(57) A process for producing a flat heat exchange tube (A) having parallel refrigerant
passages (6) in its interior and comprising flat upper and lower walls (1,2), opposite
side walls (3,4) and a plurality of reinforcing walls (5) connected between the upper
and lower walls (1,2), extending longitudinally of the tube (A) and spaced apart from
one another by a predetermined distance, using a rolling mill (33) comprising a central
work roll (35) and a plurality of planetary work rolls (36) arranged around a portion
of the periphery of the central work roll (35) and spaced apart circumferentially
thereof, the central work roll (35) being formed with parallel annular grooves (39,40)
in the periphery thereof. An aluminum sheet blank (30) comprising a brazing sheet
is rolled by the mill (33) and thereby thinned to a predetermined thickness to form
a flat portion serving as the lower wall (2), cause the annular grooves (39) at opposite
roll ends to form upright portions (12) providing the respective side walls (3,4)
and the other annular grooves (40) to form vertical ridges providing the reinforcing
walls (5), the upright portions and the vertical ridges projecting from the flat portion
integrally therewith. An aluminum sheet (20) comprising a brazing sheet is placed
over all the ridges to provide the upper wall (1) and joined to the upright portions
to make the upright portions serve as the opposite side walls (3,4), and the ridges
of the lower wall are joined to the upper wall to form the reinforcing walls (5).
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