Abstract:
A forming method for a fiber aggregate in which fibers are heated to be welded with each other, the method includes a heating step of applying upward heated air to a bottom of a block of the fibers to pass the heated air therethrough and to cause the block of fibers to float, wherein at least parts of fibers are melted while the block of the fibers float; a compression step of compressing substantially in a vertical direction the heated block of fibers into a desired height; and a cooling step of cooling the compressed block of fibers to solidify melted portions of the fibers at portions where the fibers intersect with each other.

Description:
FIELD OF THE INVENTION AND RELATED ART  
         [0001]    The present invention relates to a fibrous aggregate formed by processing fibrous material comprising fibers in particular, a fibrous aggregate which is relatively low in density and is relatively thick. It also relates to a thermal method for forming such a fibrous aggregate, and an apparatus for forming such a fibrous aggregate.  
           [0002]    Conventional methods for forming a fibrous aggregate, which are widely in use, may generally be classified into two groups: the needle punching group and the thermal group. In certain cases, a needle punching method and a thermal method are independently used, whereas in other cases, they are used in combination.  
           [0003]    Next, the two groups of fibrous aggregate forming methods will be briefly described.  
           [0004]    (1) Needle Punching Method  
           [0005]    This is a method for continuously forming a sheet of fibrous aggregate by entangling fibers among themselves; multilayered fibrous material is reciprocally punched through with the use of a needle punching machine which uses a needle called a felting needle.  
           [0006]    (2) Thermal Method  
           [0007]    This is a method for forming a fibrous aggregate by thermally welding fibers among themselves; a predetermined amount of heat is applied to multilayered fibrous material comprising plural types of fibers different in melting point, so that the fibers with the lower melting point (bonding material) melt and weld the fibers with the higher melting point (structural material), at the intersections of the fibers with the higher melting point. In other words, according to a thermal method, the fibers with the higher melting point serve as structural material, whereas fibers with the lower melting point serve as bonding agent. As for typical thermal methods, there are a method called a heated air conveyer heating chamber method, in which multilayered fibrous material is continuously fed into a heated air conveyer heating chamber to form a continuous form of fibrous aggregate, a method called a molding method, or a batch method, in which multilayered fibrous material is packed into a mold of a predetermined size and is heated to form a block form of fibrous aggregate, which has a predetermined size (size and shape).  
           [0008]    Next, the two methods will be described in more detail.  
           [0009]    (2-a) Heated Air Conveyer heating chamber Method  
           [0010]    [0010]FIG. 12 is a schematic sectional view of a conventional heated air conveyer heating chamber used for a thermal fibrous aggregate forming method. As is evident from FIG. 12, this heated air conveyer heating chamber  500  has a pair of mesh belts  510  and  520 , which are placed in a manner to vertically oppose each other, with the provision of a predetermined gap between the two belts, in order to move the multilayered fibrous material  600 , in the leftward direction of the drawing, while compressing the multilayered fibrous material  600  from the top and bottom sides (in the direction in which the fibers are stacked), as the multilayered fibrous material  600  is fed from the upper right direction of the drawing. The multilayered fibrous material  600  is actually layers of webs of sheathed fiber. Each web has been produced with the use of a carding machine (unillustrated), a cross-laying machine (unillustrated), or the like, and the fibers in each web have been laid more or less in parallel. The weight per unit of area of the multilayered fibrous material  600  is selected in accordance with its usage. Further, the multilayered fibrous material  600  comprises plural types of fibers different in melting points.  
           [0011]    The distance between the two mesh belts  510  and  520  is approximately equal to the thickness of the final product, or a continuous fibrous aggregate  650 , and can be adjusted as necessary. The thickness H of the continuous multilayered fibrous material  600  fed into the heated air conveyer heating chamber  500  is greater that the gap h between the two mesh belts  510  and  520 . After being fed into the heated air conveyer heating chamber  500 , the continuous multilayered fibrous material  600  is compressed all at once to the thickness h by the mesh belt  510  and  520 , and is thermally formed into the continuous fibrous aggregate  650  while remaining in the compressed state.  
           [0012]    In order to thermally form the continuous multilayered fibrous material  600  into a continuous fibrous aggregate  650 , an air sending chamber  530  for blowing air, and an air receiving chamber  540  for suctioning the heated air blown out of the air sending chamber  530 , are provided in the heated air conveyer heating chamber  500 . The air sending chamber  530  is provided with an air supplying hole  531  and a plurality of perforations, and is located above the path of the multilayered fibrous material  600 , within the heated air conveyer heating chamber  500 . Heated air is blown into the air sending chamber  530  through the air supplying hole  531 , and is blown out of the air sending chamber  530  through the plurality of perforations  532  to be blown at the multilayered fibrous material  600 . The air receiving chamber  540  is located below the path of the multilayered fibrous material  600 , and is provided with a plurality of perforations  542  and a plurality of air suctioning holes  541 . As the heated air having been blown at the multilayered fibrous material  600  from the air sending chamber  530 , as described above, passes through the multilayered fibrous material  600 , the heated air is suctioned into the air receiving chamber  540  through the plurality of perforations  542 , and is exhausted through the plurality of air suctioning holes  541 .  
           [0013]    Upon being introduced into the heated air conveyer heating chamber  500 , the continuous multilayered fibrous material  600  is heated by the heated air blown out of the air sending chamber  530  until its temperature rises to a predetermined one. As described above, the continuous multilayered fibrous material  600  is continuous layers of plural types of fibers different in melting point. Therefore, the fibers, which have a relatively lower melting point, can be melted by setting the temperature of the heated air to a temperature which is higher than the melting point of the fibers with a relatively lower melting point, and is lower than the melting point of the fibers with a relatively higher melting point, so that the fibers with the relatively higher melting point, can be bonded among each other at their intersections, with the melted fibers with the lower melting point acting as bonding agent, to effect a continuous fibrous aggregate  650 , which has a predetermined thickness.  
           [0014]    (2-b) Mold Based Method  
           [0015]    [0015]FIG. 13 is a drawing for depicting one of conventional methods for forming a fibrous aggregate. A block of multilayered fibrous material  610  is identical in material to the continuous multilayered fibrous material  600  used in the heated air conveyer heating chamber based method, except that it is in the form of a block. More specifically, as shown in FIG. 13( a ), the multilayered fibrous material block  610  comprises several layers of fibers, in which fibers are aligned approximately in parallel in a certain direction a, and which are stacked in a direction b perpendicular to the direction in which the fibers are aligned in each layer. This multilayered fibrous material block  610  is placed in an aluminum mold  700 , and is covered with a lid  710  as shown in FIGS.  13 ( b ) and ( c ). At this stage, the multilayered fibrous material block  610  in the mold  700  has been simply compressed in the stacking direction b, in the mold  700 . Then, a block of fibrous aggregate is obtained by heating the mold  700  until the aforementioned condition is satisfied.  
           [0016]    However, the above described methods for forming a fibrous aggregate block have such problems of their own that will be described below.  
           [0017]    (1) Needle Punching Method  
           [0018]    A needle punching method physically causes fibers to entangle, with the use of a felting needle. Therefore, a fibrous aggregate produced by a needle punching method is hard, thin, and high in bulk density. In other words, a soft and thick fibrous aggregate which is low in bulk density is difficult to produce using a needle punching method.  
           [0019]    ( 2   a ) Heated Air Conveyer heating chamber Based Method  
           [0020]    In a heated air conveyer heating chamber based method, heated air is blown at multilayered fibrous material from above, and therefore, the fibers in the layers on the top side tend to soften before those in the layers on the bottom side. As a result, the layers on the top side tend to be collapsed by the pressure from the heated air from above, and also the self-weight of the layers of fibers, causing the layers on the top side to become higher in bulk density than the layers on the bottom side. In other words, it is difficult to produce a fibrous aggregate uniform in density using a heated air conveyer heating chamber based method. One of the solutions to this problem is to reduce the velocity of the heated air. However, reducing the heat air velocity makes it impossible for the heated air to pass through the multilayered fibrous material, creating a problem in that it is virtually impossible to heat the bottom portion of the multilayered fibrous material.  
           [0021]    Therefore, producing a soft and thick fibrous aggregate which is low and uniform in bulk density using a heated air conveyer heating chamber based method is as difficult as producing it using a needle punching method, admitting that a relatively hard sheet of fibrous aggregate which is relatively high in bulk density can be as easily produced by the latter method as the former method. In addition, the layered fibrous material is heated while being kept in the compressed state by the mesh conveyer, and therefore, there is a problem in that the pattern (ridges and recesses) of the mesh conveyer is imprinted onto the surface layer of the multilayered fibrous material.  
           [0022]    ( 2   b ) Mold Based Method  
           [0023]    Referring to FIG. 14, the problems associated with methods for forming a fibrous aggregate using a mold will be described. FIG. 14 is a drawing for depicting the state of the inside of a mold during the production of a fibrous aggregate using a mold.  
           [0024]    As the mold  700  begins to be heated after the multilayered fibrous material block  610  is packed into the mold  700  and the mold  700  is sealed with the lid  710 , the multilayered fibrous material block  610  begins to gradually collapse in the gravity direction starting from its fringe. This phenomenon is not conspicuous when the plural types of fibers in the multilayered fibrous material block  610  are very different in melting point, for example, when one group of of fibers in the multilayered fibrous material block  610  is formed of polyethylene, and the other group of fibers is formed of polypropyleneterephthalate. However, if the two groups of fibers are selected from among olefinic materials alone, the phenomenon becomes very conspicuous. This may be due to the fact that in this case, there is little difference in melting point between the two groups of fibers, and therefore, the effects of the heat transmitted from the mold  700  first manifest in the fringe portions of the multilayered fibrous material block  610 .  
           [0025]    As the heating of the mold  700  is continued, heat is conducted all the way to the center of the multilayered fibrous material block  610 , causing the entirety of the adjacencies of the bottom surface of the multilayered fibrous material block  610  to collapse as shown in FIG. 14( b ). When the multilayered fibrous material block  610  is in this state, the bulk density of the multilayered fibrous material block  610  is nonuniform in terms of the gravity direction; the top portion of the multilayered fibrous material block  610  is lower in bulk density than the bottom portion of the multilayered fibrous material block  610  because the bottom side of the multilayered fibrous material block  610  is more affected by the weight of the multilayered fibrous material block  610  itself. In other words, a high bulk density region  610   a  and a low bulk density region  610   b  coexist in the multilayered fibrous material block  610 ; an undesirable bulk density gradient has been created.  
           [0026]    As described before, in the case of a conventional mold based method, bulk density gradient occurs, and therefore, a fibrous aggregate block which is relatively high in hardness and bulk density, such as the one formable by a conventional heated air conveyer heating chamber based method, can be easily formed, but a soft and thick fibrous aggregate block which is uniform and low in bulk density is difficult to produce.  
           [0027]    Further, across the portions of the internal surface of the mold  700 , with which the fibers come into contact, melted fibers (fibers which have the relatively low melting point and act as bonding agent) spread flat. As a result, a porous skin, which is smaller in porosity than the internal portion of the multilayered fibrous material block  610 , is formed in a manner to wrap the multilayered fibrous material block  610  along the internal surface of the mold  700 . Depending upon the type of fibrous aggregate usage, the presence of this skin is undesirable, and therefore, a process for removing the skin becomes necessary, which is a problem in that the removal of the skin reduces yield relative to the amount of raw material.  
         SUMMARY OF THE INVENTION  
         [0028]    The primary object of the present invention is to provide a method and an apparatus which are capable of forming a thicker fibrous aggregate which is low and uniform in bulk density, in particular, a method and an apparatus which are capable of forming such a fibrous aggregate even when the fibers in the multilayered fibrous material used for the formation of a fibrous aggregate are the same in properties, are not very different in melting point, and/or are relatively low in melting point.  
           [0029]    A fibrous aggregate forming method in accordance with the present invention for accomplishing the above described objects is a method for thermally processing fibrous material to form a fibrous aggregate, and comprises: a heating process in which heated air is blown upward through the fibrous material from below the fibrous material to melt at least a portion of each fiber of the predetermined group of fibers in the fibrous material, while keeping the fibrous material afloat and in the same state as it was prior to the blowing of the heated air; a compressing process in which the heated fibrous material is compressed to a desired thickness from the top and bottom sides; and a cooling process in which the fibrous material is cooled to solidify the melted portion of each fiber, so that the fibers are firmly welded to each other at their intersections.  
           [0030]    A fibrous aggregate forming apparatus in accordance with the present invention is an apparatus for thermally processing a fibrous material to form a fibrous aggregate, and comprises: a supporting means on which the aforementioned fibrous material is mounted; a heated air flow generating means for blowing the heated air for the heating process for melting at least a portion of each fiber, upward from below the fibrous material to lift and keep afloat the fibrous material from the supporting means; a compressing means for compressing the fibrous material toward the supporting means; and an attitude controlling means for controlling the attitude of the fibrous material kept afloat by the heated air.  
           [0031]    According to one of the aspects of the present invention, while the fibrous material is thermally processed, it is lifted and kept afloat by blowing heated air upward at the fibrous material from directly below the fibrous material, and the attitude of the fibrous material kept afloat is regulated. As a result, the effect of the gravity which affects formation of fibrous aggregate is eliminated, and therefore, relatively thick fibrous aggregate which is relatively low in bulk density can be easily obtained.  
           [0032]    In particular, a ventilatory sheet is placed in contact with the top and bottom surfaces of the fibrous material, and therefore, the surface pattern of the members used to compress the fibrous material is not imprinted onto the skin layer, or the top layer, of the fibrous material.  
           [0033]    These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    [0034]FIG. 1 is a schematic sectional view of the heating heating chamber for forming a fibrous aggregate, in the first embodiment of the present invention.  
         [0035]    [0035]FIG. 2 is a sectional view of an example of a strand of fiber in the fibrous material in accordance with the present invention.  
         [0036]    [0036]FIG. 3 is a schematic drawing for depicting a method for forming a block of fibrous aggregate using the heating heating chamber illustrated in FIG. 1, and shows the state in which the dies are placed in contact with the top and bottom surfaces of the multilayered fibrous material block, one for one.  
         [0037]    [0037]FIG. 4 is a schematic drawing for depicting a method for forming a block of fibrous aggregate using the heating heating chamber illustrate in FIG. 1, and shows the positional relationship between the bottom mold set in the heating heating chamber, and the top mold.  
         [0038]    [0038]FIG. 5 is a schematic drawing for depicting a method for forming a block of fibrous aggregate using the heating heating chamber illustrate in FIG. 1, and shows the state in which heated air is being blown at the multilayered fibrous material from below.  
         [0039]    [0039]FIG. 6 is a graph which shows the characteristic, in terms of temperature increase, of a block of multilayered fibrous material formed of such fiber that has a core portion and a sheath portion, which are formed of polypropylene and polyethylene, respectively.  
         [0040]    [0040]FIG. 7 is a schematic drawing for depicting a method for forming a block of fibrous aggregate using the heating heating chamber illustrated in FIG. 1, and shows the state in which the block of layers of fibers is being compressed by the top and bottom dies.  
         [0041]    [0041]FIG. 8 is a schematic drawing for depicting a method for forming a block of fibrous aggregate using the heating heating chamber illustrated in FIG. 1, and shows the state in which the ventilatory sheets are being peeled away after the completion of the compressing process and cooling process.  
         [0042]    [0042]FIG. 9 is a perspective view of a block of fibrous aggregate formed with the use of the heating heating chamber illustrated in FIG. 1.  
         [0043]    [0043]FIG. 10 is a schematic sectional view of the a fibrous aggregate forming apparatus in the second embodiment of the present invention.  
         [0044]    [0044]FIG. 11 is a schematic sectional view of the fibrous aggregate forming apparatus illustrated in FIG. 10, at a plane indicated by a line A-A.  
         [0045]    [0045]FIG. 12 is a schematic sectional view of a conventional heated air conveyer heating chamber used for a thermal molding method.  
         [0046]    [0046]FIG. 13 is a drawing for depicting a method for forming a block of fibrous aggregate using a conventional mold based method.  
         [0047]    [0047]FIG. 14 is a drawing for describing the problems in a conventional mold based fibrous aggregate forming method.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0048]    Next, the preferred embodiments of the present invention will be described with reference to the appended drawings.  
         [0049]    (Embodiment 1)  
         [0050]    [0050]FIG. 1 is a schematic sectional view of the heating heating chamber for forming a fibrous aggregate, in the first embodiment of the present invention.  
         [0051]    The heating heating chamber  10  depicted in FIG. 1 contains a heated air flow generating unit  11  for generating a flow of heated air. The heated air flow generating unit  11  is located in the bottom portion of the heating heating chamber  10 , and has: a plurality of heating rods  12  for generating heat; an air blowing fan  13  which is located below the heating rods  12  to generate upward heated air flow; and a perforated stainless steel plate  14  located above the heater  12 . With this structural arrangement, as the air within the heating heating chamber  10  is blown upward by the air blowing fan  13 , and is heated by the heating rods  12 . Then, the heated air flow is uniformly diffused as it passes through the perforated plate  14 . After passing through the perforated plate  14 , the heated air hits the top wall of the heating heating chamber, moves downward through a return path  15 , and is suctioned by the air blowing fan  13 , being again blown upward to circulate through the heating heating chamber  10 . The internal temperature of the heating heating chamber  10  is kept constant by an unillustrated controlling means.  
         [0052]    Located above the heated air flow generating unit  11  is a molding unit  20  which holds a block  50  of multilayered fibrous material from the top and bottom sides. The molding unit  20  has top and bottom dies  22  and  21 , which are structured so that they can be placed in, or removed from, the heating heating chamber  10 , independently of each other. The top die  22  is supported by a top die guide  26  which can be moved upward or downward by an unillustrated driving means, so that the top die  22  can be moved up or down in the heating heating chamber  10 . The left half of FIG. 1 shows the state in which the top die  22  has been moved upward, whereas the right half shows the state in which the top die  22  has been moved downward. The top and bottom dies  22  and  21  are structured so that heated air can be passed upward through them as will be described later, and also so that they do not deform when compressing the multilayered fibrous material  50 . Therefore, the top and bottom dies  22  and  21  are perforated stainless steel plates.  
         [0053]    Here, the multilayered fibrous material  50  will be described. The multilayered fibrous material  50  is a block of multilayered webs of fibers, and the fibers are extended more or less in parallel. It is produced using a carding machine (unillustrated), a cross-layer machine (unillustrated), or the like. The weight per unit of area, of the multilayered fibrous material  50  is determined depending on the usage of the finished product. It is given a predetermined size. The direction in which the webs are stacked is parallel to the gravity direction, and coincides with the vertical direction in FIG. 1. The direction in which fibers are extended is approximately perpendicular to the direction in which the webs are stacked, and coincides with the left-to-right direction, or the front-to-rear direction, in FIG. 1. In this embodiment, a large sheet of multilayered fibrous material, which is produced using the aforementioned carding machine, a cross-laying machine, or the like, is cut into approximately square pieces having a dimension of an approximately 1,000 mm x approximately 1,000 mm, and these pieces are used as the multilayered fibrous material blocks  50 . It should be noted here that it is not always necessary that the multilayered fibrous material  50  is directional; the fibers in the multilayered fibrous material  50  may extend in random directions. The bulk density of the multilayered fibrous material  50  is desired to be approximately uniform.  
         [0054]    As for the material for the fibers  51  in the multilayered fibrous material  50 , a type of fiber structured of two portions: core portion  51   a  of polypropylene, and sheath portion  51   b  of polyethylene which sheaths the core portion  51   a , as shown in FIG. 2, is used as the fiber in this embodiment (hereinafter, sheathed fiber). The melting point of polypropylene is approximately 180° C., and the melting point of polyethylene is approximately 130° C. Therefore, the difference in melting point between the two materials is approximate 50° C. As for fiber diameter, fiber with a diameter of 5 μm to 50 μm is generally used. In this embodiment, fiber with a diameter of approximately 18 μm (2 deniers) is used.  
         [0055]    Although the above described sheathed fiber  51  is used in this embodiment, the fiber structure does not need to be limited to this structure. For example, a blend between pure polypropylene fiber and pure polyethylene fiber, or a blend between sheathed fiber formed of polypropylene and polyethylene, and pure fiber, may be used. When the sheathed fiber  51  is used, the polyethylene is present at all intersections among the fibers, and therefore, virtually all fibers are securely fixed to the fibers in contact with them, at their intersections. As a result, sturdy fibrous aggregate is produced. When a blend between polyethylene fibers and polypropylene fibers is used, the ratio at which the fibers are fixed to the fibers in contact with them, at their intersections, varies depending on the blending ratio between the polyethylene fibers and polypropylene fibers. In other words, the fiber fiber-to-fiber fixation occurs only at the intersections where a polyethylene fiber is in contact with another polyethylene fiber. Thus, employment of the above described blend is useful to obtain relatively soft fibrous aggregate. Further, even though polyethylene and polypropylene are used as the material for the fibrous aggregate in this embodiment, fiber selection is not limited to the one in this embodiment, as long as a plurality of selected fibers are different in melting point from each other. Further, the number of different fibers does not need to be two; it may be three or more.  
         [0056]    Next, the fibrous aggregate forming method which uses the heating heating chamber  10  illustrated in FIG. 1 will be described with reference to a case in which fibrous aggregate with an apparent density of 0.038-0.043 g/cm 3  and a thickness of 35 mm is formed.  
         [0057]    (1-1) Preparatory Process  
         [0058]    In order to form fibrous aggregate with an apparent density of 0.038-0.043 g/cm 3  and a thickness of 35 mm using the aforementioned sheathed fibers, the thickness of the multilayered fibrous material block  50  after it is prepared, that is, after fiber stand webs are vertically stacked, are lightly compacted down, and are relieved of pressure, is desired to be approximately 120 mm (100-150 mm). In this embodiment, therefore, the multilayered fibrous material block  50  with a thickness of 120 mm was used.  
         [0059]    Referring to FIG. 3, first, the bottom die  21  is removed from the heating heating chamber  10  (FIG. 1), and a ventilatory sheet  23  is spread on the bottom die  21 . Then, the multilayered fibrous material block  50  is placed on the ventilatory sheet  23 . The edge portions of the ventilatory sheet  23  are anchored to the bottom die  21  with weighting blocks  24 . In order to assure that there will be a sufficient amount of margin used by the weighting blocks  24  to anchor the ventilatory sheet  23 , and also in order to allow the ventilatory sheet  24  to float from the bottom die  21  during the heating process which will be described later, the size (size of the entirety of the surface on which multilayered fibrous material block  50  is placed) of the ventilatory sheet  24  is rendered sufficiently large compared to the size of the exact portion of the surface of the ventilatory sheet  24 , on which the multilayered fibrous material block  50  is placed.  
         [0060]    On the top surface of the multilayered fibrous material block  50 , a ventilatory sheet  25  similar to the ventilatory sheet  24  is placed. The size of this ventilatory sheet  5  is approximately the same as the size of the top surface of the multilayered fibrous material block  50 . Of the two ventilatory sheets  23  and  25 , the bottom ventilatory sheet  23  is required to retain the multilayered fibrous material block  50  during the heating process which will be described later, and therefore, it is required that the ventilatory sheet  23  is capable of sufficiently engaging or entangling with the fibers of the multilayered fibrous material block  50 , and also capable of stretching or shrinking in an environment in which heat is applied. If the fibers of the multilayered fibrous material block  50  do not entangle with the ventilatory sheet  23 , when the multilayered fibrous material block  50  is made to float, it becomes separated from the ventilatory sheet  23 ; the ventilatory sheet  23  fails to remain in contact with the multilayered fibrous material block  50 .  
         [0061]    On the other hand, the top die  22  (FIG. 1) has been set in advance in the heating heating chamber  10 . In this state, it is desired that the top die  22  has been heated to a predetermined internal temperature of the heating heating chamber  10 , which will be described later. If the temperature of the top die  22  is too low, the fibers are rapidly cooled and solidify, making it impossible to uniformly compress the multilayered fibrous material block  50 , as the top die  22  comes into contact with the multilayered fibrous material block  50  in the compressing process which will be described later.  
         [0062]    (1-2) Heating Process  
         [0063]    After the multilayered fibrous material block  50  is mounted on the bottom die  21  as described above, the bottom die  21  on which the multilayered fibrous material block  50  is mounted is set in the heating heating chamber  10 . At this stage, the position of the top die  22  is such that as the multilayered fibrous material block  50  is set in the heating heating chamber  10 , a gap is created between the multilayered fibrous material block  50  and the top die  22 , as shown in FIG. 4. Further, the interior of the heating heating chamber  10  has been heated in advance to a desirable temperature. As described before, the multilayered fibrous material block  50  is formed of the aforementioned sheathed fiber, that is, fiber having core and sheath portions formed of polypropylene and polyethylene, respectively, and therefore, the temperature to which the interior of the heating heating chamber  10  is to be heated has only to be between the melting point (approximately 130° C.) of the polyethylene and the melting point (approximately 180° C.) of polypropylene, and also higher than the softening point (approximately 120° C.) of the polypropylene. In this embodiment, the interior of the heating heating chamber  10  was set to 140° C.  
         [0064]    After setting the bottom die  21  in the heating heating chamber  10 , the air blowing fan  13  is driven to blow heated air toward the multilayered fibrous material block  50  from below the multilayered fibrous material block  50  to heat the multilayered fibrous material block  50 . The air blowing fan  13  is set so that the velocity of the upward air flow generated by the air blowing fan  13  becomes 0.3-0.8 m/sec. As described before, the bottom and top dies  21  and  22  are formed of perforated plate, and the multilayered fibrous material block  50  is sandwiched by the top and bottom ventilatory sheets  23  and  25 . Therefore, the heated air is more uniformly passed through the multilayered fibrous material block  50 . Incidentally, in order to prevent the bottom and top dies  21  and  22  from interfering with the ventilatory performance of the ventilatory sheet  23  and  25 , the sizes and densities of the perforations of the bottom and top dies  21  and  22  are selected so that the ventilatory performances of the bottom and top dies  21  and  22  become approximately the same as, or greater than, those of the ventilatory sheets  23  and  25 . The air blowing fan  13  is driven to generate such a heated air flow that is capable of keeping the multilayered fibrous material block  50  afloat above the bottom die  21 , against the gravity G, in such a manner that the multilayered fibrous material block  50  remains in contact with the top die  22  without being compressed thereby. In other words, the fibers themselves are kept afloat by the heated air from below, while the multilayered fibrous material block  50  is being held by the top die  21  by the top surface. Therefore, the effect of the gravity which affects each fiber is reduced. Further, the interposition of the ventilatory sheet  25  between the top surface of the multilayered fibrous material block  50  and the top die  22  prevents the bulk density of the top layer of the multilayered fibrous material block  50  from becoming locally high. In other words, with the provision of the above described heating arrangement, the multilayered fibrous material block  50  can be heated while keeping the multilayered fibrous material block  50  virtually before heating.  
         [0065]    As described above, the multilayered fibrous material block  50  is caused to float by the heated air. However, the fiber stands of the multilayered fibrous material block  50  have sufficiently entangled with the ventilatory sheet  23 , and further, the edge portions of the ventilatory sheet  23  are anchored to the bottom die  21  by the weighting blocks  24 . Therefore, the ventilatory sheet  23  balloons as shown in FIG. 5; the amount of the lift of the multilayered fibrous material block  50  and the attitude of the multilayered fibrous material block  50  are regulated by the ventilatory sheet  23  as the multilayered fibrous material block  50  is lifted by the heated air. By regulating the position and attitude of the multilayered fibrous material block  50  while the multilayered fibrous material block  50  is kept afloat by the heated air, it is assured that the multilayered fibrous material block  50  is uniformly heated by the heated air.  
         [0066]    If the weighting blocks  24  are not used, the following problems occur. That is, if the velocity of the heated air blown upward from directly below the multilayered fibrous material block  50  is excessively high, the multilayered fibrous material block  50  is pressed against the top die  22  with excessive force, and therefore, the bulk density of the top portion of the multilayered fibrous material block  50  becomes greater than that of the bottom portion of the multilayered fibrous material block  50 . On the other hand, if the heated air velocity is excessively low, the multilayered fibrous material block  50  fails to be lifted, and the fibers softened by the heated air droop downward, causing the bulk density in the bottom portion of the multilayered fibrous material block  50  to become greater than that in the top portion of the multilayered fibrous material block  50 . In either case, unless the heated air is blown upward at a proper velocity, the bulk density of the multilayered fibrous material block  50  will not turn out to be uniform after the heating. Incidentally, if it is possible to control the heated air velocity so that the multilayered fibrous material block  50  is lifted and kept afloat, and the entirety of the top surface of the multilayered fibrous material block  50  remains virtually evenly in contact with the top die  22  without causing the top portion of the multilayered fibrous material block  50  to be compressed against the top die  22 , the weighting blocks  24  are not necessarily required.  
         [0067]    Further, the ventilatory sheet  23  is entangled with the fibers of the multilayered fibrous material block  50  to a proper degree, which in turn increases the frictional resistance between the ventilatory sheet  23  and multilayered fibrous material block  50 . Therefore, it is difficult for the multilayered fibrous material block  50  to horizontally shift relative to the ventilatory sheet  23 . Thus, the multilayered fibrous material block  50  is prevented from being shifted, stretched, or compressed by external physical force during this heating process, compressing process, and cooling process. As a result, a block of fibrous aggregate uniform in density is produced.  
         [0068]    Regarding the above described lifting and keeping afloat of the multilayered fibrous material block  50 , at least the opposing two edge portions of the ventilatory sheet  23  placed in contact with the polygonal flat bottom surface of the multilayered fibrous material block  50  are prevented from lifting, by being anchored by the weighting blocks  24 , and since the ventilatory sheet  23  is ballooned upward by the heated air, the multilayered fibrous material block  50  on the ventilatory sheet  23  is actually lifted and kept afloat from the bottom die  21 . Therefore, the upward flow of the heated air is prevented from escaping from the lateral sides of the multilayered fibrous material block  50 . As a result, the bulk density of the multilayered fibrous material block  50  remains as desirable as possible in terms of the horizontal direction as well as the vertical direction, that is, the direction of thickness, almost to the surfaces of the multilayered fibrous material block  50 .  
         [0069]    At this time, the characteristic, in terms of temperature increase, of the multilayered fibrous material block  50  formed of such sheathed fiber that has a polypropylene core and a polyethylene sheath will be described. FIG. 6 is a graph which shows the characteristic of the multilayered fibrous material block  50  in terms of temperature increase. In FIG. 6, the axis of ordinates represents temperature, and the axis of abscissas represents elapsed heating time.  
         [0070]    As the multilayered fibrous material block  50  is placed in the heating heating chamber  10  which has been heated to a target temperature of S 3  which is lower than the melting point S 2  (approximately 180° C.) of the polypropylene, the temperature of the multilayered fibrous material block  50  rises to the melting point S 1  (approximately 130° C.) after the elapse of a time T 1 . As the temperature of the multilayered fibrous material block  50  reaches S 1 , the polyethylene begins to melt, and the temperature of the multilayered fibrous material block  50  remains at S 1  until the polyethylene, that is, the material of the sheath portion, completely melts.  
         [0071]    Then, after the passage of a time T 2 , that is, as the polyethylene completely melts, temperature of the multilayered fibrous material block  50  again begins to rise, and reaches the target temperature S 3  of the heating heating chamber  10  after the elapse of a time T 3 . Since the temperature S 3  has been set to be lower than the melting point S 2  of the polypropylene, it does not occur that polypropylene melts and allows the structure of the multilayered fibrous material block  50  to collapse.  
         [0072]    In the case of the multilayered fibrous material block  50  in this embodiment, the size of which is 1,000 mm×1,000 mm, the proper lengths of T 1 , T 2 , and T 3  are 10-15 minutes, 10-20 minutes, and 20-25 minutes, correspondingly.  
         [0073]    In this process, causing the fibrous material block  50  to float, is advantageous irrespective of the use of the ventilatory sheet  23 . If the fibrous material block  50  is not caused to float, the state of being heated is different between adjacent the opened portions and adjacent the closed portions of the die  21 , which is the perforated plate of stainless steel in this embodiment. the heated air passes through the opened portions, and therefore, the portions adjacent the openings is more quickly heated with the result that the temperature distribution in the fibrous material block  50  is not uniform, and the produced fibrous material may be non-uniform. However, by causing the fibrous material block  50  to float as with this embodiment, there is provided a gap between the bottom die  21  and the bottom portion of the fibrous material block  50 . The perforations and the gap function like a damper such that the hot air can relatively uniformly hit the bottom of the fibrous material block  50  to uniformly heat the block  50 . Thus, a uniform fibrous material block can be produced.  
         [0074]    (1-3) Compressing Process  
         [0075]    Referring to FIG. 7, after the entirety of the multilayered fibrous material block  50  is satisfactorily heated, the top die  22  is lowered to compress the multilayered fibrous material block  50  to a predetermined thickness (bulk density). At this stage, it is desired that the top die  22  has been heated to approximately the same temperature as that of the multilayered fibrous material block  50 . This is for the following reason. If the temperature of the top die  22  is lower than the melting point of the polyethylene which acts as adhesive, the polyethylene in the topmost portion of the multilayered fibrous material block  50  solidifies, causing the fibers to be welded to the adjacent fibers. As a result, such a problem occurs that the bulk density of the top portion of the multilayered fibrous material block  50  becomes locally high; the bulk density of the top portion of the multilayered fibrous material block  50  becomes undesirably higher than that of the rest.  
         [0076]    In this compressing process, the heated air flow is not stopped, and therefore, the multilayered fibrous material block  50  is compressed while the gravity acting on each fiber is being cancelled by the flow. As a result, the multilayered fibrous material block  50  is compressed while maintaining uniform bulk density throughout its entirety. As the multilayered fibrous material block  50  is compressed, the bulk density of the multilayered fibrous material block  50  gradually increases, making it more difficult for the heated air to pass through the multilayered fibrous material block  50 , and for heat to conduct through the multilayered fibrous material block  50 . Thus, it is desired that while compressing the multilayered fibrous material block  50 , the heated air flow is slightly reduced. This is for the following reason. As the bulk density increases, the increased bulk density decreases the ventilability and thermal conductivity of the multilayered fibrous material block  50 , which in turn causes the entirety of the multilayered fibrous material block  50  to be blown upward and pressed against the top die  22  by the heated air flow, resulting in the problem that the bulk density of the top portion of the multilayered fibrous material block  50  locally increases, or the like problems. In this embodiment, the velocity of the heated air flow in the compressing process was set to 0.2-0.4 m/sec.  
         [0077]    As for the compression speed (the speed at which the top die  22  in this embodiment is lowered), it matters very little when it is intended to obtain a fibrous aggregate block with high bulk density (0.15 g/cm 3  or more). However, when it is intended to obtain a fibrous aggregate block with a low bulk density, it is desired that the multilayered fibrous material block  50  is compressed at a slower speed. This is for the following reason. If the compression speed is high, before the entirety of the multilayered fibrous material block  50  is compressed, the bulk density of the multilayered fibrous material block  50  increases on the side in contact with the top die  22 , and the fibers on this side are welded to each other while the bulk density of this side remains high. As a result, the problem that the bulk density of the top portion locally increases, or the like problems, occur.  
         [0078]    Obviously, it is desired that also during the compressing process, the top die  22  is lowered from straight above while keeping afloat the multilayered fibrous material block  50  by blowing the heated air upward from directly below the multilayered fibrous material block  50 .  
         [0079]    (1-4) Cooling Process  
         [0080]    After compressing the multilayered fibrous material block  50  to the predetermined thickness, the top and bottom dies  22  and  21  are removed from the heating heating chamber  10 , with the multilayered fibrous material block  50  remaining compressed between the two dies, and the entirety of the two dies  22  and  21  and the multilayered fibrous material block  50  is cooled. During this cooling period, the top die  22  may be kept pressed toward the bottom die  21  with the use of a weight or the like, with a spacer (unillustrated) with a predetermined height being placed between the top and bottom dies  22  and  21 , so that the state in which the multilayered fibrous material block  50  has been kept compressed in the heating heating chamber  10  can be exactly maintained during the cooling period. As for the cooling method, any method will do: natural cooling, forced cooling by a cooling fan or the like. Further, the cooling may be done within the heating heating chamber  10 ; the interior of the heating heating chamber  10  is cooled without removing the top and bottom dies  22  and  21  from the heating heating chamber  10 .  
         [0081]    After the temperatures of the surface layers of the multilayered fibrous material block  50 , that is, the temperatures of the top and bottom surfaces of the multilayered fibrous material block  50  in contact with the top and bottom dies  22  and  21 , respectively, drop below the melting point of the polyethylene, the multilayered fibrous material block  50  is separated from the top and bottom dies  22  and  21 , with the perforated sheets  23  and  25  remaining with the multilayered fibrous material block  50 . At this stage, the multilayered fibrous material block  50  has already turned into the multilayered fibrous aggregate block  55  (FIG. 9), that is, the multilayered fibrous material block  50  is practically the same as the fibrous aggregate block  55 , although the perforated sheets  23  and  25  are still firmly in contact with the multilayered fibrous material block  50  at this stage. Thus, after the cooling process, the multilayered fibrous material block  50  will be referred to as the fibrous aggregate block  55 .  
         [0082]    After the separation of the top and bottom dies  22  and  21  from the fibrous aggregate block  55 , the perforated sheets  23  and  25  are peeled from the fibrous aggregate block  55  as shown in FIG. 8 to obtain the fibrous aggregate block  55  in the state depicted in FIG. 9.  
         [0083]    By going through each of the above described processes, the fibrous aggregate block  55  with an apparent specific weight of 0.038-0.043 g/cm 3  and a thickness of 35 mm can be formed. The obtained fibrous aggregate block  55  is cut into smaller pieces of a predetermined size, or used in combination with other fibrous aggregate block  55 , depending on usage.  
         [0084]    In the above description of this embodiment, the case in which the fibrous aggregate block  55  having the aforementioned apparent specific weight and the aforementioned thickness was formed using such sheathed fiber that has a polypropylene core and a polyethylene sheath, was stated. However, various manufacturing conditions such as the aforementioned internal temperature setting of the heating heating chamber  10  or velocity of the heated air flow are adjusted in accordance with the type, thickness, and physical properties of the fibrous aggregate block to be formed. According to the method used in this embodiment, a thick and uniform block of fibrous aggregate  55  having a bulk density ranging between 0.03-0.3 g/cm 3 , can be produced using a block of multilayered fibrous material  50  having a bulk density of approximately 0.02 g/cm 3 .  
         [0085]    The thus formed fibrous aggregate block  55  possesses a proper amount of elasticity, and therefore, can be used as a preferable interior material for a seat, an armrest, a headrest, and the like for a passenger car, or a preferable cushioning material for such furniture that is represented by a bed and a sofa. Further, the fibrous aggregate block  55  is superior in water retention, and therefore, can be used as a preferable material for a water retaining member placed in various liquid containers in which various liquids are kept.  
         [0086]    The fiber aggregate comprising fibers welded at the crosing points of fibers is advantageous over aggregated of non-welded fibers as follows.  
         [0087]    When the aggregate is used of cushion, the shape may lose relatively easily, and the cushion performance varies since the fibers slide in response to the external pressure relative to each other because of the fibers are not fixed to each other at the crossing points. According to the present invention, the positional relationships among the fibers hardly changes evey by pressure, and therefore, the shape can be maintained, and the cushion perfromance can be maintained.  
         [0088]    When the aggregate is used as water-retaining material, the fibers may become non-uniform due to impact or water absorbing action with the result of bulk density of the aggregate changes so that the intended water-retaining performance is not provided. By welding the fibers at the crossing points, these problems can be avoided.  
         [0089]    Furthermore, according to the present invention, a welded fiber aggregate having a low bulk density and large thickness can be provided. The low limit of the density changes with the diameter (denier) of the fiber. Generally, the difficuly of production becomes greater with increase of the thickness. According to the present invention, such a low density fiber aggregate as 0.025 g/cm 3  with the thickness of 45 mm or 0.03 g/cm 3  with the thickness of 60 mm could be produced. With conventional methods, it has been difficult to produce the aggregate of 0.06 g/cm 3  in density. According to the present invention, the fiber aggregate having the density of not less than 0.03 g/cm 3  can be easily produced when the thickness is not less than 15 mm and not more than 60 mm. Such a low density fiber aggregate is advantageous in that the degree of deformation against the pressure is large, and therefore, it can be used for sheet of car or cushins for furniture, or packing materials particularly for ornaments of precious metal, jewels, fragile materials or the like, for which cushion of less elasticity and high restoring performance is desired.  
         [0090]    As described above, according to the fibrous aggregate forming method in this embodiment which employs the heating heating chamber  10 , heated air is blown upward at the multilayered fibrous material block  50 , which has not been compressed, from below the multilayered fibrous material block  50  during the heating process, and therefore, the heated air smoothly climbs through the multilayered fibrous material block  50  while exchanging heat with the multilayered fibrous material block  50 , efficiently heating the multilayered fibrous material block  50  and therefore reducing the heating time. Consequently, a thick block of fibrous aggregate which is low in bulk density can be formed.  
         [0091]    At this time, the description of the perforated sheets  23  and  25  will be supplemented.  
         [0092]    As described before, the perforated sheet  23  on the bottom side effectively contributes to produce a thick sheet of fibrous aggregate block  55  which is low and uniform in bulk density, by preventing the multilayered fibrous material block  50  from becoming separated from the bottom die  21  during the heating process. When only this aspect of the fibrous aggregate production is taken into consideration, the perforated sheet  25  on the top side is unnecessary. However, the perforated top sheet  25  contributes to preventing the top surface of the multilayered fibrous material block  50  from being disturbed while the multilayered fibrous material block  50  is kept afloat and heated, and also to prevent such a phenomenon that an unintended bulk density distribution is created in the multilayered fibrous material block  50  by the sudden conduction of heat from the heated top die  22 . In addition, in consideration of the compressing process, which comes after the heating process, and in which the multilayered fibrous material block  50  is compressed by the top and bottom dies  22  and  21  while polyethylene is in the melted state, if the perforated sheets  23  and  25  are not used, the textures of the surfaces of the top and bottom dies  22  and  21  are imprinted onto the multilayered fibrous material block  50 , and as a result, the top and bottom surface layers of the multilayered fibrous material block  50  are turned into the so-called skin layers. The interposition of the perforated sheets  23  and  25  between the two members used for compressing the multilayered fibrous material block  50  is effective to prevent the formation of these skin layers.  
         [0093]    As is evident from the above description, the material for the perforated sheets  23  and  25  is desired to be such a material that is capable of sufficiently entangling with the fibers of the multilayered fibrous material block  50 , is capable of stretching or shrinking in the heated environment, and does not melt during the heating process. Further, since the textures of the surfaces of the perforated sheets  23  and  25  are imprinted, to no small extent, on the surfaces of the multilayered fibrous material block  50 , the material sheet for the perforated sheets  23  and  25  is desired to be such a material sheet that is similar to the inner portion of the multilayered fibrous material block  50  in terms of the porosity. Thus, in this embodiment, a foamed polyurethane sheet with a cell count of approximately 16/cm was used as the material sheet for the perforated sheets  23  and  25 .  
         [0094]    Materials in the form of a sheet, for example, a sheet of foamed polyurethane, produced by removing cell membranes after foaming, are not much different from the multilayered fibrous material block in terms of local difference in air-flow resistance at the cell level (approximately 300-600 μm) between the areas with high air-flow resistance and the areas with low air-flow resistance. Depicted two dimensionally, the multilayered fibrous material can be compared to a large room formed by removing all the walls of a plurality of contiguous small rooms (pillars can be compared to fibers). However, if the cells of the urethane sponge are compared to the rooms of a building, the rooms are different in size (cell size). In addition, some of the walls have been removed, but the other have not been removed, hindering the traffic through the building (increasing air-flow resistance). Positioning a sheet of foamed material, as the ventilatory sheet, in contact with the top or bottom surface of the multilayered fibrous material provides an effect of rectifying air flow across the entire surface through which the heated air flows.  
         [0095]    Generally speaking, synthetic fibers are coated with various oily substances to provide them with convergence and smoothness, to prevent static electricity generation, or the like purposes; oily substances are adhered to them during a spinning process. However, in the fields of medicine or precise machinery, the oily substances are extremely disliked in some cases. In such cases, the amount of the oily substances must be reduced to an extremely low level. If the present invention is applied to such fibers, various problems that fibers entangle among themselves in an unintended manner, that bulk density becomes disturbed, and the like, occur sometimes in the presence of static electricity. Thus, it is desired as a countermeasure to such problems that the entirety of the webs are subjected to discharging blow when manufacturing fibrous aggregate. Further, a process in which ion exchange water or a water solution of nonionic surfactant is sprayed onto fibers may be provided in addition to the discharging blow process. The addition of such a process may be also very effective.  
         [0096]    (Embodiment 2)  
         [0097]    [0097]FIG. 10 is a schematic sectional view of the fibrous aggregate forming apparatus in the second embodiment of the present invention, and FIG. 11 is a schematic sectional view of the apparatus illustrated in FIG. 10, at a plane indicated by a line A-A in FIG. 10.  
         [0098]    In the fibrous aggregate forming apparatus in this embodiment, fibrous aggregate is formed by moving a unit of continuous multilayered fibrous material  150  sandwiched by ventilatory sheets  111  and  112  from the top and bottom sides, from the right side of the drawing to the left side, with the use of first to third mesh belts  101 ,  102 , and  103 , in the housing of the heating heating chamber  100 .  
         [0099]    The first mesh belt  101  is in the bottom side of the heating heating chamber  100 . The first mesh belt  101  extends across the entire range through which a unit of continuous multilayered fibrous material  150  is moved. After being fed into the heating heating chamber  100 , the unit of continuous multilayered fibrous material  150  is carried on the first mesh belt  101  and moved in the left direction indicated in the drawing through the heating heating chamber  100 , and then is discharged from the heating heating chamber  100 . Regarding the direction in which the unit of continuous multilayered fibrous material  150  is moved, a feeding conveyer is located on the upstream side of the first mesh belt  101 , and a discharging belt is located on the downstream side of the first mesh belt  101 . The vertical level at which the first mesh belt  101  conveys the unit of continuous multilayered fibrous material  150  coincides with the vertical levels at which the feeding and discharging conveyers convey the unit of continuous multilayered fibrous material  150 . With the provision of this arrangement, the unit of continuous multilayered fibrous material  150  can be smoothly transferred onto the first mesh belt  101  from the feeding conveyer, and then can be smoothly transferred out onto the discharging conveyer from the first mesh belt  101 ; in other words, the unit of continuous multilayered fibrous material  150  can be continuously moved. As for a preferable material for the first mesh belt  101 , there is a metallic belt with an approximate mesh number of 4 mesh/cm, for example.  
         [0100]    The unit of continuous multilayered fibrous material  150  is fed into the heating heating chamber  100 , with its bottom and top surfaces being covered with ventilatory sheets  111  and  112  which are placed in contact with the corresponding surfaces. Referring to FIG. 11, the ventilatory sheet  111  placed in contact with the bottom surface of the unit of continuous multilayered fibrous material  150  is wider than the unit of continuous multilayered fibrous material  150 , and the opposing edge portions of the ventilatory sheet  111  extending beyond the corresponding edges of the unit of continuous multilayered fibrous material  150  are held to the first mesh belt  101  with the use of anchoring members  113 . The width of the ventilatory sheet  112  placed on top of the unit of continuous multilayered fibrous material  150  is the same as that of the unit of continuous multilayered fibrous material  150 . The material and structure of the unit of continuous multilayered fibrous material  150 , and the materials and structures of the ventilatory sheets  111  and  112 , in this embodiment, are the same as those in the first embodiment.  
         [0101]    The interior of the heating heating chamber  100  has two separate sections: a heating section  120  on the upstream side, and a cooling section  140  on the downstream side, in terms of the direction in which the unit of continuous fibrous material  150  is moved.  
         [0102]    First, the heating section will be described. The heating section  120  has the second mesh belt  102 , which is positioned above the first mesh belt  101  in a manner to oppose the first mesh belt  101 . The second mesh belt  102  is rotated at the same velocity as that of the first mesh belt  101  and in synchronism with the first mesh belt  101 . It guides the unit of continuous multilayered fibrous material  150 , directly bearing down on the ventilatory sheet  112 , as the unit of continuous multilayered fibrous material  150  is moved by the first mesh belt  101 . The second mesh belt  102  is vertically movable by an elevating mechanism (unillustrated), for example, a hydraulic cylinder or the like, and its distance from the first mesh belt  101  has been adjusted to be greater than the thickness of the unit of continuous multilayered fibrous material  150  inclusive of the ventilatory sheets  111  and  112 , so that the top surface of the unit of continuous multilayered fibrous material  150  comes into contact with the second mesh belt  102  only when the unit of continuous multilayered fibrous material  150  is made airborne above the first mesh belt  101 . As for the preferable material for the second mesh belt  102 , there is metallic belt with an approximate mesh number of 4 mesh/cm, for example.  
         [0103]    There are a first air sending chamber  122  and a first air receiving chamber  121  a certain distance below and above, respectively the passage through which the unit of continuous multilayered fibrous material  150  is moved by the first and second mesh belts  101  and  102 . The first air sending chamber  122  has an air supplying holes  122   a  which open in the side wall of the first air sending chamber  122 , and a large number of perforations  122   b  which are in the top wall of the first air sending chamber  122 , being evenly distributed. The structure of the first air receiving chamber  121  is similar to that of the first air sending chamber  122 ; air suctioning holes  121   a  are in the side wall, and a large number of perforations  121   b  are in the bottom wall, being evenly distributed. Referring to FIG. 10, a pair of conveyer rollers  102   a  around which the second mesh belt  102  is suspended appear as if they are in the air receiving chamber  121 . However, they are positioned outside the air receiving chamber, one on each side, as shown in FIG. 11, and therefore, they do not affect the heated air flow from the air supplying holes  122   a  which will be described later.  
         [0104]    Referring to FIG. 11, the air suctioning holes  121   a  and air supplying holes  122   a  are connected to a heated air flow generating machine  105  by way of corresponding air ducts. The heated air flow generating machine  105  contains a heater  107 , and an air blowing fan  106  which generates air flow which flows from the air suctioning hole  121   a  side toward the air suctioning hole  122   a  side. As the heated air flow generating machine  105  is driven, heated air flow which flows towards the supplying holes  122   a  is generated in the heated air flow generating machine  105 . This heated air is sent into the air sending chamber  122  through the air supplying holes  122   a , and is blown into the unit of continuous multilayered fibrous material  150  from directly below through the perforations  122   b . After being blown into the unit of continuous multilayered fibrous material  150 , the heated air travels upward through the unit of continuous multilayered fibrous material  150 , is suctioned into the air receiving chamber  121  through the perforations  121   b , and is returned into the heated air flow generating machine  105  through the air supplying holes  121   a . In other words, across the range across which the unit of continuous multilayered fibrous material  150  is moved, upward flow of heated air occurs.  
         [0105]    As will be described later, in this embodiment, in order to make it possible to allow heated air to be blown upward toward the unit of continuous multilayered fibrous material  150  even while the unit of continuous multilayered fibrous material  150  is compressed, the first air sending chamber  122  and first air receiving chamber  121  are extended into the areas below and above a pair of conveyer rollers  103   a , that is, the most upstream conveyer rollers, around which the third mesh belt  103  is suspended, respectively, in the cooling section  140  which will be described later. These conveyer rollers  103   a  are also positioned outside the air receiving chamber  121  as the aforementioned pair of conveyer rollers  102   a , and therefore, they do not affect the flow of heated air from the air supplying holes  122   a.    
         [0106]    Next, the cooling section  140  will be described. The basic structure of the cooling section  140  is the same as that of the heating section  120 . In other words, it has the third mesh belt  103  which is positioned above the first mesh belt  101  in a manner to oppose the first mesh belt  101 , a second air sending chamber  142  positioned below the path through which the unit of continuous multilayered fibrous material  150  is conveyed, and a second air receiving chamber  141  positioned above the path through which the unit of continuous multilayered fibrous material  150  is conveyed. However, this cooling section  140  must quickly cool the unit of continuous multilayered fibrous material  150  after the compression of the unit of continuous multilayered fibrous material  150 , and therefore, a cold air flow generating machine (unillustrated), instead of the aforementioned heated air flow generating machine, is connected to the second air sending chamber  142  and second air receiving chamber  141 .  
         [0107]    The third mesh belt  103  is rotated at the same velocity as that of the first mesh belt  101  and in synchronism with the first mesh belt  101 . It guides the unit of continuous multilayered fibrous material  150 , bearing down on the ventilatory sheet  112 , as the unit of continuous multilayered fibrous material  150  is conveyed by the first mesh belt  101 . The third mesh belt  103  is vertically movable by an unillustrated elevating mechanism as is the second mesh belt  102 , and its distance from the first mesh belt  101  has been adjusted so that the unit of continuous multilayered fibrous material  150  is compressed to the thickness of a final product, or a unit of continuous fibrous aggregate. A preferable material for the first mesh belt  101  is a metallic belt with an approximate mesh number of 4 mesh/cm, for example.  
         [0108]    The second air sending chamber  142  has air supplying holes  142   a  and perforations  142   b  similar to the air supplying holes  122   a  and perforations  122   b  of the first air sending chamber  122 , and the cold air generated by the aforementioned cold air flow generating machine is blown upward from below the unit of continuous multilayered fibrous material  150 . The second air receiving chamber  141  has an air suctioning hole  141   a  and perforations  141   b  similar to the air supplying holes  121   a  and perforations  121   b  of the first air receiving chamber  121 , and the cold air is blown upward from the second air sending chamber  142 , is suctioned through the unit of continuous multilayered fibrous material  150 , and is returned into the cold air flow generating machine.  
         [0109]    As for the cooling air to be blown through the heated unit of continuous multilayered fibrous material  150  in the cooling section  140 , air (ambient air) with normal temperature may be used. In such a case, the aforementioned cold air flow generating machine is structured as a simple air blower, which takes in air from outside the heating heating chamber  10 , and exhausts it from the second air receiving chamber  141 . With the provision of a blower or the like for forcefully exhausting the air within the second air receiving chamber  141 , at the air suctioning hole  141   a  of the second air receiving chamber  141 , improvement in air exhausting efficiency can be expected.  
         [0110]    At least one of the rollers around which the first and third mesh belts  101 - 103  are suspended is provided with a secondary heating means constituted of a piece of electrical heating wire or the like, and any given portions of the first to third mesh belts  101 - 103  are preheated to an approximately the same temperature as that necessary in the heating heating chamber  10 , before they come into contact with the unit of continuous multilayered fibrous material  150 .  
         [0111]    More specifically, the temperature of a given portion of the first mesh belt  101  drops as it moves through the cooling section  140 , and therefore, this portion of the first mesh belt  101  is preheated to a predetermined temperature before it enters the heating section  120 , so that the efficiency with which the unit of continuous multilayered fibrous material  150  is heated in the heating section  120  is prevented from falling. The temperature of a given portion of the second mesh belt  102  also falls before it comes into contact with the unit of continuous multilayered fibrous material  150  after it becomes separated from the unit of continuous multilayered fibrous material  150 , and therefore, this portion of the second mesh belt  102  is also heated to a predetermined temperature before it comes into contact with the unit of continuous multilayered fibrous material  150  again, so that the efficiency with which the unit of continuous multilayered fibrous material  150  is heated in the heating section  120  is prevented from reducing. The temperature of a given portion of the third mesh belt  103  drops as this portion of the third mesh belt  103  comes into contact with the cooling air while it is moving between the second air sending camber  142  and second air receiving chamber  141 , and therefore, it is heated to a predetermined temperature before it comes into contact with the unit of continuous multilayered fibrous material  150 , so that the temperature of the top portion of the compressed unit of continuous multilayered fibrous material  150  is prevented from rapidly dropping. As a result, the entirety of the unit of continuous multilayered fibrous material  150  is evenly compressed across the surfaces to the core while it is kept at the temperature to which it is heated in the heating section  120 , eliminating such a problem that the unit of continuous multilayered fibrous material  150  is compressed after it begins to solidify due to the temperature drop.  
         [0112]    Next, an example of a process, in which a unit of continuous fibrous material with an apparent bulk density of 0.038-0.043 g/cm 3  and a thickness of 35 mm is continuously formed of a supply of the sheathed fibers with a fineness of 2-6 deniers, with the use of the forming apparatus illustrated in FIG. 10, will be described.  
         [0113]    (2-1) Preparatory Process  
         [0114]    First, the unit of continuous multilayered fibrous material  150  similar to the multilayered fibrous material block  50  in the first embodiment is prepared. Then, the position of the second mesh belt  102  is adjusted; the second mesh belt  102  is vertically moved to a position at which the unit of continuous multilayered fibrous material  150  which has been sandwiched by the two ventilatory sheets  111  and  112  and mounted on the first mesh belt  101  does not make contact with the second mesh belt  102 . Since the thickness of a unit of continuous fibrous aggregate into which the unit of continuous multilayered fibrous material  150  is formed is 35 mm, the position of the third mesh belt  103  is adjusted; the third mesh belt  103  is vertically moved so that the thickness of the unit of continuous multilayered fibrous material  150  becomes 35 mm in the cooling section  140 . The rotational velocities of the mesh belts  101 - 103  are set so that the velocity at which the unit of continuous multilayered fibrous material  150  is conveyed becomes 0.5 m/min.  
         [0115]    As for the heating section  120 , a temperature to which air is heated, a velocity at which air is blown, and the like factors, are set in accordance with the physical properties of the fiber. More specifically, the unit of continuous multilayered fibrous material  150  is formed of strands of such sheathed fiber that has a core portion of polyethylene and a sheath portion of polypropylene as described before. Therefore, it is required that the unit of continuous multilayered fibrous material  150  is heated to a temperature, which is higher than the melting point of polyethylene and is lower than the melting point of polypropylene, while the unit of continuous multilayered fibrous material  150  is conveyed to the downstream end of the heating section  120 . In this embodiment, the heated air temperature was set to approximately 140° C., and the heated air velocity was set to a velocity in a range of 0.3-0.8 m/sec.  
         [0116]    As for the cooling section  140 , the temperature and velocity of cooling air, and the like factors, are set based on the fact that polyethylene, that is, one of the constituents of the fiber in the unit of continuous multilayered fibrous material  150 , must be cooled to a temperature lower than the melting point of polyethylene while the unit of continuous multilayered fibrous material  150  having been heated and compressed is conveyed to the downstream end of the compressing section. It is desired that the unit of continuous multilayered fibrous material  150  is uniformly cooled in terms of its thickness direction, toward the top surface (toward third mesh belt  103 ) starting from the bottom surface (first mesh belt  101  side). In this embodiment, therefore, the cooling air temperature was set to approximately normal temperature, and the cooling air velocity was set to a velocity in a range of 0.2-0.3 m/sec.  
         [0117]    After the various sections are adjusted as described above, the unit of continuous multilayered fibrous material  150  is fed into the heating heating chamber  100 , with the unit of continuous multilayered fibrous material  150  sandwiched by the ventilatory sheets  112  and  111  from the top and bottom sides, respectively.  
         [0118]    (2-2) Heating Process  
         [0119]    After being fed into the heating heating chamber  100 , the unit of continuous multilayered fibrous material  150  is first conveyed into the heating section  120 . While the unit of continuous multilayered fibrous material  150  is conveyed through the heating  120 , it is heated by the heated air blown upward from directly below the unit of continuous multilayered fibrous material  150 . As a result, polyethylene which constitutes the sheath portion of the fiber melts, causing the fibers of the unit of continuous multilayered fibrous material  150  to be welded to each other. During this process, the unit of continuous multilayered fibrous material  150  is kept airborne above the first mesh belt  101  by the upward flow of heated air as shown in FIG. 11, the gravity acting on each fiber being cancelled by the flow. Thus, the fibers in the unit of continuous multilayered fibrous material  150  are thermally welded to each other while remaining in the same state as they were prior to the heating. The properties required of ventilatory sheets  111  and  112  are the same as those in the first embodiment, and a pair of weighting blocks  113  required in this embodiment are the same as the weighting blocks  24  required in the first embodiment. Therefore, they will not be described in detail here.  
         [0120]    (2-3) Compressing Process  
         [0121]    After being compressed by the first and third mesh belts  101  and  103 , the unit of continuous multilayered fibrous material  150  is conveyed through the cooling section  140  while remaining compressed by the first and third mesh belts  101  and  103 . In the cooling section  140 , the cooling air is being blown upward from directly below the path of the unit of continuous multilayered fibrous material  150 . Therefore, the unit of continuous multilayered fibrous material  150  is gradually cooled, and the polyethylene portions of the fibers solidify before the multilayered fibrous material block  50  is released from the compressing effect of the belts  101  and  103 .  
         [0122]    After being passed through the cooling section  140 , the unit of continuous multilayered fibrous material  150  is discharged from the heating heating chamber  100 , and the ventilatory sheets  111  and  112  are removed from the unit of continuous multilayered fibrous material  150 . Consequently, a unit of continuous fibrous aggregate is obtained. The thus obtained unit of continuous fibrous aggregate is cut into a plurality of small pieces of fibrous aggregates of different sizes in accordance with usage.  
         [0123]    As described above, according to this embodiment, the unit of continuous multilayered fibrous material  150  is mounted on a conveyer and is fed into the heating heating chamber  101 , which continuously heats the unit of continuous multilayered fibrous material  150  to a predetermined temperature without compressing it, and then, continuously cools the unit of continuous multilayered fibrous material  150 , while keeping it compressed, immediately after the heating. Therefore, a unit of continuous fibrous aggregate, which has a predetermined bulk density and a predetermined thickness, can be continuously formed. The effect of keeping the unit of continuous multilayered fibrous material  150  airborne by blowing heated air upward from directly below the unit of continuous multilayered fibrous material  150 , and the effect of placing a ventilatory sheet in contact with at least the bottom surface of the unit of continuous multilayered fibrous material  150 , are the same as those in the first embodiment.  
         [0124]    In another embodiment of the present invention, a plurality of pairs of the top and bottom dies used in the first embodiment, and a heating heating chamber capable of continuously moving the plurality of the pairs of the top and bottom dies, are used to form a unit of continuous fibrous aggregate. The preparatory process in this embodiment is the same as that in the above described first embodiment, and therefore, will not be described here. Thus, the details of the heating process, compressing process, and cooling process in this embodiment will be described below.  
         [0125]    (Embodiment 3)  
         [0126]    In this embodiment of the present invention, a unit of continuous fibrous aggregate is formed by preparing plural pairs of the top and bottom dies used in the first embodiment of present invention, and a heating heating chamber capable of continuously moving the plural pairs of the top and bottom dies.  
         [0127]    (3-1) Preparatory Process  
         [0128]    The preparatory process in this embodiment is the same as that in the above described first embodiment, and therefore, its details will not be described here, and the details of the heating, compressing, and cooling processes in this embodiment will be described below.  
         [0129]    (3-2) Heating Process  
         [0130]    A multilayered fibrous material block  50  is placed on each of the bottom dies  32  as in the first embodiment. At this stage, the position of the top die  22  is such that a gap is present between the top die  22  and the ventilatory sheet  5  on the top side. The interior of the heating heating chamber has been preheated to a desired temperature by a heater  12 . In this state, the bottom die  21  on which the multilayered fibrous material block  50  is resting, and the top die  22  set on the multilayered fibrous material block  50 , are moved into the heating heating chamber. The heating heating chamber contains a moving means for moving the top and bottom dies  22  and  21 . In the heating heating chamber, the distance between the bottom and top dies  21  and  22  is maintained at a desired distance by this die moving means. The distance between the bottom and top dies can be optionally set. As described before, the plural pairs of top and bottom dies are prepared, and are sequentially moved through the heating heating chamber. The size (length) of the heating heating chamber is determined in accordance with the required heating time and die moving speed. Since the method for heating the multilayered fibrous material block  50  in the heating heating chamber is the same as that in the above described embodiment, its description will not be given here.  
         [0131]    (3-3) Compressing Process  
         [0132]    After the entirety of the multilayered fibrous material block  50  is heated in the above described heating heating chamber, each of the above described top dies  22  is lowered to compress the multilayered fibrous material block  50  to a desired thickness (bulk density). Each bottom dies  21  is provided with a spacer with a desired height, as was the bottom die  21  in the first embodiment, and each top die  22  is lowered until it comes into contact with the spacer. The aforementioned top die  22  moving means can be vertically moved in this compressing zone. Each top die  22  has been heated to virtually the same temperature as that of the multilayered fibrous material block  50  while being moved through the heating heating chamber by the aforementioned die moving means, as in the first embodiment.  
         [0133]    Also in this compressing process, heating air is not stopped as in the first embodiment, and therefore, the multilayered fibrous material block  50  is compressed while the gravity acting upon each fiber is being cancelled by the flow of the heated air. It is obvious that also in this compressing process, it is desired that the top die  22  is lowered from above the multilayered fibrous material block  50  while the multilayered fibrous material block  50  is kept afloat by the upward flow of heated air from directly below the multilayered fibrous material block  50 .  
         [0134]    (3-4) Cooling Process  
         [0135]    After being compressed to a desired thickness, the top and bottom dies  22  and  21  remaining compressing the multilayered fibrous material block  50  are moved out of the heating heating chamber by the above described moving means, and are cooled in entirety while being kept in the same state as the state in which they were moved out of the heating chamber. As for the cooling method, they may be naturally cooled, or may be forcefully cooled with the use of a cooling fan or the like; any cooling means may be employed as the cooling means for this embodiment. After at least the temperature of the surface layer of the multilayered fibrous material block  50 , that is, the surfaces of the multilayered fibrous material block  50  in contact with the top and bottom dies  22  and  21  falls below the melting point of polyethylene, the top die  22  is moved upward, and the multilayered fibrous material  50  is moved out of the bottom die  21 . At this stage, the multilayered fibrous material block  50  is still firmly in contact with the ventilatory sheets  23  and  25 . In reality, however, the multilayered fibrous material block  50  is the same as the same as the multilayered fibrous material block  55  (FIG. 9). According to this embodiment, after the multilayered fibrous material block  50  is taken out, the next multilayered fibrous material block  50  may be set to repeat the heating-compressing-cooling processes, so that it appears as if a large number of fibrous aggregate blocks are continuously produced. The structures in this embodiment other than those described above, and their effects, are the same as those in the above described embodiment. Further, as described above, also in the cases of the structures in this embodiment, a large number of fibrous aggregate blocks can be efficiently produced. The size of the apparatus, and the number of the pair of top and bottom dies, should be determined in accordance with the heating time, compressing time, and cooling time for the multilayered fibrous material block  50 , and the speed at which the multilayered fibrous material block  50  is moved.  
         [0136]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.