GB812295A - Improvements in or relating to processes for the manufacture of sintered bodies having soft magnetic properties - Google Patents

Abstract

812,295. Powder metallurgy. SIEMENSSCHUCKERTWERKE A. G. June 8, 1956 [June 8, 1955], No. 17874/56. Class 82(1) [Also in Group XXXV] A process for producing a sintered body of soft magnetic-properties, high permeability and low eddy-current loss comprises adding to a metal or alloy powder of soft magnetic properties and high permeability an insulating material consisting of a mixture of at least two insulating materials in colloidal form which react chemically with each other under subsequent sintering conditions. Iron and silcon-containing iron are particularly suitable metals; colloidal mixtures of alummia and silica or magnesia and silica in amylacetate, water, &c., are preferred insulating materials, used in a proportion of 0.5 to 10 per cent by weight. In an example soft iron powder of mean grain size about 0.3 mm., or as wafershaped particles up to more than 1 mm. long and wide and 50# thick, is mixed in amylacetate containing colloidal alumina and silica in suspension. The amylacetate is evaporated off and the powder pressed in a mould, the alumina and silica together amounting to about 2 per cent of the weight of the powder. The compact is then pre-sintered in vacuo or in hydrogen at 900‹ to 1100‹C.; either cold compacted under 6-8 tons per sq. cm. or hot compacted at 600‹ to 800‹C. under 2-6 tons per sq. cm., sintered in vacuo or in hydrogen at 900‹ to 1300‹C., and cooled slowly. The compacting pressure p is applied, as shown in the drawing, in a direction perpendicular to the subsequent magnetic flux application. The metal particles are preferably wafer-shaped and comprise a mixture of iron containing 4 to 6 per cent combined silicon, and 20 to 40 per cent iron powder. The colloidal particles should be of the order of 10-6 mm. in size. The metal particles may be surface oxidized by pre-heating in an oxygen or steam-containing atmosphere.