Importance

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Abstract

A core shaft having lugs protruding from its outer circumference to grip winding cores such as a paper tube is provided, wherein the movement of the lugs within a shell of the shaft is inhibited thereby to secure concentrical gripping of the winding cores with the core shaft and to prevent from decentering and vibration or runout of the winding cores, eventually enabling a smooth winding or unwinding of a sheet material. The core shaft has plural sets of the lugs arranged axially in spaced relationship, at least one set of the lugs being disposed circumferentially equidistantly relative to the center of the shaft; an inner core tube for introduction of air disposed in a central part of the shaft; air cylinders having an inclined wall disposed between the inner core tube and the lugs, the inclined wall being axially movable; and slide fittings having a reverse inclined wall disposed in abutting contact with the inclined wall, the slide fittings being fitted with the lugs so that when the inclined walls are displaced by passage of air through the cylinders, the lugs protrude equally or retract from the outer circumference through the slide fittings. The air cylinders may contain therein a spring member with a retainer, a piston for the cylinder and an air chamber for the passage of air, whereby to move the inclined walls with the spring members or pneumatically, thus protruding or retracting the lugs.

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First Claim