Patent GB-804334-A (GB)
Title: Improvements in or relating to process for joining metallic surfaces and products made thereby
IPC: B23K1/00
Filed: 1955-04-19
Abstract: In joining metal parts, the parts are electroless metal plated with a nickel-phosphorus alloy and are simultaneously or subsequently bonded by the plated metal.  The alloy may contain 2.5 to 15 per cent phosphorus.  Alternate plain sheets and corrugated sheets of a low carbon steel heat exchanger core wire were held in pressure contact and immersed in the following acid bath: 10 grams per litre nickel chloride, 10 grams per litre sodium hypophosphite, 8.9 grams per litre citric acid, 15 grams per litre dibasic sodium phosphate. After twelve hours a nickel-14.15 to 14.75 per cent phosphorus layer was deposited on all faces of the sheets and the peaks of the corrugations were bonded to the adjacent sheets by fillets of plated metal.  This structure was suitable for heat exchange purposes.  In a modification, a core plated as above was heated to 1650 DEG F. in a cracked gas neutral atmosphere when the nickel-phosphorus alloy fused and formed brazed joints.  Two pieces of rod wired with a third piece to form a lap joint were plated in the above bath and then heated to 750 DEG F.  In another example, a structure of mild steel sheets was held and plated with a nickel-6.5 per cent phosphorus alloy in the following acid bath: 30 grams per litre nickel chloride, 10 grams per litre sodium hypophosphite, 50 grams per litre sodium glycollate produced from 70 per cent glycollic acid and a diluted sodium hydroxide solution, to form a plated and bonded assembly.  In a further embodiment, the core of a regenerator unit for a gas turbine engine comprising either concentric rings or two sheets wound in a spiral to form alternate plain and corrugated layers of low carbon steel was plated and bonded by a nickel-10 to 12 per cent phosphorus alloy produced from a bath the same as in the first example but with 37.5 grams per litre of dibasic sodium phosphate.  Alternate flat and corrugated sheets wired together were plated and bonded by a nickel-2.9 per cent phosphorus alloy in the following alkaline bath 30 grams per litre nickel sulphate, 50 grams per litre ammonium chloride, 100 grams per litre sodium citrate, 10 grams per litre sodium hypophosphite.  Similar plates were plated and bonded in the same bath but with 30 grams per litre of nickel chloride substituted for the nickel sulphate.  In a modification, a structure as in the last example was plated for half the time and then heated to 1850 DEG F. in dry hydrogen to form a brazed structure.  In a final example, a heat exchange element of an oil cooler was plated only on its outer sides and the halves of its steel water housing plated on all faces by immersion in the bath of the first example.  After plating, the parts were clamped together and heated to 1800 DEG F. in cracked gas to effect brazing. In the acid plating bath of the first example the dibasic sodium phosphate may be replaced by the corresponding potassium or ammonium salt.  Catalytic metal for the plating may be iron, nickel, gold, cobalt or aluminium.  Metals may be used which are non-catalytic such as brass, copper and platinum by contacting them momentarily with a more electronegative metal, e.g. aluminium, or by coating palladium or rhodium thereon prior to use. Specification 768,854 [Group XIII] is referred to.