Note: Descriptions are shown in the official language in which they were submitted.
~Z~23~
This invention relates to gas mantle technology
and, in particular, to a process of forming a mantle-support
tube subassembly.
This application is a divisional application of
Canadian application Serial No. 434,225, filed August 9
1983.
Incandescent mantles have been prepared by
impregnating yarns or sleeves of rayon or other organic
fiber with a thorium containing compound, and burning off
the organic fiber to produce a thoria mantle. Such gas
mantles are typically heated to incandescent temperature by
a gas flame and provide effective light sources. It is well
know that such mantles are extremely fragile and subject to
destruction or damage by accidental jarring or other
relatively mild stresses.
The parent application describes an improved gas
mantle structure composed substantially en-tirely of fibers
of oxides of one or more of the metals thorium, zirconium,
yttrium, hafnium, aluminum, magnesium, calcium, cerium and
other rare earth metals, and that have substantially greater
shock load resistance than prior mantles. While such mantle
shock resistance is a function of factors such as mantle
size, shape, mechanical construction (yarn size, type of
weave, open area, etc.) and mantle support, a useful shock
resistance figure of merit for a cantilever supported mantle
whose length and diameter dimensions are similar is
provided, to a first order approximation, by the product of
the shock load (in g's) thaw the mantle withstands and the
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unsupported length (in meters) of the mantle. Mantle
structures in accordance with this description preferably
have a shock resistance figure of merit of at least three g-
meters and withstand shock loads in excess of 600 g's.
Preferred gas mantle structures are composed of
oxides of a rare earth metal, hafnium, thorium, yttrium or
zirconium as a hos-t, oxides of one or more rare earth metals
different from the host metal as a radiation modifying
dopant, and oxides of one or more metals different from the
host metal such as aluminum, beryllium, magnesium, calcium,
yttrium or zirconium as a strengthening dopant. A
particular gas mantle structure includes a self-supporting
fabric of metal oxide fibers that distort elastically in a
configuration that includes a dome portion that defines a
volume of about 0.1 cubic centimeter with a skirt portion
that is shrink secured to a ceramic support tube, the mantle
fabric being composed essentially entirely of thoria, with
about two weight percent ceria and about one weight percent
alumina. The metal oxide fibers of that mantle, after
heating in an isobutane flame, have a microstructure with a
significant number of grains of dimenslons in the order of
one to two micrometers, and well-delineated grain
boundaries, and are efficient in converting thermal energy
to radiant energy. The flexibility, or ability of the
mantle fabric to undergo considerable elastic distortion
without fracture, is evidence of the high strength of this
improved material.
In mantles described in the parent application,
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the fabric is knitted in such a way that the yarn yields aself-supporting dome of metal oxide fibers which is heated
to incandescence by a gas flame. This dome of metal oxide
fibers can be distorted to a large degree by an external
force; in such distortion the yarn filaments bend or twist
elastically, and when the force is removed they regain their
original shape, restoring the initial configuration of the
mantle. Mantles in accordance with this description are
able to undergo much larger elastic distortions without
fracture than mantles of similar weaves or knits prepared by
conventional methods.
The elementary metal oxide fibers of such mantles
have a cross-sectional dimension of less than ten
micrometers (approximately one third the cross-sectional
dimension of the precursor organic fiber), the mantle fabric
has greater than fifty percent open area, and, in the dome
configuration that defines a volume of about 0.1 cubic
centimeter and with a skirt portion that is shrink secured
to a heat-resistant support tube, the mantle withstands
shock loads in excess of six hundred g's. The shock load is
the force experienced by the unsupported mantle because of
rapid deceleration on impact of the support tube against a
stop. This load is often expressed in g's, where g is the
acceleration due to gravity. Thus7 impact loads can involve
deceleration forces substantially in excess of the force of
gravity. As indicated above, such mantles preferably have
shock resistance figures of merit (as above defined) greater
than three g-meters.
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While such mantles are useful in a variety of
devices, they are particularly useful in portable light
sources of the flashlight type which in accordance with
another aspect of the parent application have a handle
portion sized to be grasped in a hand, a supply of fuel
(preferably a liquid hydrocarbon such as isobutane, propane,
gasoline or the like) in the handle portion, and a head
portion in which the mantle is mounted at the focus of
reflector structure for forming light emitted from the
mantle into a beam. A fuel supply conduit interconnects the
fuel supply and the mantle, the flashlight also includes a
fuel control for controlling the flow of fuel through the
conduit to the mantle and an igniter mechanism for igniting
the fuel to produce flame and cause the mantle to emit
light. Preferably, such light sources have wattage ratings
of less than fifty watts; include thoria mantles that have
been heated to at least l5Q0C; and have luminous
efficiencies of at least about one-half lumen per watt. In
a particular embodiment the liquid fuel is isobutane and
interposed in the conduit is a pressure regulator for
supplying fuel at a pressure of less than 3 psi and an
aspirator mechanism for supplying an air fuel mixture to the
mantle at approximately stoichiometric ratio. The fuel
(vapor) flow rate (at STP) is about seven cubic centimeters
per minute, the wattage rating is about fourteen, and the
efficiency is about one lumen per watt.
In accordance with another aspect of the parent
application, there is provided an improved process for
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producing a sturdy refractory metal oxide article which
includes the steps of heating a substrate of organic
material impregnated with a metal compound to increase at a
controlled rate the temperature of the impregnated substrate
to a temperature sufficiently high to thermally decompose
the metal compound as a step in the conversion of the metal
compound to a refractory metal oxide; further heating the
impregnated substrate to decompose and remove the organic
material from the impregnated substrate and to complete the
conversion of the metal compound to the refractory metal
oxide so that a metal oxide replica of the substrate
remains; and further heating the metal oxide replica to
sinter and densify the metal oxide replica such that the
densified metal oxide replica has a strength (shock
resistance) figure of merit of at least three g-meters,
which strength is retained after the replica has been heated
to 1500C, the resulting metal oxide article in the above
described configuration being capable of withstanding shock
forces of at least about 300g's, in contrast with more
~0 fragile prior art metal oxide replica structures. The exact
choice of reaction conditions depends on the shape and
chemical composition of the starting organic material and on
the metal compound or metal compounds employed in the
impregnation step. A preferred organic material for use in
the process for producing metal oxide articles of the
invention is low twist rayon yarn. However, other absorbant
materials that absorb adequate amounts of the imbibing
solution and that thermally decompose without melting, such
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as cotton, wool, silk, and certain synthetic materials may
also be used. The metal comyound and organic substrate
material have interaction characteristics such that (in a
suitable processing sequence in accordance with the
invention) the metal compound undergoes thermal conversion
to a skeletal substrate replica (with healable fissures or
rifts) before -thermal decomposition of the organic material
is completed, the further resulting gaseous decomposition
products being removed from the replica through the rifts.
A preferred metal compound is a nitrate, but other compounds
may also be used. The metal compound can be impregnated
into the organic material (uniformly distributed within the
fibrils) by any of several methods. Articles of various
configurations may be formed in accordance with the
invention, such metal oxide articles having a number of uses
in addition to use as gas mantles.
In a preferred process, the absorbant substrate is
a fabric, for example, a tubular sleeve that is knitted from
continuous multi~filament (40-60 filaments of about 17-20
micrometers diameter) low twist, low tenacity (highly
reticulated) viscose rayon yarn of about 150 denier to
produce a fabric with greater than 50 percent open area.
This fabric substrate is imbibed in an aqueous solution of
nitrate salts, the imbibed substrate having a white color
and a shiny texture.
The imbibed fabric substrate is then thermally
processed under controlled conditions. Initially, the
temperature of the substrate is gradually increased in an
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atmosphere with little or no oxygen present (preferably an
oxygen partial pressure of less than two mm Hg). When a
temperatureof 130C to 170C is reached! a quite vigorous
reaction occurs, involving an interaction between the
nitrate salts and the cellulosic substrate, which is
visually evidenced by a color change that starts at some
location in the substrate and produces a front which
separates a tan color from the shiny white color and
advances through the substrate in a few seconds. This
reaction is termed a "nitrate burn" and involves a partial
oxidation of the cellulose of the substrate by the
decomposition products of the nitrate ions - the gases
produced by the thermal decomposition of the nitrate salts
being strongly oxidizing and reacting with the cellulose.
The complex reaction evolves heat and a large amount of gas
(including carbon monoxide and oxides of nitrogen), the
evolved carbon monoxide being evidence that a combustion
reaction occurred. Differential scanning calorimeter data
shows this reaction to be rapid and exothermic. Rapid
denitration appears important to the subsequent formation of
mantles that are strong after heating to 1600C. and above.
After the nitrate burn, the substrate is heated in
an atmosphere that contains an increased amount of oxygen
(preferably an oxygen partial pressure greater than twenty
mm Hg) during which the remaining cellulose is pyrolyzed and
the residual carbon is removed by oxidation. During this
continued heating, there is some evidence that an
intermediate compound (which may be thorium oxynitrite (ThO
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(N02)2)) is formed, the gas evolution slows, but continues
to about 475C where the replica is thorium dioxide. The
temperature is further increased to sinter and densify the
metal oxide particles. Beneficial sintering and
densification of the metal oxide replica continue to occur
until temperatures of at least about 1500C are reached.
The resul-ting metal oxide product has a strength that is
substantially greater than the strength of prior art metal
oxide products of similar configuration.
Without intending to be bound by the same, the
theory and mechanism of this process appear to be as
follows: When a fabric of organic polymeric material, such
as cellulose, is immersed in an aqueous solution of a metal
compound, it swells and the dissolved metal compound enters
the swollen regions. Upon drying, the metal compound in the
fibers is effectively suspended and separated as small
islands. The heating of the impregnated organic material
under controlled conditions converts the metal compound to
an oxide structure that is a replica of the organic fabric
material, the oxide fibers of the replica strùcture having
healable rifts or fissures. Gaseous products which are
evolved upon further thermal decomposition of the organic
material are released through the healable fissures without
significant impairment of the oxide replica. Further
heating of the replica to higher temperatures increases the
strength of the replica. It is believed that this healing
and strengthening action involves solid state diffusion
which blunts or rounds the roots of the crack-like fissures
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or rifts, thus reducing their severity. In some cases, the
rifts may heal entirely.
In particular processes, the fabric is imbibed in
an aqueous solution of nitrate salts that have a molar
concentration of less than 1.4, preferably in the range of
007-l.0 molar, particular compositions containing thorium
nitrate9 cerium nitrate and aluminum nitrate in
concentrations such that the final sintered product contains
ceria in the amount of 0.5 - 3.0 weight percent and alumina
in the amount of 0.1 - 2.0 weight percent, and a particular
composition having about two percent by weight cerium oxide
and about one percent by weight aluminum oxide in the final
sintered product. The rayon fabric sleeve is imbibed in the
metal nitrate solution at about 20C for about ten minutes
and then is centrifuged to remove excess solution from the
surface of the fibers.
The impregnated organic fiber sleeve is then
shaped with the use of a shaping form into the desired
configuration, in a particular case a mantle sock, and then
dried. The shaped impregnated dried fabric sock is then
positioned on a support post of a processing fixture with
the sock surrounding a tube of heat-resistant material such
as stainless steel or ceramic carried on the support post
and with the closed end of the sock spaced a predetermined
distance above the upper end of the tube; and thermally
processed under controlled conditions as described above to
initiate conversion of the metal nitrates to metal oxides in
a denitration step, then to complete the decomposition of
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they rayon Eibers and the conversion to metal oxide, the
resulting gases being evolved through the fissures without
impairing the healability characteristics of fissure-type
defects in the metal oxide, and then to heat the resulting
metal oxide Eabric replica to temperatures of at least about
1000C to sinter and densify the metal oxide particles. In
one preferred product, the resulting metal oxide mantle is
composed essentially entirely of thoria, ceria and alumina.
Specifically9 the invention relates to a process
of forming a mantle - support tube subassembly comprising
the steps of supporting a fabric sock of organic material
impregnated with a metal compound on a fixture that carries
a support tube so that the closed end of the sock is a
predetermined distance from the end of the support tube with
the skirt of the sock overlying the support tube, and
heating the fabric sock to convert the metal compound to a
refractory metal oxide and to decompose and remove the
organic material from the sock and to shrink the sock until
the skirt of the sock is shrink-secured against the outer
surface of the support tube to form the mantle - support
tube subassembly.
The process may include the step of applying an
inorganic cement such as sodium silicate to the support tube
prior to the heating step and the sodium silicate may be
prefired by heating the support tube to a temperature of at
least 300C.
The following processes for producing thorium
oxide fibers from impregnated cellulosic fibers employ
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examples of preferred reaction conditions. In each process,
an open area type of absorbant cellulosic substrate is
impregnated by immersing it in an aqueous solution of
thorium nitrate. Excess solution is then carefully removed
and the impregnated substrate is formed (if desired) and
dried. In a first process, the denitration step is carried
out by heating the impregnated substrate in a flowing inert
gas atmosphere while raising the temperature at a uniform
rate (preferably at least 2C per minute) from room
temperature to 320C during which interval denitration
occurs (approximately at 150C); then an oxygen flow (about
three percent of the nitrogen flow) is added and the chamber
temperature is held at 320C for a soaking interval during
which time the cellulosic substrate pyrolyses and oxidizes
until no visual evidence of residual carbon remains; at the
end of that soaking interval the oxygen flow is increased to
about twenty-five percent of the nitrogen flow and the
chamber temperature is rapidly increased to 900C to sinter
and densify the metal oxide particles; and then the
resulting porous thoria structure is heated to a temperature
of about 1600C in an isobutane flame for about five minutes
for further thoria particle sintering and densification.
In a second process, the denitration step is
carried out by heating an impregnated porous fabric sleeve
in a low pressure environment, the temperature being
gradually increased from 100C to 200C over an interval of
about twenty minutes during which interval denitration
occurs; the denitrated fabric is then heated in an air
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atmosphere with temperature gradually increased from 240C
to 450C over an interval of about one hour during which
interval the rayon fabric is pyrolysed and the residual
carbon is removed by oxidization; the resulting metal oxide
replica is then heated at a temperature of about 1000C for
ten minutes; and finally the metal oxide replica is heated
at a temperature of about 1600C for five minutes.
Such metal oxide fabrics, in visual appearance,
substantially retain characteristic physical textile
attributes of their precursor organic fabrics, although they
are substantially reduced in dimension. Those metal oxide
fabrics are characterized by relatively high density,
strength (preferrably a shock resistance figure of merit of
at least three g-meters) and flexibility, and in preferred
mantle configurations are efficient radiation sources (a
luminous efficiellcy of at least one-half lumen per watt and
an output of at least ten lumens with a one gram per hour
isobutane flow rate) and withstand impact loads of several
hundred g's.
Other features and advantages will be seen as the
following description of particular embodiments progresses,
in conjunction with the drawings, in which:
Fig. 1 is a diagrammatic view of a portable light
source of the flashlight type;
Fig. 2 is an enlarged view of the mantle and its
support employed in the flashlight of Fig. l;
Fig. 3 is a view of a portion of a fixture used in
the manufacture of the mantle shown in Fig. 2;
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Figs. 4 and 5 are graphs indicating particular
processing sequences for the manufacture of mantles in
accordance with the invention.
Description of Particular Embodiments
Shown in Fig. 1 is a flashlight 10 that has a
handle portion 12 and a head portion 14. Disposed in handle
12 is a container 16 of isobutane fuel -- a charge of twenty
grams with an equilibrium vapor pressure at room temperature
of thirty psi -- toge-ther with pressure regulator 20 to
provide two psi fuel pressure at regulator outlet orifice
(0~05 millimeter diameter). Valve 18 controls the flow of
gas through regulator 20 and venturi 22 (that has a throat
of about one millimeter diameter and provides an air fuel
ratio of about 30:1) to support tube 28 which carries metal
oxide fiber mantle 30. Reflector 32 directs radiation from
mantle 30 in a collimated beam of light through lens 34.
Control switch 36 operates valve 20 to provide flows of fuel
to venturi 22 and to pilot tube 38. Igniter 40 includes
flint wheel 42 or other suitable igniter such as a
piezoelectric device that is operated by lever 44 to ignite
pilot fuel which in turn ignites the main flow of fuel in
mantle 30. The flashlight has a rating of about fourteen
watts, consumes fuel at a rate of about one gram per hour (a
vapor flow rate of about seven cubic centimeters per minute)
and has a luminous efficiency of about one lumen per watt.
Further details of the construction of this flashlight may
be had with reference to copending Canadian Patent
application serial number 432,488 filed July 14, 1983 in the
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names of Walter J. Diederich and George P. Gruner, entitledTWO-STAG~ PRESSURE REGULATOR, and assigned to the same
assignee as this application.
Further details of mantle 30 and its support tube
28 may be seen with reference to Fig. 2. Support tube 28 is
of mullite and has a length of about 25 millimeters, an
outer diameter of about five millimeters, and an inner
diameter of about three millimeters. Mantle 30 is a self-
supporting structure of metal oxide fiber fabric that
10 defines a hollow chamber of about seventy cubic millimeters
volume with its tip 50 about one half centimeter above the
upper end surface 52 of support tube 28. The skirt 54 of
the mantle fabric (about one-half centimeter in length) is
firmly secured (shrink fitted) to the outer surface of
support tube 28. The shape of the outer surface of support
tube 28 may be varied to achieve desired mantle
configurations, for example a fluted mantle sidewall shape.
Auxiliary means such as an inorganic cement 56 or a recess
may optionally be used to enhance the securing of mantle 30
20 to tube 28.
The mantle fabric is formed of metal oxide
multifilarnent strands 60 in an open knit array with openings
62 such that the open area of the fabric is about 60%. The
cross-sectional dimensions of the individual fibers of
strands 60 are in the range of about 5-lO micrometers and
the strands 60 have cross-sectional dimensions in the order
of about 0.1 millimeter with the openings 62 having
dimensions of about 0.5 millimeter.
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The fallowing is a process for manufacturing
mantle 30. Continuous low twist, low tenacity (highly
reticulated), viscose rayon yarn 60 (150 denier/42 filament)
is knitted into a continuous tubular sleeve using a Lamb
circular string knitter (Model ST3A/ZA) with a 7/8 inch
diameter arbor and 24 needle capaci-ty using 14 needles in
the arbor in the sequence:
NNONONONNONONNONONONNONO, where "N" represents a slot filled
with a needle and "O" represents an open slot. The yarn is
knitted with tension on both the yarn and the knitted sleeve
to attain nine stitches per linear inch of tensioned sleeve,,
and the continuous length of knitted sleeve is wound onto a
take-up spool.
An imbibing solution is formed by dissolving (1)
hydrated thorium nitrate (Th(N03)4.4 H20) powder (reagent
grade); (2) hydrated cerium nitrate (Ce(N03)3.6 H20) powder
(reagent grade); and (3) hydrated aluminum nitrate
(Al(N03)3.9 H20) powder (reagent grade) in distilled water
(together with a small amount of a non-ionic wetting agent
20 such as Triton X-100) to provide a solution 0.8 molar in
thorium nitrate, 0.03 molar in cerium nitrate and 0.03 molar
in aluminum nitrate.
knitted rayon sleeve units, in lengths of about
thirty centimeters, are immersed for about ten minutes in
the imbibing solution at room temperature, with optional
gentle agitation to promote penetration of the imbibing
solution into the rayon fibers. After the ten minute
imbibition, the sleeves are removed from the solution,
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squeeze dried and then transferred to plastic tubes of a
centrifuge. The sleeves are then centrifuged for ten
minutes at about 200g's to remove surface liquid. It is
convenient to secure a metal screen halfway from the bottom
of each centrifuge tube so that liquid does not rewet the
surface of the sleeve during or after centrifugation.
After centrifugation, the imbibed sleeves are
formed intomantle socks with aid of a Teflon sock-shaping
rod that is about fourteen millimeters in diameter and has a
hemispherical end. Each imbibed sleeve is cut into lengths
of about seven centimeters, slipped over the shaping rod,
and tied off at the hemispherical end of the shaping rod
with a piece of treated yarn unraveled from the bottom of
the know sleeve. One loop of yarn is passed around the knot
sleeve just above the hemispherical top of the rod and vied
with a double overhand knot. The free ends of the yarn and
of the sleeve above the knot are cut as short as possible.
The shaped socks 70 are then dried with a flow of hot (about
90C) air, slipped off the shaping rods, cut to lenvths of
about 3.6 centimeters, and then hung on a fixture that
includes mullite base 72 and a series of upstanding mullite
posts 74 (spaced at abou-t three centimeter intervals on
base 72. Each post 74 has adiameter of about 3 millimeters
and a length of about 3.7 centimeter and receives a support
tube 28 and spacer 76 as indicated in Fig. 3, the top of
tube 28 being spaced about five millimeters below the top of
post 7~. Optionally a ring 78 of sodium silicate that has
been pretreated by heating tube 28 Jo about 900C may be
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carried by tube 28 as indicated in Fig. 3.
The fixture with knitted imbibed socks 70 hungover the support sleeves 28 on the fixture posts 74 is then
subjected to a firing procedure to convert the metal nitrate
imbibed cellulosic mantle socks into light emitting and
mechanically strong metal oxide mantles.
In the processing sequence illustrated in Fig. 4,
the fixture with socks 70 is placed in a tubular oven that
is about 1.2 meters in length and about five centimeters in
inner diameter. At ambient temperature (about 25C (point
80)), the oven is flushed with tank nitrogen at a flow rate
of 200 cubic centimeters per minute (a flow velocity of
about ten centimeters per minute), and with this inert
atmospher in the oven, the oven temperature is increased at
a rate of four degrees Celsius per minute as indicated at
line 82. The mantle fabric 70 undergoes denitration at
about 150C (point 84). it this point the fabric color
changes rapidly from white to golden tan. Immediately after
this color change (point 84), oxygen is added to the
nitrogen flow at a rate of about five cubic centimeters per
minute. seating continues at the same rate as indicated by
line 86 to a temperature of about 320C (point 88). During
this time the color continuously changes from golden tan to
dark brown or black with modest shrinkage (about 10%) of the
fabric, which indicates additional decomposition of the
organic material. Continuing from point 88, the oven
temperature is then held at about 320C for as long as it
takes the mantles to turn from black to light gray or white
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(about two hours). During this soaking interval (indicatedby line 90 in Fig. 4) , the remaining carbon is oxidized and
driven off and the mantle shrinks to about 1/3 its original
dimensions with its skirt portion 54 shrunk onto sleeve 28
essentially as shown in Fig. 2. At the end of the soaking
interval, (at point 92) the flow of oxygen is increased to
fifty cubic centimeters per minute (a gas mixture of 20%
oxygen) and the oven temperature is rapidly increased as
indicated at line 94 to a temperature of 900C (point 96)
The heater is then turned off and the oven cools to ambient
temperature as indicated at 98.
After cooling, each mantle subassembly is removed
from its storage holder post 74 and is optionally exposed to
a burning mixture of isobutane and air (at an estimated
temperature of about 1600~C) for five minutes to further
shrink and densify the metal oxide fabric.
The mantle 30 with its support tube 28 is
evaluated for shock strength. In one test mechanism, the
mantle-support tube assembly is secured to a 1/4 pound
weight with a set screw in either a vertical or a horizontal
orientation. The weight slides on a six foot vertical steel
rod that passes through a hole in the 1/4 pound weight and,
at the bottom of the steel rod, the weight impinges on a
spring that has a force constant of 810 pounds per inch. A
drop height of six feet represents a shock load of about
620g's, a drop height of five feet represents a shock load
of about 570g's, a drop height of about four feet represents
a shock load of about 510g's, and a drop height of three
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feet represents a shock load of about 445g's. Mantles havealso been tested with a L A B Automatic Drop Shock Tester
(Model SD-10-66-30) (available from Material Technolog7
Incorporated) which is used with a Type 5520.5.85
Decelerating Device (pulse pad) for shock loads of up to
about 600g's and with a Type 5520.5.28 Decelerating Device
(pulse pad) for shock loads in the ran8e of 600g's to
1600g's. The following is a summary of results of such
tests on mantles in accordance with the invention:
STRENGTH OF MANTLES
Mantle Mantle Average Range of
Diameter Length Fracture Fracture Figure of
(D) (L) Load Loads Merit
(mm) (mm) (g's) (g's) (g-meters)
6 983 800-1600 5.9
In contrase, prior art Valor (German Railway) mantle sub-
assemblies (9 mm mantle diameter and 8 mm mantle length)
tested with the LAB Tester failed at average fracture loads
of 152g (78 -280g range) - a figure of merit value of 1.2 g-
20 meters; and prior art Colemen mantle subassemblies (25 mm
mantle diameter and 28 mm mantle length) failed at average
fracture loads of 80g (60 -90g range) - a figure of merit of
2.2 g-meters.
- The mantle-support tube subassembly is installed
in the flashlight 10. With a fuel flow of nine cubic
centime~cers per minute and a roughly stoichiometric air fuel
ratio, the flashlight has a light output in the range of 15-
19 lumens
A second processing sequence is illustrated in
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Fig. 5. Fixture 72 with hanging imbibed socks 70 is placed
in a vacuum oven (preheated to approximately to 100C -
point 100) and the oven is pumped down with a mechanical
vacuum pump over an interval of about five minutes to a
pressure of five millimeters of mercury (interval 102 -
Fig. 5). The temperatures of the oven is then increased at
a rate of about five degrees Celsius per minute as indicated
at 10~ for an in-terval of about twenty minutes to a
temperature of 200C (point 106). Deni-tration is observed
below 200C by a sudden vigourous charring wave that
propagates over the entire surface of the mantle socks 70O
Immediately after denitration, the support 72 with
denitrated socks 70 is transferred to an air oven (Kerr
Sybron model 999) preheated to 240C. (point 108). The oven
temperature i9 increased at a ra-te of about 1.7C per minute
interval 110) to a temperature of about 320C (point 112)
and then at a rate of about 2.7C per minute (interval 114)
to a temperature of 450C (point 116). ~Ieating to 320C and
above causes a continual charring and shrinkage of the
mantle until at about 400C to 420C, the charred portion is
oxidized to leave a shrunken mantle of white metal oxide.
The mantle support fixture 72 is then transferred to an air
furnace maintained at 1000C (point 118), and after a ten
minute interval (120) the mantle fixture 72 with white metal
oxide mantles 30 shrunken on support tubes 28 are removed
from the furnace. Each mantle subassembly is then exposed
to a temperature of about 1600C for five minutes to further
shrink and densify the metal oxide fabric. The resulting
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mantle subassemblies have shock resistance figures of merit
of over 3.6 g-meters and withstand shock loads of over
600g's.
The support tube-mantle subassembly is assembled
into the flashlight unit 10 as indicated in Fig, 1. In that
assembly, the flashlight has an output of about twelve
lumens with a butane fuel flow rate of seven cubic
centimeters/minute and an air fue] ratio of about 30:1. The
flashlight 10 has an operating life of about twenty hours
continuous operation.
Another mantle support tube subassembly in
accordance with the invention, formed with an imbibing
solution about 0.89 molar in thorium nitrate, 0.01 molar in
cerium nitrate and 0.02 molar in zirconium and processed
after denitration with a sequence that included a twenty-
four hour soaking interval at 320C and final heating in a
gas-oxygen flame, withstood a shock load of 850g (a shock
resistance figure of merit of about 5.0). Still another
mantle support tube subassembly in accordance with the
invention, formed with an imbibing solution about 0.89 molar
in thorium nitrate, 0.01 molar in cerium nitrate and 0.01
molar in aluminum nitrate and processed after denitration
with a sequence that included a twenty-four hour soaking
interval at 300C and final heating in an isobutane flame,
withstood a shock load of 910g (a shock resistance figure of
merit of about 5.5 g-meters).
While particular embodiments of the invention have
been shown and described, various modifications will be
- 21 -
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3~
apparent to those shilled in the art, and therefore it isnot intended that the invention be limited to the disclosed
embodiments or to details thereof, and departures ma be
made therefrom within the spirit and scope of the
invention.
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