This document describes improvements to heat exchanger tubes made of thin-walled aluminum or light alloy. It discusses two improved modes of manufacturing the tubes. The first involves forming a strip into a tube shape with the longitudinal edges turned inward and joined. The second involves forming a tube from two complementary strips with abutting longitudinal edges joined. Both methods involve coating the strips with brazing filler and brazing the joined edges.

1. * GB780045 (A)
Description: GB780045 (A) ? 1957-07-31
Improvements relating to tubes for heat-exchangers
Description of GB780045 (A)
PATENT SPECIFICATION
Inventor: ERIC MORGAN I-ITCUHEN Date of filing Complete Specification:
Jan. 4, 1956.
Application Date: Jan. 21, 1955.
No. 1853/55.
? Complete Specification Published: July 31, 1957,
Index at acceptance:-Class 83(2), A26, A122(J: K: L).
International Classification:-B23p.
COM;PLETE SiPECIOFITCATlON Improvements relating to Tubes for
Heat-Exchangers We, MORRIS MOTORS LIMITED, of Radiators Branch,
'Osberton Works, Oxford, a British Company, do hereby declare the
invettion, for which we pray that a patent may be granted to us, and
the method by which it is to be performed, to be particularLy
described in and by the following statement:-
This invention relates to heat-exchanger tubes of thin-walled brazed
aluminium or light alloy construction, and of flattened oval or
quasi-rectangular shape in cross-section..
Although tubular heat-exchangers of brazed aluminium or light alloy
construction, are comnmonly installed in aircraft, the method employed
for fabricating their tubes is too costly to be adopted for most other
applications; especially radiators for motor vehicles when it is a
question of large-scale producdon. Usually the tubes,of such radiators
are made of very thin brass or copper strip stock in a tubeforming
machine which also creates a lap or lock seam. However, aluminium or
light alloy tubes for heat-exchanger matrices of brazed construction
need to be made of 25:considerably thicker gauge stock than their
brass or copper counterparts, the thicknesses normally being of the
order of 0.01156 inch land 0.005 inch respectively. The thicker
material militates against the production 'of lock seam's by rolling,
and neither the foarm, of the joint nor the joint clearances can be

2. satisfactorily controlled with the result that flux becomes trapped in
the joint during brazing, and rapid corrosion subsequently occurs in
service.
The present invention affords two improved modes of manufacture, one
being 'a modification of the other. The first one is characterized in
that the tube is fabricated from aluminium or light alloy strip,
having a 'coating of brazing filter, by forming the strip to the
required shape with its.coating on. the outside and with the
'longitudinal edge zones turned inwardly and juxtaposed in contact,
the resulting joint being brazed.
dIn the second mode of manufacture in accordance with the invention
the tube is of twpart construction and formed by a com[Price 3s. 6d.]
plementary pair of strips of aluminium or light alloy coated with
brazing filer, the longitudinal edge zones of the strips being turned
inwardly and juxtaposed with their respective coatings abutting, and
the resulting joints being brazed.
Preferably, in carrying out either of thealternative methods of
manufacture, the abutting coated surfaces are arranged to meet in the
principal plane of the tube, the brazed jointing being situated at one
of the tubenoses or at both of them, as the case may be.
An important advantage accruing from the invention is that the tube
jointing is open to the action of the flux before the brazing filler
(which may be an aluminium-sitlicon alloy) commences to; melt, tand
the jointing does not retain the flux after brazing. Consequently
subsequent corrosion, that would otherwise result from entrapment of
flux by the tube joint,,or joints, is obviated!.
In one manufacturing process, the coated strip stock is fed at high
speed from a reel to a tube-forming machine producing a continuous
length of tube from which the individual lengths of tube are cut off
by a flying shear. {An alternative procedure is to form the tubes from
pre-cut lengths of coated strip, by employing a series of normal
press-tool operations. In either case the brazing of the tube joints
is effected in the course of brazing the assembled matrix.
Examples of heat-exchanger tubes fabricatedx in accordance with the
invention are Illustrated in the accompanying drawings, in Which:
Figure 1 is a fragmentary perspective view of one form of
construction,; Figure 2 is 'a similar view of another form of
construction, employing the same method of manufacture; and Figure 3
is a similar view of a further form of construction, employing a
modified method of tmanufacture.
The tube A (Fig. '1), of flattened oval or quasi-rectangular shape in
cross-section, is fabricated from aluminium or light aloy strip stock
fcoated on at least one side with brazing m '.' Cc1780,045 filler B
(an aluminium-silicon alloy which is available commercially). The

3. strip is formed to the required tubular shape with its coating B on
the outside, and the longitudinal edge zones C of the strip are turned
inwardly and juxtaposed in contact, the resulting joint being brazed.
In this particular embodiment the abutting coated surfaces are flat,
as depicted at D.
In the case of the tube E (Fig. 2) the same method of manufacture is
employed, but the inwardly turned longitudinal edge zones F are formed
so that their abutting portions each have a convex curvature G, and
therefore make virtually line contact when brought together.
Instead of fabricating the tube from a single strip, the modified
method exemplified in Figure 3 may be employed. The tube H is of
two-part construction, being assembled from a complementary pair of
strips J of aluminium or light alloy coated on the outside with the
brazing filler B. The longitudinal edge zones C of the two strips are
turned inwardly and juxtaposed with the coatings B abutting, the
resulting joints at the tube-noses being brazed.
The abutting coated surfaces may either be fiat, as indicated at D, or
curved as shown at G (Fig. 2).
If desired, that side of the strip stock which is to constitute the
inside of the tube may be provided with a protective coating K, such
as aluminium-zinc alloy, in order to achieve sacrificial corrosion
resistance.
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* 5.8.23.4; 93p