US2634960A - Method of mining and apparatus therefor - Google Patents

Description

April 14, 1953 w. B. LANG 2,634,960

METHOD OF' MININGl AND APPARATUS THEREFOR Filed Feb. 6, 1948 1 3 Sheets-Sheet l 33M Mrt April 14, 1953 w. B. LANG 2,634,960

METHOD OF MINING AND APPARATUS THEREFOR Filed Feb. 6, 1948 3 Sheets-Sheet 2 N. Q @A April 14, 1953 w. B. LANG METHOD oF MINING AND APPARATUS THEREFOR 3 Sheets-Sheet 5 Filed Feb. 6, 1948 Patented Apr. 14, 1953 METHOD .0F MINING AND APPARATUS THEREFOR Walter B. Lang, Washington, D. C.

Application February 6, 1948, Serial No. 6,685

19 Claims.

This invention relates to mining and aims to provide an improved method and means for increasing the useful yield of mines and preserving the geological structure -of the overburden In particular the invention has for objects, severally and inter-dependently:

l. The provision of an improved method of making useful disposition of mine wastes in such a Way as to enable removal of `the standing ore columns left in the conventional room and pillar mining method, thus increasing the yieldof the mine without danger of subsidance or need of timbering;

2. The provision of an improved method of erecting and consolidating mine wastes, and particularly crystallizable mine wastes, to form consolidated columns extending between and inte- -gralized with the hanging and foot walls of the mine opening;

3. The provision of a method 'which enables the simultaneous production in the so erected columns of indicating openings by which any tendency towardv failure thereof may be detected before any serious failure occurs; v

l4.. Thefprovision of an improved method of erecting sectional vforms to effect a tight seal thereof to the hanging and foot walls of the mine opening to provide 'for' the formation therein of such integralized consolidated columns;

5. The provision of a method and means particularly adapted for economic erection of con-r solidated detritus columns in the cleared areas of mine galleries and the like, enablingrsubsequent removal of the ore body columns therebetween; v

6.L The provision of a method and means particularly adapted for potash mines and the like for establishing therein consolidated columns of detritus or gangue such as common salt adequate to support the overburden and enable removal of the entire economic bed-or body of ore;

7. An improved method and means for Ycutting or generating in the hanging, foot'or other walls of mine galleries ring-like seats for the reception of standardized chambering forms; v

8. The provision of an improved chambering method and chambering forms for the erection of consolidated columns therein.; and

9. The 'provision of improved seatgenerating 'equipment and improved sectional Y`forms cooperable for easy transportation to, erection at 'and removal from place to place in the mine.

Other objects and advantages of the invention will be apparent from thefollowing descriptionI of preferred embodiments of methods and means exemplifying the same.

With such objects in view the invention con,-

sists in the .details of arrangement and combinations of parts and in the novel steps and com-- binations thereof hereinafter described and claimed.

In the accompanying drawings illustrating a preferred embodiment of the invention,

Fig. 1 is a diagrammatic sectional plan through a region of mine galleries,

Fig. 2 is a diagrammatic vertical section taken on the line 2-2 of Fig. 1,

Fig. 3 is a similar View after erection of columns and removal of ore bodies from between the same by the method of this invention.

Fig. 4 is a more or less diagrammatic side .elevation of a channeling device in accordance with the invention,

Fig. 5 is a diagrammatic detail of the pump arrangement taken on the line 5-5 of Fig. 4 look ing in the direction of the arrows,

Fig. 6 is a diagrammatic sectional detail through one of the cutter feed control valves,

Fig. 7 is a vertical section illustrating one embodiment of column form for practicing the invention,

Fig. 8 shows in diagrammatic form oneembodlment of liquid pressure pulsator and supply connected to the casting form.

In mining operations, and particularly in the case of potashmines and the like in which the deposits occur in overlapping lenticular form, the conventional mining method involves steps generally as follows:

Initially a shaft-is sunk through a number of overlappinglenses and beds. A gallery is then opened in the lens appearing to contain the richest ore. This lens frequently is one of the lower lenses penetrated by the shaft. Inv such case the upper lenses of less rich ore are usually bypassed and reserved for working only `after economic working-out of the richest lens. As the mine gallery progresses in the selected lens or ore body, to prevent subsidance of overlying structures, some twenty-five per cent or more of the ore is left in place in standing columns l0 as shown in Figs. l and 2. Failure to leave adequate standing walls orcolumns is apt to result in subsidence of the hanging Wall I2, loss and delay in working the selected lens, and damage or rupture of overlying beds rendering them diliicult to work. Also failure to Vhave adequate walls I0 in underlying beds which have been worked out, is apt to cause subsidance during working of overlying structures with danger tothe personnel and equipment there employed, and prevents use of the excavated working for storage and other purposes currently advocated by some authorities.

Efforts have'been made in some localities where timber isavailable, to reduce the amount of ore necessary to be left in pillar form; but timbering is expensive, involves risk of fire and rotting, is merely a temporary expedient, and is frequently not economically feasible. Furthermore when the cost of timbering is added to other production costs, the total cost per yard of the mining operation is increased, and it becomes uneconomic to work ore bodies which. otherwise would be sufIiciently rich to justify the mining thereof.

Most ore bodies contain wants or horses of lean ore or ore high in gangue which must be removed in mine tunneling in pursuit of the richer bodies of ore. amount of gangue is not only troublesome but expensive and the more of it that can be made use of in the mine, the lower the cost of operation. For example in potash mines the potash occurs in intimate association with common salt or halite and the volume of halite to be separated lfrom the sylvite is large. It cannot vbe disposed 'of in rivers, and where stacked in open piles becomes an ever increasing nuisance.

My invention, however, enables useful disposition of such mine wastes, particularly of crystallizable mine wastes such as halite and the like, while at the same time enabling the standing ore pillars to be removed, ,thus increasing the The disposal of a large yield of the mine without introducing danger of .i subsidance, and eliminating the need for timber.

columns II consisting predominantly or entirely of mine wastes, and sufficient in area to afford complete support for the overburden, and thereafter remove the ore pillars I0 from between the so erected columns H.

In the preferred practice of this method which is particularly but not exclusively applicable to potash mines and the like yielding mine Vwastes including crystallizable material, I nd that such columns may be best erected by erecting, between the ore pillars I0, casting forms embracing spaces extending from the hanging wall I2 to the foot wall I3 of the opening and sealed thereto, substantially filling said forms with such mine wastes. in solid and liquid form, pulsating the material to eliminate voids therein, and allowing the contents of the forms to consolidate by crystallization, preferably while maintaining it under pressure, to form solid columns integralized with the hanging and foot walls, the structure of which is substantially as strong as that of the original ore body.

In order to effect the sealing of the casting forms notwithstanding irregularities in the hanging or foot Walls, or both, of the mine gallery, my method contemplates the generation in the mine walls of ring-like seats I3 (Figs. 3, 4 and 7) for the reception of sealing rings I4 and I4a (Fig. 7) shown in the form of split rubber rings or gaskets or the like, against which the casting forms generally indicated at I5, Fig. 7, may beV Channeling As above noted the first step of this method comprises the formation of ring-like seats I3 in the walls of the mine between which the columns are to be erected. A preferred form of apparatus suitable for this purpose is shown in Fig- 4. In

the firm there shown the apparatus comprises a fluid pressure, preferably a hydraulic pressure, jack post having at its ends bearing plates or feet 2l with an extensible hydraulic cylinder and piston 22 and 23 positionable therebetween and adapted to be extended or collapsed by hydraulic pressure application and release through the connection 24 under control of the Valve 25.

In the form shown the cylinder portion 22 of the jack post is provided with a squared end 26 tting into a flaring squared socket in the foot member 20 to prevent rotation thereof, and the piston 23 is `provided with extension caps 2l to adapt it for various spacings of the mine walls, the last such cap 28 being coupled to the bearing plate 2l by a ball and socket connection 29.

In the form shown the-cylinder 22 has mounted thereon a rotatable frame 30 supported between two sets of antifriction bearings 3! and 32, and thus adapted for rotation on the xedly positioned cylinder. The cylinder V22 also carries a peripheral rack gear 23 and a slip-ring electrical connector 34 or the like hereinafter more fully described. 'I'he 'frame 30 in the form shown is adapted to detachably support a rotatable cutting frame, hereinafter described, so that these parts may be separated for transportation from place to place in the mine gallery. It will be observed that the separated jack post structures may be easily transported into and through the mine and may be quickly and firmly erected at any desired position in the mine opening at which a consolidated column II is to be erected.

In the form of Fig. 4 Ythe rotatable cutting frame comprises a substantially rigid frame structure 40 formed at its inner end for detachable connection to the supporting frame 30 as by wing-nut or like securing means 4I. At or near its Youter` end it is provided with rotatable cutter means 42 formed to channel the mine walls when the frame 40 is rotated.

Means is provided for feeding the cutters 42 as the depth of the channel I3 increases, this means in the form shown comprising hydraulic cylinders 42 coupled through suitable levers 44 and collars 45 to the tubular shafts 45 of the cutters 42, which are mounted for rotational and longitudinal movement in the journals 4l carried by the frame 40. Admission of measured quantities of hydraulic fluid under pressure to the cylinders 43 thus feeds the cutters 42 into the mine walls against the action of compression springs 48 surrounding tubular shafts 4B, and release of fluid from the cylinders 43 allows the springs 48 to retract the cuttersfrom the work. Such admission and release of fluid from the cylinders 43 may be controlled by suitable valves 5B, Figs. 4 and 6, which may be ganged as shown for operation by a single hand lever 5I. The uid pressure supplied from the pumps 60 hereinafter described through conduits 52 is admitted to the cylinder'connection 53 when the two-way valves 5U are turned to the position shown in solid lines in Fig. 6. When the valves are turned to the position shown in dotted lines in Fig. 6 the iluid from the cylinders 43 is vented through the vent line 54 to a suitable reservoir 55 carried by the frame 43.

The pumping means, Figs. 4 and 5, for supplying the measured volumes of liquid cylinders 43 preferably comprises two independent pumps El! having plungers 6I spring-pressed against a pump cam 62. Each of the pumps 30 in the form shown comprises the usual inlet and outlet check valves 63 and 64 (Fig. 5) and preferably is provided with independent means 65 Vfor adjusting its.vol1nnel of displacement, shown yas a s et screw projectablemore or less into the pump chamber. The pumps 60 are mounted on a suitable supportI 6B which is adjustably carried as by the frame 4I) (Fig. 5)- so that the throw of the plungers may be simultaneously adjusted with respect'to the cam'52. The pumps draw theiruid supply from the reservoir 55 (Fig. 4) and force measured quantities of vhydraulic uid to lthe cylinders 43 by way of the pressure liquid lines 52. As shown in Fig. 4 the cam 62 is rotated at a relatively low speed by a suitable drive, as the belt drive 6l connected through a speed reducer 68 to the driving motor 69.

-As shown in Fig. 4 the driving motor E9 is directly coupledto drive gearing 'Ill suitably mounted, on the frame 49 so as to rotate the cutter drive shaft II which in the form shown isl splined to the tubular cutter shafts 46. These cutter shafts are preferably provided with extensible sections 'I2 to enable quick adjustment of the cutter spacing to the `particular spacing of mine walls in which the channels I3 are to be cut.

From the gear reduction box 68 a further slow speed drive shaft 'I3 leads to gearing for rotating the cutter frame 40 relativeto the support or jack post 22.V In the form shown the slow speed drive shaft 13 connects to gearing 'I4 suitably mounted on the frame 40 which in turn drives a pinion 'I5 engaged with.the peripheral rack gear 33 which is carried by the cylinder 22 as heretofore described.

` `The power leads 'I6 from driving motor B9 are coupled, as by plug-'in connection 'I'I, to the brushes 'I8 which are carried by the frame 39 and make contact with the slip-rings 34 aswthe frame is rotated relative thereto. Details of such slip-ring connections and equivalents thereof are well known to those skilled in the art and require no further description here. As is preferable when Vemploying an electric drive, the slip-ring and brush assembly 34 and 18 may be enclosed in a housing (not shown) to isolate the openr contacts from the surroundings. The slip-rings in the form shown are connected as by'connector 19 to an electrical conduit 80 which passes to `a point beyondthe channel area I3 through a narrow trench 8| cut across Vsuch area to aV suitable source of power indicated at 82.

With the foregoing construction it. will be appreciated that after erection of the jack post 2li-,34, the cutter frame'40 and the parts carried thereby may be quickly attached to supporting frame 30. The cutters 42 may then be set by means of extensions 12 and pumps 60 to just clear the mine walls during rotation of frame 4 0. The trench 8| and electrical connections 'I1 and I9 may then bernadaafter which motor 69 may be put'into operation, the valves 50 being positioned for admission kof fluid, to the.. The cutter device Willthen op- Casting of consolidated columns ,"Aitermthe .channels I3 have been cut to an appropriate depth, thetrench 8| is -usually11led up to the level of the channel.- -In thel preferred form shown inFig. 7 thesetional castingforms I5 'may be assembledl to vforma cylinder, say ten to twenty :feet or more in diameter. 'They comprise a sealing .ring I4, -a base ring supportable thereon Ymade upof sections 90, and further sections 9| and 92 assemblable in telescoping relation thereto. In the form of Fig. '7 the sections 92 are provided with-hanged endsl and support the sealing means |411r in the complementary one of the paired channels I3.

'I'he base section in the form shown is provided With weep holes 93 connected to Vdraw-olf lines 94 controlled by valves 95.v By these any excess liquid introduced into the assembled form may be readily withdrawn jand progress of crystallization may vbe followed. f

Suitable` means is provided for holding the formsections 9| and 92 in assembled relation. As shown in Fig. 7gthe sections 9| are held in engagement to form an annular ring by transverse tie-rods 96. These tie-rods are preferably of substantial `diameter and tapered from one end toward the other. A diameter of from one and one-half to two inches is suicient. Thus when the columns have consolidated in the as.- sembled forms and the forms and tapered tierods are removed, Athe column is provided with transverse inspection openings A91 (Fig. 3). While the useof tapered rods 96 toafford such test holes is preferable throughout the column,

^ other means for securing the form sections together may be used such as the contractable hoops 96a or bolts v96h for example. The test holes 91 (Fig. 3) 4may be inspected from time to time as the ore columns l0 (Figs. 1 and 2) are being removed, as well as thereafter, and if no distortion of theV holes 91' appears `will in'- dicate that-adequate support for the overburden has been provided and maintained.

Means is provided for forcing the forms i5 into sealing relation with the channels I3. In the form shown this means comprises wedge blocks 98 inserted between opposed flanges of the telescoping sections 9|, 92 and fluid pressure expansible means in the form of collapsible hose sections99 or the like interposable between op-A posed flanges of the telescoping sections, herein the flanges of the sections Vand 9|, and inatable by fluid pressure supplied through a ,valved line or lines 00. Sealing gaskets of any conventional form are also preferably provided between the several form sections I4, 99, 9| and 92, so that on assembly and expansion the entire form becomes pressure tight.

When the forms have been erected so as to embrace a desired area of mine openings extending between hanging and foot walls thereof, as shown in Fig. 7, a mine Vwaste mixture capable of being consolidated is introduced to the yso-embraced space. Solid materials maybe shoveled, conveyed, or blown in, as through manhole I6, and may be shoveled thereon or .otherwise distributed within the space to substantially/fill the same. The manhole lcover I6 is then secured in place and consolidating materialin liquid or slurry form is. introduced through inlet connection I'I to completely ll the space within the casting form. The sludge or liquid-introduced through pipe I1 in the case of potash mines. and the like may comprise renery waste such as a strong brine or water suspension of salt crystals drawn fromA a suitable supply tank, as the tank4 |91 (Fig. 8) As the space embraced-by the forms I5 is. filledA with such liquid material, the air therein may 76 escape in any-.suitable wayas through the valved air eduction outlet |02 connected near the top of the enclosed space shown in Fig. '7.

When the voids in the enclosed space have been pumped substantially full of liquid material capable of consolidating the column, it is desirable that the contents of 'the forms be subjected to pulsations of pressure to eliminate any residual voids and cause intimate contact of the consolidating material with the solid wastes within the forms. As shown in Fig. 8 this may be effected by providing the sludge pump |03 with -a check valved inlet |04, and providing its outlet with a weighted bypass valve, such as the spring biased bypass valve |05. Thus operation of the pump |03 when the chamber I5 has been substantially lled with liquid serves to reduce the pressure in the chamber l5, to which the pump is directly connected during the suction stroke of the pump, and to then raise the pressure therein to the value necessary to open the spring biased bypass |05.

When the forms have been filled, in the case of crystallizable material, until no more air is driven out through vent |02, the contents thereof are preferably maintained under pressure during the setting or crystallizing of the column. When the crystallization has progressed substantially to completion, which may be determined by the inability to draw any substantial quantity of liquid from the weep pipes 24, the forms and sealing rings may be removed and re-erected in another location. During the setting of the column, particularly if this is effected under pressure, the column becomes integralized with the foot and hanging walls of the mine opening. In the case of crystallizable material there is hardly any boundary between the column and the foot and hanging walls since crystal growth extends across such region. When the consolidated columns have set and are suiiicient to support the overburden, the ore pillars I0, Figs. 1 and 2, may be removed.

Since the solid mine wastes may be obtained in part directly at the site of the Work, and in part merely by returning them from the surface in the mine skips which otherwise would return empty, the supply of such materials to the site involve very little expense. Moreover where two skips are operatingV in counterbalanced relation the loading of the down-coming skip actually effects a saving in power consumption. The supply of liquid material to the inlet connection may easily be effected by a simple pipe line extending from a surface tank to the underground equipment. When so supplied the liquid head or a part thereof may be employed to ll the form l (Fig. 8) and maintain pressure there.- on, and a cut-off |06 in such line may be closed to provide for pulsating operation of a pump such as the pump |03.

The invention is not limited to the particular details or order of steps or to the particular construction of apparatus described to illustrate the same, and various changes maybe made therein without departing from the principles or sacrificing the advantages of the invention, which is defined in the following claims.

What I claim is:

l. In a room and pillar system of mining ore bodies and the like, the method of increasing the recovery of ore and obviating subsidance of over' lying structures which consists in erecting, be tween the ore pillars left by the conventional room and pillar method, casting 4forms enclosing spaces extending from the hangingwall to the foot. wall of the mine opening, substantially filling said Y forms with mine wastes including settable material capable of penetrating into and bonding with the materials of the hanging and foot walls Lfor consolidating the contents of said forms to form consolidated columns integralized with and ex'- tending between said hanging and foot walls, removing the casting forms after such consolidation has occurred, and thereafter removing the ore pillars from between the so erected columns.

2. In a room and pillar system for mining of potash beds and the like yielding crystallizable mine waste, the method of increasing lthe recovery of ore and obviating subsidance of overlying structures, which consists in erecting, between the ore pillars left by the conventional room and pillar method, casting forms embracing vspaces extending from the hanging wall to the foot wall of the mine openingsubstantially nlling said forms with mine wastes including crystallizable material, introducing into said forms, to completely ll the same, crystallizable mine waste in finely broken and solution form, applying to the form-embraced body pulsations of pressure to eliminate voids therefrom and effect intimate contact of the solid and liquid portions of the material, maintaining liquid pressure on said material while allowing the material to consolidate by crystallization into a column integralized with the hanging and foot walls, removing the previously erected casting forms, and thereafter removing the ore pillars from between the so erected columns.

3. In a room and pillar system for mining of potash beds and the like using crystalliz'able mine waste, the method of increasing the recovery of ore and obviating subsidance of overlying structures, which consists in cutting ring-like seats in opposed walls of said galleries between the ore pillars left by the conventional room and pillar method, assembling casting forms in said seats to embrace casting spaces extending from the hanging wall to the foot wall of the mine open, ing, substantially filling said forms with mine Waste including crystallizable material, introducing into said forms to completely ll the same crystallizable mine Wastein finely broken and solution form, applying to the form-embraced body pulsations of pressure to eliminate voids therefrom and eiect intimate contact of the solid and liquid portions of the material, maintaining liquid pressure on said materialV while allowing the material to consolidate by crystallization into a column integralized with the hanging andfoot walls, removing the previously erected casting forms, and thereafter removing the'ore pillars from between the so erected columns. l

4.-. A method of the class described, which coin-l prises cutting ring-like seats in opposedwalls of a mine gallery, assembling sealing means in said seats with sectional forms juxtaposed thereto, jacking said forms into sealing relation to saidv sealing means, introducing into the space en-v closed by said forms a filling consisting predominantly of mine waste, consolidating said filling into a column integralized with the hanging and foot walls of the gallery, and removing the casting forms and sealing means from about the so formed column.

5. A method of the class described, which comprises simultaneously cutting a pair of ring-like seats'in opposed walls of amine gallery, assem-A bling sealing means in said seats with sectional forms juxtaposed thereto, jacking said forms into'A sealing relation to said sealing means, introducing into the space enclosed by said forms a iilling consisting predominantly of mine waste, consolidating said lling into a column integralized with the hanging and foot walls of the gallery, and removing the casting forms and sealing means from about the so formed column.

6. Apparatus for erecting columns in mine galleries comprising sealing means for forming packed seats on the walls of said galleries, sectional forms assemblable with said packed seats to enclose the space therebetween, means for retaining said forms in place, an access and lling door through at least one of said form sections, and a fluid inlet connection through at least one of said form sections. l

7. Apparatus according to claim 6, said form retaining means comprising tapered rods extending through said enclosed space.

8. Apparatus according to claim 6` further comprising a liquid pressure pulsator and supply and conduits for attaching the same to said inlet connection.

9. Apparatus according to claim 8 further comprising means for withdrawing pulsationfreed gases from said enclosed space.

10. Apparatus for erecting columns in mine galleries the hanging and foot walls of which are preformed with coaxial parallel ring seats therein, said apparatus comprising sealing rings receivable in said ring seats, sectional forms assemblable between said rings, and means for expanding said forms against said rings. Y

11. Apparatus according to claim 10, said sectional forms being assemblable in telescoping relation between said rings and said last'named means including a fluid pressure expansibleY means interposed between said telescoping sections. v

12. Apparatus according to claim 10, said sectional forms being assemblable in telescoping relation between said rings and said last named means including a wedging means interposed between said telescoping section.

13. Apparatus according to claim '10, said sectional forms comprising tapered members extending through the space embraced thereby.

14. Apparatus according to claim 10, said secv tional forms comprising means for venting fluids from the top of the space embraced thereby.

' 15. Apparatus according to claim l0, said sectional forms being substantially fluid tight whenr erected, and said apparatus comprising a source of consolidating liquid under pressure and coniduits for Vconnecting the same with the space embraced by said forms.

16. Apparatus for erecting columns betweenV the hanging and foot walls of mine galleries,

Asaid apparatus comprising a form having' the shape of an annulus and laterally separable to enable its removal from a finished column and means for securing the form against such separation during the casting of a column therein,

said form comprising a vertically expansible in-V covery of ore and obviating subsidance of overlying structures, which consists in cutting ringlike seats in opposed walls of said galleries between the ore pillars left by the conventional room and pillar method, assembling casting forms in said seats to embrace casting spaces extending from the hanging wall to the foot wall of the mine opening, substantially filling said forms with mine Waste including crystallizable material, introducing into said forms to completely ll the same crystallizable mine waste in nely broken and solution form, maintaining liquid pressure on said material while allowing the material to consolidate by crystallization into a column integralized with the hanging and foot walls, removing the casting forms from the integralized columns, and thereafter removing the ore pillars from between the so erected columns.

18. In a room and pillar system for mining of potash beds and the like using crystallizable mine waste, the method of increasing the recovery of ore and obviating subsidance of overlying structures, which consists in cutting ringlike seats in opposed walls of said galleries between the ore pillars left by the conventional room and pillar method, assembling casting forms in said seats to embrace casting spaces extending from the hanging wall to the foot wall of the mine opening, substantially filling said forms with mine waste including crystallizablev material, introducing into said forms to completely iill the same crystallizable mine waste in finely broken and solution form, applying to the form-embraced body pulsations of pressure to eliminate voids therefrom and effect intimate contact of the solid and liquid portions of the material, allowing the material to consolidate by crystallization into a column integralized with the hanging and foot walls, removing the casting forms from the integralized columns, and thereafter removing the ore pillars from between the so erected columns.

19. In a room and pillar system for mining of potash beds and the like using crystallizable mine waste, the method of increasing the recovery of ore and obviating subsidance of overlying structures, which consists in cutting seats in opposed walls of said galleries between the ore pillars left by the conventional room and pillar method, assembling casting forms in said seats to enclose casting spaces extending from the hanging wall to the foot wall of the mine opening, lling said forms with mine waste including crystallizable mine waste in iinely broken y and solution form and allowing the same to consolidate by crystallization into columns inte-A gralized with the hanging and foot walls, removing the casting forms from the integralized co1- umns, and thereafter removing the ore pillars from between the so erected columns.

WALTER B. LANG.

References cited m the fue of this patent UNITED sTATEs PATENTS Number Name Date 508,523 Mitchell Nov. 14, '1893 1,004,419 Griith Sept. 26, 1911 1,207,569 Langerfeld Dec. 5, 1916 1,330,743 Morgan Feb. 10, 1920 1,405,934 Olson Feb. '1, 1922 FOREIGN PATENTS Number Country Date Great Britain sept. 13, 1935L

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