WO1985005055A1

WO1985005055A1 - Apparatus and method for the production of fibers

Info

Publication number: WO1985005055A1
Application number: PCT/US1985/000805
Authority: WO
Inventors: Robert E. Maringer; Lynn E. Wheeler
Original assignee: Battelle Development Corporation
Priority date: 1984-05-07
Filing date: 1985-04-29
Publication date: 1985-11-21
Also published as: CA1237269A; EP0179885A1

Abstract

Molten material, especially metals, can be formed directly into fiber by allowing a stream of molten material to flow across a ramp member (12), thereby forming a thin layer (20) of molten material, under sustantially no hydrostatic pressure. At an outlet end of the ramp member, a wheel (24) bearing a plurality of ridges passes through the thin layer (20) 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 METHOD FOR THE PRODUCTION OF FIBERS

Background of the Invention

The invention relates to an apparatus and method fo the production of fibers. More specifically, the inventio relates to an apparatus and method for the production o

05 fibers in which projections are moved through a quantity o molten material, thereby drawing out filaments of molte material which solidify to form fibers.

It has long been known that fibers or filaments can b produced directly from molten material by moving a rela

"1-0 tively sharp-edged member rapidly through a quantity of th molten material. The moving member acts as a^"heat extracto and causes the formation of a partly solidifed filament o material on the edge of the member. As the member emerges from the molten material, this filament can be removed fro

15 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

20 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 5 of 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 sharp-edged member through a liquid metal, fibers can be produced having a diameter of the order of five mils (0.13mm.), although the 0 method can be used to form considerably smaller fibers.

Prior art methods for 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 application. In the former patent, the sharp-edged membe has the form of a rapidly rotating wheel, the periphery o which is V-shaped in cross-section so as to produce a smal radius of curvature at the extreme radially-outward part o the wheel. This rotating wheel is immersed just below th surface of a bath of molten material, thereby forming partially-solidified filament on the sharply-curved surfac at the lowest part of the periphery of the wheel where it i immersed in the molten material. As the wheel rotates, th partially-solidified filament is carried around the whee and is eventually flung from the wheel by centrifugal forc above the level of the molten material.

In the latter patent, a so-called "pendant drop" o molten material is formed either by melting the tip of a ro o^"f--material or allowing material to flow through an apertur in the base of a tundish or similar recepticle. The pendan drop is held in position by surface tension forces, and sharp-edged wheel, similar to that used in the first patent passes through the drop and pulls out a filament of molte material which hardens to form a fiber in the same way a before.

The processes described in the two aforementione patents can be made to give products of good quality Unfortunately, the type of rotating member illustrated i these patents, which has only a single sharp edge, wil typically produce only a few grams of fine fibers per hour whereas commercial production needs to be on a much large scale. It might at first be thought that the low rate o production could be overcome simply by either mounting number of the wheels on the same shaft, or by modifying th wheel so that its periphery bears a number of sharp edges i the form of ridges. However, empirically it has been foun that neither of these expedients is successful. Mounting number of thick wheels on the same shaft will produce a ver heavy composite wheel and will demand an excessively larg bath of metal into which such a composite wheel would di if the composite wheel is to have the number of edg required for large scale production. If one attempts place a number of ridges close together on a wheel dippi into a metal bath, the individual filaments tend to coales at least part of the time, producing either a single meta strip or a plurality of narrow metal strips depending up the degree of coalescence.

Similarly, if one attempts to use a plurality o separate wheels or a single wheel having a number of closel spaced ridges in the pendant drop technique, it is almos impossible to maintain a proper pendant drop which wil 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 elongat pendant "drop" wide enough to be used with either a com posite wheel or a single wheel bearing a plurality o spaced ridges, it is necessary to form the pendant "drop" b using a very narrow slit in the base of a tundish or simila vessel containing molten material. Because a pendant dro whose form is controlled by surface tension forces i required, the slot has to be very narrow and in practice i is virtually impossible with many molten materials t maintain a proper elongate pendant drop for any length o time. If the slot becomes too narrow because of, fo example, deposition of unmelted impurities or dirt and dus particles within the slot, flow through the slot will be s retarded that insufficient metal will be provided fo drawing out of the fibers. If, on the other hand, wear o the slot causes the slot to become even slightly too wide molten metal will tend to pour through the slot resulting i production of strip or coalesced fibers, as previousl described in relation to the metal bath method. I addition, since the size of the slot must be directl related to the surface tension of the molten material, variety of different slots may have to be provided to accommodate different molten materials and/or variations in temperature of the molten material.

There is thus a need for a method of forming fiber 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 narrow 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 plural'ity 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 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 drawing a plurality of filaments of molten material from th layer and allowing these filaments to solidify to form th fibers.

In saying that, in the instant process and method, th molten material in the outlet end of the layer^" is under pressure not substantially greater than that of the sur rounding atmosphere, we mean that there is little or n hydrostatic pressure head on the molten material at th outlet end of the ramp member due only to the hydrostati pressure of the molten material itself. As explained i more detail below, it has been found that the absence of an substantial hydrostatic pressure head on the molten materia is of crucial importance in avoiding coalescence of th separate fibers formed by the projections on the movabl member, with resultant formation of strip.

Brief Description of the Drawing

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 illustrated 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 the 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 thrαugh molten material in the 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, 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 formation 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 material 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 hydrostatic 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 strip. Similar phenomena will take place in the pendant drop type of apparatus owing to oscillations in the pendant 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, the ramp member surface underlying the layer helps promote stability in the layer, thereby rendering t process less susceptible to transient variations in hydr static pressure such as may occur in the relatively fre moving masses- of molten material in the metal bath pendant drop types of process.

Although the most common type of molten material to used in the instant apparatus and method is molten metal non-metallic molten materials can be used if they displa the proper surface tension and viscosity properties. Th molten material should have, at a temperature within 25% o its equilibrium melting point in degrees K, a surfac tension in the range of 10 to 2500 dynes/cm. and a viscosit in the range of 0.0012 to 1 poise. Metal alloys may b employed even though they display a fairly wide rang 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 an atmospheric oxygen should be avoided by either blanketin the molten metal with an inert gas_* or operating under vacuum. If the molten metal has a signficant vapor pres sure, the composition and pressure of gas surrounding th molten metal should be manipulated so as to reduce evap oration thereof. Iron, aluminum, copper, nickel, tin an zinc can be formed into fibers without protection/from th 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 th composition Nig3Crτ.2^Fe4^B13^s-*-8 ^W*>11 produce fine fibers i the instant method with little difficulty. It is a advantage of the instant method and apparatus that, sinc only the very limited amount of material required to for the thin layer need be molten at any given time, the amoun of oxidation which oxidizable metals undergo in the instan ethod 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 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-en material flows onto the ramp member. However, 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. Once the stream of molten material has been introduce into the instant apparatus, it is used to form the thi layer of molten material on the upper surface of the ram member. In some cases, the upper surface of the ram member may be horizontal so that the layer of molte material is in effect a shallow pool of molten material o the horizontal surface of the ramp member. Obviously, in a apparatus incorporating such a horizontal surface, it wil be necessary to make provisions to ensure that the molte material only passes over the edges of the horizonta surface adjacent the movable member or .members. Fo example, an upstanding rim might be provided around th ridges of the surface which do not lie adjacent a movabl member. Also, if a steady stream of molten material i being delivered onto such a horizontal ramp member surface the molten material will of course tend to flow from th point at which it reaches the surface to the point on th surface from which molten material is being removed i.e. th 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 th upper surface may have differing inclinations to th horizontal. In order to ensure a good flow of material ont the upper surface without imposing undue .hydrostati 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 large 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 will suffice. Indeed, the use of an excessive slope at or adjacent the outlet end of the ramp member tends to be undesirable in that such an excessive slope may tend to place excess hydrostatic pressure on the layer of molten material at the outlet end of the ramp member and thus tend to force the molten 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 tend 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 member 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 of 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 a plurality of sub-streams flowing along the recesses in t upper surface. Conveniently, both the tops of the ridg and the bases of the recesses are flat, so that a cros section across the width of the ramp member will have crenellated, square-wave form. When such a ridged upp surface of the ramp member is employed, it will normally desirable to make the spacing of the ridges equal to t spacing between the projections on the movable member b with the ridges 180° out of phase, so that each projecti on the movable member passes adjacent a recess at the outl end of the ramp member. This form of upper surface may ha the advantage of ensuring that each projection on t movable member receives the same quantity of molten m terial. Although the upper surface of the ramp member may th have, a variety of forms, it has been found experimentall that good results can be obtained with ramp members havin flat upper surfaces inclined at a relatively small angle typically 5-10° to the horizontal. One way to avoid contamination of the molten materia is to use a ramp member formed from a material which doe not react with or dissolve in the molten material. In mos cases, a suitably inert ramp member can be formed of ceramic material; fire-brick is an appropriate and chea ceramic material. In cases where the molten material i reactive or likely to be contaminated by fire-brick, othe materials can of course be substituted. However, in man cases it may suffice to use a fire-brick or other cerami ramp member and to allow an initial portion of the molte material to come into contact with a cold ramp member thereby forming a thin covering of solidified material o the ramp member which will serve to prevent contact of late molten material flowing across the ramp member with th underlying ceramic material. Alternatively, skull meltin may be employed to ensure that the molten material does no become contaminated. Obviously , if necessary heat can be supplied either the ramp member or to the molten material flowing there across in order to ensure that solidification of the molt material does not occur on the ramp member . The ra member can be provided with built-in heating elements , f example electrical resistance heating el ements , or radian heat could be d irected downwardly onto the molten materi on the ramp member. However, in practice s ince the molte material will normally only be in contact with the ram member for a very br ief t ime , it will not usually b necessary to heat the molten material on the ramp member.

At the outlet end of the ramp member , the molte material forms a meniscus , and it is this meniscus throug which the projections on the movable member pass. (The te "meniscus" is used herein simply to refer to the edge of t layer of mol ten material at the out let end of the molte mater ial . At the outlet end of the ramp member, and is n intended to imply anything concerning the angle of contac between this molten material and the ramp member. ) Unli the fiber-forming method using an elongate slot to product pendant drop , the instant method does not require th presence of any sol id material above the liquid layer t def ine the slot, so the problems associated with the use very narrow slots are avoided. However, if des ired a soli member may be provided dipping into the upper surface of th layer of molten material on the ramp member in order to ski off any contaminants , such as oxides , which may be restin on the surface of the molten layer, thereby avoiding foulin of the meniscus at the outlet end of the ramp member Obviously, such a upper solid member need not be immediatel adjacent the outlet end of the ramp member but can be so distance therefrom, in order to avoid the difficulties whic might be occas ioned by the presence of what would be, i effect, a narrow slot at the outlet end of the ramp member. It is desirable that the edge of the ramp member at outlet end thereof have a sharp corner i.e. that the radi of curvature of this edge be very small. Such a sha corner at the edge of the ramp member assists in producing well-defined meniscus on the layer of molten material a limits any tendency for the molten material to creep ov the edge of the outlet end of the ramp member and trick down into the gap which usually exists between the outl end of the ramp member and the movable member lying adjace this outlet end.

The movable member used in the instant apparatus a method may have a variety of forms. For example, it cou have a comb-like form in which a plurality of elonga ridges are mounted on a base member and moved linear parallel to the ridges. However, for practical purposes όr-der to ensure a high rate of fiber production, it desirable to use a form of movable member which presents endless surface to the outlet end of the ramp member so th the surface of the movable member can be moved past t outlet^' end of the ramp member without interruption. F example, the movable member can have the form of an endle belt, passing around two pulleys and provided with a seri of parallel ridges running lengthwise along the belt. Th endless belt type of movable member does have the advanta that it can be so disposed relative to the outlet end of t ramp member that the portion of the belt which actual picks up the molten material is flat, and this ability use a flat portion of the movable member to pick up t molten material may be useful in some circumstances However, in general the preferred form of movable member f use in the instant method is a substantially cylindric rotatable member having the projections disposed on it periphery. Also, desirably the projections on the rotatabl member are in the form of a series of elongate ridge separated from one another by recesses, the axial spacin between adjacent ridges being from about 0.5 to 2 times th radial difference in heights between the tops of the ridges and 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 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 the formation 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 adjacent the outlet end of the ramp member is moving downwardly, it may tend to drag the molten aterial down into the narrow gap between the ramp memb and the movable or rotatable member, which may force molt material into the recesses in the movable or rotatab member, with a tendency to produce strip. In addition, is advantageous for the movable or rotatable member to ma initial contact with the underside of the meniscus; there a tendency for any contaminants to float on the top of t meniscus, so that initial contact with the lower part of t meniscus tends to reduce the likelihood that any su contaminants will be dragged into the fiber and consequent cause malformation thereof.

The thickness of the fibers produced by the insta method and apparatus may depend upon a large number factors, including the viscosity and surface tension of th molten material, the radius of curvature of the projectio oή"-~.the movable member, the thermal conductivity of t movable member and other factors. However, it should noted that the instant method does permit a measure control over the diameter of the fibers produced since o of the factors affecting fiber diameter is the penetrati of the projections on the movable member into the layer molten material on the ramp member. The deeper th penetration, the larger the diameter of the fibers produce Accordingly, it may be desirable to equip the insta apparatus with means for adjusting the penetration of th projections on the movable member into the layer of molt material on the ramp member. In the preferred form o apparatus in which the movable member is a cylindrica rotatable member bearing a plurality of parallel ridges such adjustment of penetration may conveniently be accom plished by providing means for moving the rotatable membe and the ramp member relative to one another; for example means might be provided whereby the axis of the rotatabl member can be moved towards and away from the ramp member. 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 movable member and the drawing of a plurality of filaments of molten material from the layer. As those skilled in the art will be aware, if the movable member picks 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 3,838,185. 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 U.S. 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. Such a cooling and wiping pad also has the advan¬ tages of removing any s.tray 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 about 15° to the horizontal. A metal rod 16, which may be of copper or an alloy such as Nig3Cri2^{Fe B}13^s-i*8» **-^{s e<}-- onto the upper end -17- of the ramp member 12 formed of fire brick at an appropri rate by a suitable advancing mechanism, such as a worm dr (not shown). The lower end of the rod 16 is heated by me of an induction coil 18 so that it melts to produce a str of molten metal which rolls in a thin layelr 20 down planar upper surface of the ramp member 12 and forms, at lower or outlet end of the ramp member 12, a meniscus (The overhang of the meniscus 22 over the edge of the r member 12 is exaggerated in the figure for the sake clarity. ) The rate at which the rod 16 is melted is arran so that the layer 20 of molten material on the upper surf of the ramp member 12 is kept thin. Thus, there is s stantially no hydrostatic head of molten material forc the meniscus 22 over the edge of the ramp member 12. thickness of the layer 20 should not exceed about 6mm. ir -most cases a much thinner layer, typically about l-2m will suffice. Because the thickness of the layer 20 is small, this layer will have a width much greater than i thickness so as to provide an elongate meniscus 22 which contact the movable member to be described below.

A movable member in the form of a rotatable wheel 24 disposed adjacent the outlet end of the ramp member 12. wheel 24 is mounted upon a shaft 26 provided with appropriate drive means (not shown) such as an electr motor. The wheel 24 is cylindrical, made of copper, and i cylindrical outer surface has a screw thread cut therei the threaded surface of the wheel 24 presents a plurality parallel ridges to the meniscus 22 of the molten materia

The wheel 24 is rotated so that it rotates upwardly past t meniscus 22, thereby enabling the multiple ridges present by the screw thread to the meniscus 22 to draw a plurali of filaments of molten material from the meniscus 22. the wheel 24 leaves the meniscus 22, the filaments 28 th formed solidify on the surface of the ridges and a eventually flung from the wheel 24 by centrifugal force a land on a collecting surface 30. On the opposite side the wheel 24 from the meniscus 22, a wetted cotton pad contacts the wheel. The pad 32 serves to cool the whee thereby ensuring that it will properly produce the desir fibers, and also serves to remove stray fibers adhering the wheel, together with.any dirt or other surface co taminants which may be present on the wheel 24.

As is well known to those skilled in the art, t ridges on a wheel used for producing fiber from molt material tend to become less sharp after lengthy use i. the radius of curvature of the tops of the ridges increase This loss of sharpness tends to disrupt the production high-quality fibers. However, the screw thread on the whe 24 can be inexpensively and easily redressed using co ventional thread cutting devices. As explained in the aforementioned U.S. paten 3 8_38,185 and 3,896,203, the speed at which the wheel pass through the molten material is important in controlling t quality of the fiber. In general, the speed at which t wheel 24 passes through the meniscus 22 should normally in the range of about 3 to 30m.sec."-¹-, though the exa usable speed range will vary with a large number of par meters, including the surface tension, density, and te perature of the molten material, and possibly the_. materi from which the wheel is composed. We estimate that using a wheel 24 which is 2.5c thick, 20cm. in diameter and having approximately 25 threa era.--¹ rotating at 500 rpm. , in excess of 100kg. of 0.125m diameter steel fibers could be produced per hour; this better productivity than is currently being achieved wi fibers of three times the diameter.

The second apparatus of the invention shown in Fig. of the accompanying drawings operates in a generally simil manner to that shown in Fig 1, except that, in order increase the rate of production of fibers, two separa wheels 24 and 24* are provided. Between the wheels 24 a 24' is located a single ramp member 34 made of fabric-a having the form of a pentagonal prism the axis of which perpendicular to the plane of Fig. 2. The two upper fac 36 and 38 of this ramp member are inclined in opposi directions, sloping downwardly from a central ridge line points adjacent the wheels 24' and 24 respectively. stream of molten material 40, which may be produced pouring or otherwise allowing outflow from a bath of molt material, or by melting, for example, a metal rod suspend above the ridge line of the ramp member, flows downward onto the ridge line of the ramp member and thence down t faces 36 and 38. The wheels 24 and 24' are rotated suitable drive means (not shown) in the directions indicat by the arrow in Fig. 2 so that they pass upwardly past t lower edges of the faces 36 and 38, thereby causing fil ments 28 and 28* to be drawn from the layers of molt material on the faces 36 and 38. These filaments 28 a 28' solidify on the surface of the ridges on the wheels and 24' and are eventually flung from the wheels by ce trifuga force and land on collecting surfaces 30 and 3 respectively the same way as in the apparatus previousl described with reference to Fig. 1. The wheels 24 and 24 are equipped with pads 32 and 32' which operate in exactl the same manner as the pad 32 shown in Fig. 1.

It will be apparent to those skilled in the art tha numerous changes and modifications can be made in th embodiments of the invention described above withou departing from the scope of the invention. In particular by cutting recesses extending axially through thejthread o the wheel 24, a form of wheel having interrupted ridge comparable to the wheel shown in Fig. 6b of the afore mentioned U.S. patent 3,838,185 could be produced, thereb enabling short fibers of consistent length to be achieve rather than the more random fiber length distribution whic occurs with unbroken threads. Other changes and modi fications will be apparent to those skilled in the art Accordingly, the foregoing description is to be construed in an illustrative and not in a limitative sense, the scope of the invention being defined solely by the appended claims.

Claims

1. Apparatus for the production of fiber, sai apparatus comprising: supply means for supplying a stream of molte material; a ramp member having a upper surface for receivin 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. -22-

6. An apparatus according to claim 5 wherein sai ramp member is formed of fire-brick. *

7. An apparatus according to claim 1 wherein sai projections on said movable member are in the form parallel elongate ridges and said movable member moves pa said outlet end in a direction substantially parallel to t length of said ridges •

8. An apparatus according to claim 1 wherein sai movable member comprises a substantially cylindric rotatable member having said projections disposed on i periphery.

9. An apparatus according to claim 8 wherein sai rotatable member is arranged to rotate so that the porti of said rotatable member adjacent said outlet end of sa ramp member is travelling upwardly.

10. An apparatus according to claim 9 wherein sai projections on said rotatable member are in the form of series of elongate ridges separated from one another b recesses, the axial spacing between adjacent ridges bein from about 0.5 to about 2 times the radial difference i height between the tops of said ridges and the deepest par of said recesses.

11. Apparatus for the production of fiber, sai apparatus comprising: supply means for supplying a stream of molte material; a ramp member for receiving said stream of molt material from said supply means, said ramp memberpaving a upper surface such that said stream of molten materia flows across said upper surface to form a layer of molte material having a width greater than its thickness, sai 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 wh ich said layer of molten material is under a pressure not substantially greater than that of the surrounding atmosphere; and a substant ially cyl indr ical 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

> *) kf X rotates, said ridges pass. 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 outlet 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 i not substantially greater than that of the surroundin atmosphere; and moving a plurality of projections spaced from on another through said outlet end of said layer, thereb drawing a plurality of filaments of molten material fro said layer, said filaments solidifying to form said fibers.

14. A method according to claim 13 wherein said molte material is molten metal.

15. A method according to claim 13 wherein sai surface is disposed at any angle of not more than about 30 to the horizontal.

^■•-^ 16. A method according to claim 15 wherein sai surface is disposed at an angle of not more than about 15 to the horizontal.

17. A method according to claim 13 wherein sai projections are in the form of parallel elongate ridges an are moved through said layer in a direction substantiall parallel to the length of said ridges.

18. A method according to claim 13 wherein sai projections are carried on the periphery by a substantiall cylindrical rotatable member and are moved through sai layer by rotation of said rotatable member.

19. A method according to claim 18 wherein sai rotatable member is arranged to rotate so that said pro jections pass through said layer in an upward direction.

20. A method according to claim 18 wherein sai projections on said rotatable member are in the form of series of elongate ridges separated from one another b recesses , the axial spacing between adjacent ridges bein from about 0.5 to about 2 times¹ the radial difference i height between the tops of said ridges and the deepest part of said recesses.