Header jig

A jig for use in manufacturing header assemblies from pipe and tubing. The jig assures the proper orientation and alignment of components during fit up and joining of component parts into a complete header assembly. In addition, the jig is configured to direct a flow of a purge gas that blankets the interior surfaces of the header assembly during a joining process such as soldering, brazing or welding and thus prevents oxidation of those surfaces.

BACKGROUND OF THE INVENTION 
This invention relates generally to devices used in manufacturing 
assemblies from metal pipe and tubing. More particularly, the invention 
relates to a jig for use in fitting up and joining header assemblies used 
in heat exchangers. The jig includes an integral gas purging capability. 
A header, sometimes called a manifold, is a conduit into which a plurality 
of other conduits open. Headers are widely used in a variety of 
applications, particularly in the air conditioning and refrigeration 
industry. A typical application in that field is in conjunction with tube 
type heat exchangers. In order to reduce the total pressure drop across a 
given heat exchanger, the refrigerant flow through the heat exchanger may 
be split into two or more parallel flow paths, or circuits. This is done 
by installing an inlet header and an outlet header on the upstream and 
downstream sides of the heat exchanger, respectively. The inlet header 
receives a flow of refrigerant from a single conduit and distributes the 
flow to the various parallel flow paths in the heat exchanger. The outlet 
header receives the flow from the parallel flow paths and directs a single 
flow of refrigerant to components downstream of the heat exchanger. 
Tube type heat exchangers used in air conditioning and refrigeration 
applications are generally made of copper pipe or tube. Headers used in 
the same applications are also generally made of copper pipe or tube. Such 
a header comprises a pipe or tube of a relative larger diameter having 
smaller diameter tubes that join into it. In a typical manufacturing 
operation for the large scale production of heat exchangers, header 
assemblies are usually prefabricated with short nipples, or stubs, of tube 
of an appropriate diameter extending from the header at appropriate 
positions and orientations. The prefabricated header assembly is then 
assembled to its heat exchanger by joining the nipples to the heat 
exchanger tubing to form the parallel flow paths. 
Tube nipples are generally joined to a header by insertion into 
appropriately prepared apertures in the ends or side-wall of the header 
tube. The nipples are then joined to the header by a process such as 
soldering, brazing or welding to form a joint that is both fluid tight and 
mechanically sound. There is usually a shoulder formed in or attached to a 
nipple at an appropriate distance from the end to be inserted into the 
header in order to improve the quality of the finished joint and to assure 
the correct insertion distance. 
If the nipple is fitted up and joined to the header manually by an assembly 
worker, as is frequently the case, the nipple alignment is dependent on 
the skill of the worker. Even slight misalignment of a nipple can 
complicate assembly of a header to a heat exchanger. One technique for 
attaining the proper fit in a finished header is to bend the nipples to 
the correct alignment using, for example, an aligning jig. But such a 
procedure is labor intensive, can subject the nipples and the nipple joint 
to excessive stress and introduces another step into the heat exchanger 
assembly process. Manual joining of nipples to the header is in itself 
time consuming and labor intensive. 
In order to properly braze a joint, the metal surrounding the joint must be 
heated to a relatively high temperature. In a copper header and nipple 
assembly of the size and configuration used in the typical air 
conditioning or refrigeration heat exchanger, the entire assembly will be 
subjected to high temperatures. At high temperatures and in the presence 
of oxygen, copper will oxidize. Thus copper oxides may form on and in the 
header assembly during brazing, either as loose particles or as an oxide 
coating on the tube walls. A brazed header assembly must be free of copper 
oxides before it is installed into a refrigeration system, for loose 
particles may cause damage to other system components, e.g. the 
compressor. It is not sufficient to remove just the loose particles, for 
particles may become detached from the coating some time after header 
assembly to contaminate the system. The interior of header assemblies can 
be cleaned to remove the oxides of copper, but the cleaning process is 
difficult and expensive. 
It is axiomatic that, even at high temperatures, in the absence of oxygen, 
copper will not oxidize. Oxygen can be excluded from contact with hot 
copper by blanketing the surfaces with a suitable gas. Thus, a gas purge 
of the interior of a header assembly during brazing of the nipples will 
prevent the formation of copper oxides, leaving bright interior surfaces 
that do not require cleaning. Such a purge must, however, blanket the 
entire internal surface of the header assembly and therefore there must be 
provisions to insure that the purge gas can reach all interior areas of 
the header assembly. 
SUMMARY OF THE INVENTION 
The present invention is a jig for ensuring proper fit up and alignment of 
nipples during assembly and joining to a header. The jig includes a purge 
gas system. The purge gas is distributed to all regions of the interior of 
the header and nipple assembly so that oxygen is excluded and thus 
oxidation of the interior surfaces prevented. 
The key component of the jig is a nipple alignment and holding apparatus. 
The apparatus has nipple support sleeves that are fixed to a purge gas 
manifold in the same relative position and alignment as the tubes with 
which the header nipples will mate. Thus, when nipples are inserted into 
the sleeves, they will be in the alignment necessary for assembly into a 
heat exchanger. The purge gas manifold is generally cylindrical with its 
longitudinal axis oriented generally horizontally. The apparatus may be 
rotated about the longitudinal axis. Except for its freedom to rotate, the 
apparatus is fixed with respect to a header support means. When a header 
is placed in the header support means, the longitudinal axis of the header 
is properly oriented to the purge manifold axis. When resting in the 
header support means, the header is also at a distance from the nipple 
support sleeves that results in the nipples being properly positioned in 
the header. Because the alignment and holding apparatus rotates, it may be 
moved to a convenient position for fitting up the nipples and header into 
a complete assembly. The alignment and holding apparatus is then moved so 
that the header rests in the header support member. In this position, the 
header and nipples are fixed with respect to each other and in the proper 
relative positioning to insure a correct fit when the header assembly is 
assembled into a heat exchanger. The jig holds the assembly in the proper 
position for manual brazing or brazing by an automatic or semiautomatic 
process. 
There is a gas, for example nitrogen, supplied to the purge gas manifold. 
The nipple sleeves are in fluid flow communication with the manifold. Gas 
flows from the gas supply through the manifold, the nipple sleeves, the 
nipples and the header and exits the header through a convenient opening. 
Supplying gas to all the nipples insures that the gas reaches and blankets 
all of the internal surfaces of the nipples and the header, thus 
preventing oxidation of those surfaces during brazing operations.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 depicts, in an isometric view, a header jig embodying the present 
invention. FIG. 2 provides a detail assembly view of the nipple sleeve of 
the jig of the present invention as well as a portion of a workpiece 
header and nipple. In FIG. 1 is shown header jig 10 having jig base 11. 
Fixed to base 11 are workpiece support members 15, having at their upper 
extremities provisions for holding a workpiece header. Such a header 101 
is shown for illustrative purposes. Also fixed to base 11 are nipple 
alignment and holding apparatus support members 13. Each holding apparatus 
support member 13 has a bearing 17 at its upper extremity. Mounted in 
bearings 17 is nipple alignment and holding apparatus 19. Holding 
apparatus 19 comprises generally cylindrical manifold 12 to which are 
affixed one or more nipple sleeves 14. The orientation of the longitudinal 
axis of manifold 12 is fixed with respect to jig base 11 and thus to the 
axis of a workpiece header placed in workpiece support members 15, but 
holding apparatus 19 may rotate about the longitudinal axis of manifold 12 
in bearings 17. 
Manifold 12 and nipple sleeves 14 are most conveniently manufactured from 
rigid pipe of appropriate dimension and heat resistance. Nipple sleeves 14 
are sized so that their inner diameter is slightly larger than the outer 
diameter of the tubing that is used to form workpiece nipples 102 that 
will be used to join with header 101 to form a completed header assembly. 
Nipple sleeves 14 are in fluid flow communication with manifold 12 so that 
a gas introduced into holding apparatus 19 through gas supply fitting 16 
will flow through manifold 12 and then out of manifold 12 through nipple 
sleeves 14. 
The relative positions of the tube ends in the heat exchanger on which the 
completed header assembly will be mounted are known. Nipple sleeves 14 are 
mounted on manifold 12 so that they are in that same relative position. 
Therefore, when nipples 102 are inserted into and held in place by nipple 
sleeves 14 and then joined to header 101 by a suitable process such as 
brazing, the nipples will be correctly oriented to mate with the tube ends 
in the heat exchanger. 
In a separate manufacturing step, workpiece headers 101 are prepared by 
cutting pipe or tubing to an appropriate length and drilling nipple holes 
104 (FIG. 3) at appropriate points in the wall of the header. A particular 
header assembly design may also call for nipples at an end or ends of a 
header in which case the end or ends would also be prepared to receive 
nipples. In still another separate step, nipples 102 are prepared by 
cutting pipe or tubing to an appropriate length and by forming a 
protruding bead or shoulder 103 (FIG. 3) at an appropriate distance from 
one end of the nipple by an appropriate process. Shoulder 103 assures the 
insertion of nipple 102 into nipple hole 104 the proper distance and also 
provides a good mechanical joint for the joining process. Either the 
header preparation step or the nipple preparation step may include pipe or 
tube bending as a substep. 
In a typical header assembly manufacturing process, an operator rotates 
nipple alignment and holding apparatus 19 so that nipple sleeves 14 are at 
a convenient angle. The operator then inserts appropriate nipples 102 into 
appropriate nipple holes 104 in header 101 until shoulders 103 contact the 
header. The operator then inserts nipples 102 into nipple sleeves 14. 
Nipple sleeve internal shoulder 18 (FIG. 3) insures proper insertion 
distance. The operator then rotates nipple alignment and holding apparatus 
19, containing the assembled header assembly, down until header 101 rests 
in workpiece support member 15. With a header assembly loaded and 
positioned in header jig 10 in this manner, nipples 102 are properly 
inserted into header 101 and properly aligned by nipple sleeves 14, and 
the header assembly is held in place for joining the nipple to the header 
by an appropriate process such as soldering, brazing or welding by a 
manual, semiautomatic or automatic joining process. 
A supply of an appropriate purge gas, such as nitrogen, is connected to gas 
supply fitting 16. FIG. 3 is a schematic of the purge gas flow path 
through header jig 10 and a workpiece header assembly. Before commencing 
the joining process, the operator starts a flow of purge gas into nipple 
alignment and holding apparatus 19. The gas flows through manifold 12 and 
nipple sleeves 14 into nipples 102 and then into the interior of header 
101. The purge gas blankets the interior surfaces of nipples 102 and 
header 101, excluding oxygen that would otherwise contact those surfaces 
and thus prevents the formation of copper oxides on the interior surfaces 
in the high temperature environment caused by the joining process. Because 
purge gas flows through all of the nipples, the gas is able to completely 
blanket the interior surfaces of the header assembly. 
A useful auxiliary to header jig 10 is stripper assembly 30. After the 
brazing or other process, a completed header assembly may still be 
extremely hot for some time, causing handling problems even to an operator 
wearing gloves. 
Stripper assembly 30 allows the removal of the hot header assembly without 
manual contact by the operator. Stripper assembly 30 comprises stripper 
arms 34 fixed to stripper shaft 31. Stripper shaft 31 is mounted to jig 
base 11 in stripper shaft bearing and support members 33 so that shaft 31 
may rotate about its longitudinal axis in bearing and support members 33. 
To remove a header from jig 10, the operator rotates shaft 30 using 
operating handle 32 so as to raise stripper arms 34 to contact header 101. 
Further rotation of shaft 30 causes stripper arms 34 to draw header 101 
out of workpiece support members 15 and nipples 102 out of nipple sleeves 
14, removing the header assembly from the jig. 
One skilled in the art will appreciate that the header jig depicted in FIG. 
1 is capable of use in the production of one or, at the most, a very few 
specific header assembly configurations. Such a person will also 
appreciate that in a modern manufacturing operation, there will be 
requirements to make a wide variety of header configurations. This 
requirement may be satisfied by making a header jig that has adjustable 
workpiece and manifold support members and a number of appropriately 
configured nipple alignment and holding apparatus. A change in header 
configuration requirements could then be accommodated by adjustments in 
the support members and installation of the proper alignment and holding 
apparatus. That capability is contemplated within the scope of this 
invention. 
However, jig reconfiguration can be laborious and time consuming. The 
materials needed to make a header jig as described above are readily 
available and relatively inexpensive. It is probably more time and cost 
effective, therefore, to fabricate a separate and complete jig for every 
header assembly configuration that is required.