Abstract:
Apparatus for making glass fibers has AC induction coils for AC inductive heating of a spinner for spinning molten glass into molten glass fibers, an enclosure that at least partially surrounds the AC induction coils to protect a human worker, and electrically insulating shielding reducing AC power drain by being positioned between the AC induction coils and the enclosure to reduce inductive heating of the enclosure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. application Ser. No. 10/314,593, filed Dec. 9, 2002 (D0932-00560), now U.S. Pat. No. 7,021,084. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to glass fiber making equipment and in particular to insulation shielding for an inductive heater operable to heat a rotary glass fiber discharging spinner. 
     BACKGROUND OF THE INVENTION 
     A variety of technologies are known for heating the constituents of glass to a homogenous molten state and maintaining glass in that state as it is being processed into products. Prominent among these technologies are inductive heating systems and methods. This is because the silicon that is present as silica in sand (the primary constituent of glass) is semi-conductive and therefore susceptible to electronic induction. Inductive furnaces may be used to initially melt the raw materials of glass into a liquefied state and inductive heaters may be used to heat the spinners that rotate at high velocity and centrifugally discharge multiple fibers of molten glass which are cooled and further processed into end products such as glass fiber insulation. 
     While effective for heating rotary glass spinners, currently available induction heaters produce waste heat that reduces their efficiency. In order to inductively heat a typical glass spinner, electrical power is consumed in the medium frequency (MF) rings of the heater. However, there is considerable additional conductive metal in the immediate vicinity of the MF rings and spinner including, without limitation, guard plates surrounding the MF rings. 
     During operation of the heater, this metal is also inductively heated, due to AC electromagnetic induction to establish electrical current in the metal, thereby resulting in consumption of electrical power. The power that is required to produce this waste heat reduces the efficiency of the heater and increases its cost of operation. These increased operational costs in turn increase the cost of the end products of the glass making process and reduce the profit that can be realized from their sale. 
     An advantage exists, therefore, for an energy-efficient inductive heater operable to heat a rotary glass fiber discharging spinner. 
     SUMMARY OF THE INVENTION 
     The present heater invention provides an energy-efficient inductive operable to heat a rotary glass fiber discharging spinner. In particular, the invention includes shielding disposed between the induction coil and the metal guard plates of the heater. The shielding may comprise any electrically insulative or dielectric material that is capable of withstanding the high operating temperatures occurring in a glass making environment. The shielding inhibits inductive heating of the metal guard plates during operation of the heater, thereby reducing the electrical power that is required to maintain the spinner and molten glass therein at a desired working temperature. The reduced consumption of electrical power is translated into operational cost savings that can be used to reduce the cost of the end products of the glass making process and increase the profit that can be realized from their sale. 
     Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more readily apparent from the following description of preferred embodiments thereof shown, by way of example, in the accompanying drawings wherein: 
         FIG. 1  is a schematic view of a typical glass fiber spin process; 
         FIG. 2  is an exploded perspective view of a inductive heater operable to heat a rotary glass fiber discharging spinner and electrically insulative shielding therefor; and 
         FIG. 3  is a side elevation view in section of a presently insulative preferred embodiment of the electrical shielding according to the invention in assembled condition with a guard plate of the induction heater of  FIG. 3 . 
         FIG. 4  is a fragmentary isometric view of another embodiment of the invention comprising, electrical shielding having a bottom ledge. 
         FIG. 5  is a fragmentary isometric view of another embodiment disclosing electrical shielding having a bottom ledge and at least one side channel. 
         FIG. 6  is a fragmentary isometric view of another embodiment disclosing electrical shielding having a bottom ledge with a bottom channel and at least one side channel. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a typical glass fiber spin process begins at a melting furnace  10  which melts raw glass materials including sand and other constituents such as feldspar, sodium sulfate, anhydrous borax, boric acid, among many others. The molten glass is temperature regulated to a precise viscosity and delivered from furnace  10  by conduit  12  to the intakes of one or more rotary spinners  14  each of which reside in a heating chamber  16  such as that established by the inductive heater described in connection with  FIG. 2 . As is known, spinners  14  are rotated at high speed by an unillustrated rotational drive means. The spinners may be cylindrical or disk-shaped and include a plurality of peripheral holes through which fibers of molten glass  18  are centrifugally discharged as the spinners rotate at high velocity. As indicated by arrows  20 , hot, high velocity attenuation air may be blown into the intakes of the heating chambers. The attenuation air stretches the fibers to the point of breaking. As the fibers are created they are sprayed with a resin binder by a spraying apparatus  22  and are collected on a moving conveyor  24  where they form a mat  26 . The mat is delivered by the conveyor to an unillustrated curing oven which heats and cures the resin binder. 
       FIG. 2  shows a conventional inductive heater  28  including a plurality of MF rings  30  (only one of which is shown). The MF rings form an induction coil that is subjected to alternating electrical current from an unillustrated electrical power source to establish the heating chamber  16  of  FIG. 1 . The current flowing through MF rings  30  generates an alternating magnetic field that produces an electrical current in the rotating spinner  14  and glass contained therein. The current induced in the spinner and glass serves to keep the molten glass at a desired velocity as it is discharged from spinner  14 . 
     The typical rotary spinner inductive heater includes thick metal guard plates  32  on at least three sides thereof. The fourth side  34  is not normally fitted with guard plates to enable servicing of the inductive heater and maintenance or removal of spinner  14  (not shown in  FIG. 2  for clarity of illustration). The typical guard plate is about 52 inches in length, 36 inches in height and about ½ inch in thickness. The guard plates  32  protect the operating components of heater  28  from damage while shielding human workers from manufacturing debris and the magnetic field generated by the MF rings. As discussed hereinabove, because they are susceptible to inductive heating, the guard plates  32  constitute a considerable power drain on the power source during operation of heater  28 . 
       FIGS. 2 and 3  illustrate a presently preferred embodiment of electrically insulative shielding  36  in accordance with the invention. Shielding  36  is manufactured to provide a panel portion  38  preferably dimensioned to substantially cover the interior surface area of a guard plate  32  of inductive heater  28 . Further,  FIG. 3  discloses a structural connection  40 , or means  40  for, connecting and/or removably installing panel portion  38  to guard plate  32 . According to a preferred embodiment, connection  40  or means  40  comprises a hanger-type configuration extending the length of panel portion  38  which includes a flange  42  projecting from an upper edge of panel portion  38  and a downwardly-directed lip  44  depending from the flange. Together, flange  42  and lip  44  define a pocket or channel  46  for receiving the upper edge of guard plate  32 . It will be understood, however, that connection or means  40  may also assume other forms such as a plurality of hanger members disposed along the upper edge of panel portion  38  that may be integral with or detachable from the panel portion. As depicted in  FIG. 2 , a worker installs shielding  36  by lowering it in the direction of arrow  48  such that the panel portion  38  is positioned between the MF rings  30  and the guard plate  32 . 
       FIG. 4  discloses a further preferred embodiment of a structural connection  40  or means  40  for removably installing the insulative shielding  36  to the guard plate  32 . A laterally extending ledge  50  is machined unitary with the guard plate  32 , or alternatively, is adhesively attached as a separate piece part. Installation is completed when a downward facing edge  52  on the insulating shielding  36  is urged by gravity to impinge against the ledge  50 , which prevents toppling over and/or undesired removal of the installed insulating shielding  36  when such shielding  36  is removably connected to the guard plate  32 . 
       FIG. 5  discloses another preferred embodiment of a structural connection  40  or means  40  for removably installing the insulative shielding  36  to the guard plate  32 . In addition to a laterally extending ledge  50 , at least one elongated, substantially vertical channel  54  machined unitary with the guard plate  32 , or alternatively, is adhesively attached as a separate piece part. Each channel  54  slidably receives a corresponding, vertical side edge  56 , which prevents toppling over and/or undesired removal of the installed insulating shielding  36  when such shielding  36  is removably connected to the guard plate  32 . 
       FIG. 6  discloses another preferred embodiment of a structural connection  40  or means  40  for removably installing the insulative shielding  36  to the guard plate  32 . In addition to a laterally extending ledge  50 , as in  FIGS. 5 and 6 , and in addition to, at least one, substantially vertical channel  54 , as in  FIG. 6 , the laterally extending ledge  50  further includes an upwardly facing, substantially horizontal channel  58  machined unitary with the guard plate  32 , or alternatively, adhesively attached as a separate piece part. The channel  56  slidably receives an undercut edged  58  of the installed insulative shielding  36  to prevent toppling over and/or undesired removal of the insulating shielding  36  when the shielding  36  is removably connected to the guard plate  32 . 
     At least the panel portion  38  of shielding  36  (or all of the shielding  36  if the connections or means  40  is made from the same material as the panel portion  38 ) is fabricated from a non-conductive or low-conductivity dielectric material. Depending upon the chosen dielectric material, panel portion  38  may range from about ⅛-¼ inch in thickness. It also may be reinforced with non-conductive fabric or fibrous material such as aromatic polyamide fiber KEVLAR®) for enhanced strength and durability. 
     Suitable dielectric materials include artificial materials such as nylon, polytetrafluoroethylene (PTFE or TEFLON®), silicone rubber, chlorosulfonated polyethylene HYPALON®), polyetherimide, thermoplastic elastomer (SANTOPRENE®), and calcium silicate board (TRANSITE®), as well as natural dielectrics such as muscovite and phlogopite mica. In addition, the dielectric materials must is capable of withstanding the high operating temperatures (typically at least 300° F.) occurring in a glass making environment. 
     Although preferred embodiments of the invention have been described, other embodiments and modifications of the invention are intended to be covered by the spirit and scope of the appended claims.