Ceramic arc tube for metal vapor discharge lamps

Claim 1

A ceramic arc tube for a metal vapor discharge lamp comprising: an arc discharge portion having an outer diameter and an inner diameter; a wall thickness between said outer diameter and said inner diameter; a first electrode-holding portion, formed from an integral continuation of said arc discharge portion, at a first end of said arc discharge portion, said first end having an outer diameter, an inner diameter and a wall thickness occurring between said outer diameter and said inner diameter; a second electrode-holding portion, formed from another integral continuation of said arc discharge portion, at an opposite end of said arc discharge portion, said opposite end having an outer diameter, an inner diameter and a wall thickness occurring between said outer diameter and said inner diameter; the wall thickness of said first end and said opposite end is between 1.5 and 5.0 times the thickness of the wall of said arc discharge portion; said ceramic arc tube being produced by a method comprising the steps of: forming a tubular green body by a mixture material containing fine alumina particles and plasticizer whose main ingredient is a non-thermal plastic organic substance; shaping said tubular green body in a fusiform cavity of a die by applying fluid pressure to an inside diameter of said tubular green body, to inflate said arc discharge portion of the tubular green body more than said first end portion and said opposite end portion thereof; and firing the thus shaped green body after removal thereof from said die.