Abstract: An electrical coil assembly comprises a rectangular annular coil and a dustproof cover therefor. The cover is formed of a folded blank of electrically insulating sheet material which has a rectangular annular portion with a rectangular aperture. A first pair of opposed flaps and a second pair of opposed flaps are integrally joined to the external periphery of the portion. Each flap has a first tongue portion which is passed through the aperture and a second tongue portion which overlies a respective side of the aperture in the coil. The width of each tongue portion is greater than the length of the respective side of the aperture in the coil. The width of each tongue portion is not greater than the length of the respective side of the apertures. This blank is easy to assemble into a cover and there is a reduced risk of tearing the flaps.

Abstract: An electrical coil assembly comprises a rectangular, flat annular coil and a flexible annular covering of, for example, fibre board sheet surronding the coil so as to provide a substantially dustproof seal. The covering is formed by folding and glueing a blank around the coil. The blank comprises a rectangular annular portion a first pair of flaps extending one from each of two opposite outer peripheral sides of the annular portion, a second pair of flaps extending one from each of two opposite sides of the inner periphery of the annular portion and further flaps extending from the outer periphery of the annular portion. The annular portion is provided with fold lines and is of a size, when folded, to overlie opposite faces of the coil and the flaps fold around the inner and outer peripheries of the coil to provide a substantially dustproof seal.

Abstract: A method of manufacturing a yoke for a dynamo electric machine wherein a transversely divided two-part mandrel is inserted into a hollow ferromagnetic sleeve of wall thickness and diameter equal to that of the required yoke. The mandrel defines the shape of the poles to be produced on the yoke and a plurality of punches are driven radially inwardly towards the yoke to deform the material of the sleeve into the dies defined by the recesses of the punches.