Abstract:
An object of the present invention is to provide a ring segment of a gas turbine in which the temperature is maintained low, damage due to high temperature oxidation is prevented, and high temperature deformation is prevented. In order to achieve the object, the present invention provides a ring segment of a gas turbine which comprises a blade ring, a main shaft and moving blades comprising a plurality of individual units which define an annular form by being arranged around the peripheral direction of the main shaft, and disposed so that its inner peripheral surface is maintained at a constant distance from the tips of the moving blades, wherein grooves which extend along the axial direction of the main shaft of the turbine are formed upon of the individual units so as mutually to confront one another; a seal plate which is inserted into each mutually confronting pair of the grooves so as to connect together the adjacent pair of individual units; and contact surfaces which are formed at positions more radially inward than the seal plates, which extend in the axial direction and the peripheral direction and which mutually contact one another.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a ring segment of annular form which is disposed around the outer periphery of the moving blades in a gas turbine. 
   2. Description of the Related Art 
     FIG. 8  shows a turbine  1  in section, which is a gas turbine. In this turbine  1 , gas at high temperature which has been generated by a combustors (not shown in the figures) is supplied in the direction shown by the arrow  2  and blows against moving blades  3  and  4  so as to rotate the moving blades  3  and  4 , and the heat energy in the high temperature gas is converted in this manner to mechanical rotational energy of the moving blades  3  and  4 , so as to generate drive power. 
   The moving blades  3  and  4  are fixed to a mounting platform  5  which is fitted around a main shaft (not shown in the figure). A plurality of these moving blades  3  and  4  are provided around the main shaft, spaced apart along its peripheral direction. They receive the impact of the high temperature gas which flows from the upstream side (the left side in  FIG. 8 ) to the downstream side, and rotate along with the platform  5 . Stationary blades  6  and  7  are provided at the upstream sides of the moving blades  3  and  4  respectively. A plurality of these stationary blades  6  and  7  are provided just like the moving blades  3  and  4 , they are arranged around the main shaft, spaced apart around its peripheral direction. Furthermore, ring segments  8  are provided around the outer peripheries of the moving blades  3  and  4 , with almost constant gaps f being present between these ring segments  8  and the moving blades  3  and  4 . The ring segments  8  compose a plurality of individual units  8   a  (refer to  FIG. 10 ) which are made out of cobalt alloy. 
     FIG. 9  is a cross sectional view showing one of the moving blades  3  of the turbine  1  and the vicinity of its peripheral portion including one of the ring segments  8 . As shown in  FIG. 9 , a flow conduit  11  is formed through the blade ring  9  so as to open towards the ring segment  8 . Furthermore, isolating rings  10  are fitted in the blade ring  9 . Air, which is injected either from an air supply source provided externally to the turbine  1  or from a compressor (not shown in the figure), flows into this flow conduit  11  in the direction shown by the arrow  12 . An impingement plate  13  and the ring segment  8  are fixed to the isolating rings  10 . The impingement plate  13  is provided between the blade ring  9  and the ring segment  8 , and it is provided around its circumferential surface with a plurality of cooling apertures  14  for conducting air which is ejected from the flow conduit  11 . The ring segment  8  has two flanges  16  upon its outer peripheral surface  15 , one at its upstream side and one at its downstream side, and the ring segment  8  is fixed to the isolating rings  10  via these flanges  16 . A plurality of cooling conduits  17  are provided to the ring segment  8 , each being pierced through the inner portion of the ring segment  8  from the upstream side of its outer peripheral surface  15  to its end surface in the downstream direction. 
     FIG. 10  is a perspective view of the individual units  8   a  which make up the ring segment  8 . As shown in  FIG. 10 , each of the flanges  16  extends around the peripheral direction. A roughly rectangular concave portion  19  is provided upon the outer peripheral surface  15  between these flanges  16 . A plurality of opening aperture portions  17   a  of the cooling conduits  17  are provided at the upstream side of this concave portion  19 , arranged along the peripheral direction. Furthermore, grooves  21  are formed at each of the side edges  20  of this individual unit  8   a , so as to face the adjacent individual units  8   a . The impingement plate  13  is arranged around the outer circumferential side of the individual units  8   a . A cavity  22  is defined by this impingement plate  13  and the concave portion  19  of the individual unit  8   a.    
     FIG. 11  is a cross sectional view of prior art ring segment  8  as seen from the axial direction of the main shaft. As shown in  FIG. 11 , adjacent individual units  8   a  are linked in the peripheral direction by a seal plate  23  being inserted into both the two grooves  21  which are formed in their mutually confronting side edges  20 , so that collectively the individual units  8   a  constitute an annular ring segment  8 . These seal plates  23 , along with joining each adjacent pair of individual units  8   a  together, also serve to prevent the leakage of air and high temperature gas through the gaps between the adjacent pairs of individual units  8   a . The thickness of the thin plate portion of each of the individual units  8   a  is approximately 6 mm. By this thickness of the thin plate portion of each of the individual units  8   a  is meant the distance (shown in the figure by the symbol d) from the bottom surface of its concave portion  19  to the surface  24  on the other side of the individual unit  8   a , which surfaces  24 , in cooperation, define the inner peripheral surface  24  of the ring segment  8 . 
   When the turbine is operating, each of the individual units  8   a  expands both in the peripheral direction and in the axial direction, due to exposure to the influence of the flow of high temperature gas. In consideration of the amount of dimensional variation of the individual units  8   a  due to thermal expansion in the peripheral direction, a gap e of a few millimeters is provided between each of the individual units  8   a  and the adjacent one. 
   Next, the flow of high temperature air and gas during operation of the gas turbine will be explained. 
   The high temperature gas flows along the direction of the axis of the main shaft as shown by the symbol  2  in  FIGS. 8 through 10  and drives each of the moving blades  3  and  4 . Furthermore, air is blown and passes through the blade ring  9  for cooling each of the individual units  8   a  of the ring segment  8 . This air flows in the direction shown by the arrow A in  FIGS. 9 and 10 , and flows into each of the cavities  22  through those of the cooling holes  14  in the impingement plate  13 . This air which has flowed into the cavity  22 , after having collided with the concave portion  19  and having thereby cooled the ring segment  8 , flows in the direction shown by the arrow B, and enters through the opening aperture portions  17   a  into the cooling conduits  17 . And this air which has entered into the cooling conduits  17  flows to the downstream side through the cooling conduits  17  while further cooling the inside of the ring segment  8 , finally being ejected from the downstream ends of the cooling conduits  17  into a high temperature gas. 
   Moreover, this air is blown out at a higher pressure than that of the high temperature gas, in order for none of this high temperature gas to flow into the downstream ends of the cooling conduits  17 . When in this manner the air is blown out at a higher pressure than that of the high temperature gas, the seal plate  23  is pressed against the lower surface  25  of the grooves  21  by the pressure difference between the air and the high pressure gas, and thereby the sealing efficiency of the ring segment  8  is enhanced. Due to this, loss of driving power of the gas turbine due to leakage of air and high temperature gas is prevented. However, when the air is thus blown out at a suitable pressure, the high temperature gas intrudes between the seal plates  23  and the grooves  21  from the gaps e between the adjacent pairs of individual units  8   a , and the corner edge portions  26  which are delimited between the inner peripheral surfaces  24  and the side edges  20  are each heated up from three sides: the inner peripheral surface  24 , the side edge  20 , and lower surface  25  of the groove  21 . These heated up corner edge portions  26  reach high temperatures locally, and undesirably suffer deterioration due to the occurrence of high temperature oxidation. Furthermore, even if the air is blown out at a suitable pressure, since the corner edge portions  26  are heated up by the high temperature gas which is flowing along the inner peripheral surface  24  and also by the high temperature gas which insinuates into the gaps e between adjacent ones of the individual units  8   a , accordingly they can easily suffer high temperature oxidation, and there is a danger that they may be damaged. Yet further, in some cases, the seal plates  23  suffer temperature deformation as well, due to their lower surfaces being directly exposed to the high temperature gas. 
   If the corner edge portion  26  or the seal plate  23  suffers injury or damage, a large quantity of air will flow out into the high temperature gas side from the corresponding gap e between the adjacent individual units  8   a . Furthermore, if the air is no longer being sucked out at a suitable pressure, the high temperature gas may flow out to the outer peripheral side of the ring segment  8  via the gap e. If the high temperature gas or the air leaks in this manner, the gas turbine will suffer an undesirable loss of driving power, and its operational performance will be deteriorated. 
   Furthermore, with the above described ring segment  8 , although the thermal expansion of the individual units  8   a  in the peripheral direction is approximately absorbed by the gaps e, their thermal expansion in the axial direction is not absorbed, due to each of the flanges  16  being fitted to the blade ring  9  with no gap therebetween, and the peripheral surface of the ring segment  8  between the flanges  16  may suffer warping and may collide with the moving blades  3  and  4 . 
   The present invention has been made in consideration of the above described circumstances, and an object of the present invention is to provide a ring segment for a gas turbine, which is sufficiently well cooled by the flow of air, and which moreover can prevent loss of driving power of the gas turbine. 
   SUMMARY OF THE INVENTION 
   In order to achieve the above described objective, the present invention provides a ring segment of a gas turbine which comprises a blade ring, a main shaft and moving blades, comprising a plurality of individual units which define an annular form by being arranged around the peripheral direction of the main shaft, and disposed so that its inner peripheral surface is maintained at a constant distance from the tips of the moving blades, wherein the individual unit comprises grooves which extend along the axial direction of the main shaft, and each of which faces to a groove formed in the other individual unit; a seal plate for connecting together the adjacent pair of individual units which is inserted into the groove; and a contact surface which is formed at position more radially inward than the seal plate, which contacts another contact surface of the other individual unit in the axial direction and the peripheral direction of the main shaft. 
   In the ring segment, leakage of air from damaged locations upon the seal plate is made difficult, because the lower surface of the seal plate is not directly exposed to the high temperature gas, and thus damage does not occur to the seal plate. Furthermore, since adjacent ones of the individual units are joined together into pairs by the seal plates and the joining together contact surfaces, and also meandering conduits are defined between the adjacent ones of the individual units, thereby the flow rate of leakage of air and high temperature gas between adjacent ones of the individual units is reduced. Accordingly, it is possible to prevent loss of driving power of the gas turbine due to leakage of air and high temperature gas. 
   In addition, in order to achieve the object, the present invention provide another ring segment of a gas turbine which comprises a blade ring, a main shaft and moving blades, comprising a plurality of individual units which define an annular form by being arranged around the peripheral direction of the main shaft, and disposed so that its inner peripheral surface is maintained at a constant distance from the tips of the moving blades, wherein the individual units comprises ejection apertures for blowing out air to the adjacent individual units. 
   In the ring segment, since the high temperature gas is flushed out from between the adjacent pairs of individual units by the air which is ejected from the ejection apertures, thereby heating up of the side edges of the individual units is effectively suppressed, and it is difficult for damage to occur to the side edges due to high temperature oxidation. Accordingly, the flow rate of the air and high temperature gas leaking through the gaps between the adjacent individual units is reduced. Due to this, it is possible to reduce the loss of driving power of the gas turbine. 
   In the ring segment, it is preferable that ejection apertures upon each adjacent pair of the individual units are formed at positions which alternate along the axial direction of the main shaft. 
   In the ring segment, it is possible reliably to guarantee that the high temperature gas is properly flushed out from between the adjacent individual units, since the air streams which are ejected from the various ejection apertures do not collide with one another, and accordingly the air is smoothly injected. 
   In addition, in order to achieve the object, the present invention provide another ring segment of a gas turbine which comprises a blade ring, a main shaft and moving blades, comprising a plurality of individual units which define an annular form by being arranged around the peripheral direction of the main shaft, and disposed so that its inner peripheral surface is maintained at a constant distance from the tips of the moving blades, wherein the individual unit comprises beveled portions between its side edges which face the adjacent ones of the individual units and its inner peripheral surface. 
   In the ring segment, the temperature of the metal is moderated, since the convection cooling effect around the edges (corner portions), i.e. from the side edges to the inner peripheral surface, is no longer small. Accordingly it becomes difficult for the edge portions to suffer damage due to the occurrence of high temperature oxidation. 
   In addition, in order to achieve the object, the present invention provide another ring segment of a gas turbine which comprises a blade ring, a main shaft and moving blades, comprising a plurality of individual units which define an annular form by being arranged around the peripheral direction of the main shaft, and disposed so that its inner peripheral surface is maintained at a constant distance from the tips of the moving blades, wherein, the individual unit comprises: first cooling conduits which are pierced from the outer peripheral surface to the end surface of the individual unit along the axial direction of the main shaft, and which cool the individual unit by supplying air from the outer peripheral surface; and second cooling conduits which are pierced from the outer peripheral surface to the other end surface opposite the end surface in which the first cooling conduits, and which cool the individual unit by supplying air from the outer peripheral surface. 
   In the ring segment, the ring segment is cooled from both sides along the axial direction by the flow of air in these first and second cooling conduits. Furthermore, since it is arranged for the air which has blown against the outer peripheral surface to flow over the outer peripheral surface both to the upstream side and also to the downstream side, thereby the exchange of heat between the air and the outer peripheral surface is improved, and the outer peripheral surface of the cooling ring is efficiently cooled. Accordingly, the temperature gradient in the material of the ring segment is made more gentle, and thereby distortion of the ring segment due to thermal deformation thereof is reduced. Due to this, it is possible to prevent contact occurring between the ring segment and the moving blades of the gas turbine. 
   In addition, in order to achieve the object, the present invention provide another ring segment of a gas turbine which comprises a blade ring, a main shaft and moving blades, comprising a plurality of individual units which define an annular form by being arranged around the peripheral direction of the main shaft, and disposed so that its inner peripheral surface is maintained at a constant distance from the tips of the moving blades, wherein the individual unit comprises third cooling conduits which are pierced from the outer peripheral surface to the side edges which face the adjacent individual unit, and which cool the individual unit by supplying air from the outer peripheral surface. 
   In the ring segment of a gas turbine, the difference in temperature between the side edges and the outer peripheral surface of the ring segment becomes small, and distortion of the ring segment is reduced, since the side edges of each individual unit are cooled by the air which is passing through the third cooling conduits. Due to this, it is possible to prevent contact occurring between the ring segment and the moving blades of the gas turbine. Moreover the temperature of the side edges is kept low, since the high temperature gas between the individual units is flushed out by the air which is expelled from the side edges of the individual units. Accordingly it becomes difficult for damage caused by high temperature oxidation to take place upon the edge portions between the side edges and the inner peripheral surface, and the flow amount of air and high temperature gas which leaks through between each pair of adjacent individual units becomes small. Due to this, it is possible to reduce loss of driving power of the gas turbine. 
   In addition, in order to achieve the object, the present invention provide another ring segment of a gas turbine which comprises a blade ring, a main shaft and moving blades, comprising a plurality of individual units which define an annular form by being arranged around the peripheral direction of the main shaft, and disposed so that its inner peripheral surface is maintained at a constant distance from the tips of the moving blades, wherein the individual unit comprises least two of: the grooves which extend along the axial direction of the main shaft, and each of which faces to a groove formed in the other individual unit; the seal plate for connecting together the adjacent pair of individual units which is inserted into the groove; the contact surface which is formed at position more radially inward than the seal plate, which contacts another contact surface of the other individual unit in the axial direction and the peripheral direction of the main shaft; the ejection apertures for blowing out air to the adjacent individual units; the ejection apertures which are upon each adjacent pair of the individual units at positions which alternate along the axial direction of the main shaft; the beveled portions between its side edges which face the adjacent ones of the individual units and its inner peripheral surface; the first cooling conduits which are pierced from the outer peripheral surface to the end surface of the individual unit along the axial direction of the main shaft, and which cool the individual unit by supplying air from the outer peripheral surface; the second cooling conduits which are pierced from the outer peripheral surface to the other end surface opposite the end surface in which the first cooling conduits, and which cool the individual unit by supplying air from the outer peripheral surface; and the third cooling conduits which are pierced from the outer peripheral surface to the side edges which face the adjacent individual unit, and which cool the individual unit by supplying air from the outer peripheral surface. 
   In the ring segment of a gas turbine, distortion of the ring segment is further reduced, since at least two of the features present in the ring segments as above are present and exert their effects as described. Accordingly, the occurrence of contact between the ring segment and the moving blades of the gas turbine is prevented. Furthermore, it is possible to reduce loss of driving power of the gas turbine, since the leakage amount of air and high temperature gas becomes small. 
   In the ring segment of a gas turbine, it is preferable for a gap between the individual units to be greater than zero and less than or equal to 1 mm when the gas turbine is operating nominally. 
   In the ring segment of a gas turbine, heating up of the side edges of the individual units is suppressed, since the flow amounts of the high temperature gas flows which insinuate themselves into the gaps which appear between each pair of adjacent individual units become small, and thereby it becomes difficult for damage to take place to the edge portions between the side edges and the inner peripheral surface due to high temperature oxidation. Accordingly, the flow amount of air and high temperature gas which leaks from the gaps between the individual units becomes small. Due to this, it is possible to reduce loss of driving power of the gas turbine. 
   In the ring segment of a gas turbine, it is preferable for the thickness of the body of each of the individual units to be greater than or equal to 1 mm and less than or equal to 4 mm. 
   In the ring segment of a gas turbine, the amount of distortion due to the difference in the amount of thermal deformation between the inner peripheral surface and the outer peripheral surface of the ring segment becomes small, since the temperature difference between the inner peripheral surface and the outer peripheral surface of the ring segment becomes small. Due to this, it is possible to prevent the occurrence of contact between the ring segment and the moving blades of the gas turbine. 
   In the ring segment of a gas turbine, it is preferable that the individual unit comprises projections formed upon the outer peripheral surface thereof. 
   In the ring segment of a gas turbine, the heating surface area upon the outer peripheral surface of the individual units is increased due to the provision of these projections upon the outer peripheral surface, so that the heat exchange between the individual units and the air flow across them is performed efficiently. Furthermore, the heat exchange between the air and the outer peripheral surface is improved, because the air flow upon the outer peripheral surface is made more turbulent by these projections. Accordingly the temperature of the ring segment is moderated, and the amount of thermal deformation of the ring segment is made smaller, so that distortion of the thermal ring is reduced. Due to this, it is possible to prevent the occurrence of contact between the ring segment and the moving blades of the gas turbine. 
   In the ring segment of a gas turbine, it is preferable that the individual unit further comprises flanges for being fitted to the blade ring, and the flange comprises a plurality of slits which are formed so as to extend along the axial direction of the main shaft. 
   In the ring segment of a gas turbine, it is preferable that the individual unit further comprises strengthening ribs which are provided upon the outer peripheral surface thereof. 
   In the ring segment of a gas turbine, thermal deformation of the ring segment is alleviated, since the strength of each of the individual units is increased by the provision of these strengthening ribs. Due to this, it is possible to prevent the occurrence of contact between the ring segment and the moving blades of the gas turbine. 
   In the ring segment of a gas turbine, it is preferable that the individual unit is made from nickel alloy. 
   In the ring segment of a gas turbine, since the ring segment is made from nickel alloy, not only is the fatigue strength of the ring segment enhanced, but also high temperature oxidation of the ring segment is impeded. Accordingly, damage to the ring segment due to high temperature oxidation is prevented, and the flow amount of working fluid which leaks to the outside, and the flow amount of air which leaks to the inside, are both reduced. Due to this, it is possible to prevent loss of driving power of the gas turbine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view of a ring segment of a gas turbine according to the preferred embodiment of the present invention, as seen from the direction transverse to the axis of the main shaft of the gas turbine. 
       FIG. 2  is a perspective view of one of a number of individual units which together make up the ring segment of a gas turbine according to the preferred embodiment of the present invention of  FIG. 1 . 
       FIG. 3  is another perspective view of this individual unit which is incorporated in this ring segment of a gas turbine according to the preferred embodiment of the present invention, as seen from the corner opposite to that from which the  FIG. 2  view is taken. 
       FIG. 4  is a cross sectional view of the joining portion between two of these individual units of  FIGS. 1 through 3  which are adjacent to one another, as seen from the direction along the axis of the main shaft of the gas turbine. 
       FIGS. 5A and 5B  are both side views of this individual unit which is incorporated in the ring segment of a gas turbine according to the preferred embodiment of the present invention. 
       FIG. 6  is a side view of this individual unit which is incorporated in the ring segment of a gas turbine according to the preferred embodiment of the present invention. 
       FIG. 7  is a cross sectional view along the direction of formation of cooling conduits formed in this individual unit which is incorporated in the ring segment of a gas turbine according to the preferred embodiment of the present invention. 
       FIG. 8  shows a portion of a gas turbine in section. 
       FIG. 9  is a cross sectional view of a prior art ring segment, taken in a sectional plane similar to that of  FIG. 8 . 
       FIG. 10  is a perspective view of an individual unit, a plurality of which together make up the prior art ring segment of  FIG. 9 . 
       FIG. 11  is a cross sectional view of a portion of this prior art ring segment as seen from the axial direction of the main shaft. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the following, the preferred embodiment of the ring segment of a gas turbine according to the present invention will be explained with reference to  FIGS. 1 through 7 . It should be understood that to elements which are the same as elements of the prior art described above with reference to  FIGS. 8 through 11 , the same reference symbols are affixed as in those figures, and the explanation thereof will be curtailed. 
     FIG. 1  is a cross sectional view of a ring segment  30  of a gas turbine according to the preferred embodiment of the present invention. This ring segment  30  is made from nickel alloy. The ring segment  30  is attached to isolating rings  10  by a flange  31  which is provided on the upstream side in the flow direction of high temperature gas and a flange  32  which is provided upon the downstream side. To the ring segment  30  there are provided first cooling conduits  35  which are pierced from the outer peripheral surface  33  at its upstream side to its end surface  34  at its upstream side, and second cooling conduits  37  which are pierced from the outer peripheral surface  33  at its downstream side to its end surface  36  at its downstream side. Air which has flowed into the first cooling conduits  35  from the outer peripheral surface  33  flows towards the upstream direction and is ejected from the end surface  34  at its upstream side into the high temperature gas. And air which has flowed into the second cooling conduits  37  from the outer peripheral surface  33  flows towards the downstream direction and is ejected from the end surface  36  at its downstream side. 
   Furthermore, two seal members  38  having “E” shapes as seen in cross section are provided between the ring segment  30  and the isolating rings  10 , one at the upstream side and one at the downstream side. These seal members  38  are for preventing the leakage of high temperature gas and air from between the ring segment  30  and the isolating rings  10 . 
     FIG. 2  is a perspective view showing one of the individual units  39  which make up the ring segment  30 . In  FIG. 2 , the right front side is the upstream side with respect to the flow of high temperature gas, while the left rear side is the downstream side. And  FIG. 3  is a perspective view of the same individual unit  39  as seen from the opposite corner (i.e., from the corner shown by the arrow Y in  FIG. 2 ), and in this figure the left rear side is the upstream side with respect to the flow of high temperature gas, while the right front side is the downstream side. 
   As shown in  FIGS. 2 and 3 , “U” shaped slits  40  which extend along the axial direction are formed at the flanges  31  and  32 . Furthermore, the ends of the U shaped slits  40  in the peripheral direction are almost the same height as the flanges  31  and  32 . Convex portions  41  which extend along the axial direction are formed upon the outer peripheral surface  33  of the individual unit  39 , so as to connect together the ends of the mutually opposing flanges  31  and  32 . Strengthening ribs  42  in the form of a lattice are provided upon the outer peripheral surface  33  so as to be surrounded by these convex portions  41  and the flanges  31  and  32 . These strengthening ribs  42  consist, in the shown preferred embodiment of the present invention, of three peripherally extending ribs  43  which extend in the peripheral direction, and three axially extending ribs  44  which extend in the axial direction. Furthermore, a large number of small projections  45  are provided upon the outer peripheral surface  33 , so as to be surrounded by the convex portions  41  and the flanges  31  and  32 . These serve to increase the heating surface area of the outer peripheral surface  33 . 
   The symbol  46  in  FIG. 2  denotes an ejection aperture of one of the first cooling conduits  35  which open to the end surface  34  on the upstream side. A plurality of these ejection apertures  46  are provided upon the end surface  34  on the upstream side, spaced apart from one another at equal intervals along the peripheral direction. Moreover, as shown in  FIG. 3 , a plurality of sucking in apertures  47  of these first cooling conduits  35  are provided, located at the lower portion of the wall surface facing to the downstream side of the flange  31  on the upstream side, and they too are spaced apart from one another at equal intervals along the peripheral direction. Similarly, as also shown in  FIG. 3 , a plurality of ejection apertures  48  of the second cooling conduits  37  are provided upon the end surface  36  on the downstream side, spaced apart from one another at equal intervals along the peripheral direction. Moreover, as shown in  FIG. 2 , a plurality of sucking in apertures  49  of these second cooling conduits  37  are provided, located upon the downstream side of the outer peripheral surface  33  near the lower portion of the wall surface facing to the upstream side of the flange  32  on the downstream side, and they too are spaced apart from one another at equal intervals along the peripheral direction. 
   Grooves  50   a  and  51   a  which extend along the axial direction are formed upon the side edges  50  and  51  of each of the individual units  39  facing towards the adjacent individual units  39 . A seal plate  53  (refer to  FIG. 4 ) is inserted into the grooves  50   a  and  51   a  of each adjacent pair of individual units  39  so as to connect them together and seal between them. 
   As shown in  FIGS. 2 and 3 , the side edges  50  and  51  of each of the individual units  39  are formed differently from one another. When the individual units  39  are joined together in the peripheral direction, at each of the junctions between two adjacent individual units  39 , the side edge  50  of the one unit engages with the side edge  51  of the other unit. 
     FIG. 4  is a cross sectional view showing the joining portion between two of the individual units  39  which are adjacent to one another, as seen along the axial direction of the main shaft of the gas turbine. As shown in this figure, the groove  50   a  which is formed upon the one side edge  50  and the groove  51   a  which is formed upon the other side edge  51  are formed so as mutually to confront one another. And the seal plate  53  is inserted into these grooves  50   a  and  5 l a  and joins the two individual units  39  together while sealing the gap between them. The side of the side edge  51  of the one individual unit  39  inward of the seal plate  53  (i.e., on the side thereof towards the main shaft of the gas turbine) is formed to be convex so as to project outwards towards the side edge  50  of the other individual unit  39 . Conversely, the side of the side edge  50  of the other individual unit  39  inward of the seal plate  53  is formed to be concave, so as to receive the convex portion of the side edge  51 . And contact surfaces  54  and  55 , more radially inwards than the seal plate  53 , are defined upon the adjacent individual units  39 , with these contact surfaces  54  and  55 , when the convex side edge  51  and the neighboring concave side edge  50  are thus fitted together, mutually contacting one another over a certain extent both in the axial direction and also in the peripheral direction. 
   Respective beveled portions  56  and  57  are formed between the side edge  50  and the inner peripheral surface  55 , and between the side edge  51  and the inner peripheral surface  55 . The thickness h of each of the individual units  39  from its outer peripheral surface  33  (not counting the projections  45 ) to its inner peripheral surface  55  (i.e., the thickness of its body portion between the flanges  31  and  32 ) is approximately a few millimeters. Specifically, the thickness of the body of each of the individual units is greater than or equal to 1 mm and less than or equal to 4 mm. A heat shielding coating (hereinafter termed a TBC—“Thermal Barrier Coating”)  58  is provided upon the inner peripheral surface  55  and upon the beveled portions  56  and  57 . This TBC  58  protects the inner peripheral surface  55  and the beveled portions  56  and  57  from the high temperature gas, and operates to protect these parts from high temperature oxidation. 
   Third cooling conduits  59  and  60  are provided to the individual units  39 , and these respectively pierce through the beveled portions  56  and  57  from the outer peripheral surface  33 . The sucking in apertures  61  of the third cooling conduits  59  which are formed at the one side edge  50  are provided along the boundary between the outer peripheral surface  33  and the convex portion  41  on the side of the side edge  50 , as shown in  FIG. 2 , while their ejection apertures  62  are provided spaced apart from one another at equal intervals in the axial direction of the main shaft, as shown in  FIGS. 3 and 5A . The cooling air which is ejected from these ejection apertures  62  is blown out against the opposing beveled portion  57  of the adjacent individual unit  39 . And the sucking in apertures  63  of the third cooling conduits  60  which are formed at the other side edge  51  are provided along the boundary between the outer peripheral surface  33  and the convex portion  41  on the side of the side edge  51 , as shown in  FIG. 3 , while their ejection apertures  64  are provided spaced apart from one another at equal intervals in the axial direction of the main shaft, as shown in  FIGS. 3 and 5B . The cooling air which is ejected from these ejection apertures  64  is blown out against the opposing beveled portion  56  of the adjacent individual unit  39 . 
   A gap between the individual units, that is a gap between these ejection apertures  62  and  64  is greater than zero and less than or equal to 1 mm when the gas turbine is operating nominally. 
   Furthermore, as shown in  FIG. 6 , the ejection apertures  62  and  64  are formed so as, when the side edge  50  and the side edge  51  are mutually engaged together, to be alternately mutually spaced apart from one another in the axial direction. When this is done, the air streams which are ejected from each of the ejection apertures  62  and  64  do  not collide together, so that the air is smoothly ejected. 
   Moreover, holes are formed in the TBC which is provided upon the beveled portions  56  and  57  at the portions where the apertures  62  and  64  are located. 
     FIG. 7  is a cross sectional view along the direction of formation of the first cooling conduits  35 , the second cooling conduits  37 , and the third cooling conduits  59  and  60  which are formed in an individual unit  39 . As shown in this figure, sixteen of these first cooling conduits  35  are provided, spaced apart from one another at equal intervals in the peripheral direction. And thirty-two of the second cooling conduits  37  are provided, spaced apart from one another at equal intervals in the peripheral direction. Moreover, sixteen of the third cooling conduits  60  are formed upon the side of the side edge  51 . On the other hand, as for the third cooling conduits which are formed upon the side of the side edge  50 , there are formed eight of the sucking in apertures  61  and thirty-two of the ejection apertures  62 , and the flow conduits which face the sucking in apertures  61  and the flow conduits which face the ejection apertures  62  are connected together by a distribution conduit  65  which extends in the axial direction. Accordingly, after the air which flows in from the sucking in apertures  61  has been collected in the distribution conduit  65  which extends in the axial direction, it is divided from this distribution conduit  65  into the flow conduits which lead to the ejection apertures  62 . Due to this, it is possible to cool the entire individual unit  39  evenly from its upstream side to its downstream side. 
   Next the flow of air while this gas turbine is operating will be explained. 
   Air which has been supplied from the blade ring  9  is blown against the outer peripheral surface  33  of the ring segment  30 . This air which has thus been blown against the outer peripheral surface  33  flows along it both towards the upstream side and the downstream side and also in the peripheral direction, and cools the outer peripheral surface  33 . At this time, this air performs cooling with high efficiency because its flow is made to be a turbulent flow by the projections  45  which are provided upon the outer peripheral surface  33 . 
   The air which has flowed over the outer peripheral surface  33  towards the upstream side flows in to the sucking in apertures  47  of the first cooling conduits  35  from the direction shown by the arrow D, and flows towards the upstream side while cooling the individual unit  39 , finally being ejected from the ejection apertures  46  which are formed in the end surface  34  on the upstream side in the direction of the arrow E. And the air which has flowed over the outer peripheral surface  33  towards the downstream side flows in to the sucking in apertures  49  of the second cooling conduits  37  from the direction shown by the arrow F, and flows towards the downstream side while cooling the individual unit  39 , finally being ejected from the ejection apertures  46  which are formed in the end surface  36  on the downstream side in the direction of the arrow G. 
   Moreover, the air which has flowed over the outer peripheral surface  33  towards the side edge  50  flows in to the sucking in apertures  61  of the third cooling conduits  59 , and flows in the peripheral direction while cooling this individual unit  39 , finally being ejected (in the direction by the arrow H) from the ejection apertures  62  which are formed upon the beveled portion  56  of this individual unit  39  towards the opposing beveled portion  57  upon the adjacent individual unit  39  on this one circumferential side. Moreover, the air which has flowed over the outer peripheral surface  33  towards the other side edge  51  flows in to the sucking in apertures  63  of the other third cooling conduits  60 , and flows in the peripheral direction while cooling this individual unit  39 , finally being ejected (in the direction shown by the arrow I) from the ejection apertures  64  which are formed upon the beveled portion  57  of this individual unit  39  towards the opposing beveled portion  56  upon the adjacent individual unit  39  on this other circumferential side. The air which has been ejected from these ejection apertures  62  and  64  attempts to flow into the gap g (see  FIG. 4 ), and thus flushes out the high temperature gas therein to the inside of the turbine. 
   According to the above described ring segment  30 , the adjacent individual units  39  are joined together into a pair by the seal plate  53  and the joining together contact surfaces  54  and  55 , and moreover, since a meandering conduit is defined between the adjacent individual units  39 , the flow amount of air and high temperature gas leaking from between each pair of individual units  39  is reduced. Furthermore, since the lower surface of the seal plate  53  is not directly exposed to the high temperature gas, accordingly the seal plate  53  does not suffer damage. Yet further, since the side edges  50  and  51  and the edge portions of the inner peripheral surface  55 , which in the prior art were locally at high temperature, are formed as the beveled portions  56  and  57 , thereby their heat resistance is reduced so that their temperature is moderated. Moreover, the gaps g between the individual units  39  (the gaps between the ejection apertures  62  and  64 ) are made narrower as compared with the prior art, and accordingly the flow amount of the high temperature gas that is able to insinuate itself into these gaps g is reduced. Even further, since the air is ejected from the ejection apertures  62  and  64  which are provided in the beveled portions  56  and  57  into these gaps g, accordingly the high temperature gas is flushed out from these gaps g. Moreover, since the mutually confronting ejection apertures  62  and  64  are provided so as to alternate with one another in the axial direction, and do not directly point at one another, thereby the air streams which are ejected from these apertures  62  and  64  do not collide with one another, and these air streams are ejected smoothly, so that the high temperature gas is reliably flushed out from the gaps g. Accordingly, heating up of the beveled portions  56  and  57  is suppressed, and damage to these beveled portions  56  and  57  is prevented. Furthermore, since the above described ring segment  30  is made from nickel alloy, thereby high temperature oxidation of the ring segment  30  is prevented, and it is difficult for damage to the ring segment  30  to take place. Due to this, the flow amount of air and high temperature gas which leaks through between the individual units  39  is reduced, and thereby loss of the driving power of the gas turbine is suppressed. 
   Furthermore, with the above described ring segment  30 , the air which is supplied from the outer peripheral surface  33  is ejected from both the upstream side and the downstream side, after having passed through the first cooling conduits  35  and the second cooling conduits  36 . Accordingly the air flows smoothly upon the outer peripheral surface  33 , and the efficiency of cooling of the outer peripheral surface  33  by the air is enhanced. This beneficial effect is also described in the publication “Gas Turbine Heat Transfer And Cooling Technology”, which is published by Taylor and Francis Ltd. Furthermore, since the large number of small projections  45  are provided upon the outer peripheral surface  33 , thereby the heating surface area of the outer peripheral surface  33  is increased. Yet further, the flow of air is made to be a turbulent flow by the projections  45 , so that the heat exchange between the air and the outer peripheral surface  33  is improved. Accordingly, the outer peripheral surface  33  comes to be well cooled. 
   Since, with this ring segment  30 , the thickness h (thickness of the main body portion) from the outer peripheral surface  33  which is cooled to the inner peripheral surface  55  is quite thin by comparison with the prior art, therefore the good cooling extends all the way to the inner peripheral surface  55 , and the temperature difference between the inner and the outer peripheral surfaces of the ring segment  30  becomes small. Furthermore, with this ring segment  30 , since the peripheral portion of the outer peripheral surface  33  against which no air blows is cooled by the flow of air through the first, second and third cooling conduits  34 ,  36 ,  59  and  60 , thereby the temperature difference between the central portion and the circumferential portion of each of the individual units  39  becomes small. Accordingly, the mutual differences between the amounts of thermal expansion of each of the portions of the individual units  39  are reduced. 
   Furthermore, with the above described ring segment  30 , thermal deformation of the ring segment  30  is suppressed, since the strength of each of the individual units  39  is enhanced by the provision of the separating ribs  42 . 
   In this manner, with this ring segment  30 , along with suppressing loss of the driving power of the gas turbine, contact between the ring segment  30  and the moving blades  3  and  4  is avoided, and it is possible to prevent deterioration of the performance of the gas turbine.