US2478533A - Water-cooling attachment for projection arc lamps - Google Patents

Description

Aug. 9, 1949. H. HUFF 2,478,533

WATER'COOLING ATTACHMENT FOR PROJECTION ARC LAMPS Filed Oct. 12, 1948 INVENTOR. HAROLD I. HUFF ATTORNEY Patented Aug. 9, 1949 WATER-COOLING ATTACHMENT FOR PROJECTION ARC LAMPS Harold I. Huff, Los Angeles, Calif.

Application October 12, 1948, Serial No. 54,047

Claims.

This invention relates to arc lamps for motion picture projectors and the like, and is particularly useful in projector arc lamps of the reflector type although it is not necessarily limited to use with reflector lamps.

An object of the invention is to improve the illumination produced by a projector arc lamp.

Another object is to reduce the rate of carbon consumption without reducing the light.

Another object is to control the direction of the flame or tail of the are so as to prevent injury to the reflector in a reflector type lamp.

Still other more specific objects are: to reduce flicker; to reduce ash deposit within the lamp housing; to prevent color production and maintain a pure white light on the screen; to eliminate need of using metallic coated carbons; to maintain constant resistance in the arc circuit, which keeps the current constant and maintains a uniform crater in the positive carbon; to burn the 1 follow of a particular embodiment of the inveni tion.

Broadly, the present invention consists of water cooled apparatus for cooling and conducting current to the positive carbon of a proiecticn arc lamp at a point thereon closely adjacent to and at a constant distance from the arc. The cooling of the carbons closely adjacent the arc has the direct advantages of increasing the depth of the crater in the positive carbon, and causing the metal of a metallic coated carbon to burn clean. It also has the advantage of permitting conduction of the current to the carbon at a point thereon spaced a short, constant distance from the arc, which results in the indirect advantages of: eliminating necessity of using metal coated carbons; maintaining constant resistance in the arc circuit; enabling the use of heavier currents in carbons of given size; and facilitating the automatic feeding of the carbons in proper relation to maintain exact focus.

The invention also permits the use of larger carbons with the same current while producing the same light intensity, under which conditions it has the advantage of greatly increasing carbon life. Thus with the present invention, 70 amperes of current with a 9 millimeter carbon gives the same light on the screen as amperes through an 8 millimeter carbon with prior projectors, and the 9 millimeter carbon, when used with my attachment, will last twice as long as the 8 millimeter carbon in the conventional lamp.

The production of ash deposit on surfaces within the lamp housing is reduced, by use of the invention, to such an extent that less deposit is accumulated in a week with the invention than in a single day without the invention. The resultant cleaner reflector surface increases the light intensity and lessens the heating of the reflector.

An important feature of the invention is the simple and rugged construction of my attachment whereby it is reliable in operation and gives long service without undue maintenance expense and trouble.

In the drawing:

Fig. 1 is a side elevational view with portions broken away of a reflector type projection arc lamp incorporating a water cooled attachment in accordance with the present invention;

Fig. 2 is a plan view of the attachment, the view being taken in the plane IIII of Fig. 1;

Fig. 3 is a rear elevational view of the attachment showing a portion of the projector in section, the view being taken in the plane III-III of Fig. 1;

Fig. 4 is a detailed vertical sectional view taken in the plane IVIV of Fig. 3;

Figs. 5 and 6 are cross sections taken in the planes VV and VI-VI respectively of Fig. 4; and

Fig. '7 shows the relative shapes of a copper coated carbon after being used in a lamp not equipped with the invention, a copper coated carbon after being used with the invention, and an uncoated carbon after being used with the invention.

Referring first to Fig. 1 there is shown a conventional lamp housing In positioned back of a projector H. Near the rear (left) end of the housing I9, is a concave mirror I2 which is axially aligned with the optical system of the projector ll. Positioned in the optical axis are the negative carbon l3 and the positive carbon 1 4 between which the arc is formed. The carbons are longitudinally supported and fed by the conventional carriages, only the carriage It for the positive carbon I4 appearing in Fig. 1. As these projectors are ordinarily used, carriage I6 not only physically supports the carbon id but also supplies the current thereto.

In accordance with the present invention, a

water cooling attachment i8 is provided which engages the positive carbon hi adjacent its tip, cools the carbon, and constitutes the current connection thereto.

The carriage l6, and a corresponding carriage for the negative carbon l3, are usually motor driven to automatically feed the carbons as they burn away, and they still perform this function when my water cooling attachment i3 is ernployed. However, since automatic mechanisms are well known in the art and do not constitute a part of the present invention, no feeding mechanism is described herein.

Referring to Fig 4, the water cooling attach-- ment of the invention comprises an annular water jacket 2E having a central passage 2i of somewhat larger diameter thanthe positive carbon l4, and defining a water chamber 22 through which cooling water is circulated. This watermay be conducted into the chamber 22 through a; conduit 2-4:and exhausted from'the chamber through conduit 25:. For convenience, the conduits',-2A;@ and- 251. may, extendinto a header blocka,-26 to which copper tube-connections may be made .toganyzsuitablesource. of; supplyexhaust. Thawater'jacket-lt-is supported ina ringizz'himwhich. it: maybe looked as by a pa r of set qscrews-s289.. The ring :21 is. mountedon the uppert 'end'.otra'rrintegralj rod 25!; the latter being ldckedrbyzsetrscrews' 60 (Fig; 6) to; a member 3%] whicluin-turn has:.a; ball*sur:face thereon whichengagesrtwitl'r' a:- socket 3J5" intthexupper endof a bracket';3 2;.,the member. .39 being adapted .to bev clampediin thezsocket: in thebracket. 32b a screw 33:. .Thealiowerendof theLbracKetSZmay be secured as -by screwsfilito the. endaof. the bed 55 f the.lamp:-.-housing.z. The.:ball and. socket. connec:-.

fer' bushing 35- which: is screw threaded. into.

screw; threads; 3.! e'provi'ded for. that purpose in theiwaten jacket'mrat the. front end: of. the central passagez'litherein. By virtuelof' its-threaded connection to the water jacket, the bushing is irr-zverygood thermal conductive relation: thereto, and it is accurately dimensioned astto': its bore 33' so; that itsfitsethecarbon: Mfsufliciently closely tce be. in very:- good thermal conductive relation thereto. Because of the fact that carbon is a relatively poor' heata conductor, most of the heat generated-in the tip. portion of'thecarb'on te by theiarc istransferred-though the bushing 35 to thetwaterjacket'and' conducted away by the circulation ot water therethrough As is well known, the usual are produced in a projector lamp of the type. hereirr discussed, prodiices av relatively long flame or tail which if directed toward the mirror l2= may blacken. or cause breakage of the latter. I have found that iii-accordance with the present invention a magnetic-1 deflector for the tail of the arc can be conveniently incorporated inmy water cooling attacliment; This device consists of a U-shaped element 4010f paramagnetic material such as soft iron-,, the two arms ofwhich are clamped against the fi'ont. end 4|. of the water jacket by a shoulderAl on thebushing 35, this shoulder 42. being the rear face of an expanded head. 44 formed on the forward end of. the bushing. The enlarged feedin head 44 not only serves to anchor the U-shaped arc deflecting member 49 but also functions to absorb radiant heat from the arc and help to limit the total rise in temperature within the lamp housing. As shown in the drawing, the bow portion 40a of the U-shaped arc deflecting member is positioned at the top and the open ends 46b of the member are bent rearwardly. Itis' found that this particular configuration is most effective in some instances, but in other instances it is found best to leave the ends tiib straight and/or to orient the U-shaped member in. some. positionother than the vertical. The best position for any particular lamp can be readily determined by experiment.

As previously indicated, in accordance with thepresentinvention, current is transmitted to the positive carbon I' l adjacent the tip thereof through the water cooling attachment instead of through the usual carriage l5. Connection is made through. contact means consisting of'a pair of. substantially semi-cylindrical brushes a? and 6'8; that, slidably grip the carbon it, the brushes being pressed against the carbon by a helical tension spring 49 that is extended around the brushes Electrical connection is preferably made-to each of the brushes 4i and 48 by sepa-' ratepigtail connections 56- which-inaybe extended to the water connection block. 25 which is grounded. to the frame. of the machine. The brushes t? and 43 may be of copperor a mixture of copper and graphite, the latter having a lower coefficient.- of friction against a copper-coa-ted carbon, and the former having lower coefficient against an .uncoatedcarbon- To support the brushes 4? and as there are provided. extending fromthe rear end or" the water jacket 23 av pair of diametrically disposed extensionsgSZ- and 53- which connecttoand support at their rear end 3,. disc member 5 the latter having a central aperture 55- through which. thecarbon It extends. The extensions 52. and 53 together with the rear face 5? of the water jacket andthe front face 58 of the disc member define a pair of approximately semicylindrical brush slotsdimensioned toslidably receive the brushes 41 and 38;.

Itis well'recognizedthat the resistance of'arc carbons is high, for which reason it has been customary-toprovide them with copper coatings to conduct the current. burns; away cleanat the highly heated tips adjacentthearc in my system. However when my water cooling attachment is not employed the copper. coating sometimes fuses into globulesnear-thetips of the carbon which globules interfere with'the: production of a normal arc. The present system not-only improves the operation with copper;.coa ted, carbons. but enables the use of; uncoated carbons, which are cheaper. is becausetne brushes d! and t8 contact the carbonsrelatively close to the tips thereof and at a constant distance from the tips. The current flows through suchv a short length of the carbon that thevoltage drop therein is relatively small and the water cooling prevents materially heating of the carbons by the power consumed in them.

Theevol-tage drop in. carbon M- remailns substantially constant at all times because the distancethat the current flows through the carbon remains constant. This aids greatly in maintaining the uniformity of the are.

.It is. found. that the water cooling, attache to tr bu te iall to; t e; i ma o This copper coating This a better crater in the positive carbon l4. Specifically, the crater is deeper, larger in diameter, and remains more constant in shape during continuous operation. A deep crater is desirable because it reduces the size of the flame or tail rising from the arc. Changes in size of the crater are undesirable because they produce colors and flicker on the screen.

The use of the invention produces a flatter illumination on the screen than is obtainable with the same lamp without the water cooling. This appears to be due to the fact that the water cooling of the positive carbon adjacent the tip thereof increases the diameter of the luminous crater which constitutes the light source. Thus by comparison of carbon A and B in Fig. 7,. it will be observed that the uncooled carbon A has a longer taper and smaller tip diameter than the water cooled carbon B. This is due to the fact that because carbon B is maintained at a lower temperature, there is less external combustion rearwardly of the tip. By the same token, the copper coating does not burn as far back on the water cooled carbon B as on the uncooled carbon A. Carbon C in Figure '7 is typical of the tip shape of an uncoated carbon that has been used with the water cooler of the invention. It will be observed that it approximates the tip shape of carbon B. Uncoated carbons can be used with perfect satisfaction with my water cooler, whereas it is impossible to use them with the conventional lamp because of the heat generated within the carbon itself by the passage of the current therethrough.

The water cooling attachment reduces the heat waves in the air within the lamp housing and thereby reduces variations in intensity of light on the screen.

Although I am unable to explain the phenomenon, I find that with the water cooling attachment of the invention a larger than normal carbon can be employed without increasing the current and without reducing the light, while markedly increasing the life of the carbon.

Thus tests were run on the same projector using an 8 millimeter coated carbon without water cooling as against a 9 millimeter uncoated carbon with the Water cooler of the invention. In each case, the current was maintained at 70 amperes. tensity on the screen measured 7-10-'7 (left side, center, and right side respectively) whereas with the invention it measured 8-118. Using the smaller, copper coated carbon without the invention, the rate of carbon consumption was 3 minutes 6 seconds per inch, as against 5 minutes 7 seconds for the larger uncoated carbon with the invention. The disparity in carbon cost is much greater, the cost per hour without the invention being 22 cents as against 12 cents with the invention. Tests made under identical conditions (employing the invention) with a 7 millimeter copper coated carbon and only 50 amperes gave light intensity on the screen of 8-l0 8 (better than was obtained with an 8 millimeter carbon and 70 amperes without the invention) a rate of carbon consumption of 6 minutes 12 seconds per inch, and a cost per hour of only 9 cents.

Although for the purpose of explaining the Without the invention, the light ininvention, a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I do not desire to be limited to the exact details shown and described.

I claim:

1. An attachment for a projection arc lamp having positive and negative carbons, a frame, and means on said frame for feeding said carbons longitudinally into arcing relation, said attachment comprising: an annular water jacket dimensioned to surround one of said carbons; contact means including a plurality of contact elements between which said carbon is positioned and means slidably supporting at least one of said contact elements with respect to said water jacket for lateral movement into engagement with said carbon; spring means urging at least one of said contact elements against said carbon for producing electrical contact between said contact elements and said carbons; a bracket attachable to the lamp frame for supporting said water jacket in stationary relation to said frame and in alignment with said carbon adjacent the normal arcing position of the tip thereof; conduit means for conducting water to and from said water jacket; and electric leads for conducting current to said contact means independently of said water jacket.

2. An attachment according to claim 1 in which said contact means is positioned at the rear end of said water jacket remote from the carbon tip; and an annular heat transfer bushing of high thermal conductivity is mounted adjacent the front end of said water jacket in thermally conductive relation therewith and dimensioned to surround said carbon in more closely fitting relation than the water jacket.

3. An attachment according to claim 2 in which said heat transfer bushing is threaded into the front end of said water jacket.

4. An attachment according to claim 3 including a generally U-shaped arc-deflecting member of para-magnetic material held against the front end of said water jacket by said heat transfer bushing, the arms of the U straddling an intermediate portion of the bushing and lying against the front end of the water jacket, and the front end of the bushing extending in front of the Water jacket and having an enlarged head defining a shoulder for clamping the arms of the U-shaped member against the water jacket.

5. An attachment according to claim 1 in which said means for slidably supporting said contact means comprises a pair of diametrically disposed rearwardly extending extensions on said water jacket, and a centrally apertured disc member supported by said extensions and defining therewith and the rear end of said water jacket a pair of substantially semi-cylindrical brush slots lying on opposite sides of said extensions; said contact means comprising a pair of substantially semi-cylindrical brushes positioned in said brush slots; and tension spring means encircling said brushes for retaining them in said slots and urging them against said carbon.

HAROLD I. HUFF.

No references cited.

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