US1948121A - Bimetallic element - Google Patents

Description

Feb. 20, 1934. D, wg 948,121

BIuETALLIc ELEIIENT Fil ed March 23, 1932 j/l/CO/W CoPPEk AILOY L ATTORNEY. I

Patented Feb. 20, 1934 PATENT OFFICE BIDIETALLIC ELELIEN'I Howard D. Matthews,

Detroit, Mich, assignor to W. M. Chace Valve Company, Detroit, Mich, a corporation of Michigan Application March 23,

9 Claims.

This invention relates to bimetallic elements, and the object is to secure a bimetallic element particularly adaptable for low temperature applications in which the element is not heated to temperatures materially in excess of four hundred degrees Fahrenheit.

A bimetallic element for low temperature applications has heretofore been made of brass and invar secured together but brass is not suit- 10 able for hot rolling after being welded to the invar or nickel-steel side of the blade to secure the desired thinness of blade and further the brass and invar bimetal frequently takes a permanent set in service. Also, when bimetal is formed into various shapes as may be required for its specific application, a heat treatment is required to relieve the stresses set up by rolling as well as that produced in the forming operation. Invar and other nickel steel alloys require a temperature of about 200 degrees F. to age the steel at which temperature the brass element would be softened. Therefore the pres! ent practice in the manufacture of the brassinvar bimetal is to heat treat the element at about 350 degrees F., under which temperature the brass is properly aged but the nickel steel side has not been relieved of the internal stresses. As a result of such latter treatment of the brass-invar element, stresses in the nickel steel or invar side cause a change in position of the element thereby'introducing inaccuracies in action of the blade under variation in temperatures.

I have devised a bimetallic blade in which both elements thereof require or may be subjected to heat treatment at approximately the same temperature to properly agethe same and therefore by my invention I have secured a bi metal that can be properly heat treated to give greater accuracy in service and also as a resultant feature of my invention I have secured an element operable in all situations in which the brass-invar has heretofore been used and in which the stresses may be relieved by heat treatment set up by hot rolling as well as in the final forming for any specific use and a bimetal in which the element having the higher coefficient of expansion (usually termed the high side) is suitable for hot rolling after being welded to the nickel steel or invar element (usually termed the low side) thereby reducing factory costs below that involved in the production of the commonly known brass-invar bimetal.

These and various other objects and features 1932. Serial No. 600,642

of the invention and the manner in which they may be attained as is hereinafter more fully described and claimed.

The accompanying drawing is a representation of a bimetallic element showing a strip of nickel-steel alloy fused throughout its length to a similar strip of silicon copper alloy.

In the production of my new bimetallic element 1 preferably use a nickel steel alloy as has heretofore been commonly used in this art for the low side of a bimetallic blade, and it is to be noted that the nickel content of this nickel-steel element may be varied from ap-' proximately 36' per cent to approximately 42 per cent to secure the desired action of the blade for any specific application.

The invention, however, is not confined to the use of a nickel-steel alloy as the element having the lower coeflicient of expansion as any metal or composition of metal adaptable'for use as the low side may be used providing it may be aged by heat treatment at the same temperature as the high side herein described. For the high expansion side, which has heretofore been the element causing difiiculty' in manufacture of the brass-invar couple as above outlined, I use a composition consisting of the following ingredients in approximately the following percentages, viz:

This alloy is essentially pure copper with small amounts of alloying elements as silicon and tin. Cadmium may be used in the percentage of about .005 in the above composition to increase the ability of the alloy to be properly processed and incidentally to make it less corrosive and the cadmium can also be used in place of one or the other of said alloying elements. This composition has a coemcient of expansion of .000010 per degree F. corresponding very closely .to the coeflicient of expansion of commercial bronze.

The silicon content of the high expansion member of the bimetallic element is used to harden the copper and while 2 per cent silicon to 96 per cent copper has been found prefer-- able, the silicon content may be as high as about 5 per cent. The purpose of the silicon is to harden the copper. and it has been found in my experience that the subjection of the silicon-copper member of the element to heat tends to increase the hardness of thecopper as the temperature is increased and thus better adapts the same for use in conjunction with a low expansion element formed of a nickel-steel alloy having a nickel content within the range of 36 per cent to 42 per cent. In each of these two members of the thermostatic couple it is which has such physical characteristics that.

molecular change takes place and each member is thereby relieved of internal stress, inherent therein or caused. in the formation of the blade, by heat treating at the same temperature.' The tin and/or cadmium content reduces the tendency to corrode and also makes the composition more ductile and therefore more readily cut or tooledin manufacture of the blade.

It has heretofore been known that a desirable thermostatic element consisting of two metal alloys of dissimilar thermal characteristics may be formed by placing the same in a clamp or press of the proper shape and held under mechanical strain and heating the same to temperature above that to which it may be sub jected in use to relieve the element of such internal stresses as migh. afiect its operations at lower temperatures. method of formation of a bimetaliic element however is expensive due to the labor cost in. volved in placing the same in forms under mechanical stress and therefore by my invention I have reduced the cost of manufacture to a material degree and have further achieved a more satisfactory acting bimetallic element for use under certain degrees of temperatureas -molecular change has been produced in both members ofthe element in subjecting the same to a higher degree of heat subsequent to formation thereof than it will be subjected to in use and have also lessened the cost of manufacture in that I have found that for some uses the heat treatment need not necessarily be as high as will be required for such elements as are to be subjected to certain higher tempera= tures in use. Therefore by my invention and through choice of any two metals or alloys of metals adaptable to serve as the opposing members in a bimetallic element and having such physical characteristic that internal stress is relieved in both elements by heat treatment at the same temperature, I can produce a bimetallic blade that in its field of service is unaffected in its accuracy of operation due to the presence of internal strains in either member of the couple.

The bimetal is. formed of sheets of siliconcopper alloy and nickel-steel welded or otherwise secured together to form a couple inseparable by heat to which the blade is subjected in use and provides a blade that is as sensitive to temperature change as is the usual brassinvar bimetal element commonly known to the previously stated to relieve the internal stresses resulting from the hot rolling to the. desired thickness in manufacture subsequent to the Such previous known welding of the sheets together and to also relieve stresses .set up by any forming operations to which. the element may be subjected. I therefore, by use of the herein specified composition for the high side in conjunction with any of the metals now used in conjunction with brass for the "low side", have secured a more highly efiicient bimetal for use within a temperature range up to approximately 400 degrees F. that avoids troubles arising in the use of brass and nickel steel or invar couple due to the metal having been relieved of the internal stresses caused by rolling or forming operation and therefore avoid the inaccuracies in operation of previously known bimetallic elements commonly provided for use within the temperature range stated.

It is also to be noted that, while I have above dwelt upon the characteristics of my improved bimetal for hot rolling, this metal may be cold rolled without any danger of cracking. Brass becomes brittle with cold rolling and also cannot be hot rolled and my new bimetal therefore is superior to the previously well known brassinvar bimetal in that it may be either cold; rolled or hot rolled as may be desired.

It is also to be noted that a blade formed of silicon-copper and nickel-steel couple has a much greater activity than the brass invar or Monel metal nickel-steel couple of the prior art and is less costly than the Monel metal high sides often used. This higher degree of activity is of great importance in a bimetallic element for use in what is termed the low temperature held and, in addition to its characteristic of responding to heat treatment in relief of internal stress to approximately the same degree as the nickel-steel alloy with which it is associated, has the further characteristic of not thinning out so rapidly in the rolling process as the brass or bronze elements heretofore used in bimetal blades for low temperature work.

Having thus briefly described my invention, what I claim and desire to secure by Letters Patent of the United States is l. A bimetallic element comprising two elements of dissimilar thermal characteristics, one of said elements being a silicon-copper alloy containing 2 per cent silicon and 96 per cent copper and having a comparatively high coeificient of expansion and the other a nickel-steel alloy having a comparatively low coefllcient of expansion, the silicon-copper alloy being directly welded .to the nickel-steel alloy and hav ing the characteristic of responding to heat treatment for relief of internal stresses developed in the formation of the element approximately the same as the nickel-steel alloy.

2. A bimetallic blade comprising two metal members of dissimilar thermal characteristics welded together andhot rolled to thefldesired thickness, the element of higher thermal characteristic containing about 2 per cent silicon and 96 per cent copper and the element of lower thermal characteristic being a nickel-steel alloy having a nickel contentwithin the range of from 36 per cent to 42 per cent, both said elements responding practically alike to heat treatment for relieving internal stresses developed in manufacture of the blade, the element of higher thermal characteristic having a coeflicient of expansion of approximately .000010 per degree Fahrenheit and the other having a lower coefllcient of expansion.

3. A heat responsive device comprising two Silicon 2 per cent Tin 1 /2 per cent Copper 96 per cent Cadmium Approximately of 1 per cent and the other element being a nickel-steel alloy having a nickel content within the range of from 36 per cent to 42 per cent. 5. A heat responsive device comprising two metallic elements fused together, one of the elements being an alloy of approximately the following composition, viz:

Silicon 2 per cent Tin Approximately 1 per cent Copper 96 per cent Cadmium Approximately of 1 per cent and the other element being a nickel-steel alloy containing approximately 36 per cent nickel.

6. A heat responsive device comprising two.

metallic elements fused together-and of a relative thickness greater than the thickness desired in the final element, then submitting the same to a rolling operation to reduce the same to the desired final thickness, one of the elements being an alloy of approximately the following composition:

Silimn 2 per cent Tin 2 per cent Copper 96 per cent and having a coeflicient'of expansion of approximately .000010, the other element being a nickelsteel alloy containing approximately 36 per cent nickel and having a lower coeflicient of expansion. I

, 1,948,191 metallic elements, one 01 the elements 'being an I. A heat responsive device comprising two metallic elements of different coefllcients of expansion Iused together, the element having the higher coemcient of expansion consisting of approximately 96 per cent copper and 4 per cent of alloying elements such as of 1 per cent tin, 2 per cent silicon and cadmium to secure ductility and non-corrosiveness oi the element, and theelement having the lower coeflicient 0! expansion being a nickel-steel alloy having a nickel content within the range ofapproximately 36 to 42 per cent.

8. A bimetallic element comprising two metal members of dissimilar thermal characteristics welded together and adapted to act as a unit in response to temperature change, the member of higher coefiicient of expansion being a siliconcopper alloy substantially as specified and the element of lower coeflicient of expansion being a nickel-steel alloy substantially as specified, each of the said members having such physical characteristics that internal molecular stress existent therein is relieved on subjection to a temperature of approximately 700 degrees F. whereby the unit, subsequent to its formation, may 100 be heat treated to free the same from internal strains affecting operation thereof as a unit at temperatures below 700 degrees F.

9. A bimetallic element comprising two metal members of dissimilar thermal characteristics 5 secured together and adapted to act as a unit in response to variations in temperature within the range below that productive of molecular change, both said members having such physical characteristic that molecular change takes 0 place thereinand each is relieved of internal stress while in a mechanically unrestrained state through subjection to a temperature. higher than that to which it is to be subjected in use, said element subsequent to being formed being 1 5 subjected to the high temperature whereby the heat treated element is freed of internal strains tending to detrimentally affect operation thereoi at lower temperatures. 4

, 12o HOWARD n, MATTHEWS.

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