| 摘要 |
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. Upon subsequent induction of magnetic field, the powder is lifted from the net and onto the bottom roll wherefrom it is further transferred onto the top roll during rotation of the rolls. The action of magnetic field is discontinued after treating a prescribed amount of sheet material; the magnetic field is initiated prior to feeding a sheet material into the gap between the rolls. |
