US2854795A - Grinding apparatus - Google Patents

Description

Oct. 7, 1958 w, oc w ETAL 2,854,795

GRINDING APPARATUS 2 Sheets-Sheet 1 Filed Oct. 11, 1954 llla lrl i INVENTORS ATTORNEYS Oct. 7, 1958 W. E. MccowN ETAL 2,854,795

GRINDING APPARATUS 2Sheets-Sheet 2 Filed Oct. 11, 1954 (It Q96 A TTORNE YS finitedsates ara-11m GRINDING APPARATUS Application October 11, 1954, Serial No. 461,456 9 Claims. (Cl. 551-59) The present invention relates broadly to grinding, and more particularly to an improved method and apparatus for grinding surfaces by high frequency vibration.

Although the invention is not restricted to the grinding of any particular article or type of surface, it is especially well adapted to carry out the difiicult job of grinding the surfaces of flat glass sheets and will be described in that connection here. i I

In the regular commercial productionof plate glass, the unfinished glass blanks are ordinarily bedded upon surfacing tables in a layer of plaster of Paris or the like and then passed beneath horizontal grinding discs which are revolved in the presence of sand and water toobtain'the desired grinding efiect. Because of the pressureof the grinding discs upon the sheets of glass in the conventional processes, the sheets are subjected to a crushinglaction as the discs force the abrasive particles into the surface being ground. Consequently, the sheets oftentimes exhibit small cracks or fissures which affect the optical qualities thereof, and if numerous enough, cause the sheets to crack. 'Of course, any cracking of the sheets'not only has an adverse effect upon production efliciency, but also upon the felt-covered polishing discs used in subsequentpolishingsteps which are easily torn by sharp glass edges and chips.

' Further deficiencies are also grinding processes'in that it plic'ated precision equipment be used to maintain the grinding discsin an exact horizontal position with respectto the sheets passing therebeneath so that a'uniformly ground surface may be obtained. Also, the large amounts of wat'er anddifierent grades of sand that are necessary to obtain thede sired grinding effect cause the grinding area to be damp, dangerous and unsightly thereby incr'easing maintenance and accident prevention costs. 'According to the presentinvention, to alleviate the inherent in commercial so that the generating is necessary that heavy comabove-mentioned deficiencies that have been inherent in conventional grinding methods, vibration frequencies preferably over-100 cycles per second'are applied to the surfaces of the sheets through a suitable medium having an abrasive or grinding compound therein. These vibration frequencies are transmitted in the form of mechanical vibration sound waves, and as the sound waves are propagatedthrough the mediurn, which is preferably a fluid, the motion of the abrasive particles in said medium is related to the characteristics of the soundwaves themselves. {In'this manner, the sound waves create a cavitationlelfect iin the liquid medium; cavitation being the effect of Lthegal'ternate' formation and collapse of gas bubbles and cavities. This collapse of the cavities creates an a ation etfec tfof sufiicient magnitude to cause the abras ve particles'lto alternately bombard the surface of the sheets and torerode or grind the said surface as the sheets are movedpastifthe. cavitation area. k Ilius itlisitherefore a primary object of this invention to provide airelatively simple and light weight device which will grind flat-surfaced bodies in an expeditious 2,854,795 PatetttedOct. 7, 1 958 2 and efiicient manner by the use of sonic or ultrasonic vibrations.

Another object of the invention is to provide a means whereby a plurality of vibration generating elements may be mounted above the path of a conveying means faces thereof will completely traverse the path of the articles carriedby the conveying means as they pass beneath said generating elements.

Another object of the invention is to provide a means whereby a thin film of a liquid transmitting medium having an abrasive or grinding material therein may be confined to a very small and localized area over the surface being ground. i

A further object of the invention is to provide a method of grinding sheet material wherein relatively few grades of grinding orabrasive material are needed to produce a relatively smooth surface,

A still further object of the invention is to provide a method and apparatus for grinding glass sheets which will leave relatively few fissures or cracks in said sheets.

Other objects and advantages of the invention will become more apparent during the course of the following description when taken in connection with the accompanying drawings.

In the drawings wherein like numerals are employed to designate like parts throughout the same:

Fig. 1 is a fragmentary plan view of one form of grinding apparatus constructed in accordance with the invention; I

Fig. 2 is a transverse vertical section through a glass finishing line showing the apparatus of the invention mounted thereabove; g

Fig. 3 is aperspective view of one form of vibration generating element that may be used with the invention;..

Fig. 4 is a sectional view taken substantially along line 4- 4 of Fig. 3; i

Fig. 5 is a partial vertical sectional view: taken along line 55 of Fig. 1;" V v i 5 Fig. 6 is a partial side elevation of a means for the mounting of the vibration generating elements} and ig. 7 is a sectional view taken substantially along line77ofFig.6.

With reference now to the drawings and particularly to Figs. land 2, there is shown'one section ofafcontmuous grinding and polishing lineinade up of a series or conveying means '110 which are then passed 13. As shown in vibration generating elements are identical reciprocating supporting 14 and 15 arranged above the tables upon erally at 20 (Figs. 1 and 6) formed between guide blocks 21 suitably secured to the standards 16. l v

Movement of the respective cross beams 14 and 15 relative to one another is accomplished by'means' of'similar drive mechanisms 22. Specifically, the drive mechanisms 22 include a drive shaft 23 having'a bevel gear 24 thereon and journaled in a bearing 25. Extending in a substantially vertical direction and suitably journaled by a bearing 26 in the upper plate 27 of support frame 28 is a shaft 29. Connected to the lower end of shaft 29 is a bevel gear 30 which engages and is driven by the bevel gear 24-011 drive shaft .23. On the upper end of shaft 29 there is mounted an eccentric or crank 31 whichhas a drive arm 32 pivotally connected thereto. As shown in Fig. 6, the said drive arm 32 is in turn pivotally connected to one of the slide plates 18 by means of a pin 33 which fits in a suitable hole 34 in the said slide plate. Thus, for a purpose to be described hereinbelow, upon rotation of the drive shaft 23, the shaft 29 and the crank 31 will be rotated causing the drive arm 32 to reciprocate the respective cross beam connected thereto in the ways 20. In other words, each of the cross beams 14 and 15 are connected to similar individual drive mechanisms 22 which may reciprocate the said cross beams together or in a staggered or opposed relationship with respect to one another.

Provided on each end of the cross beams 14 and 15 adjacent the legs 17 thereof are vertical flange portions 35 and horizontal flange portions 36 which define rectangular openings 37 therebetween at the end of the beam. Slidably mounted for vertical movement in each of the openings 37 is an open frame-type clamping bracket 38. Mounted within the clamping brackets 38 and bridging the tables are especially formed channels 39 and 40 having grooves 41 therein; the channel 39 is secured to one side of each of the brackets 38 by means of screws 42, and the channel 40 is slidably mounted along a finished slot 43 formed along anopposite side ofthe brackts 38, being held therein by an adjustment screw 44.

The transducers 13, which are preferably of a magnetostrictive type having laminated core 45 and electrical coil windings 46 (Figs. 3 and 4), are supported by the channels 39 and 40 along nodal tabs 47 on the core 45 which tabs fit into the grooves 4I of the channels 39 and 40. The nodaltabs 47 are located at a point of substantially zero vibration of the transducer vibratory system so that a minimum of vibration energy will be imparted to the supporting structure thus allowing a maximum amount of energy to be expended upon the surface being ground. Secured to the vibrating ends of each of the transducer cores 45 by suitable screws 48 are upper and lower protective shoes or plates 49 and 50 respectively. In this connection, the lower shoe 50 serves as the working face of the transducer and prevents the abrasive grinding material from eroding the transducer core 45 and, in the event that the said shoe 50 should become unduly worn or eroded, it may be replaced'by simply removing the screws 48. i

When'all of the transducers 13 are properly supported along the channels 39 and 40, the whole bank of transducers may be vertically adjusted to place the transducer working surfaces or faces 50 at the desired height above the surface to be ground by means of opposed adjustment screws 51 (Fig. 6), held in place by lock nuts 52 and carried by the horizontal flange portions 36 of the cross beams 14 and 15. These adjustment screws engage the clamping brackets 38 and provide a means whereby the brackets may be raised or lowered in the opening 37 defined by the flanges 35 and 36, and thus cause the channels 39 and 40 to raise or lower the transducers 13 to place them in proper position with respect to'the surfaceof the sheets S carried by tables 10. The clamping brack' ets 38 are kept in aligned position with respect to the vertical flanges 35 by meansof keys .53 mounted on the inside of the flange portions which engage key ways 54 formed in the sides of' the clamping brackets. Thus, when the brackets are moved upwardly and downwardly, the keys 53 engage the ways 54'and allow the brackets and channels 39 and 40 associated therewith to move only in a vertical direction. Y

In accordance with the invention, as noted hereinbefore, a supply of liquid energy transmitting medium having an abrasive or grinding material thereinis maintained between the working surfaces 50 of the transducers and the surface being ground so that a cavitation elfect can be set up in the liquid medium which will cause the abrasive particles therein to bombard and erode or grind the surface of the sheets. This energy transmitting medium may be supplied between the working surfaces 50 of the transducers and the sheets S through a tube 55 (Fig. 4) passing through the central portion of the transducers 13. More particularly, the tube 55 is preferably formed of a pliable fiber or rubber material and is held in place in openings 56 formed in the transducer core 46 by suitably threaded plugs 57. The plugs 57 have an opening 58 therein which mates with a flared opening 59 provided in the protective shoes 49 and 50.

The energy transmitting medium may be brought to each of the transducers 14 by means of rubber hose conduits 60, the lower ends of which fit snugly in the upper plug 57 in the transducer core, while the upper ends may be connected by a suitable joint 61 -to individual pipe sections 62 positioned above each of the said transducers. In turn, each ofthe pipe sections 62 are connected to a main distribution pipe 63 extending along the length of each of the support beams 14 and 15. Because of the flexible hose connections 60 and the flexible tubes 55 within the transducers, the transducers may vibrate freely without having any damping, efiects exerted thereon by the said conduits or tubes and thus may impart a maximum amount of energy to the abrasive containing medium.

It will be apparent that as the abrasive containing liquid flows through the tube 55 in the transducer core under pressure, it will pass to the flared opening 59 in the lower protective shoe 50 and spread out onto the surface of the sheet 5 as it leaves the said opening. In this manner, it is possible to set up and maintain a film of fluid over a narrow area of the surface being ground. While thisfilm or layer of energy conducting liquid is extremely thin and vertically unconfined, it nevertheless completely fills the space between the transducer working faces 50 and the sheet surface due at least to some extent, to surface tension and capillary attraction effects. These effects act to maintain the energy conducting medium beneath the transducer faces at a level substantially higher than that of the unconfinedfilm ofthe liquid that flows away from the transducers onto the remaining portion of the sheet. on the other hand, for some applications, it may be desira le to place th t n d cer working faces 50 in slight pressure contact with the sheets so, that better vibratory contact may be had with the abrasive particles. If this were done, the thin film of the abrasive containing liquid may still be forced between the said working faces and the sheets being ground in the same manner as described above. In any case, however, it will be evident that the liquid medium, although unconfined may be maintained in a thin but elfective layer over the necessary narrow width'of surface being ground by the means described above, thus eliminating the need for tanks or other confining means to contain the liquid in sufficient volume to cover the transducer generating faces. 7

In order to obtain best results, the distance between the transducer working faces 50 and the surface being ground can be varied by means of the adjustment described hereinbefore, and the distance provided therebetween related to the surface tension and capillary attraction characteristics of the energy transmitting liquid being used.- For example, with liquids having the greater surface tension and capillary attraction characteristics, the transducers can be maintained at a greater distance from the surface being ground inasmuch as the surface tension will not be overcome as easily to permit the liquid to become separated from the working'faces'50.

With the transducer position so determined, the conducting medium is deposited therebeneath upon and over a narrow width of .the surface beinggroundwhere .it will substantially fill the narrowspace between the transducer generating faces 50 andthe said surfaces and be maintained therebetween by the natural forces mentioned above. The transducers are thenenergizedby an alternating voltage supplied to the coils 46 thereof causing extremely rapid vibrations to occur along the area .of the working faces 50. Since the generating surfaces 50 are in direct contactwith the liquid medium, alternate positive and negative pressure fronts which travel directly from the vibrating surfaces or faces to the surface being ground along a path normal thereto are created. These variable pressure fronts cause a cavitation or bubble effect to take place in the medium which in turn causes the abrasive particles to be alternately accelerated toward the surface and pulled away therefrom toward the vibration generating elements as the bubbles collapse and create a negative pressure area. In this manner, bynthe high acceleration of the abrasive particles toward the surface,- the said surface is subjected to agrinding and smoothing effect asthe sheetsmove relative to the. generating-faces 50 I 5 To aid in evenly distributing the grinding action of the abrasive particles over the entire surface of the sheets as they are moved past the transducers by the tables 10, the respective support beams 14 and 15 are reciprocated at a relatively high rate of speed relative to one another by the drive mechanisms 21 so that the surfaces of the sheets are swept by the eroding action of said particles. In other words, the transducers are moved transversely of the path of the sheets passing therebeneath so that a uniform grinding pattern will be obtained over the entire surface area of the sheets.

While for purposes of illustration, only two banks of transducers have been shown mounted above the path of the tables 10, it will be apparent that any number may be used along with various grades of abrasives to obtain the desired grinding and smoothing effect. Some of the abrasives that may be employed include sand, boron oxide, aluminum oxide, rouge and others, which may be used alone or in combination to produce the desired grinding effect. However, regardless of the type of abrasive used, it will be evident that the sheets may be ground by the apparatus of the invention without the crushing .efiect that is ordinarily involved with the large metal discs used in conventional processes, which as noted above, have a tendency to produce large numbers of cracks and fissures in the glass sheets.

While an energy transmitting medium of water may be advantageously used in many cases, in others it is desirable to use a detergent medium as the transmitting medium so that dirt and other undesirable particles may be removed during the grinding operation. Alternately, other methods of disturbing the molecular structure of the surface being ground using similar type vibration generating elements may be practiced. For example, if the sheets are susceptible to chemical reactions, an acid or other type medium may be used in conjunction with an abrasive to remove and grind the sheet surfaces.

Also, while the vibration generators used to produce the cavitation efiect in a liquid medium may operate continuously without interruption, it has been found that they overheat and tend to lose their efficiency when operated continuously for long periods of time. To compensate for this condition, there is herein provided a cooling means which includes a pipe 64 mounted along the beams 14 and 15 above the transducers 13. The pipe 64 is provided with spray holes 65 which act to direct water or other suitable cooling mediums upon the transducers so as to provide a cooling effect therefor and thus allow the transducers to operate at peak elficiency. However, it is to be pointed out that other types of cooling means may be employed such as cooling pipes which cool by heat absorption, or air jets, etc.

Should it be desired to move any one of the transducers fromthesupportingbeams [14 and 15, they maybe removed therefrom by mere loosening of the adjustmentscrews44 so as to allow .the channels 4ers slide in the slot 43 thus causing them to disengage the nodal tabs 47. After the channel 40 has been withdrawn from contact with the transducer tabs 47, any one of the transducers may be removed by'pulling the rubber hose 60 from contact with its associated plug 57 and by disengaging the transducer power lead 66- and plug 67 from the power supply, housing68 mounted upon the upper side of the supporting cross beams. V v 1 It :will alsobeapparent that while the grinding apparatus disclosed herein has been described in connection with the grindingof glass sheets, that it may also be used to grind sheet material such as steel plate or plastic,

and that the transducers maybe moved while the object being ground remains substantially, stationary or moves relative thereto. Also, while the abrasive. medium has been shown in the drawings to be deposited upon the sheets through a conduit passing through the transducers, it

may also be deposited upon thesheets by suitable external pipes whichmay spray thesaid medium between the working faces of the transducers and the surface of the sheets.

It is of course to be understood that the form of the invention disclosed herein is to be taken as the preferred embodiment thereof and that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of the invention or the scope of the following claims.

We claim:

1. Apparatus for grinding flat surfaced objects, comprising means for moving the objects to be ground along a definite path, a support mounted above the path of said moving objects, a plurality of elastic vibration generating elements mounted on said support in spaced relation to said objects, means for building up a layer of an abrasive containing energy transmitting medium on a localized area of said objects as they move past said vibration generating elements, and means for reciprocating said vibration generating elements laterally relative to said moving objects during grinding of the latter.

2. Apparatus for grinding surfaces of objects as described in claim 1, in which means are provided for supplying said abrasive containing medium through said vibration generating elements.

3. Apparatus for grinding glass sheets, comprising means for moving a sheet to be ground along a definite path, a support mounted above said path, a plurality of vibratory devices for inducing elastic vibrations mounted on said support in spaced relation to the glass sheet, means for depositing an energy transmitting medium containing abrasive therein between said vibratory device and said sheet, and means for moving said vibratory devices substantially transversely of the path of said sheet during grinding of the latter.

4. In a method of grinding a flat surface, the steps of moving said surface in face-to-face relation along a path past an elastic vibration generating element, providing a film of an abrasive containing energy conducting medium between said surface and said vibration generating elements and in contact therewith, and transmitting undamped elastic vibrations to said energy conducting medium from said vibration generating element while moving said element in a plane parallel to said surface.

5. In a method of grinding a flat surface as defined in claim 4, the additional step of moving said surface and said vibration generating element relative to one another during grinding of said surface.

6. In a method of continuously grinding a flat surfaced object as it moves along a definite path, the steps of arranging a plurality of vibration generating elements with their working surfaces in spaced relation with the object to be around providing a film of an abrasive containing energy conducting medium between said object and said 7 vibration generating elements, transmitting elastic vibrations' to said energy conducting medium from-said vibra sea generating :ele nents, f and moving someof said vibratibn'g'en'erating elements relative to one another in a planepar'allel to the flat surfaced object and duringgrinding thereof;

7. Apparatus for grinding glass surfaces,- comprising means for moving a" glass :s he'e t having a surface to-be ground along a definite path, support means extending across said path, elastic vibration inducing means mounted on said support means and having a working face positioned adjacent the path dftravel of the surface of said sheet, means for supplying an abrasi've containing energy transmitting medium to the'sheet surface to' be ground, and means for movingks'aid working face-transve'rsely to the direction of movement of the glass sheet during grinding of said sheet.

'8. Apparatus for grinding glass surfaces as defined in claim 7, wherein the means ground during grinding of said sheet surface.

9. A method of surfacing glasssheets which comprise positioning a glass sheet with the surface to be treated for moving the working faceincludes means forrecip'rocatin'gthe support means in a parallel with the working surfaces of a plurality of vibration generating elements, conveying said sheet surface past, said vibration generating elements along a predeterminedpathspaced from'but substantially parallel with saidparallel working faces, maintaining an unconfined mass of asuspens'ion of abrasive particles in an energy conducting li'q'iiidin the space between the parallel working' faces of said vibration generation elements and the portion ofsaid sheet surface that is moving therepast and in contact with both, and transmitting elastic vibrations to said unconfined mass of liquid.

ReferencesCited in the file of this patent UN'1 1ED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORECTIN PetenrNo, 2354 795 @m '7 58 William EC. McGown It is hereby certified that error appears in the printed specification of "the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

T w a Column 0 74, for "around" ea ground e Siged. and sealed this 27th of J 1959 (I SEAL) Attest:

ll AILLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents

Images