Enclosed-type magnetic disc recording and/or reproducing apparatus

Claim 1

An enclosed-type magnetic disc recording and/or reproducing apparatus comprising: a base, a disc cover to define an enclosed chamber between said cover and said base, a bearing unit having two ends, one end protruding into said enclosed chamber from said base and the other end exposed to open air at atmospheric pressure, a shaft borne by said bearing unit and having a tip end protruding into said enclosed chamber, a flange attached to the tip end of said shaft, fitted with a magnetic disc so as to be rotated integrally therewith, and defining along with said base a separate pressure chamber within said enclosed chamber to surround said bearing unit and isolate said bearing unit from said enclosed chamber, a spiral groove for raising the air pressure within said pressure chamber to a level above that in the enclosed chamber, and means for rotating said shaft, said flange attached to the tip end of said shaft, and said magnetic disc, said pressure chamber within the enclosed chamber having a first cylindrical projecting member projecting toward the flange from the base so as to surround the bearing member and a second cylindrical projecting member projecting toward the base from the flange so as to surround the bearing member and rotate relatively to the first projecting member with a suitable length of the free end portions of both projecting members overlapping each other with a space left between said portions, both cylindrical projecting members being concentric with the shaft and having inner diameters larger than the diameter of the bearing unit, whereby said pressure chamber is formed between the projecting members, the base and the bearing unit; and said spiral groove being formed on the overlapping portion of the second projecting member facing the first projecting member to force air through the space left between the overlapping portions of the first and second cylindrical projecting members by introducing low-pressure air which surrounds said pressure chamber into the pressure chamber by relative rotation between the projecting members as produced by rotation of the shaft.