US2786936A - Explosion-proof lighting unit - Google Patents

Description

March 26, 1957 A. 1. APPLETON 2,786,936

EXPLOSION-PROOF LIGHTING UNIT Fiied July 22, 1950 3 Sheets-Sheet l Inventor afthur I cynleton 6a,, wmmm March 26, 1957 A. l. APPLETON 2,786,936

EXPLOSION-PROOF LIGHTING UNIT Filed July 22, 1950 5 Sheets-Sheet 2 March 26, 1957 l. APPLETON EXPLOSION-PROOF LIGHTING UNIT 3 Sheets-Sheet 3 Filed July 22. 1950 lnu en tor arlhurl @242 ton United States atent O M EXPLOSION-PRUOF LIGHTING UNIT Arthur I. Appleton, Northbrook, Ill. Application July 22, 1950, Serial No. 175,430

9 Claims. (Cl. 240-112 The present invention relates to electrical lighting units in general and more specifically to a novel explosionproof lighting unit which finds particular but by no means exclusive utility in such places as refineries, chemical plants, and other installations where inflammable or explosive mixtures of gases, vapors, or dust are present in the atmosphere. This application is a continuationin-part of my earlier application Serial No. 124,051, filed in the United States Patent Olfice on October 28, 1949 and now abandoned.

In the construction of an explosion-proof lighting unit, consideration must be given even to remote possibilities of failure. For example, an electrical breakdown occurring within the unit or the power supply conduit leading thereto could result in the creation of an are capable of igniting explosive or inflammable gaseous mixtures which almost inevitably filter in from the surrounding atmosphere. Unless the lighting unit is properly designed, the resulting leakage of flame therefrom could easily ignite inflammable or explosive mixtures of gases, vapors, or dust particles in the atmosphere around the unit. Consequently, the potential arcing portions of the unit must be completely housed and segregated from such surrounding atmosphere.

One object of the present invention is to provide a novel and improved explosion-proof lighting unit which will be extremely light in weight but susceptible of use with a high margin of safety in very severe applications.

Another object is to provide a lighting unit of the foregoing type capable of avoiding the occurrence of excessive internal peak pressures by rapidly dissipating gas pressure from the interior of the unit into the surrounding atmosphere with no danger of igniting the same.

A further object is to provide an explosion-proof lighting unit of the character set forth and wherein the fixture portion may be attached to or detached from its supporting canopy by a simple mechanical operation performed entirely without danger of exposed arcing.

Another object is to provide an explosion-proof lighting unit of relatively simple, inexpensive construction which will function with a high degree of electrical safety and yet be susceptible of economical manufacture under mass productive methods.

Other objects and advantages of the invention will become apparent as the following description proceeds, taken in the light of the accompanying drawing, wherein:

Figure 1 is an enlarged fragmentary vertical sectional view through an illustrative explosion-proof lighting unit embodying the present invention.

Fig. 2 is a perspective view showing the fixture portion of the unit of Fig. 1.

Fig. 3 is an enlarged perspective view detailing the body portion of the unit shown in Fig. 1.

Fig. 4 is an enlarged fragmentary vertical sectional view illustrating the relation between certain components of the unit of Fig. 1 as the fixture is assembled upon the canopy.

Figs. 5 and 6 are enlarged transverse sectional views metallic material having flame arresting properties.

2,786,936 Patented Mar. 26, 1957 through the unit of Fig. 1 but taken in opposite directions in the plane of the line 5-5, 6-6.

Fig. 7 is an enlarged transverse setcional view through the unit shown in Fig. 1 but taken in the plane of hue 7-7.

Fig. 8 is an enlarged fragmentary vertical sectional view through a modified explosion-proof lighting unit also embodying the present invention.

Figs. 9 and 10 are transverse sectional views taken through the modified unit of Fig. 8 but in the planes of 99 and 10--10, respectively.

While the invention is susceptible of various modifications and alternative constructions, certain preferred embodiments have been shown in the drawings and will be described below in considerable detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

Referring more specifically to Fig. 1, it will be perceived that the invention is there shown embodied in an illustrative lighting unit 20 comprising a hollow supporting canopy 21 together with a fixture 22 mounted in depending relation thereon. The canopy 21 is fashioned with a neck 24 of reduced diameter and which is readily attachable to a suitable stem mounted upon a ceiling or other overhead support. The neck 24 merges with an outwardly flared portion terminating in an annular stop shoulder 25 and an externally threaded depending skirt 26. Power supply wiring (not shown) may be led through the neck 24 to terminal block 28 located within canopy terminal chamber 29.

The fixture 22 is organized upon a hub-like body 30 having an internally threaded upper end portion 31 which is susceptible of detachable engagement with the threaded skirt 26 of the supporting canopy. The opposite end of the body 30 terminates in a threaded annular flange 32 which is adapted to carry a globe ring 34. The latter is provided with a series of circumferentially spaced notches 35 to facilitate turnng. Clampingly secured to the flange 32 of the body by the globe ring 34 and a gasket 36 :is a transparent or translucent globe 38 of heat resistant glass which possesses a high degree of mechanical strength. The globe 38, together with the body 30, defines a lamp chamber 39 which -in the present instanceis adapted to house an incandescent lamp 40. Spaced from the globe 38 but nested about it is a cage-like guard 41 fixed to the globe ring 34. Also fixed to the latter and disposed in surrounding relation with the globe and the guard is a reflector 42.

Surrounding the body 30 and securely fixed thereto is a protective jacket 44 of relatively light sheet metal having a frustoconical shape. At its smaller end, the jacket 44 is formed with an inturned flange 45 overlying the upper end of the body and fixed thereto. as by means of one or more screws. 46. The upper surface of the flange 45 is smoothly machined to effect 'a tight seal with the stop shoulder 25 of the canopy. When the fixture 22-is mounted on the latter, the sealed relation between the flange 45 and the shoulder 25 is maintained as by means of one or more thumb screws 48 which lock the body 30 to the canopy skirt 26.

Provision is made in the construction of the body 30 for readily dissipating into the surrounding atmosphere internal pressue due, for example, to an explosion caused by a short circuit within the fixture 22, while at the same time precluding the passage of flame through the walls of the body. This is accomplished by forming at least a portion of the body wall structure of porous In the present instance, the body 30 is fashioned with an annular window panel 49 of porous metallic material such as sintered bronze particles (Figs. 1, 3, and 7). The window panel 49 is interposed between and imbedded :within'ashort lip 50 at the base of the sleeve like portion of the body and the threaded flange 32. Preferably, these members are reinforced as by means of a plurality of .circumferentially spaced ribs 51 overlying the window panel 49 (Fig. 3). With the foregoing arrangement, the entire body .31) maybe fashioned as an integral piece,

.the window panel 49 being first inserted into amold so that the body can be cast about it. To permit venting of gases which might have passed out of the body 30 .via the'porous panel 49, narrow annular gap 52 is provided between the protective jacket 44 and the globe ring 34.

For thepurpose of .efiecting automatic connection or disconnection of .the electrical elements of the fixture 22 and thecanopy 21 as an incident to the mechanical step of attaching the fixture .to or detaching the same from the canopy, the unit 20 is equipped with a detachable terminal assembly of the type more fully disclosed in my copending application Serial No. 175,419, filed July 22, 1950, now Patent No. 2,715,214. For the present, it might be noted that such assembly includes the terminal block 28 fixed within the canopy and a terminal block 54 mounted within the body 30 of the fixture. The block 28 has associated therewith contact elements in the 'form of resilient prongs 55, 56 while the block 54 has fixed thereto contact elements in the form of a center contact pin 58 and a surrounding contact ring 59 respectively adapted to make contact with the prongs 55, 56. The pin 58 and ring 59 are, in turn, connected via spring 60 and resilient plate 61 to the terminals of a shock absorbing lamp receptacle 62 located within the chamber 39. Such receptacle conserves the longevity of the lamp 40 not only when the fixture is attached to the canopy but also when the fixture 22 is detached and subjected to separate handling.

Means is provided for precluding exposed arcing as an incident to connection or detachment of the fixture 22 from the canopy 2-1. This is accomplished by a novel correlation of the detachable terminal assembly with the canopy and the body 30 of the fixture. In furtherance ofsuch objective, the terminal block 54 is nested well within the body 30 and substantially below the upper end thereof, being secured by the threads of the upper body portion 31 together with transverse abutment 64 and set screw 65. By the same token, the terminal block 28 is nested within the skirted portion 26 of'the canopy 21. By reason of the foregoing construction, initial abutment between or final separation of the contact elements 55, 56, on the one hand, and the contact elements 58, 59, on'the other hand, cannot begin to occur without substantial threaded engagement between the fixture body 30 and the canopy skirt 26 (see Fig. 4). To insure complete safety, at least five full threads are engaged between'the body. 30 and the canopy skirt 26 before initial 7 tact elements of the fixture and the canopy. Consequently, at the initiation of threaded engagement between these parts, a substantial air gap exists between their mating contact elements.

Turning now to'Figs. 8 to 10, inclusive, it will be noted that there is shown a modified. explosion-proof lighting unit 20A embodying certain aspects .of the present invention and comprising a canopy 21A generally similar to the canopy 21, together with a fixture 22A detachably secured thereto. The unit 26A houses a modified form of detachable terminal assembly-including terminal blocks 66, 67, mounted respectively on the canopy and the. fixture, together with a shock absorbing lamp receptacle 68. The fixture 22A is organized upona sleeve-like body 69 which in this instanceis entirely of porous metallic constructionandpossesses flame arresting properties. Thus in the event of an arc and an explosion within the fixture, the body 69 is adapted to permit dissipation of the resulting internal pressure into the surrounding atmosphere while precluding the'passage of any flame through its walls. The upper end portion of the body 69 is threaded as at 70 for engagement with the canopy skirt 71, such parts being lockable in threaded engagement by one or more retaining thumb screws 72. The lower end portion of the body 69 flares outwardly, being formed with peripheral threads 74 which. engage globe ring 75. Disposed in surrounding relation with the body 69 and portion of the globe ring 75 isa protective jacket 76 having one or more vent slots 78'therein for dissipating gases which may have filtered through the walls of the body 69 as a result of 'an'explosion within the fixture. Clampingly secured to the flared lower end portion of the body 69 by the globe ring 75 and a gasket 79 is a globe 80 similar to the globe 38. The globe ring 75 .also carries a guard 81 and a reflector 82.

While the terminal assembly of the modified unit 20A is of the slip ring and spring loaded plunger type, the arrangement of its terminal blocks 66, 67 is correlated with the dimensions of the canopy 21A and the upper portion of the body 69 so that exposed arcing incident to connection or detachment of the fixture 22A from the canopy 21A will be precluded. This is accomplished by reason of the fact that initial abutment or final separation between contact elements 84, 85 of terminal block 66 and elements 86, 88 of terminal block 67, cannot take place without substantial threaded engagement between the upper end of the body 69 and the canopy skirt 71.

I claim as my invention:

1. An explosion-proof lighting unit comprising, in combination, a supporting canopy having athreaded peripheral skirt, a flame arresting detachablebody having a threaded metallic portion engageable with said-skirt, said body also having anotherthreaded portion engageable with globe clamping means, means defining a closed explosion-proof lamp chamber within said detachable body, a first terminal block fixed to said canopy, a second terminal block fixed to said body, relatively movable contact members carried by said terminal blocks and adapted to abuttingly engage each other, the relative dimensions of said body and the location of said terminal blocks being such that an abutting relationship between said contact members can be neither established nor broken without substantial threaded engagement between said threaded metallic portion of said body and said canopy skirt.

2. An explosion-proof lighting unit comprising, in combination, a supporting canopy having a depending threaded skirt, a flame arresting detachable metallic body having a threaded portion engageable with said skirt, a globe attachable to said detachable body and defining therewith a closed explosion-proof lamp chamber, electrical contact elements fixed to said canopy, mating electrical contact elements fixed to said body outside said closed explosion-proof lamp chamber, the relative dimensions of said body together with said canopy and said contact elements being such that an abutting relationship between said mating contact elements can be neither established nor broken without engagement of at least five full threads between said threaded portion of said body and said canopy skirt.

3. .In an explosion-proof lighting unit, the combination comprising a supporting canopy having a threaded portion, a flame arresting detachable body including at least a portion of porous metallic material-and having means susceptible of threaded engagement with said canopy, means defining. a closed explosion-proof lamp chamber within said detachable body, a .first terminal block fixed to said canopy, a second terminal block fixed to. said body, contact elements mounted on one of said terminal blocks, coacting contact elements mounted on theother of said terminal blocks, said contact" elements being susceptible of entering into abutting engagement with each other as an incident to attachment of said body to said canopy, said terminal blocks being located on said canopy and said body in posf ions wherein a substantial air gap exists between respective ones of said coacting contact elements at the initiation of threaded engagement between said body and said canopy.

4. An explosion-proof lighting unit comprising, in combination, a supporting canopy having a depending threaded skirt, a hub-like body having a threaded portion engageable with said skirt, said body also having a flame arresting rigid window panel of porous metallic material integral therewith, a globe fixed to said body and defining a sealed lamp chamber therewith, electrical contact elements carried by said canopy, mating electrical contact elements fixed to said hub-like body, the relative dimensions of said body as well as said canopy and said contact elements being such that an abutting relationship between said mating contact elements can be neither established nor broken Without substantial threaded engagement between said body and said canopy skirt.

5. In an explosion-proof lighting unit, the combination comprising a supporting canopy having a depending threaded skirt, a metallic hub-like body having a flame arresting rigid window panel of porous metallic material integral therewith and having means susceptible of threaded engagement with said canopy, contact elements carried by said canopy, coacting contact elements carried by said body, said contact elements being susceptible of entering into abutting engagement with each other as an incident to attachment of said body to said canopy, said body and said canopy being so correlated with said contact elements that a substantial air gap exists between respective ones of said coacting contact elements at the initiation of threaded engagement between said body and said canopy.

6. An explosion-proof lighting unit comprising, in combination, a supporting canopy having a threaded skirt, a sleeve-like body of flame arresting porous metallic material having a threaded portion engageable with said skirt, a globe attachable to said body, electrical contact elements fixed to said canopy, mating electrical contact elements fixed to said sleeve-like body, the relative dimensions of said body as well as said canopy and said contact elements being such that an abutting relationship between said mating contact elements can be neither established nor broken without substantial threaded engagement between said body and said canopy skirt.

7. In an explosion-proof lighting unit, the combination comprising a supporting canopy having a threaded portion, a sleeve-like body of flame arresting porous metallic material and having means wsceptible of threaded engagement with said canopy, first terminal block fixed to said canopy, a second terminal block fixed to said body, contact elements mounted on one of said terminal blocks, mating contact elements mounted on the other of said terminalblocks, said contact elements being susceptible of entering into abutting engagement with each other as an incident to attachment of said body to said canopy, said terminal blocks being located on said canopy and said body in positions wherein a substantial air gap exists between respective ones of said mating contact elements at the initiation of threaded engagement between said body and said canopy.

8. For use in an explosion-proof lighting unit, a body comprising, in combination, a sleeve-like portion terminating in a narrow lip, a surrouding flange, an annular Window of porous metallic material interposed between and imbedded within said lip and said flange, and a plurality of circumferentially spaced ribs connecting said flange and said sleeve-like portion, said ribs being integral with said flange and said sleeve-like portion.

9. An explosion-proof lighting unit comprising, in combination, a supporting canopy, a hollow body attachable to and detachable from said canopy, means adjacent the upper end of said hollow body and extending transversely thereof for preventing the passage of gas through said hollow body, a globe attached to the lower end of said hollow body in gas tight relation thereto and defining therewith and with said means a closed lamp chamber Within said hollow body, and a porous metallic window integral with said hollow body and constituting a flame arresting portion therein, said hollow body, said means, and said globe being attachable to and detachable from said canopy as a unit without violating the closed condition of said lamp chamber.

References Cited in the tile of this patent UNITED STATES PATENTS 489,150 Keil Jan. 3, 1893 1,787,032 Benjamin Dec. 30, 1930 2,304,085 Griflin Dec. 8, 1942 2,530,135 Thornblom Nov. 14, 1950 FOREIGN PATENTS 640,250 France Mar. 24, 1928 444,877 Great Britain Mar. 31, 1936

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