Patent Publication Number: US-2009239095-A1

Title: Composite rods and processes for forming composite rods

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/038,754, filed Mar. 23, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     There are numerous uses and applications for composite rods that comprise an outer sleeve formed over an inner core. For many composite rod applications, it is beneficial to have a seamless interface (i.e., no gaps) between the outer sleeve and inner core. For instance, a gap between the core and sleeve could adversely affect heat transfer in the composite rod for some applications. 
     SUMMARY OF THE INVENTION 
     A composite rod in accordance with one embodiment includes an outer sleeve formed over an inner core, wherein the outer sleeve and the inner core are joined with a non-metallurgical bond that provides a tight fit therebetween. A process for forming a composite rod includes positioning a rod inside a tube to form an intermediate assembly, wherein the tube has an inside diameter that is greater than the outside diameter of the rod. The tube is then compressed around the rod to produce a non-metallurgical bond between the tube and the rod. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an intermediate assembly used in forming a composite rod. 
         FIG. 2  is an end view of the assembly of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a formed composite rod. 
         FIG. 4  is an end view of the composite rod of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a formed composite rod having end caps attached. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention generally relates to composite rods and processes for forming composite rods. One such process for forming composite rods can include bonding an outer sleeve onto an inner core without a metallurgical bond and without any gaps between the sleeve and core. That is, the process produces an airtight, gapless, non-metallurgical bond between the sleeve and core. As used herein, the term “non-metallurgical bond” refers to a bond between two articles wherein no intermelting or diffusion of the respective materials occurs. 
     Referring to  FIGS. 1-5 , one embodiment of a process for forming composite rods begins with obtaining a tube  10  and a separate rod  12 . The tube  10  is made of the material that the outer sleeve of the composite rod is to be, and the rod  12  is made of the material that the inner core of the composite rod is to be. Although they can be the same material, the two components will typically comprise dissimilar materials. The inside diameter (ID) of the tube  10  is greater than the outside diameter (OD) of the rod  12 . The tube  10  and rod  12  can be, but are not necessarily, equal in length. 
     The tube  10  and rod  12  are arranged with the rod  12  positioned inside of the tube  10  to create an intermediate assembly  14  as shown in  FIGS. 1 and 2 . The intermediate assembly  14  then undergoes a rotary forging operation that compresses the tube  10  around the rod  12 , resulting in a tight fit between these two components. The intermediate assembly  14  can be heated prior to the forging operation. The heating can be accomplished by any suitable means, such as in a furnace. If pre-heating is used, it will be done at relatively low temperatures so as to prevent the formation of a metallurgical bond between the tube  10  and rod  12 . 
     The forging operation can be performed with a rotary swager, using dies made up of two or more segments. As the intermediate assembly  14  is moved between the swager dies, the dies apply radial forces to the outer surface of the tube  10  in rapid succession. These forces bond the tube  10  to the rod  12  forming the composite rod  16  (shown in  FIGS. 3 and 4 ) wherein the tube  10  becomes the outer sleeve of the composite rod  16  and the rod  12  becomes the inner core of the composite rod  16 . This process mechanically bonds the tube  10  to the rod  12  with a full contact interface between the two components. That is, there are no gaps between the outer sleeve  10  and the inner core  12  of the composite rod  16 . The gapless interface is achieved without a metallurgical bond because the forging temperature is maintained at a sufficiently low level to prevent metallurgical bonding. 
     As an alternative to a full contact, gapless interface, the tight fit between the tube  10  and the rod  12  can comprise a low clearance interface. That is, an interface or fit between the two components that is not necessarily full contact or gapless, but has no more than a minimal clearance, typically about  2  thousandths of an inch or less. 
     The operation reduces the outside diameter of the tube  10 , but is conducted in such a manner so as to produce no deformation of the inner rod  12 . Since the material volume of the tube  10  remains constant, reducing its cross-sectional area results in an increase in length of the tube  10 , as shown in  FIGS. 3 and 4 . The process is particularly useful for, but not limited to, forming composite rods of relatively long lengths (e.g., about one foot or longer). 
     In one embodiment, one or both ends of the composite rod  16  can be closed or capped by joining a piece of material thereto. Referring to  FIG. 5 , a disc  18  is welded to each end of the composite rod  16 . The discs  18  have a diameter equal to the outside diameter of the sleeve  10  after the forging operation and are preferably made from the same material as the sleeve  10 . To prepare the composite rod ends for welding, each end will be cut square using any suitable means, such an abrasive cutting wheel. The end of the composite rod  16  can be beveled to accommodate the weld. 
     The composite rod  16  can undergo additional finishing operations. For instance, the composite rod  16  can be centerless ground or otherwise machined to the desired final diameter. 
     The process described herein can be used to make composite rods for any application and can be applied to any combination of rod and tube diameters and materials, as long as attention is paid to deformation, melting and reaction temperatures of the components. Furthermore, while the deformation process described herein was swaging, a drawing operation or a rolling operation could also be used. For example, a rolling operation could comprise passing the intermediate assembly  14  through several stages of form rolls, thereby compressing the tube  10  around the rod  12  to produce a tight fit and non-metallurgical bond between these two components. 
     In one example of a process to make a composite rod, a 0.187-inch tungsten centerless ground rod was joined with a tube made of Inconel 600 nickel-base alloy and having an OD of 0.380 inches and an ID of 0.197 inches. Both the rod and the tube were cut to 6 feet in length. 
     The tungsten rod was slid inside the Inconel tube, and the two together were transported through a pre-heat furnace where process temperatures (swaging preheat temperature) were in the range of 1100-1150° C. The rod-tube assembly was then transported into a rotary swaging machine. The rotary swager was set up such that there would be a net deformation of the OD of the tube that exceeded the diameter difference between the tungsten rod and the Inconel tube ID. In this case, the OD after the swaging operation was 0.365 inches, with a total deformation of 0.015 inches, which was greater than the Inconel tube ID-tungsten rod OD difference of 0.010 inches (0.197 inches minus 0.187 inches). A secondary smooth swaging operation was also performed to further reduce the diameter of the composite from 0.365 inches to 0.360 inches—done primarily to assure a straighter rod, (but was not necessary to achieve the closure of the original gap between the Inconel tube and the tungsten rod). 
     The tungsten core was not deformed and did not elongate. The Inconel sleeve elongated and stretched over the end of the tungsten core rod. There was no gap between the core rod and the Inconel tube.