Apparatus and process for selectively expanding a tube

An apparatus and process for selectively expanding the wall of a tube by compression and subsequent radial expansion of one or more elastomeric bars lodged within longitudinal slots of a bushing positioned inside the tube. Expansion of the elastomeric bars against the inner surface of the tube results in expansion of the tube wall at intermittent locations about the circumference of the tube.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus and process for expanding a 
tube. More particularly the apparatus and process of the present invention 
comprise the compression and resultant selective radial expansion of 
elastomeric bars against the inner surface of the tube to radially expand 
the walls of the tube at the locations of contact with the expanded 
elastomeric bars. The utility of the invention lies in its low cost 
tooling for complex tubular forming operations. The use of elastomeric 
bars allows tubular forming into a variety of shapes including elliptical, 
splined round, or corrugated round. 
2. Description of the Prior Art 
There are many methods of expanding the radius of a tube by a force located 
internally to the tube. Prior art methods of expanding tubes use metal 
rollers that move outwardly from a central position within the tube as the 
metal rollers are mechanically rotated about the central position. Metal 
rollers however can expand only to a round shape and they are limited to 
force applications near the free end of the tube. Other methods involve 
the compression and resultant expansion of high pressure fluid against the 
inner walls of the tube to radially expand the tube walls. Disadvantages 
with this method include complicated tooling involving complexly shaped 
seals which are prone to leakage. Other prior art such as U.S. Pat. No. 
4,109,365 by Tygart involve the compression of a hard rubber or elastomer 
by piston forces applied from both ends of the tube, instead of one end as 
taught in my invention, thereby making it difficult to expand the tube at 
a great distance from either end of the tube. 
U.S. Pat. No. 4,006,619 by Anderson discloses a tube expander utilizing 
hydraulically actuated pistons which compress a resilient element to 
radially expand a tube completely about its circumference. My invention 
teaches the selective expansion of a tube wall at intermittent locations 
about the circumference of a tube by compression and resultant expansion 
of elastomeric bars against the inner surface of the tube. Selective 
expansion may be used to form corrugated or splined tubular ends which may 
be useful in heat exchanger tubes to increase gas turbulence and heat 
transfer. Therefore, what is needed and what has been invented is an 
apparatus and process for selectively expanding a tube, without the 
foregoing deficiencies associated with prior art apparatuses. 
SUMMARY OF THE INVENTION 
The present invention accomplishes its desired objects by broadly providing 
an apparatus and process for expanding a tube. The apparatus comprises a 
shaft extending axially inside the tube, an inner cap bound to the shaft 
for longitudinal axial movement in combination with the shaft with respect 
to the tube, an outer cap, including at least one prong means bound 
thereto, slidably mounted on the shaft for longitudinal axial movement on 
and along the shaft with respect to the tube, and a bushing means slidably 
mounted on and along the shaft between the outer cap and the inner cap for 
longitudinal axial movement on and along the shaft with respect to the 
tube. An elastomeric means is slidably lodged within at least one 
longitudinal slot longitudinally traversing the bushing means, and the 
prong means is slidably lodged within the longitudinal slot of the bushing 
means. A means is provided for pulling the shaft in one axial direction 
while simultaneously pushing the outer cap in the opposite axial direction 
such that the inner cap contacts the bushing means and the prong means 
contacts the elastomeric means. The continuing respective axial forces 
from pulling and pushing, in combination with the prong means of the outer 
cap in contact with the elastomeric means within the longitudinal slot, 
cause the compression and resultant radial expansion of the elastomeric 
means at predetermined selective locations against the tube wall, 
subsequently resulting in selective radial expansion of the wall of the 
tube at intermittent locations about the circumference of the tube. 
The process for expanding the wall of a tube comprises placing the shaft 
axially inside the tube, binding the inner cap to the shaft, mounting the 
bushing means, including at least one longitudinal slot longitudinally 
traversing the bushing means, slidably on and along the shaft, lodging the 
elastomeric means slidably within the longitudinal slot of the bushing 
means, and mounting the outer cap slidably on and along the shaft such 
that the bushing means is between the outer cap and inner cap. The process 
also includes compressing the elastomeric means between the inner cap and 
the prong means in order to compress and subsequently radially expand the 
elastomeric means at predetermined selective locations against the wall of 
the tube resulting in selective radial expansion of the tube wall. 
It is therefore an object of the present invention to provide an apparatus 
and process for radially expanding a tube. 
It is another object of the present invention to provide an apparatus and 
process for radially expanding a tube at selective locations about the 
circumference of the tube. 
It is yet another object of the present invention to provide an apparatus 
and process for selectively radially expanding a tube at long distances 
from an open end of the tube. 
These, together with various ancillary objects and features which will 
become apparent as the following description proceeds, are obtained by 
this novel apparatus and process, preferred embodiments being shown in the 
accompanying drawings by way of example only, wherein:

DETAILED DESCRIPTION OF THE INVENTION 
Referring in detail now to the drawings wherein like or similar parts of 
the invention are identified by like reference numerals, FIG. 1 defines a 
shaft generally illustrated as 10 axially positioned inside a tube 
generally illustrated as 12. Shaft 10 is generally composed of an 
engineering alloy such as AISI 4340 or other commercial alloy of 
sufficient tensile strength. The minimum diameter of shaft 10 is limited 
by the yield strength of the metal alloy used in its construction, but it 
is normally one-third the diameter of the tube. An inner cap 14 is bound 
by nut 16 on the threaded end of shaft 10. An outer cap 18 is mounted on 
shaft 10 so as to be able to slide on and along shaft 10 in a longitudinal 
axial direction with respect to tube 12. 
As depicted in FIG. 2, at least one prong means, generally illustrated as 
20, is attached to inner face 21 of outer end cap 18. A bushing means, 
generally illustrated as 22, is slidably mounted on and along shaft 10 
between inner cap 14 and outer cap 18 for longitudinal axial movement on 
and along shaft 10 with respect to tube 12. Bushing means 22 includes at 
least one longitudinal slot 24 which longitudinally traverses bushing 
means 22 and is sized to mate with prong means 20. For convenience, prong 
means 20 may be inserted within longitudinal slot 24 prior to placing 
bushing means 22 inside tube 12. Elastomeric means 26 is sized to lodge 
within bushing slot 24. Elastomeric means 26 may consist of any elastomer, 
although an elastomer having a high resilience such as hard urethane 
rubber is preferred. Shaft 10, outer cap 18, inner cap 14, prong means 20 
and bushing means 22 may comprise any material having a strength and 
hardness greater than that of elastomeric means 26. 
As depicted in FIG. 3, a retaining means, generally illustrated as 28, 
comprises at least one groove longitudinally traversing the inner surface 
of bushing slot 24. Retaining means 28 serves to hold elastomeric bar 26 
in place when elastomeric bar 26 is in a non-expanded state. Elastomeric 
bar 26 is sized to mate with retaining means 28 when lodged within bushing 
slot 24. 
The invention also comprises a means, generally illustrated as 27, for 
pulling shaft 10 in one axial direction, an upward direction when viewing 
FIG. 4, while simultaneously pushing outer cap 18 in the opposite axial 
direction, a downward direction when viewing FIG. 4, such that when inner 
cap 14 contacts bushing means 22, prong means 20 contacts elastomeric 
means 26. The push-pull means 27 is exemplified by hydraulic pump, 
generally illustrated as 40, and a combination of an outer cylinder 42 and 
an inner cylinder 44. Inner cylinder 44 is located inside outer cylinder 
42 such that the longitudinal axes of both cylinders are concentrically 
aligned. Shaft 10 extends through outer cylinder 42 and inner cylinder 44 
along their respective longitudinal axes. Shaft 10 is secured to inner 
cylinder 44 by end cap 46 and nut 48. Fluid is delivered under pressure 
from pump 40 through fluid conduit 50 into outer cylinder 42. The 
pressurized fluid acting against the inner surface of outer cylinder 42 
transmits a push force through outer cap 18 to elastomeric means 22, while 
at the same time the fluid acting against the outer surface of inner 
cylinder 44 transmits a pull force through end cap 46 to shaft 10. The 
continuing respective axial forces from pulling and pushing, in 
combination with prong means 20 in contact with elastomeric means 26 
within bushing means 22, compress and subsequently radially expand 
elastomeric means 26 at selective locations resulting in the selective 
radial expansion of tube 12 as depicted in FIG. 5. 
When push-pull means 27 is located exterior to tube 12 as depicted in FIG. 
1, outer cap 18 is sized to extend from a location in proximity to an open 
end of tube 12 to the point of contact with elastomeric means 26 in 
proximity to the area of proposed tube expansion. The distance between the 
open end of tube 12 and the area of proposed tube expansion however, 
generally may not be more than ten feet because Euler Buckling principles 
limit the length of outer cap 18 to approximately ten feet. 
When tube 12 has a diameter of approximately three inches or more, the 
push-pull means 27 may be located inside tube 12 as depicted in FIG. 6. 
Hydraulic pump 40 is rigidly attached to outer cylinder 42 by brackets 52. 
Brackets 52 may comprise hollow conduits for the passage of fluid under 
pressure from pump 40, to outer cylinder 42. A pad eye 54, mounted to pump 
40, is attached to a cable (not shown in drawings) in order to lower the 
apparatus inside tube 12 when tube 12 is in the vertical position. The 
ability to place push-pull means 27 inside tube 12 allows tube expansion 
to be conducted at distances greater than ten thousand feet from an open 
end of tube 12 without the Euler buckling limitations of an elongated 
outer cap 18. The only limitations to placing the push-pull means 27 
inside tube 12 is the length of the cable and the abillity of the cable to 
support the weight of the apparatus. 
While the present invention has been described herein with reference to 
particular embodiments thereof, a latitude of modification, various 
changes and substitutions are intended in the foregoing disclosure, and in 
some instances some features of the invention will be employed without a 
corresponding use of other features without departing from the scope of 
the invention as set forth.