US2482421A - Flat tube electrical device - Google Patents

Description

Sept. 20, 1949.

E. LEMMERS FLAT TUBE ELECTRICAL DEVICE Filed Oct. 21, 1943- Eugene Lemmers,

M His Ai? orneg.

Patented Sept. 2Q, 1949 FLAT TUBE ELECTRICAL DEV CE Eugene :Lemmers, Cleveland Heights, Ohio, as-

signor to General Electric Company, a corpora-'-- I tion of New York 'Application fl ctober 21, l9 i3,'S'erial Korma This invention-relatesto electrical devices having tubular envelopes; such as incandescent lamps and 'heating devices and electric discharge lamps and devicesof various kinds, all of which generally have envelopes of vitreous material such as glass or silica.

In thecase of "fluorescent lamps of the usual low-pressure positive column discharge type in which phosphors'fare excited by the 2537 A. resonance radiation of mercury, .as well as in other resonance radiation lamps (such as germicidal mercury lamps and sodium lamps), it is possible. to obtain' either: greatly improved efficicncy' of operation or much greater current capacity and discharge wattage when the lamp tube. is oval or flatjf rather than substantially circular asin presentpractice. Also, the light distribution from a "ilatitube lamp is more favorable for somepurposes, than that from a round tube. But notw ithstanding these and otheradvantages .of flat tubes .oyer round tubes, flat tubes as heretofore, made have presented a Very'serious drawback which has prevented their use to any great extent: namely weakness against collapse or implosionby external atmospheric pressurewhenthey, areevacuated, even if they contain an atmosphere at greatly reduced pressure, as is usual in ordinary fluorescent lamps and in some other vresonance radiationlamps, as

well as in tubular incandescent lamps. Because 0 of this, the only flat tubelamp heretofore on the market has been a small, low-wattage fluorescent lamp known commerc'iallyas. the T2 /2 x 6, having a flattened or oval tube about inch wide by% inch thick, internally, and only 6 to 9 inches long. .1 r

. I have founda way. ofovercoming this weakness of flat-tube lamps against external pressure, by putting the longitudinal edges. or corners of the flat tube 2111.8, state of permanent precorn pression or bending strain, as I .term it. 'For maximum orlassuredsafe resistance-of the lamp against collapse or implosion, the strain in the tube edges may be made so great that even after the lamp-is evacuated and the pressure therein is brought to its minimum value during service of the device, a degree of such strain in the edges still remains, lover, and-abovethat taken up in compensating the external atmospheric pressure on the tube;,however,j'anu'improvement in the resistance to collapse'may bejproduced even'by lower degrees offprestr'ain .or' stress in the tube edges,v The proper prestra'ining of the tube edges maybe brought aboutuat any convenient 9 Claims. (01. 49-: 9) 1:

as an incident of drawing continuous flat tubing from molten glass; or,'at the-opposite extreme, aftera length of tubing has been fabricated into a "fluorescent lamp, bjut before-exhausting the lamp.

Without attempting'to define the possibly beneficial range oftube flatness, itmaybe said that for the ordinary commercial range of fluorescent lamp tube sizes from ljin'ch to 2 inches, in internal diameter, flattening to a 4:1 ratio-of internal width to internal-thickness is very decidedly advantageous, while flattening merely to a 2:1 ratio is'about th mallest degree of flattening that is o f"any"real advantage. A strictly flat tube with semicylindricaledg'es or corners is more advantageous than a pronouncedly oval one; but some "slight internal transverse concavity of the wide fflatf' -walls offers no material drawback. On the} other hand, appreciable transverse internalfconvegity'of'the wide walls is decidedly to? vc ideg i.; fbecause even whel slight, it results'm'a tendencyof the discharge to o upy n y f. the ,QflYifiY. Q hthe t to jump back and forth ldtwee'nffthe regions at opposite sidesio'fthe lin f "'ini'n'imum internal thickness'of 'thecavity,. stea'd'iof constantly filling the whole crossse ctionoffthe tube,'as is necessary if the advantage'of'a flat tube is to be realized. Slight. internal transverse concavity of the wide walls offersafmargin of safety in manufacture against accidental internal convexity of these walls in particular instances.

The methodof putting the "edges or corners of aflat tube under stress whichI at present prefer is by heat treatment: For thispurpose, the tube is heated above the strain" poin ternperature of the vitreous material, andfthe longitudinal edges of the flattened tube: are, cooledor chilled below the strain point. before its wide and substantially or approximately.flatlongitudirial walls cool below this temperature. Theihe'atingof the tube above itsstrain poir tas here referred to maybe merely incidental toidrawing outand'forming the glass into a flat tube, or may be a subsequentheating for therpurpose ofjflatten'in'g an initially roundformed tube, or may be. 'aspecial heating for the main purpose ofimpo'singstrain or stressiat the corners or edges; The'prechilling oi the tube edges in advanceof tlqlejcoolirig of its wide walls may be efiected in a varietyiqi ways as by blowing cooling fluid (e "g' airj on the edges, wholly or partially to: the exclusion 'of the wide walls; or by heating the widefwall's' to keep them above the strain point'while'the edges'are freely eX- stage of tube or lamp manufacture: for example, 55 posed to be'coole d "below this point by the circumambient atmosphere or cooling fluid, and then stopping or reducing the heat to allow the wide Walls to cool; or even by merely covering or lagging the wide walls to retain their heat, so that the atmosphere can cool the more exposed edges below the strain point before the wide walls cool down to or below this temperature. The strain poin here referred to is the temperature below which vitreous material cannot be permanently strained-a particular temperature which is a particular property of every kind of glass or other vitreous material, and generally. differs .for different materials-all as well understood in the glass art.

It is, of course, importantthat when a-ilat tube has had its edges put in strain as described, it should never afterward be heated above the strain point of the material in any subsequent step or operation of lamp manufacture; because this would relieve the strain and destroy the effectual resistance of the tube to external pressure. The usual annealing of the tubeas an incident of lamp manufacture must be altogetheromitted. 7 Various features and advantages of my invention will appear from the description of speciesor embodimentsv and modes of execution of the :invention as applied to fluorescent lamps, and from the drawings.

In the drawings, Figfl a perspective or tilted view of a form of flattubular -lamp in which my I invention may be applied fandembodied, portions of the envelope wall being broken out toexpose parts within and to" shorten thef'figure; and Fig. 2 is a cross-section of theltub'taken as indicated by the line and 'arrows 2-i-2 in Fig.1, and on a larger scale. f

Fig. 3 is a side view of apparatus for flattening and straining a lam'p'tubeinf'acordance with my invention, a portion of thetube being broken out to shorten the figure; and F g; 4"shows a crossa section through the apparatusandthe lamp tube, taken as indicated by thel'in and arrows 4-4' in Fig.3. g

Fig. 5 is a perspective 61 tiltedvi'ew of another form of flat tubular lani'p 'in'which my invention may be embodied; and Fig;- 6 shows a longitudinal section through oneend of the lamp tube shown in Fig. 5, on a larger scale."

Fig. 1 shows a fluorescent" lamp L of ordinary low pressure positive column dischargeltype in I;

which my invention may be embodied. As here illustrated, the circularly round tube ends I0, If! are annularly reduced or; shouldered and are secured in bases l2, l2 eachprovided with bipost contact terminals I3, I3. 7 Asshown at one end of the lamp L, the cathode mount Mlc'omprises a cathode M of coiled-coil tungsten wire filament type, which may be activated 'with'a coating of alkaline-earth-metal oxidels); suchas the usual mixture comprising barium and strontium oxides.

The current inlead wires ,15, I5 connecting the ends of the cathode coils I4 to-thefcorresponding biposts |3, |3 are sealed through the stem flares 58 that form the end walls of the tubular lamp envelope, one of which is s hown provided with an exhaust tube sealed or tipped off at l8. The leads l5, l5 are shown as provided with anode, extensions |9, IS. The lamp tube L'may contain a low pressure starting atmosphere of one or more of the inert rare group O gaseasuch as argonat a pressure of some 2 to 5mm. of mercury. A supply of ionizable and vaporizable, metal to serve as a working substance and provide the discharge atmosphere in operation is also indicated at 20 as a droplet of mercury exceedingin amount what 4 will be vaporized during the operation of the device. A coating of luminescent material or phosphor is indicated on the inside of the envelope wall at 2 I, to be excited by the mercury discharge, and especially by its resonance radiation of 2537 A. wavelength.

As thus far described, the lamp L is essentially similar to ordinary round tube fluorescent lamps now in common 1159.

Unlike ordinary fluorescent lamps, the lamp tube L is here shown as flattened substantially throughout its length-between the round ends m, I!) that carry the bases |2, |2 to an elongated loop-like cross section, Fig. 2, comprising wide, flat walls 22, 22 interconnected by the semicircularly rounded envelope edges 23, 23. The round ends HI, ID may merge into the flattened portion with a wedge-like taper indicated at 24, 24, Fig. 1. It is the rounded edges 23, 23 that are brought into a condition of surface compression in the material in order to render the tube resistant to the external atmospheric pressure.

Figs. 3 and 4. illustrate a form of treating apparatus F which maybe used for straining'the edges 23, 23 of a flat lamp tube.- As shown in Fig. 3, the apparatus comprises counterpart long, flat metal bars 30, ,(as of iron) which are oppositely and slopingly ofiset at 3|, 3| near their ends, in correspondence to the wedge-like taper of the tube L at 24, 24 in Fig. 1, so that their end portions 32, 32 are further apart than the intermediate portions of thebars. These bars 30,33 are made substantially narrower thanthe width of the tube L.. Provision is made for maintaining the bars 30, 30 substantially parallel and guiding their relative sidewise movement, as by means of guide rods orpins 33,, 33 fixed in the end portions 32, 32 of a bar and extending through corresponding' holes in the portions .32, 32 of the other. bar; and thus the bars are'kept in facial registry or alignment directly. opposite one another. Each bar 30 is. faced with heat insulating material or lagging to reduce and-slow up the transmission of heat from a tube'L between the bars to them, as by wrapping asbestos cloth tape 35 .around the bar 30 in overlapping convolutions. Preferably this insulation may extend beyond the bar ofisets 3|, 3|, and may nearly cover the bar end portions 32, 32. With each bar 30 may also be. associated suitable electricalheating means3l, here shown as a commercial form of strip heater comprising a suitably insulated resistance unit] encased in a flattened tubular sheet metal sheath; with terminal connectors or binding posts 38, 38 at each end of the heater31. Each heater3'l liesalong the back side of its bar 30, substantially through- -out its length between the offsets 3|, 3|, and is suitably held thereagainst, as by wrapping the asbestos sheathing 35 around the heater and the bar together. v

In using'the apparatus F, provision is made to exert a yielding force on the bars 30, 30 to press them toward one another; which may be done by arranging them one directly above the other as shown in Fig. 3, thus taking full advantage of the weight of the upper bar. The bars 30, 30 having been heated up fully by their heaters 31, 31, and an already flattened lamp tube L having been heated well above the strain-point temp rature of itsvitreous material in .any suitable way-as in a heating furnace or lehr, not shown,the heated tube L is placed between the bars .30, 30 asshown in Fig. 3, with the tube resting on the lowerbar and the top bar resting on the tube so that the full force of its weight (including that of its gisaiei .5 heater 31) is exerted on the tube. This weight is so chosen that the tube L is strained or even further flattened slightly before the exposed edges 23, 23 have cooledoff to the strain-point, below.

which they can no longer be further permanently bent or-flattened by the load. While this is taking place, the coolingrof the wide,:flattened tube walls 22, 22 is limited and retarded by the asbestos facings 35, 35, and also by heat from continued operation of the heaters 31, 31, if necessary, so that the walls 22, 22 do not cool down to and below the strain-point ahead of the edges 23, 23. Once the edges '23, 23 are below the strain-point, however, the heaters 31, 31 may be cut out of'circuit'so that the walls 22, 22 may cool off below the strain point; and as soon as convenient after this, the tube L may be removed from the apparatus F.

As shown in Fig. 4, thewidewalls 22, 22 are very slightly convex outward and concave inward, instead of being perfectly flat as in Fig. 2; but this concavity is so slight as not to impair the advantages of the flat shape appreciably.

Fig. 5 shows a lamp whose envelope tube L is flat right out of its very ends Illa, Illa, which are closed by substantially flat end wall discs Ilia, |6a instead of by stem-flares l6, l6 as in Fig. 1. In other respects, the cathode mounts Ma, Ma are just like the cathode mounts M in Fig. 1, and so need not be further described. As shown in Figs. 5 and 6, the end discs 16a, l6a are of sheet metal such as chrome iron, and the tube ends Ilia, Illa abut directly against their margins and are sealed to them by fusion of the glass. The extreme edge of each disc I60. is shown in Fig. 6 as turned or beaded over at 40 toward the tube end Illa around the seal, thus protecting the latter and minimizing the possibility of the disc being pulled away so as to impair the seal, by something catching behind the edge, besides stiffening and reinforcing the disc. is further strengthened by a central inward -circular embossment 4| between the current inlead wires I5a, I541. One of these embossments 4| is apertured through its bottom in correspondence with the end of an exhaust tube fused and sealed to the bottom, and also shelters and protects the exhaust seal tip [8a formed by sealing off the exhaust tube after the lamp L has been exhausted and charged with startin gas and working substance.

Instead of being of usual long bipost type, the contact terminals of each end disc lBa shown in Figs. 5 and 6 are in the form of pins comprising fiat or slightly rounded heads I311, I311 attached (as by welding) to the outer ends of the current leads I5a, I5a, which form the pin shanks, and projecting or outstanding from the outer disc face. For this purpose, insulative spacing washers 42, 42 are interposed between the pin heads 13a, 13a, and the disc lBa; they may consist of glass sealed by fusion to the outer disc surface and into the disc holes through which the shanks i5a, 15a extend, as well as to the rear surfaces of the heads l3a, l3a, which may be of chrome iron.

The tube and end construction illustrated in Figs. 5 and 6 lend itself especially to the use of tubing produced directly from the glass batch in flat form, with its edges 23, 23 properly strained. The weakening of the edge strain at the tube ends Isa, Illa in sealing them to the end discs lea, Ilia by fusion is amply compensated by the strength against collapse imparted to the tube ends by their strong attachment to the discs.

Each disc IBa .6 In Figs. 3 6, various parts andfeatures are marked with the same reference characters as "their counterparts in Figs. 1 and 2, as a means of dispensing with repetitive description, a distinctive letter being added where this seems needful. However, I make no claim to the special end-disc and contact terminal features illustrated in Figs. 5 and 6, since they are the invention of Paul O. caries, and are claimed in his application Serial No. 506,230, filed October 14', 1943, which issued as Patent No. 2,415,367, February 18, 1947. V What I claim as new and desire to secure by Letters Patent of the United States is:

1; An envelope for evacuated electric devices comprising a flattened tube of vitreous material having only its longitudinal edges in a state of surface compressionsuflicient in amount to effecti'vely compensate stresses set up by atmospheric pressure and tending to rupture the tube when it is evacuated.

-2. An envelope for evacuatedelectric devices comprising a flattened tube of vitreous material having rounded longitudinal edges and substantially flat wide walls with only its longitudinal edges in a state of surface compression sufficient in amount to effectively compensate stresses set up by atmospheric pressure and tending to rupture the tube when it is evacuated.

3. In the manufacture of a flattened envelope tube of vitreous material having narrow longitudinal edges and wide longitudinal walls, the method of rendering the tube effectively resistant to collapse by external atmospheric pressure when the tube is evacuated, which comprises subjecting the said longitudinal edges and wide longitudinal walls to different thermal treatments which will produce a state of surface compression in only the said longitudinal edges.

4. In the manufacture of a flattened envelope tube of vitreous material having narrow longitudinal edges and wide longitudinal walls, the method of rendering the tube effectively resistant to collapse by external atmospheric pressure when the tube is evacuated, which comprises heating the tube substantially uniformly over its whole surface to a temperature well above the strain point of the vitreous material and cooling the tube more strongly at said longitudinal edges.

5. In the manufacture of a flattened vitreous envelope tube having narrow longitudinal edges and wide longitudinal walls, the method of rendering the tube effectively resistant to collapse by external atmospheric pressure, when the tube is evacuated, which method comprises chilling the longitudinal tube edges from a temperature above the strain point of the material to a temperature below the strain point in advance of the cooling of its wide longitudinal walls below the strain point.

6. In the manufacture of a flattened vitreous envelope tube having narrow longitudinal edges and wide longitudinal walls, the method of rendering-therwtube effectively resistant to collapse by external atmospheric pressure, when the tube is evacuated, which method comprises heating. the tube above the strain point of the material, cooling its longitudinal edges below said strain point while maintaining its flattened longitudinal walls above the strain point, and thereafter allowing said walls to cool off, as well as said edges.

8. An electric lamp comprising an evacuated elongated envelope of vitreous material, at least a portionof said envelope being flattened and having narrow longitudinal edges and wide longitudinal walls, the said longitudinal edges only of the said envelope being in a state of permanent surface compression.

9; An electric lamp'comprising an evacuated elongated envelope of vitreous material flattened in cross-section throughout its length, a metallic closure member fused to and closing each end of said envelope, the longitudinal edges only of said envelope being in a state of permanent surface compression.

. EUGENE LEMMERS.

eb h P tent UNITED: STATES PATENTS Number Name Date 1,016,320 Burnside Feb. 6, 1912 1,483,461 Littlton, Jr. Feb. 12, 1924 1,981,560 Littleton 1 Nov. 20, 1934 1,994,312 1 Herre Mar. 12, 1935 2,001,852 Burner 1 May 21, 1935 2,055,981 Magriifi Sept. 29, 1936 2,062,836 Scott 1 Dec. 1, 1936 2,244,715 L0Iig June 10, 1941 V FQREIGNv PATENTS Number" f I Country Date 486,325 Great Britain June 2, 1938

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