Patent GB-876449-A (GB)
Title: Sheet or plate metal articles having hollow sections and method of making the same
Inventor: JOHNSON WALLACE COLLISTER
IPC: B23K28/00
Filed: 1959-08-11
Abstract: 876,449. Making heat exchanger panels; jointing by rolling. OLIN MATHIESON CHEMICAL CORPORATION. Aug. 11, 1959, No. 27465/59. Classes 83 (2) and 83 (4). A method of making composite plate or sheet metal articles having hollow formations, for example heat exchange structures for refrigerators, comprises forming a pack structure having outer metal members and having inner metal members in areas between said outer members which are to be welded together and also having stop weld material in other areas, heating and rolling the pack structure to effect welding in the first mentioned areas and to reduce the thickness of the structure, and applying fluid pressure between said outer members in the unwelded areas to expand the outer members to produce the desired hollow formations. In an embodiment the pack structure comprises outer metal members 20a and 20b (Fig. 3), inner metal inserts 21, side metal inserts 22, stop weld material 23 and outer metal members 24, 25, 26 and 27 coated with stop weld material on sides adjacent the outer and inner metal members and inserts respectively. The inserts may take the form of a coating or layer plated on the inner surfaces of the outer members. The stop weld material 23 comprises a mixture of 87% zirconium silicate sand, 10% mica and 3% bentonite clay. The stop weld material 28 to 31 consists of magnesium oxide, aluminium oxide or zirconium oxide. The pack structure is heated to 900‹ to 1050‹ F. for aluminium structures, 1300‹ to 1800‹ F, for copper structures and 2000‹ to 2300‹ F. for steel structures and rolled to the configuration shown in Fig. 4. The desired final thickness may be obtained by cold rolling. The outer metal members are removed and the hollow sections 20 are formed by removing the stop welds 23 and inflating by fluid pressure (Fig. 2). The inserts may be of a different metal to that of the outer metal members. In another embodiment the pack structure comprises two outer members 34 and 35 (Fig. 8), inserts 36 and 37 and stop weld material 38. This structure is treated as hitherto to form an article as shown in Figs. 10a or 10b which may be provided with an external cladding e.g. of porcelain enamel. For cladding the inside of the hollow formations as shown in Fig. 16 flattened metal tubes 50 filled with stop weld material 51 are placed between the outer members 48 and 49 of the pack structure (Fig. 14). Shaped inserts 52 may be used to fit the sides of the tubes or the latter may be trimmed to fit snugly against the straight sides of the inserts. A weld-promoting flux is provided on one or both surfaces to be bonded e.g. by spraying or dipping in a mixture of 2.6 parts potassium, 1 part boron, 1.8 parts fluorine and less than 0.1% sodium in hot water. The flux may be included in the stop weld material to give off a gas during heating of the pack structure. For example, sodium fluoride will release florine and sodium chloride, chlorine to dissolve oxides on the surfaces to be bonded. An oxidizer, as disclosed in Specification 876,448 may be used as an addition to the stop weld material to aid in the prevention of oxidation.