Abstract:
Spring constant of a bristle against the buckling of the bristle is lowered and resilient flexing is facilitated even if a rotary shaft is changed in its movement to contact a brush seal of a brush seal device. In the brush seal device, a bending portion is formed amid a bristle constituting a brush seal to facilitate the resilient buckling deformation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a brush seal device for sealing a clearance between a rotary shaft and a mating component that are relatively movable. More particularly, the present invention relates to a brush seal device that is disposed between two components relatively movable in, for example a gas turbine and an airplane and seals the clearance in away that a brush seal is deformed to follow the change in the movement of one component even if the one component changes slightly its movement relative to the other component.  
           [0003]    2. Description of the Related Art  
           [0004]    As a related art to the present invention there exists a brush seal device  100 , as shown in FIG. 9.  
           [0005]    [0005]FIG. 9 is a sectional view of a brush seal device  100  mounted between a rotary shaft  120  and a casing  110  through which the rotary shaft  120  passes. The casing  110  is a fixed component of, for example, a steam turbine or a gas turbine. The brush seal device  100  attached to the casing  110  seals fluid to be sealed between the casing  110  and the rotary shaft  120 .  
           [0006]    In FIG. 9, the brush seal device  100  is formed in the shape of a ring and its attachment section  104  on its outer circumference is attached to a channel portion  112  of the casing  110 . Main components of the brush seal device  100  are a brush seal  109 , a backing plate  102 , and a support plate  103 . In the brush seal  109 , bristles  101  are arranged around a circular circumference to form a wall having a certain width and with their outer ends being coupled to form an attachment section  104 . The free end  105  on the inner circumference side of the brush seal  109  faces the rotary shaft  120 . The diameter of a bristle  101  generally used is 0.20 mm or more.  
           [0007]    An annular backing plate  102  is disposed on a side face of the brush seal  109  with its side face  108  being in contact with the brush seal  109 , supporting the bristles  101  against the action due to the pressure of the sealed fluid.  
           [0008]    A support plate  103  formed as a ring plate is disposed on the other side face of the brush seal  109  to sandwich, in cooperation with the backing plate  102 , the brush seal  109  on its attachment section  104  side, thereby to couples them in a body. The inside diameter of the support plate  103  is made large so that the sealed fluid can effect on the side face of the brush seal  109 . The brush seal  109  is exposed at its free end  105 .  
           [0009]    Outer circumference sides of the backing plate  102 , the attachment section  104  of the brush seal  109 , and the support plate  103  are welded to form a connecting section  106 .  
           [0010]    [0010]FIG. 10 is a front view of the brush seal  109 . The brush seal  109  in FIG. 10 is in a state that the brush seal  109  and the rotary shaft  120  are normally fitted without oscillation, such that the bristles  101  extend straight and oriented to incline relative to the radial direction of the rotary shaft  120 . In the normal state of the brush seal  109 , the rotary shaft  120  is in contact with or close to the free end  105 , as shown by the solid line in FIG. 9.  
           [0011]    Another related art is also shown in FIG. 11. In the drawing, a connecting section  106  of a brush seal  109  is contained within an attachment section  131  of a brush holder  130  and is allowed to move in the radial direction. A plate spring  132  urges the connecting section  106  to bear in the radial direction of the rotary shaft  120 .  
           [0012]    When the rotary shaft  120  eccentrically presses against the brush seal, it becomes complex to calculate two spring constant, one corresponding to the resilient deformation of bristles, and the other to the resilient deformation of the plate spring  132 , due to the involvement of the complexity in friction generated from its mounting structure. Since those two spring constants and other frictions are the elements for the design of the device, it is extremely difficult to achieve optimum design or improvement in consideration of the pressure generated by the displacement of the rotary shaft  120 . Thus, the ability of the bristles  101  to follow the displacement of the rotary shaft  120  is not fully performed and it results in quick abrasion of the free end  105  of bristles. In addition, the ability of the bristles  101  having a larger diameter to follow is poor when the bristles contact the rotary shaft  120 . Moreover, as the thickness of a bundle of bristles becomes larger, the ability to follow becomes poorer. Accordingly, it is limited to make the thickness of the bundle of bristles large. Thus, the sealing ability is necessarily reduced.  
           [0013]    In the brush seal device  100  configured as above, while the brush seal  109  is pressed against the rotary shaft  120  as shown in FIG. 12, when eccentricity or vibration causes the rotary shaft  120  to contact the brush seal  109 , its tilt angle is further increased.  
           [0014]    In this condition, if the pressure of the sealed fluid is high pressure (P 1 ), since the differential pressure (P 1 -P 2 ) between the high pressure (P 1 ) and the low pressure (P 2 ) becomes large as shown in FIG. 9, the entire straight bristles of the brush seal  109  are pressed against the backing plate  102  and then it becomes difficult for them to deflect in response to the contact with the rotary shaft  120 , that is, the ability to follow in response to the rotary shaft  120  is worsened. Also, when the sealed fluid flows into spaces between bristles  101 , each bristle  101  is easily pushed apart and thus the tilted bristles  101  tend to displace at its side pushed apart such that tilt angle becomes smaller, thereby to form clearances among the bristles  101 . Then the bristles  101 , each of which was pushed apart and has a small tilt angle transit to the state that their length in the radial direction are longer. Accordingly, pressure exerted by the rotary shaft  120  is further increased to wear the bristles.  
           [0015]    In routing such behaviors as describe, the clearance C that is given between the free end  105  of the bristles  101  on the side diametrically opposite to the side where the brush seal  101  is pressed against the rotary shaft  120 , as shown in FIG. 12, is extended as shown in FIG. 13, causing leakage of the sealed fluid out of the clearance C.  
           [0016]    The present invention has been made in consideration of the problems as mentioned above and the technical problems to be solved are: to reduce the resilient force exerted on the brush seal caused by the pressure of the rotary shaft so that abrasion of the brush seal by the rotary shaft can be reduced; to improve the ability of the brush seal to follow in response to the change of the rotary shaft for increasing the sealing ability; and to achieve to obtain a brush seal in the shape of a rectangular strip so as to allow resilient deformation and increase the sealing ability.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention has been made to solve the problems as described above, and technical means for solving them are constituted as below.  
           [0018]    A brush seal device of a preferred embodiment according to the present invention is one which is mounted to one of two components rotatable each other with a clearance there between, and seals the clearance, comprising: a brush seal having an attachment section for fixing one end of a row of bristles arranged in the shape of a wall and having a free end facing the surface of the other component, wherein each of the bristles in the brush seal has a bending portion in the middle for facilitating resilient buckling deformation of the bristle.  
           [0019]    In the brush seal device of a preferred embodiment according to the present invention, in the middle of a bristle of a brush seal is defined a bending portion for facilitating resilient deformation, and the flexible bending portion can be deformed resiliently when action force from a rotary shaft exerts on the free ends of the bristles, to follow the circumference of the rotary shaft, and the sealing ability will fully perform. The brash seal may be in the shape of shape of rectangular strips, as well as the shape of wire, thereby to improve the sealing ability. Furthermore, it is allowed to reduce abrasion due to the contact of the free end of the brush seal with the circumference of the rotary shaft.  
           [0020]    Additionally, with the ability of the bristle to follow the movement of the rotary shaft, it is easy to calculate spring constants based on the bristle and the force acting on the bristle without further calculation for other elements, resulting in easy optimum design.  
           [0021]    The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-198813, filed on Jun. 29, 2001, the disclosure of which is expressly incorporated herein by reference in entirety. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a sectional view, showing in half the first embodiment of the brush seal device according to the present invention;  
         [0023]    [0023]FIG. 2 is a front view, showing a brush seal of the brush seal device of the first embodiment in FIG. 1;  
         [0024]    [0024]FIG. 3 is a plan view, showing the second embodiment of the brush seal of the brush seal device in FIG. 1;  
         [0025]    [0025]FIG. 4 is a plan view, showing the third embodiment of the brush seal of the brush seal device in FIG. 1;  
         [0026]    [0026]FIG. 5 is a side view, showing the bristle in FIG. 2;  
         [0027]    [0027]FIG. 6 is a side view, showing the bristle in FIG. 3;  
         [0028]    [0028]FIG. 7 is a side view, showing the bristle in FIG. 4;  
         [0029]    [0029]FIG. 8 is a sectional view, showing in half the second embodiment of the brush seal device according to the present invention;  
         [0030]    [0030]FIG. 9 is a sectional view, showing in half a brush seal device of one related art;  
         [0031]    [0031]FIG. 10 is a front view, showing a portion of the brush seal device in FIG. 1;  
         [0032]    [0032]FIG. 11 is a perspective view, showing a brush seal device of another relative art;  
         [0033]    [0033]FIG. 12 is a partial front view, showing the brush seal device in FIG. 1, in which the rotary shaft is contacting the brush seal;  
         [0034]    [0034]FIG. 13 is a partial front view, showing the brush seal device in FIG. 1, in which the rotary shaft is separated from the brush seal;  
         [0035]    [0035]FIG. 14 is a side view, showing the bristle in FIG. 10. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0036]    Some embodiments of a brush seal device of the present invention will be hereinafter described in detail with reference to the drawings. The drawings are not conceptual drawings but design drawings of correct configurations with correct dimensions.  
         [0037]    [0037]FIG. 1 is a sectional view of a brush seal device  1  that separates a clearance defined between a casing  50  and a rotor  60  of a gas turbine (also referred to as a rotation shaft) into a high pressure area P 1  and a low pressure area P 2 .  
         [0038]    In FIG. 1, the reference numeral  1  denotes a brush seal device. A fixing section  20  at the outer circumference side of the brush seal device  1  is attached to a step section  51  defined in an inner circumference surface of the casing  50 , which is one of the two components. A free end  5  at the inner circumference side of the brush seal device  1  is located to contact the outer circumference surface of the rotor  60 , which is the other of the two components, or is located close to the surface. Thus, the brush seal device  1  seals the fluid to be sealed at the high pressure P 1  side.  
         [0039]    The brush seal device  1  is mainly composed of a brush seal  2 , while a backing plate  6  and a holding section  10  are accessories. Therefore, only brush seal  2  may seal.  
         [0040]    The brush seal  2  has bristles  4 , the middle portion each of which is formed into a curvedly bending portion  8  in the shape of a recess with respect to the rotation direction of the rotor  60 . The bristles  4  are made by forming a thin plate into small strips as shown in FIG. 2. A plurality of brush seals  2  are stacked in the axial direction of the rotor  60  to form a wall. Also, outer circumference end portions are welded together by a bolt or the like through a backing plate  6  and a holding section  10  to form an attachment section  3 . The bristles  4  may be constituted of wires in the similar way. An embodiment of the bristle  4  has a circular or square (also, rectangular allowed) cross section. The diameter is 0.005-0.5 mm, preferably 0.02-0.2 mm or the side length is 0.01-0.1 mm and the longitudinal length is 5-50 mm. It should be determined by the sealing condition. The thickness of the wall formed by the bristles is 0.01-0.4 mm or 0.4-5 mm. As the material of bristles, steel, nickel base alloy or ceramics may be used.  
         [0041]    The backing plate  6  has a fixing section  6 A which retains the attachment section  3  of the brush seal  2  and a support surface  7  which supports the brush seal  2  against the pressure of the sealed fluid such that the brush seal  2  is not extremely bent. The brush seal  2  and the support surface  7  may contact as shown in FIG. 1, or may be separate.  
         [0042]    The free end  5  of the brush seal  2  contacts a rotor  60  when the rotor  60  is fluctuated or oscillated to a large extent. However, since the bending portions  8  in a curved shape are formed in the middle of all the bristles  4 , spring constant of the bristle  4  is small along straight direction. Thus, the brush seal  2  can be resiliently deformed in response to the oscillation of the rotor  60  even if the oscillation makes the rotor  60  contact the brush seal  2 . That is, contact force can be absorbed, depending on the spring constant set for the brush seal  2  when the rotor  60  is oscillated. In addition, the bent bristles  4  further decreases the contact pressure even if the rotor  60  oscillates to larger extent, and thus the abrasion is further hindered.  
         [0043]    An attachment section  3  of the brush seal  2  is welded together with the backing plate  6  and a support plate component  10  by electron beam or the like. The welding zone of the three components forms a fixing section  20 . The holding section  10  is formed in a ring shape with smaller width in the diameter direction than that of the backing plate  6 . In FIG. 1, the holding section  10  has the same length as of the fixing section  20 , but its length may be close to the length of the backing plate  6  in the diameter direction. When the holding section  10  is long, a space portion in which the sealed fluid can flow into is formed between the brush seal  2  and a side face of the holding plate section  10 .  
         [0044]    Material of the backing plate  6  and a holding section  10  is preferably selected according to the coefficient of linear thermal expansion of the casing  50 . For example, it is made of nickel-base alloy, iron, steel, or other non-ferrous metal. Various kinds of materials may be selected depending on the kind, temperature of the sealed fluid or other conditions in application fields.  
         [0045]    [0045]FIG. 2 is a plan view of a brush seal  2  in the first embodiment of the present invention. Inner circumference side of a ring-shaped thin plate is formed into strips, leaving partially the outer circumference, by precision processing, such as laser beam processing, chemical etching and electric discharging, to form the brush seal  2 . When bristles  4  are made of wire, they are punched to form a curved shape.  
         [0046]    The middle portion of the brush seal  2  is formed into a bending portion  8  curved in the circumferential direction. However, the bending direction may be in the axial direction of the brush seal  2 . That is, the bending portion  8  may be bent in the circumferential direction, in the axial direction, or three-dimensionally in an oblique direction of the brush seal  2 . They are bundled or stacked to form a brush seal.  
         [0047]    This machining process for making a brush seal  2  is performed such that it is press-molded first and then precisely machined into strips by etching or the like. It may be manufactured through the processes in reverse. The bending portion  8  of a curved shape may be formed so as to direct toward the rotary direction of the rotor  60 .  
         [0048]    [0048]FIG. 5 shows a shape of a bristle  4  in a brush seal  2  of FIG. 2. The bending portion  8  of the bristle  4  is shaped in a curve as shown in FIG. 5. The radius of the curve of the bending portion  8  is R 1  and is constituted such that the load F acts from an angle A with respect to the radial direction.  
         [0049]    The structure of the bending portion  8  decreases the spring constant. Thus, the spring constant of the bending portion  8  allows the brush seal  2  to contact and follow the rotor  60  in response to the pressure, so that sealing function is performed.  
         [0050]    [0050]FIG. 3 shows a bending portion  8  of a brush seal  2  in FIG. 2 that is formed sigmoidal, viewed as a plan view. The sigmoidal brush seal  2  is the second embodiment of the present invention. The brush seal device  1  in FIG. 3 is formed by precisely machining the inner circumference side of a ring-shaped thin plate into sigmoidal strips in the similar way as in FIG. 2. Those strips may be processed to finish by additional press process. Or, adverse processes may be used. Various processes may be selected, as necessary, based on the processes above.  
         [0051]    [0051]FIG. 6 shows a shape of a bristle  4  in a brush seal  2  in FIG. 3. The bending portion  8  of the bristle  4  is formed in a sigmoidal shape combined with radius of curvatures of R 2  and R 3 . The bending portion  8  is constituted such that a load F of the rotor  60  acts at an angle A with respect to the radial direction. The bristle  4  having a sigmoidal bending portion  8  has a further decreased spring constant in the buckling direction against the contact pressure of the rotor  60 .  
         [0052]    [0052]FIG. 4 shows a brush seal  2  in FIG. 2, wherein a bending portion  8  is formed as a sigmoidal, seen on a plane and its free end  5  formed as a straight portion  9 . The brush seal  2  is the third embodiment of the present invention. Since the straight portion  9  is formed in the inner circumference side of the brush seal  2  in FIG. 4, it has not directionality with regard to the rotary direction of the rotor  60 , and the rotor  60  can rotate in its direct or reverse direction. The brush seal  2  in FIG. 4 performs similar effect as the brush seal  2  in FIG. 3.  
         [0053]    [0053]FIG. 7 shows a shape of a bristle  4  in the brush seal  2  in FIG. 4. The bending portion  8  in the bristle  4  is formed as a sigmoidal shape having radii of curvature R 4  and R 5 , and a straight portion  9  is formed at the free end  5  side. Since the load F acts linearly on the straight portion  9 , the rotor  60  can rotate in its direct or reverse direction. Also, the sigmoidal bending portion  8  performs similar effect as the bristle  4  in FIG. 6 (FIG. 3).  
         [0054]    [0054]FIG. 8 is a sectional view of a brush seal device  1  according to the second embodiment of the present invention. The brush seal device  1  in FIG. 8 has almost the same structure as that of FIG. 1. The difference is that the shape of the bending direction of the bending portion  8  of the first embodiment is formed in circumferential direction within about 45 degrees, while the bending portion  8  in the shape a sigmoidal in the bristle  4  of the second embodiment is formed approximately in axial direction.  
         [0055]    In addition, the support surface  7  of the backing plate  6  facing the brush seal  2  is formed at a position away from the opposing surface of the brush seal  2  by a distance D. That is, it is formed as a step by the bent length of a bending portion  8 . The support surface  7  may be formed as an annular recessed portion around the circumference, as necessary.  
         [0056]    The bristle  4  may be formed from wire material, naturally, but it may be made of a stainless plate, copper plate, aluminum plate, ceramic plate, or the like to be formed in the shape of a strip. The bristle  4  as a strip may have a cross section of rectangular, square, elliptical, or the like, as necessaries. The thickness of the wall can be set by stacking them in the axial direction depending on the pressure of the sealed fluid. As the thickness of the wall formed of layers is the result of stacking thin plates formed as strips, assembly of the brush seal  2  is made tremendously easy.  
         [0057]    Table 1 shows the spring constant of the bending portion  8  of the bristle  4 , calculated by FEM structural analysis. The values of the comparative example in the table are defined as 1.  
                                                 CHART 1                                       Comparative   Embodiment           Item   Ex. example   1                                        displacement of a bristle   1.0   1.8           (dimensionless)           spring constant of the bristle   1.0F   0.56F                      
 
         [0058]    Comparative example 1 is the straight bristle  4  shown in FIG. 14.  
         [0059]    Embodiment 1 is the bristle  4  having a circular bending portion  8 , shown in FIG. 5.  
         [0060]    This result was analyzed by FEM structural analysis. The bristle  4  used in the analysis was formed by forming a thin plate into a strip as shown in FIG. 2. Material and the cross sections of the each bristle  4  are the same. Also, the load F and its action direction A are the same.  
         [0061]    Under the same conditions like this, load F is loaded and the amount of displacement is calculated, and spring constants are calculated from the amount of displacement.  
         [0062]    As a result of the analysis mentioned above, a bristle  4  having a circular bending portion  8  can have smaller spring constant compared to the straight bristle  4 . Accordingly, the bristle  4  is superior in its ability to follow in the resilient force, and the spring constant can be smaller with good resilient force to the same displacement.  
         [0063]    Thus, since the fixing section  20  does not have to be supported by a flat spring  132  or the like as in a related art, its structure and the fixing section  20  is easily designed and precise design with correct calculation can be realized.  
         [0064]    The brush seal  2  further adopts an embodiment having bristles  4 , among which bristles  4  made of resin arranged circumferentially in line are arranged. Also, as the bristles  4 , both metal wire bristles and resin wire bristles may be used to mix. Another embodiment adopts brush seal  2  unit plates in FIG. 2, 3 or  4  stacked alternately with unit plates of brush seals made of resin in the same shape.  
         [0065]    Still another embodiment adopts a plurality required number of brush seal  2  unit plates in FIG. 2, 3 or  4  stacked alternately with unit plates of brush seals  2  made of resin having no slits. In this case, sealed fluid can be dammed with unit plates of brush seals  2  having no slits and sliding resistance between the bristles  4  is decreased. Brush seals  2  as mentioned above can decrease sliding resistance among the bristles  4  by mixing or arranging resin and metal bristles  4 .  
         [0066]    Next, still another embodiment according to the present invention will be described. The second embodiment of a brush seal device  1  according to the present invention comprises a backing plate  6  having a support face  7  which is connected with an attachment section  3  of the brush seal  2  for supporting the brush seal  2 , and a holding section  10  for supporting the attachment section  3  of the brush seal  2  between the backing plate  6  and the holding section  10 .  
         [0067]    The third embodiment of a brush seal device  1  according to the present invention comprises a brush seal  2  having bristles  4  wherein bending portions  8  are formed in a curved shape.  
         [0068]    In the third embodiment of a brush seal device  1  according to the present invention, the curved shape allows to form easily a wall (partition wall) by stacking brush seals  2  in the axial direction, and since the curved shapes are contacted and stacked each other, action of sealed fluid cannot push away bristles  4 , leakage is prevented and sealing capability is effected.  
         [0069]    In addition, since the bending portion  8  of the bristles  4  is curved, and resilient deformation following to the load acting on the free end  5  can be improved so that responsibility of the resilient deformation to the contact of the rotary shaft is increased, the increase of sealing ability can be expected if thickness of the layers is large. Also, spring constant of the bristle  4  can be easily designed.  
         [0070]    In the fourth embodiment of a brush seal device  1  according to the present invention comprises a brush seal  2  having bristles  4  wherein a bending portions  8  of each bristle  4  is formed in a sigmoidal shape.  
         [0071]    With respect to the fourth embodiment of a brush seal device  1  according to the present invention, since the bending portion  8  is formed in a sigmoidal shape, it excels in resiliency for deformation and performs it superior ability to follow the action force of the contacting rotor  60 . Further, the length of the bristle  4  can be increased, whereby resilient responsibility is excellent.  
         [0072]    The fifth embodiment of a brush seal device  1  according to the present invention comprises a brush seal  2  having bristles  4  wherein a bending portions  8  of each bristle  4  is formed in a sigmoidal shape and a straight portion  9  is formed at the free end  5  side from the bending portion  8 .  
         [0073]    In the fifth embodiment of a brush seal device  1  according to the present invention, since the straight portion  9  is formed at the free end side from the bending portion  8 , the rotor  60  can be rotated in the direct or reverse direction against the brush seal  2 . Further, resilient deformation can be made easier against buckling when the rotor  60  contacts as mentioned above.  
         [0074]    The sixth embodiment of a brush seal device  1  according to the present invention comprises a brush seal  2  having bristles  4  formed by forming a thin plate strip.  
         [0075]    In respect to the sixth embodiment of a brush seal device  1  according to the present invention, since the bristles  4  are made by forming a thin plate strip, processing of the bending portions  8  can be made easy. Moreover, since the bristles  4  are formed from a thin plate, sealing ability can be increased and the ability to follow can be performed against contact. Thus, friction can be decreased and the ability to follow can be performed against contact of the rotor  60  to the bristles  4 .  
         [0076]    The seventh embodiment of a brush seal device  1  according to the present invention comprises a brush seal  2  having bristles  4  in an annular body made from thin resin plate or bristles  4  formed in strips from resin thin plate at the inner circumference side, which bristles  4  are interposed in the brush seal  2 . In the seventh embodiment of a brush seal device  1  according to the present invention, since the bristles  4  in an annular body made of plate resin or in strips at inner circumference side are mixed amid layers, friction resistance can be decreased when the bristles  4  are affected by the rotor  60 . In addition, an interposed annular body of a thin plate having no slits increases the dam effect on the sealed fluid.  
         [0077]    The eighth embodiment of a brush seal device  1  according to the present invention comprises a brush seal  2  having bristles  4  formed from resin wire or having bristles  4  formed from metal wire coated with low friction material to be mixed.  
         [0078]    In the eighth embodiment of a brush seal device  1  according to the present invention, since the annular body formed from resin plate or resin bristles  4  are interposed, friction resistance can be decreased when the bristles  4  are affected by the rotor  60  to tend to be deformed.  
         [0079]    Since a brush seal device according to a preferred embodiment of the present invention has a bending portion amid a bristle of the brush seal which allows easy resilient deformation, the bristle is resiliently deformed according to the function of the bending portion if action force exerted by the oscillation of the rotor is effected to the free end of the bristle, and effect of performing the sealing ability by following the rotor is expected.  
         [0080]    Also, as the brush seal may be formed by forming a thin plate into strips as well as a wire, the sealing ability can be improved and it is expected to easily manufacture the brush seal device. Further, contact abrasion on the free end of the brush seal and the circumference of the rotor is effectively prevented.  
         [0081]    Additionally, when the ability to follow of the bristles to the rotor is reviewed in design, it is easy to calculate the spring constant from the material (characteristic) of the bristle and the force acting on the bristle, without consideration of conditions relating to other springs and friction mechanism, thereby to achieve optimum design of the bending portion of a bristle.  
         [0082]    In case bristles are made of metal, mixing bristles made of resin can decrease friction. resistance when the other component contacts those mixed bristles, resulting to allow resilient deformation with superior ability to follow. Thus, an advantage of reduction of abrasion friction generated between two mating sliding surfaces is provided.  
         [0083]    Having described specific embodiments of the invention, however, the descriptions of these embodiments do not cover the whole scope of the present invention nor do they limit the invention to the aspects disclosed herein, and therefore it is apparent that various changes or modifications may be made from these embodiments. The technical scope of the invention is specified by the claims.