CA1237269A - Apparatus and method for the production of fibers - Google Patents
Apparatus and method for the production of fibersInfo
- Publication number
- CA1237269A CA1237269A CA000480775A CA480775A CA1237269A CA 1237269 A CA1237269 A CA 1237269A CA 000480775 A CA000480775 A CA 000480775A CA 480775 A CA480775 A CA 480775A CA 1237269 A CA1237269 A CA 1237269A
- Authority
- CA
- Canada
- Prior art keywords
- molten material
- ridges
- layer
- outlet end
- ramp member
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
- B22D11/0611—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by a single casting wheel, e.g. for casting amorphous metal strips or wires
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Inorganic Fibers (AREA)
Abstract
APPARATUS AND METHOD FOR THE PRODUCTION OF FIBERS
Abstract of the Disclosure Molten material, especially metals, can be formed directly into fiber by allowing a stream of molten material to flow across a ramp member, thereby forming a thin layer of molten material, under sustantially no hydrostatic pressure. At an outlet end of the ramp member, a wheel bearing a plurality of ridges passes through the thin layer of molten material thereby drawing out a plurality of filaments. The apparatus avoids the problem of strip formation encountered in prior art apparatus using a plurality of closely spaced ridges.
Abstract of the Disclosure Molten material, especially metals, can be formed directly into fiber by allowing a stream of molten material to flow across a ramp member, thereby forming a thin layer of molten material, under sustantially no hydrostatic pressure. At an outlet end of the ramp member, a wheel bearing a plurality of ridges passes through the thin layer of molten material thereby drawing out a plurality of filaments. The apparatus avoids the problem of strip formation encountered in prior art apparatus using a plurality of closely spaced ridges.
Description
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~
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 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~
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 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 .
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~
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~
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 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~
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~
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~
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~
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 ~3~
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 ~3~ }~
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 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.
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~
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 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~
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 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 .
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~
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~
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 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~
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~
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~
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~
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 ~3~
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 ~3~ }~
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 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.
Claims (20)
1. Apparatus for the production of fiber, said apparatus comprising:
supply means for supplying a stream of molten material;
a ramp member having a upper surface for receiving said stream of molten material from said supply means, said ramp member having an outlet end at which said stream of molten material forms a layer of molten material having a width greater than its thickness, said layer of molten material being, at said outlet end, under a pressure not substantially greater than that of the surrounding atmos-phere; and a movable member bearing a plurality of pro-jections spaced from one another, said movable member being capable of movement past said outlet end of said ramp member so that said projections pass through said layer of molten material and draw a plurality of filaments of molten material from said layer.
supply means for supplying a stream of molten material;
a ramp member having a upper surface for receiving said stream of molten material from said supply means, said ramp member having an outlet end at which said stream of molten material forms a layer of molten material having a width greater than its thickness, said layer of molten material being, at said outlet end, under a pressure not substantially greater than that of the surrounding atmos-phere; and a movable member bearing a plurality of pro-jections spaced from one another, said movable member being capable of movement past said outlet end of said ramp member so that said projections pass through said layer of molten material and draw a plurality of filaments of molten material from said layer.
2. An apparatus according to claim 1 wherein said supply means supplies a stream of molten metal.
3. An apparatus according to claim 1 wherein said outlet end of said upper surface is disposed at an angle of not more than about 30° to the horizontal.
4. An apparatus according to claim 3 wherein said outlet end of said upper surface is disposed at an angle of not more than about 15° to the horizontal.
5. An apparatus according to claim 1 wherein said ramp member is formed of a ceramic material.
6. An apparatus according to claim 5 wherein said ramp member is formed of fire-brick.
7. An apparatus according to claim 1 wherein said projections on said movable member are in the form of parallel elongate ridges and said movable member moves past said outlet end in a direction substantially parallel to the length of said ridges.
8. An apparatus according to claim 1 wherein said movable member comprises a substantially cylindrical rotatable member having said projections disposed on its periphery.
9. An apparatus according to claim 8 wherein said rotatable member is arranged to rotate so that the portion of said rotatable member adjacent said outlet end of said ramp member is travelling upwardly.
10. An apparatus according to claim 9 wherein said projections on said 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 about 2 times the radial difference in height between the tops of said ridges and the deepest parts of said recesses.
11. Apparatus for the production of fiber, said apparatus comprising:
supply means for supplying a stream of molten material;
a ramp member for receiving said stream of molten material from said supply means, said ramp memberhaving an upper surface such that said stream of molten material flows across said upper surface to form a layer of molten material having a width greater than its thickness, said ramp member having an outlet end at which said upper surface is disposed at an angle of not more than about 30° to the horizontal and at which said layer of molten material is under a pressure not substantially greater than that of the surrounding atmosphere; and a substantially cylindrical rotatable member having a plurality of ridges disposed on its periphery, said rotatable member being disposed adjacent said outlet end of said ramp member such that, as said rotatable member rotates, said ridges pass upward through said layer of molten material and draw a plurality of filaments of molten material from said layer.
supply means for supplying a stream of molten material;
a ramp member for receiving said stream of molten material from said supply means, said ramp memberhaving an upper surface such that said stream of molten material flows across said upper surface to form a layer of molten material having a width greater than its thickness, said ramp member having an outlet end at which said upper surface is disposed at an angle of not more than about 30° to the horizontal and at which said layer of molten material is under a pressure not substantially greater than that of the surrounding atmosphere; and a substantially cylindrical rotatable member having a plurality of ridges disposed on its periphery, said rotatable member being disposed adjacent said outlet end of said ramp member such that, as said rotatable member rotates, said ridges pass upward through said layer of molten material and draw a plurality of filaments of molten material from said layer.
12. Apparatus according to claim 11 wherein said ramp member has two separate upper surfaces separated by a ridge line, said supply means supplies said stream of molten material to said ramp member at said ridge line such that a stream of molten material flows across each of said upper surfaces of said ramp member to an outlet end disposed at the lower end of each of said surfaces, said apparatus having two substantially cylindrical rotatable members each having a plurality of ridges disposed on its periphery, one of said rotatable members being disposed adjacent the oulet end of each of said surfaces such that, as said rotatable member rotates, said ridges pass through said molten material on the associated one of said surfaces and draw a plurality of filaments of molten material from said molten material on said associated one of said surfaces.
13. A method for producing fibers, said method comprising:
providing a supply of molten material;
allowing said molten material to flow across a surface, thereby forming a layer of molten material having a width greater than its thickness, said layer having an outlet end at which the pressure on said molten material is not substantially greater than that of the surrounding atmosphere; and moving a plurality of projections spaced from one another upwards through said outlet end of said layer, thereby drawing a plurality of filaments of molten material from said layer, said filaments solidifying to form said fibers.
providing a supply of molten material;
allowing said molten material to flow across a surface, thereby forming a layer of molten material having a width greater than its thickness, said layer having an outlet end at which the pressure on said molten material is not substantially greater than that of the surrounding atmosphere; and moving a plurality of projections spaced from one another upwards through said outlet end of said layer, thereby drawing a plurality of filaments of molten material from said layer, said filaments solidifying to form said fibers.
14. A method according to claim 13 wherein said molten material is molten metal.
15. A method according to claim 13 wherein said surface is disposed at any angle of not more than about 30° to the horizontal.
16. A method according to claim 15 wherein said surface is disposed at an angle of not more than about 15° to the horizontal.
17. A method according to claim 13 wherein said projections are in the form of parallel elongate ridges and are moved through said layer in a direction substantially parallel to the length of said ridges.
-24a-
-24a-
18. A method according to claim 13 wherein said projections are carried on the periphery by a substantially cylindrical rotatable member and are moved through said layer by rotation of said rotatable member.
19. A method according to claim 18 wherein said rotatable member is arranged to rotate so that said projections pass through said layer in an upward direction.
20. A method according to claim 18 wherein said projections on said 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 about 2 times the radial difference in height between the tops of said ridges and the deepest parts of said recesses.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60793284A | 1984-05-07 | 1984-05-07 | |
| US607,932 | 1984-05-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1237269A true CA1237269A (en) | 1988-05-31 |
Family
ID=24434305
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000480775A Expired CA1237269A (en) | 1984-05-07 | 1985-05-06 | Apparatus and method for the production of fibers |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0179885A1 (en) |
| CA (1) | CA1237269A (en) |
| WO (1) | WO1985005055A1 (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3871439A (en) * | 1972-09-26 | 1975-03-18 | Battelle Development Corp | Method of making filament of small cross section |
| EP0147912B2 (en) * | 1983-12-14 | 1994-06-15 | Ribbon Technology Corporation | Melt overflow system for producing filamentary or fiber products directly from molten materials |
-
1985
- 1985-04-29 EP EP19850902390 patent/EP0179885A1/en not_active Withdrawn
- 1985-04-29 WO PCT/US1985/000805 patent/WO1985005055A1/en unknown
- 1985-05-06 CA CA000480775A patent/CA1237269A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0179885A1 (en) | 1986-05-07 |
| WO1985005055A1 (en) | 1985-11-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1078111A (en) | Continuous casting method for metallic strips | |
| US4221257A (en) | Continuous casting method for metallic amorphous strips | |
| US4142571A (en) | Continuous casting method for metallic strips | |
| US4930565A (en) | Melt overflow system for producing filamentary and film products directly from molten materials | |
| EP0147912B1 (en) | Melt overflow system for producing filamentary or fiber products directly from molten materials | |
| US4479528A (en) | Strip casting apparatus | |
| CA1237269A (en) | Apparatus and method for the production of fibers | |
| DE69215062T2 (en) | Meniscus covering of a steel sheet | |
| CA1115479A (en) | Method and apparatus for producing filamentary articles by melt extraction | |
| USRE33327E (en) | Melt overflow system for producing filamentary and film products directly from molten materials | |
| US4331739A (en) | Amorphous metallic strips | |
| GB2225740A (en) | Continuous casting of alloys containing immiscible components, for manufacture of slide elements for bearings | |
| US4285386A (en) | Continuous casting method and apparatus for making defined shapes of thin sheet | |
| US4771820A (en) | Strip casting apparatus and method | |
| US4813472A (en) | Melt overflow system for producing filamentary and film products directly from molten materials | |
| US2022571A (en) | Method of producing bimetallic strips | |
| US4942918A (en) | Controlled-flow fiber casting | |
| US5040594A (en) | Side feed tundish apparatus and method for the alloying and rapid solidification of molten materials | |
| US4614222A (en) | Method of and apparatus for casting metal strip employing free gap melt drag | |
| JPS63203254A (en) | Apparatus for pouring molten metal for metal strip continuous casting | |
| CA1180873A (en) | Strip casting apparatus | |
| DE3128063A1 (en) | Method and apparatus for the continuous casting of a solid metal strip | |
| AU611945B2 (en) | Method and device for obtaining metal thread | |
| JP3111346B2 (en) | Powder for continuous casting | |
| SU1600919A1 (en) | Method of continuous obtaining of alloying composition in the form of bimetallic wire having fusible core |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |