US 1763303 A
Description (OCR text may contain errors)
June 10, 1930. w, F GRAHAM 1,763,303
TROLLEY WHEEL Filed Nov. 14, 1928 Inventof M41: TEE F GRAHA r Attorney sliding shoe,
w without regard to Patented June 10, 1930 UNITED STATES PATENT OFFICE WALTER F. GRAHAM,
OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY 'rnoLLEY WHEEL My invention relates to current collectors used. in moving vehicles in particular.
The object of my current collector such as a trolley wheel or and the process of manufacture.
A moving current collector such as a trolley wheel or sliding shoe by means of which current is collected from the trolley wire for use in propelling a moving vehicle, isrequired to meet very severe conditions and the life and efliciency of the presentdevices are not all that might be desired.
Wheels and shoes can be made of forged or rolled commercially pure copper and from the standpoint of conductivity alone would be the best material that could possibly be used commercially, but such devices would be very expensive to make and their life would not be sufficiently prolonged over the life of the present copper alloys to warrant the increased expense of forging the wheel of pure copper as compared with a cast alloy collector.
A wheel might be produced from cast copper but this would have its disadvantages in manufacturing and in order to overcome some of the objections to the use of pure copper in the manufacture of the wheel, ingredients might be added such as lead in .smallquantities to assist the machining and casting and also fluxes might be added, but these would have a decided detrimental effect upon the physical properties of the wheel which would render the wheel unsatisfactory for the purpose intended The material in the present wheels or shoes is ordinary brass or bronze, alloyed with lead, tin, zinc, etc., in an attempt to produce a wheel which has primarily increased hardness over that of pure copper in order to increase the life of the device, but the electrical conductivity. The present collectors are not entirely satisfactory even as to wearing quality and this is largely due to the fact that these metals and the foundry manipulation thereof produces a high electrical resistance alloy without an increase in hardness and strength to the extent desired, and in the device cause increased burning due to arcing between the that is, copper exceedingly minute form.
Application filed November 14, 1928. Serial No. 319,366.
collector and the wire as the collector slides or rolls along the-wire. invention is to provide a 7 Further, as the use of the present type of wheel or shoe continues, groove becomes pitted more and more and this causes increased arcing and the life curve of the device drops off very rapidly and also the wear upon the trolley wire is increased. It is not uncommon to find wheels in which the groove has been reduced in depth, or, in other words, metal has been collected from the trolley wire and deposited in the groove.
To reduce the amount of wear on a collector of. the sliding type, some such devices are now made of special alloy steels, hardened and polished, but such devices are of high electrical resistance and tend to are badly.
All of the above conditions are very undesirable, both for mechanical and electrical reasons.
It is my desire to construct a collector which will be an improvement over the present wheels or shoes and it is possible to do this by using in their manufacture certain alloys which have properties differing from the properties of those alloys now used in current collectors, for example, I find it is possible to use an alloy which is composed largely of copper and which contains in addition thereto, nickel up to about 8% and silicon up to about 2%, in the-approximate ratio of about 4 to 1. An alloy composed of the above elements when cast into a trolley wheel, as shown in Figs. 1 and 2, which are respectively a side view and an edge view in partial section, produces a wheel in which the-nickel and silicon may be found in different conditions; in one condition Ni Si may be precipitated in an This precipitate of Ni Si increases more particularly the hardness and structure of the composition but does not affect materially the electrical conductivity and is a non-soluble compound in a solid state, the copper forming as it were a matrix.
I find that if a wheel made of the above elements is now heated to an elevated tem perature, for example, to about 1500 to 1700 degrees F. for approximately one quarter hour and then quenched in water toroom the surface of the temperature, that such treatment renders the wheel quite uniform in structure as the nickel and silicon are uniformly dispersed and in a state of solid solution.
I also find that if a wheel so made is allowed to set for a period of time, that a change takes place in that the nickel and silicon, having a strong afiinity 'for each other, unite and form nickel silicide, N i Si, whichis a stable compound and precipitated out in the matrix. This precipitated compound I find produces a hardness in the metal which was not there when the wheel was first cast with the nickel and silicon in a state of solid solution, and I also find that the longer the wheel sets or ages, the greater the segregation and the harder the piece becomes. I further find that b heating the wheel up to a temperature of a out 450 F. for about four hours and allowing it to cool, this segregation or precipitation of the nickel sillcide or ageing can be hastened and practically all the nickel and silicon precipitated by varying the time and temperature to suit conditions.
I find that a wheel made and treated as above described, will have a Brinell hardness of about 150 and over as compared with about 80 before the ageing treatment, and the spe cific electrical resistance of the alloy per cubic centimeter will be less than in standard Wheel alloys. The normal Brinell hardness of cast copper is about 35 while that of a standard trolley wheel bronze now in use is about 60.
I further find that if after the casting has solidified and cooled to about 1500 to 1700 degrees F., is then taken from the mould and plunged in water, that the constituents will then be uniformly distributed throughout the mass and it is only necessary then to heat the mass up to hasten the ageing process as before stated, thus avoiding a reheating of the castings to 1500 to 17 00 degrees F. as before explained.
The precipitated N i Si appears to have produced the above hardness referred to by obstructing or offering resistance to the movement of the slip planes. This theory of the hardenin of metals is set forth and discussed in J eries & Archer treatise entitled Science of Metals.
y improvement in current collecting devices may be effected by the use of the said alloy of copper, nickel and silicon but I do not limit myself to its use alone as other alloying metals than nickel may be added to copper, such as chromium, cobalt and iron, and produce the same or similar. effect, name ly, to precipitate in the copper matrix in the solid state in the form of a non-soluble stable compound. The effect produced by the use of 1% to 4% of chromium in place of the nickel referred to above is similar to the effect pro duced by the use of 1% to 4% of iron in that the strength and wearing properties of a current collecting device made of such material is increased. Ferro-chromium containing 1% to 3% of iron may also be used to the extent of about 1% to 4% and like results secured as given above.
To produce a wheel or slider, a cavity is provided in a sand mould by the use of a pattern, as is Well known and common practice in the foundry art, or a permanent mould of graphite, etc., may be used. The ingredients to produce the alloy as set forth above are weighed out and brought to a fluid condition in a graphite crucible or other means and mixed. The molten alloy is then cast in the mold, producing a device in the rough. This casting is then machined and, if a wheel, the center is possibly bored to fit a bushing or axle and the groove machined to size, or the casting may first be homogenized by heating to about 1500 to 17 00 degrees F. and then quenched. and quenching, then such step orsteps are carried out after machining. After the machining and homogenizing, the casting is heated to about 450 F. for about four hours or to such other predetermined temperature for such predetermined time as to give the results desired and allowed to cool. This produces a device which has higher electrical conductivity and greater strength and hardness than the devices now in general use.
It will be seen that I have produced a wheel from a cast alloy which may be composed of copper of about 95%, nickel 4% and silicon 1%, or by the use of equivalent elements, and by proper heat treatment, the wheel will have a reasonably pure copper matrix which has uniformly precipitated therein about 4% to 5% of Ni b i which imparts to the alloy a hardness of a very considerable degree, and, therefore, a Wheel which possesses a high degree of electrical conductivity and greater hardness and strength, giving the two properties most desirable in a trolley Wheel or sliding shoe.
I find, however, that in casting a Wheel of the above alloy that practical diificulties are met with, particularly shrinkage cavities unless very large risers are used, or such difliculties can be overcome by replacing in the above alloy about 15% of the copper content with zinc, giving an alloy of copper 81%, zinc 15%, nickel 3% and silicon 1%. This alloy is subjected to the same heat treatments as given above but the conductivlty is sacrificed to a degree in order to modify the working properties of metal.
The procedure in using this modified alloy to secure a wheel casting is the same as that for the zinc-free alloy given above.
I find that I can add to the copper, nickel and silicon mixture, zinc to replace the copper to the extent of 38% of the copper, and it will be recognized by those skilled in the art that copper containing up to 38% zinc is what is knownin the art as alpha brass in If machined before heating,
I which the zinc and copper forms a solid solu- 7 tion.
In forming the above alloys of copper, nickel and silicon, either with 'or without zinc, I use about four parts of nickel to one of silicon and with this proportion the nickel and silicon combine to form the Ni Si with very little nickel or silicon uncombined.
I also find that nickel can be substituted for the zinc and secure thereby the benefits of the zinc, and this can he brought about by addinfi to the molten mass nickel in ex- 'cessfof that which is required to combine "with the silicon present, thereby leaving an amount of nickel which has notbeen used to produce the lfli sikandwhich, therefore, is held in solid solution with the copperfthe same as the zinc.
I further find that such non-soluble stable carbides, as of chromium, will produce the hardening efl'ect described above as produced by certain silicides. Those skilled in the art will recognize from ,the above disclosure that I haveproduced a current collector composed of amen-ferrous alloy of copper or brass, containing a plurality of metals having a strong afiinity for each other and precipitating out of the mass after cooling, invery fine particles in the form of a stable, non-soluble compound which will increase the hardness and strength of the copper or brass alloy and if-the said plurality of metals is nickel and silicon, the stable, non-soluble compound will be Ni Si.
Modifications may be made by those skilled in the art based on the disclosure above, but I wish to be limited only by my -claim.
I claimz- 1 X The method of manufacturlng a, current collector comprising forming a bodycasting from a molten mixture of cop er 80%, zinc 15%, nickel 4%, silicon 1%, to the shape thesame. \r' i In testimony whereofl aflix, my signature.
desired in a mold, then heating the casting to about 1500-de'g. F. .and' quench to about room temperature to uniformly distribute the elements throughout the mass and then heat the mass to about 450 deg; F. and cool slowly to precipitate the nickel and silicon as a non-soluble, stable compound uniformly distributed throughoiitthe mass to harden WALTER F. SGIRAHAM; a