| 摘要 |
PURPOSE:To check a possibility of mechanical deformation as well as to prevent the occurrence of doming, by constituting a blank being formed into spherical form with boronization. CONSTITUTION:A shadow mask 9 to be built in a color picture tube is formed into the specified form with a shadow mask blank of an iron plate or the like and inserted into a borating furnace. At this time, the inside of the furnace is heated at the specified temperature in advance, and when a mixed gas of H2= 0.065mol% and BCl3=0.935mol% is made to flow therein, a boride is formed on a surface of the mask 9 whereby the surface of the mask 9 comes to a porous layer. Next, when another mixed gas of H2=0.2mol% and BCl3=0.8mol% is made to flow therein, the boride is diffused toward the inside from the surface of the mask 9 and an acicular layer is formed there. As a result, such a boride as being different in formation between the surface and the inside of the mask 9 is formed so that mechanical strength in the mask is improved as well as color shading due to doming is thus reducible. |
