Field problems on the magnet roll were generally solved and the results were applied to a cylindrical sleeve rotating around a magnet rod and conveying a magnetic carrier layer thereon. The magnetic pressure acting upon the magnetic carrier layer, the capacity of carrier conveyance on the sleeve and influences thereupon due to the friction of the sleeve surface were calculated. Further magnetic pressure acting upon toner particles between magnetic carrier particles is microscopically estimated. It is concluded that the magnetic pressure may sometimes be sufficient to crush toner particles between carrier particles, when the magnetic field is high. Roughening of the sleeve surface results in a weaker magnetic field than is usually used, in a remarkable improvement not only in the carrier conveyance capacity but also in prevention of the sleeve surface exposure which is caused near the magnetic poles by doctor scraping. Besides, by use of an apparatus freshly designed in order to measure the doctor blade resistance, conspicuos minima and maxima were found to occur a little in advance of the magnetic poles, say “P”, and of the middle points between adjacent magnetic poles, say “R”, respectively. These extremum values increase approximately in proportion to the 2nd power of the field intensity. Their distances from “P” and “R”, respectively, are approximately proportional to the doctor scrape depth, therefore the extremum points coincide with “P” and “R”, respectively, when the doctor scrape depthbecomes nil.
