Abstract:
A method for manufacturing a pipe with a rib, in which a rib portion formed inside a pipe portion includes bent portions in accordance with bending of the pipe portion or a twisted portion in accordance with twisting of the pipe portion, includes drawing out molten metal held in a furnace by using a starter, from a surface of the molten metal, and drawing up the molten metal through a shape defining member defining a sectional shape of the pipe with the rib to be cast, and cooling and solidifying the molten metal passed through the shape defining member and drawn up. The bent portions are formed by moving at least one of the starter and the shape defining member in a horizontal direction. The twisted portion is formed by rotating at least one of the starter and the shape defining member about an axis extending along a vertical direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/068,344, filed on Oct. 31, 2013, and claims the benefit of priority under 35 U.S.C. §119 of Japanese Patent Application No. 2012-240826, filed on Oct. 31, 2012. The entire contents of each of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a pipe with a rib, and a method for manufacturing the pipe with a rib. 
     2. Description of Related Art 
     In Japanese Patent Application Publication No. 2012-61518 (JP 2012-61518 A), a free casting method is proposed as an up-drawing continuous casting method that does not require a mold. As described in JP 2012-61518 A, after a starter is immersed into a surface of molten metal (or a molten metal surface), the starter is drawn up, and then, the molten metal is also drawn out following the starter by a surface film and surface tension of the molten metal. Here, the molten metal is drawn out through a shape defining member placed near the molten metal surface, and then cooled. This way, continuous casting of a casting having a desired sectional shape is achieved. 
     In an usual continuous casting method, a shape in a longitudinal direction, as well as a sectional shape, are defined by a mold. In a continuous casting method in particular, solidified metal (or a casting) needs to pass through inside of a mold. Therefore, a casting that has been cast has a shape that extends linearly in a longitudinal direction. On the contrary, in a free casting method, a shape defining member defines only a sectional shape of a casting, and does not define a shape in a longitudinal direction. Since the shape defining member is able to move in a direction parallel to a molten metal surface (or a horizontal direction), castings with various longitudinal shapes are obtained. For example, JP 2012-61518 A describes a hollow casting (or a pipe) formed into a zigzag or helical shape, instead of a linear shape, in a longitudinal direction. 
     The inventors have found out the followings. With conventional methods including extrusion molding, press forming, welding, cutting, metal mold casting, and so on, it has been extremely difficult to manufacture a pipe that has a rib inside and is non-linearly shaped. 
     SUMMARY OF THE INVENTION 
     The present invention provides a pipe that has a rib inside and is non-linearly shaped. 
     A pipe with a rib according to a first aspect of the present invention includes a pipe portion, and a rib portion formed inside the pipe portion. The rib portion has a plurality of bent portions in accordance with bending of the pipe portion. 
     In the first aspect, the pipe with the rib may be a continuous casting. Also, the plurality of bent portions may be formed continuously. The plurality of bent portions may be structured so that the adjacent bent portions are bent in opposite directions to each other. Further, the rib portion may further include a twisted portion formed in accordance with twisting of the pipe portion. It has been even more difficult to manufacture such a pipe with a rib by conventional methods. 
     A pipe with a rib according to a second aspect of the present invention includes a pipe portion, and a rib portion formed inside the pipe portion. The rib portion includes a twisted portion in accordance with twisting of the pipe portion. 
     In the second embodiment, the pipe with the rib may be a continuous casting. 
     A method for manufacturing a pipe with a rib according to a third aspect of the present invention is a method for manufacturing a pipe with a rib, in which a rib portion formed inside a pipe portion includes a plurality of bent portions in accordance with bending of the pipe portion. The manufacturing method includes drawing out molten metal held in a molten metal holding furnace by using a starter, from a surface of the molten metal, and drawing up the molten metal through a shape defining member that defines a sectional shape of the pipe with the rib to be cast, and cooling and solidifying the molten metal that has passed through the shape defining member and been drawn up. The plurality of bent portions are formed by moving at least either one of the starter and the shape defining member in a horizontal direction. 
     According to the third aspect, it is possible to manufacture a pipe with a rib which has been extremely difficult to manufacture by conventional methods including extrusion molding, press forming, welding, cutting, metal mold casting, and so on. 
     In the third aspect, cooling gas may be introduced to an inner side of the pipe with the rib to be cast, and an opening may be provided in the starter. 
     A method for manufacturing a pipe with a rib according to a fourth aspect of the present invention is a method for manufacturing a pipe with a rib in which a rib portion formed inside a pipe portion includes a twisted portion in accordance with twisting of the pipe portion. The manufacturing method includes drawing out molten metal held in a molten metal holding furnace by using a starter, from a surface of the molten metal, and drawing up the molten metal through a shape defining member that defines a sectional shape of the pipe with the rib to be cast, and cooling and solidifying the molten metal that has passed through the shape defining member and been drawn up. The twisted portion is formed by rotating at least either one of the starter and the shape defining member about an axis that extends along a vertical direction. 
     According to the fourth aspect, it is possible to manufacture a pipe with a rib which has been extremely difficult to manufacture by conventional methods including extrusion molding, press forming, welding, cutting, metal mold casting, and so on. 
     In the fourth aspect, cooling gas may be introduced to an inner side of the pipe with the rib to be cast, and an opening may be provided in the starter. 
     According to the first to fourth aspects, it is possible to provide a pipe that has a rib inside and is non-linearly shaped. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a sectional view of a free casting apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a plan view of inner shape defining members and an outer shape defining member of the free casting apparatus; 
         FIG. 3  is a cross-sectional view of a casting according to the first embodiment; 
         FIG. 4A  and  FIG. 4B  are photographs showing external appearance of an example of the casting according to the first embodiment, and  FIG. 4C  is an X-ray photograph of bent portions of the casting; 
         FIG. 5  is a photograph showing external appearance of another example of the casting according to the first embodiment; and 
         FIG. 6A  is a photograph showing external appearance of an example of a casting according to a second embodiment of the present invention, and  FIG. 6B  is an X-ray photograph of a twisted portion of the casting. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Herein below, specific embodiments, to which the present invention is applied, will be explained in detail with reference to the drawings. It should be noted, however, that the present invention is not limited to the embodiments described below. Also, statements and drawings below are simplified as necessary in order to clarify the explanation. 
     First Embodiment 
     First, a free casting apparatus (an up-drawing continuous casting apparatus) according to a first embodiment will be explained with reference to  FIG. 1 .  FIG. 1  is a sectional view of a free casting apparatus according to the first embodiment. As shown in  FIG. 1 , the free casting apparatus according to the first embodiment includes a molten metal holding furnace  101 , inner shape defining members  102   a , an outer shape defining member  102   b , inner cooling gas nozzles  103 , a support rod  104 , an actuator  105 , and outer cooling gas nozzles  106 . 
     The molten metal holding furnace  101  holds molten metal M 1  such as aluminum and an aluminum alloy, and keeps the molten metal M 1  at predetermined temperature. In the example shown in  FIG. 1 , since the molten metal is not replenished in the molten metal holding furnace  101  during casting, a surface of the molten metal M 1  (or a molten metal surface) is lowered along with a progress of casting. However, the molten metal may be replenished into the molten metal holding furnace  101  as necessary during casting so that the molten metal surface is kept constant. As a matter of course, the molten metal M 1  may be other metal or an alloy than aluminum. 
     The inner shape defining members  102   a  and the outer shape defining member  102   b  are made of, for example, ceramics or stainless steel, and arranged near the molten metal surface. In the example shown in  FIG. 1 , four inner shape defining members  102   a  and one outer shape defining member  102   b  are arranged so as to be in contact with the molten metal surface. However, the inner shape defining members  102   a  and the outer shape defining member  102   b  may be arranged so that main surfaces of the inner shape defining members  102   a  and the outer shape defining member  102   b  on lower sides (a molten metal surface side) do not come into contact with the molten metal surface. To be specific, a predetermined gap (of, for example, approximately 0.5 mm) may be provided between the molten metal surface and, the main surfaces of the inner shape defining members  102   a  and the outer shape defining member  102   b  on the lower side. The four inner shape defining members  102   a  define an inner shape of a casting M 3  to be cast, and the outer shape defining member  102   b  defines an outer shape of the casting M 3  to be cast. 
       FIG. 2  is a planar view of the inner shape defining members  102   a  and the outer shape defining member  102   b . The sectional view of the inner shape defining members  102   a  and the outer shape defining member  102   b  in  FIG. 1  is equivalent to a sectional view taken along a line I-I in  FIG. 2 . As shown in  FIG. 2 , the outer shape defining member  102   b  has, for example, a rectangular planar shape, and has a square opening in the center. The four inner shape defining members  102   a  have square planar shapes that are congruent with each other, and are arrayed in a 2×2 matrix in the opening of the outer shape defining member  102   b . A gap between the inner shape defining members  102   a  and the outer shape defining member  102   b  serves as a molten metal passage portion  102   c  through which the molten metal passes. As described above, the inner shape defining members  102   a , the outer shape defining member  102   b , and the molten metal passage portion  102   c  structure a shape defining member  102 . 
     As shown in  FIG. 1 , the molten metal M 1  is drawn up following the casting M 3  by a surface film and surface tension of the molten metal M 1 , and passes through the molten metal passage portion  102   c . The molten metal, which is drawn up from the molten metal surface following the casting M 3  by a surface film and surface tension of the molten metal, will be referred to as “retained molten metal M 2 ”. An interface between the casting M 3  and the retained molten metal M 2  is a solidification interface. 
     The four inner cooling gas nozzles (inner cooling parts)  103  are connected to center parts of the inner shape defining members  102   a , respectively, and support the inner shape defining members  102   a . At the same time, each of the inner cooling gas nozzles  103  blows cooling gas (such as air, nitrogen, argon) on the casting M 3  from the center parts of the corresponding inner shape defining member  102   a , thus cooling the casting M 3  from inside. The support rod  104  supports the outer shape defining member  102   b . A positional relation between the inner shape defining members  102   a  and the outer shape defining member  102   b  is maintained by the inner cooling gas nozzles  103  and the support rod  104 . 
     The four inner cooling gas nozzles  103  and the support rod  104  are connected to the actuator  105 . Due to the actuator  105 , the four inner cooling gas nozzles  103  and the support rod  104  are able to move in a vertical direction (a perpendicular direction) and a horizontal direction (parallel to the molten metal surface) while maintaining the positional relation between the inner shape defining members  102   a  and the outer shape defining member  102   b . With such a structure, it is possible that the inner shape defining members  102   a  and the outer shape defining member  102   b  are moved in a downward direction as the molten metal surface is lowered along with progress of casting. Also, since the inner shape defining members  102   a  and the outer shape defining member  102   b  are able to move in the horizontal direction, a shape of the casting M 3  in the longitudinal direction is freely changeable. 
     The outer cooling gas nozzles (outer cooling parts)  106  is designed to blow cooling gas (such as air, nitrogen, and argon) on the casting M 3  and cool the casting M 3 . The casting M 3  is cooled by the cooling gas while the casting M 3  is drawn up by a lifting device (not shown) connected to a starter ST. Thus, the retained molten metal M 2  near the solidification interface is solidified sequentially, thereby forming the casting M 3 . 
     Next, the casting M 3  will be explained with reference to  FIG. 3  and  FIG. 4A  to  FIG. 4C .  FIG. 3  is a sectional view of the casting M 3  according to the first embodiment, taken along a horizontal plane. As shown in  FIG. 3 , the casting M 3  is a hollow casting (or a pipe), a section of which taken along the horizontal plane (referred to as a “transverse plane” herein below) has a cross inside a square shape. In other words, the casting M 3  includes a pipe portion M 31  having a square-shaped section, and a rib portion M 32  that is formed inside the pipe portion M 31  and has a cross-shaped section. The sectional shapes of the pipe portion M 31  and the rib portion M 32  are not limited at all. For example, the sectional shape of the pipe portion M 31  may be a circular shape, an elliptical shape, a triangle, a polygon such as a pentagon or above, and so on. There is also no limit on the number and the sectional shape of the rib portion M 32 . It is also possible to change the sectional shape of the casting M 3  while casting. 
       FIG. 4A  and  FIG. 4B  are photographs showing external appearance of an example of the casting M 3  according to the first embodiment, and  FIG. 4C  is an X-ray photograph of bent portions.  FIG. 4A  is a photograph showing external appearance of an example of the whole casting M 3  in the longitudinal direction according to the first embodiment. A left side of the photograph in  FIG. 4A  is an upper side of the casting M 3 , and a right side of the photograph is a lower side of the casting M 3 . The casting M 3  shown in  FIG. 4A  includes five bent portions formed continuously.  FIG. 4B  is a photograph showing external appearance of the casting M 3  seen from obliquely above. The casting M 3  is made of an aluminum alloy A6063, and has a section having a cross inside a square shape with a thickness of 1.5 to 2.5 mm (a gap in the molten metal passage portion  102   c  is 3.0 mm).  FIG. 4C  is an X-ray photograph showing the five bent portions from the side. The bent portions were photographed by using a digital X-ray sensor NX-06 and a portable X-ray photographic apparatus PX-20HF, made by RF Co., Ltd., under conditions with tube voltage of 74 kVp and tube current time of 25 mAs. As shown in  FIG. 4C , the pipe portion M 31  of the casting M 3  includes the five bent portions  11  to  15 . The bent portions adjacent to each other are bent in directions opposite to one another. To be more specific, the bent portions  11 ,  13 , and  15  are bent in the same direction. Also, the bent portions  12  and  14  are bent in the same direction. The bent portions  11 ,  13 , and  15 , and the bent portions  12  and  14  are bent in the opposite directions to each other. Further, as shown in  FIG. 4C , the rib portion M 32  includes five bent portions  21  to  25  corresponding to the five bent portions  11  to  15  of the pipe portion M 31 . The number of the bent portions can be any number. 
     As explained above, the casting M 3  according to the first embodiment is a pipe with a rib, which includes the pipe portion M 31 , and the rib portion M 32  formed inside the pipe portion M 31 . In the pipe portion M 31 , the plurality of bent portions, which are bent in opposite directions to each other, are formed continuously. In the rib portion M 32 , the bent portions corresponding to the bent portions of the pipe portion M 31  are also formed. It has been difficult to manufacture a pipe with a rib having the above-mentioned shape by conventional methods including extrusion molding, press forming, welding, cutting, metal mold casting, and so on, and a combination of these methods. In other words, in the free casting method according to the first embodiment, it is possible to manufacture a pipe with a rib having a shape, which has not been able to be manufactured by the conventional methods and a combination of the conventional methods. The pipe with the rib may be used for, for example, a heat exchanger. Details of the free casting method according to the first embodiment will be explained later. 
       FIG. 5  is a photograph showing external appearance of another example of the casting M 3  according to the first embodiment. A total length of the casting M 3  shown in  FIG. 5  is as large as 1200 mm. As shown in  FIG. 5 , in the free casting method according to the first embodiment, it is possible to form various bent portions continuously or intermittently. Also, since cooling gas is introduced into the casting M 3  through the inner cooling gas nozzles  103 , an opening for leading out the cooling gas is provided in the starter ST. 
     Next, the free casting method according to the first embodiment will be explained with reference to  FIG. 1 . First, the starter ST is lowered so that the starter ST passes through the molten metal passage portion  102   c  between the inner shape defining members  102   a  and the outer shape defining member  102   b , and a tip end of the starter ST is immersed into the molten metal M 1 . It is preferred that a starter to be used as the starter ST has a same sectional shape as the casting M 3 , and extends linearly in the longitudinal direction. 
     Next, the starter ST starts to be drawn up at a predetermined speed. Here, even if the starter ST is separated from the molten metal surface, the retained molten metal M 2  is formed, which follows the starter ST and is drawn up from the molten metal surface by the surface film and surface tension. As shown in  FIG. 1 , the retained molten metal M 2  is formed in the molten metal passage portion  102   c  between the inner shape defining members  102   a  and the outer shape defining member  102   b . This means that the inner shape defining members  102   a  and the outer shape defining member  102   b  give the retained molten metal M 2  a shape. 
     Next, because the starter ST is cooled by the cooling gas blown out from the inner cooling gas nozzles  103  and the outer cooling gas nozzles  106 , the retained molten metal M 2  is sequentially solidified from the upper side towards the lower side, and the casting M 3  thus grows. This way, continuous casting of the casting M 3  is achieved. In addition, it is possible to give the casting M 3  the bent portions by moving the inner shape defining members  102   a  and the outer shape defining member  102   b  in the horizontal direction. Instead of moving the inner shape defining members  102   a  and the outer shape defining member  102   b  in the horizontal direction, the starter ST fixed to the lifting device may be moved in the horizontal direction. Alternatively, the inner shape defining members  102   a  and the outer shape defining member  102   b , and the starter ST may be moved in opposite directions to each other within a horizontal plane. 
     (Second embodiment) A casting M 3  according to a second embodiment will be explained with reference to  FIG. 6A  and  FIG. 6B .  FIG. 6A  is a photograph showing external appearance of an example of the casting M 3  according to the second embodiment, and  FIG. 6B  is an X-ray photograph of a twisted portion. The casting M 3  shown in  FIG. 6A  includes a twisted portion  31 . The casting M 3  is also made of an aluminum alloy A6063 and has a section having a cross inside a square shape with a thickness of 1.5 to 2.5 mm (a gap in the molten metal passage portion  102   c  is 3.0 mm).  FIG. 6B  is an X-ray photograph of the twisted portion  31  seen from above. The twisted portion was photographed by using a digital X-ray sensor NX-06 and a portable X-ray photographic apparatus PX-20HF, made by RF Co., Ltd., under conditions with tube voltage of 74 kVp and tube current time of 25 mAs. As shown in  FIG. 6B , in the twisted portion  31 , a pipe portion M 31  and a rib portion M 32  are both twisted about a longitudinal direction of the casting M 3 . 
     In a free casting method according to the second embodiment, an inner shape defining members  102   a  and an outer shape defining member  102   b  are rotated about an axis that extends along a vertical direction in order to give the casting M 3  the twisted portion  31 . Instead of the inner shape defining members  102   a  and the outer shape defining member  102   b , a starter ST fixed to a lifting device may be rotated about the axis that extends along the vertical direction. Alternatively, inner shape defining members  102   a  and an outer shape defining member  102   b , and the starter ST may be rotated in opposite directions to each other about the axis that extends along the vertical direction. 
     As stated above, the casting M 3  according to the second embodiment is a pipe with a rib, which includes the pipe portion M 31 , and the rib portion M 32  formed inside the pipe portion M 31 . The casting M 3  according to the second embodiment has the twisted portion  31  in which the pipe portion M 31  and the rib portion M 32  are twisted together about the longitudinal direction of the casting M 3 . It has been difficult to manufacture a pipe with a rib having the above-mentioned shape by conventional methods including extrusion molding, press forming, welding, cutting, metal mold casting, and so on, and a combination of these methods. In other words, in the free casting method according to the second embodiment, it is possible to manufacture a pipe with a rib having a shape, which has not been able to be manufactured by the conventional methods and a combination of the conventional methods. The pipe with the rib may be used for, for example, a heat exchanger. Due to an anchor effect of the twisted portion  31 , for example, the casting M 3  is easily fixed in the ground. 
     The present invention is not limited to the foregoing embodiments, and may be changed as appropriate without departing from the scope of the invention. In particular, the first embodiment and the second embodiment may be combined. In other words, the casting M 3  may be a pipe with a rib having both the plurality of bent portions and the twisted portion.