US3515217A - Method and apparatus for arresting an explosion in a mine - Google Patents

Description

w. B, JAMISON June 2, 1970\ METHOD AND APPARATUS FOR ARRESTING AN EXPLOSION TN A MINE Filed Oct. 25, 123g? 2 Sheets-Sheet l INVENTOR.

WILL B. JAMISON H/S ATTORNEYS June 2, 1970 w, JAMISON 3,515,217

METHOD AND APPARATUS FOR. ARRESTING AN EXPLOSION IN A MINE Filed Oct. 23, 1967 2 SheetsSheet 2 INVENTOR.

WILL B. JAM ISON BY I H/S AT TORNEVS United States Patent Office 3,515,217 Patented June 2, 1970 Int. 01. A62c 3/00 US. Cl. 169-2 8 Claims ABSTRACT OF THE DISCLOSURE Apparatus for arresting an explosion at the mine face and preventing the explosion from propogating throughout the mine. A plurality of rigid containers are positioned within a mine passageway with the container outlets directed generally toward the mine face. Each of the containers is provided with a quantity of pulverulent flame extinguishing material and has a frangible disc closing the container outlet. An explosive charge is positioned within each container in an envelope which also contains a suitable detonating mechanism. Flame sensing means are provided and are electrically connected to the detonating mechanisms in each of the containers. The rigid containers and flame sensing means may be mounted on the mining machine. When the sensing device is activated by a flame at the mine face, the detonating mechanism explodes the charge in each of the containers. The pressure created by the explosion within the container, ruptures the frangible disc and propels the flame extinguishing material from the container through the opening established by rupture of the disc. The flame extinguishing material is diffused toward the mine face and quickly extinguishes the flame at its incipiency to prevent the propagation of the flame and accompanying explosion through the mine.

The method of this invention contemplates providing a rigid extinguisher discharge container having an explosion detonator and charge, a quantity of extinguishing material and a frangible closure. The method comprises sensing for the presence of a flame within the mine passageway, automatically detonating the explosive charge responsive to the sensing of the presence of flame to rupture the frangible closure and discharge the extinguisher material through the opening established by the closure rupture.

CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of a copending application in part, entitled Explosion Arrestor, Ser. No. 554,212. filed May 27, 1966, now abandoned which in turn is a continuation application of Ser. No. 427,227 filed Jan. 22, 1965, now abandoned and bearing the same title.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a method and apparatus for arresting an explosion in a mine and more particularly to a method and apparatus for rapidly diffusing a flame extinguishing material to cover a flame shortly after ignition at the mine face and extinguish the flame before it propagates further.

Description of the prior art In coal mines, explosions have been classified as to type of fuel. Generally, the fuel for such explosions consists of either a gas, such as methane, or coal dust. While in the advanced stages of an explosion, both sources of fuel may contribute to burning, in the incipient stages of burning, these two fuel sources present very different problems.

With respect to the flames initiated from coal dust, the fuel is created by providing sufficient energy to the dust particles to gasify the volatile constituents in the coal particle. The gas given off the coal particle in this distillation process is highly combustible. The ignition of this gas creates the burning flame which begins to burn at an accelerated rate as it moves along the mine passageway. The accelerated burning establishes increased heating with resultant expansion of the combustion gas and the explosion is created through this accelerated propagation of flame.

It has been found that some protection against coal dust initiated explosions may be obtained through the use of rock dust, such as limestone dust. In using rock dust, it is periodically distributed over the structural surfaces of the mine passageway, thereby covering the coal dust particles. Should ignition of the coal dust particles occur at the face of the mine or at another area of exposed coal dust, the coal dust covered by the rock dust will tend to resist volatilization. The rock dust particles, mixed with the coal dust provide a shielding action to insulate the coal dust particles from the radiant energy of the burning flame. The coal dust, when admixed or coated with a sufficient amount of rock dust, does not receive suflicient energy because of the shielding effect, to volatilize and the production of additional combustible gas is effectively prevented. a

It will be appreciated, however, that there are some obvious limitations to this means of preventing explosion inducing burning of the volatile matter in coal particles. Coal dust particles are being continuously created by the action of the mining equipment at the working face. In time, therefore, areas previously adequately coated with rock dust will again have upon their surfaces, a layer of coal dust particles subsequently created.

In addition, other areas such as the mine face and the surfaces of coal on the endless belt type conveyor means, as Well as the mining equipment itself, cannot be conveniently or effectively covered with rock dust. In spite of the limitations present in the use of rock dust, it does serve as a reasonably effective means of minimizing the possibility of the occurrence of a mine explosion produced by the burning of the volatile constituents of coal dust.

A far more serious problem is presented with respect to explosions induced by the accelerated burning of methane gas. It is known that an air-methane mixture may be highly flammable and form the basis of an explosion. Unlike the coal dust fuel source, which requires a relatively high energy source for establishment of volatilization, such as a substantial electrical spark, the methane-air mixture may be ignited by a low energy source. An abrasion spark, such as that created by cutter bits striking a pyritic particle Within the coal at the mine face may create a spark of sufficient energy to provide ignition of the methane-air mixture.

With mechanical mining equipment, it is of course, not feasible to employ rock dust at the mine face because the machine is continuously advancing and the surface of the face and passageway or entry is being continuously advanced. The machine is of substantially the same size as the entry so that it is not feasible to continuously disperse rock dust in front of the mining machine. Even if it were possible to disperse rock dust in front of the mining machine, this would not eliminate the hazard of a methane gas explosion. Unlike the situation with respect to coal dust particles wherein coverage with rock dust provides a shielding action preventing absorp tion of radiant heat, the methane being gaseous in nature, cannot be encapsulated or effectively shielded from a heat or energy source. Also, as the methane was created during the formation of the coal and is, therefore, contained within void spaces within the coal, there is no way of accurately predicting the quantity or intensity of methane which will be released from the mine face at any given time during the mining operation.

The methane content of the air cannot be effectively controlled by attempting to provide ventilating air at the face of the mine. The mining machine, to effectively dislodge the coal, must be of substantial size which prevents full exposure to the mine face tothe ventilating air. Also, as the methane content varies substantially, there would be no effective means of controlling the amount of ventilating air required, even if the desired distribution of the air could be obtained.

It will, therefore, be appreciated that in view of the flammability hazard created by a methane-air mixture of given concentration coupled with the lack of predictability of the rate of emergence of methane from the mine face, an uncontrollable explosion risk is present in such mining. As has been stated above, all that is required is that a flammable mixture of methane and air be exposed to a source of energy which may be relatively low, and burning of the mixture will be initiated. After the initiation of burning, the heat produced by the burning causes an expansion of the gas and the burning accelerates rapidly. The speed with which the burning and resultant thermal expansion of gases increases determines whether or not detonation will result. Regardless of whether detonation in fact occurs, the accelerated, uncontrolled burning is considered to be an explosion and may result in the loss of lives of miners, as well as substantial property damage.

Experience in the study of mine explosions has indicated that the initial increase of velocity of burning of a methaneair mixture occurs at a rather slow pace and there is a finite period of time between the initiation of burning and the existence of what might be called an explosion. There have been instances where an investigation of a mine explosion of this type has shown that the mining machine operator, between the time he saw the flame initiate and the time of explosion, had sufficient time to begin to escape and may have progressed 30 to 50 feet down the entry from the mining machine before the explosion occurred.

It will be apparent, therefore, that that there is no effective means of eliminating the initiation of burning of a flammable methane-air mixture adjacent the face of the mine. Any attempts at arresting explosion must therefore be directed toward prompt and effective action taken between the time flaming or burning is initiated and the time the explosion occurs. If the flame cannot be suppressed or extinguished during this time interval, an explosion and fire, causing substantial property damage and possible loss of lives may occur.

Also, it should be noted that after the methane-air flame has increased in velocity and accelerated in terms of the amount of heat given off, additional fuel may be such particles of coal dust as are not effectively shielded by rock dust.

SUMMARY OF THE INVENTION This invention effectively solves the above mentioned problems in the suppression of explosion inducing flames of a methane-air mixture generally occurring at or near the mine face. Rigid containers having explosive means and containing pulverulent flame extinguishing material are provided and are operably connected to a flame sensing device in order to explosively discharge the flame extinguishing material responsive to the sensing of a flame. These containers may, if desired, be mounted upon a mechanical material dislodging device, such as a mining machine. The responsive explosive dispersement of the flame extinguishing material occurs sufficiently rapidly that the flame is effectively extinguished before acceleration can occur. The container is provided with a frangible disc which effectively seals the discharge end of the container. The explosion is sufficient to rupture the frangible disc and thereby permit substantially instantaneous discharge of the flame extinguishing material. The discharge end may conveniently be provided with an apertured end cap through which the material may be dispersed or may have a solid end cap adapted to be exlosively removed.

The method of this invention contemplates the sensing for the presence of flame and the automatic responsive detonation of the explosive charge to disperse the flame extinguishing material from the container.

It is an object of this invention to provide a method and apparatus for effectively and promptly extinguishing a flame within a mine passageway in order to arrest the acceleration thereof and prevent an explosion.

It is another object of this invention to provide a continuous mining machine having a flame sensing device operatively connected to explosive means within a container of pulverulent flame extinguishing material in order to rapidly disperse said material through an explosion detonated responsive to the detection of a flame.

It is another object of this invention to provide a system for the automatic extinguishing of flames of a burning methane air-mixture by fully automatic means which promptly and effectively disperse a flame extinguishing material over the fire.

It is another object of this invention to provide such a system wherein a multiplicity of rigid containers having a supply of pulverulent flame extinguishing material are adapted to be simultaneously discharged responsive to detection of flame with the discharge being such as to fully cover the fiamed area with the fire extinguishing material.

Other objects and advantages of the invention will be understood from the following description of the invention, on reference to the illustrations appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a top plan view of a borer type of mining machine, schematically illustrated, in a mine passageway and having a type of sensing device and extinguishing container contemplated by this invention.

FIG. 2 is a view similar to FIG. 1 illustrating the mining machine in side elevation with the extinguishing containers discharging the fire extinguishing material therefrom.

FIG. 3 is a schematic elevational view of the mine passageway illustrating the manner in which the mine face may be covered by the pulverulent flame extinguishing material.

FIG. 4 is a view in side elevation in section of a type of extinguishing container contemplated by this invention.

FIG. 5 is a fragmentary view in section of a modified outlet design for the extinguishing container.

FIG. 6 is a detailed view in side elevation of a detonator and explosive charge positioned within the extinguishing container illustrated in FIG. 4.

FIG. 7 is a schematic illustration of a mine passageway having a number of extinguishing containers mounted therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more specifically to the drawings and more particularly to FIGS. 1 and 2, the mine passageway 10 has a roof 12, a floor 14, and ribs or side Walls 16, 18. The mining machine which has been generally designated by the numeral 20 creates the passageway 10 in a seam of coal by dislodging the coal from the front face 22 with rotating boring arms 24, 26. During the mining operation, the arms 24, 26 dislodge coal from the vertical mine face and the dislodged coal is conveyed rearwardly on the mining machine by means of conveyor 28 which moves in the direction indicated by the arrow in FIG. 1. The vertical mine face 22 therefore advances continuously inwardly into the mine passageway. The dislodged coal is discharged from the conveyor end portion 30 onto a suitable receiving device, such as a shuttle car or the like.

The boring arms 24, 26 have suitable cutter bits 32 that dislodge the coal from the mine face 22. These cutter bits 32 are illustrated schematically in FIGS. 1 and 2. The boring arms 24, 26 each have a shaft 34, 36 which extends into a transmission case 38. Suitable gearing is provided within transmission case 38 in order to transmit the rotation of electrical motors 40* to the rotor shafts 34, 36. In

the mining machine 20 selected for illustration, there is in addition, an intermediate boring arm 42 which is arranged to dislodge the inwardly extending kerf of coal 43 as the end boring arms 24, 26 dislodge the coal from the mine face 22. Finally, drum cutters 44, 46 are also connected to transmission case 38 by shafting 50, 52 so that the drum cutters 44, 46 remove the generally triangular shaped cusps extending both downwardly from the roof 12 and upwardly from the floor 14 between the end of rotary boring arms 24 and 26. With this arrangement, a generally eliptical passageway or entry 10 (FIG. 3) is formed within the seam of coal.

The mining machine 20 has an operators compartment adjacent the rear portion of the mining machine behind the transmission case 38 and the electric motors 40. Within the operators compartment the operator has suitable controls 'by which to advance the mining machine into the mine face 22 and dislodge the coal by means of boring arms 24, 26 and 40'.

Secured to the transmission case 38 are a plurality of extinguishing containers, generally indicated by the letter B. As is shown in FIGS. 1 and 2, some of these are mounted on the top of the transmission case 38, while others are mounted on the side of transmission case 38. Some of the extinguishing containers B are generally axially aligned with the longitudinal central axis of the mining machine 20, while others are axially oriented at an angle with respect thereto. A flame sensing device, generally indicated by S, is also secured to the transmission case 38.

Before considering the structure and functioning of these elements in detail, a brief description of their operation might be of value. When flame detector S receives an indication of the presence of a flame, it emits a signal to the extinguishing containers B. The extinguishing container has a supply of pulverulent fire extinguishing material and also has a detonator and explosive charge. The signal from the flame sensing device is communicated to the detonator which is discharged thereby. The detonation sets off the explosive charge that establishes an explosive pressure and causes the rupture of a frangible closure member and discharge of the pulverulent flame extinguishing material from the container.

As is shown in FIGS. 1 through 3, the numbering and positioning of the extinguishing containers B are selected so as to substantially completely cover the cross sectional area of the passageway 10 upon discharge thereof. It is seen that extinguishing containers B B B and B are disposed substantially parallel to the longitudinal central axis of mining machine 20. Containers B and B are disposed angularly outwardly away from the mining machine axis. In FIG. 2, it is seen that containers B and B are disposed generally angularly downwardly, while container B is disposed substantially horizontally. As is shown in FIG. 3, the discharge pattern of the pulverulent material substantially completely covers the generally elliptical passageway 10, thereby insuring an effective and complete flame barrier.

Considering now the containers B in greater detail, attention is directed towards the FIGS. 4 through 6. In FIG. 4, it is seen that the container B has a rigid metallic tubular body 60 which is provided with a detonating end 62 and a discharge end 64. The container has a supply of a pulverulent flame extinguishing material 66. At the discharge end of the container is a frangible disc or closure 68 which effectively seals the container interior from the exterior. An end cap 70 having discharge apertures 72 is secured to the container body 60 by means of annular collar 74. At the detonating end of the container body 60, which in the form illustrated is tapered, is a detonator, which has been shown to be a squib 76. The squib 76 is housed within envelope 78 which also contains an explosive charge 80. Envelope 78 is secured to housing member 82 which is threadedly attached to the detonating end 62 of container body 60. Lead wires 84, 86 connect squib 76 with flame sensing means S. At the bottom of the container B is a mounting bar 88 having mounting holes 90 through which a suitable fastener may be passed.

Considering the explosive means in greater detail, at-

tention is directed toward FIG. 6. It is seen that envelope.

78 contains an explosive charge 80 and squib 76. Envelope 78 is secured to housing member 82 which is in turn threadedly secured to body member 60. The squib 76 is secured to resilient member 92 which in turn is secured within a recess of housing member 82. Lead wires 84, 86 which connect the flame sensing means with squib 76 pass through communicating bores in resilient member 92 and housing member 82.

The frangible disc of closure 68 should preferably be adapted to provide a seal against passage of foreign particles and moisture into the container, as well as passage of the extinguishing material out of the container. The disc 68 should preferably be adapted to rupture under the explosive discharge either into a number of fine particles or with no flying particles to minimize the risk of injury to anyone near by.

In operation, the flame sensing means S which is powered by suitable means such as a battery, upon detecting the presence of flame sends a signal by means of lead Wires 84, 86 to squib 76. Squib 76 responsive to such signal detonates explosive charge 80 within envelope 78. The shock Wave of this explosion causes the frangible disc 68 to rupture, thereby permitting passage of the flame extinguishing material out of the container B. In the form illustrated in FIG. 4, the end cap 70 remains secured to container body 60 and the material passes outwardly through the apertures 72 in end cap 70. The apertures are preferably so placed as to provide the desired high dispersion of the flame extinguishing material 66 so as to insure effective extinguishing of the flame.

In the form of container B shown in FIG. 5, a frangible disc is present as in the form shown in FIG. 4. The discharge end 102, which is tapered, contains substantially solid end cap 104. With this type of container B, the explosion must fracture the frangible disc and remove the protective cap thereby establishing a single opening through which the pulverulent flame extinguishing material may pass.

While the container B is being stored, the frangible disc 68, 100 serves a very important function. It provides an effective barrier against the entry of moisture and foreign material such as coal dust, into the flame extinguishing material 66. The entry of such materials into the container B could serve to contaminate and reduce the effectiveness of the flame extinguishing material 66. Also, the frangible disc prevents undesired escape of such materials 66 out of the discharge end 64 of container B prior to a desired use in extinguishing a flame.

As has been stated above, while there is no effective means of completely eliminating the initiation of flame caused by a flammable air-methane mixture, there is a subsequent finite time period within which quick action will extinguish the flame and prevent acceleration thereof tending to lead to an explosion. The apparatus of this invention is designed to act effectively and quickly within this time interval to arrest the expansion or propagation of such flame. Thus, the instant a flame is detected by sensing device S, a signal is transmitted to container B which causes detonation of squib 76 which in turn sets off explosive charge 80. The shock Wave from this charge 80, ruptures frangible disc 68, 100 and simultaneously discharges the pulverulent fire flame extinguishing material to effectively put out the flame before acceleration could take place.

The containers B are preferably provided in such number and are positioned in such fashion that a single signal from the flame sensing device will establish simultaneous explosive discharge of the flame extinguishing material from a multiplicity of containers B and thereby effect complete extinguishing of the flame.

The pulverulent flame extinguishing material 66 may be any suitable particulate fire flame extinguishing material. It preferably is one which may be stored in a container of this sort for an indefinite period of time without any substantial loss of pulverulent structure. Among the suitable materials for such use are the alkali metal bicarbonates. Preferred materials for use in the container of this invention include sodium or potassium bicarbonate. Also, if desired, the material selected may be protected against water absorption during storage independently of the container seal, as by providing a coating of a water resistant material such as silicone, for example.

It is desired not only to limit flame growth in its incipiency at the mine face when the passageway is being worked, but it is also essential to effectively isolate any flaming passageway from any connected passageways within the mine. For this reason, as is shown in FIG. 7, it may be desirable to mount one or more containers B within mine passageways. By so doing, not only will any flames originating within any mine passageway be restricted to that passageway, but also such flames may be extinguished prior to an increase in velocity to the point where an explosive detonation may occur. The containers may be mounted on the roof, walls or any convenient place.

The method of this invention, therefore, contemplates providing a rigid solid particulate extinguisher discharging container having an explosion detonator and charge, solid particulate extinguishing material and a frangible closure member 68. The method contemplates sensing for the presence of flame within a mine passageway, automatically detonating the explosive charge by means of the detonator within said container responsive to the sensing of the presence of flame in order to rupture the frangible closure and discharge the solid particulate extinguishing material through the opening established by the rupture of closure 68.

In the preferred form, the sensing is effected by sensing means mounted on the mining machine and the container is also mounted on the mining machine. It is also preferred that the sensing be effected continuously and automatically, and that the sensor automatically provide a detection signal to the container. For more environments, it will be desirable to simultaneously detonate a multiplicity of containers in order to establish substantially simultaneous dispersement of the solid particulate extinguishing material uniformly and completely from all containers onto the flamed region.

It will be appreciated, therefore, that the method of this invention takes advantage of the relatively slow rate of acceleration or burning of an air-methane mixture. It promptly extinguishes the flame in sufficient time to arrest the explosion or propagation of the flame and avoid the substantial risk of injury or loss of life to the mining machine operator, as well as substantial property damage. This method, therefore, provides an inexpensive means of substantially completely eliminating the risk of harm from this relatively uncontrollable source of explosion creating fire.

8 It will further be appreciated, that this invention provides an economical system for extinguishing flame which is adapted for re-use. Once the container, or cannon as it is sometimes referred to, has been fired, all that is required to place it in condition for further use, is that it be refilled with the solid particulate flame extinguishing material, the charge and squib be replaced and a frangible disc be inserted.

It will be further noted that the actuation of the extinguishing devices is accomplished Without the need for any positive action of the part of the mining machine operator or other personnel. This is, of course, desirable, in View of the need to act Within a relatively short time after ignition of the flame.

It should be understood that any suitable flame sensing devise that is operable to sense the presence of a flame, transmit a signal to the detonator to actuate the detonator may be used with the previously described invention.

I claim: 1. A method of arresting explosions in a mine adjacent the mine face by directionally propelling extinguishing material into and extinguishing a flame comprising mounting a rigid extinguisher having a discharge opening on :a mobile machine positioned adjacent the mine face, said mobile machine arranged to advance with the mine face during the mining operation,

directing said discharge opening of said extinguisher toward said mine face, mounting a flame sensing device on said mobile machine, said sensing device being operable to sense the presence of a flame in the vicinity of the mine face,

connecting said flame sensing device to said extinguisher so that said flame sensing device, upon sensing a flame, actuates said extinguisher, and

said extinguisher upon actuation dispersing an extinguishing material through said discharge opening in a preselected direction toward said mine face and into said flame, and

extinguishing said flame.

2. A method of arresting explosions in a mine adjacent the mine face by directionally propelling extinguishing material into and extinguishing a flame as set forth in claim 1 in which said extinguisher comprises a rigid nonfrangible container having a discharge opening, said container having a quantity of solid particulate extinguishing material therein and pressure generating means to propel said particulate material through said discharge opening,

said flame sensing device, upon sensing a flame, actuating said pressure generating means and propelling said particulate material through said discharge opening and dispersing said particulate extinguishing material into said flame and extinguishing said flame.

3. A method of arresting explosions in a mine adjacent the mine face by directionally propelling extinguishing material into and extinguishing a flame as set forth in claim 1 which includes a plurality of extinguishers mounted on said machine,

said extinguishers each includes a rigid nonfrangible container having a discharge opening, a detonator, an explosive charge, a quantity of solid particulate extinguishing material and a frangible closure for said discharge opening,

said flame sensing device, upon sensing a flame, detonating said explosive detonator in said extinguisher, said detonator detonating said explosive charge and rupturing said frangible closure and propelling said particulate extinguishing material through said discharge openings and dispersing said particulate extinguishing material into said flame and extinguishing said flame.

4. A method of arresting explosions in a mine adjacent the mine face by directionally propelling extinguishing material into and extinguishing a flame as set forth in claim 1 which includes:

mounting said plurality of extinguishers and said flame sensing device on a continuous mining machine adjacent the material dislodging elements, and

continuously operating said flame sensing device during the operation of said mining machine.

5. A method of arresting explosions in a mine adjacent the mine face by directionally propelling extinguishing material into and extinguishing a flame as set forth in claim 3 which includes substantially simultaneously detonating said detonators in said plurality of extinguishers when said sensing device senses a flame.

6. In apparatus for arresting mine explosions,

flame sensing means adapted to detect the presence of flame within a mine passageway, rigid container means having a rigid nonfrangible elongated generally tubular metallic container housing a flame extinguishing material said container means positioned adjacent to said flame sensing means,

explosive means within said container means to substantially instantaneously discharge said flame extinguishing material from said container means being responsive to detection of a flame by said flame sensing means,

said metallic container having a discharge end provided with a frangible closure and an end cap, said container having a detonating end provided with said explosive means,

said explosive means having a squib connected by electrically conductive means with said flame sensing means, and

said squib disposed Within an elongated tubular envelope containing an explosive material and adapted to detonate said explosive material responsive to detection of a flame by said flame sensing means.

7. In apparatus for arresting mine explosions as set forth in claim 6 wherein,

a multiplicity of said containers are secured to a mining machine in such position that said discharge ends of said containers are directed generally toward said mine face when said machine is in use,

said flame sensing means so positioned on said mining machine to detect a flame originating in the immediate vicinity of the mine face, and

each said squib operatively adapted to detonate said explosive material responsive to a signal indicating detection of a flame in the vicinity of said mine face by said flame sensing means and thereby substantially simultaneously produce explosive discharge of said flame extinguishing material toward said mine face from all said containers.

8. In apparatus for arresting mine explosions as set forth in claim 7 wherein said flame extinguishing material is a solid pulverulent material.

References Cited UNITED STATES PATENTS 2,693,240 11/ 1954 Glendinning et al 1692 1,000,236 8/ 1911 Cochrane 1692 2,799,781 7/1957 Joyce et al. 169-2 X 2,808,114 10/1957 Parker et al 16928 X 2,869,647 1/ 1959 Mathisen 1694 2,873,806 2/ 1959 Bittner 169-36 3,235,860 2/1966 Vassil 169-28 X 3,333,896 8/1967 Diamanti 169-2 X LLOYD L. KING, Primary Examiner US. Cl. X.R. 169-28

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