Patent GB-1253342-A (GB)
Title: Improvements in methods of manufacture of laminated structures
IPC: H01F41/02
Filed: 1970-02-20
Abstract: 1,253,342. Welding by pressure; making laminated metal structures. INTERNATIONAL BUSINESS MACHINES CORP. 20 Feb., 1970 [28 Feb., 1969], No. 8192/70. Headings B3A and B3R. [Also in Division C7] A method of making a laminated structure from a plurality of metal laminµ comprises coating at least one surface of each lamina with a thin electrically insulating coating, stacking the laminµ with a coated surface between each adjacent pair of laminµ and heating the stacked laminµ to a temperature and for a time sufficient for metallic tacks to be formed by diffuson bonding, which tacks penetrate the coating in a random pattern to bond each lamina with its adjacent laminµ. The method is described with reference to the making of laminated polepieces 22 and shields 16 for a magnetic recording transducer but is stated to be applicable to other forms of laminated structure, for use e.g. in transformers, motors and generators. For the polepiece 22 the laminµ are of magnetically permeable ductile metallic materials including nickel-iron compositions containing as a minimum about 30% nickel with 1 to 15% of one or two added elements from the group: molybdenum, chromium, manganese, copper, vanadium, titanium, silicon aluminium and tungsten; also included are the iron-nickelcobalt alloy compositions with 1 to 15% of added elements and iron-cobalt alloys having an iron content of 25% or higher the balance cobalt with possibly small amounts of added elements. Specific compositions referred to include the following: 77-83% nickel, 3-6% of molybdenum, balance iron; 47% nickel, 3% molybdenum, balance iron; 77% nickel, 5% copper, 2% chromium, balance iron; 78% nickel, 6% copper, 4% molybdenum, balance iron; 45% nickel, 6% chromium, balance iron; 45% nickel, 5% copper, balance iron. For the inter-track shield 16 the outer laminµ are of conductive magnetically non-permeable material such as copper, brass, silver, bronze, phosphor bronze or aluminium while the inner laminµ may be of the materials referred to for the polepiece 22. The laminµ are normally of thickness of the order of 0À1-5À0 mils. The insulating coating may be an oxide of aluminium, silcion, zirconium, titanium, iron, magnesium, lithium, beryllium, strontium, barium, boron, lead, thorium, tantalum, tin or cerium, or calcium silicate, aluminium silicate, calcium phosphate or magnesium phosphate and may be applied in suspension or formed in situ by the decomposition of suitable compounds or formed by oxidation of the surfaces of the laminµ. In the case of magnetically permeable materials the heating step effects diffusion bonding simultaneously with annealing of the material of the laminµ. Heating may be carried out with the laminµ in an atmosphere of hydrogen or in an inert or reducing gas or under vacuum. A magnetic field may be applied during annealing. In a process, Fig. 5, for manufacturing a polepiece 22, blanks 341 are punched, cut or etched from strip foil 46, coated, stacked on a jig 54, a cover 56 placed on the stack to ensure flatness and contact of the laminµ and the stack heated for a predetermined time to annealing -temperature; unwanted tab sections 58, 62 are then removed and if necessary the polepiece 22 again annealed.