Note: Descriptions are shown in the official language in which they were submitted.
APPARATUS AND ME~HOD FOR T~E PRODUCTION OF FIBERS
Backqround of_the Invention
The invention relates to an apparatus and method for
the production of fibers. More specificallyr the invention
relates to an apparatus and method for the production of
05 fibers in which projections are moved through a quantity of
molten material, thereby drawing out filaments of molten
material which solidify to form fibers~
It has long been known that fibers or filaments can be
produced directly from molten material by moving a rela-
tively sharp-edged member rapidly through a ~uantity of the
molten material. The mo~ing member acts as a heat extractor
and causes the formation of a partly solidifed filament of
material on the edge of the member. As the member emerges
from the molten material, this filament can be removed from
lS the moving member and allowed to completely solidify,
thereby forming a fiber. Metal fibers formed in this
fashion can be made of small diameter and of high tensile
strength. Such metal fibers are useful in fiber-reinforced
composites; for example, such fibers are used to reinforce
concrete in road pavements and other civil engineering
applications where high strength concrete and similar
materials are required. Forming such fibers with a sharp-
edged member passing through a quantity of molten fiber-
forming material avoids the difficulties inherent in the use
o~ the very small orifices needed to make thin metal fibers
- - by more conventional methods such as forcing molten material
through a die. Typically, by passing the sharD-edged member
through a liquid metal, fibers can be produced having a
diameter of the order of five mils (0.13mm.), although the
method can be used to form considerably smaller fibers.
Prior art methods ~or the formation of fibers by
passing a sharp-edged member through molten metal are shown
in U.S. patents 3,838,185 issued September 24, 1974 and
3,896,203 issued July 22, 1975; both these patents have one
inventor (Robert E. Maringer) in common with this appli-
cation and are assigned to the same assignee as this
~23t72i59
application. In the former patent, the sharp-edged member
has the form of a rapidly rotating wheel, the periphery of
which is V-shaped in cross-section so as to produce a small
05 radius of curvature at~the extreme radially-outward part of
the wheel. This rotating wheel is immersed just below the
surface of a bath of molten material, thereby forming a
partially-solidified filament on the sharply-curved surface
at the lowest part of the periphery of the wheel where it is
immersed in the molten material. As the wheel rotates, the
partially-solidified filament is carried around the wheel
and is eventually flung from the wheel by centrifugal force
above the level of the molten material.
In the latter patent, a so-called "pendant drop" of
molten material is formed either by melting the tip of a rod
o`f material or allowing material to flow through an aperture
in the base of a tundish or similar recepticle. The pendant
drop is held in position by surface tension forces, and a
sharp-edged wheel, similar to that used in the first patent,
passes through the drop and pulls out a filament of molten
material which hardens to form a fiber in the same way as
before.
The processes described in the two aforementioned
patents can be made to give products of good quality.
Unfortunately, the type of rotating member illustrated in
these patentst which has only a single sharp edge, will
typically produce only a few grams of fine fibers per hour,
whereas commercial production needs to be on a much larger
scale7 It might at first be thought that the low rate of
production could be overcome simply by either mounting a
number of the wheels on the same shaft, or by modifying the
wheel so that its periphery bears a number of sharp edges in
the form of ridges. ~owever, empirically it has been found
that neither of these expedients is successful. Mounting a
number of thick wheels on the same shaft will produce a very
heavy comp~site wheel and will demand an excessively large
~3~7~
--3--
bath of metal into which such a composite wheel would dip,
if the composite wheel is to have the number of edges
required for large scale production. If one attempts to
place a number of ridges close together on a wheel dipping
05 into a~~metal bath, the individual filaments tend to coalesce
at least part of the time, procl~cing either a single metal
strip or a plurality of narrow metal strips depending upon
the degree of coalescence.
Similarly, if one attempts to use a plurality of
separate wheels or a single wheel having a number of closely
spaced ridges in the pendant drop technique, it is almost
impossible to maintain a proper pendant drop which will
allow production of multiple fibers without coalescence.
Since a drop pendant from a metal rod is always approxi-
mately part-spherical in shape, to produce an elongate
pendant "drop" wide enough to be used with either a com-
posite wheel or a single wheel bearins a plurality of
spaced ridges, it is necessary to form the pendant rdrop" by
using a very narrow slit in the base of a tundish or similar
vessel containing molten material. Because a pendant drop
whose form is controlled by surface tension forces is
required, the slot has to be very narrow and in practice it
is virtually impossible with many molten materials to
maintain a proper elongate pendant drop for any length of
time. If the slot becomes too narrow because of, for
example, deposition of unmelted impurities or dirt and dust
particles within the slot, flow through the slot will be so
retarded that insufficient metal will be provided for
drawing out of the fibers. If, on the other hand, wear on
the slot ca~ses the slot to become even slightly too wide,
molten metal will tend to pour through the slot resulting in
production of strip or coalesced fibers, as previously
described in relation to the metal bath method. In
addition, since the size of the slot must be directly
related to the surface tension of the molten material, a
~2~72'~9
--4--
variety of different slots may have to be provided to
accommodate different molten materials and/or variati~ns in
temperature of the molten material.
There is thus a need for a method of f~rming fiber
05 directly from molten material which is capable of large
scale production without causing coalescence of fibers, and
which does not involve the disadvantages associated with the
use of very n~rrow slots. This invention seeks to provide
such a method and an apparatus for use therein.
Summary of the Invention
The invention provides apparatus for the production of
fiber comprising means for supplying a stream of molten
material, and a ramp member having a upper surface for
receiving this stream of molten material. The ramp member
forms the molten material into a layer having a width
greater than its thickness, this layer of molten material
being, at an outlet end of the ramp member, under a pressure
not substantially greater than that of the surrounding
atmosphere. The apparatus also includes a movable member
bearing a plurality of projections spaced from one another,
this movable member being capable of movement past the
outlet end of the ramp member so that the projections pass
through the layer of molten material and draw a plurality of
filaments of molten material from the layer.
The invention also provides a method for producing
fibers in which a supply of molten material is allowed to
flow across a surface; thereby forming a layer of molten
material having a width greater than its thickness, this
3~ layer having an outlet end at which the pressure on the
molten material is not substantially greater than that of
the surrounding atmosphere. In this method, a plurality of
projections spaced apart from one another are moved through
the outlet end of the layer of molten material, thereby
6~
--5--
drawing a plurality of filaments of molten material from the
layer and allowing these filaments to solidify to form the
fibers.
In saying that, in the instant process and method, the
05 molten material in the outlet end of the layer is under a
pressure not substantially greater than that of the sur-
rounding atmosphere, we mean that there is little or no
hydrostatic pressure head on the molten material at the
outlet end of the ramp member due only to the hydrostatic
pressure o the molten material itself~ As explained in
more detail below, it has been found that the absence of any
substantial hydrostatic pressure head on the molten material
is of crucial importance in avoiding coalescence of the
separate fibers formed by the projections on the movable
member, with resultant formation of strip.
Brièf Description of the Drawinq
Fig. 1 is a schematic side elevation of a first
apparatus according to the invention; and
Fig. 2 is a schematic side elevation of a second
apparatus according to the invention.
Detailed Description of the Invention
It has been discovered that, in order to avoid co-
alescence of multiple fibers produced on different pro-
jections on the same movable member, it is important to
control the pressure on the molten material as it contacts
the projections. As ill~strated in Fig. 4 of the afore-
mentioned patent 3,838,185 and in Fig. 3 of the afore-
mentioned patent 3,896,203, when a wheel having only a
single sharp edge is used as the movable member in th-e two
prior art processes, the molten material makes contact only
with a very small area adjacent the sharp edge of the wheel,
so producing a fiber of small diameter. If, however, one
attempts to pass a wheel bearing a plurality of projections
or ridges spaced from one another by intervening recesses
~3t7~,~9
thro~ugh mblten material in t:he form of either a bath or a
pendant drop, the molten material tends not only to make
contact with the tops of the ridges but also tends to be
forced down from the tops of the ridges into the recesses,
05 so that eventually the molten material is in contact with
both the ridges and the recesses, thereby causing the
formation of strip. Obviously, at an intermediate stage of
movement of the molten material down into the recesses, some
pairs of adjacent fibers may coalesce while others may not,
resulting in a format;on of a plurality of narrow strips.
It has been found that the major factor involved in the
movement of the molten material down from the tops of the
ridges into the recesses is the hydrostatic pressure on the
molten material. It might be thought that, when such a wheel
bearing multiple ridges is rotating above a bath of molten
màterial so that only the extreme lower edge of the wheel
dips into the molten material, there should be effectively
no hydrostatic pressure on the molten material in contact
with the wheel, and thus strip formation should be avoided.
However, although hydrostatic pressure on the molten
material in contact with the wheel is theoretically zero in
this arrangement, in practice disturbances of the molten
material caused by the heating method used and coning
effects can cause considerable transient hydrsstatic
pressures to develop in the molten material adjacent the
wheel, and such transient hydrostatic pressures force the
molten material into the recesses between the ridges,
thereby causing the apparatus to produce stripr Similar
phenomena will take place in the pendant drop type of
apparatus owing to oscillations in the pendan~ drop or, as
already mentioned~ enlargement of the slot through which
material flows down onto the wheel.
In the instant invention, the problem of excess
hydrostatic pressure is overcome by forming the molten
material into a layer in which no substantial hydrostatic
pressure exists at the outlet end of the layer. In addition,
~2372~9
--7--
the ramp member surfaee underlying the layer helps to
promote stability in the layer, théreby rendering the
process less susceptible to transient variations in hydro-
static pressure such as may occ~r in the relatively free-
05 moving masses of molten material in~ the metal bath orpendant drop types of process.
Although the most common type of molten material to be
used in the instant apparatus and method is molten metal,
non-metallic molten materials can be used if they display
the proper surface tension and viscosity properties. The
molten material should have, at a temperature within 25% of
its equilibrium melting point in degrees R, a surface
tension in the range of 10 to 25D0 dynes/cm. and a viscosity
in the range of 0.0012 to 1 poise. Metal alloys may be
employed even though they display a fairly wide range
between the liquidus and solidus temperatures. Obviously,
if the metal is one which is highly susceptible to atmos-
pheric oxidation, contact between the molten metal and
atmospheric oxygen should be avoided by either blanketing
the molten metal with an inert gas or operating under a
vacuum. If the molten metal has a signficant vapor pres-
sure, the composition and pressure of gas surrounding the
molten metal should be manipulated so as to reduce evap-
oration thereof. Iron, aluminum, copper, nickel, tin and
zinc can be formed into fibers without protection'from the
atmosphere, whereas chromium, titanium, columbium, tantalum,
zirconium, magnesium and molybdenum, and alloys thereof,
will normally require protection from the atmosphere.
It has been found that copper and an alloy having the
composition Ni63Crl2Fe4B13Si~ will produce fine fibers in
the instant method with little difficulty. It is an
advantage of the instant method and apparatus that, since
only the very limited amount of material required to form
the thin layer need be molten at any given time, the amount
of oxidation which oxidizable metals undergo in the instant
.
--8--
method will be substantially less than, for example, in the
prior art methods which require melting of a large bath of
metal.
The means for supplying a stream of molten material
05 used in the instant apparatus can be of any convenient form.
For example, the supply means might have the form of a
vessel containing a bath of molten material and provided
with an aperture which permits a stream of molten material
to drop onto the ramp member~ Obviously, if desired means
might be provided for varying the size of the aperture in
order to vary the rate at which the molten material flows
onto the ramp member. Alternatively, the supply means might
comprise a vessel containing molten material together with
means to tip the vessel to pour a stream of molten material
on the ramp member, or provided with a weir over which the
molt~n material flows onto the ramp member. ~owever, in
general we prefer to use a supply means which does not
necessitate maintaining a substantial bath of material in a
molten state, since maintaining such a bath increases the
risk of chemical change in the molten material. Thus, in
general it is preferred to use a supply means in which a
solid piece of material is steadily melted by a source of
heat and the molten material thus produced immediately used
to form the thin layer of molten material on the ramp
member. For example, bar or plate stock could be fed into
an oxyacetylene flame which would effect melting of the
material. If such an oxyacetylene flame is used with
oxidizable material, it will usually be desirable to keep
the flame rich in acetylene, thereby producing a reducing
atmosphere which will limit oxidation of the metal. Alter-
natively, heat could be applied to the bar or plate by an
induction coil, an electric arc or electron beam heating;
electron beam heating of course requires that the heating be
conducted in vacuum.
~L~37~,~i9
g
Once the stream of molten material has been introduced
into the instant apparatus, it is used to form the thin
layer of molten material on the upper surface of the ramp
member. In some cases, the upper surface of the ramp
05 member may be horizontal so that the layer of molten
material is in effect a shallow pool of molten material on
the hori~ontal surface of the ramp member. Obviously~ in an
apparatus incorporating such a horizontal surface, it will
be necessary to make provisions to ensure that the molten
material only passes over the edges of the horizontal
surface adjacent the movable member or ~embers~ For
example, an upstanding rim might be provided around the
ridges of the surface which do not lie adjacent a movable
member. Also, if a steady stream of molten material is
lS being delivered onto such a horizontal ramp member surface,
the~molten material will of course tend to flow from the
point at which it reaches the surface to the point on the
surface from which molten material is being removed i.e. the
edge of the surface adjacent the movable member.
The upper surface of the ramp member need not ne-
cessarily be planar. For example, different sections of the
upper surface may have differing inclinations to the
horizontal. In order to ensure a good flow of material onto
the upper surface without imposing undue hydrostatic
pressure on the layer of molten material at the outlet end
thereof, in some cases it may be convenient to use a ramp
member with an inlet end having a relatively lar~e slope and
an outlet end having a relatively small slope, so that the
upper surface is concave upwardly. Whether or not the slope
of the upper surface is constant~ it will be apparent to
those skilled in the art that the angle of inclination of
the upper surface need only be sufficient to cause flow of
molten material to the outlet end of the ramp member at the
required rate; thus, in many cases relatively gentle slopes
of a few degrees to the horizontal wlll suffice. Indeed,
the use of an excessive slope at or adjacent the outlet end
~372~
--10--
of the ramp member tends ~o be undesirable in that su~h an
excessive slope may tend to place excess hydrostatic
pressure on the layer of molten material at ~he outlet end
of the ramp member and thus tend to force the molten
~ 05 material into the recesses between adjacent projections on
the movable member, thereby increasing the risk of formation
of strip. Desirably, the slope of the upper surface of the
ramp member adjacent the outlet end thereof is not more than
about 30, and preferably not more than about 15~, to the
horizontal. Obviously, if any given slope does tena to
cause strip formation to occur, it may be necessary or
desirable to reduce the angle of inclination of the upper
surface adjacent the outlet end~
Not only may the upper surface of the ramp member be
curved lengthwise so that different portions of the ramp
me`mber have different slopes, it may also be desirable to
curve the upper surface of the ramp member across its width
i.e. perpendicular to the direction in which the molten
material flows along the ramp member. In particular, with
certain molten materials there is a tendency for the central
part of a layer of molten material to be thicker than the
peripheral portions of this layer, and such differences in
thickness of the layer of molten material tend to cause the
diameter o the fibers produced from such molten material to
vary across the width of the layer of molten material. With
such molten material, if uniformity of fiber diameter is
important, it may be desirable to use a ramp member which is
somewhat convex upwardly across its width so that the
central part of the ramp member is higher than the two
sides. This tends to reduce the thickness of the central
part of the layer of molten material, thereby ensuring
greater uniformity of fiber diameter.
In some cases, it may also be desirable to form the
upper surface of the ramp member with a series of alter-
nating ridges and recesses running lenthwise along the ramp
member so that the stream of molten material is divided into
ti;2~;~
a plurality of sub-streams flowing along the recesses in the
upper surface. Conveniently, both the tops of the ridges
and the bases of the recesses are flat, so that a cross-
section across the width of the ramp member will have a
05 crenellated, square-wave form. When such a ridged upper
surface of the ramp member is employed, it will normally be
desirable to make the spacing of the ridges equal to the
spacing between the projections on the movable member but
with the ridges 180D out of phase, so that each projection
on the movable member passes adjacent a reces~ at the outlet
end of the ramp memher. This form of upper surface may have
the advantage of ensuring that each projection on the
movable member receives the same quantity of molten ma-
terial.
Although the upper surface of the ramp member may thus
hàve a variety of forms, it has been found experimentally
that good results can be obtained with ramp members having
flat upper surfaces inclined at a relatively small angle,
typically S-10 to the horizon~al.
One way to avoid contamination of the molten material
is to use a ramp member formed from a material which does
not react with or dissolve in the molten material. In most
cases, a suitably inert ramp member can be formed of a
ceramic material; fire-brick is an appropriate and cheap
ceramic material. In cases where the molten material is
reactive or likely to be contaminated by fire-brick, other
materials can of course be substituted. ~owever, in many
cases it may suffice to use a fire-brick or other ceramic
ramp member and to allow an initial portion of the molten
material to come into contact with a cold ramp member,
thereby forming a thin covering of solidified material on
the ramp member which will serve to prevent contact of later
molten material flowing across the ramp member with the
underlying ceramic material. Alternatively, skull melting
may be employed to ensure that the molten material does not
become contaminated.
~37~
-12-
Obviously, if necessary heat can be supplied either to
the ramp member or to the molten material flowing there-
across in ordèr to ensure that solidification of the molten
material does not occur on the ramp member. The ramp
05 member can be provided with built-in heating elements, for
example electrical resistance heating elements, or radiant
heat could be directed downwardly onto the molten material
on the ramp member. However, in practice since the molten
material will normally only be in contact with the ramp
member for a very brief time, it will not usually be
necessary to heat the molten material on the ramp member.
At the outlet end of the ramp member, the molten
material forms a meniscus, and it is this meniscus through
which the projections on the movable member pass. (The term
"meniscus" is used herein simply to refer to the edge of the
layer of molten material at the outlet end of the molten
matèrial. At the outlet end of th~ ramp member, and is not
intended to imply anything concerning the angle of contact
between this molten material and the ramp member.) Unlike
the fiber-forming method using an elongate slot to product a
pendant drop, the instant method does not require the
presence of any solid material above the liquid layer to
define the slot, so the problems associated with the use of
very narrow slots are avoided. ~owever, if desired a solid
member may be provided dipping into the upper surface of the
layer of molten material on the ramp member in order to skim
off any contaminants, such as oxides, which may be resting
on the surface of the molten layer, thereby avoiding fouling
of the meniscus at the outlet end of the ramp member.
Obviously, such a upper solid member need not be immediately
adjacent the outlet end of the ramp member but can be some
distance therefrom~ in order to avoid the difficulties which
might be occasioned by the presence of what would be, in
effect, a narrow slot at the outlet end of the ramp member.
~3~f;~ig
-13-
It i~ desirable that the edge of the ramp member at the
outlet end thereof have a sharp corner i.e. that the radius
of curvature of this edge be very small. Such a sharp
corner at the edge of the ramp member assists in producing a
05 well-defined meniscus on thle layer of molten material and
limits any tendency for the molten material to creep over
the edge of the outlet end of the ramp me~ber and trickle
down into the gap which usually e~ists between the outlet
end of the ramp member and the movable member lying adjacent
this outlet end.
The movable member used in the instant apparatus and
method may have a variety of forms. For example, it could
have a comb-like form in which a plurality of elongate
ridges are mounted on a base member and moved linearly
parallel to the ridges. However, for practical purposes in
or~er to ensure a high rate of fiber production, it is
desirable to use a form of movable member which presents an
endless surface to the outlet end of the ramp member so that
the surface of the movable member can be moved past the
outlet`end of the ramp member without interruption. For
example, the movable member can have the form of an endless
belt passing around two pulleys and provided with a series
of parallel ridges running lengthwise along the belt. This
endless belt type of movable member does have the advantage
that it can be so disposed relative to the outlet end of the
ramp member that the portion of the belt which actually
picks up the molten material is flat, and this ability to
use a flat portion of the movable member to pick up the
molten material may be useful in some circumstances.
However, in general the preferred form of movable member for
use in the instant method is a substantially cylindrical
rotatable member having the projections disposed on its
periphery. Also, desirably the projections on the rotatable
member are in the form of a series of elongate ridges
separated from one another by recesses, the axial spacing
between adjacent ridges being from about 0.5 to 2 times the
31 ~372~
-14-
radial difference in heights between the tops of the ridgesand the deepest parts of the recesses. The ridges are
desirably substantially triangular in cross-section so that
they provide sharp edges on which the molten metal actually
05 solidifies, in a manner similar to the prior art fiber-
forming methods described above. Although the ridges can be
formed as a series of discrete ridges each of which extends
completely around!the cylindrical rotatable member, a
convenient technique is to form a conventional helical screw
thread on the rotatable member; such a helical thread acts
as a series of ridges where it passes through the meniscus
of the molten material~
The ratio between the spacing of the ridges and the
depth of the recesses is of importance. As already men-
tioned~ it has been discovered that the reason for thefo~rmation of strip in prior art processes is the tendency
for the liquid metal to be forced from the tops of the
ridges into the recesses on the movable member, resulting in
the formation of strip when the whole surface of the movable
member in contact with the molten material becomes wetted
with the molten material. Obviously, the greater the ratio
between the spacing of the ridges and the depth of the
recesses,-the greater the tendency for the liquid meniscus
to be forced into the recesses, and hence the greater the
tendency to produce strip. In general, a spacing:depth
ratio of about 1:1 is satisfactory, but if the ratio becomes
too large the production of strip is more likely.
The movable or rotatable member is desirably arranged
so that the portion of the member adjacent the outlet end of
the ramp member is traveling upwardly. Since the meniscus
of the molten material extends slightly beyond the outlet
end of the ramp member, there is of necessity a small gap
between the outlet end of the ramp member and the surface of
the movable member. If the portion of the movable or
rotatable member adjaoent the outlet end of the ramp member
is moving downwardly, it may tend to drag the molten
~L23~iZ~
-15-
material down into the narrow gap between the ramp member
and the movable or rotatable member, which may force molten
material into the recesses in the movable or rotatable
member, with a tendency to produce strip. In addition, it
05 is advantageous for the movable or rotatable member to make
initial contact with the underside of the meniscus; there is
a tendency for any contaminants to float on the top of the
meniscus, 50 that initial contact with the lower part of the
meniscus tends to reduce the likelihood that any s~ch
contaminants will be dragged into the fiber and consequently
cause malformation thereof.
The thic~ness of the fibers produced by the instant
method and apparatus may depend upon a large number of
factors, including the viscosity and surface tension of the
molten material, the radius of curvature of the projections
on~the movable member, the thermal conductivity of the
movable member and other factors. However, it should be
noted that the instant method does permit a mea~ure of
control over the diameter of the fibers produced since one
20 of the fac~ors affecting fiber diameter is the penetration
of the projections on the movable member into the layer of
molten material on the ramp member. The deeper this
penetration, the larger the diameter of the fibers produced.
Accordingly, it may be desirable to eguip the instant
apparatus with means for adjusting the penetration of the
pro~ections on the movable member into the layer of molten
material on the ramp member. In the preferred form of
apparatus in which the movable member is a cylindrical
rotatable member bearing a plurality of parallel ridges,
such adjustment of penetration may conveniently be accom-
plished by providing means for moving the rotatable member
and the ramp member relative to one another; for example,
means might be provided whereby the axis of the rotatable
member can be moved towards and away from the ramp member.
~%3~
-16-
As in the prior art patents discussed above, the
movable member of the instant apparatus serves to extract
heat from the molten material, thereby causing partial
solidification of the molten material in contact with the
~ 05 movable member and the drawing of a plurality of filaments
of molten material from the layer. As those skilled in the
art will be awarer if the movable member pic~s up too much
heat from the molten material and thus becomes too hot, it
will not extract sufficient heat from the molten material
with which it is in contact and hence either fibers will not
be formed or the quality of fibers formed will be unsatis-
factory. A variety of methods may be used to cool the
movable member; for example, the movable member could be
provided with internal channels through which a cooling
liquid is pumped, as illustrated in Fig. 5 of the afore-
mentioned U.S. patent 3,838rl85. However, since in the
instant apparatus the movable member is only in contact with
a relatively small quantity of molten material, rather than
a large bath of molten material such as that used in V.S.
20 patent 3,383,185, the heat flow into the movable member
tends to be less and hence the cooling problem is sim-
plified. In practice when using a rotatable member in the
instant apparatus, we have found that sufficient cooling can
be effected simply by allowing the side of the rotatable
member which does not face the ramp member to wipe against a
damp pad of absorbent material, such as a pad of cotton
fibers. Sach a coolins and wiping pad also has the advan-
tages of removing any stray fibers which may still be
adhering to the rotatable member.
Fig. 1 of the accompanying drawings shows a highly
schematic side elevation of an apparatus of the invention
generally designed 10. The apparatus comprises a ramp
member 12 formed of fire-brick and having a planar upper
surface 14 which is inclined at an angle of ab~ut 15~ to the
horizontal. A metal rod 16, which may be of copper or an
alloy such as Ni63Crl2Fe4B13Sig, is fed onto the upper end
3~
-17-
of the ramp membcr 12 formed of fire brick at an appropriate
rate by a suitable advanciny mechanism, such as a worm drive
(not shown). The lower end of the rod 16 is heated by means
of an induction coil 18 so thal: it melts to produce a stream
05 of molten metal which rolls in a thin layer 20 down the
planar upper surface of the ramp member 12 and forms, at the
lower or outlet end of the ramp member 12, a meniscus 22.
(The overhang of the meniscus 22 over the edge of the ramp
member 12 is exaggerated in the figure for the sake of
clarity.) The rate at which the rod 16 is melted is arranged
so that the layer 20 of molten material on the upper surface
of the ramp member 12 is kept thin. Thus, there is sub-
stantially no hydrostatic head of molten material forcing
the meniscus 22 over the edge of the ramp member 12. The
thickness of the layer 20 should not exceed about 6mm. and
in- most cases a much thinner layer, typically about 1-2mm.,
will suffice. Because the thickness of the layer 20 is so
small, this layer will have a width much greater than its
thickness so as to provide an elongate meniscus 22 which can
contact the movable member to be described below.
A movable member in the form of a rotatable wheel 24 is
disposed adjacent the outlet end of the ramp member 12. The
wheel 24 is mounted upon a shaft 26 provided with an
appropriate drive means ~not shown) such as an electric
motor. The wheel 24 is cylindrical, made of copper, and its
cylindrical outer surface has a screw thread cut therein;
the threaded surface of the wheel 24 presents a plurality of
parallel ridges to the meniscus 22 of the molten material.
The wheel 24 is rotated so that it rotates upwardly past th~
meniscus 22, thereby enabling the multiple ridges presented
by the screw thread to the meniscus 22 to draw a plurality
of filaments of molten material from the meniscus 22. As
the wheel 24 leaves the meniscus 22, the filaments 28 thus
formed solidify on the surface of the ridges and are
eventually flung from the wheel 24 by centrifugal force and
land on a collecting surface 30. On the opposite side of
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the wheel 24 from the meniscus 22, a wetted co~ton pad 32
contacts the wheel. The pad 32 serves to co~l the wheel,
thereby ensuring tha~ it will properly produce the desired
fibers, and also serves to remove stray fibers adhering to
05 the wheel, together with~ar,y dirt or other surface con-
taminants which may be present on the wheel 24.
As is well known to those skilled in the art, the
ridges on a wheel used for producing fiber from molten
material tend to become less sharp after lengthy use i.e.
the radius of curvature of the tops of the ridges increases.
This loss of sharpness tends to disrupt the production of
high-quality fibers. However, the screw thread on the wheel
24 can be inexpensively and easily redressed using con-
ventional thread cutting devices.
lS As explained in the aforementioned U.S. patents
3,838,185 and 3,896,203r the speed at which the wheel passes
thro~gh the molten material is important in controlling the
quality of the fiber. In general, the speed at which the
wheel 24 passes through the meniscus 22 should normally be
in the range of about 3 to 30m.sec.~l, though the exact
usable speed range will vary with a large number of para-
meters, including the surface tension, density, and tem-
perature of the molten material, and possibly the material
from which the wheel is composed.
We estimate that using a wheel 24 which is 2~5cm.
thick, 20cm. in diameter and having approxi~ately 25 threads
cm.~i rotating at 500 rpm., in excess of lOOky. of 0.12Smm.
diameter steel fibers could be produced per hour; this is
better productivity than is currently being achieved with
fibers of three times the diameter.
The second apparatus of the invention shown in Fig. 2
of the accompanying drawings operates in a generally similar
manner to that shown in Fig 1, except that~ in order to
increase the rate of production of fibers, two separate
wheels 24 and 24' are provided. Between the wheels 24 and
24' is located a single ramp member 34 made of fabri~-and
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having the form of a pentagonal prism the axis of which is
perpendicular to the plane of Fig. 2. The two upper faces
36 and 38 of this ramp member are inclined in opposite
directions, sloping downwardly from a central ridge line to
05 points adjacent the wheels 24' and 24 respectively. A
stream of molten material 40, which may be produced by
pouring or otherwise allowing outflow from a bath of molten
material, or by melting, for example, a metal rod suspended
above the ridge line of the ramp member, fl~ws downwardly
1~ onto the ridge line of the ramp member and thence down the
faces 36 and 38. The wheels 24 and 24' are rotated by
suitable drive means (not shown) in the directions indicated
by the arrow in Fig. 2 so that they pass upwardly past the
lower edges of the faces 36 and 38, thereby causing fila-
ments 28 and 28' to be drawn from the layers of moltenmaterial on the faces 36 and 38. These filaments 28 and
28' solidify on the surface of the ridges on the wheels 24
and 24' and are eventually flung from the wheels by cen-
trifuga force and land on collecting surfaces 30 and 30'
respectively the same way as in the apparatus previously
described with reference to Fig. 1. The wheels 24 and 24'
are equipped with pads 32 and 32' which operate in exactly
the same manner as the pad 32 shown in Fig. 1.
It will be apparent to those skilled in the art that
numerous changes and modifications can be made in the
embodiments of the invention described above without
departing from the scope of the invention. In particular,
by cutting recesses extending axially through th~thread on
the wheel 24, a form of wheel having interrupted ridges
comparable to the wheel shown in Fig. 6b of the afore
mentioned U.S. patent 3,838,185 could be produced, thereby
enabling short fibers of consistent length tc be achieved
rather than the more random fiber length distribution which
occurs with unbroken threads. Other changes and modi-
fications will be apparent to those skilled in the art.
.
3~2
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Accordingly, the foregoing description is to be construed in
an illustrative and not in a limitative sense, the scope of
the invention being defined sollely by the appended ~laims.
