Oval bell concept

This invention relates to apparatus for facilitating the construction of a heat exchanger, such as a condenser or evaporator employed in an air conditioning system, wherein exchanger tubes extending through a plate fin assembly are joined together by means of return bend connections or the like. The ends of the tube are provided with an oval shaped bell in which are telescoped the return bends. Diametrically opposed nibs are formed on the outer surface of the return bend connectors near the distal end thereof. The outside diameter over the nibs is slightly larger than the minor inside diameter of the oval bell. The nibs are inserted into the bell aligned along the minor diameter of the opening. The nibs are thus caused to ride in engagement against the wall of the bell to frictionally support the connector in assembly. The joint is then immersed in a molten solder bath whereby solder flows freely into the joint region along the major axis to create a highly reliable joint.

BACKGROUND OF THE INVENTION 
This invention relates to a bell and spigot joint arrangement for 
facilitating the assembling of a heat exchanger and, in particular, a heat 
exchanger utilizing aluminum tubes and tube connectors. 
The joints between tubular components of a heat exchanger as commonly 
utilized in an air conditioning system must provide a high strength fluid 
tight seal. The soldering of this type of joint, particularly where one or 
both of the components making up the joint are formed of aluminum, has 
presented a number of problems in the art. With the advent of the 
ultrasonic dip soldering process, some of these problems have been 
alleviated. However, the configuration of most generally employed tubular 
joints will not allow the male member to penetrate deeply into the bell 
while at the same time providing for a relatively free flow of solder 
material into the deep joint region. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to improve the joints 
formed between tubular components. 
A further object of the present invention is to facilitate the joining of 
aluminum tubular components in a heat exchanger assembly. 
A still further object of the present invention is to provide a bell and 
spigot joint wherein the male member is deeply seated within the bell and 
solder is allowed to freely move into the deep joint region. 
These and other objects of the present invention are attained by means of a 
tubular joint including a male member and female member, the male member 
having a pair of diametrically opposed nibs formed close to one end 
thereof which project outwardly from the surface of the male member, and 
the female member having an oval bell formed in the end thereof having a 
major inside diameter which is substantially greater than the outside 
diameter of the male member, and a minor inside diameter which is slightly 
less than the diametrical overall distance across the nibs whereby 
interference engagement is provided between the male and female member 
when the male member is inserted within the oval bell with the nibs 
aligned along the minor axis thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIGS. 1 through 3, there is shown a tube joint 
generally referenced 10 employed in a heat exchanger 11. The heat 
exchanger can be of the plate fin type wherein a number of parallel rows 
of tubes, such as tube 12, are extended transversely through a plurality 
of spaced apart plate fins 15 supported between two planar tube sheets 16 
(only one of which is shown) to form what is known as "plate fin coil". 
The ends of the tube 12 are brought through one of the tube sheets and the 
ends of the tubes connected by U-shaped return bends connectors 20 or any 
other suitable connector element, such as cross-over tubes, header tubes 
or the like, to complete one or more flow circuits passing through the 
plate fin coil. 
As best illustrated in FIGS. 2 and 3, the outer ends of the tubes passing 
through the tube sheet are expanded outwardly to form what is herein 
referred to as an oval bell 22 having a major axis 23 and a minor axis 24 
(FIG. 1). The bottom portion of the oval is necked or taped down at a 
given angle "A" in reference with the axial center line of tube 12. The 
neck 25 terminates at about the point where the tube passes through the 
tube sheet. In practice, a conventional straight walled bell is first 
formed in the end of the tube utilizing standard tooling. Upon formation 
of the standard bell, an oval shaped punch or bullet is passed into the 
bell to finish the bell geometry without collapsing the tube column. 
The return bend 20, or any other suitable connector, is provided with 
diametrical opposed nibs 27, 28 which protrude outwardly in a radial 
direction from the surface of the connector tube. The dependent nibs are 
formed by scarving a groove 29 axially within the end of the connector 
tube. Sufficient metal is displaced or pushed back during the groove 
forming operation to create the two nibs. The nib forming operation is 
controlled so that the diametral distance over the nibs is brought to a 
desired dimension. This diametral dimension is slightly larger than the 
inside minor diameter of the oval bell. A slight interference is thus 
obtained when the male member is inserted into the bell with the nibs 
aligned along the minor axis as shown in FIG. 1. 
In assembly, the distal end 30 of the connector 20 is passed into the 
necked down portion of the bell and seated tightly against the inside wall 
of the neck 25 adjacent to the tube sheet. By maintaining the angle of the 
taper between 10.degree. and 30.degree., a void is estalished about the 
end of the male connector for accepting solder during the joint forming 
operation. Similarly, by providing taper in this region, the male member 
can be deeply seated within the bell thus reducing the possibility of the 
filler material entering the tubes during the joint forming operation. 
As best seen in FIG. 1, when the male member is seated in the bell as 
described above, two generous flow passages 33, 34 are established along 
the major diameter of the bell between the outer surface of the male 
member and the interior wall of the bell. These generous openings allow 
solder to freely flow into the entire joint region. 
With the male connector inserted with the oval bell as shown, the nibs 
engage the inner surface 35 (FIG. 1) of the bell so as to center the male 
member therein and thus seats the distal end of the male connector in 
continuous contact against the tapered bell region. As illustrated in FIG. 
3, upon completion of the assembly, the joint or joints are passed into a 
solder pot 36 containing a bath of molten solder 37 or any other suitable 
filler material or alloy thereof. One or more transducer elements 38 are 
affixed to the bottom wall of the solder pot which, upon actuation, create 
ultrasonic vibrations within the liquid bath material. As can be seen, the 
generous openings formed along the major axis of the bell allows the 
liquid solder to freely flow into the tapered regions so as to establish a 
complete filling of the joint with molten metal. Applying ultrasonic 
energy to the bath brings the energy to the joint region where it acts to 
break down any unwanted oxides which form on the tube surface. This, in 
turn, permits the solder to wet the tube surfaces and thus produce good 
metallurgical bonding resulting in the formation of a reliable joint. 
The use of the oval bell arrangement in conjunction with the ultrasonic dip 
soldering process provides for the efficient bonding of the tubular 
elements particularly when one or more of the elements are formed of 
aluminum or aluminum based alloys. As should be clear from the disclosure 
above, when the male member is frictionally secured in the bell and the 
bell immersed in the bath, the grooves 29 formed below the nibs 27, 28 
vent the soldering cavity to the interior of the tubular elements. 
Accordingly, any gases generated during the soldering operation are passed 
into the tubes from where they can be drawn in a manner known and used in 
the art. 
While this invention has been described with reference to the structure 
herein disclosed, it is not confined to the details as set forth and this 
application is intended to cover any modifications or changes that may 
come within the scope of the following claims.