Since beryllium is by far the most expensive of the metallic constituents, a reduction in the quantity required is advantageous. For example, when copper only is alloyed with the beryllium at least 1 per cent of beryllium must be present to give an alloy with a high degree of hardness. But, upon the addition of from 5 to 25 per cent of one of the other metals mentioned, the beryllium content may be reduced to about 0.3 per cent to obtain the same degree of hardness.

The heat treatment required for these multimetal alloys is the same as that described previously. The two-step process is advantageous.

One of the above described alloys which is especially adapted for the manufacture of springs is that from which the beta modification separates upon solidification. This type of alloy is capable of being hardened to a point surpassing the hardness of spring steel. It may be softened to a point at which it may be worked by prolonged heating or annealing between 150 and 500 C. The alloy may then be rolled into sheet, stamped or punched and finally bent into desired form,

after which it may be readily hardened by heating above the transition point and quenching.

Alloys from which the beta modification does not separate upon solidification may be softened by heating above the transition point and quenching. Metal working operations may then be performed, after which the finished spring may be hardened by prolonged heating, at temperatures below the transition point. In both types of alloys the metal is annealed, worked and then hardened, although the steps of annealing and hardening are specifically different.

The springs produced from the described alloys may be of any desired form or shape. They may be spiral, helical or leaf springs. They are adapted for many uses for which no suitable spring material is now known. Thus, even marine instruments equipped with such springs have been found to remain reliable; the corrosion caused by the sea air appears negligible,

By the term balance substantially copper occurring in the claims, we mean that the alloy springs called for may also contain small amounts of addition metals, such as phosphorus, tin, zinc, iron, cobalt, and aluminum, these metals occurring in quantities insufficient to substantially alter the characteristic properties of the said alloys.

What we claim is:

i. A spring comprising a heat hardened copper-beryllium alloy containing from about 0.3 to 12 per cent by weight of beryllium with a remainder substantially copper, the said spring having hardness and othrr mechanical properties produced by heating said copper-beryllium alloy to temperatures below its melting point, but somewhat above a transition point lying in the neighborhood of 580 to 600 C., quenching and agehardening by prolonged heating to temperatures above 580 C. but below said transition point.

2. The spring of claim 1 wherein said copperberyllium alloy also contains from about 0.1 to 1 per cent of phosphorous.

3. A spring comprising a heat hardened copper-beryllium alloy having a beryllium content above about 0.3 per cent but below percentages at which the beta modification separates upon solidification, ranging from about 3 to 5 per cent by weight, with a balance substantially copper, the said spring having hardness and other mechanical properties produced by heating said alloy at temperatures below its melting point but above about 600 C. and age-hardening by prolonged heating at temperatures ranging from about 150 to 500 C.

4. The spring of claim 3 wherein said copperberyllium alloy also contains from about 0.1 to 1 per cent of phorphorus.

5. A spring comprising a heat hardened copper-beryllium alloy containing suflicient beryllium to cause separation of the beta modification upon solidification, ranging from about 3 to 12 per cent by weight, with a balance substantially copper, the said spring having hardness and other mechanical properties produced by heating said copper-beryllium alloy at temperatures below its melting point but above about 600 C. and quenching.

6. The spring of claim 5 wherein said copper-beryllium alloy also contains from about 0.1 to 1 per cent of phosphorus.

7. A spring comprising a heat hardened copper-beryllium alloy containing from about 0.3 105 to 12 per cent by weight of beryllium with a balance substantially copper, the said spring having hardness and other mechanical properties produced by chill-casting said copper-beryllium alloy and ag -hardening by prolonged heating at v temperatures between about 150 and 500 C.

8. The spring of claim 5 wherein said copperberyllium alloy also contains from about 0.1 to 1 per cent of phosphorus.

GEORG MASING. OTTO DAHL.