US2491068A - Record stamper - Google Patents

Description

Dec. 1 3, 1949 w. M. ADAMS RECORD VSTAQPER Original Filed Jan. 28, 194*? v INVENTOR- WILLIAM M ADAMS 'IITTGF/YEYS Patented Dec. 13, 1949 UNITED STATES PATENT OFFICE RECORD STAMPER William M. Adams, Los Angeles, Calif.

Original application January 28, 1947, Serial No. 724,743. Divided and this application June 23, 1947, Serial No. 756,525

6 Claims. 1

My invention relates to phonograph record stampers, and the present invention is a division of my co-pending application, Serial No. 724,743, filed January 28, 1947.

In the manufacture of phonograph records, copper is electrolytically disposed on wax master records to form molding plates known as stampers. It is conventional practice to place the stampers or duplicates made from master stampers on confronting surfaces of steel jacketed molds. Heretofore, the stampers have had fiat margins which are clamped by marginal rings. These rings or other marginal portions of the mold were employed to space the stampers from each other a distance equal to the thickness of the phonograph record. This practice has had at least two inherent disadvantages.

First, due to the fact that the stampers are formed by electrolytic deposits, their thicknesses vary. As a result, the thickness of the completed phonograph record varies some times to an eX- cessive amount. Close thickness tolerance is of increasing importance due to the increased use of record changers.

Second, it is extremely difilcult, if not impossible, to form a perfect edge around the record. It is customary to grind the edge of the record after forming, but such grinding operation varies in depth depending upon the imperfections in the margin of the record. Unless such imperfections are superficial, the records may vary widely in diameter, a further disadvantage when the records are used in automatic record changers.

Accordingly, then, included in the objects of Second, to provide a record stamper which pro- .1:

duces a more perfect marginal finish than has heretofore been possible so that the final grinding operation is eliminated or at least reduced to a minimum.

Third, to provide a stamper which requires no change in the process of forming the record impression portions of the stamper or in the pressing equipment in which the stampers and their mold blocks are mounted.

Further objects of the invention will appear hereinafter.

In the drawings:

Figure 1 is a fragmentary elevational view of my record stamper shown in position on a mold block.

Figure 2 is an enlarged fragmentary sectional view through 2-2 of Figure 1 showing both an upper and lower stamper as they initially appear before the press in which the stampers and their mold blocks are mounted is initially operated.

Figure 3 is a similar fragmentary sectional view showin the stampers as modified when the press is brought into operation.

Figure 4 is a diagrammatical View illustrating a feature of my record stamper, e. g., that variations in thickness of the stamper do not cause variation in thickness of the completed phonograph record.

The plates which form the phonograph record surfaces are known in the art as stampers. These plates are formed by electrolytically depositing copper on a wax master record until the stamper sheet thickness is approximately to 60 thousandths of an inch. In some processes, these stampers are used in actual forming of the phonograph record, and in other processes these stampers serve as master stampers from which duplicate stampers are made and used in the phonograph record press. In either case, whether an original or duplicate stamper is employed, it has been the practice heretofore to place the stamper over a steel jacket mold block and clamp the margins of the stamper. This has been done without any preforming or shaping of the marginal portions of the stamper. The stampers are used in pairs to form opposite sides of a phonograph record and heretofore the marginal clamps or other portions of the mold blocks have served to space the stampers the requisite distance.

My improved stamper incorporates a preformed margin arranged for direct contact with the margin of a mating stamper. The process of forming the marginal portion of the stamper is set forth in detail in my copending application, Serial No. 724,743.

My improved stamper designated generally by I is provided with a central opening 2 surrounded by a record area 3 in the manner of a conventional stamper. Radially outwardly of the record forming portion 3, the stamper is provided with a beveled portion 4, preferably sloping abruptly from the record surface 3 at approximately a 45 degree angle. The height of the bevel is initially slightly greater than one-half the thickness of the record to be formed and is rounded as indicated by 5 in Figure 2. The rounded portion 5 joins an outer beveled margin 6 which slopes in the reverse direction to the beveled inner margin 4, preferably at an angle of approximately 30 degrees. The outer margin 6 continues to a point below; that is, beyond the side of the stamper opposite from the inner margin 4.

The mold block designated II on which the stamper is mounted includes a smooth flat surface l2 which backs the record portion 3 and is provided with a marginal rim [3 which fits into the annular groove or cavity defined by the inner bevel 4, curved portion 5, and outer bevel 6, as shown in Figure 2. outwardly of the rim l3, the mold-block is beveled in conformity with the 3 outer beveled portion 6 of the stamper as indicated by M. Outwardly of this beveled portion, the mold block is provided with a channel 15 which receives a mounting ring 16 having a clamping lip I! adapted to overlie the extreme periphery of the beveled portion 6.

Except for the change in the shape of its upper surface, the mold block is conventional; that is, the mold block is equipped with the usual passages for the circulation of steam and a cooling fluid, usually water. These are supplied and withdrawn through pipes l8.

It will be observed from Figure 2, that, initially, the marginal portion of the stamper overlying the rim is is not in contact therewith, but spaced slightly therefrom. When, however, the stampers are mounted in corresponding mold blocks and the press is operated to force the mold blocks together, the rounded portions are flattened until they bear against the rim [3, as shown in Figure 3. The amount of initial clearance, and, therefore, the amount of deformation occurring when the mold blocks are brought into pressure contact is, of course, exaggerated in the drawings for purposes of illustration. The initial pressing operation is preferably accomplished with the cavity defined by the record forming portions 3 of the stamper filled with record material or similar plastic. As a consequence, the internal pressure prevents any distortion of the inner margin or beveled portion 4. The width of the outer margin or beveled portion 6 between the crest of the rim [3 and the portion clamped by the ring 56 is sufficient to permit slight bending or displacement as indicated by l, which may be caused by a resultant radial force as the stampers are pressed together and by radial expansion of the stampers when heated, the coefficient expansion of the stampers being greater than the mold disk. Also by reason of the expansion of the stamper due to heat, clearance between the rims l3 and the beveled portions 4 is desirable.

By reason of the fact that the inner bevel 4 is integral with the record forming portion of the stamper, the only region in which flash may form is the region between the engaging portions of the stampers themselves. Thus, after molding a phonograph record, only an extremely thin flash need be trimmed from the record. Above and below the flash line, the finished record has a smooth beveled edge which needs no further treatment and having, inherently, a close tolerance, particularly suits the record for use in automatic record changers.

In the process of electroplating the stampers a gradual variation in thickness from one side to the other of the stamper may result. This condition is exaggerated in Figure 4. If this condition obtains, the record thickness will remain uniform as the mold blocks are free to tilt slightly with respect to each other until the portions of the stampers overlying the rims i3 engage each other.

Many otherembodiments f the invention may be resorted to without departing from the spirit of the invention.

I claim:

1. A phonograph record stamper having an integral marginal rim beveled upwardly at its radially inner side to mold one-half the edge of a phonograph record and to form an annular contact land, and beveled downwardly at its radially outer side to receive a clamping ring whereby, upon assembly of a pair of stampers, said stampers are capable of contact solely at their contact lands.

2- A single-piece phonograph record stamper having a flat circular area prepared to cast the grooves of a phonograph record; a narrow integral marginal rim offset from the surface of said circular area one-half the thickness of a finished phonograph record, said rim being beveled at its junction with said circular area to form a record edge molding shoulder, and reverse beveled at its outer periphery to form an integral clamping flange, said stamper adapted to engage a mating stamper solely by said narrow marginal rim.

3. A mold for phonograph records, comprising: a pair of record stampers having confronting circular areas prepared to mold the grooves of phonograph records, and integral mating rims adapted to bear against each other; and heated mold disks having circular areas for backing the circular record stamping areas of said stampers, and rims fitting into and backing the rims of said stampers; and means for securing said stampers by their margins to said mold disks, the rims of said stampers initially clearing the rims of said mold disks to permit radial expansion of said stampers upon application of heat and permit metal deformation of said stamper rims upon pressing said stamper rims together.

4. A mold for phonograph records as set forth in claim 4 wherein the rims of said stampers between said mold disk rims and said securing means are free to separate from said mold disks under urge of radial compression forces.

5. A mold for phonograph records, comprising: a pair of heated mold disks each having a circular central area, a circular ridge and a channel radially outwardly of said ridge, a clamping ring fitting said channel, a pair of stampers, each in sheet form, having a circular area prepared to print a side of a phonograph record and adapted to cover the central area of a mold disk, an annular rim adapted to overlie the ridge of a mold disk, and a flange adapted to fit into said channel for engagement by said clamping ring, the radially inner wall of each mold disk ridge being spaced from the corresponding wall of said stamper rim to permit radial expansion of said stamper.

6. A mold for phonograph records as set forth in claim 5 wherein each stamper between its rim and said clamping rim is free to buckle thereby to relieve radial compression loads.

WILLIAM M. ADAMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 167,527 Hart Sept. 7, 1875 326,878 Lemassena Sept. 22, 1885 1,372,992 Beadle Mar. 29, 1921 1,576,642 Bishop Mar. 16, 1926 2,258,579 Dunn Oct. 7, 1941 2,336,578 Skoning Dec. 14, 1943 2,354,241 Anderson July 25, 1944

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