US2655189A

US2655189A - Production of fibrous elements from woody material

Info

Publication number: US2655189A
Authority: US
Inventors: James D A Clark
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-02-28
Filing date: 1949-02-28
Publication date: 1953-10-13
Anticipated expiration: 1970-10-13

Description

J. D'A. CLARK PRODUCTION OF FIBROUS ELEMENTS FROM WOODY MATERIAL Filed Feb; 28, 1949 2 Sheets-Sheet l INVENTOR. James d 34. C lurk BY 0 fly.

Oct. 13, 1953 J. D'A. CLARK 2,655,189 PRODUCTION OF FIBROUS ELEMENTS FROM WOODY MATERIAL Filed Feb. 28, 1949 2 Sheets-Sheet 2 INVENTOR.

Y James dZLCZar'k HZiy Patented Oct. 13, 1953 PRODUCTION OF FIBROUS ELEMENTS FROM WOODY MATERIAL James dA. Clark, Longview, Wash. Application February 28, 1949, Serial No. 78,692

7 Claims.

The present invention relates to a method of and apparatus for mechanically defi-berizing wood and other fibrous materials. It more particularly relates to the provision of a method and apparatus by means of which long, tapered fibrous elements having controlled, uniform dimensions and being especially suitable for the composition of low density felted structures may economically and expeditiously be-produced.

The present invention and its relationship to the prior art are considered herein with reference to the accompanying drawings wherein:

Figure 1 is a schematic illustration of the manner of forming fibrous element from a solid piece of Wood by conventional mechanical methods;

Figure 2 is a schematic illustration of the manner of forming fibrous element from a piece of wood by the presently disclosed method;

Figure 3 is a plan view of apparatus suitable for use in the practice of the herein disclosed method of producing fibrous element from pieces of wood;

Figure 4 is a view in elevation of the apparatus of Figure 3; 1

Figure 5 is a detail view in elevation of a mechanismfor adjusting the cutter in the apparatus of Figures 3 and 4;

Figure 6 is a sectional view of a bearing for mounting the adjusting mechanism of Figure 5; and

Figure 7 is a view in elevation partly in section of a resilient spacing element for use in the scoring mechanism of the apparatus of Figures 3 and 4.

As is well known to those versed in the fiber .art, the form and dimensions of the individual fibrous elements comprising a fibrous felt are primarily determinative of the structural properties and appearance of the consolidated products fabricated therefrom. This is particularly true where the consolidated products are of low density, e. g. of a density of about 0.5 or less. The properties of the fibrous elements also are of very great significance in determiningtheir suitability for use in the felting and consolidating mechanisms of conventional board making plants. If they are too long in relation to their width or thickness, they tend to mat together so that their conversion into a felt of uniform thickness is difiicult. If, on the other hand, they are too short in relation to their width or thickness, they do not interlace well during the felting and consolidating operations and a product of low strength is produced. If the length of the fibrous elements is out at an angle to the grain of the wood, instead of strictly parallel to the grain, the individual fibrous elements are intrinsically weak and easily broken. This fact again tends to make a weak consolidated product. If the fibrous elements are of non-uniform dimensions in any respect from batch to batch, it is difficult if not impossible to produce a series of consolidated products of reproducible strength and other properties. If the ends of the fibrous elements are square or blunt, they do not intertwine Well, and the surface of the consolidated product is not as smooth as where the fibrous element ends are gradually tapered to a point.

Although mechanisms for converting wood to fibrous elements by contacting it with one or a plurality of cutting elements have the advantages of simplicity of construction, high capacity, and economy of operation, the conventional mechanisms of this class uniformly possess the disadvantage of not producing a fiber product having the controlled, uniform dimensions necessary to the production of consolidated products of optimum properties as described above. Thus, it is well known reciprocally to traverse wood blocks lengthwise against a rotary cutter which may comprise a large number of needles suitably mounted about a common axis and rotated at high speed. This apparatus gives very little control over the length, width, or thickness of the fibrous elements produced, and the fibrous element character changes with the direction of the traverse and with wear of the needle points during use of the machine.

Similarly, excelsior type fibrous element has r been produced by traversing wood blocks with respect to serrated cutter blades which plane ofi fine filaments having the same length as the blocks. Alternatively, the blocks may be scored longitudinally and passed across a continuous knife which planes off the filaments. This type of apparatus gives control over the width and thickness of the fibrous elements but not of their length; andv auxiliary means are required to shorten the long filaments. Such auxiliary shortening means furthermore, may be of impractical construction, or, if practical in operation, produce short fibrous elements having square cut ends. As is brought out above, fibrous elements of this character do not lend themselves Well to the production of consolidated products of acceptable properties.

In still another type of mechanical defibrator, and one which is of particular interest in connection with that disclosed herein, the face of a wood block is scoredin a preliminary opera- 3 tion, after which it is passed across a planing head or other rotary cutter, which forms fibrous elements by shaving oil the scored face of the block. In a modification of this type of apparatus, the use of a prescoring operation is eliminated by employing a cutter consisting of multiple circular saws bolted together upon a common axis. In apparatus of this type, the width of the fibrous elements is controlled by the spacing of the scoring in the one embodiment or to some degree by the thickness of the individual saw blades in the other. However, since it is conventional practice to pass the wood block across the cutter face at a traversing speed which is negligible as opposed to the peripheral speed of the cutter, i. e. at a traversing speed of usually considerably less than about 200 linear feet per minute as opposed to a peripheral cutter speed of the order of about 6,000,linear feet per minute,

the thickness and length of the fibrous element produced are functions solely of the diameter of the cutter and the depth of the cut. This will be more apparent from a consideration of Figure 1.

In Figure 1, the numeral It] represents the periphery of a rotary cutter rotating in the indicated direction. Upon traversal of the cutter by a piece of wood H at the conventional low rate of speed, as compared with the high peripheral speed of the cutter, a tooth lfla of the latter will cut from the piece of wood a fibrou element l2 having the illustrated configuration ABC. The length (AD, approximately) of the fibrous element produced in this manner will be determined by the diameter (DE, approximately) of the cutter and the depth (CD) of the cut. It will be approximately equal to the square root of the product of the depth of cut and the cutter diameter, since, by familiar geometrical principles:

- AD XTD=DEX D (Fibrous element lengthfiszcutter diameterxdepth of cut and f "Fibrous element lengtli= cutter diameter-x depth of out It will be apparent further that a fibrous element so cut will be tapered at one end only, the other end being relatively thick and chunky,

Also, the grain of the wood will, on the average,

lie at an angle CAD to the fibrous element so cut and thus make it intrinsically weak. Variations in fibrous element length to meet varying product specifications will be impossible to obtain except by varying the cutterdiameter or depth of cut :taken. However, it will be seen that the deeper the cut, the more the fibrous element will lie across the grain of the wood rather than parallel thereto with the result that it will be weaker and more wedge shaped, with one end very blunt, when deep cuts are made.

For the foregoing reasons, it would be desirable to provide a method of and a rotary cutting apparatus for producing fibrous elements which are relatively long as compared with their thickness, which are cut substantially parallel to the grain'oi the wood, and which have tapered ends. It would further be desirable to provide a method of and apparatus for defiberizing wood in which the width and thickness as well as the length of the fibrous elements produced may be controlled to within predetermined limits to form fibrous elements which are of optimum shape and characteristics for various applications, particularly the fabrication of low density boards. It would also be desirable to provide an apparatus in which fibrous elements of controlled dimensions may be produced, economically, continuously, in large volume, and with a minimum production of wood dust, slivers, and fibrous elements of random shape.

In accordance with the present invention, the foregoing and other objects are attained by traversing the wood and a rotary cutter relative to each other at a speed which is at least comparable to the peripheral speed of the cutter. Thus, whereas it is conventional practice to traverse the wood at a linear speed of less than about 200 feet per. minute using a cutter having a peripheral speed of more than about 5,000 feet per minute, in the'practice of the present invention the traversal speed of the wood is increased to at least this time, the traverse of the wood relative to the one-tenth preferably at least one-fifth of the peripheral speed of the cutter, for example 500 to more than 1,000 feet per minute where the cutter peripheral speed is M300 feet per minute. When such is the case, each cutting edge exerts a pronounced planing efiect along the rain of the wood in addition to its normal cutting action, and the fibrous element produced is, elongated correspondingly.

The shape of the fibrous element produced by the present method is illustrated in Figure '2,

wherein a rotary cutter i5 is depicted traversing the piece of wood 16, the tooth lfia engagin the wood to produce fibrous element I! having the configuration GI-II. It will be noted that the fibrous element ii is relatively long and thin, tapered at both ends and with a major proportion cut substantially parallel to the grain. Its

-maximum thickness equals the depth of cut made by each tooth. Furthermore, its length is equal to the square root of the product of its thickness times the cutter diameter, as developed above, plus a substantial traversing speed. The effect of this increased traversing speed will be evident from a comparison of Figures 1 and 2. In the conventional method of Figure l, the cutter engages the wood as it rotates through the angle AFC to produce the fibrous element [2. During cutter is represented by the distance d, which adds but little to the fibrous element length. In themethod of the present invention, as illustrated in Figure 2, the cutter engages the wood as it rotates through the angle GJK to form fibrous element 17. During this time the travaerse of the wood equals the distance d, which adds considerably to the length of the fibrous element. I

Since the length now has become a substantial function of the traversing speed, a convenient means is afforded for controlling the fibrous element length by varying the rate of traverse relative to the cutter speed. To increase the fiber-length, all-that is necessary is to increase the traversing speed or decrease the peripheral speed of the cutter, or both. Conversely, to decrease the fibrous element length, the traversing speed may be decreased, the cutter speed increased, or both. This offer a simple but very effective manner of controlling the fibrous eleselective spacing of the elements of the scoring device. Alternatively, it may be controlled by employing in place of a continuous cutter one which comprises a plurality of circular saws or cutting elements bolted or otherwise secured toa common axis. In this case, the fibrous element width will be determined to some degree by the thickness of the cutting elements. The fibrous element thickness may be controlled by varying the setting of the cutter to take either a light, intermediate, or heavy cut as desired. In this manner, there may be produced a, fibrous element of variable but controlled and uniform dimensions which is best suited to conform to predetermined specifications.

The apparatus whereby fibrous element of the above described controlled dimensions of length, thickness and width may be produced broadly comprises means for holding one or more pieces of wood, a rotary cutter, and means for traversing the wood and the cutter relative to each other at a rate which is at least comparable to the peripheral speed of the cutter, being at least one-tenth of the latter. Suitable apparatus is illustrated in Figures 3 to 5 of the drawings, to which attention now is directed.

In the apparatus of these figures, a frame work of suitable construction supports a hopper 2| adapted to contain a plurality of pieces of wood 22. The hopper may be of any desired dimen- Sions as determined principally by the size of the wood pieces it is designed to accommodate, and is open at the top and at the bottom. To support the wood within the hopper and also to provide a mounting for the cutter, there is provided the horizontal disc or table 23. This is mounted rotatably upon the vertical shaft 24 journaled at its upper end in the bearing 25 and at its lower end in the pedestal bearing 26. Tab-1e 23 preferably has a relatively large radius in comparison with the length and width of the hopper so that the wood in the latter will be cut substantially parallel to the grain.

Attached to the table 23 are the cutting elements for reducing to fibrous element the wood contained in the hopper. These may comprise a plurality of individual cutting elements secured to a common shaft, this being of known construction and not illustrated. If very fine fibrous elements are desired, the cutter may consist of an abrasive wheel or of a cylinder covered with abrasive paper. In this case, each of the abrasive particles serves as an individual cutter which shaves off a thin fibrous element having a thickness and width determined substantially by the size of the abrasive particles. Illustrative of a suitable abrasive cutter is one comprising a cylinder covered with floor surfacing emery paper having 20 mesh grit spaced on the average about 3.5 mm. apart. At low traversing speeds such a cutter produces a kind of wood flour or sander dust not well suited for use in the manufacture of fibrous boards. At the high traversing speeds disclosed herein, however, it produces elongated fibrous elements of superior board making properties. This will be apparent from a consideration of the examples given below.

' Alternatively, the cutter may comprise a continuous rotary cutter operated in conjunction with a scoring device as illustrated in the drawings (Figures 3 and 4). In the embodiment illustrated, the cutter 28 consists of a cylinder on a. shaft 29 and having on its periphery a plurality of continuous, longitudinally disposed cutting edges of suitable size and pitch. Rotatable mounting of the'cutter is secured by attachment of the shaft 29 in bearings 30-30 which may be bolted or otherwise secured to the under side of the table 23 preferably sq as to be adjustable with respect thereto. Its length is Substantially coextensive with the width of the hopper 2| and its upper edge extends upwardly through an opening of suitable dimensions in the table 23. Since the wood in the hopper is supported by the table, the distance to which the cutter projects above the upper surface of the table determines the depth of cut taken in the wood and hence the thickness of the fibrous elements. The extent of cutter projection may be varied in any suitable manner, as by means of jack screws (Figures 5 and 6). In this construction, the cutter shaft 29 is journalled in bearings 3| provided with

guideways

32, 32 and slidably mounted on brackets 33 bolted to the table 23. The bearings 3| are held between

screws

34, 34 with

lock nuts

35, 35. Hence, by adjustment of the screws, it is possible to vary the setting of the cutter as desired.

The scoring device which cooperates with the cutter 28 may be of any suitable construction and may comprise for example a plurality of circular disks 36 having cutting edges and separated by a plurality of spacing elements 31. Both cutting disks and spacing elements may be mounted slidably on the common shaft 38 journalled in the

bearings

39, 39 which are attached to the under side of the table 23 by means of bolts or other suitable means. The scoring disks 36 project upwardly through an opening of appropriate size and disposition in the table 23. The depth of the scoring thus is dependent upon the amount by which the scoring disks extend above the table. Its spacing is determined by the distance apart of the disks, which, in turn, is determined by the thickness thereof and also the thickness of the spacing elements 31. By changing either of these variables, the distance apart of the scoring may be varied as desired.

To secure adjustment of the distance between the cutting disks and the scoring mechanism without rebuilding it or replacing it, there may be provided resilient spacing elements which by proper means may be compressed or expanded to move the cutting disks closer together or farther apart respectively. The spacers may be constructed out of a material such as natural or synthetic rubber which inherently is resilient, or from metal, using a construction designed to impart the desired resiliency. Thus they may consist of perforated, thin, cupped metal disks 40 (Figure 7) which are compressible and expansible upon the application and release of pressure. Such pressure may be applied through any suitable means, as by means of a nut 4| threaded onto the shaft 38 of the scorer. Such a nut may be provided at one end only of the shaft, as

shown, or one may be provided at each end. Taking, up on the nut compresses the resilient spacers and moves the cutting disks closer together. Releasing the nut allows expansion of the resilient spacers and corresponding separation of the disks. Obviously in this construction the entire scoring unit should be made sufficiently long so that it is at least as long as the bottom of the hopper even when the resilient spacers are compressed by the maximum amount.

The cutter 28 may be driven either directly or indirectly by means of any suitable prime mover, for example by cutter motor 44 the shaft of which is attached to the miter gear 45. The latter drives the miter gear 46 attached to the sleeve 47 wh ch: .fr e y ot 't ble abou 'b Ver ic l. haf 2 sec is ur or b t e t ust b a i c l ar 5!- re sc att ch d to e eve i t e m e rear 18 whi h d ves h m t r-se r 5 s u to the shaft .8 at th r ta y s it s.- Hence P- ,er np t e cutte o r. d s. th eutte a as -ds e mined b the spee o h motor as .w aser. th rati s. 9 t r use ar in th li ta en 9 h ta e 3 and ens of e cutis 8 andsqc em unted t e eo ma b o ta ed b securing tes b e d v t e v rtica -s a t y mean o h el e -fill a acb dio the ve tical Shaft .4 th miter se r fiifi his eeeserat s w t t e r n t e sha t oi the m tor.- He ce p i n of the tabl m tes-54. ro ates b t b 23 at a s e t rmined b th sear ti and m tor p e I i-operation, a plurality of blocks of wood are r I n the beare 2L These may f ,d mleustba d s ap in thei w g ca e them to bear down on the top of the table sulfieic tl s tha the. ut er maynsa hem, and sinc the rotation of the table against which they r serves to abut, all of them against a common ye l Q i bann r. s sh w r i a l i Fi urfi. The cutter motor 4.4 and the table motor dfljtlien are started and operated at relative speeds such that. the table will traverse the wood at a rat which i$ at lea t I speed of the. c utter. Obviously the direction of rotationoi the table should be in the direction of motionof the cutting edges of the cutter. Thus where the motion of the latter is clockwise viewed g @hemotion of the table as viewed from above should be counterclockwise.

As the cutter and the scorer traverse the wood, fibrous elements will be produced which drop down below the cutter into suitable, well known collecting apparatus, such as a d ct leading to i the intake of a, conveyor fan (not shown). As

the production of fibrous elements continues, the blocks. of wood within the hopper feed downwardly by gravity and are replenished as necessary. 'If it is desired to increase the capacity of theapparatus, a plurality of cutters and scorers may be mounted on the table 23 so that all ops crate upon the wood within the hopper as the table rotates. Furthermore, a plurality of hoppers may be stationed at suitable intervals around the trance. zuabove the table, so. that a, maximum WQQd Su fa-2o is. Presented to the cutters.

The dimensions of the fibrous element produced may be controlled in the manner indicated above. Thus the fibrous element length may be varied by varying the relative. speed oi the table and of the, cutter. To increase the fibrous element length, the table motor may be accelerated, the cutter motor decelerated, or both. Conversely, to decrease the fibrous element length the rate of the table motor may be deeelerated, the speed of the cutter motor accelerated, or Tosecure maximum. production from the apparatus, it is. preferred to. drive either the cut .e'r motor or the table motor at its maximum practical speed, the other motor being adjusted as necessary to produce the desired speed ratio. h fib q em w th and; th ckness-also are easily controlled, the former being adjusted by varying the spacing between the di ks on, the scorer, and the latter being regulated by varying the. depth of out made by the cutter.

Thus. by the present invention there is provided iorthe. first time an apparatus for reducone-tenth of the peripheral g the left-hand side of the apparatus in 1* ing-economically large volumes of scrap wood into fibrous elements all of. the dimensions .of which may be determined as desired. The fibrous elements, moreover, are relatively elongated, tapered onboth ends, and cut substantially parallel to the grain. These properties make them admirably suited to the fabrication of a variety or felted and consolidated wood products such as resilient fibrous blankets and the various grades 0; fiber board, particularly the softer grades. Their significance in determining board properties is illustrated in the following examples in which are compared the proper-ties of insulating boards made from the convention fibrous elements produced mechanically by means oi a cutter and scorer traversing wood blocks and the long, tapered fibrous elements produced by the herein, described method of traversing the wood at a speed comparable to the peripheral speed or the cutter. I

In all cases, the boards were made by reducing the kiln dried wood. to fibrous elements under the specified conditions, mixing the fibrous element with enough water to give 15% by weight of moisture, and thoroughly mixing with 5% by weight of liquid (40% solids) phenolic resin, and sifting thematerial through a. coarse screen-into a mold to give a uniform layer of material. The resulting mat was pressed between heatedplatens at 350 F. for 15 minutes with sufiicient pressure .to give a product having a thickness of /2 inch.

Example 1 Kiln dried Douglas. fir wasv reduced to fibrous elements using a rotary-cutter having continuous blades set to make a cut 0.015 inchdeep and operated in conjunctionwith ascoring device which scored the surface of the. wood ahead of the cutter at intervals of 0.0l5-inch. The peripheral speed of the cutter was 2,520 feet per minute, and the traversing speed of the wood relative to the cutter was 656 feet per minute. The fibrous elements. produced were long, thin, and tapered at both ends. Boards made therefrom in the manner described above had a rupture modulus of il0 pounds per square inch at densities of 0.33. A oard. maelst om fib eme t prod ed on the same apparatus and in the same manner but employing a traversing speedo-f only 60 feet p r minute and the sam cutter sp dd a modulus Qf. rupture of only 225 pounds per square ncbattbesame ensi y- Emmple 2 Kiln driedDouglas firwas reduced to fibrous elements using as a rotary cutter a. surfacing Wheel covered with ZO-mesh emery grit having a spacing on the average of 3 /2 millimeters. There was no prescoring. As in Example 1, the peripheral speed of the cutter was maintainedat 2,520 feet per minuteand the traversing speed at 656 feet per minute. A uniform, hair-like fibrous element about 0.004 inch thick and 0.004 inch wide. which was elongated and tapered at both ends was produced. As opposed to the fibrous elements. of-Example l which were curled, this fiber was substantially straight. Whenmade into board, it had a rupture modulus of 405 P un s. 119 s uar inch at a density. of 0.33.

when. the above abrasive cutter .was operated at the samev peripheral speed and a traversing speed of only .60 feet per minute, short fibrous elements resulted which upon being made up. into board by the. proceduredescribed above, pro.- du adaa. b rd havin .a modulus of rupture of I only 245 pounds per square inch at the same density.

Hence by an evaluation of the data presented in the foregoing examples, it i apparent that application of the long, tapered fibrous elements of the present invention to the fabrication of insulating boards has a significant and advantageous effect on the strength of the boards. By their use, boards may be made having rupture moduli nearly double those of boards prepared under identical conditions from conventional fibrou elements. This fact obviously is of the greatest significance in determining the commercial utilization of the boards.

Having now described my invention in preferred embodiments, I claim as new and desire to protect by Letters Patent:

1. The method of producing fibrous elements tapered at both ends and cut substantially parallel to the grain of the wood which comprises traversing pieces of wood and a rotary cutter relative to each other at a traversing speed of at least one-fifth of the peripheral speed of the cutter, the direction of the traversal being substantially uniformly against the direction of cutter rotation.

2. The method of producing fibrous elements tapered at both ends and cut substantially parallel to the grain of the wood, and of controlled length and width, which comprises prescoring the surface of the wood at a spacing corresponding to the width of the fibrous elements desired, and traversing the scored wood relative to a rotary cutter at a traversing speed of at least onefifth the peripheral speed of the cutter, the direction of the traversal being substantially uniformly against the direction of cutter rotation.

3. The method of producing fibrous elements tapered at both ends and of controlled length, width, and thickness which comprises placing a piece of wood on the surface of a supporting structure through which projects the cutting surface of a rotary cutter, adjusting the extent of projection of the cutting surface above the support and thereby determining the thickness of the fibrous elements produced, prescoring a surface of the piece of wood at predetermined intervals and thereby determining the width of the fibrous elements produced, and traversing the scored wood relative to the cutter at a predetermined r traversing speed which is not less than about onefifth of the peripheral speed of the cutter, the direction of the traversal being substantially uniformly against the direction of cutter rotation, thereby controlling the length of the fibrous elements.

4. Apparatus for producing fibrous elements tapered at both ends and cut substantially parallel to the grain of the wood which comprises a rotatably mounted table, a rotary cutter mounted on the table with a surface projecting beyond the surface thereof, means on the table for holding a piece of wood with its surface pressed against the surface of the table, means operatively connected to the rotary cutter for 6a driving the same, means operatively connected to the table for rotating the same, whereby to traverse the wood across the cutter, andmeans for controlling the speed of the cutter and of the table so that the traversing speed is at least onefifth the peripheral speed of the cutter.

5. Apparatus for producing fibrous elements tapered at both ends and cut substantially parallel to the grain of the wood'which comprises a frame, a tablerotatably mounted on the frame, a rotary cutter mounted on the table with its surface projecting beyond the surface thereof, a scoring means mounted on the table with its surface projecting beyond the surface thereof on the same side as the surface of the rotary cutter, means on the table for holding a piece of wood with its surface pressed against the table surface, means operably connected to the rotary cutter for driving the same, means operably connected to the table for rotating the same whereby to traverse the wood firstacross the scorer and then across the rotating cutter, and means for controlling the speed of the cutter and the table so that the traversing speed is at least one-fifth the peripheral speed of the cutter.

6. The apparatus of claim 5 wherein the wood holding means comprises a hopper superimposed upon the table with its bottom open and adapted to contain a plurality of pieces of wood which rest upon the rotating table and hence contact the scoring means and rotary cutter.

7. Apparatus for producing fibrous elements tapered at both ends and cut substantially parallel to the grain of the wood which comprises a substantially horizontal table, a hopper positioned above the table and opening onto the same, a rotary cutter mounted beneath the table and extending upwardly through an opening in the same, the opening in the table being aligned with the opening in the hopper, a pivotally mounted vertical shaft affixed centrally to the table, motor means connected to the shaft for rotating the same, thereby traversing the rotary cutter with respect to the hopper, a sleeve mounted on the shaft and freely rotatable thereon,

gear means interconnecting the sleeve and the rotary cutter, and motor means connected to the sleeve for rotating the same thereby contemporaneously rotating the cutter and reducing to fibrous elements wood contained in the hopper.

JAMES DA. CLARK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 351,285 Ritchie Oct. 19, 1886 449,097 Williams Mar. 24, 1891 495,239 Bate Apr. 11, 1893 906,318 Smith Dec. 8, 1908 1,795,064 Wiener Mar. 3, 1931 1,994,137 Leguillon Mar. 12, 1937 FOREIGN PATENTS Number Country Date 454,623 Great Britain of 1936