US2445557A - Grinding apparatus - Google Patents

Description

July 20, 1948. BLAslER 2,445,557

GRINDING APPARATUS Filed Jan. 31, 1944 2 Sheets-Sheet 1 flees/275.624 5/553,

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ATro/e/vEx y 1948. H. E. BLASIER GRINDING APPARATUS Filed Jan. 31, 1944 Patented July 20, 1948 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to a grinding apparatus; and more particularly, to an apparatus for edge grinding piezo-electric crystals.

It is an object of this invention to provide such an apparatus, wherein a plurality of the articles to be ground are assembled in a stack for advance with respect to a, grinding surface, the articles being capable of individual movement in the stack toward the grinding surface.

It is another object of this invention to provide rotary apparatus for bevelling simultaneously the edges of a substantial number of crystals in a single operation.

It is another object of this invention to provide an arrangement wherein the articles are mounted in a member which is adapted to be rotated within a surrounding grinding surface, the rotation of the member causing the articles to be urged against the grinding surface by centrifugal force.

It is another object of this invention to provide an arrangement wherein work carried by a rotating member is urged by centrifugal force against a grinding surface at a predetermined angle.

It is another object of this invention to provide an arrangement wherein work carried by a member rotating in one direction is urged by centrifugal force against a grinding surface and at a chosen angle, and at another angle when the member rotates in the opposite direction.

In the preparation of piezo-electric crystals, particularly where they are to be used for accurately determining the frequency of high frequency electric currents, it has been found that it is important, for the crystal to have proper operating characteristics, that the edge surfaces be smooth. As an incident to the preparation of such crystals, the corners where the edge surfaces meet the faces of the crystal are roughened and pitted. While such pitting is only microscopic and wholly invisible to the unaided eye, nevertheless the electrical characteristics of a crystal with edges in this condition are not satisfactory, and the edges should be smoothly bevelled for optimum results. Heretofore, such bevelling of the edges has been done manually, by a grinding operation involvin holding the crystal by hand to appropriately incline the crystal with its edge against an abrasive surface, and causing relative movement between the crystal and the surface. Since these crystals are of very hard, brittle material and usually of small size such manual method is quite laborious. It is accordingly another object of this invention to provide an improved method of and apparatus for bevelling the edges of the crystals.

It is still another object of this invention to provide rotary apparatus for bevelling the edges of crystals in which the crystals may be appropriately inclined optionally to bevel the op-f posite sides of the same edge without the need of removing the crystals from the apparatus, such grinding of the opposite side edges being accomplished by reversal of the direction of rotation of the member carrying the crystals.

It is still another object of this invention to provide apparatus for supporting a plurality of crystal plates on their edges and in a Vertical position to form a horizontally extending stack, the crystals being independently movable with respect to each other and to their support, into contact with a grinding surface.

It is a still further object of this invention to provide a rotary apparatus for grinding the edges of a stack of crystals to a desired contour as well as, if desired, to simultaneously bevel these edges during such grinding.

This invention possesses many other advan-.

tages and has other objects which may be made more easily apparent from a consideration of several embodiments of the invention, For'this purpose there are shown several forms in the drawings accompanying and forming part of the present specification. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure l is a pictorial view on an enlarged scale showing a crystal finished in accordance Figure 6 is a pictorial view on an enlarged scale of a stack of crystals after completion of one stage of the grinding operation;

Figure '7 is a fragmentary section greatly en- I larged showing the bevelled edge of a crystal; ,Figures 8 and 9 are views similar to Figure 7 showing optional variations in the bevelled edge of a crystal;

Figures 10 and 11 are fragmentary sections similar to Figure 3, but showing apparatus for 3 grinding different edge contours on the crystal; and

Figures 12 and 13 are views similar to Figure 4, showing modified forms of grinding apparatus.

Referring to that form of the invention disclosed in Figures 1 to 7 inclusive, the crystal which is to be bevelled is shown as comprising a straight sided plate I which may be in the form ofa square, accurately processed to the required thickness and dimensions. In such processing the edge surfaces 2 as well as the faces 3, 4 of the crystal are ground to the requisite smoothness, but as an incident to such grinding, the corners 5 (see Figures 1, 6 and '7) where the edges 2 meet the faces 3 and 4 are frequently pitted and roughe'ned. While such pitting and roughening is extremely minute and generally invisible to the unaided eye, it nevertheless interferes with the proper functioning of the crystal, such for example as when used to control the frequency of an electrical circuit. For removing such roughness, all the corners 5, where the edges 2 meet the opposite side faces 3 and 4 of the crystal, must be smoothly bevelled as indicated at 8 (Figures 1, 6 and 7). While such bevelling involves the removal'of a very minute amount of material, the harness and fragility of the material and the small size of the piece to be handled combine to make the methods heretofore employed costly and unsatisfactory. In the present instance a mechanical grinder is employed in which the required handling of the crystal plates is substantially reduced.

For this purpose a fiat circular member or jig I is supported for rotation about the axis of a vertical shaft H, and coaxially within a stationary cylindrical well I2 defined by a circular wall I3 The member I0 is provided with a plurality of axially extending slots I4 spaced about its periphery and closed at their lower ends as by a plate I secured on the bottom of the member II) by screws I6, and adapted to receive several of' the crystals I which are to be ground. Since the crystals are quite thin and fragile, it is preferred to grind them in the form of a stack I'I comprised of a small number of crystals, for example four, supported in a vertical position to form a horizontal stack so that they mutually support one another and thus better resist the forces incident to the grinding operation. Further, by grinding them in such groups or stacks a larger output is obtained from given apparatus.

The crystals I which comprise the stacks ll are supported on their edges in a vertical position by the plate I5 and are freely slidable in a generallyradial direction in the slots I4 with respect to each other and the slots. member it) rotates, the plates I under the influence of the resulting centrifugal force slide outwardly of the slots I4, so that the outer edges 2 of the plates I engage the wall I3 and are ad- Thus, as the vanced slidingly therealong as the member IIl-reformed to include. a diamond charged or other 7 form of abrading surface, or an abrasive in powdered or liquid form may be applied to the wall I3. For example, levigated alumina in liquid form may be applied to the center of the member Ill and thrown against the wall I3 by centrifugal force to form a grinding surface thereon due to the rotation of the member ID. The plates I are of course moved by engagement with the rear walls of the advancing slots. Hence, by appropriately inclining these walls, the corners 5 of the edges of the plates I are presented to the wall I3 and bevelled or ground at an angle determined by the inclination of this wall. Further, the stacked plates I may be caused to be engaged by the other and oppositely inclined walls of the slots I4 and thus present the corners 5 on the other side of the plates I to the grinding surface, so that upon rotation of the member ID in the opposite direction these other corners will be ground or bevelled. In this way both corners 5 of an edge 2 may be ground without the need of removing the plates I from the member It.

The slots I4 are each formed in part by a pair of oppositely inclined vertical walls I9 and 20 which converge toward the axis of the shaft II. The walls I9 and 20, as shown, each extend about half the length of a plate I, and at their points of termination 2I and 22 are spaced apart by a distance slightly in excess of the thickness of a stack II. The walls I9 and 26 are met respectively by correspondingly diverging walls 23 and it, which extend to provide a suitable clearance space 25 for the inner end of the crystal stack IT. The arrangement is such that as the member IIl rotates in a clockwise direction as shown in Figures 2 and 4, the stacked plates II are confined between the walls 26 and 23, and thrown outwardly by centrifugal force so that the leading corner 5a of each of the plates I engages the abrading wall I3 and is bevelled or ground at an angle determined by the inclination of the walls ZII.

When it is desired to grind the corners 5-b on the opposite side of the plate, light pressure is applied to the rear end of the stack IT by the operator, causing the lowermost plate I of the stack il (referring to Figure 4) to pivot about the point 22 so that the upper plate of the stack engages the wall I9 (as shown in Figure 5), the remaining plates of the stack slidingly following this lower plate until the stack I1 is confined between the walls I9 and 24. Thus, the corner 5b of each plate I opposite to the one just bevelled is presented to the abrasive wall It at an angle determined by the angle of the walls I9. To facilitate such change in position of the stack of plates IT as well as the placement and removal of the plates I in and from the slots It, a shallow circular groove 2'! is provided in the surface of the member IE3. As clearly shown in Figure 3, this exposes an inner upper corner of the plate stack I! so that the plates may be readily manipulated by the operator.

As just pointed out, the slope of the bevelled surfaces 6 is determined by the inclination of the walls I9 and 20; the amount of the bevel depending on the length of time of the grinding and the rate at which the material is removed.

In the example so far considered such bevelling of the opposite sides of the plate edges has been shown as being substantially equal in amount, and of equal but opposite inclination. By continuing the grindin for longer periods the extent of the bevel may be increased. If desirable the bevels on opposite sides may be caused to meet along a line forming an apex 28 (Figure 8), and this apex 28 may be located centrally of the thickness of the plate I by grinding equal amounts from the opposite edges of the plate, or it may be located to one side'or the other of such central position as indicated by the broken lines 28a in this figure, by varying the length of time of the grinding operations. Further, by varying the inclination of the walls I9 or of the slots 14, the slope of the bevel may be varied; as shown in Figure 9, for example, the inclination of one bevel is shown as much steeper than that of the other.

Variations in the contours of the edges 2 may also be ground by providing an abrading wall I3 having an appropriately shaped cross section.

Thus, as shown in Figure 10, the well l-2 may be provided with a circular wall having a shal low V-shaped groove 31 extending around its inner surface. This will form a V-shaped contour 32 on one edge of the crystal 1. Or, as shown in Figure 11, a wall 33 having a concave groove 34 may be provided, which will form a convex contour 35 on the edge of the crystal I.

Other forms of the slots for holding the crystal stacks II also may be provided. Thus, in Figure 12 a slot 36 is shown which has parallel vertical side Walls 37 and 38 terminating in a clearance space 39. The walls 31 and 38 are space to slidingly accommodate the stacked crystals I! between them and direct them substantially radially or at some other angle as indicated by the broken lines 31-11 and 38-a toward the abrading wall 13. With a slot arranged in this manner the stack 11 of the crystals I are always presented to the wall I 3 at the same anglc.

Figure 13 shows a simplified form of slot for the stack I1. Thus, the slot 40 is formed by a pair of oppositely inclined vertical side walls 41 and 42 converging toward the axis of the memher It]. The walls 41 and 42 may have the same or different rates of inclination with respect to a radius through the slot and may have a length somewhat less than that of the plates I, but sufficient to provide adequate support for the plates. They are so spaced with respect to their length that the points 43 and 44 at which they terminate are spaced apart a distance to slidingly accommodate the stack l1. As before, a clearance space 45 is provided at the inner end of the slot 40. When the member ID rotates in a clockwise direction the plates l are in contact with the wall 4| and the angle of the bevel is determined by the inclination of the wall 4|. When the member 10 rotates in the opposite direction, the plates I are in contact with the Wall 42 and the corners on the opposite sides of the plates 1 are bevelled at an angle determined by the inclination of the wall 42.

I claim:

1. In a centrifugal grinder for performing a grinding operation on the edge portion of each plate of a stack of plates, a member rotatable about a vertical axis, means formin an axially extending slot in the periphery of said member, the walls of said slot converging toward the axis of the member and terminating at a point such that each wall has a length less than the length of the plates, said walls at their closest parts being spaced apart a distance greater than the thickness of said stack, means providing a clearance space at the inner ends of said walls for said stack, means supporting said stack in said slot, and means forming a grinding surface surrounding said member, said stack being adapted to be engaged and advanced by one wall of the slot upon rotation of the member in one direction, the centrifugal force causing the plates to be urged outwardly of the slot against said grinding surface at an angle determined by the slope of said one wall, said stack being adapted to be engaged and advanced by the other wall of the slot upon rotation of the member in the other direction, the centrifugal force causing said plates to be urged outwardly of the slot against the grinding surface at an angle determined by the slope of said other Wall.

2. In a grinder, a circular member supported for rotation about a vertical axis, axially extending peripheral slots in said member, each of said slots being formed by a pair of outwardly flaring vertical plane wall surfaces and. being closed at its lower end, and means forming a grinding surface closely surrounding said member.

3. In a grinder, a circular member supported for rotation about a vertical axis, means forming a grinding surface closely surrounding said member, an axially extending peripheral slot in said member formed by a pair of spaced vertical surfaces and closed at its lower end by a horizontally extending wall, said Wall and said surfaces cooperating to slidingly support a work piece for movement outwardly of the slot into engagement with the grinding surface in response to rotation of said member.

4. In a grinder for bevelling a plate, a member mounted for angular movement about a vertical axis, means forming a curved grinding face surrounding said member, and means forming a pair of diverging surfaces on said member on opposite sides of a radial line through said axis and extending outwardly with respect to the axis, between which a plate is adapted to be supported on edge for movement with said member, movement of said member serving to urge the plate outwardly to engage the grinding face, one of said surfaces serving to maintain said plate in bevelling relation with the grinding face in accordance with the direction of movement of said member.

I HERBERT E. BLASIER.

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

UNITED STATES PATENTS Number Name Date 369,074 Pearce et a1 Aug. 30, 1887 474,024 Meigs et a1. May 3, 1892 629,634 West July 25, 1899 760,765 Stutz May 24, 1904 1,405,032 Heepe Jan. 31, 1922 1,570,242 Georz et al Jan. 19, 1926 1,870,571 Kadzik Aug. 9, 1932 1,986,537 Schafer Jan. 1, 1935 FOREIGN PATENTS Number Country Date 150,686 Great Britain July 7, 1921 272,112 Germany Mar. 24, 1914 316,384 Germany Nov. 26, 1919 317,618 Germany Dec. 23, 1919

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