US2594799A - Method and apparatus for the manufacture of mineral wool - Google Patents

Description

E. R. POWELL April 29, 1952 METHOD AND APPARATUS FOR THE MANUFACTURE OF MINERAL WOOL Filed July 18, 1946 w N R EMWA MB D E i atented Apr. 29, 1952 ATUS FOR THE MAN U- METHOD AND APPAR MINERAL WOOL North Plainfield, N. J., assignor FACTURE E Edward R. Powell,

to Johns-Manville Corporation,

New York,

N. Y., a corporation of New York Application July 18, 1946, Serial N 0. 684,466

Claims. 1

The instant invention relates to the formation of artificial fibers of the types of which glass wool, slag wool, rock wool and the like are the principal commercial examples. More particularly the invention is concerned with an economical method and apparatus which will produce a stronger fiber than heretofore and provide a better control of fiber size.

Prior to the instant invention the methods of converting a raw material, such as glass, slag, rock and other fusible raw materials into fiber form, have been of two sharply different types. The first involves individual formation of a fiber from a single source of liquid material. This method is employed principally in the production of fibers of glass and like materials Where the fibers or filaments are drawn from individual orifices of a furnace or other source of molten material. Even though, as is often the case, there may be from 60200 orifices in the orifice plate of the melting furnace, the process is expensive due-to the still relatively low production rate.

and uniform fibers produced.

The second method is directed to multiple fiber formation involving the disintegration of a molten stream of the rawmaterial simultaneously into several thousand fibers. In a conventional method of this kind the molten stream is subjected to the action of a steam blast which shreds the stream into minute droplets which are drawn out into fiber form by the force of the blast. In another method the stream is projected onto the peripheral surface of one or more rotors rotating at high speed, the rotors serving to break up the stream into droplets and to draw them into fibrous form. The multiple formation methods are relatively economical but the fiber does not have many of the desirable properties exhibited by the drawn fibers and the fiber size cannot be readily controlled.

The principal object of the instant invention is the provision of a method, and of an apparatus for carrying out the method, which will have the advantages of both methods of the prior types, but without the disadvantages of either.

Another object of the invention is the provision of such method which ermits the use of selected compositions of the raw material not previously usable in multiple fiber production operations. There is a sharp contrast in the fiuidities of the melts which have been employed in the two types of procedures described above; for example, in the method involving the drawing of individual fibers, the glass compositions employed for the most part are those which do not become a mo bile fiuid at the temperatures at which their ingredients begin to volatilize. These melts, such for example as molten plate glass at a temperature of from 2400-2600" F., therefore have a well defined fluidity which will cause them, under controlled conditions, to flow for example before solidifying. The melts employed in multiple fiber formation by the use of a steam blast or high speed rotors, may fiow from 8-12 under the same conditions. The more viscous melts as employed in individual fiber production processes produce a tough fiber under definite tension, the toughness being due to molecular orientation or to other causes. The fibers obtained by the multiple fiber production system, on the other hand, are relatively Weak and irregular.

Another object of the invention is the provision of a method of the multiple fiber production t pe which may be successfully used with the more viscous melts of the kind previously employed only for drawn fibers.

The multiple formation methods, while commercially practicable with the more fluid melts, have not produced the desired high proportion of fine fibers, due to the fact that the separation or division of the molten stream into molten particles or bodies from which the fibers are drawn is not uniform or definitely controllable. As a result the bodies are of different and relatively uncontrolled size, and produce fibers of a wide range of diameters. It has not been unusual for such methods to produce fibers from 1 -15 microns in diameter and with 30-70% of shot or unfiberized material. This is due specifically to the fact that it has been necessary to spray the original large stream into several thousand droplets or incipient fibers, either by the use of the steam blast or the rotors, and then stretch the droplets or incipient fibers. Only a part of even the more fluid melts separate into the proper droplet size for fine fiber formation. Since coarse fibers made of any of the known inorganic compositions are irritating to the skin and are more or less brittle, the control of the fiber size is of primary impor tance. Where attempts have been made to use the more viscous melts, it has been found impossible to obtain either uniformity of the droplets or the conversion of any large portion of the stream into droplets of the right size. Accordingly, a further object of-the invention is the provision of a method and apparatus which will insure proper control of the droplet size from which the fibers are individually drawn,

A still further object of the invention is the provision of a method and apparatus for the preparation of the molten material to be converted into fibers by a spinning process involving one or, suitably, a plurality of rotors rotating at high speed. The rotors may be generally of the type and driven at the speed of those shown and described, for example, in my copending applications,'S. N. 446,067, filed November 18, 1942, now Patent No. 2,399,383, S. N; 486,009, filed April 29, l9 i3,now Patent No. 2,428,810, and S. N. 555,359, filed September 22, 1944, now Patent No. 2,520,168. Mechanical examination of the fibers heretofore formed by processes in which a molten stream of raw material is permitted to fall directly on one of the rotors, and is sprayed therefrom onto adjacent rotors, as described in my said co-pending applications, reveals that fiber of l /2-2 microns diameter is formed from particles of 100-200 mesh size, as determined by standard testing sieves. This relationship between particle and fiber size may readily be checked. It can be assumed that the fibers will be about a foot in length since the rotors involved in the process are roughly 1 foot in diameter, and can be expected to make fiber of alength approximately equal to their diameters. That is, the fiber, when drawn tosuch length, is carried into contact with the rotor and broken off. It may be easily shown that a particle of the size referred to above contains enough material to form a foot of fiber within the l -2 micron range, assuming a fair percentage of fiberization. Control of the particle size as provided by the instant invention therefore permits the rotor process of fiberization to become definite and controllable, at least to the right order of magnitude of the fibers.

My invention will be more fully understood and further objects and advantages thereof will become apparent when reference is made to the more detailed description of a preferred embodiment of the invention which is to foliowand to the accompanying drawing in which:

Fig. l is a diagrammatic, sectional view of an apparatus embodying the instant invention and suitable for carrying out the method thereof; and, 1

Fig. 2 is a sectional view taken on the line 2-2 of Fig. l and lookin in the direction indicated by the arrows.

Referring now to the drawings, an air-heating furnace is shown at 10, the furnace including a combustion chamber l2 and a heat transfer chamber M. The transfer chamber [4 is traversed by a plurality of tubes l6 opening at one end into the combustion chamber [2 through a header l8, and at the other end into a stack througha rear wall 22. Combustion chamber l2 includes a fuel burner 24 which may be of any conventional type and adapted to consume any suitable fuel. coal, oil orgas, as desired.

A blower26 is mounted. preferably abovethefurnace as shown, to have its discharge side in communication with an air entry port 28 leading into the rear of the transfer chamber i4. Chamber I4 is provided with bafiie walls 30 positioned intermediate the front and rear walls of the chamber and extending alternately from its top and bottom walls toward but short of the opposite wall to require air entering port 28 to make a plurality ofpasses around'tubes 16 before it is discharged through a discharge port 32. In theconstructionshown two bafliesare employed to obtainthree passes of air around the tubes, but

For example, the burnermay useit will be understood that additional baflies may be-employed to increase the number of passes where desired.

Theair heater described above is of generally conventional type and may be purchased commercially. Itimay be made of any suitable refractory materials, for example, refractories such as sillimanite or mullite. The tubes 16 may be of ahighly heatyresistantmaterial such as-a high -75 grade silicon carbide refractory of the type sold under the name Carbofraxf In accordancewith the instant invention, stack 20 includes a hopper bottom 34 (see particularly Fig. 2) in communication through a tubular passageway 35 with a material discharge port 38 opening into a furnace 50. Adjacent the upper end of stack at, or at least at a point remote from the hopper bottom of the stack, is a supply device indicated generally at 40 for feeding a granulated furnace to the stack where it falls, counter-current to the flow of gases exhausted through the stack, to the hopper bottom 34. Device il] includes a hopper 42 having a bottom orifice in communication with a duct 44 which, in turn, penetrates the wall of the stack. Within duct M is a screw feed 46 rotated by any suitable means (not shown) and preferably at a controlled rate to carry the material from the hopper and into the stack. Located in the hopper bottom is a similar screw feed 48 extending into tubular passageway 36 to deliver material from the hopper bottom to the material discharge port38. The latter screw is made of an alloy steel or nonferrous alloy which will withstand a high temperature such as 2000 F.

Below air heater ID is a furnace 50 having. preferably, a dome section 52, cylindrical section 54, and a flattened, generally conical section 56. although the shape of the furnace is not critical and may be varied in a number of particulars, the necessary features being made evident as the description proceeds. The furnace is made of refractory material, similarly as air heater [0. The furnace is in communication with the port 32 of air heater l0 through passage 58 leading into the cylindrical section of the furnace. A burner 60 is located, preferably centrally of dome section 52, the burner utilizing fluid or powdered fuel, similarly as burner 24.

The mouth 62 of the furnace is positioned above the peripheral faces of, preferably, a pair of rotors 64. These rotors, which may be, say,-

12" in diameter are made of, or at least include rims or tires of, a heat-resistant steel. The rotors are carried by shafts 65 mounted in planes at an angle to the horizontal, as shown. Shafts 65 are driven by suitable means (not shown) to cause movements of the upper peripheral surfaces of the rotors, preferably towards each other. In the operation of the apparatus described above, burner 24 is regulated to raise the temperature in combustion chamber l2 to, say, from 2700-2800 F., the flames from the burner being directed by wall [8 into tubes I5. The burnt gases pass from the tubes into stack 20 where they raise the temperature to, say, 2000 F. and are discharged to the atmosphere through the top of the stack. Blower 26 is operated to cause a flow of air through the air heater at a relatively low velocity so that it will be heated to, say, 1600- 2000 F. when it reaches exit port 32. As stated above, the construction illustrated provides for three passes ofthe air around tubes 16 but con ditions may require a greater number of baffles to increase the number of passes inorder to bring the air to the required temperature. The heated air flows through passage 58 into furnace 50.

Burner 68 is regulated to raise the temperature in furnace 50 above the melting temperature of the raw material, say, a temperature of in' granulated form by conventional crushing and the heated gases into hopper bottom 34.-

be subjected to the air separation operations to have a predetermined, relatively definite particle size determined by the diameter of the fibers to be produced but, say, of 100-200 mesh, is supplied to hopper 42 and transferred from the hopper at a controlled rate by screw conveyor 46, and discharged into stack 20 where it fallscounter-current to the flow of The crushed particles of a size to produce fibers of diameters here referred to, say -:fibers of 1 -2 micron diameter, will have a fairly definite .falling rate such as, say, 7-10 feet per second. The length of the stack between the hopper bottom and supplydevice 4D is proportioned relatively to the velocity of gas flow up the stack and the temperature of the gases so that. the particles. will heated. gasesfor a sufficient period to raise them to a temperature approaching that of the gases. This temperature, however, will be below the melting point :of the particles. The hot but still solid particles are fed by screw feed 48 through port 32'into furnace- 50 where the particles are melted by the relativelyhigher temperatures present. The enlarged, cross-sectional areas of the cylindrical section and the adjacent end of the conical section of the furnace insures that the fiame velocities'and the rate of fall of the particles through the furnace are relatively low at this point. The radual taper and the flattening of the conical section 56 directs the particles along with the flame onto the peripheral surfaces of rotors 64, the flame serving to convey the particles and also to maintain them above their melting tempera ture until they impinge against and bond to the rotor surfaces. The rotors, suitably about 12" in diameter, as previously stated, are driven at speeds, say, from 4300 5000 R. P. M., although higher speeds may be employed for the produc-- tion of extremely fine fibers. When the still fluid particlesare bonded to the rotors, the particles. stretch under the centrifugal forces set up by rotation of the rotors, and are drawn out individually into fibrous form.- The fiber formed as described above may be collected by any suitable mechanical or pneumatic equipment (not shown) In the priorrotor fiberization processes, for example inthe processes described in my said pending applications, the use-pf two or more rotors is essential in that one or more must serve as sub-dividing means to' initially divide the molten stream into a storm or cloud of molten particles or droplets which arethrown onto the other rotor or rotors, the latter performingall, or at least a major part of, the fiberizing step. In the instant invention, on the other hand, inasmuch .as the molten material is previously subdivided into particle form, each rotor acts' individually as a fiberizing means. Consequently,only a single rotor may be .used, or if a plurality of rotors' areused, they may be rotated so that their upper'peripheral surfaces'move either toward or. away from each other. However, the use of a pair of rotors with their upper peripheral surfaces moving toward each other, as shown in Fig. 1 is preferred, to obtain the desired higher fiber recovery. In order that the molten particles may be drawn out into fibrous form, it is essential that they'be bonded to the rotors so that the small. molten body making up each particle will be carried by the rotor and a fiber drawn therefrom by the centrifugal forces setup. The preferred direction of rotation of the rotors with their upper surfaces moving toward each other insures such bondingin that,if the force 1 of the furnace and of the particle in initially'striking the .rotorri's insumcient to cause it to bond, it will immediate ly be projected by such rotor and at an increased velocity onto the surface of the opposite rotor',:the increased velocity of the particle causing itwto strike the opposite rotor with suflicient force. to adhere to it. The rotation of the-rotors. in. .this preferred direction also produces amore tangled mat of fibers desired in most cases.

A certain portion of the material striking the rotor surfaces will solidify on them. Such solidi.- fied materialis usually so refractory that the surfaces of the rotors could. not reasonably be kept upto the necessarily high temperature. 'The use of two rotors, as shown, has the further ad.- vantage thatflli difiiculty is eliminated as the rotors are mutually self-cleaning whenever the solidified material becomes excessive in thick ness. 'I'hat';is,' the solidified material on the opposite rotors. will come into contact which causes its dislod'gment. r

In the operation of the apparatus, by...far' the greater proportion of the molten droplets falling through furnace 50 will retain their individuality and remain free from other droplets orfromthe walls of the furnace. However, some of the droplets will strike the walls and form astream which fiows down the side walls and drips from the lower edge of the furnace. Where definite control of the fiber size is required for extremely uniform products, this drip may be discarded by drawing it off from the lips in any suitable maniner. However, where it is desired to include this material with that to be fiberized, the mouth of the furnace is preferably provided withpoints 66, as indicated, which tend to break up this stream into a plurality of individual fine streams or drips which become elongated until they contactithe rotor surfaces: and are drawn out into practically continuous fiber. In order to damp the movement of the particles through the conical section to minimize the impingement on the walls, and also to impart additional heat to the particles, a magnetic flux is preferably set up within the conical section. For this purpose a coil 68 surrounds this section of the furnace, the terminals of the coil being. connected to any suit.- able source of high frequency current, say, a current having a frequency of 1-10 milli-cycles per second.

Numerous raw materials maybe reduced .:to fine particle size and fiberized by the instant method. Baw materials of particular merit in clude plate glass or glass'cullet of. conventional character, e.,.that having a fluidity which will cause it to flow approximately /2" before. solidi fying when heated to a temperature of from 2400-2600 F., basalt, volcanic g1ass,-pyroxene minerals, slag, ash, rock and synthetic ,mix-es which may be specifically prepared for the purpose. These materials ;will usually; require crushing and in this operation the particles are suitably air floated or screened to separate out the predetermined particle size-to be employed, the oversized particles being crushed further and the fines being discarded for the present purpose.

Basalt, when crushed to the proper size to pro.- duce fibers of the diameters referred to, contains complex fiberwhich has a greater tendencyto curl than fiber formed from other of the .materials referred to above, and thereforemay bare.- ferred where heavily curled fiber is desired. However, normally if, the rotorsarerotatedto curledfiberwill be made,

have theirpupperiisurfaces .moving. towards: each other; a cdescri'bediabove, arsufiicient quantity of irrespective of therparticularurawamaterial, to give the producttgood heat-insulating. and sound-absorbing properties. Amumber. of .the above materials, particularly gltssflfurnace .slag, furnace clinker and basalt, remain solid up to 2000 F. and melt to axductile fluid condition between -.23I)0.;'and 2500i becoming watery when heated above this temperature. Others Ofthe materials will havezdifferent characteristics :in. theserrespects. Thereiora. it :will beunderstood thatthet'temperatures selected Iorithe operation will be governed byutheraw'materia'lused. flThe preheating operation is: designed stoiraise :the temperature of the granulated material :close to, but never over, the melting pointniithe materialwhereby it is still'granular andfree-flowing when fed intothe-melting furnace. 'The process is thus conducted throughoutsoithat it is'not necessary to have working partsnsuch as screw :fee'ds 45 and 48 raised totthe melting pointof the material which ;is to be fiberized. .The process therefore-his:especially adapted to fiberizing maiterialls which are extremelyrefractory and which economicallyproduce very toughand stable fiber. Several .of the most desirabl and most. available materials of those referred to above, including volcanic glass, basalt, fused. shale and..ash,.such materials. normally containing combined silica andalumina percentages of over 65%, the balance being mainly lime, iron and magnesia fluxes, and other highsilicamaterials are of the type which producethese stable andtoughfibers.

.=The inventions. as described above, provides ionithe production of fibers from numerous raw materials with complete control of the fiber size and uniformityof fiber production, the. method of the invention comparing favorably in these respects with the prior individual fiber drawing processes. high' capacity and economy of the prior multiple fiber forming operations.

- :Having thus described my invention in :rather :fulldetail it will be understood thatthese details need not be strictly adhered to but that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by "the subjoined claims, 1

-- :What I claim is:

1, In an apparatus for forming fiber from dis- Icreteparticles of a fusible raw material,.means lfor subjecting the particles to heated gases to preheat the particles, means .for'forming a gaseous blast, flame forming means'for raising the -temperature of the blast above the melting point of the particles, means for discharging the particles. from the preheating means into the blast to be conveyed thereby and melted therein, and a flberizin'g means in the pathoi the blast for convertin'g the individual particles into fiber form.

2. In an apparatus for forming fiber of controlled size iromdiscrete particles of controlled size or a fusible raw material, means for subjectinglth particles to heated gases to preheat the particles to below their melting temperatures, means vfor creating a heated gaseousblast, flame :ionning'means for raising the temperature of the blast-above the melting point of the particles, meansrfor discharging'the particles from the preheating means 'mto the blast to be conveyed thereby and: melted therein, and a fiberizing *deviceiinti thepath ofssaidblast, said fiberizing At the same time the process has the .for causing: a

8 devicezincludlng rotors and means ion-driving the rotors atihighispeed.

3..Inan apparatus for .formlngfibersrirom 'discrete'particles of afusible material comprising a stack, ayparticle collecting-zone in said for discharging the particles .from 'saldlcollecting zone into said blast to beconveye'd therebyzand melted therein,:a'.fiberizing deviceand means for directing-the gaseous blast andithe' particle's to'e ward said device to deliverthe molten particle's thereto.-

4. In an apparatus forfOrming' fibers from discreteparticles of .a fusible raw material, a stack, a particle collecting zone in-said stack, means in said stack aboveusaid collecting zone for discharging particles to permit themioifall by gravity to said collecting zone, means to cause afiow of heated gases at a temperature below-the melting point of the particles and countercurrent to the direction of fall of said particlesymeans for forming a heated gaseous blast, flame forming means for raising the temperature of 'the blast above the melting point of the particles, means for discharging par-tlcles from' the collecting zone into the blast to be conveyed thereby and melted therein, and means in the'path of the blast for converting the'individual particles into fibers.

5. In an apparatus for formingi'fiber from discrete particles of a fusible raw materialpa stack, a particle collecting zone in saidstack, means in said stack above said collecting zone for discharging particles to permit them to -fall by gravity to said collecting zone, means to cause a flow of heated gases at a temperature below the melting point of the particles'and countercurrent to the direction of 'fallor said particles, means for forming a heated gaseous :blast, flame forming means for raising the temperature of 'the blast above the melting point ofthe particles,

means for discharging particles from the collecting zone into the blast to-be conveyed-thei by and melted therein, andmeans'in the path of the blast for converting thelndividualparticles into fibers, said last-named-meansincluding rotors adapted to be driven'at} high "speed,"-and means for drivingsaid rotors.

6. In an apparatus for forming 'fiber' from discrete particles of a fusible raw material ournprising heating means, a stack adjacent" said heating-means, said stack having a particlecollecting zone and means'in said stack'above said collecting zone for discharging particles into said stack to'permitsaid partlcles to. fall by gravity into said collecting zone; means to discharge heated ases at a temperaturebelow themeltlng point of the particles from said-heating means into said stack and to cause them to flow countercurrent to the direction of fall of "said particles, a melting chamber separate'from said stack and having an open mouth, flame forming "means'in said chamber, means for causing a gaseous blast in said chamber directed toward said open mouth, and means for discharging the-particles from said collecting zone into '-said-*chamber.

' '2." In an apparatuslior forming fiber from Hiscrete particles of a fusible raw material comprising heating means, a stack adjacent said heating means, said stack having a particle collecting zone and means in said stack remote from said collecting zone for discharging particles into said stack to permit said particles to fall by gravity into said collecting zone, means to discharge heated gases at a temperature below the melting point of the particles from said heating means into said stack and to cause them to flow counter-current to the direction of fall of said particles, a melting chamber separate from said stack and having an open mouth, flame forming means in said chamber, means for causing a gaseous blast in said chamber directed toward said open mouth, means for discharging the particles from said collecting zone into said blast, and fiberizing means opposite said open mouth of the chamber in position to intercept particles carried by said blast from said chamber.

8. In an apparatus for forming fiber from discrete particles of a fusible raw material, means for suspending the particles in a gaseous blast maintained at a temperature above the melting point of the particles, means for directing the particles into a fiberizing zone, and means to establish a magnetic flux within the directing means for damping the particle movement and for maintaining the particles in individualized relationship.

9. In a method of forming fiber from discrete particles of fusible material, the steps comprising subjecting the particles to hot gases in a preheating operation, suspending the preheated particles in a gaseous blast maintained 10 at a temperature above the melting point of the particles to melt the particles, conveying the particles in the blast and in discrete relationship to a fiberizing zone, and subjecting the particles in said zone to accelerated movement to draw them out into fibrous form.

10. In an apparatus for forming fiber from a fusible raw material, means for establishing a gaseous blast at a temperature above the melting point of the fusible raw material, means for suspending discrete particles of the fusible raw material in the gaseous blast, means for maintaining the blast at a temperature above the melting point of the particles to melt the particles in said blast, a fiberizing device comprising rotor means, means for rotating the rotor means at high speed, and means for directing the gaseous blast and the discrete particles therein toward said rotor means to deliver the molten particles thereto.

EDWARD R. POWELL.

REFERENCES (JITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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