Abstract:
A carbon fiber centrifugal head includes an interior mechanism that at least partially controls flow of precursor material to exterior holes of the head during spinning.

Description:
BACKGROUND 
       [0001]    Carbon fibers were first developed in 1958. Since that time, carbon fibers have found use in a wide variety of applications, including, for example, reinforced composite materials, filtration of high-temperature gasses, and additives in graphite electrodes. Due to the continued demand for carbon fibers, there is a need in the art for improved fiber producing methods. 
       SUMMARY OF THE EMBODIMENTS 
       [0002]    According to one embodiment, a centrifugal spinning head for producing fibers is provided and includes an outer housing that forms an interior volume. The outer housing has an outer shell with a plurality of exterior apertures. An inner screen is positioned inside the interior volume and is spaced from the outer shell to form a gap therebetween. The inner screen includes a plurality of interior apertures. A fiber precursor material is received in the interior volume, and upon spinning the head, flows through the interior apertures, into the gap and thereafter through the exterior apertures. 
         [0003]    According to another embodiment, a method of producing carbon fibers includes providing a head having an outer housing that forms an interior volume and includes a plurality of exterior apertures. The head further including a screen positioned with the interior volume. A gap is formed between the outer housing and screen. Fiber precursor material is added into the interior volume. The head is spun and the fiber precursor material is heated to a temperature above the softening point of the fiber precursor material. The flow of the fiber precursor material out of the exterior apertures is controlled by controlling the size of the gap. The fibers are captured after being ejected from the exterior apertures. The fibers are thereafter stabilized and carbonized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a side elevated view of a spinning head. 
           [0005]      FIG. 2  is a sectional view taken along the line A-A of  FIG. 1 . 
           [0006]      FIG. 3  is a sectional view taken along the line B-B of  FIG. 1 . 
           [0007]      FIG. 4  is a partially schematic view of a centrifugal spinning apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    With reference now to  FIGS. 1-3 , a fiber spinning head is shown and generally indicated by the numeral  10 . Head  10  has an outer housing including a bottom wall  12 , a generally cylindrical outer shell  14  and a tapered frusto-conical section  16  extending inwardly and upwardly from the top edge of shell  14 . The frusto-conical section  16  terminates at a top opening  18 . Top opening  18  provides access to an interior volume  20  of the head  10 . 
         [0009]    Outer shell  14  includes a plurality of apertures  15  which may be randomly arranged or uniformly arranged or a combination thereof around outer shell  14 . In this or other embodiments, the apertures  15  may be circumferentially spaced around outer shell  14 . Apertures  15  may be positioned in one or more vertically spaced circumferential rows which may be aligned or offset. Advantageously, apertures  15  may have a diameter of from about 0.5 mm to about 5 mm. More advantageously, apertures  15  may have a diameter of from about 1 mm to about 2 mm. 
         [0010]    Positioned inside of interior volume  20  and radially inwardly of the outer shell  14  is an interior screen  22 . Optionally, a heating element  24  may be positioned within interior volume  20  and inwardly of the interior screen  22 . Interior screen  22  extends circumferentially around the entire interior  20  of head  10  and includes a plurality of apertures  23  which may be randomly or uniformly arranged or circumferentially spaced around interior screen  22 . In this or other embodiments, apertures  23  may be positioned in one or more vertically spaced circumferential rows which may be aligned or offset. Advantageously, apertures  23  may have a diameter of from about 0.5 mm to about 5 mm. More advantageously, apertures  23  may have a diameter of from about 1 mm to about 2 mm. In a preferred embodiment, substantially all apertures  23  are unaligned with apertures  15 . In a particularly preferred embodiment, none of apertures  23  are aligned with apertures  15 . 
         [0011]    The total area of the interior apertures is defined herein as the average area of the interior apertures times the number of interior apertures. Likewise, the total area of the exterior apertures is defined herein as the average area of the exterior apertures times the number of exterior apertures. The ratio of the total area of the interior apertures divided by the total area of the exterior apertures (“interior area to exterior area ratio”) may affect the flow rate of the precursor material out of head  10 . The interior area to exterior area ratio may be from about 0.1 to about 100. The interior area to exterior area ratio may be further advantageously from about 0.5 to about 10. The interior area to exterior area ratio may further be advantageously from between 0.5 to about 5. 
         [0012]    A gap  26  is formed between the outer shell  14  and interior screen  22 . The gap size in particular affects the flow rate of precursor out of apertures  23  during spinning of the head  10 . The gap  26  may be from about 0.025 mm to about 2 mm. Advantageously, gap  26  is from about 0.075 mm to about 0.5 mm. Gap  26  may be maintained by one or more spacers (not shown) positioned between interior screen and exterior shell. 
         [0013]    In use, fiber precursor material is charged into the interior volume  20  of head  10  through opening  18 . In one embodiment, the precursor material may be preheated prior to insertion into the head  10 . In this or other embodiments, the heating element  24  may heat the precursor material while inside the interior volume  20  of the head  10 . 
         [0014]    Once charged with precursor material, head  10  may be rotated about axis  27 . This rotation causes centrifugal forces that in turn cause the precursor material to be drawn radially outwardly against interior screen  22 . 
         [0015]    As head  10  spins, precursor material flows into the gap  26  via apertures  23  and thereafter flows out of apertures  15  of the outer shell  14 . As precursor material is expelled out of apertures  15 , it solidifies or hardens in the air and falls to a receptacle in the form of a fiber. 
         [0016]    The fiber creation process may be batch, wherein the head  10  is charged and spun until the precursor material within is exhausted. Alternately, the process may be continuous. For example, with reference to  FIG. 4 , a precursor supply  30  may carry a supply of precursor material therein. The precursor may be fed through an optional heating element  32  and thereafter into head  10 , which is spinning on a platform  34 . The fibers  36  are continuously ejected from head  10  and thereafter collected in a receptacle  38  for additional processing. 
         [0017]    In one particular preferred embodiment, the precursor material is a pitch material. Pitch material may be a coal tar pitch or petroleum pitch. Advantageously, the head  10  enables precursor pitches having a Quinoline-Insoluable value (hereinafter QI) of from between 0 and 50 percent by weight. In other embodiments, the QI value of the precursor pitch is greater than 1 percent by weight. In still other embodiments the QI value of the precursor pitch is greater than 5 percent by weight. In still other embodiments the QI value of the precursor pitch is greater than 10 percent by weight. In still other embodiments the QI value of the precursor pitch is from between 5 and 25 percent by weight. In other embodiments, the QI value of the precursor pitch is from between 10 and 20 percent by weight. 
         [0018]    Precursor pitch may have softening points between about 90 degrees and 350 degrees C. Advantageously, precursor pitch has a softening point between about 150 degrees and about 330 degrees C. More advantageously, the precursor pitch has a softening point between about 200 degrees and about 330 degrees C. 
         [0019]    Precursor pitch may have coking values between about 30% and about 95%. Advantageously the precursor pitch has a coking value between about 70% and 95%. Even more advantageously, the precursor pitch has a coking value between about 80% and about 95%. 
         [0020]    After formation using the head  10 , the fibers are stabilized by heating in an air atmosphere at a temperature of from about 30 to about 350 degrees C. for a period of from about 5 to about 600 minutes. After stabilization, the fibers are carbonized in an inert atmosphere at a temperature of from about 800 to about 1500 degrees C. for a period of from about one to about five hours. 
       Example 1 
       [0021]    A cylindrical head included an interior screen having apertures with a diameter of 3 mm and with apertures through the outer shell with a diameter of 1.1 mm. A spacer was positioned between the interior screen and outer shell to maintain a gap therebetween of 0.1 mm. A total of 15 apertures were provided through the interior screen and 100 apertures were provided through the outer shell giving a ratio of inner aperture area to outer aperture area of 1.1. 
         [0022]    A coal tar pitch precursor material with a softening point of 220 degrees C., a carbon yield of greater or equal to 80% and a QI of 11 wt % was charged into the head. The precursor was in powder form and added to the head without any preheating and while the head was stationary. The head was simultaneously spun and heated. The head spun at approximately 4000 RPM and the heater was maintained at from 280-350 degrees C. The spun fibers were collected in a receiving bowel. 
         [0023]    Thereafter, the spun fibers were stabilized and carbonized. The resultant carbon fiber was of good quality and isotropic in texture, implying good insulation properties. The fiber diameter had a distribution of from 10 to 20 μm. 
         [0024]    It should be appreciated that, though the above describes the fiber precursor as a pitch material, other precursor materials may be used with the above centrifugal spinning head. For example, precursors such as lignin, polymers and blends thereof may be used. So long as the precursor material has sufficient viscosity and is capable of stabilization, the precursor material may be used in the above described centrifugal spinning apparatus. 
         [0025]    The various embodiments described herein can be practiced in any combination thereof. The above description is intended to enable the person skilled in the art to practice the invention. It is not intended to detail all of the possible variations and modifications that will become apparent to the skilled worker upon reading the description. It is intended, however, that all such modifications and variations be included within the scope of the invention that is defined by the following claims. The claims are intended to cover the indicated elements and steps in any arrangement or sequence that is effective to meet the objectives intended for the invention, unless the context specifically indicates the contrary.