Method for the joining of tubular parts in a heat exchanger and tool for practicing the method

The invention relates to a method for joining tubular parts of a heat exchanger that are inserted into each other, as well as to a tool for practicing the method.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for the joining of tubular parts 
in a heat exchanger that are inserted into each other, as well as to a 
tool for practicing the method. 
German Offenlegungsschrift No. 23 32 241 describes a process for the 
joining of tubes that are inserted into each other, whereby the 
telescopically inserted tubes are deformed elastically by means of a 
shaping ring so that a sealing pressure acting in the radial direction is 
obtained in the area of the shaping ring between the inserted tube ends. 
The shaping ring has an orifice, the diameter of which is at least in one 
portion smaller than the diameter of the outer tubular part and is 
sufficiently strong to deform the tubular ends elastically in the radially 
inward direction. When the shaping ring is released, the tubular ends 
regain their original shape elastically and are thereby separated from 
each other. 
Tube joining methods of this type are not suitable for large scale 
industrial production, since the application and the compression of each 
individual shaping ring is highly labor intensive and, consequently, 
expensive. Furthermore, the shaping element must remain in the area of the 
tube joint or otherwise the joint will separate. This has the 
disadvantage, especially in the case of heat exchangers for automotive 
vehicles, that the shaping elements remaining around the tube joint 
increase the weight of the heat exchanger, contrary to the requirements of 
the car manufacturer to reduce the weight. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide an improved method 
for the joining of tubular parts in a heat exchanger that are inserted 
into each other. 
It is also an object of the invention to provide a method wherein several 
tube joints may be created simultaneously and the weight of the heat 
exchanger reduced. 
It is a further object of the invention to provide a tool for the execution 
of the claimed method. 
In accomplishing the foregoing objects, there has been provided in 
accordance with one aspect of the present invention a method for joining 
tubular parts of a heat exchanger, comprising the steps of inserting a 
first inner tubular part into a second outer tubular part and radially 
inwardly deforming an area where the tubular parts are inserted by an 
amount sufficient to cause a plastic deformation of the outer tubular part 
and an at least partial elastic deformation of the inner tubular part. The 
radially inwardly deforming step of the process may include annularly 
surrounding the outer tubular part with a pressure element and then moving 
the pressure element axially over the area where the tubes are inserted. 
In addition, the deforming step may also include radially or tangentially 
moving the pressure element in an open state to the insertion area, 
closing and locking the pressure element around the outer tubular part, 
and, after axial movement, opening the pressure element and removing it 
from the insertion area. 
A tool for practicing the method in accordance with the invention is also 
provided. One embodiment of such a tool comprises at least one pressure 
element comprising first and second segments, said segments being 
displaceable relative to each other and having a parting plane extending 
longitudinally, along which plane each segment provides a recess 
representing one section of an orifice formed when the pressure element is 
in a closed state, said orifice being capable of engaging tubular parts in 
a form-fitting manner; and means for moving the segments of the pressure 
element axially along telescopically inserted tubular parts. 
In another embodiment, the tool is provided with locking means in the form 
of a ram or rams displaceable longitudinally relative to the pressure 
elements. A plurality of rams may be arranged in a comb like manner 
relative to a plurality of the pressure elements. 
In still another embodiment of the present invention, a method is provided 
for joining tubular parts of a heat exchanger comprising the steps of 
placing a first tubular part end-to-end with a second tubular part, the 
tubular parts having circumferential grooves on their respective outer 
surfaces; moving a connecting tube into a position annularly surrounding 
the abutting ends of the tubular parts; and radially inwardly deforming an 
area where the tubular parts abut by an amount sufficient to cause a 
plastic deformation of the connecting tube into the circumferential 
grooves of the tubular parts.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The invention makes possible the joining in a simple manner of tubular heat 
exchanger parts that are inserted into each other, particularly the ends 
of heat exchanger tubes joined with the connecting fittings of a header 
plate or a connecting compartment (for example, the collector tank or 
cooling medium distributing and collecting tank of an evaporator), such 
that a plurality of tube connections may be effected simultaneously and 
the pressure elements are reusable. This has the advantage that the 
production of the heat exchanger takes place in a more economical fashion 
and the weight of the pressure elements is reduced. 
The pressure element is preferably in two parts and is passed in the open 
state radially or tangentially into an area adjacent to the joint location 
over one of the tubes, then is closed and locked and, following the 
completion of the tube joint, it is unlocked and removed in the opposite 
direction. If the distance between two evaporator tubes is large enough so 
that the pressure elements for each tube joint may be introduced 
simultaneously, it is convenient to effect all of the tube joints of a row 
of tubes simultaneously. If the distance between two heat exchanger tubes 
is very small, it is proposed to form every second tube joint of a row of 
tubes in a first working step and subsequently to form the remaining 
joints of the same row in a second step. 
In order to assure the appropriate functioning of the pressure element, 
means to lock the pressure element in the closing position are preferably 
provided. The two parts of the pressure element must be movable relative 
to each other for the insertion and removal of the tool, whereby it is 
possible to arrange the parts of the pressure element pivotingly or 
displacingly in the longitudinal and transverse directions. In such 
arrangements of the pressure elements, the means to lock the pressure 
elements generally consist of rams or specially-shaped elements set in the 
manner of a comb and designed to enter between two pressure elements, 
thereby wedging two adjacent pressure elements against each other. 
A further arrangement of the pressure elements and locking means consist of 
designing the pressure elements in the form of scissor-like devices with 
the orifice of the pressure element being located on one side of the pivot 
point and actuating levers on the other side. The means to lock the tool 
are in the form of rotating cams, acting on the actuating levers. 
The tool according to the invention may have different configurations 
depending on the type of the heat exchanger, wherein the pressure elements 
may have orifices with circular cross sections or with elliptical or oval 
cross sections, for use with heat exchangers with elliptical or oval 
tubes. To adapt the tool to a specific type of heat exchangers it is 
therefore necessary merely to replace the pressure elements with elements 
having the orifice with the necessary cross section; the arrangement 
remains unchanged otherwise. In order to obtain a uniform deformation of 
the tubes and automatic centering during the axial displacement of the 
pressure elements over the tubular parts, the orifice of the pressure 
elements has two axially successive conical sections opening in the same 
direction but with different angles relative to the axis of the tubes. 
The method according to the invention and the tool for its execution will 
become more apparent from the following description of preferred 
embodiments, with the aid of the drawings. 
In FIG. 1, two ends of tubes 1 and 2 are inserted into each other, with 
tube 1 having an expanded end 3. The length of expanded end 3 of tube 1 
determines the length of insertion of tube 2 into tube 1. Symbols 4 and 5 
designate two parts of a pressure element 6; the parts are arranged in the 
open state of the pressure element. Arrows 7 indicate the direction of 
motion of parts 4 and 5 of pressure element 6. 
FIG. 2 shows tubes 1 and 2 in the perspective of FIG. 1. 
Parts 4 and 5 of pressure element 6 are arranged in the closed state of the 
pressure element, producing a conical orifice 9 in pressure element 6. On 
the side facing the bell-like end 3, the conical orifice 9 has a cone 10 
having an angle relative to the axis of expanded end 3 ("opening angle") 
that is greater than the opening angle of orifice 9, serving to center the 
tubes in the pressure element. Arrows 8 indicate the relative motion of 
the pressure element with respect to the tubes after the closing of parts 
4 and 5 of pressure element 6. The diameter of conical orifice 9 is 
smaller on the side facing away from tube 1 than the outer diameter of 
expanded end 3. 
In FIG. 3 tubes 1 and 2 are shown after the deformation effected by the 
axial movement of pressure element 6. It is seen that the originally 
expanded end of the tube 1 is now deformed plastically in the radially 
inward direction, thereby compressing the inserted end of the tube 2. The 
end of the tube 2 is deformed in the radially inward direction, with this 
deformation being at least in part elastic, resulting in a strong press 
fit with the tube 1. 
As seen in FIG. 4, after production of the tube joint, parts 4 and 5 of the 
pressure element are moved in the radially outward direction, indicated by 
the arrows 11; i.e., the pressure element 6 is opened and may be removed. 
If a tube joint of this type is intended for evaporators or condensers of 
air-conditioning installations, it is appropriate to cover the end of the 
tube 2, to be inserted in the expanded end 3 of the tube 1, on its 
circumference with an adhesive, in order to obtain the tight fit required 
to contain the cooling medium. The adhesive is not necessary to increase 
the mechanical strength of the joint. 
FIG. 5 shows a pressure element 6, consisting of two parts 4 and 5 and 
having a conical orifice 9, with the parting plane of the pressure element 
6 passing through the center of said conical orifice 9. 
FIG. 6 shows a pressure element 6' for tube joints with elliptical cross 
sections, wherein the pressure element 6' consists of parts 4' and 5' and 
the parting plane passes along the principal axis of the orifice 9', which 
is elliptical in its cross section and conical in the axial direction. 
FIG. 7 shows the front elevation view of a pressure element 6 with a 
conical orifice 9 and the stopping cone 10. Part 4 of pressure element 6 
has in the parting plane a projection 16 directed toward opposing part 5, 
which projection engages a corresponding recess 17 in part 5, thereby 
forming a tight fit in the direction of the vertical axis of pressure 
element 6. In this manner, it is assured that parts 4 and 5 of the 
pressure element 6 in the closed state do not deviate in the direction of 
the vertical axis and that the conical orifice 9 is always accurately 
formed. 
FIG. 8 shows a tube fitting of a header plate 3 of a heat exchanger, upon 
which an expanded end 3 of tube 1 is placed. On the circumference of tube 
fitting 12, several projections 14 extending in the circumferential 
direction are provided, such that grooves 15 are formed between them. 
Pressure element 6 is located between the bottom 13 and the expanded end 3 
of tube 1, with parts 4 and 5 already closed and surrounding tube fitting 
12 in an annular manner. 
FIG. 9 shows the arrangement according to FIG. 8 after the axial 
displacement of pressure element 6. As described in connection with FIGS. 
1-4, due to the difference in the conical orifice 9 in pressure element 6 
relative to the external diameter of expanded end 3, a deformation of 
expanded end 3 in the radially inward direction takes place during the 
relative axial displacement of the pressure element. Because of the radial 
deformation, the material of expanded end 3 is partially squeezed into 
grooves 15, thereby creating a tight fit joint of the tube fitting 12 with 
the tube 1. 
FIG. 10 shows a top view of a heat exchanger 18, comprising two rows 19 and 
20 of tubes. In row 19, tubes 1 and 2 are telescopically inserted into 
each other. The tool to produce the tube joints includes several pressure 
elements 6, with the number of pressure elements corresponding exactly to 
one-half the number of tubes in a row, and the arrangement is such that 
between two tubes associated with a pressure element there is always a 
tube without a pressure element. 
Each pressure element 6 has two parts 4 and 5, supported pivotably in 
relation to each other on a shaft 21 and shown in FIG. 10 in their open 
position. Each of parts 4 and 5 has a recess 9. A ram 22 is located 
between every two of the pressure elements 6, which are in the extracted 
position, so that parts 4 and 5 of the pressure elements 6 may be pivoted 
apart. In this position the pressure elements may be moved against the 
tubes to be joined and removed after the completion of the joint. 
Expanding springs may be provided for the automatic pivoting apart of 
parts 4 and 5 after unlocking, said springs biasing parts 4 and 5 in the 
direction of the opening of the pressure elements 6. 
FIG. 11 illustrates a heat exchanger 18 according to FIG. 10, wherein the 
pressure elements 6 are closed, i.e., in the position producing the tube 
connections. The closing of the pressure elements 6 and the maintenance of 
their closed state during the production of the tube joints are effected 
by the rams 22 moving between the pressure elements 6 and performing the 
locking of pivoting parts 4 and 5. The rams 22 have recesses 23 to engage 
the tubes 19 located between two pressure elements 6. 
As described in FIGS. 10 and 11, in a first working step only every second 
tube joint of row 19 of tubes is effected, and the remaining tube 
connections created in a subsequent second step. To produce the tube 
joints for row 20, the heat exchanger is suitably rotated, and the process 
described in regard to FIGS. 10 and 11 is repeated. 
FIG. 12 shows a variant of the embodiment in FIG. 11, with a heat exchanger 
18' being displayed again in top view. The heat exchanger has several rows 
19, 24, 25 of tubes, with an odd number of tubes in each row. Every tube 
24 of the inner row is connected with one tube 25 of the following row by 
means of a tube bend 26, the tubes 24 and 25 being connected with the tube 
bends 26, for example, by brazing or by another known method. The tube 
joints of tubes 19 of the border row are produced by the process according 
to the invention and described hereinabove. FIG. 12 shows the pressure 
elements 6 in a closed state with rams 22' in the position locking the 
pressure elements. In contrast to FIG. 11, in the case of the heat 
exchanger shown in FIG. 12, there is sufficient space between two adjacent 
tubes 19 to insert the pressure elements 6 of two adjacent tubes in an 
open state, so that with this configuration all of the tube joints of a 
row (19) may be produced in a single step. 
In FIG. 13 a section on the line XIII--XIII of FIG. 12 is represented. On 
the right side of FIG. 13 a part of the evaporator block 18' is shown, 
with tubes 19 and 24 protruding from it. The end of tube 24 is connected 
with a tube bend 26. A connecting fitting 12 of the cooling medium 
distribution tank 28 is inserted in the expanded end of tube 19. A main 
body 27 of the tool is shown at the left side of FIG. 13; it is equipped 
with a shaft rotatably suporting parts 4 and 5 of the pressure element 6. 
To stabilize parts 4 and 5 in the axial direction, the upper part of shaft 
21 is supported in a strap 9 screwed to the main body 27. On the upper 
edge of main body 27 of the tool, rams 22' are arranged in a comb like 
manner and are displaceable in a longitudinal direction relative to the 
pressure elements. The two parts 4 and 5 of the pressure element surround 
connecting fitting 12, the diameter of which is slightly less than the 
smallest diameter of conical bore 9 of pressure element 6. The symbol 
XII--XII indicates the sectioning line followed by the view of FIG. 12. 
To produce the joint between connecting fitting 12 and tube 19, the 
evaporator block is moved upwardly, whereby pressure element 6 is moved 
over the evaporator tube 19. As described in detail with regard to FIGS. 
1-4, this process causes a radially inwardly directed deformation of tube 
19 and an at least elastic deformation of fitting 12. 
FIG. 14 shows a top view of heat exchanger 18 with two rows 19 and 20 of 
tubes. Corresponding to the number of tubes in a row, pressure elements 
6*, consisting of parts 4* and 5*, are provided. In the parting plane of 
each pressure element 6* there is always one-half of a conical orifice 9*, 
corresponding to orifice 9 as described with regard to FIGS. 10 and 11. In 
the parting plane, part 5* has a projection 30, while in part 4* a recess 
31 is provided. The projection 30 and the recess 31 are arranged so that 
they engage each other in a tight fit when parts 4* and 5* form conical 
orifice 9* in the closed state of pressure elements 6*. Parts 4* and 5* 
are fastened to the tool so that they are supported displaceably in the 
longitudinal and the transverse directions, relative to each other. FIG. 
14 shows the pressure element 6* in the open state, i.e., in the position 
wherein the tool may be introduced in the row of tubes and removed 
following the completion of the tube joints. 
FIG. 15 shows the arrangement according to FIG. 14, with pressure elements 
6* in the closing position. It is seen that in this position the 
projection 30 is completely engaged in recess 31 and that parts 4* and 5* 
engage each other in a tight fit. Pressure elements 6* form conical 
orifices 9*, by which the tubes to be joined are tightly surrounded. To 
immobilize pressure elements 6* in their closed position, punches 22' are 
provided in a comb like arrangement so that they wedge the parts 4* and 5* 
against each other. 
FIG. 16 shows a heat exchanger 18 comprising two rows 19 and 20 of tubes. 
The pressure elements 6 consist of parts 4 and 5 in a scissors-like 
arrangement, supported pivotingly on a shaft 21. On one side of the pivot 
formed by shaft 21, parts 4 and 5 each incorporate one-half of conical 
orifice 9. On the other side of the pivot, parts 4 and 5 of pressure 
elements 6 are extended in the form of actuating levers 37 and 38, which 
are acted on by rotating cams 32. Rotating canms 32 are arranged in pairs 
facing each other on a shaft 33, so that by an angular turn of 90.degree. 
the pressure elements 6 may be moved from the closed position into the 
open position. 
While FIG. 16 shows the pressure elements 6 in the open state, FIG. 17 
displays the arrangement in the closed position. It is seen in FIG. 17 
that the cams 32 are rotated by 90.degree., thereby clamping pressure 
elements 6. Two opposing cams 32 are arranged on shaft 33, and two cams 32 
on a shaft 33 act on lever 37 of a pressure element 6 and on lever 38 of 
the next pressure element 6. The rotating cams 32 thereby clamp not only 
the individual parts 4 and 5 of pressure elements 6, but also two 
successive pressure elements 6 against each other. 
FIG. 18 demonstrates how two tube fittings, which, for example, due to 
their wall thickness, cannot be telescoped together, or which in view of 
their material properties cannot be deformed plastically, may still be 
joined together by the process according to the invention. FIG. 18 shows 
two tube ends 34 and 35, which are fitted end-to-end against each other. 
Tube ends 24 and 25 have circumferential grooves 15 on their peripheral 
surfaces, similar to the tube ends 12 in FIGS. 8 and 9. A connecting tube 
36 is slid over tube end 34 and tube end 35. By means of the pressure 
element consisting of parts 4 and 5, connecting tube 36 is deformed 
plastically in an inward direction and thereby is squeezed into grooves 15 
.