US2970392A

US2970392A - Strip subgrader for roads

Info

Publication number: US2970392A
Application number: US691760A
Authority: US
Inventors: Glen E Perkins; George W Dale
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-10-22
Filing date: 1957-10-22
Publication date: 1961-02-07
Anticipated expiration: 1978-02-07

Description

Feb. 7, 1961 G. E. PERKINS ETAL 2,970,392

STRIP SUBGRADER FOR ROADS Filed 001;. 2 2, 195'? 5 Sheets-Sheet 1 N x m kg m (Z7272 fferkz'ns 'eozye 11/: Dale Feb. 7, 1961 G. E. PERKINS ETAL 2,970,392

STRIP SUBGRADER FOR ROADS 5 Sheets-Sheet 2 Filed Oct. 22. 1957 Feb. 7, 1961 G. E. PERKINS El'AL 2,970,392

STRIP SUBGRADER FOR ROADS- Filed Oct. 22, 1957 5 Sheets-Sheet s Feb. 7, 1961 G. E. PERKINS EI'AL STRIP SUBGRADER FOR ROADS Filed Oct. 22, 1957 5 Sheets-Sheet 4 Inzn Z0719: len E Zerkz'ns Feb. 7, 1961 G. E. PERKINS I ETAL 2,970,392

STRIP SUBGRADER FOR ROADS Filed 001;. 22, 1957 5 Sheets-Sheet 5 finfnians:

m Glen E Perkins E Gear 6 a 6 United States Patent srnlr SUBGRADER'FOR ROADS Glen E. Perkins, 1428 40th Ave., and George W. Dale, 1919 16th Sty-both of Rock Island, .111.

Filed Oct. 22, '1957,'Ser. No. 691,766

'6 Claims. (Cl. 37-171 In Pmparing a road site for paving, it is necessary to cut away or subgrade the site preparatory to laying the pavement thereon. In those types of road making operations wherein fixed formsuponwhich the subgrader and paving machine .are adapted toride ,are not used, the laying of "the finished pavement can be accomplished with greater facility and more economically if the subgrade is cut to an accurate level and is devoid of humps and undulations. However, the subgrader, in order to accomplish this desired end, .must itself travel over a relatively smooth properly cut path since the character of the subgrade reflects the character of the path over which the wheels or. tracks ofthe subgrader travel.

The present invention relates to a machine which functions to cut paths or strips of relatively narrow width over which the wheels or tracks of the main subcomprise a portion of the .main subgrader or the machine may be used as a separate unit. If employed as an integral portion of the main .subgrader, two strip subgrading units may be employed which may be secured to the main subgrader and be disposedin advance of the paths of travel of the Wheels or tracks of the main subgrader on each lateralside of the road site. Thus, the motive powerfor driving the main .subgrader functions also to drive the strip sul agraders-andfthe strip subgraders cut accurately gradedrelatively narrow strips over which the following wheelsor tracks of the main subgrader travel. Of course, if the strip subgraders are used asseparate units they can be operatedindependently of the main subgraders and may operate as far in advance of the main subgrader as desired.

One of the importantfeatures of the strip-subgradercomprisingthe presentinvention resides in the mounting of the cutter blade .with respecttothe machine frame wherein it maybe raised and lowered conveniently and quicklyby the operation of a single control.

Another-feature of the invention resides in the mounting of the cutter bladeof .the. strip subgrader-which permits convenient adjustment of the blade as the blade wears.

A further important feature of the inventionresides in a guide orgauge mechanism whichpermitsan'operaor accurately to follow a. grade line with a minimum of deviation therefrom.

Other important objects and features of the present invention will be .a psr mr the accompanying drawipgs and following detailed description.

,In thedrawingsf.

sv istoplp answiofa st n-t bs ade aembo y ing t s )Q lhsj ssmin es sn side ,elevational view of the device. shown p 21,970,392 Patented Feb. 7, 1963 Fig. 3 is a transverse sectional view taken on line 33 of Fig. 2.

Fig. 4 is a transverse sectional view taken on line 44 of Fig. 2.

5 is a slightly enlarged detailed sectional view taken on line 5-5 of Fig. 2

Fig. 6 is a transverse sectional view taken on line 66 of Fig. 5.

Fig. 7 is anenlarged detailed sectional .view taken on line 7--7of Fig. 2.

Fig. -8 is a top plan view of a main subgrader, shown diagrammatically, with which two strip subgraders, comprising the present invention, are associated.

Fig. 9 is ;a sideelevational view of a strip subgrader which'can be employed .as a separate unit.

Referring indetail to the drawings and .with particular reference to "Fig. 8 thereof, '1 indicates generally a subgrader which comprises as a unitary portion thereof two strip subgraders 2 which embody thefeatures of the present-invention. The suhgrader proper is shown diagrammatically'and comprises parallelspaced beams or frame members-3 over which tracks or articulated treads 4 travel in an endless path. The beams 3 may be bridgedby transverse "frame members 5 which may -carry suItabIe subgradingapparatus (not shown) and may also carry an engine or other prime mover (not shown) if the device is selfipowered. Of course, if desred, the devire may not be self-powered and rnay'bepulledby a tractor or other traction member.

The device;l,shown may span thewidth of the proposed roadand the opposite tracks 4 may move along the lateral edges of the: road. The function of the subgrader 1 is to cuttheearth toa predetermined level or grade so as to provide a foundation surface for the pavement material which willconstitute the finished road. To provide a tinished road of predetermined con'tant thickness and with a surface brought to a predetermined grade,'-the subsurface cut by the subgrader must be cut to a desired predetermined grade andelevation. Further, in view'of the fact that the cutting implements carried by the subgrader cut to a level determinedby the sur ace over which the tracks 4 travel, it isvital that the surface of the strips or path's over which thetracks travel be cut to 'a predetermined grade. Hence, the provision ofthe strip subgraders 2 which cut the strip or path over which the tracks 4 travel.

;In commencing operations, the engineer sets grade stakes two feet outside of thepavement area on each side of the road." Thesestakes are normally set at fifty-foot intervals, and represent the predetermined grade of the road at these points. Rods are driven into the ground at these points'land a chalk line is strung upon these rods eighteen inches above the tops of the grade stakes. Also, to eliminate excessive .Sag in the chalk line, additional rods are driven into the ground between the original grade stakes andthe operator sights downthe line making corrections to obtain a smooth grade. The grade lines referred to 'hereinbefore are designated by the lines 5 in the drawingsf Governed by these lines, both for lateral guidance and'princip ally' for elevational guidance,

secured :therein: a'lheiprot'ruding .endsiofsaid shaft function as journals for sleeves 10 on each side of the standards, said sleeves being rigidly secured to the ends of swingable arms 11. The arms 11 are thus disposed parallel to the beam 3 and are swingable in vertical planes on each side of the beam. 1

At the forward or face ends of the arms a sleeve 12 is rigidly secured to the arms 11, said sleeve spacing the arms from each other. In addition, the arms themselves terminate in sleeves 13 which are in alignment with sleeve 12. Each of the sleeves 13 is broken intermediate its length, as at 14 in Fig. 1, and a pin or shaft 14' bridges each break. A pair of depending arms 15 carry sleeves 16' at their upper ends, said sleeves being journaled upon the bridging pin 14' whereby the arms are swingably depending from arms 11.

posed channel 19 is rigidly secured to each gusset and to each side of the beam 3. A plate 20 is secured to plate 16 and extends transversely across the subgrader 2'.

The plate 20 functions to stiffen and reinforce plate 16,

and also has secured thereto resilient blocks or bumpers 21, preferably constructed of rubber, which are carried within the channel 19. The blocks 21 are preferably secured to plate 20 by bolts or the like (not shown). Thus the swingable assembly comprising arms 15 and plate 16 is resiliently cushioned by blocks 21.

The plate 16 is V-shaped at its front end and supports a backing plate which is preferably welded to said plate. A front skirt 22 is also rigidly secured to the plate 16, said skirt also being rigidly secured, preferably by weld ing, to the depending arms 15. The skirt 22 is V-shaped and is rigidly secured to a mold board 23 which is curved at its upper edge portion 24 and is inclined forwardly at its lower edge portion 25. A cutter 26 is bolted, by means of bolts 27 between the mold board 23 and the backing plate 21, and comprises the active cutting element of the strip subgrader. Additional bracing is furnished to the mold board assembly by spars or braces 28 and 29 (Fig. 1).

Thus, the cutting assembly of the strip subgrader is swingably mounted upon arms 15 and is resiliently cushioned by the blocks 21. r

A top deck plate 30 is rigidly secured to the plate 20, preferably by welding, said deck plate also extending across the subgrader, as shown best in Fig. 3. At its front, the deck plate 30 is rigidly secured to the front skirt 22. An electric motor 31 is mounted upon the deck plate 30 and said plate is provided with suitable openings whereby V-belts 32 trained around pulleys 33 carried by motor shaft 34 may pass downwardly and wrap around pulleys 35 mounted upon shaft 36 of a vibrating device 37 which is secured to plate 16 by bolts 38.

The vibrating device 37 is shown in detail in Figs. and 6 and comprises a casing 39 in which sh ft 36 is journaled. A second shaft 40 is also journaled in the casing 39 and is disposed horizontally parallel to shaft 36.

Gears

41 and 42 are respectively mounted upon shafts 36 and 40 and, hence, both shafts are driven together by motor 31, but in opposite directions. An ec centric weight 43 is carried by shaft 36 and a similar weight 44 is carried by shaft 40.

The

weights

43 and 44 are so positioned upon shafts 36 and 40 and said shafts are so geared together that, during rotation, the weights pass both horizontal positions together on the same sides of their respective supporting shafts. However, they are both rotating in opposite angular directions when the above described position obtains. Accordingly, horizontally said weights are in phase and the weights exert concurrent thrusts in horizontal directions. However, when the weights are dis placed 90 from their horizontal positions the weights are out of phase vertically. and their thrusts are st atically balanced or neutralized, as shown by the dotted position of the weights in Fig. 6.

Hence, the vibrating device produces a maximum horizontal vibration and a minimum vertical vibration. Inasmuch as the vibrating device 37 is mounted upon plate 16, this horizontal vibration is imparted to the entire swingable assembly comprising arms 15, mold board 23 and cutter blade 26. Hence, a substantially horizontal chiseling action is produced by blade 26 upon the ground. The vibration hereinbefore described is resiliently damped by the blocks 21 and is not transmitted to the machine proper.

It is to be understood, however, that the present invention in its broadest aspects contemplates other types of vibrating mechanisms. For instance, a simpleeccentric rotating weight may be employed or a mechanism wherein an elliptical pattern of vibration and wherein the major vibration may occur along a horizontal line may be used. V 4

A hand wheel 45 is secured at the upper'end of a vertical shaft 46 by nut 47. Shaft 46 is journaled in a vertical housing 48 which is secured to a cross bar 49, preferably by welding 50, the cross bar being, in turn, secured to the opposite arms 11. Beneath the cross bar 49 a hub 51 is secured to shaft 46 and is locked thereon by set screw 52. The hub 51 carries two

sprocket pinions

53 and 54. Bearing blocks 55 and 56 are carried between the fiang'es of opposite arms 11,- being' secured in place by screws 57. A self-aligning bearing 58 is car- 'ried by hearing block 55, and a similar bearing 59 is positioned in bearing'block 56. A screw shaft 60 is secured to the inner race of bearing 58 by nut Gland, in similar fashion, shaft 62 is secured to the inner race of bearing 59 by nut 63.

The shanks of both

screws

60 and 62 carry

threads

64 and 65, respectively, and a sprocket wheel 66 is threadedly mounted upon screw 60, said wheel being fastened by set screw 67. In similar fashion a sprocket wheel 68 is threadedly mounted upon screw shaft 62, being held in desired position thereon by set screw 69. A sprocket chain 70 operatively connects sprocket pinion 53 and sprocket wheel 66, and chain 71 similarly connects pinion 54 and wheel 68.

A tie plate 72 extends across the device and is secured to the beam 3 and the upper ends of the channel 19, preferably by welding. A nut 73 is carried by the underside of the tie plate 72 adjacent screw shaft 60 and a similar nut 74 is similarly secured to the tie plate adjacent screw shaft 62. The

screws

60 and 62 are respectively threaded in the nuts 73 and 74.

The arrangement is such that when hand wheel 45 is rotated,

screw shafts

60 and 62 are rotated and, hence, arms 11 are moved upwardly or downwardly relative to beam 3. Inasmuch as the suspended assembly comprising arms 15, plate 16, mold boar d 23, etc. are suspended from arms 11, movement of

screwshafts

60 and 62 raises or lowers the cutting mechanism relative to beam 3. In view of the fact that movement of arms 11 is along an arc,

screw shafts

60 and 62 will have a slight degree of angularity in their movement. This contingency is compensated for by the self-aligning bearings 58 and 59. M

It will be noted that the

sprocket wheels

66 and 68 may be rotated freely about the

respective screw shafts

60 and 62 by loosening the

respective set screws

67 and 69. By this arrangement an adjustment for uneven wear of blade 26 may be brought about. For instance, were blade 26 to wear to a greater degree on one .side or the other, one or the other of the

set screws

67 or 69 may be loosened and hand wheel 45 may be turned. This causes the loosened sprocket wheel to rotate to a degree upon its shaft. Thereafter the sprocket wheel may be locked by its set screw. This operation tends to warp the portion of the machine comprising arms. 11, arms 15, plate 16, etc., and thereby transversely cant the cutter blade '26. The frame, although essentially rigid, will permit a moderate degree of warpsutficient to adjust normal uneven wear-of the blade 26.

To further provide for wearof the blade 26, the holes therethrough for the reception of bolts 27 are centrally disposed transversely of the blade and, hence, said blade may be reversed .edge-forredge when the active edge wears to an excessive degree- I To inform the operator of the necessityof manipulating the hand wheel 45 to raise or lowernthe-blade 26 and its supporting vstructure relative to beam 3, a sys' tem of levers 75 are employed. The system of levers 75 comprises a lever 76 which is pivotally mounted upon shaft 14'. its length but the pivot point is closer to the rear end of the lever thanto its front end. The lever 76, at its rear end is pivotallyconnected to a link 77 by pivot pin '78 and the latter link is pivotally connected .at its opposite end to a second link 79, .the pivot comprising-pin 80. Link 79 is fulcrumed upon pin 81 which is carried by tube 82 secured to beam 3, the tube being also secured to channel 19. The fulcrum 81 is positioned adjacent the rear end of link 79 whereby the lever arm of the forward portion of said link is relatively greater than the rear lever arm. At the rear end of link 79, said link is pivotally connected to clevis 83 by pin 84. A similar clevis S5 is pivotally mounted upon arm 11 by pivot pin 86. A screw 87 is threadedly connected at its opposite ends to

clevises

83 and 85, the threads at the opposite ends of the screw being pitched in opposite directions. A nut 38 is carried intermediate the length of screw 87 whereby said screw may be conveniently ro tated to change the efiective distance between pins 84 and 86. Hence, by manipulating nut 88 the forward end of lever 76 may be raised or lowered, a slight mo tion of screw 87 resulting in a large motion of the free end of lever 76.

At the forward or free end of lever 76 a pair of spaced cars 89 are carried and'a sleeve 90 is positioned therebetween. A pin 91 is carried in sleeve 90 whereby said sleeve may rotate about said pin. A tube 92 is fixed to the sleeve and carries .at one end a pointer 93. A coil spring 94 is anchored at one end upon lever 76 and .at its opposite end upon tube-92. I It will be noted thatsleeve 90 is offset outwardly from the face of lever 76 and, hence, under the tension of spring 94, the tube 92 laterally abuts the-end of said lever. In this position, :the tube and pointer 93 extend at substantially right-angles to the outer face of lever 76. It will also be noted that the tube 92 and pointer "93 are free to rotate in the opposite direction against the tension .of spring 94 to a position substantially parallel to the face of the lever 76.

A pin 95 is slidably positioned in the'hollow shaft 9. The pin 95 is normally in retracted position. wherein. flange 96 carried by said pin abuts the end of the shaft. However, when occasion demands the ,pin may be moved to-extended position, as shown best-in Fig. 1.

It will be noted that the point of pin 95 is at a fixed elevation above the lower face of the treads 4, that is, the level of the surface cut by thestrip-subgrader. It is desired that the point of pin 95 be at the same elevation as the grade line 5' and that the strip subgrader cut suflicient of the earth to normally have t-hiscondition .obtain. Hence, by 'the manipulation of nut 88 the point of pointer -93 is so set as to be the same distance above @the cutters ;rnentof pointer 93. Converselya relatively large move- The lever 76 is pivoted intermediate mentof pointer 93 represents a relatively small movement of arms '11 and, hence, cutter blade 26. Accordingly, a relatively smallv movement of .hand wheel 45 represents a relatively large movement of pointer .93.

The particular purpose of the pointer 93 and its motion multiplying linkage is to mitigateduplication in the-strip being graded of the deviations from intended grade elevation of the grade line or chalk string 5, especially the deviations resulting from sagging of the string or line .between grade stakes and inaccurate sight placement of line supporting rods intermediate the grade stakes. Inuse of the device, initial portions of the strips to .be graded. are leveled oil to the intended grade, and the .strip subgraderis moved onto these leveled areas with itsip oin ters 93 and level with the chalk line. The strip subgrader is then moved forwardly and as it is moved an operator at each hand wheel 45, by appropriate. .manipulationof the. wheel, causes the respective pointer :93 to .bernaintained level with the respective string line 5. As willbe appreciated from the foregoing, relatively greatmovement .of the pointer 93 by thehand wheel will result in only a relatively slight movement of .thecutter blade 26. Thus, deviations of the string fromintended elevation, as by sagging, will be reduced in transmitting this deviation from the pointer -tothe cutter blade.v For example, with a thirteen-to-one linkage arrangement, a one inch sag in the string line will, withappropriate manipulation of the hand :wheel 45, re-

sult in only one thirteenth of an inch deviation in .the

over which the tracks 4 subsequently ride, whereby the device under normal conditions willqcontinue to cut extremely accurate foundation strips. The. pointer and its multiplying linkage, of course, will not operate properly in reverse. If forsomere a son the track..4 orthe blade 26 werecaused .to deviate, which would be most unusual when considering customary working conditions and the uormaloperation of the blades and tracks, any deviation of .the track would be directly reflected by an equal deviation of the .pointer .93, andadjustment of the hand wheel 45 .to bring the pointer back to .the .grade line would bring the blade 26 only partiallybackrto intended position, thereby resulting in error in the grading operation. However, anysuch error would be revealed to the operator the next time the .pointer v95 passed a grade stake, since this pointer should be level with the string at each and every grade stake, so that the error would be revealed and could be corrected within no .more than 50 feet of travel of the stripsubgrader.

Hence, during the operation of the device, the operator-attempts to maintain the pointer 93 opposite the grade line 5. The human element, .however, prevents an .exact..alignment, but if anapproximate alignment is maintained errors in .the raising and loweringof the cutter blade 26 will be extremely small. Accordingly, abrupt and'large-changes of elevation ,of .the strip being cut will .beavoided since all .theHoperato-r need do is maintain an approximate alignment of pin -93, with grade line 5, and check the pin .95 relative to the line at each grade stake.

In :the .form of the invention illustrated in-Figs. l

to 18 inclusive, the'strip subgrader is shown as .beingan integral portion of the main subgrader. Accordingly, only :the front tcrminalsprockets 97 for the treads or In 'Fig. 9

of the invention, all of the mechanism hereinbeforedes cribed is identical and corresponding reference numerals will "{be "applied without further detailed description.

7 99 and 100 for the tracks are carried by the unit strip subgrader itself.

The unit strip subgrader 98 may be used as a separate unit or units in front of the main subgrader or the unit strip subgrader may be employed to prepare a properly graded path for a so-called slip form paver or the unit may be separately employed to prepare a properly graded strip for any desired purpose.

We claim as our invention:

1. A strip subgrader which comprises in combination, a frame having a front and rear portion, a pair of spaced arms pivotally mounted at corresponding ends upon said frame and having their opposite ends extending toward the front portion of said frame, a support pivotally carried at said opposite end portions of said arms and depending substantially vertically therefrom, a cutter blade carried by said support, and control means carried by said arms and bearing on said frame for vertically moving'said arms relative to said frame ,to raise and lower said cutter blade relative to said frame, said control means comprising screw means journalled in said arms and threadedly engaging said frame, shaft means carried by said arms for manipulating said screw means to change the position of said arms relative to the frame, said shaft means comprising a rotatable shaft, sprocket wheels carried by said shaft, sprocket wheels threadedly carried by said screw means, sprocket chains respectively engaging said shaft sprocket wheels and said screw sprocket wheels, and separate means for locking each of said screw sprocket wheels upon said screw means.

2. A strip subgrader which comprises in combination, a frame having a-front and rear portion, spaced arms pivotally mounted at corresponding ends upon said frame and having their opposite ends extending toward the front portion of said frame, a support pivotally carried at said opposite end portions of said arms and depending substantially vertically therefrom, a cutter blade carried by said support, and control means carried by said arms and connected to said frame for vertically moving said arms relative to said frame to raise and lower said cutter blade relative to said frame, said control means comprising spaced vertical screws threadedly engaged with said frame, each of said arms bearing upon one of said screws and being movable with axial movement of said screws, and means carried by said arms for simultaneously rotating said screws.

3. A strip subgrader which comprises in combination, a frame having a front and rear portion, spaced arms pivotally mounted at corresponding ends upon said frame and having their opposite ends extending toward the front portion of said frame, a support pivotally carried at said opposite end portions of said arms and depending substantially vertically therefrom, a cutter blade carried by said support, control means carried by said arms and connected to said frame for vertically moving'said arms relative to said frame to raise and lower said cutter blade relative to said frame, and vibratory means carried by said support for vibrating said support and cutter blade carried thereby, said control means comp-rising spaced vertical screws threadedly engaged with said frame, each of said arms bearing upon one of said screws and being movable with axial movement of said screws, means carried by said arms for simultaneously rotating said screws, said means comprising a shaft rotatably carried by said arms, means connecting said shaft to each of said screws to rotate said screws simultaneously to axially move said screws.

4. A strip subgrader which comprises in combination, a frame having a front and rear portion, spaced arms pivotally mounted at corresponding ends upon said frame and having their opposite ends extending toward the front portion of said frame, a support pivotally carried at said opposite end portions of said arms and depending substantially vertically therefrom, a substantially horizontal- 1y disposed platform carried by said support', a cutter l 8 blade carried by said platform, vertical screw means threadedly engaged with said frame and rotatably-but nonaxially movable with respect to said arms for vertically moving said arms relative to said frame to raise and lower said platform and cutter blade carried thereby relative to said frame, a shaft rotatably carried by said arms, separate means connecting said shaft to each of said vertical screw means to simultaneously rotate said screw means, and means carried by said separate means for rendering selectively a separate means inoperative, and vibrating means carried by said platform to vibrate said platform and cutter blade carried thereby.

5. A strip subgrader which comprises in combination, a frame having a front and rear portion, spaced arms pivotally mounted at corresponding ends upon said frame and having their opposite ends extending toward the front portion of said frame, a support pivotally carried at said opposite end portions of said arms and depending substantially vertically therefrom, a cutter blade carried by said support, control means carried by said arms and bearing on said frame for vertically swinging said arms relative to said frame to raise and lower said cutter blade relative to said frame, a multiplying linkage pivotally connecting one of the arms and said frame, an index carried by said linkage for alignment with a grade line, said index being simultaneously movable with said arm in the same direction but at a multiplied rate.

6. A strip subgrader which comprises in combination, a frame having a front and rear portion, spaced arms pivotally mounted at corresponding ends upon said frame and having their opposite ends extending toward the front portion of said frame, a support pivotally carried at said opposite end portions of said arms and depending substantially vertically therefrom, a cutter blade carried by said support, control means carried by said arms and bearing on said frame for vertically moving said arms together relative to said frame to raise and lower said cutter blade relative to said frame, a multiplying linkage pivotally connecting said arms and said frame, an index carried by said linkage for alignment with a grade line, said index being movably responsive in a multiplied degree to the movement of said arms, said multiplying linkage comprising a plurality of pivotally connected links, means connecting one link to said frame, a second link pivotally connecting said frame-connected link to said arm, a third link pivotally connected to the forward end portion of said arm and having a free end, a fourth link pivotally connecting said frame-connected link to said third link, said index being carried by the free end of said third link and movable in response to movement of said control means, one of said links being adjustable in length to calibrate said index with respect to the position of the arms relative to the frame.

References Cited in the file of this patent UNITED STATES PATENTS 1,031,919 Elliott July 9, 1912 1,387,875 Wellensiek Aug. 16, 1921 1,506,634 Hartshorn Aug. 26, 1924 1,508,786 Grimes Sept. 16, 1924 1,744,801 Rimple et al Jan. 28, 1930 1,834,110 Ricks Dec. 1, 1931 1,936,518 McColm Nov. 21, 1933 1,973,830 Tomkin Sept. 18, 1934 2,163,662 Buffington June 27, 1939 2,163,682 Heeren June 27, 1939 2,503,408 Phillips Apr. 11, 1950 2,678,508 Reuter et al May 18, 1954 2,725,799 Day et al Dec. 6, 1955 2,749,630 Nave June 12, 1956 2,787,846 Everds et a1. Apr. 9,; 1957 FOREIGN PATENTS 113,305 Great Britain Feb. 12,1918