US2419056A - Mica splitting process and apparatus - Google Patents

Description

April 1947- I H. H. BURTON 2, 19,056

MICA SPLIT'I'ING PROCESS AND APPARATQS 7 Filed Feb. 19, 1943 Patented Apr. 15, 1947 2,419,056

UNITED STATES PATENTOFFICE;

MICA SPLI TTING PROCESS AND APPARATUS Harry H. Burton, Worcester, Mass, assignor, by

' opposed surfaces.

- mesne assignments, to Aerovox Corporation, a

corporation of Massachusetts Application February 19, 1943, Serial-No. 476,435

24 Claims.

This invention relates in general to mica splitting; more particularly, it contemplates the rapid and economical division or separation of books or thin blocks of sheet mica, each into a number of thin films, such as condenser splits or sheets, or, as desired, into still-thinner fsplittings or mica flakes, such as are required for the manufacture of built-up board or plate mica. The present application is a continuation-in-part of my copending application Serial No. 454,722, filed August 13, 1942.

I There have been numerous attempts to obtain mechanical splitting or filming of sheet mica; however, the industrystill is wholly dependent upon lmife-splitting (a manual operation requiring the utmost in patience and dexterity) for the commercial production of these extremely thin and delicate mic'a sheets or films. Occasionally, the wielder of a splitting knife encounters a book of mica which yields readily to the desired filming or splitting, but in most cases, this knife-splitting, even for operators of long training and experience, is a, very slow and tedious operation; also, it has always been extremely wasteful of the material, since a great many films despite the most careful manipulation of the splitting knife, undergo scratching or fracture in the act of peeling them from the block or book, this being due not only to thevery fragile character of the material, but also, in'even greater measure, to the wide and unpredictable variations encountered in the strength and resistivity to splitting of the natural bond or adhesion in the difierent planes of cleavage of the material and in'different parts or zones of any givenplane of cleavage.

Numerous efforts have been made to overcome or to materially reduce this bond or adhesion betweenthe layers orclaminations of sheet mica; one such treatment, for example, was to first heat the .mica to just under redness and then to quench it in water. Up to now, all such attempts at pro-Conditioningof the mica, to facilitate its splitting orfilming have met with failure, due primarily to the inability of the water, or other bath liquid emp1oyed,,to penetrate appreciably between the layers or laminations, or to ventlon contemplates a. splitting or filming technique or practice, made feasible in large degree by the aforesaid preconditioning of the material, which not only eliminates the great amount of waste and loss that inevitably occurs with knifesplitting, but enables the splitting or filming operations to be rapidly performed by unskilled operators' needing no more than a, few hours of training and instruction-in contradistinction to the many months of practice and instruction required to train an operator for knife-splitting.

Other and further objects and advantages of my invention will be made apparent by the following detailed description thereof, taken in connection with the accompanying drawings, in which Fig. 1 is a sectional view, exemplifying a step by which the book mica is conditioned, according to my invention, for splitting or filming.

Fig. 2 is aperspective view, illustrating an implement employed by an operator in the splitting or' filming :of book mica according to my invention.

Figs. 3,4, 5, 6 and 7 are a series 01 line diagrams representing an operatorfs successive manipulations of a mica book, relative to the implement of Fig. 2, in securing splitting or filming according to my invention.

Fig. 8 is a sectional view of an implement similar to that of Fig. 2, but equipped with adjustable means by which to predetermine the thickness of the successive films that are split ofi from the book.

Like reference characters refer to like parts in I the latter simply illustrating a suitable receptacle I, filled to the level 2 with liquid, in which are submerged the books a, 3 of sheet mica. Preferably, but not necessarily, such :books have previously been cut, trimmed and reduced in thickness to substantially the conditions under. which materially aifect-the strong bond betweentheir My invention, in one of-its aspects, contemplates a pre-conditioning ofthe book mica to facilitate its splitting or filming; that does in fact materially break downand minimize this bond or adhesion, without harm to the delicate films themselves, this treatment being based on my,

discovery thata remarkably widespread liquid they would be subjected to knife-splitting.

It has long been recognized in this art that the bond or adhesion between the laminations terial into thinv films, or still-thinner splittings,

as the case may be. I have discovered, however,

that a very marked reduction in the strength of penetration between even themost strongly bondedifilmscan be obtained, bysoaking the books ina water bath containinga wetting agent or surface-active material of special constituency .aridproperties. l In another of itsaspects my inthis bond is obtained by soaking the mica books or blocks, such as shown at 3, ,3, in a water bath containing in small quantity an organic water-soluble wetting agent or surface-active go material at the type exemplified by the aliphatic a very low value the interfacial tension between water, mica. and air, thus to make the bath liquid capable of permeating, penetrating, and materially breaking down the strength of the bond 'or adhesion between the laminations of sheet mica in book or block form; that is to say, a highly satisfactory bath for this purpose can be made by the addition of twenty-five drops of a dilute solution of aerosol (aerosol O. T. to each quart of water. The bath may be improved, if desired, by the addition of a few drops of ammonia, the effect of this being to clean any fog or film from the surfaces of the thin mica laminations or sheets into which the book is readily divisible, as hereinafter described.

Prolonged soaking of the mica in the conditioning bath of my invention has no harmful effect whatsoever on the material, nor do the thin films or splittings into which the mica books are subsequently divided suffer anyimpairment of their di-electric strength, or the other properties, that render thin sheet mica so indispensable in the manufacture of condensers, spark plugs radio tubes, and other electric devices. But my improved bath liquid does act very noticeably on blocks or books of sheet mica submerged therein, to render them readily susceptible to division into thin films and splittings; this action, unobtainable by any soaking of mica books in ordinary water and other liquids of relatively high surface tension, is possibly explainable on the theory that my bath liquid, by virtue of its extremely low surface tension, is able very quickly to spread and penetrate through minute gaps, breaks, or weak zones of the bond in each plane of cleavage, the liquid thus seeping inwardly to attack the bond in its unweakened areas and to obtain its gradual disintegration. Whatever the action may be, it is a fact that blocks or books of mica, after soaking in a bath of the above-described character, are much less resistant to splitting or filming; with some mica, only a relatively short period of soaking is required to effect a material breaking down of the bond between the laminations, but with other mica where the bond is stronger to start with, the soaking period may need to be of several hours duration before the bond is sufficiently weakened to permit of easy splittingor filming. In any case, I have found that the action of my conditioning bath is best served by maintaining same at a fairly warm temperature, not, however, as high as the boiling point of the water or other liquid ingredient of said bath.

Book mica which has been soaked or treated as above described for a sufiicient period to materially weaken the strong bond or adhesion between its laminations, can of course be'divided and sub-divided by a knife-splitting operation that requires the exertion of much less force on the part of the operator to push the knife through and between the laminations of the material, thereby speeding up the operation and decreasing to some extent the spoilage and fracture of the films. But even as thus made easier, such knife-splitting practice is always fraught with the hazards of film fracture and scratching,

4 due to-the fact that the laminations of the book rarely present a mathematically flat surface; these deviations from absolute flatness, though very slight and minute, make it very difficult to open up a plane of cleavage with the splitting knife without damaging or fracturing the film surfaces on one side or the other of said plane. Although my above-described soaking of book mica is of substantial benefit in conditioning the mica for knife-splitting, its greatest usefulness lies in the fact that it renders themica susceptible to splitting or filming by the novel technique or practice now to be described, which not only avoids the numerous inherent disadvantages of knife-splitting, but enables the books to be rapidly divided and sub-divided without appreciable waste by operators having only a minimum of skill, experience and training.

Such new splitting or filming technique or practice is based on equipping each operator with one or more implements or devices of the character depicted by Fig. 2, such implement or device, designated as-a whole by the numeral 4, being a hollow body of any suitable material such as metal, which is preferably secured to a table or bench 5 at which the operator works, and which presents as its working face a convex surface 6.

Said surface 6 preferably faces the operator, and rises from the table surface 5 at a convenient distance from the edge thereof, the implement or device 4 being held in this position by any suitable means, here shown as in the form of a tubular extension I, projecting from the bottom surface 8 of said implement or device 4, and received snugly in a hole or opening 9 of the table or bench 5 This tube 1 communicates with the interior of thebody 4, and at its other end is connected, as by a tube l0, with'any suitable source of vacuum, such as a suction pump or air exhauster, not shown.

Such partial vacuum or suction thus maintained interiorly of the hollow body is made effective on its convex working surface 6 by suitable slots or openings II, II in the wall l2 that provides said surface 6, these suction apertures or openings l I,

I I, as best shown in Fig. 2, being preferably a In the utilization of such an implement or de- I vice for the progressive splitting or filming of books orblocks of sheet mica, according to my invention, the operator, either seated at or standing before the table 5, removes a conditioned mica book of appropriate size or area from the bath of Fig. l and presents it face foremost to the aforesaid suction zone or band of the surface 6, taking care only to see that the books face portion so opposed to and seized by the suction apertures is a portion which is relatively close to an edge, or extremity of the book. The eflect of such a presentation is for the book 3 to be seized and supported by the suction, against the working surface 6, in substantially the tangential relationship indicated by th diagram, Fig. 3-that is. with its face seized and held suctionally against relation to the surface 6,

the surface 6 only near the book's edge portion IS. the remainder of said face and the opposite edge or extremity l4 of said book being in spaced because of the latters convexity. With the book's support thus transferred to the suction device or implement 4, as indicated by Fig. 3, it only remains for the operator to exert a light thumb or finger pressure against the book in the vicinity of its free edge 14; such pressure, in the direction of the working surface Gas indicated by the diagram Fig. 4, procures a cleavage starting at edge [3 between the suctionally-gripped surface lamination l5 and the book's remaining laminations, the latter collectively retaining their flat or planar character, and thereby peeling away gradually from the former (the suctionally-gripped surface lamination I5) as the pressure forces the books edge l4 nearer and nearer to the surface 6, (see diagram Fig. 5). During this peeling action, the suctionally-held surface lamination I5 being thin and flexible enough to conform itself to the curvature of the surface 6, is supported and sustained by said surface. Thus, there is no appreciable strain or stress imposed on the lamination l5 by this peeling-away from it of the fiat relatively rigid body I6 constituted by the books other laminations.

That is to say, the above-described movement or manipulation is one which effects a gradual planar tilting or rolling of this rigid body, relative .to the curved surface 6, in such a manner that the relation of virtual tangency between its plane and the surface 6 is always preserved, notwithstanding that the movement causes the zone of tangency to shift progressively farther and farther away from its original position, i. e., the suction zone defined by the slits. I I, ll. Thus as the book edge i4 comes nearer to the Surface 6, the D- posite edge l3 of body is all the time movingaway from said surface, giving opportunity for the operator, at or about the stage depicted by Fig. 5, to seize the body l6 between thumb and finger, to hasten the peeling away from the lamination 55 by an upward swinging movement, (see diagram Fig. 6), about a pivot or axis afforded by the contact or proximate contact, of edge M with surface 6.

With the body 16 thus peeled awayand stripped clear from the suctionally, held lamination 15, the latter (see diagram Fig. 7) isleft standing alone against the surface 6, in position for ready removal, either by pulling it off said surface, or by a momentary release of the'vacuum to allow its drop by gravity into a convenient receptacle, not shown; such release or momentary breaking of the vacuum can be effected in any convenient way, as by providing a suitable valve, not shown,

in the tube or connection H), for letting atmo's-' pheric air into the interior of the device 4, upon being opened momentaril by the operators depression of a suitably placed foot treadle, or the like.

As soon as any such separated lamination I5 is removed from the surface 6, the operator simply re-presents the same book, in its slightly reduced or thinner form Hi, to the suction apertures H, H, and repeats the above-described manipulation to obtain the separation of another external layer or lamination, and so on until the book by successive separations therefrom of its layers or laminations is completely divided, or is reduced to a residue so extremely thin that the relative stiffness or rigidity needed for the abovedescribed manipulation is no longer present.

6 However, the needed stiffness or rigidity is usually not lost or eliminated until the book residue has been reduced to a. thickness of about 1 or 2 onethousandths of an inch, thin enough, that is, for the residue itself to constitute a mica film or splitting that is fully as useful for many electrical purposes as any of the thinner films or laminations into which the major portion of the book, in the manner above described, may have been previously divided and sub-divided.

Such filming operation involving, in effect, successive peelings away of the book residue from the layer undergoing separation (in contradistinction to knife-splitting where the layer und rgoing separation is peeled away from the book) is a cycle of simple manipulation that can be quickly imparted and taught to operators who have had no previous experience in the handling of mica; with only little practice, such operators are able to performthe manipulations so speedily as to obtain a much higher rate of production of mica films and splittings than can be obtained by an experienced knife-splitter; moreover, by my method of splitting, the waste or spoilage (which is always very heavy with knife-splitting) is reduced to an almost negligible factor. The material is successively presented to and manipulated on the implement or device 4, always in the same way, by a routine which is simple and easily learned; in fact, it is perfectly possible for sheet mica, under the conditions and with. the equipment contemplated by my invention, to be split or filmed by blind operators, once they have been taught the hand movements that are involved. It will be understood, of'course, that the implements or devices 4 will ordinarily be provided in a variety of sizes, those of small size being used with small area books, and those of larger size being used with large area books.

. Fig. 8 shows a suction device or implement, similar in construction and operation to that of Fig. 2, but equipped with an arrangement by which to adjust or predetermine the thickness of the films that are split off in succession from the book material. For this purpose, the working surface 6' of the suction device or implement 4 is formed just below the suction slits H, II with a small hole H, in which is slidably but snugly received a stem E8, the latter at its outer end having an upward projection IS, in the form of a'small chisel-point substantially paralleling the surface 6 and of sufiicient sharpness to penetrate by a minute amount the edge of -a book or block of sheet mica, when the latter, in the manner above described, is presented by the operator to the suction slit H, H. The stem l8 at its other end is secured to the'upper portion of a metal plate I 20, slightly spaced from the wall I2 except along its lower edge portion, the latter being anchored to said wall l2 as by means of screws 2|, 2|, or the like. At. an intermediate point, between its upper and lower portions, the plate 20' has a threaded hole receiving an adjusting screw 22 of very fine pitch, said screw 22 passing through thewall i2, with its head exposed on the surface 6' 'to permit it to be manipulated for slight flexure's of the plate 20, thereby to vary 0 adjust adhesion between the laminations of said material.

2. The herein described treatment of sheet mica in block or book form to facilitate its splitting or filming, which consists in plunging the same into water containing a small percentage of a dioctyl ester of sulfosuccinate the effect of which is to materially reduce the surface tension of the water.

3. The herein described treatment of sheet mica in block or book form to facilitate its splitting or filming, which consists in immersing the books in water containing a small amount of aerosol O. T. solution the effect of which is to materially reduce the surface tension of the water.

4. The herein described treatment of sheet mica in block or book form to facilitate its splitting or filming, which consists in immersing the books in water containing a small amount of "aerosol O. T. 10%" solution, namely, twenty-five drops of said solution to each quart of water the effect of which is to materially reduce the surface tension of the water.

5. The herein described treatment of sheet mica i block or book form to facilitate its splitting or filming, which consists in subjecting it to a water bath containing in solution a small amount of the wetting agent known as "aerosoP and a few drops of ammonia.

6. In the art of splitting or filming sheet mica,

' the improvement which consists in holding a mica book in fixed position, by suction applied to its face, against a'surface which falls away from the plane of said book, and then deflecting the book toward said surface, whereby to peel or strip it bodily from the suctionally held outside lamination thereof.

'7. In the art of splitting or filming sheet mica, the improvement which consists in supporting a, mica book in fixed position by suction effective on a limited area of the books face near one edge 8 10. In the art of splitting or filming sheet mica, the improvement which consists in suctionally gripping and holding a mica book at a limited face area near one edge in fixed position, and then tilting the plane of said book about a fulcrum between its free edge and the suctionally gripped face zone, to'strip said book bodily from its suctionally-held external lamination.

11. In the art of splitting or film sheet mica, the improvement which consists in suctionally gripping and holding stationary a mica book, in a limited face area near one edge, simultaneously engaging and piercing said edge in a plane of cleavage having a predetermined spacing from the suctionally-engaged outside lamination of said book, and then tilting the plane of said book about a fulcrum between the books free edge and its suctionally-gripped face zone, to divide said book on said plane of cleavage.

thereof, and then, by pressure against the free edge of the book, procuring a planar deflection thereof which strips it bodily from the suctionallyheld lamination.

8. In the art of splitting or filming sheet mica, the improvement which consists in gripping and holding a mica book in fixed position near one edge of its face by suction exerted through a surface which extends in divergent relation to the remainder of said face, and then subjecting the sosupported book to planar deflection in the direction of said surface, to strip it bo'dily from the suctionally-held external lamination.

9. In the art of splitting or filming sheet mica, the improvement which consists in engaging a mica book in a limited area near one edge of. its face with suction apertures, the latter being provided by a fixed surface which stands in divergent relation to the remaining face area of the sosupported book, and then, by pressure against the free edge of said book in the direction of said divergent surface, procuring a planar deflection to strip the sam bodily from the suctionally-held external lamination thereof.

12. A device for use in the splitting or filming of sheet mica, comprising a stationary body having suction apertures adapted to support and hold stationary a mica book by contact with a face thereof near one edge, said body providing a fulcrum for the planar tilting of said book, between the latters free edge and said suction apertures, and means on the opposite side of said suction apertures from said fulcrum to pierce said book edge in a plane of cleavage at a predetermined spacing from the suctionally-held outer surface area.

13. In the art of splitting or filming sheet mica, the improvement which consists in soaking each mica book in water containing an ester of dicarboxylic or sulfodicarboxylic acid in sufficient amount to reduce materially the interfacial tension between water, mica and air, then supporting and holding the so-treated book in fixed position by suction effective on the face of an external lamination, near one edge thereof, and finally, by pressure applied near the free edge of said book, procuring its planar deflection to strip it bodily from said suctionally-heldlamination.

14. In the art of splitting or filming sheet mica, the improvement which consists in immersing each mica book in water containing an organic water-soluble wetting agent or surface-active material in suflicient amount to materially reduce the waters surface tension, prolonging such immersion substantially in proportion to the strength of the natural bond or adhesion between the laminations of the book, procuring with each so-treated book successive contacts with suction apertures effective over a limited face area near one edge of said book, to stationarily support said book with its remaining face area in a, plane divergent from the surface containing such suction apertures, and, during each period of such support, urging said book toward said surface by pressure applied near its free edge, thereby procuring its planar deflection to strip the same bodily from the suctionally-held external lamination thereof.

'15. In the art of splitting or filming sheet mica, the improvement which consists in soaking each mica book in water containing a small amoimt of aerosol O. T. 10% solution, thereby through the materially lowered surface tension of said waterto obtain the latters penetration between the laminations of said book, presenting the sotreated book successively to suction apertures formed in a convex surface, to stationarily support said book, tangentially to said surface, by suction exterted on the face of an external lam ination near one edge of the book and in the and weaken period ofeach such support, producing the book's planar deflection toward said surface, whereby to peel or strip it bodily from its suctionally-held external lamination.

16. In the art of splitting or filming sheet mica, the improvement which consists in soaking each book in amoderately heated water bath containing the wetting agent aerosol and a few drops of ammonia in suiiicient amount to materially reduce the waters surface tension, procuring successive supports of said book, by suction applied to its face, near one edge thereof, against a surface which falls away from supported book, and in the instance of each such support, causing planar deflection of the book toward said surface, to peel or strip it bodilyfrom its suctionally-held external lamination.

17. In the production of mica films and splittings from book mica, the improvement which consists in submerging the book material in water containing the wetting agent known as aerosol in sufiicient amount to materially reduce the water's surface penetrate any breaks or gaps in the bond between the materials layers, prolonging such submergence a sumcient time for the penetrant liquid to attack and weaken said bond, thereby to promote formation of cleavage planes between said layers, and-then splittingsaid material in said planes.

18. In the production of mica films and plittings from book mica, the consists in submerging the book material in water containing the wetting agent aerosol in sufficient amount to materially reduce the waters surface tension, thereby enabling it to penetrate any breaks or gapsin the bond between the materials layers, prolonging such submergence a sufiicient time for the penetrant liquid to attack said bond, thereby to establish planes of cleavage between said layers, and then splitting said material on the planes of cleavage so established.

19. In the splitting or filming of book mica which has been previously treated to reduce the strength of the bond or adhesion between its layers, the improvement which consists in repeatedly manipulating the book material, to establish cleavages between its residue and the successively-exposed external layers thereof, in the following sequence or order, viz., (l) supporting the material in fixed position by suction effective on its face near oneedge thereof, against a surface which falls away from the plane of the so-supported material, and (2) procuring a planar defiection of said material toward said surface, to open up a cleavage plane between the suctionally held face lamination and the remainder of said material.

20. In the splitting or which has previously been treated to reduce the strength of the bond or adhesion between its layers, the improvement which consists in repeatedly manipulating thebook material, to effect cleavages between itself and successively-exposed surface layers thereof, in the following order or sequence, viz., (1) presenting a face of the material near one edge to suction apertures provided by a fixed convex surface, thereby to support said material substantially in tangential relation to said surface, and (2) pressing the free edge of said material toward said surface, thereby to open up a plane of cleavage atthe opposite edge bethe plane of the sofilming of book mica sented facewise tension, thereby enabling it to improvement which i0 tween the suctionally-grlpped layer and the remaining layers.

21. Mica splitting apparatus, including a device having a generally convex surface and an adjacent aperture, means for exerting suction through said aperture, and a projection adjacent said aperture and minutely offset from said surface in positon'to pierce the edge of a mica book preto said aperture and held by said suction in substantially tangential relation to said surface.

22. Mica splitting apparatus, including a device having a generally convex surface and an adjacent aperture, means for exerting suction through said aperture, a projection adjacent said aperture and minutely offset from said surface in position to pierce the'edge of a mica book presented facewise to said aperture and held by said suction in substantially tangential relation to said surface, and means for adjusting the offset of said projection from said surface.

23. In the splitting or filming of book mica, the improvement which consists in first soaking the books in a water bath containing an organic water-soluble wetting agent whose effect is to materially reduce the interfacial tension between water, mica and air, then stationarily supporting each book so-treated repeatedly by successive presentations of its face, near one edge, to a suction aperture provided in a surface which falls away from the plane of the so-supported book, and after each such presentation procuring the planar deflection of the book toward'said surface by finger pressure thereon at a point appreciably removed from said suctionally-engaged portion, whereby to strip the book-residue bodily from the successive suctionally-held external laminations thereof.

24. The herein-described method of splitting or filming book mica which consists in repeatedly presenting a book, for temporary stationary support by face engagement therewith, to suction means effective only on an edge portion of said face, and in each period of support, by finger pressure exerted on said book at a point remote from its support zone, procuring its planar deflection, to initiate stripping or cleavage of the residue of book material away from the suction- The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name I Date 686,929 Heard et al Nov. 19, 1901 1,194,155 Edgecomb Aug. 8, 1916 1,823,136 Frederick Sept. 15 1931 1,829,031 Atwood Oct. 27, 1931 1,870,835 Cofley et al Aug. 9, 1932 1,722,082 Frederick July 23, 1929 1,771,943 Tinnerholm July 29, 1930 2,306,292 Atwood Dec. 22, 1942 2,176,423 J aeger l Oct. 17, 1939 2,028,091 Jaeger Jan. 14, 1936 FOREIGN PATENTS Number Country Date 12,570 British 1908 British Feb. 28, 1910

Images