Abstract:
A method of forming fibers from molten mineral material is provided. The method comprising the steps of: rotating a spinner having an orificed peripheral wall, the orificed peripheral wall having a top row of orifices, introducing molten mineral material to the spinner to create a fan of primary glass fibers, creating an annular combustion flow of heated gas and directing the annular combustion flow of heated gas substantially through the primary fibers, creating an annular flow of attenuating air with an annular blower, the annular flow of attenuating air being sufficient to attenuate the primary fibers into secondary fibers, directing the annular combustion flow of heated gas and the annular flow of attenuating air so that they are radially spaced apart at the level of the top row of orifices, and directing the annular combustion flow of heated gas and the annular flow of attenuating air so that they are brought together at a position below the top row of orifices.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/919,242, filed Mar. 21, 2007, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to forming fibers from molten mineral material, such as forming glass fibers from molten glass. More particularly, the present invention relates to an apparatus for manufacturing fibers from the molten mineral material. 
     BACKGROUND OF THE INVENTION 
     Fibers of glass and other thermoplastic materials are useful in a variety of applications including acoustical and thermal insulation materials. Common methods for producing glass fibers for use in insulation products involve producing glass fibers from a rotary process. In a rotary process, glass composition is melted and forced through orifices in the outer peripheral wall of a centrifuge, commonly known as a centrifugal spinner, to produce the fibers. One commonly used spinner is generally cup-shaped and has a bottom wall with a central hole, a top opening and an outer peripheral sidewall that curves upward from the bottom wall, forming the top opening. Another commonly used spinner uses a slinger cup to propel the glass composition to the sidewall for fiberization. A drive shaft is used to rotate the spinner and is typically fixed to the spinner with a quill 
     It would be advantageous if spinners could produce fibers more efficiently. 
     SUMMARY OF THE INVENTION 
     According to this invention there is provided a method of forming fibers from molten mineral material, the method comprising the steps of: rotating a spinner having an orificed peripheral wall, the orificed peripheral wall having a top row of orifices, introducing molten mineral material to the spinner to create a fan of primary glass fibers, creating an annular combustion flow of heated gas and directing the annular combustion flow of heated gas substantially through the primary fibers, creating an annular flow of attenuating air with an annular blower, the annular flow of attenuating air being sufficient to attenuate the primary fibers into secondary fibers, directing the annular combustion flow of heated gas and the annular flow of attenuating air so that they are radially spaced apart at the level of the top row of orifices, and directing the annular combustion flow of heated gas and the annular flow of attenuating air so that they are brought together at a position below the top row of orifices. 
     According to this invention there is also provided an apparatus for forming fibers from molten mineral material. The apparatus comprises an annular burner and an associated combustion chamber. The combustion chamber has an annular chamber exit. The annular burner is configured to create a combustion flow of heated gas flowing through the annular chamber exit. A flame ring extends downward from the annular chamber exit. The flame ring has a downwardly extending flame ring lip. A spinner is mounted for rotation. The spinner has an orificed peripheral wall. The orificed peripheral wall has a top row of orifices. The spinner is configured to create a fan of primary fibers. An annular blower is configured to create an attenuating air flow sufficient to attenuate the primary fibers into secondary fibers. The flame ring lip is positioned to direct the combustion flow of heated gas and the attenuating air flow in a manner such that the combustion flow of heated gas and the attenuating air flow are radially spaced apart at the level of the top row of orifices, and are brought together at a position below the top row of orifices. 
     According to this invention there is also provided an apparatus for forming fibers from molten mineral material. The apparatus comprises an annular burner and an associated combustion chamber. The combustion chamber has an annular chamber exit. A spinner is mounted for rotation. The spinner has an orificed peripheral wall. The orificed peripheral wall has a top row of orifices. The spinner is configured to create a fan of primary fibers. An annular blower configured to attenuate the primary fibers into secondary fibers. The annular chamber exit is below the level of the top row of orifices by a distance in a range of from about 1.4 inches (35.6 mm) to about 1.6 inches (40.6 mm). 
     According to this invention there is also provided an apparatus for forming fibers from molten mineral material. The apparatus comprises an annular burner and an associated combustion chamber. The combustion chamber has an annular chamber exit. A flame ring extends vertically downward relative to the annular chamber exit. The flame ring has a flame ring bottom surface. A spinner is mounted for rotation. The spinner has an orificed peripheral wall. The orificed peripheral wall has a top row of orifices. The spinner is configured to create a fan of primary fibers. An annular blower is configured to attenuate the primary fibers into secondary fibers. The top row of orifices is at a level below the bottom surface of the flame ring by a distance in a range of from about 0.08 inches (2.0 mm) to about 0.10 inches (2.5 mm). 
     Various objects and advantages will become apparent to those skilled in the art from the following detailed description of the invention, when read in light of the accompanying drawings. It is to be expressly understood, however, that the drawings are for illustrative purposes and are not to be construed as defining the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a prior art rotary fiberizing system. 
         FIG. 2  is a cross-sectional view of a portion of the prior art rotary fiberizing system of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the present invention showing a rotary fiberizing system. 
         FIG. 3A  is a enlarged cross-sectional view of a portion of the fiberizing system of  FIG. 3 . 
         FIG. 4  is a graph comparing the fiber diameter of glass fibers produced by the prior art fiberizing system of  FIG. 1  with glass fibers from the fiberizing system of  FIG. 3 . 
         FIG. 5  is a graph comparing the drape length of fibers produced by the prior art fiberizing system of  FIG. 1  with fibers from the fiberizing system of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, there is illustrated in  FIG. 1 , one example of a known fiberizing system, indicated generally at  10 , for use in producing fibers from a mineral material. The fiberizer system  10  includes a spinner  12  attached to the lower end of a rotatable shaft or spindle  14 . The spinner  12  can be attached to the spindle  14  in any suitable manner. In operation, the rotating spindle  14  causes the spinner  12  to rotate. The spinner  12  includes a spinner base  18  extending from spindle  14  to the peripheral wall  19 . A plurality of orifices  20  are positioned through the peripheral wall  19 . Typically, the spinner has approximately 20,000-40,000 orifices  20 . Alternatively, the spinner can have more than 40,000 orifices or less than 20,000 orifices. The orifices  20  are configured to form primary fibers  22  as the molten mineral material is centrifuged out of the peripheral wall  19  of the spinner  12 . 
     The spinner  12  is supplied with a stream  78  of a molten mineral material. One example of a molten mineral material is molten glass. Other examples of molten mineral materials include molten rock, slag and basalt. 
     A delivery mechanism  82  is used to supply the stream  78  of molten glass. The delivery mechanism  82  can be any mechanism, apparatus or structure, such as for example forehearths or channels, suitable to supply the stream  78  of molten glass from a furnace. The molten glass in stream  78  drops into a chamber  42  of spinner  12 . In operation, the centrifugal force created by the rotating spinner  12  forces the molten glass in the chamber  42  against the peripheral wall  19  of the spinner  12 . The molten glass forms a head  90  of molten glass adjacent to the peripheral wall  19  of the spinner  12 . As the spinner continues to rotate, the molten glass is forced through the plurality of orifices  20  thereby forming a fan  21  of primary fibers  22 . The term “fan” as used herein, is defined to mean a quantity of primary fibers emanating from the peripheral wall  19 . 
     Referring again to  FIG. 1 , the primary fibers  22  are maintained in a soft, attenuable condition by the heat of an annular burner  24 . As will be explained in more detail below, the annular burner  24  is configured to provide a combustion flow  25  of heated gas directed to the fan  21  of primary fibers  22 . The annular burner  24  can be any structure or mechanism, such as for example a gas burner, sufficient to provide the combustion flow  25  of heated gas directed to the fan  21  of primary fibers  22 . 
     As shown in  FIG. 1 , an annular blower  28  is configured to provide an attenuating air flow  31  through a plurality of blower apertures  52 . The attenuating air flow  31  flowing through apertures  52  engages the primary fibers  22 , thereby attenuating the primary fibers  22  to form secondary fibers  32 . In the illustrated embodiment, the secondary fibers  32  are suitable for use in a product, such as wool insulating materials. The secondary fibers  32  are then collected on a conveyor (not shown) or other suitable apparatus for formation into a product, such as a glass wool pack. Alternatively, the secondary fibers  32  can be further processed in downstream operations (not shown). 
     Referring again to  FIG. 1 , an optional quill pan  46  is used to substantially cover the bottom of spinner  12 . The quill pan  46  can have any shape sufficient to cover the bottom of the spinner  12 . The spinner  12  and the quill pan  46  are mounted on a hub  54 . The hub  54  is mounted for rotation with the lower end of spindle  14 . The hub  54  can have any configuration suitable for rotation with the lower end of spindle  14 . 
     Referring now to  FIG. 2 , the annular burner  24  is associated with a combustion chamber  26 . The combustion chamber  26  includes an annular chamber exit  27 . The annular burner  24  is configured within the combustion chamber  26  such that combustion within the combustion chamber  26  produces combustion flow  25  of heated gases in direction DJ through the annular chamber exit  27 . While the annular burner  24  shown in  FIG. 2  is positioned at the top of the combustion chamber  26 , it should be understood that the annular burner  24  can be located in any position relative to the combustion chamber  26  sufficient to produce combustion flow  25  in direction DJ through the annular chamber exit  27 . 
     As shown in  FIG. 2 , the combustion flow  25  flows in direction DJ along the bottom center casing  34  and the flame ring  36 . The bottom center casing  34  has a height HBCC. In the illustrated embodiment, the height HBCC is approximately 1.5 inches (38.1 mm). The bottom center casing is a structural framework positioned between the spinner  12  and the annular burner  24 . 
     The flame ring  36  is configured to direct the combustion flow  25  exiting the combustion chamber  26 . The flame ring  36  includes a downwardly extending flame ring lip  38 . The flame ring lip  38  has a bottom surface  39 . The flame ring lip  38  extends downward relative to the chamber exit  27  for several purposes. First, the flame ring lip  38  creates a pinch area  50  in the passage  30  between the flame ring  36  and the blower  28 . The pinch area  50  is configured to throttle the induced air flow flowing through the passage  30 . Second, the flame ring lip  38  extends downward to separate the combustion flow  25  flowing from the combustion chamber  26  and the induced air flow flowing from the passage  30 . Third, the flame ring lip  38  directs the combustion flow  25  flowing from the combustion chamber  26  in the direction that will intersect the fan  21  of primary fibers  22 . 
     As shown in  FIG. 2 , the blower  28  includes a plurality of apertures  52 . The blower  28  is configured to provide an attenuating air flow  31 , in direction DB, through the apertures  52 . The attenuating air flow  31  flowing through apertures  52  engages the primary fibers  22 , thereby attenuating the primary fibers  22  to form secondary fibers  32 . 
     Referring again to  FIG. 2 , the orifices  20  are configured to form the fan  21  of primary fibers  22  as the centrifugal force of the spinner  12  forces the molten glass through the orifices  20 . The orifices  20  can be formed in rows, with a top row  60 . A first distance D 1  is formed between the top row of orifices  60  and the bottom surface  39  of the flame ring  38 . In the illustrated embodiment, the first distance D 1  is approximately 0.406 inches (10.3 mm). 
     As shown in  FIG. 2 , a second distance D 2  is formed between the top row of orifices  60  and the chamber exit  27 . In the illustrated embodiment, the second distance D 2  is approximately 1.856 inches (47.1 mm). 
     Referring again to  FIG. 2 , a third distance D 3  is formed between the top row of orifices  60  and the apertures  52  in the blower  28 . In the illustrated embodiment, the distance D 3  is approximately 0.097 inches (2.5 mm). 
     As shown in  FIG. 2 , the combustion flow  25  and the induced air flow are initially radially spaced apart by the flame ring lip  38 . In the illustrated embodiment, the combustion flow  25  and the induced air flow are brought together at a Point A, which is positioned vertically above the top row of orifices  60 . 
     Referring now to  FIG. 3 , the fiberizer system  10  includes a spinner  12  and the blower  28  moved vertically upward relative to the chamber exit  27 . Moving the spinner  12  and the blower  28  vertically upward relative to the chamber exit  27  allows the top row of orifices  60  and the resulting fan  21  of the primary fibers  22  to be positioned closer to the flame ring  38 . Positioning the orifices  60  and the primary fibers  22  vertically closer to the chamber exit  27  results in a significant and unexpected improvement in the efficiency of the fiberizing process. One possible reason for the improvement in the efficiency of the fiberizing process could be that the combustion flow  25  flowing from the combustion chamber  26  flows substantially through the fan  21  of the primary fibers  22  prior to mixing with the induced air flow. Since the combustion flow  25  moves substantially through the fan  21  of primary fibers  22  prior to mixing with the induced air flow, an increased amount of heat is transferred to the primary fibers  22 . 
     The improvement in the efficiency of the fiberizing process can manifest itself in several ways. First, primary fibers, having the same fiber diameter, can be produced using less energy in the annular burner. Using less energy in the annular burner results in a cost savings. Second, the diameter of the resulting secondary fibers  32  can be reduced for a given level of annular burner energy. Trial results have shown a reduction in fiber diameter of about 1.2 HT (hundred thousanths of an inch) (0.3 microns) at constant gas flow, and alternatively a gas flow reduction of up to 20% at constant fiber diameter. Lastly, a combination of using less energy in the annular burner and a reduction in the fiber diameter can be realized. 
     As shown in  FIG. 3 , a first distance D 1 ′ is formed between the new position of the top row of orifices  60  and the bottom surface  39  of the flame ring  38 . In the illustrated embodiment, the first distance D 1 ′ is approximately 0.0935 inches (2.4 mm). In other embodiments, the first distance D 1 ′ can be in a range from about 0.08 inches (2.0 mm) to about 0.10 inches (2.5 mm). 
     As shown in  FIG. 3 , a second distance D 2 ′ is formed between the new position of the top row of orifices  60  and the chamber exit  27 . In the illustrated embodiment, the second distance D 2 ′ is approximately 1.544 inches (39.2 mm). In other embodiments, the first distance D 2 ′ can be in a range from about 1.4 inches (35.6 mm) to about 1.6 inches (40.6 mm). 
     Referring again to  FIG. 3 , a third distance D 3 ′ is formed between the new position of the top row of orifices  60  and the apertures  52  in the blower  28 . In the illustrated embodiment, the distance D 3 ′ is approximately 0.160 inches (4.1 mm). 
     Referring again to  FIG. 3 , the vertical upward movement of the spinner  12  relative to the chamber exit  27  is accomplished by a reduction in the height HBCC of the bottom center casing  34 . In the illustrated embodiment, the height HBCC of the bottom center casing  34  has been reduced by approximately 0.3125 inches (7.9 mm) to a revised height HBCC′ of approximately 1.200 inches (30.5 mm). In other embodiments, the height HBCC of the bottom center casing  34  can be reduced by more or less than 0.3125 inches (7.9 mm). In other embodiments, the vertical upward movement of the spinner  12  can be accomplished in other manners. 
     Referring now to  FIG. 3A , the combustion flow  25  and an induced air flow  33  are radially spaced apart at Point A by the flame ring lip  38 . The combustion flow  25  and the induced air flow  33  remain radially spaced apart until the combustion flow  25  and the induced air flow  33  are brought together at Point B, which is positioned at a level vertically below the level of the top row of orifices  60 . 
     Referring again to  FIG. 2 , the blower  28  has an upper inside corner  56 , helping to define passage  30 . The upper inside corner  56  of the blower  28  has a radius R 1 . Referring now to  FIG. 3 , the upper inside corner  56  of the blower  28  has been modified to have a radius R 2 . In the illustrated embodiment, the radius R 2  is larger than the radius R 1  such that the pinch area  50  can be maintained at a desirable throttling level. In other embodiments, the vertical movement of the blower  28  can be accomplished in other manners. 
     As described above, trial results have shown a reduction in fiber diameter of about 1.2 HT (hundred thousanths of an inch) (0.3 microns) at a constant gas flow. As shown in  FIG. 4 , an average fiber diameter of approximately 18.6 HT (4.6 microns) (as shown by curve  92 ) was realized prior to the movement of the spinner  12  and the blower  28 . After movement of the spinner  12  and the blower  28 , an average fiber diameter of approximately 17.4 HT (4.4 microns) (as shown by curve  93 ) was realized. 
     The R-value of an insulation batt can be determined by the thickness (T) of the fibrous insulation and the thermal conductivity (k) using Equation 1. 
     
       
         
           
             
               
                 
                   R 
                   = 
                   
                     T 
                     k 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     R-value may be increased by decreasing the thermal conductivity, k, of the insulation. Decreased k-values are typically obtained by increasing the density of the insulation or by decreasing the fiber diameter of the insulation. 
     It is clear from the data shown in  FIG. 4  that the fiber diameter reduction occurs at a constant gas flow and the k-value is expected to decrease; however, the k-value is reduced even further than the expected reduction as shown by the reduction in thermal conductivity (k) below the expected k-value shown in the k curve of  FIG. 4  found in U.S. Patent Application Publication No. 2007-0000286, which is hereby incorporated by reference in its entirety. Thermal conductivity is measured in k-points where a k-point is a change in the third decimal of the overall k-value. As shown in Eq. 1 (above) an improvement (i.e. reduction) in k-value causes an improvement in overall insulation or R-value. Large producers of insulation glass fibers may produce hundreds of millions or billions of pounds of insulation in a year so even small improvements in k-value lead to dramatic savings in material costs. 
     An additional unexpected benefit of the fiberizer system  10  is shown in the data of  FIG. 5 . As shown in  FIG. 5 , the drape length of the resulting fibers of the fiberizing system prior to the vertical movement of the spinner  12  and blower  28  was higher (as shown by curve  95 ) at various levels of gas flow than the drape length of the resulting fibers of the fiberizing system after the vertical movement of the spinner  12  and blower  28  (as shown in curve  96 ). 
     The principles and mode of operation of this invention have been described in its preferred embodiments. However, it should be noted that the rotary fiberizer may be practiced otherwise than as specifically illustrated and described without departing from its scope.