Abstract: An apparatus is provided with two rolls made of a magnetically conductive material, spaced to define a passage for a sheet being worked. Either at the first ends, or at both ends of the rolls there are provided means for inducing a magnetic field, so arranged that the magnetic lines extend axially of the rolls and cross the gap therebetween, whereby the rolls act as the opposite pole pieces of a single magnetic system and are designed to retain the ferromagnetic powder which, with the rolls rotating, is pulled through the gap therebetween in a layer used to work the sheet material. The apparatus incorporates a device for levelling out the distribution of the grains of the ferromagnetic powder throughout the length of the gap. The device can be made in the form of a blade positioned to cut off a part of the magnetic powder body at the extremities of the rolls, which enhances the uniform distribution of the grains.

Abstract: An apparatus comprises two rolls having a gap therebetween for the passage of sheet material to be treated and rotating in opposite directions. There is also provided a means for exciting magnetic field, with the lines of force passing along the axes of the rolls and across the gap formed therebetween. The rolls, therefore, serve as opposite poles of magnetic system which enables the ferromagnetic powder used to be retained on the surfaces of said rolls under the effect of magnetic field. Mounted underneath a bottom roll is a net with the mesh size thereof being slightly less than a minimum permissible size of the powder grains. The net is disposed within the zone of magnetic field of said magnetic system. The apparatus is fitted with a switch adapted to discontinue the action of magnetic field, whereupon the powder pours down on the net and through it if unsuitable for further use.