Method for forming a green body of ceramic arc tubes used for a metal

Abstract

A ceramic green arc tube for a metal vapor discharge lamp wherein an outer diameter of the arc discharging portion is larger than that of the end portions holding the discharging electrodes is produced by preparing a stiff plastic body consisting mainly of a ceramic material or which main component is alumina, and a binder of which main component is thermal geltinizing organic substance; forming the prepared body into a straight tubular body by means of an extruder; placing the tubular body into an inner cavity of molding die having the above described ceramic arc tube shape wherein the molding die has been previously heated; closing one end portion of the tubular body; applying a compressed fluid from another opened end portion of the tubular body into the inside of said tubular body to inflate the central portion of tubular body until contacting to the inner cavity surface of the molding die,; hardening and drying the inflated body with the heat of previously heated molding die; and ejecting the dried body from the die. This production is characterized in that the forming is effected by using a die comprising two halves of die divided by a plane parallel to an axial direction of the tube, said two halves forming an inner circumferential cavity conforming to the shape of the tube when the two halves are engaged, vents provided at the cavity portion and perforating from the inner surface of the cavity to the outside, and heating means.