US2216539A - Process for surfacing sheets of zinc or copper or other metals - Google Patents

Description

Oct. 1,1940; 1-. J. MASSE 2,216,539

PROCESS FOR SURFACING SHEETS-OF ZINC 0R COPPER OR OTHER IETALS Filed July 28. 1939 I.\\'E.\'TUR. THOMAS JEROME MASSE \TTORNIJYS Patented Oct. 1, 1940 UNITED STATES PATENT-OFFICE! PROCESS FOR SURFACING SHEETS OF ZINC OR- GOPPER OR OTHER METALS Thomas Jerome Masse, Alexandria, near Sydney, New South Wales, Australia, assignor to The Edes Manufacturing Company,

.Plymouth,

Mass, a, corporation of Massachusetts Application July 28, 1939, Serial No. 286,954

' In Australia May 12, 1936 9 Claims. (Cl. 29-148) This invention relates to a new and useful process for surfacing sheets of zinc, copper or other metal, and particularly to a process for imparting to 'metal sheets a highly uniform thickness and surface finish. The invention finds a valuable field of use in the manufacture of photo-engraving plates of zinc, copper and the like, which must possess high standards of accuracy'in thickness, flatness and surface finish o in order to be etched most satisfactorily and to permit optimumprinting results and optimum on a about a horizontal axis and beneath which the sheets are moved back and forth while an abrasive powder is distributed onto the sheets.

In the use of this conventional process, faults in thesurface of the cast slabs are accentuated in the rolling operations-surface spots and 80 streaks being produced on the rolled sheets by the elongation of pit holes or other structural irregularities-so that the slabs must be cast ,with particular care in order to produce good surfaces on them. Irregularities in the thickness of the rolled sheets are inevitable because a uniform temperature condition cannot be held throughout the sheets during the rolling operations. Given a certain pressure on the mill rolls, the reduction of thickness effected by the rolls 0 will vary according to the hardness of the sheet, which varies with the temperature of the sheet, and this temperature is rarely, if ever, uniform over the whole area of a sheet throughout a pass. a

After the sheets have been rolled to approx-- imatelythe required thickness, they are subjected to the grinding operations for the purpose of cutting away surface defects and exposing the sub-surface metal; These grinding operations,

however, give no assurance of a truly plane surface because the felt pads on the grinding rolls have a certain flexibility and are incapable of eliminating excess thickness and wave defectstimes introduce further non-uniformity in the surface of thesheets, because the grinding pads may be worn at some spots more than at others,

resulting in an inequality of pressure on the sheets, or the distributionof grinding power over '5' the sheet may not-be uniform and may cause more metal to be ground away from some parts of the sheet surface than from other parts.

Where the surface defects on the sheets are such that 'a considerable depth of metal must 1 be ground away in order to remove them, coarse grinding powder must be used, and then further grinding with finerspowd'er becomes necessary to remove scratches and roughnesses which resuit from the coarse grinding. A high degree of 5 skill is required in thesegrinding operations to bring the sheets withinapermitted thicknesstolerance andxto produce a surface that is not marred by defects, and the operations are timeconsuming and therefore costly. Even when the go.

grinding is carried out with extreme 'care the sheets are rarely finished quite fiat and uniform in thickness, .and pits and dentsfrequently remain in their surface. To reduce these defects, tapping up of the metal is commonly resorted to,- 25

I with the risk that the presence of tapping-up I marks may affect the trade value of the sheet. For the above-mentioned and other reasons it is a practical impossibility, when using the known process, 'to produce sheets having a uniform a) smooth surface'texture and a very high degree of accuracy in their flatness or thickness. In commercial production the thickness of the sheets varies as much as three thousandthsof I an inch, even when a high degree of care has been exercised in the manufacturing operations,

and either this or the presence of surfacedefects which would affect their etching qualities causes many; of the sheets to be discardedby discriminating users. When etched plates are used 0 on a printing press for direct printing work ofhigh quality, thickness variations of as much as one thousandth of an inch entail a great deal of work in shimming up the plates to align their printing surfaces evenly. .A difference of more 45" than a few ten-thousandths of an inchin the level of the printingsurfa'ces causes a substantialdiiference in the weight and appearance of the print.

These shortcomings of existing practice have long been recognized, but no solution of ,them has beenprovided prior to the present invention. It is therefore an object of the present invention to provide a new process for producing metal sheets which avoids such difliculties and permits the commercial production of metal sheets having surfaces of hitherto unattained flatness and having thicknesses that are uniform within an unprecedented small range of tolerance.

Another object of the invention is to produce sheets of uniform flatness and thickness whose surfaces have a uniform smooth finish and are free from defects that would cause trouble in etching operations.

A further object of the invention is to render the commercial production of ensravers sheets and the like more economical and more efllcient than heretofore.

According to the present invention, I have found that the above mentioned and other desirable objects and advantages may be attained by a new process in which cast slabs of copper, zinc or other metal are rolled or otherwise worked to a thickness slightly greater than the desired thickness of the finished sheets, after which the rolled sheets are subjected to a novel planing operation to remove surface metal and expose sub-surface metal while reducing the sheets to an exceedingly uniform thickness, after which the planed sheets are ground andpolished in a novel operation to remove objectionable ridges,

streaks or other minute irregularities from their planed surfaces and to produce finished sheets having the desired thickness uniformity and fiatness and a new kind of surface finish.

In the accompanying drawing, Figures 1 to 4, inclusive, illustrate diagrammatically the several steps of the process by which molten zinc, copper or other non-ferrous metal is converted into finished photo-engraving sheets of improved quality; Figures la, 20, 3a and 4a illustrate characteristics ofthe products resulting from the respective process steps; and Figures 2b, 3b, and 4b are photo-macrographs which show surface characteristics of the metal sheets after the rolling, planing and grinding operations; respectively.

Figure 2) may be carried out in any suitablemanner, using ordinary rolling equipment, sinceit is not necessary to ensure that the sheets leave the rolling mill with a substantially uniform thickness and a smooth surface. The slabs are rolled into sheets of a thickness somewhat greater than the desired thickness of the finished sheets. Figure 2a illustrates one of the rolled sheets B and indicates the presence of longitudinal streaks on its surface. The surface appearance and streaks'are shown more fully in Figure, 2b. After the rolling operations the surplus metal is completely removed from the surface of the rolled sheets by the planing operation,- in such manner that surface defects and variations of thickness which remain after the rolling operations are eliminated and clean, fine-grained sub- -surface metal is left exposed for the final grinding and finishing operations.

The processof planing or machining the surface of the metal sheets, in itself, constitutes an important novel feature of the invention. (See Figure 3.) In this operation rolled sheet B is placed and held securely onto a trued upper surface of a carriage l2, and the sheet is traversed by the carriage in a true linear path with its entire surface exposed to the action of one ormore fast-moving cutting tools T. The cutting tool is preferably a diamond cutter and is revolved at a very high speed in a true circular path overlying the path of the sheet. The path of the tool includes a minor circular arc which and the carriage surface is concaved transversely,

to correspond precisely to the swath of the tool, by machining the carriage surface with its own cooperating tool while .moving the tool at approximately the usual cutting speed. Figure 3 illustrates this planing operation diagrammati cally, the concavity of the carriage surface and the tilting of the cutting tool axis being indicated to an exaggerated extent. The apparatus employed for this operation is fully disclosed and claimed in my aforesaid copending application, and certain additional features or improvements of such apparatus are disclosed in my copending application, Serial No. 386,952, filed July 28, 1939.

The depth of the cutting swathof the tool into the sheet is adjusted so that the tip of the tool removes skin metal from the surface of the sheet and leaves a minute arcuate furrow extend-1 ing entirely across the sheet, the thickness of the sheet at the bottom of this furrow being substantially identical with the desired thickness of the planed sheet. With the cutting tool so adjusted and revolving at the desired high speed, the sheet or sheets to be planed are traversed at a uniform rate through the swath of the diamond, and the rate of-movement of the sheet is controlled so that successive swaths of the diamond overlap.

By this planing operation surplus metal is quickly removed from the entire surface of the sheet, and the surface of the sheet is planed to a flatness or uniformity which conforms to an exact standard within a tolerance of five ten-thousandths (.0005) of an inch or less. At the same time, all surface defects and variations of surface working of the sheets are eliminated.

In carrying out the planing of the sheets it is important to employ diamonds as the cutting tool,

since no other hard material will endure the severe conditions of operation and continue to make a uniform cut in the sheets for'a practical period of use. Sapphire cutters will operate quite well, though riskily, for a limited period of time, but they do not hold their edge sufficiently long for practical purposes. It is also quite important that the cutting tool or tools be moved at a speed The planing operation, in the case of v'vellrolled zincfand copper sheets, is ordinarily carried height which result from the casting, rolling or I out so as to remove at least one thousandth (.001) of an inch of metal from the surface at the thinnest part of the sheet. A well-rolled sheet usually does not vary more than two though the depth of out be very small minute ridges are left on the surface of the sheets between successive swaths of the diamond. Figure 3a seeks to illustrate the appearance of a sheet C after the casting, rolling and diamond-cutting, or planing, operations, although in actual appearance the ridges are not nearly so prominent. Figure 3b is afphoto-macrograph of part of the sheet surface. The ridges are believed to be produced under the heel of the cutter, not on the sides of the cut. They are so small that they form a light grating which produces a rainbow effect when exposed to light. Nevertheless, the ridges would impair the value of the sheets for photo-engraving work, and "it is important to re-'- move all ridges or other surface irregularities that would interfere with the quality of the photoengraving. This is accomplished by the final step of the process, in which the surface of-the planed sheet is subjected to a light grinding and polishing operation to give it a smooth finish throughout its area.

The light grinding or finishing operation may be carried out according to conventional methods, using yieldable grinding pads" of felt or the like and'a fine grinding powder for erasing the minute ridges fromthe sheets. Since the sheets are uniform in thickness and there is no problem of removing substantial amounts of metal, the use of very coarse abrasive is notnecessary. For assurance of uniform and satisfactory results, however, and to enable the finishing operations to be performed with maximum efficiency, I prefer to employ a novel method and apparatus for grinding or finishing the sheets, such as disclosed and claimed in my copending application, Serial No.

286,953, filed July 28, 1939. See, Figure 4 for a diagrammatic illustration.

According to that method, a planed sheet such as indicated at Cis held on a table 20 which moves back and forth in a fixed path beneath abrasive-- surfaced pads 22 which rotate at high speeds about an axis at right angles to the sheets, and the pads are simultaneously moved back and forth across the sheets in another fixed path so that the circular grinding swaths of the pads overlap and cover the entire surface of the sheets uniformly. The pads are held onto the sheets under constant pressure during their rotation. Throughout the operation, a continuous stream of kerosene or other suitable flushing liquid L is flooded onto the surface of the sheets from a point adjacent the axis of rotation of the pads. This liquid, aided by centrifugal force from the rapid rotationof the pads, sweeps through the path of the pads and is over-run by them so that metal particles removed from the sheet are picked up by the liquid, and the liquid is then swept .away from the path of the pads and carries with liq-substantially all of the free metal and grit that is removed during the grinding. The elimination of free metal immediately after its removal from the sheets prevents the pads from becoming clogged with metal and from grinding irregularly or scratching the sheets. In this way the grinding action of the pads is kept uniform, the surface of the sheets is protected against scratches or othermarring, and the minute ridges on the sheets are erased efllciently. The operation may be completed within a period of only a few minutes. The finished product D, as indicatedby the reduced photograph of Figure 4a, has a surface appearance characterized by the apparent presence of a broad zigzag line running from one end to the other end of the sheet and covering most of its breadth. This characteristic appearance is caused by light reflection from certain of the scratch intersections produced by the last swath of the abrasive papers over the sheet. The

actual surfacefinish is .shown by the photomacrograph of Figure 4b, from which it is evident that the surface is composed of an infinite number of tiny scratch lines which intersect in all directions. This finish isof advantage in the use of; the product for photo-engraving, as the tiny intersecting scratch lines assist in holding photo-sensitive enamel evenly on plates cut from the finished sheets.

In making a heavy cut from the surface of a sheet in the machine cutting operation a plurality of diamonds may be used to advantage, the

diamonds being arranged on the tool head of the cutting machine to keep the latter dynamically balanced. Two, or even four, diamond tools may be used; When using two diamonds, one of them may serve as a finishing tool, to improve the surfaceof the planed sheet by removing a minute film of irregular or strain-hardened material left diamond is tilted so that its backward point does the cutting work. When aplurality of diamonds I are used, their cutting paths are spaced slightly eighths of an inch in order that the swath of the higher'diamond will precede and be followed by the swath of the diamond set at a lower elevation.

The diameter of the swath of the diamond tools is somewhat greater than the width of the sheet or sheets to'be planed, so that a cut is obtained in each revolution of the tool which extends across the entire surface of the sheet, from edge to edge, and so that the backward sweep of the tool does not contact the sheet.

The diamond cutters are preferably ground to a truncated pyramid shape with their faces either turned or faceted. The face of the diamonds may be raked about 6 to 8, although this setting is not critical. The diamond tools apparently give satisfactory planing results even though their lips be more or less chipped.

.Before effecting a planing operation, the cutting tools having been adjusted to the desired feet per minute to the diamond tools, for example, a speed of the order of 8000 feet per special precautions to obtain a smooth surface I minute. With the machine ready for the planing operation, the carriage is slowly traversed beneath the path of the diamonds, and the rate of movement of the carriage is controlled so that successive cutting swaths of the diamonds into the surface of the sheet will overlap. A single pass of the sheet beneath the swath of the tools completes the planing operation, and the sheet is removed from the carriage surface with a thickness that is uniform within.a tolerance of less than five ten-thousandths (.0005) of an inch. Successive sheets subjected to the same planing operation possess a thickness which is almost precisely identical. After the sheets have been planed in this manner they are ready for the final grinding and finishing operation, as hereinabove described.

An important advantage of the planing operation herein disclosed is that it does not require attention by an operator during the planing, and the accuracy of the product is not dependent upon the skill of an operator in passing sheets beneath grinding pads and distributing grinding powder on them, as in the case of the conventional process. The diamonds used according to the present operation show negligible wear and remain sharp for an indefinitely long time. The uniformity of the planed sheets does not vary during the life of the diamonds.

The process of the present application, among other advantages, greatly increases the efficiency and economy of manufacturing operations in the production of metal sheets having commercially perfect surface. The casting of the metal into slabs is rendered more economical than heretofore because it may be accomplished without on the slabs. The working of the slabs into rolled sheets may be'accomplished more economically and more rapidly because the sheets leaving the rolling mill are slightly thicker than required heretofore, and because it is unnecessary to roll them to as uniform a thickness as possible. The rolling can be carried out with less expensive equipment. The planing of the sheets and the subsequent light grinding of their planed surfaces to impart a uniform smooth finish are effected with important economies because the number of machine units required for a given out-put of finished sheets is greatly reduced, because careful attention to the operation of the machine is not necessary in order to secure products of the desired quality and because there is much less waste of metal and much less loss from the discarding of unsatisfactory sheets than in the case of the conventional process.' In addition to all of these advantages, the present process produces a new product having a quality and utility impossible to attain with the conventional process.

I claim:

1. A process for producing metal sheets of highly uniform gauge and smooth surface finish which comprises rolling cast slabs of the metal into sheets having a thickness slightly in excess of the desired final thickness, machine cutting the excess metal from a surface of each rolled sheet to expose sub-surface'metal and impart a highly uniform thickness to the sheet, said cutting operation leaving minute ridges on the sheet surface, and thereafter grinding the machine cut surface to produce a smooth finish free from objectionable irregularities.

2. A process for producing metal sheets of highly uniform ga e and smooth surface finish which comprisesrolling cast slabs of the metal into sheets having a thickness slightly in excess of the desired final thickness, reducing each rolled sheet to the desired thickness by subjecting an entire surface thereof to overlapping swaths of a, cutting tool moving at high speed in a fixed circular path at a level established to remove said excess thickness, and thereafter erasing minute irregularities from the aforesaid surface by light grinding.

3. A process for producing metal sheets of highly uniform gauge and smooth surface finish which comprises working castslabs of the metal into sheets having 'a thickness slightly in excess of the desired final thickness, placing and holding each sheet on a trued surface of a carriage that is movable in a true linear path, moving the carriage at a slow rate in its path and so traversing the sheet thereon through the cutting path of a fast moving cutting tool while revolving the tool at high speed in a fixed circular path including a minor circular are which extends truly parallel to the surface of the carriage and across the sheet at a level below the sheet surface, thereby machining the excess thickness from the sheet, converting the same into a product of highly uniform thickness and producing on its surface minute ridges, and thereafter subjecting the machined surface of the sheet to a light grinding operation to erase minute ridges therefrom. 1

4. A process for producing engravers plates of zinc, copper or other non-ferrous metal having a highly uniform thickness which comprises securing a rolled sheet of the metal onto a trued surface of a carriage with 'an entire surface of the sheet exposed, revolving a cutting tool at a speed of at least several thousand feet per minute in a fixed path above said carriage, said path including a minor circular arc, of greater diameter than the width of the sheet, which extends truly parallel to the carriage surface at a spacing therefrom corresponding to the desired thickness of the sheets, and moving said carriage and sheet in a fixed linear path through the arcuate sweep of the tool at a rate such that successive swaths of the tool overlap.

5. A process for producing metal shets of highly uniform. thickness which comprises securing a sheet of the metal in close contact with a trued carriage surface that is straight in longitudinal direction and slightly concave in traverse direction, revolving a diamond cutter at a. speed of at least several thousand feet per minute in a fixed path abovesaid carriage, said path ineluding a minor circular arc, of greater diameter than the width of the sheet, which extends truly parallel to the curved carriage surface at a spacing therefrom corresponding to the desired thickness of the sheets, and moving said carriage and sheet in a fixed linear path through the arcuate sweep of the diamond at a rate such that successive swaths of the diamond overlap.

6. A process for producing metal sheets of highly uniform thickness which comprises securing a. sheet of the metal in close contact with a trued carriage surface that is straight in longitudinal direction andslightly concave in transverse direction, revolving a plurality of diamond the curved carriage surface in a plane lying below the exposed surface of the sheet, and moving said carriage and sheet in a fixed linear path through the arcuate sweeps of the diamonds at a rate such that successive swaths of the diamonds overlap.

7. As a new article of manufacture, a worked and machined non-ferrous metal sheet for photoengraving or the like, said sheet having a thickness which does not vary more than five tenthousandths of an inch and said sheet having a smooth abraded surface characterized by the presence, over the entire surface area, of an infinite number of almost microscopic arcuate scratch lines which intersect in all directions.

8. As a new article of manufacture, a semifinished photo-engraving sheet blank of nonferrous metal having a thickness of absolutely uniform gauge within a tolerance of less than five ten-thousandths of an inch and having a machine-cut surface composed of uniformlyspaced, almost-parallel, minute arcuate ridges which project a minute distance above the plane of continuous surface metal.

9. As a new article ofmanufacture, a worked and machined metal sheet having a thickness which does not vary more than five ten-thousandths of an inch and having a smooth abraded surface characterized bythe presence over the entire surface area of an infinite number of almost microscopic scratch lineswhich intersect in all directions, the intersections of said scratch lines being such that said abraded surface appears to have a broad zigzag line thereon running from one end of the sheet to the other with each leg of the zigzag line covering most of the sheet breadth.

' THOMAS J. MASSE.

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