US2237328A - Metal-coating bulbs or the like - Google Patents

Description

April 8, 1941.

l c. BIRDSEYE Erm., 2,237,328

METAL-COATING BULBS 0R THE LIKE Filed Feb. 19, 1938 5 Sheets-Sheet l April 8, 1941 l lCLEalRDsEYE Erm. l 2,237,328

METAL-comme BULBS 0R THE LIKE Filed Feb. 19, 1958 5 Sheets-Shea?l 2 y afg.

April 8, 1941. c. BIRDSEYEv TAL 2,237,328

METAL-COATING BULBS 0R THE LIKE Filed Feb. 19, 1958 5 Sheets-Sheet 5 Aprirl 8, 1941. c. BIRDSEYE Erm. 2,237,328

METAL-'COATING BULBS OR THE LIKE Filed Feb. 19, 1938 5 SheetS-Slleefl 4.

A c. BlRnsEYE Erm. 2,237,328

METAL-COATING BULBS OR LIKE April 8', 1941.

Filed Feb. 19', l1958 I 5 sheets-sheet s ?atented Apr.. 8, llil iii Peretti Marat-comune autres on una man (Clarence Birdseye and Pincus liberen, Gloucester, Mass., assignors, by mesme assignments, to

Birdseye Electric Corporation,

Gloucester,

Mass., a corporation of Massachusetts Applica-tion February i9, 193g, Serial No. 191,493

(Ci. Eiltall 'i Claims.

This invention relates to the manufacture. of incandescent lamps and particularly to the art of providing lamp bulbs upon a selected or predetermined area with a metallic reecting coat.- ing, such as silver, in order to reflect and direct the light of the lamp emciently into the desired field.

The invention consists in a novel process of applying a continuous and permanently ladherent metallic coating to the inside of an evacuated bulb under conditions which permit the use of .automatic or semi-automatic equipment at low labor cost and in such manner as to minimize the loss of silver in the process. also includes within its scope the novel apparatus herein shown as employed in the practice of the process of our` invention.

Metallic coatings have been heretofore applied to lamp bulbs and to radio tubes under somewhat dierent conditions and with somewhat different objects than those contemplated by the present invention. For example, in the production of electronic tubes it has been customary to evaporate a small piece of magnesium or aluminum as a getter in the nished tube, after evacuation and as the tube is being sealed oi and while the glass walls are still hot from that process. The amount of metal so volatilized as a getter has always been considerably in excess over that required to combine with the oxygen present in the tube and this excess condenses on the inner walls of the tube in a bright or dark coating. The method used to evaporate the getter depends upon the particular substance chosen and the When the getter choice of location in the tube. is readily volatile a gas ame impinging on the tube is suiicient to evaporate it. Sometimes a getter is vaporized as a bead on a tungsten resistance wire or as a small piece of metal placed in a high frequency field.

In carrying out our improved process of producing a reiiecting coating on the' inside of a lamp bulb by the evaporation within the bulb of a metal or alloy, we are able to employ with advantage either the resistance heating or the high frequency heating steps above referred to.

Before proceeding to a detailed description of our process and apparatus, it will beconvenient to discuss briey some of the problems with which we are concerned and to indicate the solution achieved by our invention.v

Whensilver and certain. other metals or alloys are melted in air, small quantities of air, chiefly oxygen, dissolve into the molten metal and most of this oxygen is subsequently evolved when the The invention.

metal is subjected to changes in temperature or pressure. The mechanism of this phenomenon is not completely understood, but in the case of silver it is probably due to the formation of silver oxide which dissolves in the molten silver, but which decomposes with the evolution of oxygen at a temperature near the melting point. When this oxygen is evolved the molten silver spits and sputters. We have found that a pellet of silver suitable for coating a bulb ordinarily contains suicient adsorbed gas to sputter in vacuo if it is rapidly heated above its melting point and near its boiling point. This sputtering must'be avoid- 'ed if uniform coatings are to be formed on the reiiecting surface of the lamp bulb.

Silver that has been fused and allowed to cool in a vacuum or in an inert gas atmosphere does not absorb oxygen and therefore does not sputter evenwhen heated rapidly in a vacuum. However, in silvering lamp bulbs it is convenient to employ the same boat or crucible for holding silver for coating operations on successive bulbs and it becomes necessary to introduce additional silver into the'boat from time to time. Such added silver may preferably take the form of small pellets or short lengths of silver wire which always contain adsorbed gases likely to cause sputtering if heated rapidly to vaporizing temperatures. It is therefore essential to provide against sputtering at all times, particularly if automatic machinery is to be used in the process. We accomplish this important result by raising the temperature of the boat, together with its charge of silver, slowly to a temperature well above its melting point, for example at about 1100 C. and holding it at this temperature for a denite period and then abruptly raising the temperature to the Vaporizing point (about 1800" C.) for a short period of time, or until the desired amount of silver has been vaporized. For small lamps-50 watts forexample-the period of vaporization need not exceed a few seconds and this interval may b varied depending on the size of the bulb to be coated, on the number of boats or crucibles of silver placed within the bulb, and on the amount lof current passing through the heating element. However, the length of time that the higher or dashing voltage must be eective is not only critical, but must be varied depending on the size of the bulb being silvered and upon other factors. In silvering the bulb-of a 50 watt lamp the preliminary interval at which the silver ismaintained in a molten condition may be from ten to twenty seconds, while the flashing period must be restricted to about six seconds to vapor- 2 c c y ize the desired amount of degassed. silver. desirable under some conditions to vaporize the It is silver as rapidly as possible in order to obtain a Vbrilliant coating. While the desired amount of silver maybe vaporized at a slower rate, the

' coating tends to take a whitish color'under such conditions, probably due to the individual crystals of silver having time to reach appreciable size. A ne crystalline deposit is essential if a brilliant coating is desired.

The thinner the coating of silver and the more I rapidly it is applied to the glass of the bulb, the

more nearly amorphous and therefore the brighter is they reflecting coating provided. On the other hand when the silver coating is allowed to become of relatively coarse crystalline structure the light reflected thereby is of a bluish tinge. A coarse crystalline area, by causing multiple reectio'n between'the facets of the crystals with resulting selective absorption of the light rays toward the red end of the spectrum, causes the light ultimately leaving the reflecting area to have a larger percentage of blue rays than in the light leaving the filament. Therefore the light i from a lamp having `such a crystalline area has a less -yellowish tinge than light leaving a similar lamp having a homogeneous brilliant reflecting area. v'Ihis result is desirable for many uses and may be secured in practising the process of our invention by controlling the distribution of vaporized metal so that certain zones of the coating are somewhat thicker and of different crystalline form or size than others; as by employing two sources of metal for evaporation within the bulb which may overlap in. a zone of the coating produced within the bulb, or by any means reducing the rate of vaporization and increasing the time.l

' In carrying out the process of our invention, it is desirable to heat the glass of the bulb substantially while the bulb is being evacuated and during the metal vaporizing step in order to remove adsorbedv gases and water vapor from the pores of the glass and so to insuresl secure and permanent bond between the metallic coating vand the glass walls of the bulb. On the other hand, the sealing of the bulb must be efiicient and reliable throughout the steps of the process even though portions of the bulb may be heated vto an annealing temperature in the neighborhood of 400 C. Our invention accordingly contemplates the step of temporarily sealing the bulb with a cooled medium. for example. by a rubber sealing member cooled yby a watercirculating system. It is important not to overheat the sealing medium to a degree which would cause its deterioration or suiiiciently to cause vapor or other distillation products to be evolved therefrom and enter the bulb. We rely upon a cooling system to obviate this danger. This is supplemented, of course, by the action of the evacuating system in immediately withdrawing from the bulb any vapor which may be momentarily envolved from-the sealing means.

The bulb may be heated by any convenient means during the exhausting and vaporizing.

bulb the metal charge may be conned so that when vaporized ya portion of the vapor is directed laterally'against the bulb walls and a greater portion ofthe vapor directed upwardly into the globularlend of the bulb. The selective distribu-V tion of the'metalllc vapor may be further controlled by the provision of shielding devices, as

for example, a shield disk arranged to limit the amount vofvmetal vapor the neck'- of lthe bulb.

'An important and novel feature of the ap-v passing downwardly into paratus herein shown consists in a container or boat which isge'nerally conical in shape and provided with peripheral openings for the passage of v metallic vapor in a lateral direction. The shape oupies a volume many times that of the molten metal and in the act of escaping from the latter at `a rapidl rate .of vaporization, the vapor expands almost with explosive violence. Thus there is a practical limit to the rate of vaporization as above explained. and this explosive force can in part be directed in any desired direction by .he shape of the boat containing the molten metal. Y

For the purpose of controlling the rate of vaporization, adjustable resistance may be introduced into the power circuit. The resistance of the boat and -its Ycontents inthe circuit is preferably arranged to be but a small' part of the total resistance .of the entire circuit. This has its advantages in that changes in the resistance of the boat itself, or changes due to variations in its contents, do not greatly eiect the resistance of the circuit as a whole. It is desirable that such eiects may be as nearly constant as possible since the resistance of the boats directly eiects the amount'of heat generated at that point.

In addition to the essential step of maintaining the glass of the bulb at a proper temperature.

Ait is also imperative to have a chemically clean glass surface upon which to deposit the metallic coating.- In'many cases, it is desirable to subject the bulb to a preliminary cleaning with chromic. sulphuric or hydroiiuoric acid solutions eiecting the removal of a surface illm from the inner walls of the bulb.

Another important 'feature of our invention c consists in'controllably timing the dashing interval. The preheating period required to degas a silver charge is not critical, but the vaporizing period is critical for reasons already discussed and to control the length of this period the apparatus of our invention is provided with an automatically acting switch in the heating circuit which may be adjusted in accordance with the requirements of the work in hand. In this manner we provide means for controlling the amount of silver vaporized in a bulb of any given size. By maintaining relatively constant the im- A pressed voltage and the resistance of the boat 'the rate at which 'heat is developed and at which the metal is vaporized willbe regulated and the amount of metal: evolved as vapor may be controlled. In applying a silver coating to a bulb for a 50 watt lamp we dnd that about 0.03 gram of silver is required. If more than this amount is vaporized from the boat it tends to become lost since it is likely to settle upon the electrodes.

A more complete understanding of the invention may be had from the following description of a typical manner of putting it into practice, together with the description'of one form of apparatus which may be advantageously employed and which is shown in the accompanying drawings in which,

Fig. 1 is a view in perspective of a portion of the apparatus,

Fig. 2 is a view in elevation, partly in section, of one station of the apparatus showing a bulb in position therein,

Fig. 3 is a view in elevation on an enlarged scale of container or boat for the metal to be vaporized,

Fig. 4 is a corresponding plan view of the container,

Fig. 5 is a diagrammatic view of the apparatus illustrative of the cooling system,

Fig. 6 is a view similar to Fig, 2 showing` further details of construction and an alternative form of electrodes,

Fig. 7 is a diagrammatic view illustrative of the cycle of the apparatus,

Figs. 8, 9 and l0 are views in elevation illustrating alternative arrangements of electrodes and metal containing boats,

Fig. 11 is a View in perspective of the operating mechanism of the apparatus and certain circuitbreaking mechanism thereof, and

Fig. l2 is a view in elevation of the circuitbreaking mechanism.

The apparatus herein illustrated is of the turret type in its general construction and includes a fiat 'annular ring I0 having twenty-four stations thereon, and arranged to be rotated in` counterclockwise direction and in a step-by-step manner. The mechanism for rotating the ring In is of secondary importance only and is suggested in Fig. 11, which shows a vertical shaft 50 to which the ring is connected and which carries a disk 5I having slots spaced about its circumference and arranged to receive consecutively a roll 52 carried on a crank 53 upon the upper end of a driven shaft 54. The ring I is made hollow as shown in Fig. 6 to receive 'cooling water and at each station it is traversed by a hollow cylindrical stud il which is sealed or brazed securely into the ring and projects somewhat above its upper surface.v

A bulb-supporting unit is secured to the projecting end of each of the hollow studs II and rests upon the face of the ring I0. Each unit comprises a cylindrical body I2 recessed to receive the projecting end of the stud and having a water chamber i3 in its upper portion which is closed by a metal cover disk I4 secured permanently in place. The water chamber I3 is traversed by two or more vertical insulating tubes I which extend through the cover plate I4 attheir upper ends and downwardly at their lower ends into the body of the unit I2 below the chamber I3. The tubes I5 serve to insulate the vertically disposed electrodes I'I which, as best shown in Fig. 2,

extend through the water chamber I3 and up-- wardly for a considerable distance through the cover plate I4. Supported upon the cover plate I4 is a shouldered disk I6 of rubber or other solid compressible material which serves as a sealing seat for the bulb being treated and to this end it is 'shouldered to extend somewhat into the open neck of the inverted bulb and to provide a circular more especially below that at which any of its material may be vaporized and so impair the vacuum within the bulb or admit impurities which would interfere with a permanent bond between the metallic coating and the glass walls of the bulb. Accordingly the illustrated apparatus includes a water cooling system diagrammatically shown in Fig. 5. This system includes the hollow ring Ill and the water chamber I3 in each of the bulbholding units. The system is supplied with cooling water by gravity from a centrally disposed reservoir 39 which, as shown in Fig. 1, is constantly supplied with cooling water by means of a feeder pipe 40. Cooling water passes from the reservoir 39 through a number of radially extending tubes 38 to one bulb-holding unit of a group of four units. Cooling water flowing through the tube 38 circulates through the chamber I3 of the first unit of this group, then passes successively through intermediate connecting tubes 4I to the cooling chambers of the other units of the group and is iinally discharged to the ring l0 through a downwardly curved outlet pipe 42. The ring I0 is provided with three return ducts 43 extending inwardly from spaced points in its periphery to a common discharge pipe not shown. The eiiect of the cooling water circulating in this system is continuously to cool the thin cover plate I4 upon vwhich the sealing -disk i6 is supported and to cool the electrodes which pass upwardly through the disk I6, and in general, to maintain the disk Ill and the bulb-supporting units against any undue rise of temperature.

Each electrode, as shown in Fig. 2, may comprise a lower cylindrical portion II and an upper portion I8 of the same diameter, the two portions being adjustably connected by an enclosing sleeve i9. The effective length of the electrodes may be varied by loosening clamping screws set in the sleeve I9 and by moving the upper portions I8 of the electrodes up or down and again clamping them in position. The lower end of each electrode is connected to an outwardly extending metal arm 20 which is insulated from the body of the unit as shown in Fig. 6 and provided at its outer end with a terminal 2i for the electric heating circuit which includes the lead 22. The upper portions I8 of the electrodes are surrounded by a refractory disk 23 of aluminum or other refractory material and upon this rests a thin nickel disk 24 perforated to clear the electrodes and extending at its edge into close proximity with the neck of the bulb. The disks 23 and 24 constitute one satisfactory form of shield for preventing vaporized metal from passing downwardly and being deposited in the neck of the bulb where it is not required, and confine the vaporized metal to the bowl portion of the bulb where it is desired.

The electrodescarry between their upper ends the container or boat in which is placed the slug of silver or other metal to be vaporized. `The boat comprises a resistor held between the two heavy electrodes. It acts'as the crucible or boat holding the charge of metal to be vaporized, by its resistance to the passage of the electric current it producesv the required heat, and by its shape and design it directs the vapors of the boiling metal. The size of this boat should be as small as possible so that its heat capacity will not be sufilcient to prolong unduly either the heating up period or the cooling period, and it should have a capacity of perhaps twoor threetenths of a gram of silver. It must be made of a highly refractory material, that is, an electrical vconductor such as tungsten or molybdenum. Its

electrodes ll which have. sulcient conductive surface of the globular portion of the. bulb.

However, it is essential that some smaller part of the vapors strike the side walls of the bulb,

A-in the vicinity of the boat, and that a still smaller amount pass down into the neck of the bulb. Since these vapors occupy a denite space and since the high vacuum pump is operating during the ashing period there is a' slight tendency for these vapors to pass downwards towards the neck -with almost any form of boat. However, we have found that it is possible to direct and control the amount of metallic vapors that strike the side walls and the neck of the bulbs by perforating the boat with small holes or small slits at the sides and at the bottom. Evaporation of the metal, during the flashing period, occurs in part through these small openings and is thereby directed towards the side walls and the neck,.the

bulk of the vapors leaving the flaring top of the boat and serving to coat the large surface of the globular part of the bulb. The boat herein shown comprises a heavy molybdenum wire 25, perhaps .050 inch in diameter, bent to present two vertically extending legs and an intermediate verticapacity to carry the requisite current without the development of any substantial amount 'of heat. The heating of the circuit is thuscon'- centrated in the boat and in the metal charge contained therein.-

Lead wires 22 extend downwardly from the electrode terminals 2l to a pair of -spring contact shoes'60 movable with the ring l0, there being one pair of shoes for each bulb-supporting unit. The individual shoes are-located one above the other as shown in Fig. 1 and project rearwardly and outwardly with reference to the ring ,l0 and somewhat below the ring. The shoes @Il are arranged to wipe along and make electrical Vcontact with a pair of-segmental terminals 6i ar-A ranged concentric with the axis of the ring l0 and spaced from its circumference at the same height as the contact shoes 60. The terminals cal coil of fouror five turns converging downwardly. The molybdenum wire 25 is encircled by a'coil 26 of ne tungsten wire substantially 0.0055

in diameter. In making the boat the molybdenum wire, previously wound withV the tungsten finally a second tungsten wire 2 is wound reversely about the upper end of each leg and about the conical helix inthe valley between adjacent turns. The purpose of this construction is to provide a receptacle in which the molten metal may be retained, partly mechanically and partly by capillary action, during the preliminary heating step and before vaporization takes place.

'that is to say, the greater-part of the charge is flashed upwardly in a divergent field to cover the globular end of the bulb. A portion of the charge is flashed laterally through the peripheral cracks ofthe boat against the side walls of the globular part of the bulb, and a still smaller portion of the charge is ashed downwardly toward the neck of the bulb for coating the walls above the shield disks 23 and 2d.

It win be understood that the boat may be bod- 'ily adjusted vertically to locate it at the proper height for most advantageously treating bulbs of -wire 26, may be shaped as a conical helix, and l the particularshape and size in process, or,.as

will be explained hereinafter, two boats may be located atdiierent levelswithin the bulb and a vmetallic charge vaporized simultaneously or su :cessively.from them in coating a large bulb 6l are carried at one end by a block 52 secured to the upper'end of a xed bracket 63. They are insulated from the block 62 but connected to the wires 6d of the power circuit. The terminals El extend circumferentially to include two stations of the apparatus, that is to say, stations No. I3 and No. Id as shown in the diagram of Fig. 7. Accordingly, when any pair of contact shoes 6l! are moved into contact with the stationary segmental terminals 6 I, the heating circuit is closed through the bulb-supporting unit which has just arrived at station No. 'I3 and current is maintained flowing until the `ring is advaned to carry that particular unit beyond station No. It. The current supplied during 4this interval is sufficient to melt the silver chargecontained Within the boat in .the bulb-supporting unit and maintainit in molten condition at a temperature of about 980 C. for a period of ten tc twenty seconds, with the result that oxygen orv other gases absorbed in the metal are driven ol and thus the danger of sputtering is obviated, as already explained.

The segmental terminals 6l are supported at their forward ends by the block 62 and bracket $3 and at their rear ends by a similar block 65 and bracket 66. Beyond the terminals 6l is located another bracket Bl carrying an insulated block 58 having upon its inner face a pair of terminal plates 69 located one above the other at the same level asv the segmental terminals 6l. .The terminal plates 69 are connected to leads 'lil of the power circuit which is employed to ash the molten silver in the boat when thering has been advanced to carry a bulb supporting unit to i station No. l5 in the cycle of the machine. Since th-e period of rest of the ring between its successive steps in itsl rotation i's longer than the interval required for flashing the metal charge, an automatic timing switch is included in the circuit with the leads Til. `This mechanism' is shown more orless diagrammatically in Figs. 11 and 12, to which attention is now invited. The turret operating shaft 5d is connected through bevelled gears toa horizontal shaft 55 and this in turn is connectedthrough elliptical gears 55 to a horizontal shaft 5l which, through a pair of bevel gears, drives a cam shaft 53. The cam shaft 58 is journalled in the frame of the machine and carries a' cam 59 on its-right `hand end as seen in Fig. 11'. This cam 'acts to reciprocate a rod of adjustable length comprising the threaded sections ll and 'l2 connected by a coupling member 'i3 having right and left threaded connection with the sections il and 12. Bearings 7d support the rod for endwise reciprocation and a spring 'l5 interposed between the right hand bearing and 'a pin in the rod section 12 holds the rod at all times in contact with the periphery of the cam 59. At its right hand end the rod carries a head to which is connected one end of the lead L1I. The head is also provided with a flat spring contact plate 16. As the rod is reciprocated the contact plate 16 makes and breaks the circuit by engaging a terminal in a iixed block 11 which is connected to a lead 18 in the power circuit.

The reciprocation of the switch rod is timed positively through the mechanism above described with relation to the intermediate movement of the ring l so that the power circuit through the terminal blocks BS is made and broken while one of the bulb-supporting units is at rest in station No. l5. The interval during which this circuit is closed may be adjusted and controlled by turning the coupling member 13 to adjust the length of the switch rod and so regulating the interval of engagement between the contact plate 16 and the block 11. The circuit has a substantially higher Voltage impressed thereon than the power circuit 64, with the result that when the switch 'I6-11 is closed, suihcient current is delivered to the boat to raise the temperature of the metal therein abruptly to its vaporizing point, for vexample, 1800" C. for silver. The temperature is maintained for a regulated interval of six seconds or less and it is during this interval that the molten metal is vaporized or raised to the point of active ebullition and a bright metallic coating formed upon the walls o1 the evacuated bulb located at station No..i5.

As already intimated it is important to maintain the bulb being treated 'under substantial vacuum and continuously withdraw from the bulb any gas vapor evolved from the molten metal in the boat. 'I'o this end each station is connected to an exhaust system and includes a vertical tube 3Q which passes upwardly through the body of the unit and opens above the rubber seal i6 in a cavity'provided between the electrodes il. At its lower end the tube 3ll is sealed into the upper end of a heavy rubber tube 3l which passes out through the bottom of the ring i0 and downwardly through perforations in a pair of spaced plates 32 which are secured in Aposition beneath the ring at each station. Between the plates 32 is mounted a shut-off valve 33 which maybe closed by engagement with a stationary cam, not

shown, in the rotation of the ring and at the proper point in the cycle of operations. A stationary cam is also provided yfor opening the shut-'off valve` and admitting air to the coated bulb toward the end of the cycle. system is of the general character employed in lamp making machinery and since it forms only one element of the present invention it will not be more fully described herein. It will be under-- stood that the arrangement of the vacuum system herein disclosed is illustrative only and may be varied as desired. The connection to the pump is indicated at 35.

Referring to the diagram of Fig. 7 it will be `noted that when each unit reaches the No. I station the rough vacuum pump begins to operate,

The vacuum comes into action and continues to exhaust the bulb up to the sixteenth station.

At the sixteenth station the shut-ofi valve 33 is operated to close the exhaust tube 3| with the bulb in evacuated condition. At that time the operation of flashing the silver has been completed and it remains only to cool the coated bulb gradually and without creating undue strains therein. The cooling of the bulb is effected during its movement from station No. l1 to station No. 23 and at station No; 23 the shut-01T valve 33 is opened admitting atmospheric pressure to the bulb so that it may be removed from the sealing disk I6.

It is important to maintain the glass of the bulb at a'high temperature during the coating operation in order to insure a permanent bond between the metal coating `and the glass of the bulb, and also in' order to avoid chilling the metal-containing boat within the bulb. To this end an annular oven 45 isr arranged concentrically with and above the ring l0 and in such position that successive bulbs upon the bulb holding units of the ring are passed through it throughout substantially 210 of their movement in the circular path of the ring. The oven is of heat insulating material and provided with a pair of circumferentially disposed gas pipes 46 perforated so as to direct a continuous series of ilames toward the bulbs in their passage through the oven. As indicated in the diagram of Fig. 7 the annular oven 45 extends from the second to the sixteenth station and includes those stations at which the high vacuum pump is working, the stations-at which the metallic charge is maintained in molten condition and the station at which the charge is flashed or vaporized. As each coated bulb passes out of the oven at the sixteenth station it is ready to be subjected to the cooling operation which begins at the seventeenth station. The oven 45 terminates at the sixteenth station and in leaving that station each bulb supporting unit moves into range of a curved perforated duct from which cooling air is blown against. the bulb in its movement from the sixteenth to the twenty-third station. The operator is free to remove the coated bulb from the bulbsupporting unit at any time between the 23rd and the first station. In the regular practice of our process the completed bulbwill be removed and a new bulb presented to the unit while the latter remains at rest at the 24th station.

A preferred construction of adjustable electrode is shown in Fig. 2 and a somewhat different form of electrode is shown in Fig. 6. In the latter instance the electrodes 8| are not in themselves adjustable but are provided at their upper ends with longitudinal bores in which are ad- 1K justably received the vertical rods 82 each of 'which' is provided with an adjustable collar 83.

Each rod has at its upper end a holder in the form of a sleeve 84 in which is inserted one of the downwardly extending legs of a boat 85 similar'in its general construction to the boat already `described and as illustrated in Figs. 3 and 4. The

rods 82 may be adjusted vertically in the electrodes to locate the boat 85 at the desired level in the bulb./ The collars 83 adjustably support a shield 86 comprising a disk of refractory mate- 'rial at the desired level in the neck of the bulb trode 9i) isa common element.

Fig. 6 is 'shown as provided withareiractory lshield in the shape of a disk 88. perforated to permit passage of the electrodes andthe exhaust tube 2l and spaced above the surface vof the sealing disk I6 so as to still further shield that element from heat developed at the boat 85.

In Figs. 8, 9 and 10 are illustrated illustrative forms of electrodes for supporting two boats within a bulb to be coated. 'Ihe use oftwoboats is a convenience in coating bulbs of large size or of special shape as already explained. Y In. Fig. 8

three electrodes are provided, the outerl electrodes passing upwardly through the sealing disk I6 of the unit andsupporting the boat SI'between their upper ends. A thirdl and shorter electrode 92 extends upwardly through 'the sealshown. In this instance it will be'seen thatthe two boats are included in circuits which may be operated independently :'and-of whichthe elec- In Fig. 9 two electrodes 96 are shown as passing upwardly through the sealing disk Iii.v These carry at their upper end a boat 91 and are provided with a pair of adjustable collars' carrying a second'boatA 99. As before, theY boatsa'i and 98 may be independently adjusted as toheight. In this instance they are included in parallel in .a single circuit and must accordingly be ashed' simultaneously.

In Fig. 10 -an electrode constructionisshown in which two boats I and I 0I are arranged in series.. An' electrode IIIZ passing` vupwardly through the sealing disk I9 is provided at its upper end with a socket for onev leg of the boat I 09.. A short velectrode H03 passing up through the sealing disk I6 is provided in its vupper end with a socket for one leg of the boat mi. The other leg of the boat Ii and one leg of the boat |06. are connected in series through an electrode member H35. In this arrangement also the 'bulbs may be adjusted as to vertical height and are arranged to be flashed simultaneously.

From the foregoing description of the/particular apparatus herein illustrated it will be apparent that the process of our invention involves the essential steps of sealing each bulb with a cooled medium while the bulb contains a charge of fusible metal, exhausting and heating vthe bulb,"melt ing the metal charge and maintaining it in molten condition in the exhausted' bulb.; and finally flashing or vaporizing the-molten metal. These steps will now be summarized as they are carried out with the assistance of the illustrated apparatus. It may be assumed that the ring I o ing disk I Ii and supports at its upper end Aa. second boat 93 which is connected to-'an adjustable the annular oven 45. In the successive steps of the ring the unit is advanced .to stations No. 3,

to station No. 4 where .the leak detector operates and to stations Nos. 5, 6 and 'l where the high vacuum pump begins to operate. In its move-1 ment to these stations and to the ensuing stations, the bulb is gradually brought to a high temperature by the oven and a high-degree of evacuation is reached within the'bulb. At station No, I3 the metal charge in the boat is re-V duced to molten condition, and maintained in this condition while the high vacuum pump is st ill at work and is effective to withdraw any oxygen or other-gas evolved by the molten metal.

At station No. I3 the flashing oper-ation occurs in Y* a controlled interval of time and at station No. I6

the bulb passes from the oven and the vacuum tube of that unit is sealed. From station No. I6

`around to station 23 the bulb is gradually cooled `i and at the latter station atmospheric pressure is y' admitted to the bulb and thereafter it may be7 removed from the apparatus.

While we have referred to the hashing operation as occurring at the thirteenth station it is a fact that some vaporization of the metal charge may take place before this station is reached but this does not interferewith the application of a 'A complete metallic coating in the flashing opera;y

tion as above outlined.

l It will be understood that while the apparatus above described is well adapted for usein carryis at rest with the oven d5 in heated condition and cooling water circulating through the cooling system and one of the bulb-holding units positioned at the 24th station of the diagram of 6 Fig. '7. The operator has thus the opportunity to place a pellet of silver or other metal in the boat of this unit, and to place an inverted bulb over.

bulb. In the next step the unitis carried to sta- `tion No. -2 where it enters the receiving end of ent of the Uni-ted States is:

ing out the process of our invention, *other forms of apparatus may be used with good advantage within the scope of our invention. Our invention includes within its scope the novel electric lamp bulbk provided with fine and coarse crystalline areas in its reflecting coating', herein. shown asy produced by the process of our invention.

Having thus described our invention, what we claim as new and desire to secure by Letters Patl. 'I'he process of metal-coating bulbs or the like,v which comprises closing the /bulb with a solid compressible seal, moving the bulb through a heated zone, simultaneously coolingithe seal and thereby preventing vaporizaticn from the seal inte the bulb, substantially exhausting the bulb, and then locally heating a metal charge within the bulb to the point of vaporization.

2. The process of metal coating lamp bulbs, which consists in inverting a bulb over a charge oi' metal, sealing the neck of the bulb with a solid compressible seal. supporting the seal upon a at Water-cooled surface, and meanwhile raising the metal charge to its vaporizing temperature.

3. The process of metal coating lamp bulbs which includes the steps of inverting a bulb ovei a charge of metal, cushioning thev end ofthe neel; of the bulb upon a resilient cushion, supporting the cushion upon a flat water-cooled surface and Athus preventing vaporization from the cushion into the bulb, and meanwhile heating the charge to the point of vaporization.

4. The .process of metal coating'lamp bulbs', A

which includes the steps of inverting a bulb over a charge of metal, cushioning the end of the neck of the bulb upon a resilient cushion, sealing the. neck with a projecting part of the cushion,4 water-cooling the cushion and seal to preventy vaporization from them into the bulb, and mean- Y time heatin g the charge and vaporizingV it.

5. Thel process of metal coating lamp bulbs,

which includes the steps of inverting a bulb over a charge ot metal, sealing the neck of the bulb with a solid compressible seal, maintaininga substantial body of Water adjacent to the seal for cooling the same and thus preventing vaporization therefrom into the bulb, and meantime heating the metal charge to the'vaporlzing point.

6. The process of metal coating lamp bulbs,

which includes the steps of inverting a bulb over a metal charge carried at the top of an elongated support, sealing the neck of the bulb about the support by a solid compressible seal, water-cooling the seal and the lower end of the support, and meantime heating the metal charge to the vaporizing point while vaporization from the seal and 10 tion of the bulb.

support into the bulb is prevented by the said water cooling thereof.

7. The process of metal coating lamp bulbs, which includes the step of vaporizing a. charge of fusible metal While confined within the bulb by walls which are inclined to( direct most of the vapor of the charge toward the bowl end of the bulb and are apertured to direct a minor portion of the vapor of the charge toward the neck por- CLARENCE BIRDSEYE. PINCUS DEREN.

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