U.S. patent number 3,847,650 [Application Number 05/326,632] was granted by the patent office on 1974-11-12 for flashlamp with improved combustion foil and method of making same.
This patent grant is currently assigned to Airco Inc.. Invention is credited to Eric Gregory, William G. Marancik, Walter J. Shattes.
United States Patent |
3,847,650 |
Gregory , et al. |
November 12, 1974 |
FLASHLAMP WITH IMPROVED COMBUSTION FOIL AND METHOD OF MAKING
SAME
Abstract
A photo flashlamp containing an improved metallic combustible
foil composite comprising a layer of a pyrophoric metal, for
example, yttrium, interposed between two layers of nonpyrophoric
metal, wherein nonpyrophoric metals such as aluminum, hafnium,
magnesium or the like may be used. A method for making a metallic
combustible foil composite comprising depositing, in a vacuum
chamber, a layer of pyrophoric metal on a layer of combustible
nonpyrophoric metal and then depositing a layer of combustible
nonpyrophoric metal on the exposed surface of the pyrophoric metal
layer.
Inventors: |
Gregory; Eric (Bernardsville,
NJ), Marancik; William G. (Basking Ridge, NJ), Shattes;
Walter J. (Bloomfield, NJ) |
Assignee: |
Airco Inc. (Montvale,
NJ)
|
Family
ID: |
26874879 |
Appl.
No.: |
05/326,632 |
Filed: |
January 26, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
178978 |
Sep 9, 1971 |
3749547 |
|
|
|
Current U.S.
Class: |
427/250; 428/649;
428/655; 427/255.19; 427/405; 428/650; 428/660 |
Current CPC
Class: |
F21K
5/02 (20130101); Y10T 428/12771 (20150115); Y10T
428/12729 (20150115); Y10T 428/12736 (20150115); Y10T
428/12806 (20150115) |
Current International
Class: |
F21K
5/08 (20060101); F21K 5/00 (20060101); B44d
001/16 (); C23c 013/02 () |
Field of
Search: |
;117/107,107.1,71M,62
;29/194 ;431/95 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosdol; Leon D.
Assistant Examiner: Pitlick; Harris A.
Attorney, Agent or Firm: Fitzpatrick; Donald J. Bopp; Edmund
W. Mathews; H. Hume
Parent Case Text
This is a division of application Ser. No. 178,978, filed Sept. 9,
1971, U.S. Pat. No. 3,749,547.
Claims
1. A method for producing a combustible composite foil suitable for
use in flashbulbs, comprising the steps of:
vapor depositing on a stainless steel substrate in a vacuum furnace
a layer of combustible non-pyrophoric material wherein said
material is selected from the group consisting of aluminum,
hafnium, magnesium and mixtures and alloys thereof;
vapor depositing a layer of combustible pyrophoric material of
yttrium on said non-pyrophoric layer; and
protecting the exposed surface of the pyrophoric material by
forming a protective layer thereon wherein said layer is selected
from the group consisting of yttrium oxide or a layer of the
non-pyrophoric material before said composite foil is removed from
said vacuum furnace.
2. A method as defined in claim 1 wherein the non-pyrophoric
material is aluminum.
3. A method as defined in claim 1 wherein the non-pyrophoric
material is hafnium.
4. A method as defined in claim 1 wherein the non-pyrophoric
material is magnesium.
5. A method as defined in claim 1, wherein electron beam
bombardment is used to form the vapor of pyrophoric and
non-pyrophoric material.
6. A method as defined in claim 1 wherein the exposed surface of
the pyrophoric material is protected by vapor depositing thereon a
layer of non-pyrophoric material.
7. A method as defined in claim 1 wherein a parting layer of
CaF.sub.2 is vapor deposited on the substrate prior to the
application of the non-pyrophoric material.
8. A method as defined in claim 1 wherein the substrate is caused
to move during the vapor deposition from the point of application
of the non-pyrophoric material to the point of application of the
pyrophoric material whereby the application of material proceeds
substantially continuously.
9. A method as defined in claim 1 wherein the exposed surface of
the pyrophoric material is protected by a gradual and controlled
exposure to the atmosphere whereby a protective oxide coating is
formed on said surface.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed toward a combustible material for photo
flashlamps in composite foil form and to photo flashlamps
containing the novel combustible material.
This invention further pertains to methods for making the novel
metallic combustible foil composite for photo flashlamps.
2. Description of the Prior Art
The source of actinic light in photo flashlamps is the rapid
combustion of filamentary combustible material. Actinic light is
generally defined as light capable of including chemical changes,
as for example in the emulsion of a photographic plate. These
combustible materials are customarily made in the form of wire,
foil, shredded foil or wool. The production and manufacture of
these materials directly affects the ultimate performance of the
flashlamps. For example combustion rate is affected by the
characteristics of the filamentary material such as cross section
area, chemical composition, amount of cold work and product
uniformity.
It is well known that variations in wire diameter may detract from
the uniformity and quality of photo flashlamps made with such
material. Aside from variation in wire diameter, production of such
wire is characterized by considerable breakage and low product
yield during wire drawing. To obviate breakage those skilled in the
art have developed various alloys of combustible metals such as
aluminum-magnesium alloys. These alloys draw better but do not
entirely solve the wire breakage problem attendant to such a
manufacturing process.
Foil, another form of combustible filling for photo flashlamps is
generally produced by hammering or cold rolling material of
relatively thick cross section to foil thickness. The rate of
combustion is considered to depend primarily on thickness; however,
other factors affect combustion rates, such as variation in
chemical analysis and trace elements. The known methods of making
foil have been found troublesome in practice in that it is
difficult to obtain a foil of constant thickness by hammering or
cold rolling. Furthermore, cold rolling adversely affects
electrical and thermal conductivity. It has been found that an
additional annealing step is often necessary to negate the effects
of cold rolling. Making foil in this manner has increased the
overall cost of the material.
With the development of smaller photo flashlamps and mounting a
plurality of small flashlamps in an individual photo flashlamp unit
the shape of the filamentary material changed. The combustible
material commonly used now is in the form of shredded foil. This
material has a width comparable to its thickness and is produced by
shredding foil. If the foil made in accordance with the prior art
techniques exhibits poor thermal conductivity resulting from cold
rolling or has an analysis containing undesirable trace elements
the resultant shredded foil will also be so affected.
SUMMARY OF THE INVENTION
The instant invention involves methods for making an improved
combustible foil which methods avoid the serious drawbacks
described above in connection with the prior art forms of making
flashlamp material. The invention entirely avoids the use of
hammering or cold rolling to produce the foil. In summary the
inventive method employs a unique series of vacuum techniques to
form the desired layers of combustible material. The utilization of
the vacuum furnace in the unique manner to be described hereinbelow
assures both the purity of the layer being deposited, its thickness
and also the interface adherence of the dissimilar layers.
The invention further involves the use of a heretofore unknown
combination of elements in a unique arrangement to produce a
composite foil containing at least one pyrophoric layer at least
partially covered by a non-pyrophoric layer whereby the pyrophoric
layer is protected from contacting the atmosphere surrounding it.
In the preferred embodiment a pyrophoric layer of yttrium is
encased in non-pyrophoric layers of aluminum or the like. In order
for the non-pyrophoric material to be suitable for flash bulb
material it must be combustible and have the desired color
temperature, time to peak and short duration light characteristics.
The particular pyrophoric and non-pyrophoric materials are selected
on the basis of their individual aforementioned characteristics and
the layer thicknesses are also selected to give the desired flash
results.
The instant invention also contemplates utilizing multiple layers
of pyrophoric and non-pyrophoric materials. The combustible foil
made in accordance with this invention may or may not be shredded
depending on the flash bulb requirements.
It is, therefore, an object of this invention to provide vacuum
furnace techniques for the production of a combustible composite
foil suitable for use in a flash bulb.
Another object of this invention is to provide a combustible
composite foil composed of a pyrophoric film protected on at least
one side by a combustible non-pyrophoric film.
A further object of this invention is to provide a metallic
combustible composite composed of at least one layer of yttrium
interposed between layers of a metal selected from aluminum,
hafnium or magnesium.
Another object of this invention is to provide a metallic
combustible composite made by vacuum vapor deposition.
BRIEF DESCRIPTION OF THE DRAWINGS
With the above and related objects in view, this invention will be
more fully understood from the following detailed description when
read in conjunction with the accompanying drawings in which:
FIG. 1 is an elevational view, partly in section, of a photo
flashlamp containing the unique material made in accordance with
the present invention.
FIG. 2 is a representation of a cross section (partly broken away)
of a combustible foil made in accordance with this invention.
FIG. 3 is a representation of a cross section of a combustible foil
having a plurality of pyrophoric layers and made in accordance with
this invention.
FIG. 4 is an elevational view, partly broken away, partly in
section, of one form of vacuum vapor deposition apparatus for
producing a composite foil in accordance with this invention.
FIG. 5 is an elevation of a further apparatus for carrying out the
methods of the instant invention to produce the unique combustible
foil.
DESCRIPTION OF PREFERRED EMBODIMENT
The invention can best be explained by reference to the drawing
wherein FIG. 1 represents a conventional flashlamp containing the
unique composite foil made in accordance with the present
invention. The lamp comprises a hermetically sealed glass envelope
2 containing a combustion supporting atmosphere (usually
pressurized), such as oxygen 3 and a shredded metallic combustible
composite 4 capable of producing actinic light. In one form of the
instant invention the combustible composite 4 is composed of a
pyrophoric metallic layer interposed between non-pyrophoric
metallic layers. The envelope 2 may be internally coated with a
blue lacquer 5 in accordance with known practice. The thickness of
the lacquer layer depends on the color temperature characteristics
desired from the flashbulb. For outdoor daylight photography, high
color temperature characteristics are desired. One well-known
drawback to the application of the lacquer is that it absorbs light
and thereby reduces the total level of illumination created by the
bulb.
A typical lamp, such as shown in FIG. 1, further contains an
ignition mechanism consisting of an explosive paste 6 applied to
the terminals of the current supply wires 7 and 7' and filament 8.
The current supply wires are supported within envelope 2 by support
means 9. The current supply wires are connected to conventional
base contacts (not shown) contained within base 10 in a manner well
known in the art. The current supply wires transmit an electrical
current through filament 8 causing the ignition of paste 6. The
paste in turn ignites the composite combustible foil in the oxygen
atmosphere.
The present invention may be employed in any number of photo
flashlamp configurations such as a multiple lamp assembly, as shown
in U.S. Pat. No. 3,315,070, issued to Pfefferle.
FIG. 2 is a graphical representation of a laminated composite 11
made in accordance with one form of the present invention and
usable as the combustible composite in the bulb of FIG. 1.
Composite 11 consists of a layer of a pyrophoric material 14, such
as yttrium, interposed between layers 12 and 16 of a non-pyrophoric
material such as aluminum, hafnium, magnesium, or the like, or
combinations thereof.
The use of pyrophoric materials in flashlamp is well known;
however, in the applications heretofore known the pyrophoric
material was placed in an evacuated atmosphere in the bulb to
prevent ignition. When it was desired to ignite the material, the
bulb was punctured or the atmosphere was in some way allowed to
contact the pyrophoric material. When this occurred, the material
flashed producing the desired light. Producing such bulbs was a
costly undertaking and the pyrophoric materials heretofore used
have not produced the desired results.
The instant invention contemplates the use of yttrium foil as the
basic pyrophoric material. This material produces highly acceptable
actinic light and has suitable color temperature and other
characteristics. The invention involves manufacturing such foil by
the use of vacuum vapor deposition techniques. These techniques are
used in order to achieve accurate film thickness and avoid film
contamination with impurities. It was also recognized that such
methods would avoid the problems encountered when films are formed
by hammering or cold rolling.
No difficulty was encountered in forming yttrium layers by vapor
deposition techniques; however, it was found that when the layers,
which were of approximately 1.0 mil. in thickness, were suddenly
exposed to the atmosphere, they immediately flashed due to the
rapid exposure to the air. Thus when the yttrium foil was stripped
from the substrate or when the vacuum was rapidly broken, the foil
ignited and was consumed. In order to prevent the ignition of the
yttrium foil, the pyrophoric material was encompassed in a layer of
non-pyrophoric material whereby the surface of the pyrophoric
material was protected from the atmosphere. Such a composite could,
therefore, be removed from a vacuum furnace or other place of
manufacture and modified so as to be in a form suitable for
insertion into a flashbulb. In accordance with known techniques the
composite foil could be shredded and then used in the bulb. It
would seem that shredding of the composite foil would expose the
pyrophoric material to the atmosphere; however, the non-pyrophoric
material is deformed in the shredding process and is pinched over
the pyrophoric material to maintain a layer thereover and prevent
appreciable exposure to the atmosphere. Furthermore, any small
exposed portion of the pyrophoric material, such as the edges,
would be protected by an oxide and would not ignite
spontaneously.
The representation in FIG. 2 shows a typical foil in cross section.
In one embodiment of the invention a composite foil of aluminum
layers surrounding a layer of yttrium was successfully produced.
The aluminum layers were each approximately 0.1-0.2 mil. in
thickness and the yttrium layer approximately 0.5-0.6 mil. in
thickness. The thicknesses of the layers may be correlated to
provide the desired flashbulb characteristics. Aluminum has long
been used as a flashbulb material and its characteristics are
well-known. By combining this material with yttrium which has great
capacity for producing actinic light and high temperature color
characteristics, a new flexibility is afforded flashbulb
manufacturers and photographers. In addition to using aluminum,
this invention also contemplates using other combustible
non-pyrophoric foils to encompass the pyrophoric material. For
example, hafnium and magnesium may be used. In addition, mixtures
and alloys of the aforementioned materials may be used. It is also
contemplated that different non-pyrophorics on opposite sides of
the pyrophoric layer will be used. Such non-pyrophorics must be
combustible and, in addition, are capable of being vapor deposited
on the pyrophoric material.
It is also within the scope of the invention to use other than
planar layers of material. Thus the pyrophoric material may be in
the form of wire, rods, arcuate shapes, etc. The non-pyrophoric
material may be deposited to cover either all or only a part of the
external surface of the pyrophoric material. In addition, as
discussed above, it is contemplated that more than one type of
non-pyrophoric material to cover a pyrophoric layer will be used.
Thus aluminum could be applied to one side and magnesium to
another.
Although we have referred to yttrium as our preferred pyrophoric
material we also contemplate using other pyrophoric materials of
similar character. Such material would have good capability for
producing actinic light and be vapor depositable.
FIG. 3 is a cross section of a composite consisting of five layers
of material. Yttrium layers are designated by 21, 23 and magnesium
layers by 25, 27, 29. In composing such composite layers care must
be taken to select materials which have desired and compatible
burning characteristics. The thickness of the individual layers and
the total thickness of the composite foil regulates the burning
rate of the composite. The outer layer of the composite foil may be
of a material different from that contained in the inner layers.
The outer layer material should generally be selected on the basis
of ease of ignition. Thus magnesium has been selected as a most
suitable material for the outer layer. The inner layers of material
must also be selected to create the desired burning rate. Volatile
materials such as magnesium and aluminum may, therefore, be
interspersed as the interior layers in concert with the pyrophoric
layer or layers. By layering the materials as desired, the
combustion rate of the composite can be regulated.
The embodiment shown in FIG. 3 is only representative of one
possible composite of pyrophoric and non-pyrophoric layers. Other
combinations of multiple layering of the desired pyrophoric and
non-pyrophoric layers are within the scope of this invention.
pg,10
Having described the characteristics of the novel composite foil,
we will now describe in greater detail the apparatus and methods
used to make the composite.
In FIG. 4 there is illustrated in pictorial form an apparatus
suitable for making the subject composite. The apparatus comprises
an electron beam furnace 15 which includes an outer enclosure 17
which is constructed to permit evacuation to very low pressures via
a conduit 19. This conduit leads to a suitable vacuum pump (not
shown).
Supported in the vacuum chamber are a plurality of hearths 20, 22,
24 with associated electron guns 26, 28, 30 which are capable of
producing sufficient electron bombardment 26a, 28a, 30a
respectively to heat the substance in each hearth or crucible to
the desired temperature for evaporation. Electron guns of any
suitable construction may be employed. Suitable control systems may
be used to regulate the evaporation rate utilizing feedback from
monitors (not shown), to proportionately increase or decrease the
power being supplied to the associated electron gun in order to
obtain evaporation of the substance in the associated crucible at
precisely the desired rate.
Electron beam bombardment has proven to be the most satisfactory
technique for heating the material contained within the crucibles.
However, other techniques such as resistance heating, induction
heating, or the like may be employed without departing from the
spirit and scope of this invention.
Spaced above the crucibles and supported in the chamber is metallic
substrate 32. The substrate is preheated by heating means 34 to at
least approximately one-third to one-half of the absolute melting
point of the material to be deposited in order to improve the
metallic properties of the resultant vapor deposited coating. The
selection of the pre-heat temperature depends upon the material to
be deposited. Interposed between substrate 32 and the crucibles is
a shutter 35. The shutter is movable about a vertical axis so that
it can be moved over the substrate to shield the same from the
crucibles.
Deposition is controlled by activating the electron beam gun
adjacent to the crucible containing the material to be evaporated.
The shutter 35 remains over the substrate until the desired
evaporation rate is achieved. Then the shutter is swung away and
the desired thickness of material is deposited on the substrate. At
that time the shutter is swung back over the product and the gun is
turned off. In this manner the crucibles are sequentially activated
to place the desired layers of material on the substrate. In one
form of the invention a layer of aluminum is first applied to a
substrate which was previously treated with a parting agent, a
layer of yttrium is then applied and finally a layer of aluminum is
again applied. The composite foil is then stripped from the
substrate by known techniques.
In accordance with the above principles, a composite foil in an
apparatus such as schematically described in FIG. 4 was
successfully produced. This operation will now be described in
detail; however, it should be understood that this example is
merely illustrative of one embodiment of the invention and is not
to be considered as in any way limiting the scope of the invention
as defined in the following claims.
A stainless steel substrate was positioned within the chamber 15 as
illustrated by the reference numeral 32. The chamber was evacuated
to a pressure of approximately 10.sup..sup.-5 to 10.sup..sup.-6
torr.
Crucible 20, containing the parting agent calcium fluoride, was
energized by applying a power level of 0.5 kw to electron beam gun
26. When the CaF.sub.2 was heated to the desired temperature for
evaporation, the shutter 35 was swung away from the substrate 32,
exposing the substrate to vapor deposition. A layer of CaF.sub.2,
approximately 1000-3000 A in thickness was then applied. The
thickness of the applied layer was determined by the power level
applied to the gun correlated with the time of deposition. The
shutter was then moved to mask the substrate and the gun 26
de-energized. The temperature of the substrate and parting layer
was then adjusted to 800.degree.F by heater 34.
Approximately 2 kw of power was then supplied to gun 28 so as to
evaporate the aluminum metal contained within the crucible 22. The
distance from the crucible to the substrate was about 13 inches and
it was determined that at this power level a deposit of aluminum
would build up to from 0.1 to 0.2 mil. in about 1 minute. When the
aluminum reached its vaporization temperature the shutter 35 was
swung away and aluminum was deposited for one minute resulting in a
layer thickness of 0.1 to 0.2 mil. The shutter then masked the
composite and the gun 28 was shut down.
Approximately 6 kw of power was then supplied to the electron beam
gun 30 so as to heat and then evaporate yttrium metal contained
within the crucible 24. The source to substrate distance was
maintained at approximately 13 inches. Deposition time to deposit
about 1 mil of yttrium at these conditions was approximately at 10
to 15 minutes. When the yttrium reached its vaporization
temperature the shutter 35 was swung away from the substrate and a
coating thickness of approximately 0.5 to 0.6 mil of yttrium was
deposited. Shutter 35 was then rotated to close off the path of the
vapor and the electron beam gun 30 power level was turned off.
Another 0.1 to 0.2 mil layer of aluminum was then deposited on the
yttrium layer from crucible 22 in the manner as hereinbefore
described.
The substrate was then allowed to cool and the vacuum broken in the
furnace. The resultant composite, approximately 0.7 to 1.0 mil.
thick was then stripped from the substrate in a manner well known
in the art. The material did not flash when exposed to the
atmosphere and was of a quality suitable for shredding and usage as
a combustible foil in a flashbulb.
The apparatus of FIG. 4 could also be used for the deposition of
additional layers of material such as described above in connection
with the embodiment shown in FIG. 3. Magnesium and/or hafnium
layers could, therefore, be deposited in the same manner in
combination with a pyrophoric material to produce the desired
foil.
In FIG. 5 there is shown a still further embodiment of an apparatus
for forming the novel composite foil. This apparatus is designed
for depositing a series of layers of materials on a continuously
moving substrate. The apparatus includes an electron beam furnace
41 having an outer enclosure 42 adapted to maintain the desired
vacuum. The connection 44 is associated with proper equipment,
vacuum pump, etc. for pulling and maintaining a desired vacuum.
The substrate 40, which may be a belt of stainless steel or other
desired material, is trained around a series of pulleys, at least
one of which has a power driven connection.
Separate heaters 78 are positioned over the substrate at each
evaporation region so as to heat the substrate to the desired
temperature for deposition of each layer.
Supported in the chamber on hearth 46 are a series of crucibles 48,
50, 52 and 54 containing the desired materials 56, 58, 60 and
62.
Electron beam generators 64, 64a, 64b and 64c produce electron
beams 66, 66a, 66b, and 66c which are directed on to the top of
these molten baths for bombardment heating thereof in order to
maintain said baths in a molten state. Shields or baffles 68 are
located between crucibles 48, 50, 52 and 54 respectively to
maintain vapors 70, 72, 74 and 76 in a pure, uncontaminated
state.
As substrate 40 passes over crucible 48 a vaporized parting agent
such as calcium fluoride or the like is emitted from molten bath 56
and deposited upon the substrate, forming a thin coating of
approximately 1000 to 3000 A in thickness thereupon. As the
substrate passes over crucible 50, a nonpyrophoric metallic vapor
72 emitted from molten bath 58, for example, aluminum, hafnium,
magnesium or the like is deposited upon the substrate forming a
coating thereupon. As the coated substrate then passes over
crucible 52 a vapor 74 emitted from molten bath 60, for example,
yttrium is deposited upon the exposed surface of the previously
deposited non-pyrophoric metal, and forms a coating of yttrium
thereon. The coated substrate then passes over crucible 54 and a
non-pyrophoric metallic vapor 76 emitted from molten bath 62 is
deposited upon the yttrium layer. Thus a substrate may be coated
sequentially with pyrophoric and non-pyrophoric layers of material
to produce a laminated combustible foil uniquely suited for use in
flashbulbs.
The formed composite is thereafter stripped from the substrate in a
manner well known to those skilled in the art. Such a process could
be continuous and therefore avoid the problems associated with
batch operations.
The thickness of the various deposited layers can be varied thereby
permitting the composite to exhibit different combustion rates.
Varying coating thickness can be accomplished by adjusting the
power level of the guns, by altering the speed at which the
substrate travels or by moving the baffles, thereby altering the
exposure time in the respective vapor zones.
The apparatus and methods which are pictorially represented in FIG.
5 can also be used to apply additional layers of materials to the
composite.
In addition to the embodiments of the invention discussed above, it
has also been found that the unique combination of pyrophoric and
non-pyrophoric layers may occur in still another form. It was found
that when a pure yttrium layer, whose external surface had oxidized
to the point where flashing did not occur, was stripped from a
substrate, the quick exposure to the atmosphere of the non-oxidized
surface resulted in flashing of the material. Therefore, it was
necessary to develop a process whereby yttrium could be deposited
on a layer of combustible non-pyrophoric material in a manner that
permits stripping the resultant composite without flashing. In this
embodiment the exposed surface of the yttrium must be allowed to
oxidize slowly such as by very gradual exposure to oxygen or air,
so that it prevents pyrophoric flashing. This can be accomplished
by allowing the air to enter the vacuum chamber slowly. Thus one
side of the pyrophoric material will be protected by an oxide and
the other by a vapor deposited layer of non-pyrophoric material. We
claim:
* * * * *