US1764088A - Cutting sections of piezo crystals - Google Patents

Description

C. B. SAWYER CUTTING SECTIONS OF PIEZO CRYSTALS Filed Jan. 26, 1928 INVENTOR ATTORNEY June 17, I930.

Patented June 17, 1930 UNITED STATES PATENT OFFICE CHARLES B. SAWYER, OF CLEVELAND HEIGHTS, OHIO, ASSIGN-OR, BY MESNE ASSIGN- MENTS, TO THE CLEVELAND TRUST COMPANY, OF CLEVELAND, OHIO, A CORPORA- TION OI OHIO CUTTING SECTIONS OF IP IEZO CRYSTALS Application filed January 26, 1928. Serial No. 249,778.

This invention relates to piezo-electrio crystals of the Rochelle salt type and more particularly to an improved method of cutting sections from such crystals.

| It is frequently necessary in using crystals of the Rochelle salt type to cut them into portions of various shape to procure the desired sections for accomplishing various results in their application to acoustic apparatus. It has been customary to do this cutting with a wet string which is usually made to run over pulleys and is applied with water. The cutting action seems to be the result of a combination of abrasion and solution and at best is somewhat tedious and not ada ted to rapid production of sections of the esired shape and orientation from Rochelle salt crystals.

The thickness of the sections to be cut from the Rochelle salt crystals is usually quite a small dimension in comparison with one or both of the other dimensions of the section, that is, the width and length, and consequently it has been relatively difficult to out such sections with substantially uniform thickness in an eflicient manner from the frail and brittle Rochelle salt crystals.

In addition to the extreme brittleness of crystals of the Rochelle salt type, these crys- 80 tals have a low melting point, a e coefficient of thermal expansion and low heat -conductivity, and these several properties make it very diflicult to readily cut sections from such a crystal. It has been found, however, that by carefully giving consideration to these various properties Rochelle salt crystals can be sawed successfully and efliciently under certain conditions as disclosed in my process.

In order to successfully saw such sections from a brittle crystal of the Rochelle salt type it is necessary to prevent the application of even' a small side pressure to the sides of the crystal when a kerf is being cut through a crystal. It is also necessary in view of the large coeflicient of thermal expansion and the low heat conductivity of the crystal to avoid, as far as possible, frictional effects on the crystal, such as rubbing 50 or abrasion on the sides of the kerf, as these would necessarily raise the temperature of a localized portion of the crystal and thus cause cracking or breaking of the crystal. Furthermore, owing to the low melting point of the crystal, frictional or abrasive action by the saw tends to melt a minute portion of the crystal dust which thereby becomes attached to the saw. Such dust may be melted directly on the saw blade or may become firmly attached to the sides of the saw blade by being pressed against the saw blade while the blade is traveling through the saw guides. Any such adhesion' of packed or molten crystalline dust to the blade increases the effective Width of the saw and also fills up the interstices between the teeth, thereby further increasing the frictional eifect. It will be seen that the frictional effects are therefore cumulative. As a Rochelle salt crystal begins to melt at approximately degrees C. and melting is rather complete at degrees C., it is obvious that frictional contact between the saw blade and the crystal, suflicient to produce a slight rise in temperature, will cause quite disastrous results and therefore must be kept at a minimum. An appreciable and very localized rise of temperature can thus be easily caused which will result in cracking or breakage of the crystal, primarily due to the large thermal expansion of the crystal.

It is therefore essential that any dust or crystalline matter which adheres to the saw either as the result of the proximity of the saw to the crystal being cut or on account of the loose material carried down by the saw being pressed against it either by the saw guides or the Wheel over which the saw passes, be removed in order to prevent the thickness of the saw blade from building up to such an extent that it will rub against the sides of the crystal in which the kerf is being out.

One way of accomplishing this is to hold a hard metal tool, such as a file, .for example, against the side of the saw blade, but not in contact with the teeth, while the saw is running to scrape this material from the saw blade and also to cause sulficient friction to raise the temperature sufficiently to same as the guides and saw blade, in order to avoid temperature inequalities tending to produce cracking .or warping of the slabs during and after sawing. For if the crystal has portions differing in temperature, then, after sawing, mechanical deformation may occur which can result in producing a slab in which the cut surface is not a plane, when the temperatures have equalized.

Reference should be had to the accompanying drawings forming a part of this specification in which:

Figure l is a side elevation of a band sawing machine.

Fig. 2 is a fragmentary section on line 2--2 in Fig. 1 showing the work table.

Fig. 3 is an end elevation of the table and guides shown in Fig. 2.

Fig. 4 is a side elevation from the line 4-4 in Fig. 3.

In the drawings, the sawing machine has a suitable base frame 1 and carries the wheels 2 and 3 over which the band saw 4 passes. The wheel 3 is driven .from any suitable source of power, not shown, which drives the small wheel 5, shaft 6 and belt 7 which passes over pulleys 8 and 9. The upper portion of the sawing machine is provided with a standard 10 to support the upper wheel 2 with its shaft 11 and extending from the frame 10 is a support arm 12 on which is mounted a suitable adjustable guide member 13, carrying fixed guide blocks 14 and adjust-able guide blocks 15 between which the band saw 4: passes.

A suitable support or table 16 is carried by the frame of the machine on which the crystal to be cut may be fed to the saw. On the table 16 is mounted a guide 17 to guide the crystal as it is fed toward the saw blade, and below the table 16 are mounted fixed guides 18 and adjustable guides 19, between which the band saw 4 passes.

In order to successfully saw such crystals rapidly and, with a minimum of breakage, I have found that it is necessary to use a saw with very sharp teeth and with the teeth set evenly with respect to the blade so that i there are no teeth projecting considerably beyond the average plane of the teeth. Also it is essential that the saw must be trued and held so that it has substantially no play sidewise or in the plane of the blade. In order to prevent the sidewise play rigid guides 14, 15 and 18, 19 may be secured above and below the table or support 16 on which the crystal is fed.to the saw and the saw blade must be trued up properly to prevent movement in the plane of the blade. The teeth of the saw must be so filed and set that the teeth are sharp and project substantially uniformly beyond the planes of the blade of thesaw so that the sidesof the blade of the saw will not contact with the sides of the crystal when a kerf is being cut.

Furthermore, I have found that it is necessary to run the saw at a speed which is a function of the extent or Width of the crystalline material in contact with the saw teeth. In general, the greater the width of crystalline material, the slower the speed of the saw. This is to prevent undue localized heating of the crystalline material. I have found, for example, in cutting a crystal in which the portion of the crystal in contact With the teeth is approximately 2 that a relatively slow speed, such as 500 lineal feet per minute is a desirable operating speed, whereas if the extent of material is very small, as in sawing a section from one of the slabs already out, then the speed may be very materially increased without any ill effects. In any event, the relation of the speed to the extent of surface cut must be such that the temperature of the crystal in contact with the saw teeth must not exceed 50 degrees C. over a relatively large area, and owing to the high coelficient of thermal expansion a much smaller rise in a sharply localized area will produce disastrous cracklng.

It is also essential that the vibration of the band saw machine be reduced to a minimum. The crystal must fed substantially without vibration to the saw blade and further must not be subject to too violent shocks while resting on the table. In order that the crystal may be fed'to the saw in a substantially straight line it is, of course, essential that a suitable guide 17 be provided against which the crystal is fed to the saw blade and it is desirable in order to obtain the best results that this guide have a width above the table at least as wide as the width of the largest crystal to be sawed so that there is no danger that the crystal will not be fed toward the saw substantially in a plane. For the same reason this guide should extend on each side of the saw a distance approximately equal to the length of the largest crystal to be sawed.

It is to be observed that, in general, the less heat there is generated and allowed to remain in the crystal, the higher the cutting speed there can be, and also that the type of saw may be varied so long as its operation conforms to the herein disclosed principles for the successful cutting of sections of Rochelle salt crystals.

If desired, a suitable cooling or lubricating liquid may be used in connection with the sawing of the crystal. However, if a cooling or lubricating liquid is used, it is preferable not to use such a liquid that is ighly volatile, as this is liable toproduce cracks in the crystal, due to the cooling ac-,'

tion of the volatile liquid, unless special preventative cautions are taken.

To those skilled in the art many modifications of and widely differing embodiments and applications of my invention will suggest themselves without departing from the spirit and scope thereof. My disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

-lVhat I claim is:

1. The method of cutting sectionsfrom piezo-electric crystals of the Rochellesalt type, which includes bringing the crystalline material to a predetermined temperature suitable for the material to be cut separating a section from the crystal in substantially a single plane by removing the crystalline particles continuously in the same direction at a rate of speed low enough to substantially prevent localized heating of the crystalline material. i

2. The method of cutting sections from piezo-electric crystals of theRochelle salt type, which includes bringing the crystalline material to an o crating temperature, separating a section 0 the crystalline material from the crystal by removing continuously in the same direction small articles of crystalline material at a rate su ciently low to prevent a substantial localized rise of temperature of the crystalline material, and eliminating localized heating of any part of the crystalline material by preventing the return of the particles removed.

3. The method of cutting sections from piezo-electric crystals, which includes bringing the crystal to a temperature suitable for cutting such material, cutting said material by continuously removing crystalline articles from the crystal at a predetermmed speed which is inversely proportional to the width of the material being cut, feeding the crystal in a straight line, and preventing engagement between the side walls of the kerf and the cutting means to avoid cracking of the crystal.

4:. The method of cutting sections from piezo-electric crystals, which includes bringing the crystal to a uniform cutting temperature throughout, cutting said material by continuously removing crystalline particles from the crystal at a predetermined speed which is inversely proportional to the width of the crystal being cut, feeding the crystal in a straight line, preventing engagement between the side walls of the kerf and the cutting means, and preventing the return of crystalline particles to the crystal being cut.

5. The method of cutting sections from piezo-electric crystals of the Rochelle salt type, which includes bringing the crystal to be cut to substantially the same temperature as the cutting means, continuously removing crystalline particles from the crystal at a predetermined speed to separate the sections, continuously feeding the crystal, and preventing engagement between the side walls of the kerf and the cutting means to avoid cracking of the sections beingcut.

6. The method of cutting sections from.

piezo-electric crystals of the Rochelle salt type, which includes bringing the crystal to substantially the same temperature as the cutting means, separating the crystal by contlnuously cutting it in a single plane, movmg the crystal in a plane substantially parallel to the cutting plane of the sections to be cut, and preventing the return of agtially parallel to the plane of se aration ofthe sections, whereby a section 0 the crystal may be cut without undue heating and breakage of the crystal or section thereof.

8. The method of cutting sections from piezo-electric crystals of the Rochelle salt type, which includes continuously removing crystalline particles from the crystal in one direction and in substantially a single plane, preventing the return of the removed particles of the kerf of the crystal being cut, and feeding the crystal in a plane parallel to the plane of separation of the crystalline sections being cut.

9. The method of cutting sections from crystals of the Rochelle. salt type which consists in separating a section of the crystalline material. from the crystal by removing continuously in the same direction small particles of crystalline material at a rate sufficiently low to prevent a substantial localized rise in temperature of the crystalline material, and eliminating localized heating of any part of the crystalline ma terial by preventing the return of agglutinated crystal dust to the kerf being cut. 7

10. The method of cutting sections from crystals of the Rochelle salt'type, which consists in separating a section from the crystal by continuously cutting it in a single plane and in a single direction, moving the crystal in a plane substantially parallel to the cutting plane of the section to be cut, and preventing the return of agglutinated crystal dust to the section bein cutto avoid frictional contact between t e sides of the kerf being cut in the crystal and the body portion of the vcutting means, thereby eliminating localized heating of any part of the crystal.

11. The methodof cutting sections from crystals of the Rochelle salt type, which consists in cutting the material by removing crystalline particles from the crystal at a rccletermined speed which is inversely proportional to the width of the material being cut, preventing engagement between the side walls of the kerf and the body of the cutting means, and preventing the return of the removed crystalline particles to the spaces between the side walls of the kerf and the cutting means to obviate cracking and localized heating of any part of the crystal and section being removed therefrom.

In testimony whereof I afiix my signature. v

' CHARLES B. SAWYER.

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