Abstract:
The present invention provides a blasting apparatus for an outer surface of a pipe which ejects a blast material to an outer side of a pipe and grinds the outer surface, comprising: a blast head containing a nozzle which ejects the blast material and a suction port which sucks a blast material used for grinding and dust particles; a guide member which is provided along a longitudinal direction of the outer surface of the pipe, and guides the blast head along the longitudinal direction of the outer surface of the pipe; and a ring member which is a ring member constructed by connecting at least two half-split members and having an inside diameter larger than an outside diameter of the pipe, and which is disposed to have the pipe inserted through the ring member, holds the guide member, and guides the blast head in a circumferential direction of the outer surface of the pipe by turning in the circumferential direction on the outer surface of the pipe.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a blasting apparatus, and more particularly, relates to a blasting apparatus for an outer surface of a pipe, which ejects a blast material to an outer surface of a pipe and grinds the outer surface of the pipe to perform surface preparation. 
   2. Description of the Related Art 
   For example, a vent pipe (piping) placed inside a suppression chamber, which is a part of a nuclear reactor containment facility of an atomic power plant, has its outer peripheral surface and inner peripheral surface coated by recoating it with a plurality of coating materials excellent in corrosion resistance, decontaminability and the like. The repainting construction is carried out with about 10 years after the start of operation as a guide, and as a pre-construction of the repainting construction, grinding and decontaminating operations of grinding the coating film including radioactive substances on the outer peripheral surface and the inner peripheral surface and roughening the coated surface to perform surface preparation are performed. 
   Conventionally, no apparatus for grinding and decontaminating the inner peripheral surface of a vent pipe is available, and grinding and decontaminating of only the outer peripheral surface is carried out by a blasting technique. The blasting technique is a technique of causing a blast material such as sand, and steel grit ejected by high speed air to collide against a substance to be treated, grinding the surface of the substance to be treated with the impact force to roughen the surface (for example, see Japanese Patent Application Laid-Open No. 9-109029). 
   SUMMARY OF THE INVENTION 
   However, since the sand blasting technique as described in the above described Japanese Patent Application Laid-Open No. 9-109029 adopts the method of a worker moving a blast ejection nozzle on a surface to be treated by gripping the blast ejection nozzle, it is inefficient, and has the problem in hygiene. 
   Further, the worker performs an operation as he or she makes one round of a pipe, and there is the problem that when the pipe is laterally arranged, operability becomes extremely bad, and when the pipe is close to a wall surface even if it is vertically arranged, operability also degrades. 
   The present invention is made in view of the above circumstances, and has an object to provide a blasting apparatus for an outer surface of a pipe, which is capable of efficiently grinding the outer surface of a pipe with excellent operability. 
   In order to attain the above-described object, the invention according to a first aspect provides a blasting apparatus for an outer surface of a pipe, in a blasting apparatus for an outer surface of a pipe which ejects a blast material to an outer side of a pipe and grinds the outer surface, characterized by including a blast head containing a nozzle which ejects the blast material and a suction port which sucks a blast material used for grinding and dust particles, a guide member which is provided along a longitudinal direction of the outer surface of the pipe, and guides the blast head along the longitudinal direction of the outer surface of the pipe, and a ring member which is a ring member constructed by connecting at least two half-split members and having an inside diameter larger than an outside diameter of the pipe, and which is disposed to have the pipe inserted through the ring member, holds the guide member, and guides the blast head in a circumferential direction of the outer surface of the pipe by tuning in the circumferential direction on the outer surface of the pipe. 
   According to the invention described in the first aspect, the blast head containing the nozzle which ejects the blast material, and the suction port which sucks the blast material used for grinding and dust particles is guided along the longitudinal direction of the outer surface of the pipe by the guide member provided along the longitudinal direction of the outer surface of the pipe, and is guided along the circumferential direction of the outer surface of the pipe by the ring member which is disposed to have the pipe inserted through the ring member. Therefore, the blast head can be easily moved along the longitudinal direction and the circumferential direction of the outer surface of the pipe with a simple mechanism, and the blasting treatment of the outer surface of the pipe can be efficiently performed under the clean environment. 
   Further, the ring member is constructed by the member which is divided into at least two, and therefore, the ring member is easily attached to and detached from the pipe. Operability at the time of changing setting in the longitudinal direction past the support portion which supports the pipe is especially excellent. 
   In the invention of the first aspect, the invention according to a second aspect is characterized by further including a longitudinally driving device which moves the blast head along the longitudinal direction of the outer surface of the pipe, and a circumferentially driving device which moves the blast head along the circumferential direction of the outer surface of the pipe, and in that the longitudinally driving device is constructed by one guide member, one feed screw provided parallel with the one guide member, a nut which is threadedly fitted onto the feed screw and connected to the blast head, and a drive device which rotationally drives the feed screw, and the circumferentially driving device is constructed by the ring member, a large-diameter gear provided integrally with the ring member, a small-diameter gear which is meshed with the large-diameter gear, and a drive device which rotationally drives the small-diameter gear. 
   According to the invention described in the second aspect, the longitudinally driving device having the one guide member and the one feed screw which is rotationally driven by the drive device, and the circumferentially driving device having the ring member, the large-diameter gear provided at the ring member, and the small-diameter gear which is rotationally driven by the drive device are provided, and therefore, the movement of the blast head in the longitudinal direction of the outer surface of the pipe and its movement in the circumferential direction can be automated with a simple mechanism. 
   The invention according to a third aspect provides a blasting apparatus for an outer surface of a pipe, in a blasting apparatus for an outer surface of a pipe which ejects a blast material to an outer side of a pipe and grinds the outer surface, characterized by including a blast head containing a nozzle which ejects the blast material and a suction port which sucks a blast material used for grinding and dust particles, and in that the blast head is constructed by connecting at least two half-split members, formed into a ring shape having an inside diameter larger than an outside diameter of the pipe, and disposed to have the pipe inserted though the blast head, and a plurality of spherical rolling seats which abut on the outer surface of the pipe and guide the blast head movably in a longitudinal direction and a circumferential direction of the outer surface of the pipe are provided on the inside diameter side of the blast head. 
   According to the invention described in the third aspect, the ring-shaped blast head disposed to have the pipe inserted through the blast head is provided with a plurality of spherical rolling seats which abut on the outer surface of the blast head, and therefore, the blast head can be moved along the longitudinal direction and the circumferential direction of the outer surface of the pipe with a simple structure. 
   Since the blast head is constructed by the member which is divided into at least two, the blast head is easily attached to and detached from the pipe. Operability when setting is changed in the longitudinal direction past the support portion which supports the pipe is especially excellent. 
   In the invention in the third aspect, the invention according to a fourth aspect is characterized by further including a longitudinally driving device which moves the blast head along the longitudinal direction of the outer surface of the pipe, and a circumferentially driving device which moves the blast head along the circumferential direction of the outer surface of the pipe, and in that the longitudinally driving device is constructed by one feed screw provided parallel with the longitudinal direction of the outer surface of the pipe, a feed nut which is threadedly fitted onto the feed screw and connected to the blast head so as to restrain only movement of the blast head in the longitudinal direction of the outer surface of the pipe, and a drive device which rotationally drives the feed screw, and the circumferentially driving device is constructed by a large-diameter gear provided integrally with the blast head formed into the ring shape, a small-diameter gear which is meshed with the large-diameter gear held by the feed nut, and a drive device which rotationally drives the small-diameter gear. 
   According to the invention described in the fourth aspect, the longitudinally driving device having the one feed screw which is rotationally driven by the driving device, and the circumferentially driving device having the large-diameter gear provided integrally with the blast head and the small-diameter gear rotationally driven by the air motor are provided, and therefore, the movement of the blast head in the longitudinally direction and its movement in the circumferential direction of the outer surface of the pipe can be automated. 
   In the invention according to the invention of any one of the first, second, third and fourth aspects, the invention according to a fifth aspect is characterized by having an illuminating device which illuminates a base of the outer surface of the pipe ground by the blast material, and an image pickup device which picks up an image of the base of the outer surface of the pipe illuminated by the illuminating device. 
   According to the invention described in the fifth aspect, the image of the base of the outer surface of the pipe after blasting can be picked up. Therefore, the rust removal degree and the ground state can be observed, the finished state can be recorded, and the finished state can be compared with a sample and automatically judged. 
   In the invention of any one of the first, second, third, fourth and fifth aspects, the invention according to a sixth aspect is characterized in that the blast material is a blast medium in a sponge piece form in which abrasives are contained in a porous elastic body. 
   According to the invention described in the sixth aspect, the blast medium in the sponge piece form in which the abrasives are contained in the porous elastic body is used as the blast material. When the blast medium collides against the outer surface of the pipe, the blast medium becomes flat, and the contained abrasives directly collide against the outer surface at a high speed. Therefore, the outer surface can be ground as in a sand blasting technique. The dust particles which float in the air in the ordinary sand blasting are taken into the sponge pieces and directly drop. Therefore, scattering of the dust particles can be significantly reduced, and the operation environment can be remarkably improved. 
   According to the blasting apparatus for an outer surface of a pipe of the present invention, the blast head containing the nozzle which ejects the blast material and the suction port which sucks the blast material used for grinding and the dust particles is guided to be movable in the longitudinal direction and the circumferential direction of the outer surface of the pipe. Therefore, the used blast material and dust particles can be sucked, the blast head can be easily moved along the outer peripheral surface of the pipe with a simple mechanism, and blasting treatment of the outer surface of the pipe can be efficiently performed under the clean environment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an explanatory view showing a basic construction of a sponge blasting apparatus; 
       FIGS. 2A to 2C  are views explaining a mechanism of sponge blasting; 
       FIG. 3  is a perspective view showing a blasting apparatus for an outer surface of a pipe according to a first embodiment of the present invention; 
       FIG. 4  is a perspective view showing a blasting apparatus for an outer surface of a pipe according to a second embodiment of the present invention; 
       FIG. 5  is a sectional view showing a blasting apparatus for an outer surface of a pipe according to the second embodiment of the present invention; 
       FIG. 6  is a perspective view showing a blasting apparatus for an outer surface of a pipe according to a third embodiment of the present invention; 
       FIG. 7  is a perspective view showing a blasting apparatus for an outer surface of a pipe according to a fourth embodiment of the present invention; and 
       FIG. 8  is a perspective view showing a blasting apparatus for an outer surface of a pipe according to the fourth embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A preferred embodiment of a blasting apparatus for an outer surface of a pipe according to the present invention will now be described in detail with reference to the accompanying drawings. In this embodiment, explanation will be made with an example of a sponge blasting apparatus using a blast medium in a sponge piece form in which abrasives are contained in a porous elastic body as a blast material. The same members are assigned with the same numerals and characters in each drawing. 
     FIG. 1  is an explanatory view showing a basic structure of a sponge blasting apparatus  20  which is applied to the blasting apparatus for an outer surface of a pipe of the embodiment. Explaining the sponge blasting technique using the sponge blasting apparatus  20  first, the blast medium  26  as the blast material used in this technique is made by sticking abrasives (also called a grinding material in the case of an urea resin) of a different material (steel grit, alumina, star light, an urea resin and the like) in accordance with the use purpose to a sponge piece  24  (porous elastic body) as shown in  FIGS. 2A to 2C . The blast media  26  are ejected to a coating film  28  by high pressure air, grind the coating film  28  and roughen the coated surface  30  to perform surface preparation. 
   For example, when the coating film  28  is contaminated with radioactive ray as a vent pipe placed inside a suppression chamber which is a part of an atomic reactor containment facility of an atomic power plant, the coated surface  30  can be decontaminated by the blast media  26 . 
   According to the sponge blasting technique, when the blast media  26  collide against the coating film  28  as shown in  FIG. 2A , the blast media  26  become flat as shown in  FIG. 2B , and the abrasives  22 ,  22  contained therein directly collide against the coating film  28  at a high speed. Thereby, as in the sand blasting technique, the coating film  28  can be ground as in  FIG. 2C . 
   Further, dust particles  32 ,  32 , which float in the air in an ordinary sand blasting technique, are taken into the sponge pieces  24  and directly drop, and therefore, scattering of dust particles can be prevented. Further, the repulsive force is also absorbed by the sponge pieces  24 , and therefore, rebound of the blast media  26  can be suppressed. 
   The sponge blasting apparatus  20  is constructed by a sponge blast supply device  34 , a compressor  36 , a nozzle  38 , a suction machine  40 , a recycle separator  42  and a hopper  44 , as shown in  FIG. 1 . 
   High pressure air is supplied from the compressor  36  and the blast media  26  (see  FIG. 2A ) is supplied from the hopper  44  to the sponge blast supply device  34 . The blast media  26  are ejected to a target  48  at a high speed from a tip end of the nozzle  38  by being transported by air via the hose  46  by the high pressure air from the compressor  36 . The used blast media  26  directly drop in a state in which dust particles  32 ,  32  (see  FIG. 2C ) are taken therein, are sucked into the suction machine  40  through a suction port  50  placed in the vicinity of the drop position, and fed into the recycle separator  42 . 
   The recycle separator  42  is constructed by stacking two sieves  52  and  54 , which respectively have sieve openings of large and medium sizes, in layer on a vibration generator  56 . The blast media  26  are first fed into the sieve  52  with the large sieve openings, and the sieve  52  is vibrated by the vibrator of the vibration generator  56 , whereby the large-sized blast media  26  are separated and taken out from the sieve  52 . The blast media  26  which pass through the sieve  52  drop into the sieve  54 , and the medium-sized blast media  26  are separated and taken out by the sieve  54  which is similarly vibrated by the vibrator. 
   The large-and medium-sized blast media  26  removed from the sieves  52  and  54  can be directly used, and therefore, they are conveyed to the hopper  44 . Fine blast media  26  which pass through the sieve  54  are not reusable, and therefore, stored in a container  58  and discarded. Reusable blast media  26  constitute about 90% of the entire blast media  26 . The above is the basic structure of the sponge blasting apparatus  20 . 
     FIG. 3  is a perspective view showing a first embodiment of a blasting apparatus for an outer surface of a pipe which uses the sponge blasting apparatus  20 . A blasting apparatus  10  for an outer surface of a pipe according to the first embodiment is constructed by a blast head  11 , a pair of ring members  12  and  12  which encircle an outer periphery of a pipe P, two guide members  14  and  14  which are mounted to the ring members  12  and  12  and guide the blast head  11  along a longitudinal direction of the outer surface of the pipe P, and the like. 
   In the blast head  11 , a nozzle  38  and a suction port  50  of the sponge blasting apparatus  20  are mounted inside its casing. The nozzle  38  is connected to a flexible hose  46 , and ejects the sponge blast  26  to the outer surface of the pipe P from its tip end. The suction port  50  is connected to a flexible hose  51 , sucks the used blast media  26 , and feeds the blast media  26  to the recycle separator  42  via the suction machine  40 . A seal member  11   a  made of an elastic material such as rubber is mounted to a region of the blast head  11  in contact with the outer surface of the pipe P. 
   A pair of ring members  12  and  12  have their inside diameters formed to be slightly larger than an outside diameter of the pipe P, are rotatable in a circumferential direction along the outer periphery of the pipe P, and are each constructed by one member  12 A and the other member  12 B which are made by dividing the entire ring member. The one member  12 A and the other member  12 B are set to the pipe P, and are connected with two latch fasteners  13  and  13 . 
   The two guide members  14  and  14  are fixed to a pair of ring members  12  and  12  to be faced to the longitudinal direction of the pipe P, and the blast head  11  are movable along the longitudinal direction of the outer surface of the pipe P by being guided by the guide members  14  and  14 . The blast head  11  is rotatable in the circumferential direction of the pipe P together with a pair of ring members  12  and  12  via the guide members  14  and  14 . 
   A screw hole  12   a  is formed in one of a pair of ring members  12  and  12 , so that by fastening a fixing screw  15 , the ring member  12  is fixed to the pipe P to stop the rotation in the circumferential direction, and by loosening the fixed screw  15 , circumferential rotation of the ring member  12  is made possible. 
   Next, an operation of the blasting apparatus  10  for an outer surface of a pipe constructed above will be described. First, the one members  12 A and  12 A of a pair of ring members  12  and  12  are fitted to the region to be treated by blasting of the pipe P. Next, the other members  12 B and  12 B of the ring members  12  and  12  are combined with the one members  12 A and  12 A, and are respectively connected each with the two latch fasteners  13  and  13  to be made a pair of ring members  12  and  12 , and the ring members  12  and  12  are fixed by fastening the fixing screw  15 . 
   The operation of blasting treatment starts from here. First, the blast media  26  are ejected to the outer surface of the pipe P from the nozzle  38 , and the used blast media  26  and dust particles are sucked from the suction port  50 . In this state, the worker slowly moves the blast head  11  along the longitudinal direction of the outer surface of the pipe P. Blasting treatment of one row is performed by this. 
   At this time, the seal material  11   a  made of the elastic material such as rubber is mounted to the periphery of the casing opposed to the outer surface of the pipe P of the blast head  11 , and therefore, the blast media and dust particles inside the blast head  11  can be prevented from spouting outside. 
   Next, the fixing screw  15  which fixes the ring member  12  is loosened, the blast head  11  is turned by the amount of the blast width of one row along the circumferential direction of the outer surface of the pipe P, and the fixing screw  15  is fastened. Next, the blast head  11  is slowly moved along the direction opposite to the previous direction in the longitudinal direction of the pipe P to perform blasting treatment of the second row. By repeating the movement of the blast head  11  in the longitudinal direction of the outer surface of the pipe P and its movement in the circumferential direction in this manner, blasting treatment is applied to the entire periphery of the outer surface of the pipe P. 
   When all the portions in the circumferential direction of the pipe P are blasting-treated, the blasting apparatus  10  for the outer surface of the pipe is moved to the untreated position in the longitudinal direction of the pipe P. At this time, the ring members  12  and  12  have the structure in which they are split into halves, and therefore, when setting is changed in the longitudinal direction past the support portion which supports the pipe P, setting can be easily changed. 
   In the above described embodiment, the explanation is made with the manual mode in which the movement of the blast head  11  in the longitudinal direction of the outer surface of the pipe P and its movement in the circumferential direction are performed by a worker, but the mode in which a drive mechanism is provided and the blast head  11  is automatically moved can be adopted. 
     FIGS. 4 and 5  show a second embodiment,  FIG. 4  is a perspective view, and  FIG. 5  is a sectional view. In a blasting apparatus  10 A for an outer surface of a pipe according to the second embodiment, a blast head  61  itself is constructed to be movable along the longitudinal direction of the outer surface of the pipe P and the circumferential direction of the outer surface of the pipe P. 
   As shown in  FIG. 5 , the blast head  61  forms a cylindrical shape, and eight spherical rolling seats  62 ,  62  in total which are placed in two rows in the width direction at each of the positions where the circumference is divided into four equal parts on the circumference are provided in the casing. A spherical body  62   a  of each of the spherical rolling seats  62  is caused to abut on the outer surface of the pipe P via an elastic member  62   b , and the blast head  61  is supported movably in the longitudinal direction and the circumferential direction of the pipe P. 
   The blast head  61  is constructed by one member  61 A and the other member  61 B which are formed by dividing the entire blast head  61  into two. The one member  61 A and the other member  61 B are set to the pipe P, and are connected with the four latch fasteners  13  and  13  in total, two of which are placed in the width direction and two of which are placed at the opposed position. 
   The nozzle  38  and the suction port  50  of the sponge blast apparatus  20  are mounted inside the casing of the blast head  61 . The nozzle  38  is connected to the flexible hose  46 , and ejects the sponge blast  26  to the outer surface of the pipe P from its tip end. The suction port  50  is connected to the flexible hose  51 , and sucks the used blast media  26  and fed them to the recycle separator  42  via the suction machine  40 . 
   A fixing air cylinder  63  is mounted at the position opposed to the nozzle  38  and the suction port  50 . The fixing air cylinder  63  is used for securing the present position or the like when the operation is temporarily stopped during the operation, for example. Further, a seal member  61   a  made of an elastic material such as rubber is mounted to the region of the blast head  61 , which is in contact with the outer surface of the pipe P. 
   Further, an illuminating device  92  which illuminates a base of the outer surface of the pipe P which is ground, and an image pickup device  91  which picks up an image of the base of the outer surface of the pipe P illuminated by the illuminating device  92  are provided in the casing of the blast head  61 . Thus, the image of the base of the outer surface of the pipe P after blasting can be picked up, and the rust removal degree and the ground state can be observed. Further, the finished state can be recorded, and the finished state can be compared with a sample and judged. 
   Further, as described above, the blast head  61  is divided into two, and therefore, even when setting is changed in the longitudinal direction past the support portion which supports the long pipe P, setting can changed by dividing the blast head  61 . Therefore, setting can be easily changed. 
   In the case of the second embodiment, the explanation is also made with the manual mode in which the movement of the blast head  11  in the longitudinal direction of the outer surface of the pipe P and its movement in the circumferential direction are performed by a worker, but the mode in which a drive mechanism is provided, and the blast head  11  is automatically moved may be adopted. 
     FIG. 6  is a perspective view showing a third embodiment. A blasting apparatus  10 B for an outer surface of a pipe according to the third embodiment is constructed by a blast head  71 , a base plate  78 , a longitudinally driving device  74  which moves the blast head  71  along the longitudinal direction of the outer surface of the pipe P, a circumferentially driving device  77  which moves the blast head  71  along the circumferential direction of the outer surface of the pipe P, a control device not shown which controls the operation of each part and the like. 
   The nozzle  38  and the suction port  50  of the sponge blasting apparatus  20  are mounted inside the casing of the blast head  71 . The nozzle  38  is connected to the flexible hose  46 , and ejects the sponge blast  26  to the outer surface of the pipe P from its tip end. The suction port  50  is connected to the flexible hose  51 , and sucks the used blast media  26  and fed them to the recycle separator  42  via the suction machine  40 . 
   A seal material  71   a  made of an elastic material such as rubber is mounted to a region of the blast head  71 , which is in contact with the outer surface of the pipe P. Further, the image pickup device  91  and the illuminating device  92  are mounted in the casing of the blast head  71 . 
   The longitudinally driving device  74  is constructed by a guide member  73  mounted to a pair of ring members  72  and  72  which will be described later, a feed screw  74 A, a feed nut  76  which is threadedly fitted onto the feed screw  74 A and is connected to the blast head  71 , an air motor  75 A as an explosion-proof type prime mover being a drive device which rotationally drives the feed screw  74 A, and the like, as shown in  FIG. 6 . By reciprocally rotating the feed screw  74 A with the air motor  75 A, the blast head  71  can be reciprocally moved along the longitudinal direction of the outer surface of the pipe P. 
   As shown in  FIG. 6 , the circumferentially driving device  77  is constructed by a pair of ring members  72  and  72 , large-diameter gears  72 G and  72 G which are respectively formed on the outer peripheries of a pair of ring members  72  and  72 , a shaft  77 A which is mounted on a base plate  78 , small-diameter gears  77 G and  77 G which are fixed to the shaft  77 A and are respectively meshed with the large-diameter gears  72 G and  72 G, an air motor  75 B as an explosion-proof type prime mover being a drive device which rotationally drives the shaft  77 A, and the like. 
   By reciprocally rotating the shaft  77 A with the air motor  75 B, the blast head  71  can be reciprocally moved along the circumferential direction of the outer surface of the pipe P via the small-diameter gears  77 G and  77 G, the large-diameter gears  72 G and  72 G, the longitudinally driving device  74  and the like. 
   The ring member  72  has its inside diameter formed to be slightly larger than the outside diameter of the pipe P, and is constructed by one member  72 A and the other member  72 B which are formed by dividing the entire ring member into two. The one member  72 A and the other member  72 B are set to the pipe P, and are connected with the two latch fasteners  13  and  13 . 
   Magnet stands  79  and  79  each having a V-shaped notch are mounted at both end sides of the base plate  78 , and by switching a lever  79   a  of the magnet stand  79 , the base plate  78  can be attached to and detached from the outer surface of the pipe P. 
   Since the ring member  72  is divided into two as described above, when setting is changed in the longitudinal direction past the support portion which supports the long pipe P, setting can be changed by dividing the ring member  72 , and therefore setting can be easily changed. 
   Next, an operation of the blasting apparatus  10 B for an outer surface of a pipe constructed as above will be described. First, the one members  72 A and  72 A of a pair of ring members  72  and  72  are attached to a region of the pipe P to be blasting-treated. At this time, they are mounted with the blast head  71  and the longitudinally driving device  74  mounted to the one members  72 A and  72 A. Next, the other members  72 B and  72 B of the ring members  72  and  72  are combined with the one members  72 A and  72 A, and are respectively connected with the latch fasteners  13  and  13  to make a pair of ring members  72  and  72 . 
   Next, the magnet stands  79  and  79  of the base plate  78  are caused to abut on the outer surface of the pipe P so that the small-diameter gears  77 G and  77 G mounted on the base plate  78  are meshed with the large-diameter gears  72 G and  72 G, the lever  79   a  of the magnet stand  79  is switched to fix the base plate  78  to the outer surface of the pipe P. 
   This completes setting of the blasting apparatus  10 B for an outer surface of a pipe to the pipe P, the operation of each part is controlled by a control device, and automatic operation of blasting treatment is started. First, the blast media  26  are ejected to the outer surface of the pipe P from the nozzle  38  and the used blast media  26  and the dust particles are sucked from the suction port  50 . In parallel with this, the feed screw  74 A is rotationally driven by the air motor  75 A, and the blast head  71  is moved along the longitudinal direction of the outer surface of the pipe P. 
   Since the seal member  71   a  made of the elastic member such as rubber is mounted to the region of the blast head  71 , which is opposed to the outer surface of the pipe P, the blast media and the dust particles inside the blast head  71  are prevented from spouting outside at this time. While the blast head  71  moves in the longitudinal direction, the ring members  72  and  72  are restrained from rotating in the circumferential direction by holding torque of the air motor  75 B. 
   A terminal sensor not shown is provided at a stroke end in the longitudinal direction, and detects the stroke end in the longitudinal direction of the blast head  71 . When the stroke end in the longitudinal direction is detected, the small-diameter gears  77 G and  77 G are rotated a predetermined angle by the air motor  75 B next, and the blast head  71  is rotated by a predetermined amount in the circumferential direction of the pipe P together with a pair of ring members  72  and  72 . The rotation amount is set in accordance with the blast width in the circumferential direction. 
   When the rotation in the circumferential direction is finished, the blast head  71  is moved to a stroke end in the opposite direction along the longitudinal direction of the outer surface of the pipe P by the reverse rotation of the air motor  75 A while performing blasting treatment. A terminal sensor is also provided at the stroke end at this side, and detects the stroke end. 
   When the stroke end in the opposite direction is detected, the blast head  71  is further rotated by the predetermined amount in the circumferential direction of the pipe P, and the operation is repeated. When all the portions in the circumferential direction of the pipe P is blasting-treated in this manner, the blasting apparatus  10 B for an outer surface of a pipe is moved to an untreated position in the longitudinal direction of the pipe P. At this time, the ring members  72  and  72  has the structure in which they are divided into two, and therefore, even when setting is changed in the longitudinal direction past the support portion which supports the pipe P, setting can be easily changed. 
   Since the illuminating device  92  which illuminates the base of the ground outer surface of the pipe P, and the image pickup device  91  which picks up an image of the base of the outer surface of the pipe P illuminated by the illuminating device  92  are provided inside the blast head  71 , the image of the base of the outer surface of the pipe P after blasting is picked up, and the rust removal degree and the ground state are observed. The finished state may be recorded, and the finished state may be compared with a sample and automatically judged. 
   Next, a fourth embodiment will be described.  FIGS. 7 and 8  show the fourth embodiment,  FIG. 7  is a perspective view, and  FIG. 8  is a sectional view. A blasting apparatus  10 C for an outer surface of a pipe according to the fourth embodiment is constructed by a blast head  81 , a base plate  85 , a longitudinally driving device  82  which moves the blast head  81  along the longitudinal direction of the outer surface of the pipe P, a circumferentially driving device  83  which moves the blast head  81  along the circumferential direction of the outer surface of the pipe P, a control device not shown which controls the operation of each part and the like. 
   As shown in  FIG. 8 , eight spherical rolling seats  62 ,  62  in total which are placed in two rows in the longitudinal direction at each of the positions where the circumference is divided into four equal parts on the circumference are provided in the casing of the blast head  81 . A spherical body  62   a  of each of the spherical rolling seats  62  is caused to abut on the outer surface of the pipe P via an elastic member  62   b , and the blast head  81  is supported movably in the longitudinal direction and the circumferential direction of outer surface of the pipe P. A large-diameter gear  81 G is formed at one end surface side of the blast head  81 . 
   The blast head  81  is constructed by one member  81 A and the other member  81 B which are formed by dividing the entire blast head  81  into two. The one member  81 A and the other member  81 B are set to the pipe P, and are connected with the two latch fasteners  13  and  13 . 
   The nozzle  38  and the suction port  50  of the sponge blasting apparatus  20  are mounted inside the casing of the blast head  81 . The nozzle  38  is connected to the flexible hose  46 , and ejects the sponge blast  26  to the outer surface of the pipe P from its tip end. The suction port  50  is connected to the flexible hose  51 , and sucks the used blast media  26  and fed them to the recycle separator  42  via the suction machine  40 . 
   A seal member  81   a  made of an elastic material such as rubber is mounted to the region of the blast head  81 , which is in contact with the outer surface of the pipe P. Further, the image pickup device  91  and the illuminating device  92  are mounted in the casing of the blast head  81 . 
   As shown in  FIG. 7 , the longitudinally driving device  82  is constructed by a feed screw  82 A which is mounted to a base plate  85 , a feed nut  84  which is threadedly fitted onto the feed screw  82 A and is connected to the blast head  81 , an air motor  75 D as explosion-proof power being a drive device which rotationally drives the feed screw  82 A, and the like. 
   The feed nut  84  holds a side surface of the large-diameter gear  81 G of the blast head  81  which will be described later with two balls  84 A and  84 A, and its bottom surface contacts the base plate  85  to act as a detent, and by reciprocally rotating the feed screw  82 A with the air motor  75 D, the blast head  81  can be reciprocally moved along the longitudinal direction of the outer surface of the pipe P. 
   As shown in  FIG. 7 , the circumferentially driving device  83  is constructed by the large-diameter gear  81 G formed integrally with the blast head  81 , a shaft  83 A mounted to the feed nut  84 , a small-diameter gear  83 G which is fixed to the shaft  83 A and is meshed with the large-diameter gear  81 G fixed to the shaft  83 A, an air motor  75 C as explosion-proof power being a drive device which rotationally drives the shaft  83 A, and the like. 
   By reciprocally rotating the shaft  83 A with the air motor  75 C, the blast head  81  can be reciprocally moved along the circumferential direction of the outer surface of the pipe P via the small-diameter gear  83 G and the large-diameter gear  81 G. While the blast head  81  moves in the longitudinal direction, it is restrained from rotating in the circumferential direction by holding torque of the air motor  75 C. 
   Magnet stands  86  and  86  each having a V-shaped notch are mounted at both end sides of the base plate  85 , and by switching a lever  86   a  of the magnet stand  86 , the base plate  85  can be attached to and detached from the outer surface of the pipe P. 
   Since the blast head  81  is divided into two as described above, when setting is changed in the longitudinal direction past the support portion which supports the long pipe P, setting can be changed by dividing the blast head  81 , and therefore, setting can be easily changed. 
   As described above, according to the blasting apparatus for an outer surface of a pipe, the outer surface of a pipe can be ground efficiently with favorable operability. 
   In the above described embodiments, the explanation is made with an example of the sponge blasting apparatus using the blast medium  26  in a sponge piece form in which abrasives are stuck in a porous elastic body is used as the blast material, but the present invention is not limited to this, and a large effect can be also obtained when the present invention is applied to steel grit blasting in which a blast material  22  such as steel grit is directly ejected without containing it in a medium, and sand blasting in which sand is ejected. 
   The feed screws  74 A and  82 A and the feed nuts  76  and  84  are used as the mechanisms for the longitudinally driving devices  74  and  82  which move the blast heads in the longitudinal direction of the pipe P, but the other known mechanisms such as a rack and pinion mechanism and the like can be used. The large-diameter gears  72 G and  81 G and the small-diameter gears  77 G and  83 G are used as the circumferentially driving devices  77  and  83 , but the other known mechanisms such as a belt mechanisms and the like can be used. Further, the air motor with air as power is used as the drive device, but an explosion-proof type electric motor can be used.