Abstract: A developing device has a development roller for carrying toner on a surface thereof, a toner supply roller for supplying the toner to the development roller, a flat spring which comes into contact with the development roller, charges the toner to be supplied to the development roller and applies the toner to the development roller while regulating the thickness of a layer of the toner. The flat spring has a plurality of flat-plate parts including a contact flat-plate part which comes into contact with the development roller, and a curved part which connects the flat-plate parts to each other. In this structure, by arbitrarily selecting dimensional parameters of the flat spring, it is possible to easily obtain various flat springs having different properties. Therefore, for example, the stress to the toner and the stress to the members can be easily reduced simultaneously with a design of the flat spring.

Abstract: A screen printer effects a printing by moving a squeegee in contact with a screen to force a printing paste through a printing pattern formed on the screen. The squeegee is held by a squeegee head. The squeegee head includes a support member for supporting the squeegee in such a manner as to move the squeegee upward and downward, and at least one moving member which swingably supports the support member and is movable together with the support member. When the squeegee is to be exchanged, only the support member is angularly movable relative to the moving member so as to provide a sufficient space above the screen to facilitate the exchange of the squeegee.

Abstract: An oxidation-resistant silicon nitride material possessing a surface layer of a phase of closely packed crystals is produced by a procedure which comprises covering the surface of a silicon nitride substrate with a layer of an alkali metal compound, firing the coated substrate at a temperature of between 800.degree. C. and 1,300.degree. C., thereby forming an alkali metal-containing vitreous coating layer on the surface of the silicon nitride substrate, and thereafter removing the coating layer.

Abstract: An oxidation-resistant sialon material and an oxidation-resistant silicon carbide material each containing a phase of closely packed crystals in the surface region are produced by coating a sialon substrate and a silicon carbide substrate with a layer of an alkali metal compound and a layer of a mixture of an alkali metal compound and a carbonaceous substance respectively, firing the resultant coated substrate at a temperature in the range of 800.degree. to 1,300.degree. C. thereby forming an alkali metal-containing vitreous coating layer on each substrate, and thereafter removing the each coating layer.