Ovens, discharge nozzle plates for distribution of gas through an oven, and methods to operate an oven are disclosed. Example ovens include a heating system to heat gas, a substrate heating volume, and a plenum comprising a side wall having a plurality of passages formed therein, the plenum configured to direct heated gas into the substrate heating volume from the plurality of passages, each of the plurality of passages formed in the plenum having a respective tapered cross-sectional shape.

Ovens, discharge nozzle plates for distribution of gas through an oven, and methods to operate an oven are disclosed. Example ovens include a heating system to heat gas, a substrate heating volume, and a plenum comprising a side wall having a plurality of passages formed therein, the plenum configured to direct heated gas into the substrate heating volume from the plurality of passages, each of the plurality of passages formed in the plenum having a respective tapered cross-sectional shape.

Provided are: a carbon fiber bundle which has a large value of single-fiber fineness and excellent productivity and which, despite this, contains few interlaced single fibers therein and has excellent spreadability; and precursor fibers which are suitable for use in producing the carbon fiber bundle. The precursor fibers are a carbon-fiber-precursor acrylic fiber bundle which comprises a polyacrylonitrile copolymer comprising 95-99 mol % acrylonitrile units and 1-5 mol % hydroxyalkyl (meth)acrylate units and which has a single-fiber fineness of 1.5-5.0 dtex. In the acrylic fiber bundle, the cross-section of each single fiber which is perpendicular to the fiber axis has a shape that has a roundness of 0.9 or less. The roundness is a value determined using equation (1) where S and L are the cross-sectional area and the circumferential length, respectively, of a single fiber which are obtained by examining, with an SEM, the cross-section of the single fiber which is perpendicular to the fiber axis and analyzing the obtained image.

Roundness=4 pS/L.sup.2(1)

Provided are: a carbon fiber bundle which has a large value of single-fiber fineness and excellent productivity and which, despite this, contains few interlaced single fibers therein and has excellent spreadability; and precursor fibers which are suitable for use in producing the carbon fiber bundle. The precursor fibers are a carbon-fiber-precursor acrylic fiber bundle which comprises a polyacrylonitrile copolymer comprising 95-99 mol % acrylonitrile units and 1-5 mol % hydroxyalkyl (meth)acrylate units and which has a single-fiber fineness of 1.5-5.0 dtex. In the acrylic fiber bundle, the cross-section of each single fiber which is perpendicular to the fiber axis has a shape that has a roundness of 0.9 or less. The roundness is a value determined using equation (1) where S and L are the cross-sectional area and the circumferential length, respectively, of a single fiber which are obtained by examining, with an SEM, the cross-section of the single fiber which is perpendicular to the fiber axis and analyzing the obtained image.

Roundness=4 pS/L.sup.2(1)

One embodiment is directed to an oven for heating fibers. The oven comprises a supply structure disposed within the oven between first and second ends of the oven. The supply structure comprises a plurality of plenums stacked one above each other with gaps therebetween. The plenums are in fluid communication with a heating system. At least one plenum comprises at least one side wall comprising a plurality of passages formed therein, said at least one plenum configured to direct at least a portion of the heated gas into an interior of the oven from the plurality of passages. Each of the plurality of passages formed in said at least one plenum has a respective tapered cross-sectional shape.

One embodiment is directed to an oven for heating fibers. The oven comprises a supply structure disposed within the oven between first and second ends of the oven. The supply structure comprises a plurality of plenums stacked one above each other with gaps therebetween. The plenums are in fluid communication with a heating system. At least one plenum comprises at least one side wall comprising a plurality of passages formed therein, said at least one plenum configured to direct at least a portion of the heated gas into an interior of the oven from the plurality of passages. Each of the plurality of passages formed in said at least one plenum has a respective tapered cross-sectional shape.

A carbon fiber bundle, wherein an average single-fiber fineness is from 1.0 to 2.4 dtex and a roundness is from 0.7 to 0.9 in a shape of a cross-section perpendicular to a fiber axis of a single fiber; the roundness being determined with equation (1): roundness=4S/L.sup.2, where S is a cross-sectional area of the single fiber and L is a circumferential length of the single fiber, and S and L are obtained by observing, under an SEM, the cross-section of the single fiber perpendicular to the fiber axis of the single fiber and analyzing the obtained image.

A carbon fiber bundle, wherein an average single-fiber fineness is from 1.0 to 2.4 dtex and a roundness is from 0.7 to 0.9 in a shape of a cross-section perpendicular to a fiber axis of a single fiber; the roundness being determined with equation (1): roundness=4S/L.sup.2, where S is a cross-sectional area of the single fiber and L is a circumferential length of the single fiber, and S and L are obtained by observing, under an SEM, the cross-section of the single fiber perpendicular to the fiber axis of the single fiber and analyzing the obtained image.

A modular furnace, in particular for the oxidative stabilization of a carbon fiber starting material comprising a cuboidal furnace chamber, on the upper face of which first deflecting rollers are arranged in a mutually spaced and parallel manner and on the lower face of which second deflecting rollers are arranged in a mutually spaced and parallel manner such that the carbon fiber starting material runs upwards and downwards in a laterally adjacent and slightly spaced manner so as to meander vertically in the area of the furnace chamber. A carbon fiber inlet locking device and a carbon fiber outlet locking device are provided on the upper face of the furnace chamber, and an air guiding device is connected to the furnace chamber. A supply air portion of the air guiding device is connected to a vertical air inlet side of the furnace chamber, and a discharge air portion of the air guiding device is fluidically connected to a furnace chamber vertical air outlet side opposite the vertical air inlet side. The air guiding device has an air drive device between the supply air portion and the discharge air portion.

A modular furnace, in particular for the oxidative stabilization of a carbon fiber starting material comprising a cuboidal furnace chamber, on the upper face of which first deflecting rollers are arranged in a mutually spaced and parallel manner and on the lower face of which second deflecting rollers are arranged in a mutually spaced and parallel manner such that the carbon fiber starting material runs upwards and downwards in a laterally adjacent and slightly spaced manner so as to meander vertically in the area of the furnace chamber. A carbon fiber inlet locking device and a carbon fiber outlet locking device are provided on the upper face of the furnace chamber, and an air guiding device is connected to the furnace chamber. A supply air portion of the air guiding device is connected to a vertical air inlet side of the furnace chamber, and a discharge air portion of the air guiding device is fluidically connected to a furnace chamber vertical air outlet side opposite the vertical air inlet side. The air guiding device has an air drive device between the supply air portion and the discharge air portion.