US 2918762 A
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Description (OCR text may contain errors)
Dec. 29, 1959 E. HURST ABRASIVE DEVICES 3 Sheets-Sheet 1 Filed May 6, 1957 It Lz/EL E W W m2 YE L l INVENTOR. Fa wm'ci jfius'f Dec. 29, 1959 E. HURST ABRASIVE DEVICES 3 Sheets-Sheet 2 Filed May 6, 1957 United States Patent ABRASIVE DEVICES Edward Hurst, 'Duxbury, Mass., assignor to Rexall Drug C0., Los Angeles, Calif., a-corporation of Delaware Application May'6, 1957, Serial No. 657,070
14 Claims. (Cl. 51-188) This invention relates to the general art of abrading and polishing and particularly to a complete line of abrasive devices for performing many of the abrading, polishing and bufiing operations Well known in that art. It especially pertains to various forms of abrasive devices such as abrasive belts, discs, wheels, pads, drums or the like embodying a suitable supporting structure in the form of a hub, core or backing member to which is secured a plurality of individually and collectively acting abrasive elements.
Many abrasive operations involve dressing, restoring, polishing, bufling, finishing, or otherwisealtering the surfaces of innumerable articles of manufacture, and especially articles of irregular contour, in which little or no stock removal is frequently desired, but the primary objec'tive is the thorough and uniform treatment of the entire surface of the workpiece, irrespective of the amount of material to be removed. Rigid bonded abrasivearticles of the conventional grinding wheel type have never been particularly well adapted for such purposes because of the inability of such articles to follow the contour of the workpiece except in the case of articles having planar surfaces. Consequently, other means have been employed heretofore for carrying out many of the various surfacing operations demanded by industry. For example, despite the almost complete lack of control over the regularity and evenness of action and the inordinately low level of performance obtained from the individual abrasive particles through their instantaneous impact with the workpiece, sandblasting has been used in which a loose abrasive material is forcefully impinged against the surface of the article to be polished or otherwise dressed. Wire brush devices have also been used to scratch the surface of the article to give the desired surface finish. While sand-blasting and wire brushing operations are more or less uncontrollable and irregular in performance, they have had the advantage of offering no loading problem.
Fabric bufiing wheels in conjunction with loose abrasive materials have been used for'many polishing operations. Likewise, abrasive coated materials such as abrasivecoated paper and cloth products, supported by contoured or yieldable backing means, have been used to perform many of the abrasive and polishing operations on articles of ire'gular surface contour. All these devices have required frequent replacement of the abrasive materials or elements, have been irregular or uneven in their application and action on the entire surface of the workpiece, have frequently presented loading problems, and for these and other erasons have not been entirely satisfactory.
Furthermore, in all those techniques very inefficient use has been made of the particular abrasive element which has been discarded without obtaining the benefit of its full potential of usefulness.
The present invention is founded upon a fundamentally novel concept of providing an abrasive article in which the abrasive media,whether particulate or filamentary in character, is not only forcibly presented to the surface pulling apart beyond the desired amount by adhesively ice of the work, regardless of the irregularities of the workpiece surface, with all the forcefulness of a sandblasting operation, but with far greater uniformity of action over the area of the workpiece. Furthermore, the abrasive material of the abrasive article is subject to a controlled action and restrained against premature release from its supporting background by being adjustably secured in a release from its supporting background by being adjustably secured in a more or less resilient matrix without being rigidly anchored in permanently fixed position in a hardened bonding medium, whereby the individual abrasive particles or filaments of the abrasive material are repeatedly presented to the workpiece from new positions. As a result of this controlled positional freedom of movement of the abrasive matter in abrasive articles of the present invention the abrasive material is utilized effectively to a far greater extent than has heretofore been accomplished with articles in whichthe'abrasive constituent has been rigidly fixed or anchored ;in its bonding medium. Despite the numerous ramifications of the present invention a manifested in the different embodiments described later herein, it is to benoted that these fundamental, novel concepts are structurally designed into the product in all its forms. The abrasivearticles of the present invention are characterized to a marked extent by the following combination of desirable and long sought-for functional properties:
(a) Non-loading, free-cutting character.
(b) Coolness of cutting action.
(c) Thorough utilization of the abrasive material.
(d) Uniformity of abrasive action on both plane and irregular surfaces of workpieces.
(e) smoothness of operation.
(f) Efficiency of performance.
(.g) .Extraordinarily long life of the abrasive product.
The above andother objects and advantages accruing from the present invention will become apparent as the description herein proceeds.
Inaccordance with the present invention, abrasive -'articles such as abrasive and polishing wheels,-abrasive=anrl polishing discs and belts, set-up wheels, bufiing wheels and devices, sanding pads for oscillating sanders of both the stationary and portable types, and similar types of abrasive articles are constructed of a shirred abrasive strip or sheet material adhesively attached or secured .to :a backing or other structural supporting member whereby the shirrs or pleats of abrasive material constitute .2! highly mobile, yieldable and conformable working "face of the abrasive device. Where reference is madeherein and in the claims to a shirred material orto the shirrs thereof it is intended tomean and cover a material which has been shirred or pleated to form a folded material in which the pleats or shirrs are pulled or brought together and held in the desired folded or pleated relationship either by a draw string or strings and/or held against tacking or bonding the shirrs or pleats to their backing or other supporting structure in the desired-conformed position.
The abrasive strip or sheet material embodied inthe article can be so shirred that the individual shirrs either fully or partially overlap one another, depending upon the specific type and form of abrasivedevice desired. Also, the individual shirrs making up the functional face or faces of the article can be closely adjacent one another or they can be individually spaced or separated one from the other to produce an open faced workingstructure, depending upon the particular type of product to be made and the specific use for which it is intended. The shirred ness, although this does not exclude the use of shirred abrasive materials which are reinforced by filamentary, fibrous or fabric reinforcing means, providing the latter is not such that will interfere with the uniform cutting action and breakdown of the shirred material in use. I have had highly satisfactory results in the making of abrasive belts, discs and bufiiug wheels in accordance with the present invention utilizing as the shirred abrasive material an abrasive-included fibrous sheet material such as that disclosed and described in my US. Patent No. 2,284,738 issued on June 2, 1942. Such abrasive-included fibrous sheet material can be used alone or in combination with abrasive-coated fabrics or layers of matted steel wool or other filamentary or fibrous abrasive materials. Such abrasive-included fibrous sheet material can be described as a non-lamellar web structure of individual cardable interlocked textile fibers, adhesive binder and abrasive granules which are distributed internally of and throughout the fibrous web and are secured in the web by being surrounded by the long fibers. Although the uppermost granules penetrate through and above the surface of the web, they are also securely attached by the surrounding fibers, which with the aid of the adhesive binder secures them in position.
Such an abrasive-included fibrous sheet material, either alone or combined with other materials, when shirred and secured to a suitable backing or support to form an abrasive device in accordance with the teachings herein, provides an abrasive device embodying the principles of the present invention in that the functional or abrading component of the device is of substantial depth and therefore of relatively long life, is expendable throughout, allows readjustment of abrasive grain positions in use without premature release of the abrasive particles, and at the same time is yieldable and conformable to irregulari- 'ties in the surface of a work piece presented to the device.
However, it is not intended that the present invention should be limited to the use of any specific abrasive substance in the abrasive-included fibrous sheet material referred to above. Any of the particulate abrasive materials in common use may be employed in practicing my invention. Such materials include silicon carbide, fused aluminum oxide, flint, natural corundum, emery, rouge, tripoli, and similar substances. The size of the abrasive may vary from the finest polishing or buffing powders to the coarser grit sizes used in grinding. Other granular, fibrous or filamentary materials suitable for various abrasive or polishing purposes and which can be embodied in the form of a shirred strip or sheet material of any desired width can be similarly utilized to carry out the present invention. For example, steel wool can be laid down in the form of a layer or sheet of intertangled steel wool fibers and the resulting sheet or strip of steel wool shirred and the shirred material secured to a backing to form an abrasive device in accordance with the practices laid down herein. When steel wool or other fibrous or filamentary material is used as the abrasive substance and is fabricated into a shirred sheet or strip it is usually desirable to impregnate or treat the fibrous layer with a resilient binder such as a rubber latex to hold it in suitably compressed form.
In order to understand better the nature of the herein described articles and the methods of making and using the same, reference is made to the accompanying drawing showing specific examples of abrasive devices made in accordance with the present invention, and in which Figure 1 is an elevational view of an endless abrasive belt made in accordance with the present invention;
Figure 2 is a top plan view of a fragment of the abrasive belt shown in Figure 1, the left hand portion showing the fold lines of the shirred material before the material has been folded;
Figure 3 is a highly enlarged vertical section through the line 33 of Figure 2 the unfolded left hand portion not being included;
Figure 4 is a view similar to that of Figure 3 showing a modified form of abrasive belt made in accordance with the present invention;
Figure 5 is a top plan view of a fragment of an abrasive belt embodying further modifications of the present invention, the left hand portion again depicting the disposition of the transverse fold lines of the material prior to their being shirred;
Figure 6 is a top plan view of an abrasive disc embodying principles of the present invention;
Figure 7 is a vertical diametrical sectional view through the lines 7-7 of Figure 6;
Figure 8 is a top plan view of an abrasive disc according to another modification of the present invention;
Figure 9 is a vertical sectional view through the line 9-9 of Figure 8;
Figure 10 is a highly enlarged vertical section, similar to the views of Figures 3 and 4, showing still another modification of the present invention;
Figure 11 is a side elevational View of a polishing wheel embodying the principles of the present invention;
Figure 12 is a frontal view of the wheel shown in Figure 11;
Figure 13 is a top plan view of a fragment of an abrasive belt with portions broken away, embodying other features of the present invention;
Figure 14 is a vertical sectional view through the line 14-14 of Figure 13;
Figure 15 is a vertical sectional view through the line 1515 of Figure 13; 7
Figures 16 and 17 are views similar to Figure 13 of still other modified forms of abrasive belts, the greater portion of the shirred abrasive strip material in Figure 16 being omitted with its disposition on the backing diagrammatically indicated by the dot-dash lines; and
Figure 18 is a fragmentary plan View of the back side of an abrasive belt, showing the filamentary reinforcing means thereof.
Figures 1, 2, and 3 depict one embodiment of the present invention in the form of an endless abrasive belt comprising a flexible fabric backing member 15, to which is adhesively secured by means of a layer of adhesive 16 a shirred abrasive sheet material 17. Using a fibrous abrasive-containing sheet material such as that disclosed and described in my US. Patent No. 2,284,738 issued on June 2, 1942, I have made abrasive belts of the type shown in Figures 1, 2, and 3, as for example an abrasive belt 4" wide and 54 long as follows.
A long continuous 4" wide strip of abrasive-included fibrous sheet material 17 is first folded transversely of the strip to form a shirred strip material having a spacing of 8 strips to the lineal inch with each shirr 18 having a pitch or height of when the shirred material is mounted upon its backing. The number of shirrs per lineal inch is called the spacing; the space between theshirrs is called the valley; the tip of the shirr is called the ridge; the fiat space between the shirrs when they are compressed is called the overlap; and the length of each shirr from the base of the shirr to the ridge is called the pitch or height. The specific belt shown is one in which the shirred material is so shirred with the individual shirrs 18 partially overlapping one another so that, looking down upon the material, a portion or band A" wide of each individual shirr is exposed to view when the shirred material is lying in flattened condition. The thusly shirred material is adhesively attached to the fabric backing 15 by means of a thin layer of permanently flexible, rubber-base adhesive applied to the underface of the shirred material and/or the fabric backing. The adhesively coated shirred material is superimposed on the backing and the adhesive cured while the two are held under light pressure in close contact with one another. The adhesive, in addition to forming a thin layer 16 between the backing and the shirred material, is
The ends of the backing of the desired length. The diagonal splicing of the back- 'ing fabric obviously is not coincident with the transverse splice of the shirred material which is spliced normal to the length-wise direction of the belt, so that as a result there is practically no bumping of the belt during operation.
The resulting endless belt has been found highly satisfactory for the performance of many abrasive and polishing operations. An analytical study of the structural details of such a belt will readily reveal why abrasive belts when so constructed have a life of useful service far beyond that obtained with coated abrasive belts of the conventional type consisting of a single layer of abrasive grits adhesively bonded to a paper or cloth backing. Referring'for example, to an endless abrasive belt of the described type 54" long and 4" wide with the individual shirrs of pitch or height it should be noted that each individual shirr is duplex in character, i.e., composed of two folds of material. The shirrs lie at an angle of 15 deg. when compressed; about 30 deg. when uncompressed; and about 60 deg. when the shirred belt is passing over a 4" diameter pulley. The area of each shirr is therefore approximately 4 x 7 and,
taking into consideration the duplex character of the shir lgthe total area in each shirr is thus twice 4 x WithS'shirrs to the lineal inch the total number of shirrs for a belt 54" long is 432, and multiplying this by the total area of each duplex shirr, the total area of abrasive material in the belt is 1080 sq. in. By comparison, the total abrasive area for a conventional coated abrasive belt 4" x 54" is 216 sq. in. Furthermore, it should not be overlooked that the abrasive strip material is charged with abrasive throughout its entire thickness so that the total number of abrasiveparticles available for work is many times in excess of the number of abrasive grains available in a conventional abrasive coated belt of the same size. Furthermore, the abrasive grains in a belt of the present construction undergo positional shifting in all directions during use so that the grains are constantly presenting fresh facets or cutting edges to the work with the result that each individual abrasive grain is fully utilized before its release whereas by contrast the individual abrasive grains as fixedly mounted upon an abrasive coated belt of the conventional type are firmly anchored in one immobile position and as soon as the upper cutting edge is worn otf or becomes dull the belt either becomes loaded or the abrasive grain is broken from its bond and released without performing further abrasive action. When all these factors are taken into consideration the unusually long life obtained from abrasive belts of the present invention is readily understandable.
Figure 4 depicts a modified form of abrasive belt made in accordance with the present invention in which the shirred material, instead of being shirred with individual shirrs partially overlapping one another as in the belt shown in Figure 1, is so shirred that the individual shirrs completely overlap. The resulting shirred material 19 is adhesively secured to the backing 20 along the alternate transverse fold lines along one side of the shirred material by means of adhesive 21 with the individual duplex shirrs 19 extending upwardly from the backing to provide an abrading face composed of a plurality ofindividual abrasive elements which are highly flexible and mobile in character. By varying the pitch of the individual shirrs of the shirred material, or the extent to which the shirred material is forced together or extended when it is mounted upon the backing 2%) (in other words, the spacing), or both, any specific type of abrasive or polishing action desired can be obtained in the ultimate article depending upon the use er -purpose to which the belt is designed.
Figure 5 shows still another modified form of abrasive belt in which the abrasive-bearing sheet material can be shirred as shown in Figures 1, 2, and 3 or in the form shown in Figure 4, but in order to provide greater lateral mobility to the individual abrasive elements constituting the Working face of the belt the shirred material is slotted lengthwise of the belt by a plurality of lengthwise slots 23 and 24, the shirred material being left unslotted 'at intervals 25 to give needed stability to the belt. The unslotted shirrs are called the tie-in shirrs. 'Slits 23 are preferably staggered laterally with respect to slits 24 so that the abrasive action of the belt will be uniform across the belt width.
Figures 6 and 7 show an abrasive disc made in accordance with the present invention and comprising "a flexible backing 27 and an abrasive annulus 28 adhesively secured by adhesive 29 to the backing. The backing can be of vulcanized fiber, spring steel, one or more plies of rubber-impregnated sisal fiber or other fabric or material, singly or in combination, providing suitable support for the shirred abrasive material. The abrasive annulus 28 is constructed of a shirred material folded with the individual shirrs partially overlapping in the same manner as the shirred material used for forming the abrasive belt shown in Figure 1. A narrow band or area of each individual shirr is exposed at the annular working face of the disc and as the individual shirrs are worn away in use fresh areas of each shirr are exposed for abrasive action. As in the case of the abrasive belts, the pitch or height of the shirrs and/or the spacing or degree of overlapping of the shirred structure can be varied, depending upon the particular abrading characteristics desired in the disc.
Figures 8 and 9 depict a modified form of abrasive disc comprising a flexible backing 30 and an abrasive annulus 31 adhesively secured to the backing. The annulus 31 is composed of a narrow strip of abrasive-included fibrous sheet material shirred with the shirrs fully overlapping and mounted upon the backing in a series of concentric configurations from the periphery partially in to the arbor portion of the disc. Instead of a series of individual concentric strips of shirred material, a single strip of shirred material can be spirally mounted upon the backing. In the specific modification shown in Figures 8 and 9, instead of adhesively attaching the shirred material along alternate fold lines of the shirred material, as in the case of the shirred material constituting the annulus of the abrasive disc shown in Figures 6 and 7, the shirred material is adhesively attached to the backing along one side of the shirred strip material with the fold lines of the individual shirrs of'the shirred material extending in a direction normal to the plane of the backing. Abrasive discs of this type have been unexpectedly effective in the stripping of paint from painted surfaces without loading of the abrasive disc with the paint and detritus removed in the abrading operation.
Figure 10 depicts an abrasive belt similar to that shown in Figure 2, but in which the shirred abrasive material 33 which is adhesively secured to the backing 34 consists of a shirred layer of matted steel wool fibers. The layer of matted steel wool fibers is desirably impregnated with a rubber latex to assist in retaining the fibrous material in layered form of suitable thickness prior to the shirring of the layer or sheet of steel wool fibers. However, other adhesives can be used for holding the steel wool fibers together, if desired, such as any of the various thermosetting or thermoplastic adhesives, or synthetic rubber latices or elastomers such as .polychloroprene or silicone latices, glue, casein, hard soap and waxes or the like, or in fact, for some purposes no holding adhesive for the fibers need be used. Such an abrasive beltis other operations where conventional abrasive belts are found to load up quickly with shellac, varnish, resin, and
other material removed from the surface.
Figures 11 and 12 show an abrasive wheel or drum constructed of a hub 36 to which is adhesively attached by means of adhesive 38 an abrasive-included fibrous sheet material in shirred form. The shirred material 37 is secured to the hub along the alternate fold lines of the shirred material with the individual shirrs extending radially outward from the hub. If desired, particularly in drum structures in which the pitch of the shirred material is not great, the hub structure can be covered with a layer of foam or sponge rubber or other resilient material to provide further cushioning of the shirred abrasive material which is then adhesively attached to the periphal covering of foam or sponge rubber or the like. Abrasive wheels of this type can be subject to many modifications by changing the radial depth or pitch of the shirred material and also the slitting of the shirred material circumferentially of the wheel to provide a multitude of individual abrading elements in the form of abrasive fingers. Also, an abrasive drum embodying the Various features and advantages of the present invention can be constructed by provision of an endless abrasive belt structure embodying the shirred abrasive elements of the herein described type and the belt mounted upon an expandable hub to provide an abrasive drum. Set-up wheels and like structures with replacement peripheries can be obtained, the rim or peripheral portions being readily attachable and removable by provision of suitable means for mounting on the hub or base portion.
Figures 13, 14, and 15 show still another modified form of abrasive belt, a fragment only being shown, in which the shirred material 41 is shirred in partially overlap ping conformation and the shirred material is adhesively attached to the flexible fabric backing 42 by means of a rubber-base adhesive with the individual shirrs of the shirred material spaced apart to provide an open faced working surface which is extremely cool in abrasive action and has no tendency to load with detritus during use. is so attached to the backing that it is disposed at an approximate angle of 45 to the lengthwise direction of the belt so that a very effective abrading action is secured. The particular construction of belt shown in Figure 13 is one in which the abrasive surface is made up of a plurality of parallel courses of shirred strip material extending circumferentially around the belt structure. Other configurations of the shirred material can be used such as a series of strips or single zigzag strip of shirred material adhesively attached transversely or diagonally of the belt width. Figures 16 and 17 show two further modifications of belt structures in which in Figure 16 the abrasive surface is formed of a single strip of shirred abrasive material 45 spirally extending in a plurality of courses the length of the belt and covering the backing 46 from side to side. Figure 17 shows a belt in which the backing 47 has adhesively secured thereto a series of strips 48 of shirred material in which the shirrs are directionally disposed in one direction and are alternated with a series of strips 49 of shirred material in which the shirrs are disposed in a different direction.
Figure 18 is a back view of an abrasive belt fragment, as for example a belt such as shown in Figures 13 and 14, showing the reinforcement of the backing 42 by means of a plurality of lengthwise filaments or strands 5% and 51 of high tensile strength material such as nylon or glass fiber cording. As shown, the specific reinforcing strands 50 and 51 are right and left hand windings, respectively, moving outwardly from the transverse center line of the belt to the lateral sides.
It is to be understood that the present invention is not restricted to the specific embodiments shown in the vari ous figures of the drawing and described in connection therewith. For example, the structural features and spec'ific materials disclosed for the fabrication of particular It is to be observed that each of the shirrs abrasive belts, discs, or wheels can be interchangeably applied to the making of the other types of articles disclosed without departing from the true scope of the invention. Also, it is obvious from the manifold types of abrasive devices herein described and illustrated in the drawing that numerous other forms of abrading devices can be constructed of shirred material embodying the various features and principles herein set forth. For example, abrasive annuli or sticks can be constructed in which the shirred abrasive strip material is toroidally wrapped about an annular or bar-shaped core member as a support to provide articles suitable for internal dressing operations, honing or the like.
Having described the invention in detail, it is desired to claim:
1. An abrasive device comprising a shirred abrasive strip material flexibly mounted upon a support or backing, said shirred abrasive strip material being adhesively secured to the backing along the fold lines of the shirred strip material with the individual shirrs thereof at least partially overlapping one another in the direction of movement of the device during use and forming a plurality of separate abrading elements constituting the working face of the abrasive device, each of said abrading elements being hingedly mobile so as to have individual mobility.
2. An abrasive device according to claim 1 in which said shirred abrasive strip material is an abrasive-included fibrous sheet material.
3. An abrasive device according to claim 1 in which said shirred abrasive strip material is a shirred layer of steel wool.
4. An abrasive belt comprising a flexible backing and a shirred abrasive strip material in which the individual shirrs partially overlap one another in the longitudinal direction of said belt, the shirred strip being adhesively and flexibly secured to said backing along alternate fold lines of the shirred strip material, each of said individual shirrs being hingedly mobile so as to have individual mobility.
5. An abrasive belt according to claim 4 in which the shirred abrasive strip material is an abrasiveincluded fibrous sheet material.
6. An abrasive belt according to claim 4 in which the shirred abrasive strip material is a layer of steel wool.
7. An abrasive belt according to claim 6 in which the steel wool is impregnated with a resilient binder.
8. An abrasive device comprising a supporting member and a flexible shirred abrasive strip material adhesively secured thereto, the individual shirrs of said strip material being so shirred that the individual shirrs partially overlap one another in the direction of movement of the device during use, the shirred strip material being flexibly attached to the supporting member along the fold lines on one plane or face of the shirred strip whereby the individual shirrs of the strip material constitute a plurality of independently and hingedly mobile double leaved abrading elements forming the working face of the abrasive device.
9. An abrasive belt comprising a flexible backing and shirred abrasive bearing fibrous strip material having a single strip width laterally co-extensive with said backing adhesively secured thereto, the individual shirrs of said strip material being so shirred that the individual shirrs partially overlap one another in the longitudinal direction of said belt, the shirred strip material being flexibly attached to the supporting member along the fold lines on one plane or face of the shirred strip whereby the individual shirrs of the strip material constitute a plurality of independently and hingedly mobile double abrading elements forming the working face of the abrasive device.
10. An abrasive belt according to claim 9 wherein the shirred abrasive strip material is slit lengthwise of said belt to divide each of the shirrs thereof into a plurality,
of individual abrading elements transversely ofsaid belt.
11. An abrasive belt according to claim 10 wherein the slits in said strip material at one lengthwise stretch of the belt are staggered laterally in relation to the slits in the strip material at adjacent lengthwise stretches of the belt.
12. An abrasive device comprising a supporting mem her and a plurality of shirred, abrasive-bearing strips adhesively secured thereto, said strips being flexibly secured to the supporting member along the fold lines of the shirrs with the individual shirrs thereof at least partially overlapping one another in the direction of movement of the device during use, whereby the individual shirrs of the shirred strip material extend from the supporting member and are individually and hingedly movable over most of the area of the shirrs.
13. An abrasive device according to claim 12 in which the fold lines of the shirrs are disposed in a plurality of directions.
14. An abrasive device according to claim 12 in which the individual shirred strips of abrasive-bearing fibrous material secured to the flexible supporting member are 10 disposed at alternating acute angles to the transverse direction of the device whereby the abrading face of the device is composed of a multiplicity of short abrasivebearing flexible leaf-like abrading elements forming a herringbone pattern at the surface.
References Cited in the file of this patent UNITED STATES PATENTS 449,239 Webster Mar. 31, 1891 735,632 Webster Aug. 4, 1903 1,140,424 Webb May 25, 1915 1,839,139 Brockman Dec. 29, 1931 I 1,913,261 Brockman June 6, 1933 1,924,975 Blustein Aug. 29, 1933 2,199,615 Casper May 7, 1940 2,259,941 Primeaux Oct. 21, 1941 2,284,716 Benner et al. June 2, 1942 2,335,902 Ball et al Dec. 7, 1943 2,468,686 Sax Apr. 26, 1949 2,704,916 Peterson Mar. 29, 1955 2,769,284 McLaughlin et a1. Nov. 6, 1956