Patent Publication Number: US-7591709-B2

Title: Blasting device

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a blasting device, and particularly relates to a blasting device which is for carrying out a blasting operation and easy to carry. 
   2. Description of the Related Art 
   On the occasion of recoating a coated wall surface, a blasting operation of preparing the surface by grinding the coating film on the wall surface, and roughening the coated surface is performed as preliminary work. The blast medium which is used in such an occasion is generally sand or steel as in Japanese Patent Application Laid-Open No. 2005-66724, but recently, a method of using a blast medium in the shape of a sponge piece with an abrasive bonded inside a porous elastic body, a so-called sponge blast method has attracted attention from the viewpoint of improvement in a working environment. 
   According to the sponge blast method, when the sponge blast medium ejected from a nozzle with high-speed air collides against a coated surface, the blast medium becomes flat, and the abrasive mixed therein directly collides against the coated surface at a high speed. Therefore, the coating film can be ground and removed as with a sand and steel blast method. Since generated powder dust is entrapped in the sponge, the advantage of improving a working environment is provided. 
   Incidentally, in the structure of the above described conventional blasting device, the force feeding device for blast medium is constituted of large devices such as the pressure tank and the blower of the main body, and therefore, much time is required for setup and much effort is also required. For the blasting operation for a region having a large area, the number of process steps required for the setup and the blasting operation efficiency can be kept in balance. However, for the blasting operation for a region having a small area, the blasting operation takes a short time as compared with the setup time, and therefore, the conventional blasting device has the disadvantage of the balance being extremely unfavorable. 
   SUMMARY OF THE INVENTION 
   The present invention is made in view of the above circumstances, and has an object to provide a blasting device which is capable of reducing the number of process steps of setup, that is, easy to carry. 
   In order to attain the above described object, a first aspect of the present invention is characterized by including a container in which a blast medium is stored, a suction pipe which is inserted in the container to be rotatably supported, and is formed substantially in an L-shape with a lower suction port bent at a right angle, a rotary drive part which rotates the suction pipe, a hose connected to the suction pipe via a rotary joint, an ejector nozzle connected to the hose, and an air compressor which supplies compressed air to the ejector nozzle. 
   The first aspect of the present invention provides a compact and simple blasting device by using the air compressor which sucks the blast medium by negative pressure and ejects the blast medium, in place of the large-sized blower conventionally used, in order to reduce the number of setup process steps. 
   Specifically, according to the first aspect of the present invention, the suction pipe is rotated in the blast medium stored in the container by the drive force from the rotary drive part. Since large rotational torque is required in this case, the operation of advancing the lower suction port while rotating the lower suction port to the place where the blast medium is removed, in a word, is performed, while sucking the blast medium from the lower suction port of the suction pipe. Suction of the blast medium is performed by utilizing the ejector effect which occurs as a result of supplying the compressed air from the air compressor to the ejector nozzle. Thereby, the blast medium which is sucked is guided to the hose connected to the suction pipe via a rotary joint, and is ejected from the ejector nozzle. According to the blasting device with such a constitution, the air compressor is used in place of the large-sized blower as described above, and the structure of sucking the blast medium by negative pressure by rotating the suction pipe in the container is adopted. Therefore, the number of setup process steps can be significantly reduced, and the blasting device is easy to carry. Thus, the blasting device is favorable for a blasting operation for a region with a small area. 
   A second aspect of the present invention is, in the first aspect, characterized by having a pressure sensor which measures pressure in the suction pipe, and a control part which controls a rotational frequency of the suction pipe by the rotary drive mechanism based on a measured value by the pressure sensor. 
   When the rotating speed of the suction pipe is higher than the suction rate of the blast medium, the blast medium is lodged in the suction pipe and the negative pressure inside the suction pipe becomes too high. Therefore, it is necessary to rotate the suction pipe while keeping proper negative pressure. According to the second aspect of the present invention, the pressure sensor is provided at a part of the suction pipe, and the control part controls the rotary drive mechanism based on the measured value measured by this pressure sensor to control the rotational frequency of the suction pipe to be a rotational frequency at which clogging does not occur to the suction pipe. Thereby, the blast medium is favorably ejected from the ejector nozzle without lodging in the suction pipe. 
   A third aspect of the present invention is, in the first and second aspects, characterized by having an inclined plate disposed at the lower suction port of the suction pipe to be spaced by a predetermined amount, and disposed to be inclined at a downstream side with respect to a rotating direction of the lower suction port. 
   According to the third aspect of the present invention, when the suction pipe rotates with the inclined plate pushing away the blast medium, an empty space is formed in a gap between a back surface of the inclined plate and the lower suction port, and due to this empty space, suction of the blast medium from the lower suction port easily occurs. Therefore, by providing the inclined plate, the blast medium can be stably sucked. 
   A fourth aspect of the present invention is, in the third aspect, characterized by having an adjusting member which adjusts an inclination angle of the inclined plate. 
   According to the fourth aspect of the invention, the inclination angle of the inclined plate can be set at an angle at which the blast medium can be easily sucked in accordance with the kind (sand, steel and sponge) of the blast medium. 
   A fifth aspect of the present invention is, in the fourth aspect, characterized in that the inclined plate is formed into a comb shape. 
   According to the fifth aspect of the present invention, the blast medium can be taken into the gap from gaps of the comb teeth of the inclined plate. In this case, this is not preferable for the blast medium such as sand and steel, since the gaps are sometimes blocked, but in the case of the sponge blast medium, this is preferable since the gaps are not completely blocked, and the sponge blast medium is loosened by the comb teeth. 
   A sixth aspect of the present invention is, in the fifth aspect, characterized by being provided with an opening area changing device which makes opening areas between comb teeth portions of the inclined plate variable. 
   According to the sixth aspect of the present invention, by making the opening areas between the comb teeth portions of the inclined plate variable, the suction rate of the blast medium, especially the sponge blast medium can be controlled. 
   A seventh aspect of the present invention is, in the second to the sixth aspects, characterized in that the control part conducts control to supply compressed air from the air compressor to a part of the hose other than the ejector nozzle as supplementary compressed air to suck the blast medium in the suction pipe by an ejector effect to feed it into the hose when the measured value by the pressure sensor exceeds a predetermined value, and conducts control to stop the supply of the supplementary compressed air to the hose when the measured value by the pressure sensor becomes the predetermined value or less. 
   According to the seventh aspect of the present invention, a blasting operation is usually performed by supplying compressed air to the ejector nozzle from the air compressor, but when the negative pressure of the suction pipe exceeds the predetermined value to be large, but the ejection amount of the blast medium is comparatively small, the compressed air is also supplied to a part of the hose from the air compressor as the supplementary compressed air. Thereby, the blast medium in the suction pipe is sucked by the ejector effect and is fed to the hose. After that, when the negative pressure of the suction pipe returns to the original favorable numerical value, and the ejection amount returns to normality, the supply of the supplementary compressed air to the hose is stopped. The supplementary compressed air may be always supplied to a part of the hose, but by supplying it only when it is required, energy conservation can be achieved. 
   According to the blasting device according to the present invention, the air compressor is used in place of a large-sized blower, and the structure of sucking the blast medium by negative pressure by rotating the suction pipe inside the container is adopted. Therefore, the number of setup process steps can be significantly reduced, and the blasting device becomes easy to carry. Accordingly, the blasting device which is favorable for a blasting operation for a region with a small area can be provided. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an explanatory view showing an entire constitution of a blasting device of an embodiment; 
       FIG. 2  is a perspective view of a container of the blasting device shown in  FIG. 1 ; 
       FIG. 3  is a perspective view showing a lower suction port of a suction pipe of the blasting device shown in  FIG. 1 ; 
       FIG. 4  is a perspective view showing a mode in which an inclined plate is disposed at the lower suction port of the suction pipe; 
       FIG. 5  is a side view of the inclined plate shown in  FIG. 4 ; 
       FIGS. 6A and 6B  are perspective views of assembly of an inclination angle adjusting mechanism shown in  FIG. 5 ; 
       FIG. 7  is a perspective view showing a mode in which a comb-shaped inclined plate is disposed at the lower suction port of the suction pipe; and 
       FIG. 8  is a plane view showing a mode in which two comb-shaped inclined plates are disposed to be stacked in layers and slidable. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A preferred embodiment of a blasting device according to the present invention will be described in detail hereinafter in accordance with the attached drawings. 
     FIG. 1  is an explanatory view showing an entire constitution of a blasting device  10  of the embodiment.  FIG. 2  is a perspective view showing a container  12  of the blasting device  10 . 
   As shown in these drawings, the blasting device  10  is constituted of a cylindrical container  12 , a suction pipe  14 , a motor (rotary drive part)  16 , a hose  18 , an ejector nozzle  20 , an air compressor  22 , a negative pressure sensor (pressure sensor)  24 , a valve  26 , a control part  28  and the like. 
   The container  12  is installed on a seat  30 , and a sponge blast medium  32  that is a blast medium is stored in it. By providing casters at lower portions of three leg portions  31 ,  31  and  31  of the seat  30 , the container  12  can be easily moved to a desired position. As a blast medium, a sponge blast  32  is shown as an example, but the blast medium is not limited to this, and it may be other blast media such as sand and steel. 
   The suction pipe  14  is inserted into the container  12  along a center axis P of the container  12 , and is rotatably supported via a bearing  36  by a plate  34  in the shape of a cross which is fixed to an upper opening of the container  12  by screws. At a lower portion of the suction pipe  14 , a lower suction port  38  is bent at the right angle as shown in  FIG. 3 , so that the entire suction pipe  14  is formed substantially in an L-shape. The lower suction port  38  is disposed with a predetermined gap with respect to a bottom surface  12 A (see  FIG. 1 ) of the container  12 . 
   As shown in  FIG. 2 , the motor  16  is fixed to the plate  34 , and a gear  40  is fixed to its rotary shaft. The gear  40  is meshed with a gear  42  fixed to the suction pipe  14 . Accordingly, when the power of the motor  16  is transmitted to the suction pipe  14  via the gears  40  and  42 , the suction pipe  14  is rotated around the center axis P. In order to guide the rotation smoothly, a bearing part  44  is provided at a center portion of the bottom surface  12 A of the container  12 , and a lower protruded portion  46  of the suction pipe  14  is rotatably supported by the bearing part  44 . 
   A base end portion  18 A of the hose  18  is connected to an upper portion of the suction pipe  14  via a rotary joint  48 , and an ejector nozzle  20  is connected to a tip end portion of the hose  18 . The base end portion  18 A of the hose  18  has an ejector structure ( FIG. 1  does not show the details), and a compressed air supply port  50  of it is connected to an air compressor  22  via a valve  26 . 
   The ejector nozzle  20  is of a gun type having a lever (trigger)  52 , and is connected to the air compressor  22  via an air hose  54 . When an operator triggers the lever  52 , a nozzle (not shown) incorporated in the ejector nozzle  20  is opened, and thereby, the compressed air from the air compressor  22  is introduced into the ejector nozzle  20 . By the ejector effect caused by this, the sponge blast medium  32  in the container  12  is sucked into the ejector nozzle  20  through the suction pipe  14  and the hose  18 , and is ejected from an ejection port  56  of the ejector nozzle  20  together with the compressed air. 
   A negative pressure sensor  24  is provided near a seal  58  which shields the rotary joint  48  and the base end portion  18 A of the hose  18 , and is mounted to a position at which it can measure the negative pressure inside the suction pipe  14 . The information indicating the negative pressure measured by the negative pressure sensor  24  is outputted to a control part  28 . The control part controls the rotational frequency of the motor  16  and opening and closing of the valve  26  based on the information. 
   An operation of the blasting device  10  constituted as described above will be described next. 
   First, the blasting device  10  of the embodiment uses the air compressor  22  which sucks the sponge blast medium  32  by negative pressure and ejects it instead of a large-sized blower conventionally used in order to reduces the number of setup process steps. Thereby, the compact and simple blasting device  10  is provided. 
   Specifically, the blasting device  10  of the embodiment rotates the suction pipe  14  at a predetermined rotational frequency by the drive force of the motor  16  in the sponge blast medium  32  stored in the container  12 . In this case, the sponge blast medium  32  becomes the resistance, and large rotational torque is required for rotation of the suction pipe  14 . Therefore, the operation of advancing the lower port  38  to a place where the sponge blast medium  32  is removed while rotating it, in a word, is performed while sucking the sponge blast medium  32  from the lower suction port  38  of the suction pipe  14 , by using the ejector effect which is caused by supplying the compressed air to the ejector nozzle  20  from the air compressor  22 . 
   The sponge blast medium  32  sucked by the ejector effect is guided to the hose  18  connected to the suction pipe  14  through the rotary joint  48 , and is ejected from the ejection port  56  of the ejector nozzle  20 . 
   According to the blasting device  10  constituted like this, the air compressor  22  is used instead of a large-sized blower as described above, and the structure of sucking the sponge blast medium  32  by negative pressure by rotating the suction pipe  14  in the container  12  is adopted. Therefore, the blasting device  10  is favorable for a blasting operation for a region with a small area since the number of setup process steps can be significantly reduced, and the blasting device  10  is easy to carry. 
   When the rotational speed of the suction pipe  14  is higher than the suction rate of the sponge blast medium  32 , the suction pipe  14  is clogged with the sponge blast medium  32 , and the negative pressure in the suction pipe  14  becomes too high. Therefore, it is necessary to rotate the suction pipe  14  while keeping proper negative pressure. 
   In the blasting device  10  of this embodiment, the control part  28  controls the motor  16  based on the negative pressure inside the suction pipe  14  which is measured by the negative pressure sensor  24 , and controls the rotational frequency of the suction pipe  14  to be the rotational frequency at which the suction pipe  14  is not clogged. Specifically, the control part  28  properly controls the rotational frequency of the suction pipe  14  so that the negative pressure measured by the negative pressure sensor  24  becomes the negative pressure which gives a proper suction force. Thereby, the sponge blast medium  32  is favorably ejected from the ejector nozzle  20  without lodging in the suction pipe  14 . 
   When the measured value by the negative pressure sensor  24  is lower than a fixed value (the value at which the suction pipe  14  is assumed to be surely clogged with the sponge blast medium  32 ), the control part  28  opens the valve  26 , and also supplies the compressed air from the air compressor  22  to the base end portion  18 A of the hose  18  as supplemental compressed air. Thereby, the ejector effect occurs in the base end portion  18 A of the hose  18 , and by this ejector effect, the sponge blast medium  32  lodged in the suction pipe  14  is forcefully sucked by the hose  18 . Thereby, clogging in the suction pipe  14  is eliminated. When the measured value by the negative pressure sensor  24  returns to the above described fixed value, the control part  28  determines that the clogging is eliminated and closes the valve  26 , and stops the supply of the supplemental compressed air to the base end portion  18 A of the hose  18 . 
   Specifically, the blasting device  10  of the embodiment usually performs a blasting operation by supplying the compressed air to the ejector nozzle  20  from the air compressor  22 , but when the negative pressure of the suction pipe  14  becomes lower than the fixed value, it determines that clogging occurs to the suction pipe  14 , and also supplies the compressed air to the base end portion  18 A of the hose  18  from the air compressor  22  as the supplemental compressed air. 
   Thereby, the sponge blast medium  32  lodged in the suction pipe  14  is sucked due to the ejector effect and is fed into the hose  18 . After that, when the negative pressure of the suction pipe  14  returns to the original favorable numerical value, supply of the supplemental compressed air to the suction pipe  14  is stopped. The compressed air from the air compressor  22  may be always supplied to the hose  18  as the supplemental compressed air, but by supplying it only when it is needed, energy conservation can be achieved. 
     FIG. 4  shows an example in which an inclined plate  60  is disposed at the lower suction port  38  of the suction pipe  14 . 
   The inclined plate  60  is attachably and detachably mounted to a lower portion of the suction pipe  14  by an inclination angle adjusting mechanism  62  shown in  FIG. 5 , and an inclination angle θ is adjustable. 
   As shown in  FIG. 6A , the inclination angle adjusting mechanism  62  includes a base plate  92  which is fixed to an upper wall surface of the lower suction port  38  and has semicircular bearing portions  90  and  90  fixed to both end portions of the base plate  92 , and a rocking plate  98  in which semicircular brackets  94  and  94  are fixed to both end portions of the lower portion of the rocking plate  98  and the inclined plate  60  is fixed to it by a flat screw  96  as shown in  FIG. 6B . The brackets  94  and  94  are connected to the bearing portions  90  and  90  to be rockable via threads not shown, whereby the inclined plate  60  is tilted via the rocking plate  98 , and is held at a predetermined inclination angle by fastening wing nuts  100  which are secured in the above described threads. 
   As the inclination angle adjusting member of the inclined plate  60 , the inclined angle adjusting mechanism  62  is used, but the inclination angle adjusting member is not limited to this, and any member can be used if only it is capable of adjusting the inclination angle of the inclined plate  60 . 
   The inclined plate  60  is disposed to be opposed to the lower suction port  38 , and is disposed to incline at the downstream side with respect to the rotating direction of the lower suction port  38 . Further, the inclined plate  60  is disposed to be spaced by a predetermined amount from the lower suction portion  38  so as to form a gap  64  between the inclined plate  60  and the lower suction port  38  as shown in  FIG. 5 . 
   By disposing the inclined plate  60  at the lower suction port  38  like this, when the suction pipe  14  rotates as the inclined plate  60  is pushing the sponge blast medium  32 , the sponge blast medium  32  does not exist in the gap  64  between the back surface of the inclined plate  60  and the lower suction portion  38 , and the gap  64  becomes an empty space. Due to the existence of the empty space, suction of the sponge blast medium  32  from the lower suction port  38  easily occurs. Thereby, by providing the inclined plate  60 , the sponge blast medium  32  can be stably sucked. This action is similar in the case of the blast media other than the sponge blast media  32 . 
   The inclined plate  60  is adjustable in the inclination angle θ by the inclination angle adjusting mechanism  62 , and therefore, in accordance with the kind of the blast medium for use (sand, steel, and sponge), the inclination angle of the inclined plate  60  can be set at an angle at which the blast medium is easily sucked. 
     FIG. 7  shows an example in which an inclined plate  70  in the shape of comb teeth is disposed at the lower suction port  38  of the suction pipe  14 . In this mode, the blast medium can be taken into the above described gap  64  (see  FIG. 5 ) from gaps  72 ,  72 , . . . between the comb teeth of the inclination plate  70 . In this case, the blast media such as sand and steel are not preferable since the above described gap  64  is clogged, but in the case of the sponge blast medium  32 , it is preferable since the above described gap  64  is not completely clogged, and the sponge blast medium  32  is loosened by the comb teeth. 
     FIG. 8  is a plane view of an inclined plate unit  80  in which the two inclined plates  70  and  70  in the shapes of comb teeth are disposed in layer to be slidable. 
   In the inclined plate unit  80  shown in the drawing, through a long hole  82  formed in one inclined plate  70 , a bolt  84  mounted to the other inclined plate  70  is inserted, and thereby, the two inclined plates  70  and  70  are slidably jointed with the long hole  82  and the bolt  84  as a guide. By relatively sliding these inclined plates  70  and  70 , the size (opening area) of the gaps  72  between the comb teeth can be adjusted as shown in  FIG. 8 . After adjustment, by fastening a nut (not shown) to the bolt  84 , the size of the gaps  72  between the comb teeth can be kept. By making the size of the gaps  72  between the comb teeth of the inclined plate  70  variable like this, the suction rate of the blast medium, especially, the sponge blast medium  32  can be controlled. In this embodiment, as the opening area changing device, the sliding structure using the two inclined plates  70  and  70 , and connecting them with the long hole  82  and the bolt  84  is shown as an example, but the opening area changing device is not limited to this, and any device is applicable if only it can change the size of the gaps  72  between the comb teeth of the inclined plate  70 .