US3142946A

US3142946A - Grinding runner

Info

Publication number: US3142946A
Application number: US120899A
Authority: US
Inventors: John M Byal
Original assignee: Libbey Owens Ford Glass Co
Current assignee: Libbey Owens Ford Glass Co
Priority date: 1961-06-28
Filing date: 1961-06-28
Publication date: 1964-08-04
Anticipated expiration: 1981-08-04

Description

- Kw I Aug. 4, 1964 J BYAL 3,142,946

r GRINDING RUNNER Fil$d June 28, 1961 5 Sheets-Sheet 2 0. 10 20 so 40 so 54 a0 4,? INVENTOR.

066a fart/(#16 ATTORNEYS Filed June 28, 1961 5 Sheets-Sheet 4 INVENTOR fiowefdrwpe ATTORNEYS J. M. BYAL GRINDING RUNNER Aug. 4, 1964 5 Sheets-Sheet 5 Filed June 28, 1961 ATTORNEYS United States Patent 3,142,946 GRHQDMG RUNNER .iohn M. Byai, Toledo, Ohio, assignor to Libbey-Owens- Ford Giass Company, Toledo, Ghio, a corporation of Ohio Filed .iune 28, 1961, Ser. No. 120,899 '7 Claims. (Cl. 512W) This invention relates broadly to the surfacing of flat sheets and particularly to improvements in surfacing tools for use in the grinding and polishing of plate glass.

This application is a continuation-in-part of my copending application Serial No. 761,820, filed September 18, 1958, now abandoned.

It is conventional when grinding a continuous ribbon of glass, which has been formed from molten glass in a tank, to grind the. opposite faces of the ribbon, either simultaneously or by two separate operations, after it emerges from the annealing lehr. This grinding can be performed either by a series of single spindle grinding runners, positioned to operate on one surface, or by a series of opposed pairs of single spindle grinding runners positioned so as to operate upon both surfaces simultaneously, the runners being usually provided with generally uniformly spaced glass contacting noggins arranged around a central opening, and in any event, an abrasive fiuid or slurry such as a mixture of sand and water is applied between the surface of the glass and the runners during grinding. The noggins generally are in the form of raised bosses or other upwardly extending projections and constitute the physical means by which the glass surface is ground.

It has been found that a glass ribbon, ground by either of these methods as heretofore practiced, shows a variation in thickness on its ground surface that reflects a grinding pattern established by the portion of the grinding runner that engages the glass to be ground. Thus a glass ribbon or sheet, when ground under the action of a rotating runner, has thick outer edges from which the thickness gradually decreases on moving towards the center of the ribbon, to the central portion of the sheet in proximity to the central hole or well of the runner Where it slightly thickens again.

Because of this variation in thickness, when the sheet subsequently passes between either another opposed pair of substantially parallel grinding runners or under a second single grinding runner, it will be subjected to unequal pressures. If the difference in thickness is too great, the pressure in the thicker areas near the edges or at the center of the ribbon will be sufficient to cause breakage, with a resultant waste of material and loss of time in removing broken pieces from the grinding area.

It is, therefore, a primary object of the present invention to provide more uniform grinding action across the surface of a glass ribbon when acted upon either by a conventional table runner or twin type grinding runner so as to produce a glass ribbon of relatively uniform thickness and uniform quality after grinding.

It is another object of this invention to eliminate longitudinally extending quality streaks in the ground glass surface.

It is still another object to reduce the amount of grinding by finer sands required to reduce ridges resulting from rough grinding.

It is yet a further object of this invention to improve the uniformity of the finished surface of ground plate glass.

It is still a further object of this invention to provide a grinding runner for a grinding unit used in surfacing sheet material having a grinding surface accurately controlled across its entire width with respect to its sheet surface contacting area.

3,142,946 Patented Aug. 4, 1964 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 pants throughout the same:

FIG. 1 is a graphic representation of the surfacing action of different surfacing runners on a glass ribbon;

FIG. 2 is a graphic representation of the noggin concentration curve for a runner made according to the present invention;

FIG. 3 is a plan view of one octant of the grinding surface of a runner made according to the present invention;

FIG. 4 is a plan view of the entire grinding surface of a runner made according to the present invention;

FIG. 5 is a plan view of another embodiment of the improved grinding runner made in accordance with the present invention; and

FIG. 6 is a plan view of yet another embodiment of the improved grinding runner made in accordance with the present invention.

With particular regard to FIG. 1, there is shown a conventional grinding runner 20, normally operating on a glass ribbon 21 and in contact therewith during grinding. When the runner 20 is of the present conventional design, that is, when the ratio of the effective grinding area of the noggins, lying in a concentric ring or annulus at any selected radius on the runner to the total area of the same ring is substantially the same as the ratio for a concentric ring taken at any other selected radius, the runner will develop the grinding energy curve shown at 22. While it is true that the width of the ring itself might have some effect upon the ratio due to the size and location of the individual noggins, particularly if an extremely narrow ring is chosen, this effect will be negligible since it has been found that the ratio is substantially the same for a ring having a width of one inch as for a ring having a width of one foot. This effective noggin grinding area is actually the total of all of the glass contacting portions of each of the individual noggins over which the concentric ring passes, or it might be described as the total area of the runner, within a complete concentric ring at a selected radius, actually in contact with the glass. The total runner area within the ring includes the effective grinding area as well as the area of the slurry distributing spaces between the individual noggins within the same ring. As described above, in conventional runner design it has been noted that the ratio of the effective noggin grinding area to the total runner area is substantially the same for concentric rings taken at any radius across the entire surfacing face of the runner. As the specification proceeds, it will become ap parent that this is not true of the runner of the present invention.

Now referring again to FIG. 1, the curve 22, representing the energy curve of the conventional runners made in accordance with the aforementioned principles, is derived on the basis of the following assumptions:

(1) The energy curve is calculated as though there is no overhang (complete coverage of runner face by the glass). Effect of runner overhang at edges of glass can be ignored without serious error.

(2) Wear rate of noggins is directly proportional to pressure (P) times distance traveled on the glass per revolution (S) and since, for purposes of plotting the curve, it is assumed that the noggins wear down essentially uniformly; SP=K where K is a constant.

(3) Energy expended on any point of glass is proportional to total noggin length passing over point times pressure.

(4) Slurry action at all parts of all noggins is the same.

(5) Effect of glass travel is negligible.

aliases Referring further to FIG. 1, there is shown at 23 the general physical appearance of the glass after rough grinding by a runner developing the energy curve 22. The glass presents high spots or ridges along the edges of the glass at 24 and at the center 25 of the sheet substantially coincident with the central cutout 26 of runner 20. These high spots 24 and 25 extend longitudinally of the glass, parallel to the line of movement of the ribbon 21, and appear essentially as ridges. Between ridges 24 and 25 are valleys 2'7 which shall herein later be referred to as primary streaks in the glass surface being ground. In order to facilitate the description, only the contour of one glass surface has been shown, that is, the surface ground by a single grinding runner. However, it is understood that the same effect would result on both faces of the ribbon if simultaneously ground by opposed pairs of grinding runners.

The valleys 27 are the result of over grinding because of the greater energy expended at these points. They are referred to as primary streaks because they show up as streaks of poor finish in the glass ribbon when there is insufficient grinding in these areas by later grinding runners.

It is well understood that in order to obtain a plate or sheet having a uniformly smooth surface, all of the glass above line xx (FIG. 1) must be removed by fine grinding. Therefore, if the primary streaks 27 could be eliminated or their depth into the glass surface substantially reduced, the work subsequently required in removing the glass above line x-x by fine grinding could instead be used to improve the smoothness of the entire glass ribbon surface.

We have found that the depth of these primary streaks can be eliminated or substantially reduced by the provision of a special type of substantially circular grinding runner 28 (FIG. 4), which will develop the grinding curve 29 shown in dotted outline in FIG. 1 instead of the curve 22 as hereinbefore described. As seen in FIG. 1, this curve 29 does not have excessively high energy peaks such as the energy peaks a of curve 22, but rather has a substantially uniform, i.e. flat or even, contour. Therefore, the primary streaks that are caused by these energy peaks a are substantially eliminated from a glass sheet or ribbon ground according to curve 29, and a substantially fiat contour on the glass surface, as seen at 30, is achieved. The contour is substantially flat along the portions 31 and there is a single ridge 32 along the center coincident with opening 26. It naturally follows that a lesser amount of grinding is required to remove the glass above line y-y when the glass is ground by a runner developing curve 29 than is required to remove the glass above line xx.

It has been found that a grinding curve 29 (FIG. 1) will be developed by a runner in which the area of the runner face portion or working surface which engages the glass to surface the same is controlled across the face of the runner so that the ratio of the eifective noggin grinding area to the total runner area, as above defined and discussed, is greatest about the periphery of the runner and gradually diminishes across the runner grinding face on moving towards the runner center.

This principle will be best understood if it is examined in its basic concept without referring to the glass per se. Therefore, the principle will be expressed by a ratio, to be more particularly defined hereinafter, and this ratio will be identified throughout this specification as the noggin concentration of the runner, a term familiar to those versed in the plate glass grinding art.

The term noggin concentration is best defined by first considering an arc of a circle as being drawn about or on the surfacing face of the runner of the present invention at any given radius from the runner center, this surfacing face itself being defined by a plurality of individual noggins as hereinbefore defined, with spaces therebetween. The arc, whose length will be defined in detail as the This ratio (expressed above as a mathematical equation) of the length of the are that passes over the actual runner surfacing area determined by the noggins to the total length of the are, including those areas covered by the arc which are actually the spaces between the noggins, is therefore a value capable of mathematical determination alon any arc of any runner independently of the shape, dimensions, area and orientation of the noggins.

Ideally, the noggin concentration value should be uniform along any are at any given radius no matter how small in length be the reference arc chosen to make the determination. However, since the noggins have a finite size, as do the spaces between the noggins, there is a minimum practical length of are which may be used in the determination of noggin concentration. Actually, in the design of a runner, it is practical and advisable to have a modular noggin pattern (i.e. in other words, a circumferentially repeating noggin pattern). It follows, therefore, that for a selected radius, the length of are chosen for the determination of noggin concentration at that particular radius should be a whole multiple of the circumferential length of the smallest module of the noggin pattern at that radius. For example, referring to FIG. 4, this would be ,4; of the circumference or some whole multiple thereof.

Now considering the runner as a whole, rather than only a segment of the runner, the circumference of a circle at a selected radius can be substituted for the value of the length of the arc (L so that the expression of the noggin concentration mathematically becomes:

Noggin Concentration=- To relate this to the derivation of the calculated grinding action curve, and for this curve to be rigorously accurate considering noggin concentration only, the noggin concentration would have to be the same at every point on the circle described at any radius. This is important to consider since it must be remembered that the glass is moving as it is ground. Actually, the noggin concentration, as hereinbefore defined, at every single point along a given circumference is not the same because the runner face has spaces as well as surfacing noggins. Therefore, to achieve as closely as possible on the glass a surfacing action in accordance with the calculated grinding action curve 29, the modules should be made as small as possible. In other words, considering a point on the glass, its travel should be as short as possible during the time that one module of the runner is passing over the point.

In the present conventional runner, i.e. that developing curve 22, this noggin concentration, as above defined, is normally substantially constant or has only slight differences in its value on moving across the operating surface of the runner from the center cutout to the periphery. However, the noggin concentration of the improved runner of the present invention follows a graduated curve, or it has a progressively decreasing value on moving from the periphery to the center cutout. This is illustrated by the curve 33 in FIG. 2. In FIG. 2, the horizontal axis represents the radius of the runner as measured from its center 34, and the vertical axis represents the ratio CKg Kw where C is the noggin concentration as above described, while Kg and Kw are the glass removal coefiicient and noggin wear coefficient, respectively, for a particular type of glass, grinding slurry and noggin material.

In this regard, it has been found that for a given grinding system including a particular glass, grinding slurry and noggin material, the rate of glass removal and the noggin wear rate are related to noggin speed and noggin pressure as follows:

where G=rate of glass removal S=noggin speed with respect to the glass P'=noggin pressure Kg=glass removal coeflicient W=SPKw where W=noggin wear rate Kw=noggin wear coefficient S and P are as above defined Kg and Kw are, in general, constant for a given grinding system, that is, for a uniform glass sheet being surfaced by a single type of runner and grinding slurry. If the system is changed, as for example by changing the noggin material as will later be described, then the values of Kg and Kw may be altered. It will thus be seen that for a grinding system using runners having a single, uniform noggin wear coefiicient, the ratio of will be constant. As a result, the curve 33 of FIG. 2 will represent the noggin concentration C, multiplied by a constant which can be disregarded when considering the noggin concentration ratios across the face of the runner. Curve 33 thus becomes the noggin concentration curve for the runner and is plotted by joining the individual noggin concentrations at different radii of the runner as measured from the center of the runner. It is here noted that curve 33 is a specific noggin concentration curve for a 108 inch runner, surfacing a 100 inch glass ribbon. The zero point 34 represents the actual center or" the runner, and the radius values (i.e. R) represent the runner radius moving from the center 34 toward the runner periphery. Although the curve 33 has been shown as theoretically extending to the center of the runner, it will be understood that there are no noggins in the central cutout 26 for reasons to be hereinafter explained, and therefore in actual runner design the curve 33 would stop at the edge of the cutout.

The results achieved by the use of the improved runner are, as above noted, best illustrated in FIG. 1 where there is shown at 30 the general contour of a glass sheet after grinding by the improved runner developing curve 29. It is specifically noted that in addition to the flat contour 31, the ridge 32 (FIG. 1) is of substantially reduced height as measured from fiat portions 31 when compared to either ridges 24 or 25. Accordingly, much less fine grinding will be necessary to remove the ridge 32 to secure a uniformly smooth surface across the entire sheet than would be needed to level the contour of a sheet ground according to curve 22. The resulting saving of energy necessary for fine grinding can therefore be used to improve the uniform smoothness of the sheet and, accordingly, an improved ground glass ribbon can be obtained.

Referring to FIGS. 3 to 6 inclusive, there are illustrated a number of specifically different forms of grinding runners which can be used to achieve the uniform smooth distribution of grinding energy and to develop the grinding curve 29 in accordance with this invention. In connection with these, it will be understood that it is most desirable to strive for structural simplicity and yet at the same time to achieve the improved results that follow from the application of this invention. Since the general configuration of conventional grinding runners is well known, only those portions of the runner which are believed to be necessary for a complete understanding of this invention have been shown and will now be described.

In FIGS. 3 and 4, there is shown one runner which will develop the curve 29. While this embodiment of FIGS. 3 and 4 will be described by reference to a specific number of noggin lines and their arrangement within two general areas, it is to be understood that this embodiment represents but one application of the broad concept of the invention to a particular runner, and it is not intended to restrict or limit the invention to the specific configuration illustrated and hereinafter discussed. The runner surface or operating surface is composed of a plurality of noggins 35 disposed so that the noggin concentration, as above defined, diminishes on moving from the periphery 36 of the runner to the edge 37 of the central opening 33. In FIG. 3, there is shown one octant of the improved runner and the noggins 35, as shown in this preferred embodiment, are arranged in two general areas, one indicated at 39 adjacent the periphery 36 and the second indicated at 40 adjacent edge 37 of the central opening 38. In area 40 there is illustrated, in this embodiment, five outwardly spiraling noggin lines 41, 42, 43, 44 and 45. Each of these noggin lines is composed of a series of individual noggins 35 that form what is similar to a continuous bar that has been interrupted by graduated spaces 42. These spaces form a channel to be later described. The number, size and shape of the noggins 35 in each line, as well as the number of lines of noggins, will vary in a manner calculated to provide the desired noggin concentration as above defined, it being necessary according to the present invention to increase the noggin concentration, or grinding area per unit of runner area, in moving from the central portion toward the outer edge or periphery in order to attain the grinding curve 29.

As each noggin line in area 40 passes into the second area 39, it is noted that instead of a line of single noggins, each noggin line, for example line 45, is composed of two

parallel noggin lines

46, 47 of single noggins 35 that continue the general spiral noggin line form toward the outer edge 36. Therefore, the even spiral initiated by the noggin line 45 in area 40 is split into two

noggin lines

46, 47 that continue spiraling outwardly toward the periphery 36. Likewise, the outwardly directed channels 48, between the noggins in area 40, split into an increased number of additional channels 49 between the more numerous noggins 35 of area 39. The channels 49, however, remain in parallel relationship to one another and continue the same spiraling pattern established by channels 48. The channels 49, on arriving at the periphery 36, turn slightly in a direction away from arrow 50 which indicates the direction of rotation of the runner, and channels 49 are in free communication with openings 51 formed in periphery 36.

Each octant (FIG. 3) is the same as all others, and when each is placed in proper relationship to all others, they combine to form a runner as shown in FIG. 4. In FIG. 4, the spiral form of the noggins 35 in each octant is clearly evident from the joining of all octants into a single unit. Thus, it is seen that the spiraling noggin lines 41-45 of each octant are all formed so as to spiral from the center opening 38 and to bend or spiral toward the direction of rotation of the runner (arrow 50), while the channels 52, to be later described, spiral outwardly and counter to the direction of rotation.

The 2:1 ratio of lines of noggins between

areas

39 and 49, as shown in the embodiment of FIGS. 3 and 4, has been found desirable under certain circumstances. However, other ratios of lines of noggins could be used, or the noggins could be arranged in more than two areas as long as their arrangement would result in the noggin concentration across the operating surface of the runner being substantially that shown by curve 33 in FIG. 2. In addition, if desired, there could be a single noggin area instead of the

separate areas

39 and 40 shown and discussed above, in which case the noggin lines 41 through 45 could be continued and only the size of the noggins 35 increased or otherwise varied on moving toward the periphery of the runner, it being necessary only to secure the proper progressive variation of noggin concentration according to the curve 33 (FIG. 2). Furthermore, it is desirable that when the proper noggin concentration is realized, the noggins themselves be individually arranged to avoid discontinuities as will later be discussed.

Referring to FIG. 4, it is noted that the noggins 35 are positioned and shaped to follow a second series of spiral lines or rows, i.e.

rows

53, 54 and 55, which spiral outwardly with respect to the runner center 38, and describe a spiraling path of ever increasing radius which follows a course substantially counter-directional to the path of rotational movement of the runner indicated by arrow 50.

The channels 52 formed between

rows

53, 54, 55 which decrease in width in running from the center 38 toward the periphery 36, have been carefully located so as to avoid any discontinuities in the noggin concentration curve 33 which would produce secondary streaks. Such secondary grinding streaks across the face of the surfaced glass result when the runners used have concentric rings of grinding noggins with the rings of noggins being separated by channels also formed concentrically about the center of the rotating runner. Thus, according to the present invention, the noggins are overlapped to avoid discontinuities in the noggin concentration curve, that is, the rows of noggins spiral in a manner which insures proper noggin overlap so that the noggin concentration at any radial distance from the center of the runner, determined in the manner earlier defined, will fall along the desired noggin concentration curve, in this instance the curve 33 of FIG. 2.

This overlapping of the noggins is best illustrated by reference to FIGS. 3 and 4. It will be: seen therein that the noggins 35 of adjacent octants which lie in the same spiral noggin row, i.e.

rows

53, 54, 55, are positioned so that, for example, point 56 of one noggin is located a further lineal distance from the center opening 38 along the spiral noggin line 45 than is point 57 on a corresponding noggin in spiral noggin line 41 of the same octant. The point 58 of the first noggin in the adjacent octant in row 53 is aligned with point 56, and the same relationship exists between points of the first and last noggins of this octant as exists between the

points

56 and 57 of the preceding octant. In other words, in going from the center 38 to the periphery of the runner along the spiral noggin rows, i.e. 53, 54, 55, each succeeding noggin extends outwardly from the center of the runner a greater distance than the noggin preceding it, while at the same time extending inwardly beyond the outer end of the preceding noggin. It will be seen, therefore, that as the runner rotates through one complete revolution, each. row of the noggins 53,. 54, 55 etc. will traverse the entire surface of the glass ribbon passing therebeneath, thereby minimizing secondary grinding streaks.

As a result of the arrangement of the noggins, eight outwardly spiraling channels 52 are formed between the rows of noggins. Each channel 52 sweeps successively through adjacent octants, intersecting channels 48' and 49, and terminates at periphery 36 in an opening 51 where two adjacent octants meet. It istherefore seen that

channels

48, 49 and 52 constantly intersect across the surface of the runner to direct the flow of abrasive around all the grinding noggins and outwardly toward the periphery of the runner.

Referring now to FIG. 5, there is shown a modification of the present invention wherein the solid bar type of noggin 59 extends from the edge 60 of center opening 61 to the peripheral edge 62. It is noted that the continuous bar 59 spirals generally in the direction of arrow 63, the direction of rotation, and also that the individual bars 59 are of a reduced Width at or near the edge 60 of center opening 61 and progressively increase in size on moving towards peripheral edge 62. Thus, the runner conforms to the noggin concentration curve 33 of FIG. 2,

, while at the same time eliminating the possibility of discontinuities in the curve.

With grinding runners of the type heretofore used, it is necessary to leave a rather large central opening, or area free of noggins, in the runner to eliminate possible breaking of the glass ribbon caused by excessive pressure at the runner center. The greater pressure at the center of the runner is caused in part by the natural tendency of the runner to distort when a load is applied at its center. However, a greater portion of the variation in pressure across the face of the runner is caused by uneven wearing of the noggins. Since the noggins near the periphery of the runner travel a greater distance in contact with the glass ribbon than do the noggins nearer to the center of the runner, they tend to wear down faster than the interior noggins. Consequently, the noggins exert a greater pressure on the central portion of the ribbon than on its edges and may cause it to break.

To overcome this variation in pressure across the face of the runner, noggins having different wear coefiicients may be provided in different areas of the runner. Thus, the noggins near the central opening of the runner may be made of a material having a faster wear coefiicient than the noggins near its periphery. By the proper selection of noggin materials, it is possible to compensate for the difference in distance traveled in contact with the glass ribbon by the noggins located at different positions on the runner face, thereby causing the noggins near the center of the runner to be worn away, or shortened, by the same amount as those near the periphery during each revolution of the runner. As a result, the noggins, even after extended use, will exert approximately the same pressure upon the ribbon near the periphery of the runner as at the center thereof.

Referring to FIG. 6, there is shown a further modification of the present invention wherein the noggins are positioned upon the runner according to the noggin concentration principles hereinbefore discussed, that is, so that the noggin concentration progressively increases from its minimum at or in proximity to the edge 64 of the central opening 65 of the runner to a maximum value at the peripheral edge 66. Additionally, the embodiment of FIG. 6 is particularly adapted to the use of noggins having different wear coefiicients, although it will be understood that the principle of varying the wear coefiicients of the noggins may also be applied to any of the earlier described runners.

Thus, attached to the runner deck 67 in a series of repeating modules are an inner pad 68, an intermediate pad 69 and an outer pad 70 having rows of

noggins

71, 72, 73, 74, '75, 76 and 77 cast integral therewith. The

pads

68, 69 and 70 are secured to the runner deck at 7 8 by bolts or other suitable fasteners. The individual noggins 79 in adjacent rows are positioned so that the channels 80 between the noggins are irregular, thereby insuring an adequate flow of abrasive completely around each grinding noggin during rotation of the runner. Discontinuities in the noggin concentration curve are avoided by overlapping the noggins in adjacent rows (i.e. rows 71-77) an amount suiiicient to provide the desired noggin concentration in the region'of overlap. By this overlapping of the noggins, secondary streaking of the glass ribbon being ground is avoided.

While the noggins of the embodiment of FIG. 6 have been shown as attached to three separate pads or bars 68, 69 and 70, it is contemplated that each row of noggins 71-77, or any combination of the rows, may have a different wear coefiicient to thereby provide the desired variation from the center opening to the periphery of the runner. The variation in noggin wear coeflicient may be obtained in a number of ways, as for example by making the noggins from different materials or by heat treating or annealing the noggins differently. Cast iron, hot-rolled steel and cast aluminum are examples of metals which have been found satisfactory as noggin material.

Substantial reductions in the variation of pressure across the runner face have been obtained in the embodiment of FIG. 6 by providing noggins attached to the outer pad 70 having one wear coefiicient and noggins attached to the intermediate pad 6? and the inner pad 68 having a second, faster wear coeificient. Thus the noggins in rows 71-75 may be made, for example, from annealed cast iron while these in

rows

76 and 77 may be made from unannealed cast iron or some other material having a slower wear coefiicient than annealed cast iron.

When the wear coefiicient of the noggins is varied across the face of the runner, the value of as hereinbefore described also may vary, that is, each different noggin wear coeflicient may produce a different value of Since it is desirable to obtain the flat grinding energy curve 29 of FIG. 1 with the runner having noggins of varying wear coefiicient, it is necessary that the values of CKg for the runner, as earlier defined, fall along the curve 33 of FIG. 2. The curve 33 may not, however, represent the noggin concentration because the value of may have changed. Instead, for a runner having noggins with two different wear coeflicients as described in connection with the embodiment of FIG. 6, the noggin concentration curve may appear as shown in broken lines at 33' in FIG. 2, with b representing the radius at which the noggins change from the faster to the slower wear coefiicient. It will be seen that in order to obtain a continuous curve 33 for the value of CKg Kw Kg W for the different noggins.

By arranging the noggins according to the curve 33 as hereinbefore discussed, the areas of over grinding near the center opening of the runner, as shown at 27 in FIG. 1, are eliminated. Likewise, the excessive pressure at the central portion of the ribbon caused by uneven wearing of the noggins is eliminated by using noggins having different wear coeflicients as earlier described. It is thus possi ble to position noggins closer to the center of the runner than has heretofore been practicable with runners having uniformly distributed noggins of the same wear coefiicient, thereby allowing for more grinding action in the central portion of the ribbon.

According to one specific embodiment of the invention, the effective noggin working surface extends to within 15 /2 inches of the runner center where the runner is 108 inches in diameter and operates on a glass ribbon inches wide. It will be understood, of course, that the same principles are applicable to runners of various diameters operating on different width ribbons. As a result of extending the effective noggin working surface nearer to the center of the runner, the grinding curve 29 of FIG. 1 is further flattened and the central ridge 32 on the glass ribbon coincident with the center cutout 26 of the runner is reduced in width.

It is to be understood that the forms of the invention herewith shown and described are to be taken as illustrative embodiments only of the same, and that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of the invention.

I claim:

1. A substantially circular grinding runner adapted to provide more uniform distribution of grinding action across the width of the glass sheet, said runner having a working surface comprising a plurality of noggins positioned so as to provide an ever increasing noggin concentration from the runner center to the runner periphery, said noggins being arranged in individual lines outwardly spiraling from the runner center in the direction of rotation of the runner, a plurality of first channels between said noggins, said first channels spiraling outwardly from the runner center in a direction counter to the direction in which the runner is rotated, and a plurality of second channels formed between said noggins, said second channels spiraling outwardly from the runner center and in the same direction as the direction in which the runner rotates.

2. A substantially circular glass surfacing runner having a working surface engaging the surface of the glass, said working surface compiising a plurality of noggins positioned so as to provide an ever increasing noggin concentration from the runner center to the runner periphery, the noggins in proximity to the runner center having a faster wear coeflicient than the noggins positioned outwardly thereof and in proximity to the runner periphery.

3. A substantially circular glass surfacing runner having a working surface engaging the surface of the glass, said working surface comprising a plurality of noggins positioned on the runner in a plurality of concentric rows, the noggins in the rows in proximity to the runner center having a faster wear coelficient than the noggins in the rows positioned outwardly thereof and near the runner periphery, the noggins being arranged so that the ratio CKg H ever increases from the runner center to the runner periphery, where C is the noggin concentration, Kg is the glass removal coefficient, and Kw is the noggin wear coefficient.

4. Apparatus for use in the surfacing of glass sheets to achieve uniform grinding action across the width of the sheet, comprising a substantially circular runner adapted to rotate about an axis normal to said sheet and having a working surface engaging the sheet, said runner including a runner deck, a plurality of pads secured to said runner deck in concentric circles about said axis, said working surface being formed by a plurality of individual noggins cast integrally with said pads and positioned in a plurality of concentric rows about said axis so as to form irregular channels therebetween for receiving a flow of abrasive medium, the noggins in adjacent concentric rows overlapping, and the noggins in the inner concentric rows having a faster. wear coefiicient than those in the rows positioned outwardly thereof near the runner periphery, said noggins being arranged so that the ratio CKg Kw ever increases from the runner center to the runner periphery, where C is the noggin concentration, Kg is the glass removal coefiicient, and Kw is the noggin wear coeflicient.

5. A substantially circular glass surfacing runner having a Working surface engaging the surface of the glass, said working surface comprising noggins arranged on the runner face so as to be separated by channels through which the grinding slurry is distributed across the runner face and so that the ratio of the length of the glass engaging portion of all of the noggins encountered by a concentrio circle described on the runner face at any radius to the circumference of the circle at the same radius, including the spaces between the noggins, is always greater for a concentric circle taken at a greater radius on the runner face than for a concentric circle taken at a lesser radius, said noggins being positioned about the runner in concentric rows, the noggins in adjacent rows overlapping, and the channels between the noggins being discontinuous to thereby provide an adequate supply of slurry around each noggin.

6. Apparatus for use in the surfacing of glass sheets to achieve uniform grinding action across the width of the sheet, comprising a substantially circular runner adapted to rotate about an axis normal to said sheet and having. a Working surface engaging the sheet, said runner including a runner deck, a plurality of pads secured to said runner deck in concentric circles about said axis, said working surface being formed by a plurality of individual noggins cast integrally with said pads and positioned in a plurality of concentric rows about said axis so as to form irregular channels therebetween for receiving a flow of abrasive medium, the noggins in adjacent concentric rows overlapping, said noggins being arranged so that the noggin concentration ever increases from the runner center to the runner periphery.

7. A method of increasing the uniformity of distribution of grinding action across the Width of a glass sheet to produce a sheet of relatively uniform thickness after grinding, including the steps of moving the glass along a predetermined path at a substantially uniform rate, moving a plurality of noggins, some of which have different wear coefficients than others, in a plurality of circular paths about a common center and in abrasive contact with at least one surface of the glass, with the concentration of said noggins increasing outwardly from said center and With noggins that exhibit the fastest wear coefiicient nearest said center.

References Cited in the file of this patent UNITED STATES PATENTS 1,692,635 Drake Nov. 20, 1928 1,828,663 Jopp Oct. 20, 1931 2,088,392 Waldron July 27, 1937 2,088,393 Waldron July 27, 1937 2,577,937 Waldron et al Dec. 11, 1951 FOREIGN PATENTS 10,903 Great Britain Nov. 20, 1908