In a conventional electromagnetic relay of a closed type intended to guard against the ambient atmosphere, a coil block, which is an internal component of the electromagnetic relay, has sometimes been coated with an insulating resin through injection molding to enhance the insulating properties between a coil of the coil block and a contacting point.
To seal the electromagnetic relay of the above-described type, the electromagnetic relay is first installed in the vacuum space at high temperatures for vacuum process. After the air inside the electromagnetic relay is discharged and an inert gas fills the electromagnetic relay in the inert gas atmosphere, the electromagnetic relay is sealed.
Meanwhile, an example of a compact-size electromagnetic relay such as proposed in Japanese Patent Laid-Open Publication No. 02-319922 (319922/1990) secures an insulation distance between the coil and contacting point by providing an insulating member between a movable block arranged at the lower side of the coil block and the coil block.
If the insulating resin is coated all over the coil winding section of the coil block through injection molding, it is necessary for a mold to be vented in order to prevent a short shot (insufficient filling) or a burn mark, and moreover, it is quite difficult to set the molding conditions, e.g., injection pressure, temperatures of the mold and the like.
Since the electromagnetic relay is put in the high temperature atmosphere during the vacuumizing process, the coated resin may be broken by the gas generated from the coil or the like, thus making it hard to obtain a desired dielectric strength between the coil and contacting point.
Moreover, an extraordinary force exerted on the coil resulting from the pressure of the resin during injection molding causes the coil to break in some cases.
USPTO Backgrounds
USPTO Backgrounds