Memory metal plug
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Memory metal plugs adapted to seal tubes are formed with a central post and laterally extended disks or rings. The plugs are formed from memory metal that is machined and heat treated to establish favorable temperature profile for the memory metal. The plugs are deformed in an apparatus that holds the plugs and cools the plugs to transform them into the martensitic state. A ram is used to force the cooled plugs through a die to decrease their diameter. These plugs can then be inserted into a tube and heated, causing them to return to their original state and thereby plug the tube.

Hollaender, Douglas L. (Loveland, OH, US)
Rhorer, William (Newport, KY, US)
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1. A method of swaging a memory metal plug, said plug having at least one laterally extended disk comprising positioning said plug in contact with a die aligned with an opening in said die; spraying a coolant onto said plug to convert said plug from an austenitic state to a martensitic state, forcing said plug through said die to deform said disks thereby decreasing the diameter of said plug.

2. The method claimed in claim 1 wherein said refrigerant is carbon dioxide.

3. The method claimed in claim 2 wherein said plug is held in a housing and a spacer is placed on said plug, and wherein said plug is forced through said die by forcing said spacer downwardly through said die.

4. The method claimed in claim 1 wherein said plug is held in said die and said refrigerant is sprayed through said die onto said plug.

5. The method claimed in claim 4 further comprising measuring the temperature of said die to determine the temperature of said plug and forcing said plug through said die when a predetermined temperature of said die is detected.

6. An apparatus to swage a memory alloy plug, said plug having a plurality of laterally extended disks comprising an annular die having an inlet opening, an upper untapered portion, and a lower tapered portion; said upper portion adapted to support said memory metal plug; a plurality of coolant inlets through said upper portion of said die; and a ram adapted to force said plug from said upper portion of said die through said die.

7. The apparatus claimed in claim 6 wherein said coolant inlet comprises a plurality of orifices.

8. The apparatus claimed in claim 6 further comprising a thermocouple associated with said die said thermocouple associated with a second switch which controls aid ram.

9. The apparatus claimed in claim 7 comprising a first switch adapted to activate said ram to force said plug into an upper portion of said die and said second switch adapted to activate said ram to force said plug completely through said die.

10. The apparatus claimed in claim 8 further comprising a container adapted to catch a plug that has been forced through said die.

11. The apparatus claimed in claim 7 further comprising means to set a temperature where said second switch is activated by means of said thermocouple detecting said temperature.

12. A memory metal plug having a central post and at least one disk extended radially outward from said post, a radiused portion between a juncture of said post and said disk extended around said post.

13. The plug claimed in claim 12 wherein said plug has a plurality of disks.

14. The plug claimed in claim 13 wherein each disk includes a first and second surface and wherein said radiused portion is at a juncture of said post and said first surface.

15. The plug claimed in claim 13 having a first disk and a second disk, said post extended from said first disk through said second disk, and wherein said radiused portion is at a junction of said rod and said second surface of said second disk.

16. The plug claimed in claim 12 having first, second and third disks, each disk having first and second surfaces, said plug having radiused portions at the junctures of said post and said first surface of said first disk, and at the junctures of said post and said first and second surfaces of said second disk.

17. The plug claimed in claim 12 wherein said radiused portion has a radium greater than about 0.015 inches.

18. The plug claimed in claim 17 wherein said radius is at least about 0.03 inches.

19. A memory metal plug comprising a central post and at least one disk, said post having a tip extended out from a surface of said disk, a metallic heat conducting rod compression fitted to said tip.

20. The plug claimed in claim 19 wherein said metal rod is steel.



This application is a regular utility application of U.S. Provisional Patent Application Ser. No. 60/741,621, filed on Dec. 2, 2005, the entire disclosure of which is incorporated herein by reference.


Frequently, it is necessary to plug or seal a tube or circular opening. Plugs can be used to seal bores formed in diesel engines, such as the plug disclosed in U.S. Pat. No. 6,053,992. Plugs are also used to seal tubes in heat exchangers. There are a wide variety of different methods used to seal such devices, none of which are totally satisfactory. In certain applications, explosive devices are used to seal off a tube. But, this is very expensive. Mechanical devices can also be used; but, in high pressure applications, these may fail.

A potentially useful plug to seal tubes is disclosed in Hall U.S. Pat. No. 5,189,789. This discloses the use of a memory metal or Nitinol plug. Memory metals are alloys that undergo a reversible transformation from an austenitic state to a martensitic state with changes in temperatures. At colder temperatures, the alloy enters the martensitic state and reverts to the austenitic state at higher temperatures. A plug in the martensitic state can be bent or shaped. When the metal reverts to the austenitic state it reverts to its original shape.

The plug disclosed in Hall U.S. Pat. No. 5,189,789 is formed from such a memory metal and includes a central post with a plurality of disks that extend perpendicular to the post. The disclosed plug is placed in a bath of methanol and dry ice to cause it to enter the martensitic state. It is then forced through a die which bends or swages the disks, decreasing the exterior diameter of the plug. The plug can then be manually place into a tube and heated, causing it to revert to the austenitic state at which point in time it will bend back to its original shape, increasing its diameter and, thus, plugging the tube. These plugs are preferably formed from Nitinol, which is an alloy of nickel and titanium.

Unfortunately, the plug disclosed in the Hall reference tends to break when swaged. The design of the plug as well as the disclosed method of swaging the plug produced very unreliable results.


The present invention is based on the realization that an apparatus can be utilized that supports the unswaged memory metal plug in a holder and chills it while it is in the holder to transform it to the martensitic state. Preferably, the plug is chilled using liquid carbon dioxide or other cryogenic fluids at temperatures below the lower martensitic transition temperature of the memory metal alloy. Preferably, the plug is placed in a die and coolant is forced through the die walls onto the plug. The plug, while in the holder, can then be forced by a ram through a die to swage it, allowing it to be used.

This ensures that the plug is cooled adequately. A thermocouple can also be used to measure the plug temperature and prevent the ram from activating before the plug reaches the martensitic state.

The plug is designed with radiused regions between the disks and central rod which further prevents breakage.

The deformed plug connected to a heat conducting holder is inserted into a tube. The holder and plug are heated, causing the plug to revert to the austenitic state and into its original configuration, thus expanding and sealing the tube.

The objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings, in which:


FIG. 1 is a perspective view of a plug for use in the present invention;

FIG. 2 is a plan view of a plug and holder assembly for use in the present invention in its austenitic state;

FIG. 3 is a plan view of a plug and holder assembly for use in the present invention in its deformed martensitic state;

FIG. 4 is a diagrammatic depiction of the insertion of the plug of the present invention into a tube.

FIG. 5A is a cross sectional view of the apparatus used in the present invention showing the plug above the die.

FIG. 5B is a cross sectional view of the apparatus shown in FIG. 5A with the plug in the upper portion of the die.

FIG. 6 is a diagrammatic depiction of the operation of the present invention.

FIG. 7A is cross sectional view of a Nitinol plug inserted into a tube in the swaged condition, as shown in FIG. 3.

FIG. 7B is a cross sectional view of a Nitinol plug inserted into a tube in its austenitic unswaged configuration.


As shown in FIG. 1, the present invention utilizes a plug 10 that includes a central axial post 12 and first, second and third circular disk-shaped flanges 14,16, and 18, generally referred to as disks. The plug 10 is shown with three disks but can be made with as few as one and as many as desired. Two or more disks are preferred because multiple disks help align the plug in use. Each of the first, second and third disks have first and second surfaces 13a and 13b. At the junctures between the surfaces and post 12 are radiused portions 15. The radiused portions can be located at any of the junctures between the posts and the disks. Preferably, they are at the juncture of the first surface 13a of the first disk 14 and at the junctures between the post 12 and the first and second surfaces 13a, 13b of the second 16 and third 18 disks.

Each of these radiuses should be greater than 0.003 inch, more preferably greater than 0.015 inch, and, in a preferred embodiment, is greater than about 0.03 inch. As shown, they are a complete radius of about 0.093. These radiused portions provide stress relief in both the deformation of the plug 10, and during use of the plug 10. This allows the plug to be deformed more, thus further reducing the diameter of the deformed plug.

Generally, for a plug having a diameter of 1 inch, the post 12 will have a diameter of 0.10 to 0.3 and the disks will be 0.05 to 0.25 inch thick. For a 0.5 to 1 inch diameter plug, a thickness of 0.187 functions well.

Plug 10 is formed from a memory metal alloy. As discussed below, it is important to select a memory metal alloy that has an appropriate temperature profile so that the conversions between the martensitic state and austenitic state are accomplished at temperatures that make the plug 10 commercially useful. Preferably, the memory metal is Nitinol. Such memory metals can be purchased. One supplier of such materials is Special Metals, Shape Memory Alloy Division, located in New Hartford, N.Y. A preferred material is one with 50 mole percent nickel and 50 mole percent titanium.

Preferably, plug 10 is machined from Nitinol which converts to the martensitic state at about 0° F., and remains in the martensitic state until heated to a temperature of about 95° F., or higher. Such material is generally purchased as bar stock or rod stock, and must be further machined in its austenitic state to provide a plug 10, as shown in FIG. 1. In order to form such a plug, a rod of the material having the desired cross sectional dimension is machined using, for example, a CNC lathe screw machine or grinder to provide the plug 10 with center post 12 and a plurality of disks 14, 16 and 18 (as shown). The peripheral edges of these disks are radiused to facilitate swaging. The trailing peripheral edges are not radiused. This provides a better seal in use.

During the machining of these plugs 10 the temperature profile may be modified. Accordingly, after machining, the plugs 10 are subjected to a heat treatment to restore the shape memory response of the alloy. Preferably, subsequent to machining, the plug 10 is heated to a temperature of about 900° F. for a period of 30 minutes.

The plug 10, as shown in FIG. 1, is swaged or deformed utilizing an apparatus 30, shown in FIGS. 5A and 5B. The apparatus 30 includes a central housing 32 that has an upper opening covered with cover 34. A die 38 is located within housing 32. Cylindrical metal die 38 is supported in a cylindrical support 46 which in turn is supported on a ledge 48 in housing 32. The support 46 includes an annular outer passage 41 which communicates between cryogenic inlets 42 and 44. This outer annular passage 41 communicates with a series of holes 45 which are directed to an inner annular passage 47 which surrounds die 38. Die 38 is in turn supported on a ledge 48 of support 46 and includes a series of holes 49 that align with the inner annular passageway 41 of the support 46. A thermocouple 50 is located on ledge 48 in contact with die 38 to measure the temperature of the die.

The die 38 includes an upper portion 52 and a lower portion 54. The upper portion 52 includes a cylindrical passage that is not tapered and adapted to receive the unswaged plug 10 as shown in FIG. 5A. The lower portion 56 of die 38 is tapered so that the bottom opening has a diameter equal to the desired diameter of the swaged plug. Cover 34 located above container 32 includes a central opening 56 aligned with the ram 58 of press 60 as well as the central axis of die 38.

The bottom 62 of housing 32 includes a channel 64. A cup 66 with a rim 68 attaches to the lower portion 62 of housing 32 with the rim 68 located in channel 64. Cup 66 is aligned directly beneath the die 38.

Exterior of housing 32 is a frame 65 with two side frame members 72 and 74 and a horizontal upper frame member 80. Press 60 is supported on upper surface 80.

As shown in FIG. 5A, an unbent Nitinol plug 10 (which is in the austenitic state) is positioned above die 38. The central opening of the upper portion of die 38 is slightly smaller than the outer diameter of plug 10. A holding rod 84 having a central bore at a first end 86 is placed on the post 12 of plug 10, centered with the opening through cover 34. The second end 88 of the holding rod 84 has a conical shape. An extension rod 90 is placed through the opening in cover 34. This has a first end 92 adapted to be engaged with the ram 58 from the press 60 and a second end 94 having a conical recess adapted to engage the second end 88 of holding rod 84.

FIGS. 5A, 5B, and 6 combine to show a diagrammatic depiction of the operation of the present invention. With the plug 10 in position as shown in FIG. 5A and a safety shield (not shown) in place, switch 100 is activated which causes the first portion 102 of press 60 to force ram 58 down a predetermined distance which causes the extension 90 to engage the holding rod 84 and force the plug 10 into the upper untapered portion 52 of die 38. This is shown in FIG. 5B. Switch 100 also causes cryogenic fluid to be forced through inlets 42 and 44 through the annular passage 41 through passages 45 in the holder to the inner annular passage 47 and, subsequently, through the passages 49 in the die 38 chilling the plug 10. Thermocouple 50 measures the temperature of the die 38 and, in turn, the plug 10. When this temperature reaches a predetermined set temperature, generally about −50° F., the second portion 106 of press 60 is automatically activated, which forces the ram 58 further, as indicated by arrow 108, forcing the plug 10 with the holder 84 through the die 38 into cup 66, as indicated by arrow 110. The tapered lower portion of die 38 bends the discs 14, 16 and 18, leaving the plug 10 in the configuration shown in FIG. 3. Thus, the swaged plug 10, shown in phantom in FIG. 5B, will be collected in cup 56.

The die 38 is configured to bend the disks 14, 16, 18 between 10 and 25 degrees from their originally perpendicular relation to post 12 so that the effective plug diameter is decreased 2-5% for plugs with a nominal diameter of 0.5 to 1 inch. In the embodiment shown in FIGS. 5A and 5B, the entry diameter of die 38 is 0.703 inch and the exit diameter is 0.688 inch corresponding to a disk bending of 15° for a plug having a nominal 0.187-inch diameter central post.

To use the plug to seal a tube, the plug 10, in the deformed state, i.e., martensitic state, as shown in FIG. 3, is inserted into a tube 111 as shown in FIG. 7A in the direction of arrow 112. Holding rod 84is attached to post 12 to facilitate this. As shown in FIG. 4, the plug 10 can be inserted anywhere in tube 111, including at the tube plate 113, as shown by plug 10(a). The deformed plug should be of a size wherein the outer diameter of the deformed plug is about 0.03 inches less than the inner diameter of the tube.

Once inserted into the tube with the holder 84 still in position, the plug is heated to a temperature effective to cause the plug to convert to the austenitic state. This should not exceed 550° F. The heating can be the result of residual heat in the tube or an external heat source such as a blow torch. Holder 84 is a thermally conducting metal such as steel. Therefore, it facilitates heating the plug 10. When the temperature of the plug reaches the transition temperature to the austenitic state, the plug 10 reverts to its original condition, increasing its diameter and, in turn, pressing against the side walls of tube 111 as shown in FIG. 7B.

Once in position with the plug 10 back in the austenitic state and sealing the tube 111, the holder 84 can be pulled from the plug. The friction fit between the holding rod 84 and post 12 allows one to remove the holder 84 using a pair of pliers.

The compression fit between the expanded plug 10 and the inner wall of tube 111 as shown in FIG. 7B is sufficient with at least 0.004″ interference to withstand a pressure of about 6,000 psi. Thus, this will withstand repeated heating and cooling cycles remaining securely in place, providing a reliable seal. This, in turn, allows a heat exchange tube which has a leak to be sealed off quickly and reliably, allowing the heat exchanger to be put back into operation quickly and inexpensively.

This has been a description of the present invention along with the preferred method of practicing the present invention. However, the invention itself should only be defined by the appended claims, WHEREIN WE CLAIM: