US1603374A - Metallic shell - Google Patents

Description

Get. '19 1926.

B. BART METALLIC SHELL Original Filed Jan. 1. 1923 patented Got 19, 1926,

u stares METALLIC SHELL.

Original application filed January 11, l923ySerial'No. 612,133.

November 10, 1923.

The'invention relates toa thin metallic shell formed by the deposit 'of-metalon a glass mold and usedlas'a grinding tool, in which aspect of the disclosure this application is a division of application, Serial No. 612,133, both filed January 11, 1923.

One-of the objects of the invention is to provide a thin metal shellwhich will be an exact replica of a'pr-epared' surface of a glass mold and the surface-of which so' formed on themold shall beof fine, homogenous particles cohering toproduce a smooth continuous surface corresponding in the minutest details to the surface of the mold.

I attain this phase of the invention by depositing the metal" as fine particles on the mold surface either'by depositing astream of metal on the mold to form a thin layer asmore particularly described in'my pend ingapplication, =-Serial No. 387,974, filed June 10, 1920, or by forming on the mold a thin metal coating by electrolytic precipitation. VVhe're-thesh'ell is tobe utilized as the replaceable toolof a a grinding chuck it is preferably formed of ,electrolytically deposited copper as'descr-ibed inapplicatlon, Serial No. 612,138, due "to its'capacity to reproduce faithfully the moldsurfacein'all its details and due tojthefiffectiveness ofthe smooth surface -when formed -ofelectrochemically fdepositedcopper as a grinding The invention relates specifically toan im provement in the art of forming metallic reflectors of the type "generally known as parabolic or spherical reflectors." It is a commercial requirementof such reflectors that the curved-portions'be outlined'by a flat outstanding attaching or reinforcing 1 flange. As such reflectors must be formed on similar shaped-glass molds and as these molds must be molded andpolished tothe desired shape, the invention features a shell having the same configuration, including the flange, as the finished reflector and which can .be utilized to form or grind the. molds to shape.

Another-object ofthe invention is to provide a simple form of shell,-which can be produced in large numbers from a single master m0ld,all of'which willhave surfaces exactduplicates of-each-other andof the and which; can be constructed without deleterious action or wear on the master mold. Further featuring economy 1n construction Divided and this application f led Serial No. 673,976. a

meansof the reflector, be formed accurately with relation to the opticaXis or other point of referenceof the-reflector.

Accordingly,.another object of the present disclosure is to, provide a form of mold so that it willact to form exactly the desired configuration and dimensions of the curved or parabolic portion of the reflector, as well as its associated outstanding flange and which will insure the definitelocatingof the flange with referenceto the curved portion of-it'he reflecting surface. .Various other objects and advantages of the invention .will be'in; part obvious from 'an inspection of the accompanying-drawings and inwpart will-be more fully set forth'in the "following '--particular "description of one form of 'inecha'nism embodying my invention, .'-and' the. invention also consists in icertainunew and novel features of'con- -'st-ruction1:andcombination of parts hereinafter set'forth and claimed.

a In the drawings: Figure.- tratinga means for forming the shell by chemical-reaction on a rotating glass mold; Figure 2 is aplan view of .the mold shown in Figure 1;

Figure 13 is a view largely in diagrammatic outline'ofan electrolytic {tank illustrating a means for forming the shell by electrolyticprecipitation on a mastermol'd; Figure 4 is an; axial sectional view of a grinding chuck illustrating a use of the shell -When employed as the grindingtool ofsuch a chuck; and I I Figure 51s ft'nPGlSPQC'ElVQ view of the shell "formed by any o f'the methods herein-disclosed, and which may be used'to illustrate a ---.grinding tool. .1

correspondingsurface of "themaster mold,

fj'There is shown in Figure'l a master mold 10, thefcentral portion" ofwhich. isconvezed with 1 a forming surface 11, symmetrically 1 'isiaiview'in axial section illusiii tion indicated by the line a-O. 1n the device illustrated the mold is intended to define the reflecting surface of a parabolic reflector indicated at 12 and provided with an outstanding flange 13. However, it is obvious that the shell 12 may be used for other purposes and as an illustration of such other use it may be employed as the replaceable tool of a grinding chuck for the purpose of grinding molds such as is shown at 10.

The flange 13 of the shell, reflector or tool, is formed on the upper side of an outstanding flange 14:, which projects integrally from the curved portion of the glass mold. The top surface 15 of the flange 1 1 is contained in a plane normal to the line (1-4), that is, at right angles to the optic axis of the reflector. The flange 14 is outlined by an upstanding rim 16, which rirn provided with a plurality of over-flow recesses 17.

The glass mold is mounted for rotary movement about the axis 66"?) and for this purpose is operatively connected to a power shaft 18. A spray of metal capable of forming. a reflecting or grinding surface is directed on to the surface of the mold from a depositing apparatus indicated symbolically by the spray nozzle 19, and the nozzle 19 may represent a drip nozzle of the type disclosed in my application, Serial No. 67 3,97 5. In operation and assuming for instance that it is desired to provide a sliver faced parabolic reflector, a fine spray of a solution of silver, together with a reducing reagent of the type usually employed in such operations, is directed through the nozzle on to the glass mold adjacent its crown portion 20, and while the mold is rotating at low speed a silver film will form on the. glass mold and flow down the inclined sides of the glass mold and on to the outstanding flange. "The operation is continued until the desired thickness of metal, which is usually about one-one hundred thousandth of an inch, accumulates on top of the curved and flange portion of the glass mold. Any surplus of metallic fluid accumulating on the flange will overflow through the recesses in the rim and in this way the thickness of the flange portion of the reflector is regulated.

The thickness of the deposit on the curved portion of the mold is regulated in two ways; first, by varying the VQ OCHY of feed of the silver solution and its reducing reagent; and second, by regulating the speed of rotation of the mold itself. It is obvious that at the higher rates of rotary speed there will be developed greater centrifugal forces which will tend to whirl the more or less mobile coating toward the periphery of the mold before the silver has solidified, conversely at relatively slow speed the layer will tend to accumulate adjacent its point of application. Further, by ncreasing the proportion of reducing agent to s lver soluof an inch.

tion, the more rapid will be the formation of the metallic silver and consequently the greater will be the depth of the formation adjacent the point of applicat cn on the mold.

\Vhen the desired coating of silver is formed on the mold, it is the usual pract ce to separate the mold, with the coating so formed, from the driving parts indicated by the shaft 18 and to mount the covered mold in an electrolytic tank where the coating is backed by a layer of metal, usually copper or nickel.

The overflow recesses formed in the rib provide convenient means for securing the electrodes. Preferably the mold is not highly polished in the recesses 17 but is matted so as to provide a relatively r nigh surface. The effect is that the reduced silver solution tends to accumulate at the reces es and in this way there is formed an electric connection between the shell and the electrodes which connection is of relatively great crosssection and therefore of imp oved conductivity. In this way a positive electric connection is provided between the several electrodes and the extensive area of the silver faced flange. The portion of the glass rim between the recesses provides insulators be tween the electrodes.

When the proper thickness of electrolytically deposited backing has formed, the metallic shell is readily removed from the glass mold by subjecting the same to a heat treatment. This is most conveniently attained by spraying hot water on the back of the shell which is sufficient to expand the shell and thus readily separate the shell from the glass mold. Usually, it will be l'lcCGSSELIY to trim the resulting shell at the po'nts which fitted in the recesses, but this will be immaterial as it is not extensive.

In case it is desired to formthe shell by electrolytic precipitation the mold 10 is p0- sitioned in an electrolytic tank 18, such for instance, as a tank containing copper electrolyte 19 with copper anode plates 20 and there subjected to the usual copper precipitation by electric current admitted to the tank through leads 21. A thin bowl shaped layer 22 of copper is formed on the curved and adjacent flat faces of the mold and the electrolytic precipitation is continued until a layer of the desired thickness is provided. On the ground of economy, however, this copper layer will be extremely thin, usually an amount merely suflicient to cover the mold completely, about twenty-five thousandths Under some circumstances the copper layer is strengthened in any manner in which thin metallic shells are strengthened, and it is herein suggested that an outer layer of nickel 23 may be precipitated electrolytically on the back of the copper layer. This is done usually by transferring the lilii mold with its copper coating to a nickel depositing tank where a desired thickness of nickel is formed on the back of the copper.

The inner copper layer, hereinafter referred to as a grinding tool with or without the nickel backing, is removed from the master mold preferably by pouring warm water over the layer. The heat from the hot water causes the thin metal to expand and due to difference in co-efiicient of expansion between metal and glass the metal shell separates readily from the glass especially when the insertion of a knife between the metal layer and the glass permits the entrance of air between the glass and the coating.

The tool thus formed is placed in a grinding chuck of conventional design and one form of which is shown in outline in Figure 4:. This chuck includes a driving shaft 24 on which is fitted aniron bowl 25 which corresponds somewhat to the old grinding chuck and is of course formed approximately to shape so as to receive with a. fairly snug fit the tool for which it is intended. A tool formed as described is fastened to the iron bowl usually by means of screws 26 passed through apertures 27 in the flange 13 of the tool and into the periphery of the bowl 25. The chuck is thus equipped for operation and is designed to rotate usually at low speed about an axis of rotation indicated by the line 0cZ and which is co-incident with the line ab in so far as the tool is concerned.

While specific reference is made in this feature of the disclosure to copper as the precipitated metal it will be understood that this metal is suggested due to its relative cheapness and due to the effectiveness of forming a uniform layer of such metal, but copper is to be regarded simply as an example of one suitable metal used in forming such shells. In other cases as where a brilliant reflector is desired the use of some other metal, such for instances, as silver is sug gested. lVhen constructed for use as a grinding tool the shell is positioned in a grinding chuck of conventional design as more fully disclosed in application, Serial No. 612,133.

Having thus described my invention, I claim:

A thin metallic shell constituting a tool for grinding flanged parabolic glass molds, said tool adapted to be rotated about an axis and being symmetrical relative to said axis, said tool comprising a curved central body portion parabolic in cross section through its axis and outlined at its periphery with an integral outstanding flange, said flange being in a plane perpendicular to the axis of the parabolic central portion, one side of the tool constituting a grinding surface accurate to molecular proportions.

Signed at New York city, in the county of New York and State of New York, this 31 day of October A. D. 1923.

BLASIUS BART.

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