US2896341A - Dredge - Google Patents

Description

R. CHANCE 7 July 28, 1959 DREDGE Filed April 25, 1955 3 Sheets-Sheet 1 m m 11: mm: 1|: 142717 291112 $7111 91! k "MINININI III III I I INVENTOR.

R. CHANCE July 28, 1959 DREDGE 5 Sheets-Sheet 2 Filed April 25, 1955 INVENTOR.

United States Patent DREDGE Ray Chance, Lexington, Ind. Application April 25, 1955, Serial No. 503,390 claims. or. 37-58) This invention relates to a dredge and more particularly to a suction dredge having an excavating or solids loosening head.

This application is a continuation-in-part of my copending application Serial No. 334,110, filed January 30, 1953, and now abandoned.

In the dredging of solids forming the bottom or bank of a body of water such as a stream, river, lake, or the like, it is often necessary to loosen the compacted solids to allow the suction action of the dredge to remove the material. For this purpose burrowing or digging mechanisms are utilized and in some instances provided as part of the suction dredging device. The loosening means now found in the art however possess certain disadvantages limiting their usefulness and discommoding the operators thereof. Such dredges are often provided with a screen or grating means at the mouth of the suction tube to prevent the entrance of large sized objects such as rocks and logs into the tube. Such means often become clogged with matter jammed within their inter stices or held across the front thereof by the suction action.

A further serious disadvantage is found in suction dredges of the type above described wherein parts susceptible to wear and requiring replacement must, nevertheless, because of the destructive quality and magnitude of the forces involved in the operation of the dredge, be rigidly and permanently incorporated.

It is, therefore, the principal object of the invention to provide a new and improved suction dredge.

Another object is to provide a suction dredge having new and improved solids loosening or excavating means provided as a part thereof.

Still another object of the invention is to provide a suction dredge having integral solids loosening means arranged to cooperate with suction tube members to effect a self-cleaning operation thereof.

A further object is to provide a suction dredge of the character described above having novel reciprocatory means for driving the solids loosening means arranged to cause self-cleaning of the loosening means.

A further object is to provide driving means as described above which will automatically effect the selfcleaning operation of the loosening means.

A still further object is to provide a suction dredge having means for crushing solids obstructing the suction tube inlet.

Yet another object is to provide a suction dredge having new and improved means for replacing wearing members thereof.

Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings, wherein:

Figure 1 is a side elevational view of a dredge head embodying the invention and with hydraulic control means shown diagrammatically;

Figure 2 is an enlarged sectional view taken approximately along the line 2--2 of Figure 1;

Figure 3 is a fragmentary and enlarged, side elevational view of the intake end of the dredge head;

Figure 4 is an end elevational view of the intake end of the dredge head;

Figure 5 is a sectional view taken approximately along the line 5-5 of Figure 3; Figure 6 is a sectional view taken approximately along the line 6-6 of Figure 3; and

Figure 7 is an elevational view of a modified form of lip and center brace assembly.

Referring now to the drawings and in particular to Figure l, a suction dredge head embodying the invention may be seen wherein a suction tube 10 is. providedat its intake end with solids loosening means generally desig nated 15 arranged to be reciprocatorially' rotated by hydraulic piston and cylinder means 20 mounted on the suction tube 10 at a distance from the intake end. For automatically controlling and powering the piston and cylinder means 20, a hydraulic control means generally designated 21 is provided; this means 21 comprises a. hydraulic pump 22, the output of which .is fed to piston and cylinder means 20 through a two-position, solenoid actuated, spool valve 23 by suitable ducts. Pressure actuated switches 24a and 24b are interposed in. the ducts between the valve 23 and the means 20 to automatically control the valve 23, the specific functioning of which will be made more clear hereinafter. For purposes of understanding the invention at this point, it need merely be understood that control means 21 functions to reciprocate the piston of means 20 by reversing the direction of motion whenever a pre-determined value of retarding force acts upon the loosening means 15; such a retarding force may be produced by the loosening means reaching the limit of its rotational movement in a given direction or by the jamming of the loosening means during its rotational movement.

t In use, the dredge head is disposed in. the body of water with the inlet end of the suction tube 10 carrying the loosening means 15 lowermost so that means 15 by are provided.

its reciprocatory action may excavate or loosen the solids of the body of water. Suitable suction means (not shown) are applied to the suction tube 10 to draw a volume of water containing the loosened material upwardly through the suction tube so that it may be disposed of as desired. For raising and. lowering the dredge head, a support cable 25 is secured to the suction tube adjacent the mounting of the piston and cylinder means 20; so that the dredge may have relatively free mobility, the cable 25 is secured pivotally thereto by means of brackets 25a fixedly secured to sides of the suction tube 10 and carrying a pin 25b adapted to be received loosely in the end link 250 of the cable. As best seen in Figure 2, preferably a pair of such cables Referring now more particularly to Figures 2 to 6, suction tube 10 is seen to comprise a tube of rectangular cross-section having an open inlet end 11 extending angularly from the remainder of the tube. Spaced side walls 11a and 11b of inlet end 11 gradually increase toward an outer arcuate edge 11c causing inlet end 11 to be outwardly flared. Spaced walls 11d and 11e extending trans versely between side walls 11a and 11b are provided at their straight outer edge 11d and 11e' with protecting lips 11 Lips 11 are secured to walls 11d and 11e by suitable nuts and bolts 111"" so that replacement may be readily effected.

Across the mouth of the inlet end and extending be-? tween outer edges 11c, 11d and 11e' is a cross shaped center brace 11g comprising a laterally extending crushing bar 11g and a pair of generally parallelogram shaped supported bars 11g" each secured at one end to the crushing bar 11g and at the other end to a lateral wall 11d or 11e. Lips 11 are provided with a central notch 11f allowing the passage of the supporting bars 11g" therethrough so that they may be secured as by welding to the walls 11d and He. The lateral crushing bar 11g is secured as by welding at its ends to the spaced side walls 11a and 11b, The center brace 11g thus forms a rigid, strong unit dividing the opening to the inlet end 11 into four equal areas, each having approximately one quarter of the cross-sectional area of the inlet end at the outeredges 11c, 11d, and 11e'. Thus any material passing through the openings of the center brace would be small enough readily to pass through the remainder of the suction tube. Further,'to assure the passage through the center brace of material having dimensions approximately equal tothe dimensions of the center brace areas, the thickness of lips 11 is decreased inwardly so that the widest lip cross-section and. consequently the smallest passage cross-section will be at the lip outermost tip 11f. .Spaced from the outer edge 11c and medially between the lateral walls 11d and 11e, the side walls 11a and 11b are provided with outwardly extending trunnions 12, each having a cylindrical inner portion 12a with its inner end secured as by welding tothe side wall, and having an outer end 12b reduced in diameter and threaded. In order to more securely retain the trunnions 12 on side walls 11a and 11b an annular holding plate 120 surrounding the trunnion is fixedly secured to the trunnion and the side wall as by welding. A lubricating passage 12c is provided extending radially through the holding plate 120 and in communication with a lubricating passage 12a provided in the inner portion 12a of the trunnion. Lubricating water is provided to the passages from within a water jacket or casing 13 spaced from and extending around the lateral wall 11d and the immediately contiguous portions of the side walls 11a and 11b. To preclude the water containing suspended material, which is.

passingthrough the suction tube from finding ingress into the water casing space, sealing angles 13a are aifixed to the suction tube 10 so as to cover the joint between the side walls 11a and 11b and the lateral wall 11d. Means of any suitable type (not shown) may be utilized for providing clear water through the casing 13 and to the lubricating passages 12a and 12c.

Solids loosening means 15 comprises a pair of generally disc shaped spaced side plates 16 having a plurality of laterally extending crushing blocks 17, circumferentially spaced on and secured to the side plates 16, and a plurality of radially extending excavating teeth 18 fixedly secured to the crushing blocks 17. Journal means 19 are provided for mounting the side plates 16 onto the trunnions 12 so that the side plates may have free rotative movement relative to the suction tube 10. A portion of the periphery of each of the side plates 16 is caused to project radially outwardly so as to form an arm 16a which at the outer end 16a is pivotally secured to the hydraulic piston and cylinder means 20 whereby linear reciprocatory movement of the piston thereof will cause the side plates 16 to have oscillatory rotation about the trunnions 12. Such oscillation causes the teeth 18 to burrow into the solids with an excavating or loosening action.

Side plates 16 are formed of relatively thick and rigid material such as steel and are provided centrally with a circular hole 16b having a diameter somewhat larger than the diameter of the trunnion portion 12a allowing a cylindrical bushing 19a to be mounted on the trunnion and extend through the hole 16b. Circumferentially. spaced approximately 45 apart and adjacent the periphery of the side plates are fixedly mounted, as by welding, a plurality of spaced block securing clips 16c. Suitable bolt assemblies 160' are provided to extend through and between each pair of clips for holdingv the crushing block 17 securely therebetween; the clips 16c extend generally radially and the bolt assemblies 160 extend generally perpendicular thereto so that the crushing blocks may be secured to extend radially outwardly from the clips. The radius of the periphery of the side plates 16 is made such that the clips 160 may be positioned radially to allow the crushing block 17 extending laterally across the mouth of the inlet end 11 of the suction'tube 10 to have a slight clearance with the outer edges of the side walls 11a and 11b. So that this clearance is maintained over the entire range of movement of the discs, the center of curvature of edges 11c and the center of rotation of the discs is made to coincide with the trunnion 12.

Crushing blocks 17 comprise rigid metal bars preferably formed of a wear-resistant steel and extend laterally sufficiently so as to have their ends aligned generally with the outer ends of the trunnion 12. Each block 17 is provided with a plurality of laterally spaced teeth 18 each having an outer tapered end 18a adapted to penetrate and dig into the solids, The inner end of teeth 18 is provided with a slot 18b, the teeth being mounted on the crushing block 17 by having the crushing block inserted fully into the slot 18b and the assembly thereof rigidly secured as by welding. A center tooth 18' on each block 17 is positioned slightly to the side of the center of the block and center braces 18c extending circumferentially between the blocks 17 are secured to the centers of the blocks as by welding. Center brace 18c acts in conjunction with the clips to maintain the crushing blocks 17 rigid laterally. The end teeth 18" are secured at the outer ends of the crushing block allowing the burrowing or excavating action to extend laterally the width of the entire solids loosening means and precluding jamming of the loosening means in the excavation.

The crushing block and tooth assembly comprises an extremely rigid and rugged unit. Replacement thereof is readily and easily made by cutting the center braces 18c, removing the bolts 16c, and radially withdrawing the blocks 17 from the clips 160. The replacement blocks having teeth 18 secured thereto as by welding, may then be inserted into the clips and secured therebetween by the bolts 160. Center braces 18c are then fixedly secured to the center of the blocks, as by welding, to reinforce the unit. While the number of crushing bars and teeth may be varied to suit the requirements of the specific dredge head on which they are employed, I have shown, for purposes of illustration of my invention, three such bars each having three such teeth.

To effectively minimize wear on the crushing members 11g and 17 and lips 11 and reduce the frequency of replacement thereof, I provide a beaded edging 26 of a hard, tough material such as Stellite, Stoodite or Stoody which is laid on the mating edges of the crush-. ing members and lips as by welding. Further, to effectively minimize wear on the loosening means, the teeth 18 may be of suitable material for the specific type of solids loosened, e.g. where the bottom is comprised generally of sand, an abrasive resistant alloy may be used; where rocks are to be encountered, a tough, less brittle alloy may be used. As the crushing means and teeth are readily replaceable, such provision is easily eifected.

As the inner edge of each crushing block 17 is arranged to oscillate circumferentially at a distance slightlyoutwardly from the outer edge of the lips 11f and the laterally extending crushing bar 11g of the center brace, large objects such as rocks which have partially entered one of the spaces formed-by the center brace 11g and the tube outer edges and which may become lodged therebetween will tend to be crushed laterally by action of the circumferentially moving crushing block 17. As seen for example in Figure 3, if such an object were jammed between the crushing bar 11g and the lip 11 shown uppermost, counter-clockwise movement of the side plates 16 would cause the middle crushing block 17 to crush any outwardly projecting portion of the object against the lip 11 tending to reduce it to a smaller sized object capable of being readily moved through the suction tube 10. If the object proves too strong for this crushing action, hydraulic control means 21 will automatically cause a reversal of'the movement of side plates 16 so that middle crushing bar 17 will move clockwise releasing its pressure on the object and possibly allowing it to fall free or assume a different position.

The clockwise rotation of the side plates may continue until the crushing block 17 shown uppermost in Figure 3 abuts the upper side of the object tending to crush it against the crushing bar 11g of the center brace 11g or move itin this opposite direction. Such clockwise ro- 'tation continues until the pressure is again increased and an automatic reversal is effected. When the rotation ofv the side plates 16 again is counter-clockwise, if the object has not been removed, the center crushing block 17 will again strike the projecting portion of the object and this cycle will be continued until the object is removed or crushed. By making loosening means 15 rugged and providing suflicient force, this novel self-cleaning action,

as a concomitant of the excavating and solids loosening action, is effected.

As considerable forces are developed during the operation of the bottom loosening means 15, the journal means 19 must be of a rugged. type. For this purpose I provide a cylindrical outer bearing member 19b in which bushing 19a is journalled and which is fixedly attached at its inner end as by welding to an annular plate 19c. Plate 19c is secured to the side plate 16 by suitable bolt means 19c. Bushing 19a is preferably fixedly secured to the trunnion inner portion 12a so that sliding occurs between the bushing and the outer bearing 1%. So that the interfaces of the bushing and outer bearing may be lubricated, a passage 19a is provided through the bushing 19a communicating at its inner end with the lubricating passage 12a of the trunnion and at its outer end with the space between the bushing and bearing. The bushing and bearing extend outwardly somewhat less than the tunnion inner portion 12a so that the lubricating water may be allowed to escape from the resultant space between the end of the bushing and bearing and an annular Washer 19d secured against the outer end of the trunnion inner portion 12a by means of a nut 19d, threaded on outer end 12b of the trunnion. Washer 19a further acts as a limiting abutment for any lateral movement of the side plates 16.

Should wear of the bushing 19a or outer bearing 1% occur, a replacement outer bearing may be readily installed by merely removing the nut 19d and washer 19d, removing the bolt means 190 from the annular plate 190 and removing the plate and outer bearing 1% secured thereto. As bushing 19a is fixedly secured to the trunnion as by press fitting precluding wear therebetween, machining of the trunnion will not be necessary.

For causing automatic reversal of the loosening means 15, a first pair of stop brackets 14a are provided, extending laterally outwardly from the side walls 11a and 11b of the suction tube 10. A longitudinally extending brace plate 14a is secured to the outer side of the wall 11d to which the inner end of the bracket 14a is secured. Brackets 14a are positioned to be abutted by side plate arm 16a when the side plate 16 is in the extreme counterclockwise position as seen in Figure 3. Extending laterally between the side plates 16 is a second stop bracket 14b positioned to abut wall lie of the suction tube when the side plates are in the extreme clockwise position. These stop brackets are provided as positive stop means at each extreme of the side plate rotation for causing the hydraulic control means automatically to reverse the movement of the side plate and effect a reciprocation thereof.

Hydraulic piston and cylinder means 20 is of a type well known in the art, comprising a closed-ended cylinr 6 der 20a having inlets 20b and 200 at opposite ends thereof and carrying internally a linearly reciprocable piston 20a having a piston arm 20d attached thereto and extending longitudinally outwardly through one end of the cylinder. When hydraulic fluid is forced into the cylinder 20a through inlet 20b the piston 20a is moved to the right, as seen in Figure 1, and when hydraulic fluid is forced into the cylinder through inlet 20c the piston 20a is moved to the left; This generally linear reciprocation is transmitted to the outer end 16a of the side plate arm 16a by suitable pivotal securing means 20d. As indicated above, the side plates 16 are rotatively carried on the trunnions 12 so that the generally linear motion of the piston arm is converted into rotation of the side plates. To accommodate the slight lateral movement of the piston arm 20d, the hydraulic cylinder 20a is provided with laterally. extending trunnions 20e pivotally journalledin a pillow block supported bearing member 20f which is carried on the suction tube 10.

To cause the reciprocatory rotation of the solids loosening means 15 and allow an automatic reversal of the direction of movement when an uncrushable object becomes wedged between the crushing blocks 17 and the lips 11 or crushing bar 11g, the hydraulic control means 21 is caused to be pressure responsive. As best seen in Figure 1, pump 22 is provided with a pair of outlet conduits 22a and 22b communicating with different portions of the interior of the solenoid operated valve 23. Valve 23 is of a type well known in the art comprising a closed-ended cylindrical housing 2301 having an internal longitudinally movable valve element 23b extending transversely through which are passages 23c and 23d arranged to be in alternative alignment and disalignment with the inlets from conduits22a and 22b. A conduit 23a is providedjextending from the valve 23 to the cylinder 20a having one end communicating with the inlet 20b of the cylinder and the other end communicating with the passage 230 when it is in alignment with the inlet from conduit 22b. A similar conduit 23f is provided communicating between cylinder inlet 20c and passage 23d when it is in alignment with the opening from conduit 22a. Thus, depending upon the positioning of valve element 23b pressurized hydraulic fluid may be delivered from the pump 22 to either end of the cylinder 20a.

To receive the hydraulic fluid discharged from the end of the cylinder 20a toward which the piston 20a is moving, discharge conduits 23g and 23h are provided communicating between a reservoir 22c and different portions of the interior of the valve 23. The ends of conduits 23e and 23f adjacent the valve 23 are bifurcated so as to allow a second passage from each thereof to have communication with the passages 23c and 23d when aligned with the openings from outlet conduits 23g or 23h. Thus, for example, with the valve element 23b positioned as shown in Figure 1, pump 22 will cause hydraulic fluid to flow through conduit 2212, through passage 230 of the valve element, through conduit 23e, and into inlet 20b of cylinder 20a. This will cause the piston 20a and arm 20d to move to the right as seen in Figure l and rotate the side plates 16 in a clockwise direction. Hydraulic fluid will be discharged from cylinder 20a through inlet 200, through conduit 23 through passage 23d in the valve, and through conduit 23h to the reservoir. Interconnecting conduit 22a is provided between the reservoir and the pump 22 to complete the circuit.

In conduit 232 is provided a pressure actuated switch 24a and in conduit 231 is provided a similar pressure actuated switch 24b. Each switch is provided with a set of normally open contacts 24c which are closed when the pressure in the conduit reaches a pre-determined point. The contacts of switch 24a are connected in series with the coil of an electric solenoid 23i having its. plunger; connected to one end of valve element 2311. Switch.

24b has its contacts connected in series with the coil. of a similar solenoid 23 having its plunger secured to the opposite end of valve element 23b. The solenoid coils and contacts are electrically connected to a suitable source ofelectric potential (not-shown). When the pressure of the fluid being supplied to the cylinder 20a through valve 23 reaches a pre-determined point, switch contacts 240 close and allow current to flow through the solenoid coil associated therewith, thereby moving valve element 23b to the opposite end of the housing 23a and reversing the direction of flow in the conduits. Such reversal occurs whether the movement of the side plates 1-6 is prevented by the stop brackets 14a and 14b or by an object being jammed in the bottom loosening means 15.

Preferably the pump 22, reservoir 22c, solenoid valve 23 and pressure switches 24a and 24b are disposed at a distance from the inlet end 11 of the dredge and the conduits 23a and 23 are made flexible to accommodate the motion of the dredge. The hydraulic cylinder-piston means 20 is mounted on the suction tube 10 relatively near, the inlet end 11 and is disposed below the surface of the water in normal use. The dredge is lowered into the body of water by means of the support cable 25 until the solids loosening means 15 contacts the bottom. Normally, the suction tube 10 will assume a somewhat vertical position with the loosening means 15 at the bottom thereof. Where the side of a river bank or shore of a body of water is being excavated, the loosening means will tend to act somewhat horizontally and the suction tube will assume a more horizontal position.

With the dredge head thus disposed, loosening means 15 is oscillated, causing the tapered ends 18a of the teeth 18 to burrow or dig into the solids, thereby loosening the material. Material thus loosened is drawn with the water sucked into the inlet end 11 of the suction tube 10 and discharged from the suction tube as desired.

In Figure 7 is shown a modified form of a lip and center brace assembly wherein supporting bars 111g" are secured at their outer ends to laterally extending lips 111 which are similar to lips 11 except that no notches are provided therein, with the supporting bars being secured as by welding directly to the lips. A crushing bar 111g similar to bar 11g is provided being secured as by welding between the inner ends of the supporting bars 11g so that a unitary assembly of the center brace 111g and the lips 111 is obtained. The entire assembly is secured to the walls 111d and 111e at the interior of the mouth of the inlet end 11 of the suction tube 10 by bolts 1117" so that it may be readily replaced while yet being rigidly mounted therein.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes therefore in the consbruction and arrangement may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a suction dredge, a suction tube having an open end with a rectangular cross section, a pair of reinforcing lips, one each removably Secured to an opposite edge of said open end, said lips having a laterally enlarged outer end and being mounted on the suction tube so that the minimum spacing between the lips occurs at the outer end, a crushing bar extending transversely across said tube and spaced between and parallel to said lips within said open end, a crushing block extending generally parallel to the crushing bar and exteriorly of said open end adjacent the crushing bar, and means for oscillating the crushing block laterally relative to the crushing bar to alternately space and juxtapose said bar and block for crushing matter lodged between said crushing bar and said lips.

2. In a suction dredge, a suction tube having an open inlet end with parallel, spaced transverse edges and spaced side wall edges, each of said transverse edges having a lip, a crushing bar extending between said side wall edges and generally parallel to and intermediate said transverse edges substantially flush with the open end of the tube, a plurality of crushing blocks disposed adjacent said edges exteriorly of said inlet end and extending generally parallel to said lips and crushing bar, and means for reciprocating said crushing blocks gen erally parallelly to said side wall edges and transversely to the lips and crushing bar, whereby said blocks may alternately act to crush material held between said lips and crushing bar by successive forces applied in opposite directions.

3. In a suction dredge having a suction tube with an outlet end terminating in outer edges, means for loosening solids to be drawn through said suction tube, comprising: a cross-shaped member extending across the outlet end at the outer edges and having a lateral crushing bar; lips secured to said tube edges and extending generally parallel to said crushing bar; a pair of spaced plates pivotal-1y carried by said tube at opposite sides thereof about an axis parallel to said crushing bar, said plates extending beyond the outer edges and having a plurality of crushing blocks secured thereto adjacent said edges, said blocks extending generally parallel to said crushing bar and provided with a plurality of outwardly projecting teeth for loosening solids; and means for oscillatorily moving said plates whereby said crushing blocks may forcibly press against solids disposed between said blocks and said crushing bars and bet-ween said blocks and said lips.

4. In a suction dredge having a suction tube with an outlet end terminating in outer edges, means for loosening solids to be drawn through said suction tube, comprising: a cross-shaped member extending across the outlet end at the outer edges and having a lateral crushing bar; lips secured to said tube edges and extending generally parallel to said crushing bar; a pair of trunnions fixedly secured to opposite sides of the outlet end of the suction tube and projecting laterally parallel to said crushing bar; a pair of spaced plates each having an opening and an outer bearing member removably secured thereto spaced outwardly from and surrounding said opening; a pair of annular bushings, one of said bushings between one trunnion and its associated outer bearing member, and the other bushing between the other trunnion and its associated outer bearing member, said bushings being removably secured to said trunnions and having sliding engagement with said bearing members for allowing pivotal movement of said plates about an axis parallel to said crushing bar, said plates extending beyond the outer edges and having a plurality of crushing blocks secured thereto adjacent said edges, said blocks extending generally parallel to said crushing block and provided with a plurality of outwardly projecting teeth for loosening solids; and means for oscil-latorily moving said plates whereby said crushing blocks may press against solids disposed between said blocks and said crushing bar and between said blocks and said lips.

5. In a suction dredge for removing solids from a body of water, a suction tube provided with an open end, a crushing element fixedly secured to said tube and extending across said tube at said open end, solids loosening means movably carried by said tube and disposed adjacent said crushing element, means carried by said tube for reciprocating said solids loosening means to cause loosening of the solids in the body of water and crush solids against said crushing element, control means associated with said reciprocating means and responsive to a prevention of a movement of said solids loosening means to [reverse the direction of movement of said solids loosening means, and stop means associated with said tube to be engaged by the means being reciprocatedat the ends of the normal movement thereof and prevent movement therebeyond, whereby said thereof.

References Cited in the file of this patent UNITED STATES PATENTS Sackett -1 July 29,- 1913 Reid Apr. 23, 1918 Swintek May 6, 1924 Thurston Feb. 5, 1929 10 Macomber May 23, 1933 Clute et a1. May 23, 1933 Walker Feb. 27, 1934 Harrington et a1 Oct. 29, 1940 Ragsdale June 30, 1953 FOREIGN PATENTS Great Britain 1913

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