EXPANSION BULLET FOR HEAT EXCHANGER TUBE

Abstract

An expansion bullet for a heat exchanger tube includes a leading edge face, a trailing edge face, and a bullet body insertable into a tube of a heat exchanger to expand the tube. The bullet body extends from the leading edge face to the trailing edge face and has an outer profile defined by a single radius. An expansion mechanism for a tube of heat exchanger includes a bullet driving device and an expansion bullet drivable by the bullet driving device. The expansion bullet includes a leading edge face, a trailing edge face, and a bullet body insertable into a tube of a heat exchanger to expand the tube. The bullet body extends from the leading edge face to the trailing edge face and has an outer profile defined by a single radius.

Description

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to heat exchanger tubes. More specifically, the subject disclosure relates to expansion bullets for manufacturing heat exchanger tubes.

Heat exchangers of, for example, air conditioners, include a plurality of heat exchanger fins and a plurality of heat exchanger tubes. The tubes are passed through holes in the fins, then are expanded to force the tubes into interference fit with the fins, thereby securing the tubes in place relative to the fins. Typically, the tubes are expanded via a bullet having a maximum diameter the same as that of the desired final inner diameter of the tube. The bullet 100, an example of which is shown in FIG. 3, is fixed to a mandrel for inserting into the tube, and typically has a radiused leading edge 102 and a conical or cylindrical body 104. The typical cross-sectional shape of an expansion bullet requires application of a high force in order for the bullet to successfully expand the tube. Further, especially when expanding aluminum tubes, aluminum material builds up on the bullet, resulting in galling and further increase in the necessary applied force.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, an expansion bullet for a heat exchanger tube includes a leading edge face, a trailing edge face, and a bullet body insertable into a tube of a heat exchanger to expand the tube. The bullet body extends from the leading edge face to the trailing edge face and has an outer profile defined by a single radius.

According to another aspect of the invention, an expansion mechanism for a tube of heat exchanger includes a bullet driving device and an expansion bullet driveable by the bullet driving device. The expansion bullet includes a leading edge face, a trailing edge face, and a bullet body insertable into a tube of a heat exchanger to expand the tube. The bullet body extends from the leading edge face to the trailing edge face and has an outer profile defined by a single radius.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of an embodiment of a tube expansion bullet;

FIG. 2 is another cross-sectional view of an embodiment of an expansion bullet; and

FIG. 3 is a cross-sectional view of a typical expansion bullet.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Shown in FIG. 1 is a schematic of an expansion mechanism 10 for a tube 12 of, for example, a heat exchanger. The illustrated tube 12 is formed of an aluminum material, but other materials, for example, copper, may be utilized. The mechanism 10 includes a mandrel 14 which supports an expansion bullet 16. The expansion bullet 16 has a maximum diameter 18 greater than an unexpanded diameter 20 of the tube 12. The mandrel 14 and bullet 16 are driven into the tube 12 to expand the tube 12 to an inner diameter substantially equal to the maximum diameter 18 of the bullet 16. Though, expansion utilizing a mandrel 14 to drive the bullet 16 is shown in FIG. 1 and described herein, it is merely exemplary. It is to be appreciated that other bullet 16 driving means, such as a fluid applied to the bullet 16, are contemplated within the present scope.

To reduce the force necessary to expand the tube 12 to the desired diameter, the bullet 16 has a specific cross-sectional shape, as shown in FIG. 2. The bullet 16 is substantially symmetrical about a bullet axis 22 extending along a length 24 of the bullet 16. The bullet 16 has an inner diameter 26 defining a bullet opening 28 for mounting the bullet on the mandrel 14. The bullet has a leading edge face 30 and a trailing edge face 32 which are substantially planar and perpendicular to the bullet axis 22, and a bullet body 34 extending the length of the bullet 16 between the leading edge face 30 and the trailing edge face 32. A surface profile of the bullet body 34 is a single continuous radius 36. While a single continuous radius is shown in FIG. 2, it is to be appreciated that other configurations to reduce friction may be utilized. For example, the radius 36 may be interrupted along its length by on or more chamfers or steps.

A center point 38 of the continuous radius 36 is shown in FIG. 2. In some embodiments, an axial position of the center point 38 is biased toward the trailing edge face 32 such that, a leading edge face diameter 40 is less than a trailing edge face diameter 42. In some embodiments, the center point 38 is located along the length of the bullet 16 between about ¼ and ⅓ of the distance from the trailing edge face 32 to the leading edge face 30. Further, in some embodiments, the center point 38 is offset radially from the bullet axis 22. For example, as shown in FIG. 2, the center point 38 may be located outside of the bullet 16.

By way of example, a bullet 16 utilized to expand a tube 12 having about a ⅜″ outer diameter 44 is shown in FIG. 2. For such a bullet 16, the leading edge face diameter 40 is about 0.188 inches and the trailing edge diameter 42 is about 0.321 inches. The continuous radius 36 of the bullet 16 is about 0.350 inches. The continuous radius 36 is substantially proportional to the outer diameter 44 (shown in FIG. 1) of the tube 12 to be expanded. For larger outer diameters 44 a larger radius 36 is utilized, while for a smaller outer diameter 44, a bullet 16 having a smaller radius 36 is utilized.

In some embodiments, the bullet opening 28 is chamfered at the leading edge face 30 and the trailing edge face 32 to ease installation of the bullet 16 on the mandrel 14.

In some embodiments, the bullet 16 is formed from a steel material, for example, tool steel. It is to be appreciated, however, that other suitable materials may be utilized and are contemplated within the present scope. To decrease buildup of aluminum material on the bullet 16 during use, and thus reduce galling between the bullet 16 and the tube 12, the bullet 16 may include a coating material applied to the bullet 16. This coating may be, for example, a metallic coating, a plastic coating, a nano coating, and/or a surface treatment, or the like to reduce friction and galling, add wear resistance, and/or increase corrosion resistance. In some embodiments, the coating is a hard chrome plating.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. An expansion bullet for a heat exchanger tube comprising:

a leading edge face;

a trailing edge face; and

a bullet body insertable into a tube of a heat exchanger to expand the tube, the bullet body extending from the leading edge face to the trailing edge face, the bullet body having an outer profile defined by a single radius.

2. The expansion bullet of claim 1, wherein the single radius is substantially continuous and unbroken from the leading edge face to the trailing edge face.

3. The expansion bullet of claim 1, wherein a center point of the single radius is axially offset along a length of the expansion bullet.

4. The expansion bullet of claim 3, wherein the center point is axially offset such that a leading edge face diameter is smaller than a trailing edge face diameter.

5. The expansion bullet of claim 1, wherein the leading edge face and/or the trailing edge face are substantially axially-oriented planar faces.

6. The expansion bullet of claim 1, wherein a center point of the single continuous radius is radially offset from a central axis of the expansion bullet.

7. The expansion bullet of claim 6, wherein the center point is offset such that the center point is located outside of the expansion bullet.

8. The expansion bullet of claim 1, further comprising a coating applied to the expansion bullet.

9. The expansion bullet of claim 8, wherein the coating is one or more of a metallic coating, a plastic coating, a nano coating, or a surface treatment to reduce friction.

10. The expansion bullet of claim 1, further comprising a bullet opening to secure the expansion bullet to a mandrel.

11. An expansion mechanism for a tube of heat exchanger comprising:

a bullet driving device; and

an expansion bullet configured to be driven by the bullet driving device: a leading edge face; a trailing edge face; and a bullet body insertable into a tube of heat exchanger to expand the tube, the bullet body extending from the leading edge face to the trailing edge face, the bullet body having an outer profile defined by a single radius.

12. The expansion mechanism of claim 11, wherein the single radius is substantially continuous and unbroken from the leading edge face to the trailing edge face.

13. The expansion mechanism of claim 11, wherein a center point of the single continuous radius is axially offset along a length of the expansion bullet.

14. The expansion mechanism of claim 13, wherein the center point is axially offset such that a leading edge face diameter is smaller than a trailing edge face diameter.

15. The expansion mechanism of claim 11, wherein the leading edge face and/or the trailing edge face are substantially axially-oriented planar faces.

16. The expansion mechanism of claim 11, wherein a center point of the single continuous radius is radially offset from a central axis of the expansion bullet.

17. The expansion mechanism of claim 16, wherein the center point is offset such that the center point is located outside of the expansion bullet.

18. The expansion mechanism of claim 11, further comprising a coating applied to the expansion bullet.

19. The expansion mechanism of claim 18, wherein the coating is one or more of a metallic coating, a plastic coating, a nano coating, or a surface treatment to reduce friction.

20. The expansion mechanism of claim 11, wherein the bullet driving device is a mandrel to which the bullet is secured.