Rotary forming unit for fine mineral fibers
United States Patent 3928009

An improved apparatus for the formation of fine fibers from mineral materials, especially glass, in which molten material feeds continuously into a rotor turning at high speed, and discharges by centrifugal force thru multiple orifices in the outer peripheral rotor wall as fine filaments, and with hot gaseous means to control the temperature of the zone immediately beyond the rotor outer wall. This invention specifically concerns improvement in the rotor unit itself. The rotor is preferably built with a main structure of base metal, and an outer peripheral wall of precious metal with filament forming orifices therein. Means are provided to reduce centrifugal forces on the outer wall to permit using relatively weak platinum alloys, and larger diameters than presently used, and attaining the additional advantages of longer life and more uniform filaments. A closely spaced inner wall with platinum metering orifices insures uniform feed, permits using larger orifices for longer wear. Insulating means provided to shield the rotor parts from heat loss to cool rotor shaft, and uniform temperature of inner rotor parts is assured. Alternately outer wall may be base metal clad with platinum. The invention applies to and is continuation-in-part of my Ser. No. 231,347. In former application the rotary apparatus had improved outer attenuation blast, the elements of the annular blast having directional control, each element having a component of velocity tangential to and in the same direction as the rotor outer wall. Subject invention applies to this system, and as well to those systems well known in the art in which the filaments leaving the rotor outer wall are further attenuated by an annular gaseous blast, the gases being air, steam, or products of combustion.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
65/522, 425/8
International Classes:
C03B37/04; (IPC1-7): C03B37/04
Field of Search:
65/6,14,374M,374RM 425
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Primary Examiner:
Lindsay Jr., Robert L.
Parent Case Data:

This invention relates to rotary forming apparatus for forming fine fibers from molten mineral materials, especially glass. This application is a continuation-in-part of my application Ser. No. 231,347, which was filed Mar. 3, 1972 now U.S. Pat. No. 3,785,791, granted Jan. 15, 1974.
What I claim is

1. In an apparatus for forming fine fibers from heat softened viscous thermoplastic mineral material, such as glass, said apparatus comprising,

2. Apparatus according to claim 1 in which said superposed filament forming orifices are arranged in a plurality of separate circular bands, and with each band extending around said outer peripheral wall, and with a line of spacing extending between adjacent bands, and with said corrosion resistant alloy material welded to said base metal outer annular support means along said line of spacing to provide additional support to said corrosion resistant alloy material against centrifugal forces.

3. In an apparatus for forming fine fibers from heat softened viscous thermoplastic mineral material, such as glass, said apparatus comprising,

4. Apparatus according to claim 3 in which said orifices in said inner wall are lined with corrosion resistant alloy consisting essentially of platinum group metals.

5. Apparatus according to claim 3 in which said corrosion resistant alloy material in said outer peripheral wall of said rotor comprises an alloy consisting essentially of platinum and rhodium.

6. Apparatus according to claim 3 in which grooving is formed in said corrosion resistant alloy material in said outer peripheral wall of said rotor, and with said grooving extending around the circumference to provide for thermal expansion.

7. Apparatus according to claim 3 in which said outer peripheral wall area of said rotor which is made of said corrosion resistant alloy is divided into a plurality of lengths of arc around the circumference, and with said arc lengths welded to said outer annular support means.

8. Apparatus according to claim 3 in which said filament forming orifices in said corrosion resistant alloy material in said outer peripheral wall of said rotor have the metal around the orifices formed in the shape of individual outwardly projecting nozzles.

9. Apparatus according to claim 3 in which said superposed filament forming orifices are arranged in a plurality of separate circular bands, and with each band extending around said outer peripheral wall, and with a line of spacing extending between adjacent bands, and with said corrosion resistant alloy material welded to said base metal outer annular support means along said line of spacing to provide additional support to said corrosion resistant alloy material against centrifugal forces.

10. Apparatus according to claim 9 in which each said band of orifices in said outer peripheral wall has a separate partitioned off inner annular compartment immediately radially inward of it, and with each said inner annular compartment having circumferentially spaced metering orifices in that section of said inner annular wall which forms the back of said separate inner annular compartment.

11. Apparatus according to claim 3 in which there is a supplementary outer peripheral overflow wall band positioned adjacent to said outer peripheral wall and with filament forming orifices therein, and said overflow wall band connected by passageway to receive excess molten material when the thickness of the layer of molten material back of said main outer peripheral wall exceeds a specified limit, and to discharge said excess thru said filament forming orifices as fine filaments.

12. In an apparatus for forming fine fibers from heat softened viscous thermoplastic mineral material, such as glass, said apparatus comprising,

13. Apparatus according to claim 12 in which said lamination of corrosion resistant alloy comprises an alloy consisting essentially of palladium and ruthernium.

14. In an apparatus of the character disclosed for forming fine fibers from heat softened viscous thermoplastic mineral material, such as glass, said apparatus comprising,

15. Apparatus according to claim 14 in which said heat insulating means comprises fibrous insulation.

16. Apparatus according to claim 14 in which heat insulating material is interposed between said flange wall of said rotor and said shaft means.

17. Apparatus according to claim 14 in which heat insulating material is interposed between said inner members of said rotor structure and said flange wall of said rotor.

The instant application includes several novel means for improving the rotary apparatus and its temperature controls which are transferred from my Ser. No. 231,347 application, and which were described in the previous specification, and are shown in the drawings in FIGS. 1 thru 11. The associated claims are also being transferred. My continuation application also includes additional inventions which are described in this specification and are shown in the drawings FIGS. 12 thru 22, and which substantially improve the quality and uniformity of the fine fibers formed by the apparatus, and also greatly increase the operating life of the rotor.


1. Field of the Invention

This invention relates to the formation of fine fibers from heat softenable mineral materials, more particularly glass, by intorducing a stream of the hot softened material into a hollow rotor which is turning at high speed, and which has multiple orifices in its outer peripheral wall thru which the molten material discharges outwardly by centrifugal force to form fibers, and with gaseous means to control the temperatures in the zone immediate to the rotor outer wall, and with additional high velocity gaseous means provided to further attenuate the fibers to substantially decrease their diameters. It also relates to the production of fine fibers using apparatus in which the outer attenuation blast is eliminated, and the necessary fineness is attained by providing smaller orifices in the rotor wall, and depending on this plus the rotational drag to give the required fineness of fiber.

The fibers so produced are then generally spray impregnated with a thermo-setting resinuous binder and collected on a foraminous conveyor, supplemented with the output of several additional fiberizing units, and with the blanket so formed then sized to thickness and the resin cured in a continuous oven.

2. Description of Prior Art

The means and apparatus heretofore used to accomplish the formation of fine fibers by similar rotary process have had several serious drawbacks which prevented attainment of the desired physical properties of the fibers and prevented their proper orientation, and as a result reduced the quality of the end products into which the fibers were formed. For instance the means used up to now have resulted in the fibers being too coarse and non-uniform in size, relatively short in length, and excessively twisted and balled up. If the fibers are too short they are less likely to lie horizontally in the formed blanket, and instead a large number will stand inclined or on end, in which positions heat is conducted along the body of the fiber and thru the thickness of the insulating mat, reducing its insulating value. Coarse fibers also transfer more heat because of their larger size. Excessive twisting and balling up of the fibers produces porous spots in the blanket, which results in a higher thermal conductivity, or k value for the insulation. The k value is defined as the amount of heat expressed in Btu's transmitted in 1 hour thru 1 square foot of a homogeneous material one inch thick for a difference in temperature of 1° Fahrenheit between the two surfaces of the material. Short fibers and poor orientation also make a weaker sheet in products requiring tensile strength and rigidity. Among the more common products manufactured by this rotary process are insulation mats and blankets, sound absorbing panels, sheets for air ducts, and chopped fibers for plastic reinforcement.

Major drawbacks in the apparatus used up to now in the centrifugal fiber forming process have been due to excessive and uneven heat loss from the rotor by radiation, by windage, and by conduction to the cooled driving shaft, and by uneven replacement of this heat to maintain the glass at its optimum attenuating temperature, and also to non-uniform or excessive temperatures and velocities in the zone immediately adjacent to the outer wall of the rotor where the filaments are first formed, and also and primarily to lack of proper directional control of the final gaseous attenuation blast with respect to the direction of rotation of the rotor outer wall.

Another serious drawback up to now has been in the construction of larger size rotors, such as those over 6 inches in diameter. The larger sizes range up to 12 or more inches in diameter, and are needed to produce increasingly larger outputs of fine fibers per rotor. The smaller sizes have been successfully made of precious metals, such as platinum-rhodium alloys, but in large sizes this metal is both too expensive and does not have the necessary strength to resist the centrifugal forces. As a result it has been necessary to construct the larger sizes of base metal alloys. These are very difficult to drill or pierce, especially with the very small size of orifice used in apparatus in which an attenuating outer annular blast is not used. Further, and more important, at the high operating temperatures required the orifices are rapidly eroded to larger size, resulting in a life of only 10 to 20 hours, and even during this period of time there results a constantly changing filament and fine fiber size, and a diminution in insulating quality.


It is a primary object of the invention to produce fine fibers which are more uniform in size and of substantially greater length than is possible with apparatus known before. Another primary objective is to minimize the tendency of the fibers to twist together such that they form a blanket which is not uniform in density thru-out its thickness and length.

Still another object of the invention is to hold the gaseous flame which maintains the temperature in the initial attenuation zone just beyond and adjacent to the outer perforated wall of the rotor at a uniform level just above the glass filament temperature and free of uncontrolled infiltrated air, and this same flame serving to hold the perforated wall temperature just above that of the glass.

Another object of the invention is to optionally control the angular direction of the annular flame discharged from the burner exit slot serving the first attenuation zone so it moves in a direction tangential to that of the rotor outer wall.

Still another object of the invention is to maintain the temperature of the flanged parts of the rotor adjacent to the outer wall by a separate heat source so these parts do not draw heat from the perforated wall.

A further object of the invention is to construct the rotor with its perforated outer wall and its glass receiving inner disc independent of its shaft mounted supporting flange, and with light weight insulation between the two parts. This reduces heat loss from the rotor disc which receives the stream of molten glass, so heat make-up to maintain the required temperature comes largely from the incoming molten material.

A further object of the invention is to partially insulate the lower rotor supporting flange from the shaft in order to reduce still further the loss of heat to the water cooled rotor shaft.

Another object of the invention is to form the rotor flange elements in such a way as to reduce windage, which both causes a loss in temperature of parts of the rotor and also entangles the fibers in the first attenuation zone, which is just as the filaments leave the rotor outer wall.

Another object of the invention is to provide a composite rotor construction with the main body elements made of base metal, and with the outer cylindrical wall made of precious metal and with multiple orifices therein, thereby reducing the rate of orifice wear, providing more uniform fiber size, and with much longer rotor life. An object is to form the metal into projecting nozzles.

Another object of the invention is to construct the rotor with one or more inner cylindrical walls thru which the molten mineral material flows outwardly at a metered rate thru calibrated orifices, and to provide precious metal linings for these orifices to reduce wear.

Still another object of the invention is to provide means to control the thickness of the layer of molten material which is held by centrifugal force against the inner side of the precious metal outer wall, and to hold it in a thin layer to minimize the pressure against the relatively weak precious metal outer wall.

Another object of the invention is to divide the outer wall into two or more levels in a vertical direction, and with a separate annular compartment back of each level to provide more uniform distribution of the molten mineral material to the outer wall.

Another object of the invention is to provide distribution means to distribute molten material to each of two or more levels of the outer wall perforated bands.

Still another object of the invention is to provide an overflow compartment around the lower level of the rotor wall, and with a corresponding circular band of discharge orifices, and for the purpose of preventing overloading of the upper compartments, which would strain the precious metal walls.

Another object of the invention is to construct the outer wall of the rotor of base metal which is clad on one side with a lamination of precious metal in which the orifices are formed, and thereby to obtain long life of the orifices, and with the base metal providing the strength to resist the centrifugal forces.

Still a further object of the invention is to divide the outer wall precious metal band into multiple sections of arc around the circumference to reduce the temperature expansion in the band, and to lower the centrifugal force the band must resist.

Another object of the invention is to form off-set grooves in the precious metal outer wall material to provide resilience for uneven temperature expansion between the base metal framework and the precious metal wall material.

Still another object of the invention is to provide means to minimize the distorsion of the rotor supporting flange member caused by temperature changes and uneven expansion.


Other objects and advantages of the invention will become apparent from the description given in the specification and by reference to the following drawings:

FIG. 1 is a vertical sectional view thru the part of the apparatus forming the subject matter of the invention.

FIG. 2 is a cross-sectional view of part of the outer annular blast means showing the angular positioning, and is taken on line 2--2 of FIG. 1.

FIG. 3 is a horizontal sectional view taken along line 3--3 of FIG. 2, and shows the adjacent positioning of the individual blast nozzles.

FIG. 4 is a sectional view similar to FIG. 3, but showing an alternative positioning of the lower ends of the tubular nozzles.

FIG. 5 is a sectional view taken on line 5--5 of FIG. 1, showing the construction of the tangential burner elements which make up the main burner assembly for control of the temperatures and gas currents adjacent to the outer wall of the rotor.

FIG. 6 is a side view of the forming unit assembly which shows the angular and partially tangential paths of the gaseous elements in the outer annular blast with respect to the direction of rotation of the rotor, and with the blast elements moving with a velocity component in the same direction as the rotor outer wall.

FIG. 7 is similar to FIG. 6, but with the outer blast elements moving vertically and parallel to the axis of the rotor.

FIG. 8 is also similar to FIG. 6, but with the outer blast elements moving with the tangential component of velocity moving against the direction of the rotor outer wall.

FIG. 9 is a vertical sectional view of an alternative design which incorporates some of the main features of the invention.

FIG. 10 is a cross-sectional view of part of the outer annular blast means similar to FIG. 2, but an alternative design.

FIG. 11 is a horizontal sectional view taken on line 11--11 of FIG. 10 to further explain the construction method.

FIG. 12 is a partial cross-sectional elevation showing an improved method of constructing a centrifugal rotor with a base metal framework and a precious metal perforated outer wall.

FIG. 13 is a cross-sectional elevation showing an alternative design of rotor which has interior parts made of base metal, mainly, and with a precious metal perforated outer peripheral wall.

FIG. 14 is a cross-sectional elevation showing another alternative design of rotor with precious metal outer wall, and with additional means to insure uniform molten mineral distribution.

FIG. 15 is a partial cross-sectional view taken along line 15--15 of FIG. 13 to show segmental arc construction.

FIG. 16 is a partial side view of a rotor outer wall showing means to reduce heat expansion strains in the outer wall material.

FIG. 17 is a horizontal cross-sectional view taken along line 17--17 in FIG. 16.

FIG. 18 is a partial cross-sectional elevation showing another construction of the rotor with a composite outer wall.

FIG. 19 is a vertical cross-sectional elevation taken along line 19--19 in FIG. 16.

FIG. 20 is a partial view of the underside of the rotor of FIG. 18, and showing the use of a modified bottom support flange.

FIG. 21 is a partial cross-sectional elevation showing still another method for constructing the rotor with a composite outer wall.

FIG. 22 is a partial cross-sectiional view showing the construction of a precious metal outer wall with projecting nozzles press formed in the metal.

FIG. 23 is a partial cross-sectional elevation showing an alternative construction in keeping with the invention.

FIG. 24 is a partial cross-sectional elevation showing a construction in which the glass is fed thru a hollow shaft, and the rotor main support flange is on the upper side, and incorporating features of the invention.


The present invention provides improved apparatus for forming fine fibers from heat softenable mineral materials. The principle use for the apparatus is for producing fine fibers from molten glass, and the word glass will be used often in the following discussion. The glass must first be heated to a fluid state above its liquidus temperature, and maintained above the liquidus temperature thru-out the fiberizing process. The molten glass may be produced by melting cullet or marbles in a retort, pot, or bushing. The most usual and efficient method, however, is to position the fiber forming apparatus under the forehearth at the finishing end of the glass producing furnace, and then to discharge the melted glass directly into the fiberizing unit at the correct temperature. The most usual practise is to provide several fiberizing units, each receiving a glass stream from the forehearth, and generally arranged in line, one after the other.

FIG. 1 shows the general arrangement of the rotary fiber forming apparatus, and this drawing incorporates some of the novel features of this invention. Other novel features are shown in the other drawings. Additional equipment is also required beyond this unit, such as spray means for applying resinous binder to the fibers, a foraminous collection conveyor under the fiber forming unit on which the fibers are collected with suction means under the conveyor to draw down the fibers into mat form, and an oven for sizing and curing the resin impregnated mat, but these are not shown as such equipment is well known in the art.

Referring now to FIG. 1 of the drawings, a section of the forehearth of the glass making furnace is shown at 14. A stream of molten glass 12 discharges from orifice 13 in the bottom of the forehearth. The rate of flow and the temperature of the glass are closely controlled. A water cooled compartment 15 is located under the forehearth to protect the driving unit from excess heat. A supplemental vertical section 18 serves to absorb the radiation from the glass stream 12. The cooling water enters at 16 and discharges at 17 for the two sections.

The stream of glass discharges continuously into rotor 45. This rotor is mounted on shaft 20 and is rotated at high speed. The speeds range from 2000 to 4000 RPM, depending on the diameter of the rotor. The rotor diameters vary from 6 inches to 12 inches, the lower speeds being used for the larger size rotors. Whereas the spinner is shown with a vertical shaft, it may be inclined or horizontal in accordance with prior art, provided suitable changes be made in means to introduce the glass stream into the rotor.

The rotor shaft may be driven by electric motor, preferably mounted to one side as shown, with pulley 27 on the motor shaft which drives belt 26 engaging pulley 25 on shaft 20. Shaft 20 is mounted on ball bearings 21 and 22 which are positioned in sleeve 23, which in turn is supported on the main frame, not shown. The sleeve is cooled by spiral water piping 24. Cooling means are also provided for shaft 20, and include water supply 28 at the top, inner tube member 29 thru which the water flows downward and out thru hole 34 into the cavity 35 between the tube 29 and the wall of the shaft. The cooling water rises and discharges thru nozzle 31 into collecting chamber 32 and then out drain 33. The rotor design has several novel features in keeping with the invention. Heretofore the rotors have been connected to the cooled mounting shaft in such a way as to draw excessive heat from the rotor, and this heat is difficult to replace while still maintaining a uniform temperature thru-out the inner working areas of the rotor, where the temperature of the glass must be maintained above its liquidus temperature and close to its optimum working range.

In keeping with my invention, the rotor is constructed with a hollow shaped bottom flange 42 which supports the main section 45 of the rotor, and serves to drive it. Member 42 is mounted on insulating collar 39, which is made of hard machinable refractory insulation, and serves to reduce the heat flow to shaft 20. It is held by nut 40. The contour of flange 42 is designed with an outer curved edge 43 curving downward as shown. I have found that a hollow disc of this design with its cup shaped outer peripheral section can be rotated at high speed without forming any appreciable wind currents on its hollow underside. This compares with the usual convex shaped bottom heretofore used, and which results in the formation of excessive windage. Such windage heretofore served to cool the rotor body on its underside, especially at the outer wall, and also adversely affected the fiber formation by causing balling up of the fibers.

The main body of the rotor is 45 with outer wall 46, and with several thousand small orifices 47 arranged in superposed rows in the outer wall thru which the molten glass flows to form molten filaments 49 under the pressure of centrifugal force due to the rotation of the rotor assembly. Member 45 may be of precious metal, such as an alloy of platinum and rhodium. or it may be made of one of the many high temperature base metal alloys now available, and containing varying percentages of nickel, iron, chromium, molybdenum, and other elements. These alloys are marketed under the trade names of Inconel, Hastelloy, Nichrome, Nimonic, Duranickel, and numbered stainless steels. Lower flange 42 may be made of one of these high temperature base metal alloys, and may be attached to 45 by welding, or preferably using a circle of rivets 44 of nickel alloy. This construction minimizes the flow of heat from the rotor part 45 to the shaft, both because of the small metallic contact and because high temperature nickel alloys are poor heat conductors. Member 45 has an inner formed section 50 of the approximate shape shown, and preferably with a shoulder at 51. Shoulder 51 is roughly in line with the center of the band of perforations in the rotor outer wall. Glass stream 12 falls onto rotating surface 50 and the glass flows down the incline to the shoulder 51, whwnce it is thrown out by centrifugal force to the inner side of wall 46, providing uniform distribution within the limits required. Some glass can flow down the incline below 51 to the lower region of the outer wall. A low density insulation 52 is provided to reduce the loss of heat downward from section 50. It may preferably be of fibrous type, and extend down between 42 and 45 at the rivet line.

The upper flange 53 of the rotor also has a reverse bend, both to reduce windage, and further to facilitate heating by a single burner 37 located above the rotor and 180 degrees from the glass stream. This burner is supplied with air-gas miixture thru pipe 38, and its flame is directed to heat all surfaces 46, 50, and 53. The flame of this burner has a considerably higher temperature than that of burner 60 in order to effect more rapid heat transfer so a single burner is sufficient. The flame temperature of 37 may be 3000° to 33000° F.

The usual glasses used in this type of operation have an optimum fluidity for centrifugal ejection at temperatures ranging from 1900° to 2100° F. The glass is held at a somewhat higher temperature in stream 12 to compensate for a small temperature drop before it passes thru the perforations. The heat from this temperature drop helps to hold member 50 close to the glass temperature, but some additional heat is added to 50 by burner 37. Prior art shows the same burner for heating the rotor flanges as for heating the initial attenuation zone 48, and since to effectively transfer heat to the flanges requires a higher flame temperature than is permissable in zone 48, such prior art depends on infiltrated air to partially cool the flame to the 1900° to 2100° F. required in zone 48. It is impossible to mix high temperature flame with cool infiltrated air is such a small and confined area and obtain uniform temperatures at all points.

Referring still to FIG. 1, a burner assembly 60 is provided to produce a hot gaseous flame 70 to maintain zone 48 at close to the glass filament temperature, which ranges from 1900° to 2100° F., depending on the glass composition being used. Flame 70 is preferably low velocity because the attenuation of filaments 49 into very fine fibers is to be accomplished primarily by gaseous blast 81. It is advantageous that flame 70 discharge from the annular burner exit slot with a component of its velocity in a direction tangential to the rotor outer wall, and moving in the same direction. This is accomplished by the burner design shown in FIG. 1, and in the sectional view of FIG. 5, in which the section is taken along line 5--5 of FIG. 1.

Burner 60 is constructed with multiple burner tunnel assemblies similar to that shown in FIG. 5 arranged around its circumference. Four or six tunnels is the preferred arrangement to obtain uniform exit velocities and temperatures. Referring to FIG. 1, air-gas mixture is supplied thru annular header 61 and connecting pipe section 62, with individual control orifice 52 to insure each burner receiving the same flow of air-gas mixture. Optionally orifice 52 may be replaced by an automatic thermo-couple controlled valve for exact temperature control of each burner. Referring to FIG. 5, the header is 61a, the connecting pipe 62a, and the orifice 52a. The air-gas mixture passes thru ceramic screen 63a, and shoulder 64a becomes incandescent to maintain combustion. The combustion is generally complete within refractory tunnel 59a before the gases reach the main burner annular chamber defined by outer refractory wall 66a and inner refractory wall 65a. A lean air-gas mixture is used in order to hold the flame temperature down as close as possible to the exit temperature desired at the rotor wall. It is generally necessary to add additional cooling air, and this is accomplished thru pipe connection 54a, which discharges air into the tunnel 59a where it mixes with the hot gases. A compressed air annular header 56a supplies the cooling air, and orifice 55a regulates the amount to this burner, and with over-all control by varying the pressure in the header. By introducing the cooling air at this point it is thoroughly diffused by the time the flame exits at 70, so the temperature at 70 is very uniform.

In FIG. 1 the tangential burner is 57, the ceramic screen is 63 with incandescent circular shoulder 64, and the tangential burner tunnel wall is 58. The main annular burner refractory walls are 65 and 66, and these converge downward to where the annular exit slot is defined by stainless steel walls 67 and 68, cooled by water tubes 69. Optionally annular wall 68 has inclined thin spaced fins 73, and wall 67 has similar but staggered inclined fins 72, these fins helping to control the tangential component of the flame. The tangential arrangement of the burners 57 serves to rotate the hot gases in the main tunnel and to also give the exit gases at 70 a tangential velocity component preferably in the direction of the movement of the rotor outer wall.

In FIG. 1 the flame 70 also assists in holding outer rotor wall 46 at the temperature of the glass flowing thru the perforations. Further it supplies the gases for the windage created by the high velocity of wall 46, so the windage does not cool the wall. Further, flame 70 provides the hot gases which are drawn down by the inspirational effect of high velocity blast 81, described below. Otherwise cool room air would be inspirated, cooling the rotor. It is important to note that flame 70 is relatively low in velocity, and is used for temperature control and not for substantially attenuating the filaments. The diameter of the filaments as they leave the rotor wall is on the order of 10 microns, or 0.0004 inch.

Final attenuation of the filaments to the finished size is effected by high velocity annular gaseous blast 81. The fineness desired depends on the product being manufactured, and it will vary normally over a range of 21/2 to 5 microns, with 4 microns satisfactory for most insulations. The blast is preferably warm air, but may be hot air, cool air, steam, or other gas. The blast should be as close to the wall 46 of the rotor as convenient without resulting in cooling of the wall. If too far away the fibers become entangled excessively.

An important element of the invention which is covered by my previous application, Ser. No. 231,347, is the manner in which the outer gaseous blast is formed, and the guided direction in which it moves. This feature of the invention is described herein to explain the drawings more fully, although it is not part of the subject matter covered in the claims of this continuation-in-part. Referring to FIG. 1, an annular header 75, with removable cover 76, is supplied with filtered compressed air, or other gaseous medium, thru supply pipe 83. In the most desirable form the gas is air.

In order to obtain the most efficient conversion of gaseous pressure to gaseous velocity and kinetic energy, in accordance with the invention the annular outer blast is discharged thru a series of tubular nozzles designed for maximum efficiency from the aerodynamic standpoint. One of these nozzles 77 is shown in FIG. 1, and the next adjacent one is 79. It will be noted that each tube is flared out at the upper inner end and every other nozzle is slightly longer and bent sufficiently so the flared ends do not interfere to prevent close spacing of the nozzles around the periphery.

FIG. 2 shows a cross-section thru several nozzles taken along line 2--2 in FIG. 1. In FIG. 2 are shown four adjacent nozzles 77a, 79a, 91a, and 92a. Each nozzle has an upper flared end so the entrance can be formed to the exact shape required to attain maximum entrance efficiency with the least turbulance. For greatest aerodynamic efficiency the outer diameter of the flare at 78a should be twise the inside diameter of the tubular section of the nozzle.

The positioning of the lower discharge ends of the nozzles is shown in FIG. 3, and is a section taken along line 3--3 in FIG. 2. It will be noted that the ends of the four nozzles are close together at 92b, 91b, 79b, and 77b. FIG. 4 shows a similar cross-section, but with the nozzles staggered at 92c, 91c, 79c, and 77c. The preferred material for construction of the nozzles is stainless steel to provide a smooth surface for laminar flow and maximum jet velocity. It also prevents the surface from becoming rough from rust.

Each nozzle should also have its lower end set at the most advantageous angle with respect to the nearest vertical wall or outer face of the rotor. This angle is shown as 82 in FIG. 1, and it has been found that for best operation the nozzle lower end and the discharging jet should point somewhat toward the rotor face as shown in the drawing. The outer gaseous blast should be slightly conical, converging downward, rather than cylindrical, and the gaseous elements should also move in a rotational or spiral direction, preferably in the direction of rotation of the rotor. Whereas I show the rotor with a vertical outer face, this face can also be somewhat inclined in accordance with prior art.

A circular baffle member 84 in FIG. 1 is provided to enclose the attenuation zone to reduce inspiration of ambient air from the outside. A shield 71 also limits inspiration of air from above, and an opening 74 is provided for passage of the glass stream 12.

The angular discharge of the outer gaseous blast is further illustrated in FIGS. 6, 7, and 8. Referring to FIG. 6, this shows a side view of the fiber forming assembly with rotor 111 turning on shaft 110, burner housing 116, and gaseous header 112, where the view is broken away to show the gaseous blast nozzles 113 inclined at an angle so the gaseous blast elements 114 discharge at an angle 115 with respect to the axis of the shaft, or the vertical. The near side of the rotor is moving to the right in the direction of the arrow.

This is the preferred angular setting of the outer gaseous jets to obtain the finest and longest fibers. Optionally, however, the unit can be designed with the jet discharge vertical, and parallel to the shaft, as shown in FIG. 7, in which the shaft is 110a, the the rotor 111a, the burner 116a, the gaseous supply header 112a, and the broken away view shows the blast nozzles 1131 positioned vertically and with the blast 114a moving straight down. For some operations requiring shorter fibers the jets can have a reverse angle as shown in FIG. 8 in which the shaft is 110b, the rotor 111b, the burner 116b, the gaseous supply header 112b, and the jet nozzles 113b angled backward with the blast against the direction of rotation.

FIG. 9 shows a modified form of the invention. The glass stream 124 falls directly onto inner member 125 of rotor 131, and is carried by centrifugal force to the outer wall 136 of the rotor, whence the glass is forced thru orifices 137 by centrifugal force to form filaments 138. Rotor body 131 is supported on hollow bottom plate 132 to which it is attached by circle of rivets 123, and plate 132 has outer curved down edge 122. Insulation 133 and insulating bushing 134 serve to reduce the heat loss from the rotor 131. Nut 135 holds the assembly to shaft 130. Burner 139 provides an annular discharge of hot gases 140 to control the temperature in the initial attenuation zone adjacent the rotor wall 136 close to the 1900° to 2100° F. range required to sustain the temperature of the discharging filaments.

Annular header 144 supplies compressed gaseous medium, such as compressed air, to an initial circle of nozzles 146, which discharge attentuation blast 150 to attenuate the filaments into fine fibers. A second circle of nozzles 153 is also provided, and with the lower ends of these nozzles protected by annular shroud 148. This row of nozzles discharge attenuation blast 151, and they are backed up by shroud 154 to reduce air infiltration. The double circle of nozzles makes it possible to attenuate efficiently with a rotor wall of greater height with more rows of orifices for greater output.

FIG. 10 shows an alternative, but less efficient method for constructing the nozzle elements. A circular annular member 102 has formed across its face a series of ridges 103 set at angle 104. FIG. 11 is a cross-section taken along line 11--11 of FIG. 10, and shows outer cover facing 106a to form the spaces between the ridges into discharge slots or nozzles. This construction is less efficient aerodynamically because the entrance ends can not be flared properly.

In FIG. 9 three separate burners are provided to control the temperatures in the different parts of the rotor. Burner 164 with air-gas mixture supply pipe 161 heats the upper flange 141 of the rotor, burner 165 with supply pipe 162 heats member 125, and burner 166 with supply pipe 162 heats member 125, and burner 166 with supply pipe 163 heats the rotor outer wall 138 from the inside, and also adds heat to the glass at this point. By providing individually controlled burners for the three elemental parts of the rotor it is possible to hold the temperature of each part close to the desired temperature of the glass at that point. Thermo-couples may be used to control each flame for increased accuracy. Whereas the drawing shows a single burner for each element, two or more burners may be arranged in parallel around the circumference.

Referring to FIG. 1 it will be noted that the gaseous blast 81 is shown moving down at an angle 82 with the vertical, or with the axis of the rotor. This angle is shown to an exaggerated scale in the drawings for clarity. Each individual gaseous element has a major velocity component which is downward and in the same plane as the axis of the rotor, and which is substantially parallel to the rotor axis, even though the combined downward gaseous velocity components are slightly conical.

In an alternative arrangement, a second annular outer gaseous blast is provided, and is positioned radially outward from the first annular blast nozzle assembly, and mounted further down in the direction of the blast, and just below the bottom of the rotor. The nozzles are angled so this blast has a velocity component tangential to the rotor outer wall, but discharging in a direction against the direction of rotation of the rotor wall. The second blast has a much lower velocity, and its purpose is to counteract the spiral motion of the falling fibers, and cause them to fall instead straight down to the collection conveyor, eliminating any centrifugal tendency to spread out the cone of fibers.

This arrangement with two annular rings of blast nozzles is quite similar to that shown in FIG. 9, except that annular shroud 148 extends down close to the level of the lower edge of rotor 131, and ring of nozzles 153 is also positioned lower down so its blast 151 starts at the lower edge of shroud 148 in its lower position. Also a separate supply header is required for these nozzles as the blast is of considerably lower velocity. The lower blast in this arrangement has a tangential velocity component against the direction of movement of the rotor outer wall.

Where previous reference is made to air-gas mixture for burners, it is to be understood that gas refers to any combustible gas, preferably natural gas (methane), or propane. Further, the heating method used for the rotor parts and for the initial attenuation zone just beyond the rotor outer wall, and used in conjunction with the direction oriented outer gaseous blast, is not necessarily restricted to gas burners. The heating may be accomplished by, or supplemented by, electric or gas radiant heat, high frequency induction heating, or oil burner flame.

FIG. 9 also illustrates the usual way to apply thermosetting phenolic binder to the glass fibers as they pass down to the foraminous collection conveyor. A ring of atomizing guns serves to apply binder to the fibers, and one of these guns is shown at 171. The binder solution is supplied from a header thru pipe connection 172, and compressed air is similarly supplied thru pipe connection 173 for atomizing the solution.

Heretofore rotors used in this centrifugal process have been made all of precious metal, such as platinum alloys, in the smaller sizes, and base metal for the larger diameters. In accordance with this invention, the rotors can be successfully made using a composite of the two types of material.

An improved rotor design in accordance with this invention is shown in FIG. 12. Referring to FIG. 12, cylindrical inner wall member 190 is made of base metal, and two circumferencial outer wall members 192 and 193 are welded to it as shown at 179 and extending around the circumference. Walls 192 and 193 are made of precious metal, preferably a platinum-rhodium alloy containing 10 to 20 percent rhodium. Wall 190 has two rings 187 and 189 which may be made integral by precision casting, or may be attached by welding. A center ring 188 is split and welded in place, as it has a circle of holes 194 which serve to give a passageway to equalize the thickness of the glass layers against the inner faces of the outer walls of the two compartments.

Inner annular curved member 197 is also made of base metal and has a supporting conical member 198 which is attached to wall 190, and 197 and 198 are backed up to low density fibrous insulation 199. The rotor assembly is supported on bottom flange member 184, which is secured to the rotor shaft 180 by washers 181, insulating collars 182, and nut 183. Since flange 184 operates at a lower temperature than rotor elements 197, 198, and 190, and ring 186, it is attached to ring 186 by a circle of shoulder rivets 185, each of which has a space under its head just sufficient to be taken up by the expansion differential when the rotor is brought up to operating temperature.

The stream of glass 200 from the fore-hearth flows down 197 and out to the inner face of member 190 where a relatively deep layer of glass 201 is maintained because of the restricted metering passages of precious metal orifices 195. There are several rings of orifices 195, each ring extending around the circumference of wall 190. There is an equal number connecting to the lower and to the upper compartments back of outer walls 192 and 193 so each outer wall receives the same quantity of glass. When the operating temperature of the rotor parts and of the glass are stabilized at the desired levels, the layers of glass 202 and 203 back of the outer walls are relatively thin, say on the order of one sixteenth inch in thickness, or just enough to create sufficient centrifugal force to discharge the quantity of glass received thru the filament forming orifices 191. The quantity received is metered thru the orifices 195 with great accuracy and uniformity. If, however, orifices 195 discharge a little too much glass at any time, such as might be caused by too high a temperature, it is readily seen that it would require very little change in the thickness of the glass layers 202 and 203 to discharge this added quantity. It is thus seen that this system provides means to insure the relatively weak precious metal outer walls against over stressing.

Upper flange 196 serves to catch any splash from stream 200. Independently controlled burner 204 serves to hold 197 and the inner rotor parts at the correct temperatures, and very little added heat is required because of insulations 199 and 182, which greatly reduce the heat conducted to the water cooled shaft 180, and that lost by windage and radiation. Independent heater 205 maintains the temperatures of members 196 and 189, and by conduction wall 190 and its three outer rings. The low velocity annular flame from burner 206 maintains the temperature in the initial attenuation zone adjacent the rotor outer wall, and also in the wall itself.

It is seen that the double wall arrangement with metering orifices greatly reduces the possible forces on the precious metal outer walls both by reason of the thin layer of molten glass, and also by the reduced spans on the outer wall material. This permits the use of precious metal for very large size rotors with much higher output than heretofore possible. The strong inner wall absorbs all the uneven forces from incoming glass flow fluctuations, such as from momentary stoppages in the flow from the forehearth.

The orifices in precious metal outer walls 193 and 192 may be drilled or punched. They may also be formed in the shape of nozzles as shown in cross-section in FIG. 22, where the wall is 300. The nozzle shaped orifices are 301 and 302, and the metal is press formed to extend outward as protruding nozzle bodies at 303 and 304. The advantage of the nozzle extension is that is reduces wetting of the surface by the glass, which sometimes causes two or more streams to run together. The orifice tips shown at 195 in FIG. 12 may be made of platinum alloyed with 10 percent rhodium, or they may be palladium alloyed with ruthenium, which is lower in cost and will last almost as long. The tips should be a friction fit in reamed holes. The existing filaments are shown at 305.

A simplified single level construction with the double wall is shown in FIG. 13. Base metal wall 212 has two outer rings to which the precious metal outer wall 214 is welded. Wall 214 has several thousand orifices formed therein, and the inner wall has precious metal orifice tips 213 to meter the glass flow. The outer orifices may be plain holes as shown at 215, or may be formed into nozzles. Glass stream 217 falls on inner cone 209, which is insulated by low density insulation 216. The inner glass layer is relatively heavy at 218, and the outer layer at 219 is very thin to reduce the centrifugal forces on the platinum outer wall 214. The assembly is supported on bottom flange 211.

FIG. 14 shows still another modified form of the invention. Glass stream 220 is picked up on inner conical member 221, and flows into an annular pocket member 222 where it accumulates at 223. From the pocket half of the glass flows thru a circle of orifice tips 224 of precious metal and into the lower compartment, and the other half flows thru a circle of similar tips 225 into the upper compartment. Since the entrances of all orifices are on the same level, the flow is equally divided between the two levels, and kept separate by annular partition 237. Intermediate wall 236 has metering orifices 228 to hold equal and heavy glass levels 226 and 227 back of the wall, and to insure a thin layer of glass at 229 and 230 back of each precious metal wall 231 and 232. The final discharge of the fine filaments is thru multiple orifices 235.

There is a circle of equalizing openings 242, and a circle of overflow openings 243, thru which glass flows only if the layers 229 and 230 have become dangerously heavy to over strain the outer walls. Any surplus glass which feeds down thru the 243 openings will immediately be discharged thru the orifices 245 in precious metal lower supplementary band 233, and attenuated into fine fibers. The whole assembly is supported on lower disc 238 attached by a ring of expansion rivets 239.

FIG. 15 is a partial cross-sectional view taken on line 15--15 in FIG. 13, and shows an alternate means for reducing the length of arc, and thereby the forces on the outer wall tending to overstrain it in tension. There are spacer members 208 extending between wall 212 and the outer wall sections 214 and 214', and the ends of 214 and 214' are welded to them. In this way the circumference of the precious metal outer wall band can be divided into any number of arc segments as required to reduce the centrifugal total pressure on the outer wall areas. Lower flange 211 may have openings cut in it, as at 207, to make it more susceptable to deflection radially and to compensate for uneven temperature expansion due to its being cooler than the upper parts of the rotor assembly.

Whereas the inner wall orifice locations have been shown uniformly spaced back of the compartments between the inner and outer walls, they can be positioned close to the spacer members, such as 189, 188, and 187 in FIG. 12. In these positions the glass would flow outward along the sides of these members, and to some degree reduce the forces on the outer walls 192 and 193.

The parts of the rotors used in this invention which are in contact with the molten glass and close thereto operate at temperatures ranging from 1900° to 2100° F. The thermal expansion of the rotor members from room temperature to these temperatures is greater for the base metal alloys than for the precious metal alloys by 10 to 25 percent. The base metal alloy composition used for these parts should be selected to obtain the lower coefficient of expansion commensurate with other necessary properties. The various constructions shown in the drawings will minimize the stresses and distorsions produced because of the difference in the coefficient of expansion between the base metal and the precious metal alloys.

Another means to off-set uneven expansion is shown in FIG. 16, which is a side view of a section of an outer rotor wall comprising base metal framework 260 to which is welded precious metal wall 261. The orifices in wall 261 are shown at 262. To allow additional metal for expansion horizontal grooves are formed in 261 at 263 and 264, and vertical grooves at 265 and 266, and so on around the circumference of the outer wall. FIG. 17 is a cross-section taken on line 17--17 of FIG. 16, and shows the vertical grooves at 265 and 266. Similarly FIG. 19 is a cross-section taken along line 19--19 of FIG. 16, and shows the horizontal grooves at 263 and 264.

Still another way to provide outer wall orifices that are formed in precious metal with its attendant longer wear and greater uniformity advantages is shown in FIG. 18, which is a partial sectional view of a rotor constructed in accordance with the invention. The rotor 271 is supported on shaft 270, and attached to the shaft by a spoked flange 272, which has multiple spokes 273 which are welded to rotor base 274. Rotor 271 has outer wall 277, upper flange 276, and inner cone 275, on which molten glass stream 278 falls and runs down to inside the rotor wall 277. Low density insulation 279 serves to hold the temperature of cone 275 from being drawn down appreciably by conduction of heat to the cool rotor shaft. The very little additional heat needed to maintain the temperature of cone 275 can be provided by the incoming glass. The outer wall is formed of a base metal strip 277 to which has been clad a thin lamination of platinum alloy 280. Cladding is a commercial process by which two different metals are plied together at high temperature and under heavy rolling pressure. The bond is similar to a surface weld. Strip 277 may be perforated with oversize openings 282 before the cladding operation. After cladding the smaller orifices 281 are drilled or punched in line with the 282 openings. The strip is then curved, either as one full length piece, or a number of arc sections, and the ends welded together to make up the circular outer wall of the rotor.

The inner layer of molten glass is 283. The base metal backing provides the necessary strength to resist the centrifugal forces, and the smaller orifices 281 in the precious metal meter the flow of molten glass and insure uniform filament size over the long life of the outer lamination. The precious metal alloys, such as platinum, have great resistance to erosion caused by the flow of glass, and as a result the size of the smaller openings remains constant for a long period of time.

In FIG. 18 the rotor body is supported on flange 272. In this alternate design flange 272 has spokes 273 which are attached by welding to 274, and there are corrugations 284 in the spokes to give resilience for uneven heat expansion. FIG. 20 is a bottom view of the rotor, and shows how the ends of the spokes are attached. A similar construction is to use a solid bottom disc, without the spokes, and to form circular corrugations extending around the circumference for resilience in expansion, plus rigidity.

FIG. 21 shows a composite outer wall 290, but with the precious metal lamination toward the inside at 291. Glass stream 297 is gathered on cone 298 and accumulates at 287 back of inner wall 295. It is metered thru the circles of precious metal orifice tips 286 and collects back of the outer wall at 294. Since this wall is strong, the layer of glass 294 does not need to be maintained thin in order not to overstress the metal of the wall. The metering system, however, insures greater uniformity of the fine fibers. The larger openings in the base metal are 292, and the smaller metering orifices in the precious metal are 293. Orifices 293 resist erosion, and their size controls the rate of feed of glass and the filament size. The arrangement of FIG. 18 with the platinum alloy on the outside is preferred, however, both to reduce surfaces wetting and resist oxidation of the base metal bores.

In FIG. 21 the bottom flange 288 is shown convex for greater rigidity and more space for insulation 296. Also it has a number of spaced radial ribs formed in its surface, as at 289, to give added resistance to warpage from heat.

Still another recommended form of the invention is shown in FIG. 23. Rotor 316 is mounted on vertical drive shaft 310, and is supported on bottom flange 313 connected to shaft 310 thru insulating bushing assembly 311 held by nut 312. Flange 313 has expansion off-set 314. The main outer body of the rotor comprises members 317 and 319 to which are welded the upper and lower flanges of outer U-shaped circular member 320, which has several thousand orifices 321 in its outer wall. Outer wall 320 is preferably of precious metal, such as platinum-rhodium alloy, and may be welded at the corners as shown. Wall 320 can also be of base metal.

In FIG. 23 ring members 317 and 319, and bottom flange 313, are formed into a rigid assembly by a number of vertical pins 318. There may be six or more of these pins arranged equispaced in a circle, and with the ends turned down to provide shoulders for fastening by riveting at 327 and 327' to top ring 319 and lower flange 313. Ring 317 is fastened to pin 318 by welding at 326. The ends of the pin may also be welded instead of riveted at 327. Glass stream 322 from the forehearth falls on inner cone member 323, and the glass runs down into the pocket at its outer rim where it collects in layer 330. The glass is metered as it flows outward thru orifices 325 to form a thin layer 331 in back of the relatively weak precious metal wall 320. This layer is sufficient to generate enough centrifugral force to discharge the glass thru orifices 321, forming fine filaments 332.

A low density refractory is shown at 333, and a fibrous back-up insulation at 334. The glass stream is surrounded by a heated base metal tubular member 340, which extends down far enough to catch any spatters with the help of flange 324. The use of tube 340 permits 324 to be positioned down low enough in the rotor so as not to be cooled by windage. Tube 340 is heated by spiral electric heating coil 341, which may be of Kanthal or the like, which can be operated at temperatures up to 2500°F. Outer insulated housing 342 surrounds the coil.

The outer top face of the rotor is heated by gas burner 335, supplied with air-gas mixture thru 336. Since member 323 is well insulated on the underside it can obtain sufficient heat from the passage of the glass without cooling it appreciably.

In any of the constructions using a precious metal outer rotor wall the orifices may be drilled or punched. If the outer wall is of base metal, or clad base metal, the orifices may be drilled, cast, or formed by sparking. Whereas the orifices in the clad outer walls are shown with two sizes, they may also be drilled as straight holes as shown at 285 in FIG. 18. Referring to FIG. 23, the burner 335 is shown adjacent to the glass feed tube 340, but actually it should be positioned 180° away on the other side of the rotor.

The novel features of this invention apply equally well to the type of fiberizing unit in which the glass stream is fed into the rotor thru a hollow shaft. This arrangement is shown in FIG. 24. The main flange 367 of rotor 350 is mounted on hollow supporting shaft 351, and fastened thereto thru insulating refractory disc 352 by a circle of cap screws 357. Glass stream 353 feeds down into circular cup 354. The cup has orifices 355 spaced around its periphery, and sized with larger orifices near the top in order to maintain a glass liquid level 356 at sufficient height in the cup to insure a uniform distribution outward thru the orifices.

The bottom flange of the rotor is 358, and it is insulated below by fibrous insulation 359 retained by casing 360. The main rotor supporting flange 367 is insulated by fibrous insulation 368 retained by housing 369. The outer peripheral wall 361 is optionally, and preferably, precious metal with filament forming orifices 362. An inner cylindrical wall 364 holds the top and bottom members together, and has precious metal metering orifices 365 arranged in circles around the circumference, and the size of the orifices and the number provided is carefully designed to insure a thick layer of glass at 366, and a thin layer back of the weaker precious metal wall at 363.

All of the rotor parts except 361 and 365 may be made advantageously of base metal. Because the rather complete insulation of the rotor body minimizes heat loss, most of the heat required can be taken from the glass without an appreciable drop in its temperature. It is advisable, however, to provide a burner above the outer rim of the rotor, not shown, but positioned like burner 335 in FIG. 23, to add heat to the rim of 367 and to inner wall 364 by conduction. The outer wall 361 and the initial attenuation zone adjacent thereto is heated by an outer annular low velocity burner similar to 206 in FIG. 12.

The insulations used in various rotor designs shown in the drawings may be a low density bubble alumina castable refractory having a density on the order of 50 pounds per cubic foot, or a fibrous high temperature insulation such as J-M Fiberchrome, having a density of about 10 pounds per cubic foot. In the constructions of this invention, the glass carrying guidance means are within the interior of the rotor, such as 323 in FIG. 23, and this combined with the insulation minimizes their loss of heat.

Centrifugal force varies directly as the weight of the object, such as the layer of glass, and varies as the square of the RPM. By reducing the thickness of the glass layer just inside the outer wall, the centrifugal force is reduced in direct proportion. This not only permits the use of the weaker precious metal for the outer wall of larger size rotors, but also permits the use of larger diameter orifices. The larger the orifice, the slower the rate of wear by erosion by the glass. This gives longer rotor life before replacement is necessary, and a more uniform product. Further, the use of the inner wall with its metered discharge gives better results with base metal outer walls because the orifices can be made larger, and they will then wear more slowly.

Whereas base metal rotorss used heretofore have had to be replaced after 24 hours or less of use, it is expected that the rotors of this improved design will operate for several hundred hours with base metal walls, and over a thousand hours with walls of precious metals.

My original application Ser. No. 231,347 concerned principally the use of a final annular attenuation blast after the filaments leave the outer rotor wall. The improvements in rotor design of the instant invention can be applied to most of the various other types of apparatus in use in the industry. They can be applied for instance to the rotary process in which a high velocity downward flame attenuation blast is provided immediately adjacent to the rotor outer wall. It also applies to those systems where a low velocity flame or radiant heat is provided in the zone adjacent the rotor wall, and then a high velocity annular gaseous blast further out from the wall provides the final attenuation to fine fibers. This blase may be hot gas, air, or steam. The improvements of the invention are even of greater advantage to more recent systems where the orifices are made smaller in diameter, and such that the existing filaments are fine enough without using an outer annular blast, depending only on the smaller orifices plus the attenuation caused by drag as the filaments leave the rotor.

The rotor parts may be fabricated of base metal and welded or riveted together, or they may be cast as one unit by precision casting using the lost wax process.

In the claims the term "base metal" refers to any of the refractory metals which have properties suitable for this application, and with melting points around 2550°F. Included are the various stainless steels, more preferably the high cobalt alloys with 50 to 60% cobalt and 25 to 30% chromium, and the high nickel alloys with 40 to 60% nickel and 20 to 40% chromium, and all alloys with small amounts of the other associated elements.

In the claims the term "precious metal" refers to the various very high temperature alloys of platinum and palladium, such as platinum alloyed with 5 to 30% rhodium, 10 to 20% preferred, platinum with 5 to 20% iridium, palladium with up to 5% ruthenium, platinum-palladium alloys, and others similar.

In the claims the expression "main flange" of the rotor is the bottom supporting flange on rotors with off-center glass feed and solid shafts, and is the upper supporting flange on rotors mounted on hollow shafts with center glass feed.

The radial spacing between the outer peripheral wall and the inner metering wall should be fairly close, varying from about one quarter inch to one half inch or slightly more.

It should be noted that whereas it is recommended that the rotor body be made of base metal and the outer peripheral wall and the metering orifices in the inner wall of precious metal, it does not follow that all of the other parts of the rotor body must be base metal. For instance, a base metal surface oxidizes and erodes very slowly when it is fully submerged in molten glass. But at the liquid line, where there is not full liquid coverage all the time, and air can get at the surface, much faster oxidation and erosion will take place. There is also likely to be flaking, which can cause plugging of the orifices in the outer wall.

It is therefore advantageous to protect some of the inner parts, such as part 323 in FIG. 23, especially in the upper regions where glass coverage is spotty. Protection can be obtained by cladding the metal, or electro-plating the surface with platinum or palladium. Or even the whole piece 323 can be made of precious metal, for instance, and re-using it in rebuilt rotors.

It will be apparent that while I have shown and described the invention in several preferred forms, changes may be made without departing from the scope of the invention, as sought to be defined in the following claims.