Multi-stage door opening device

A multi-stage door opening device comprising:

• an arm hinged to a door support frame at one end thereof and including a metal core coated with an engineering plastic material over a major portion of its surface area, said arm having a notched fixing portion in said metal core at the other end thereof and partially thinned in order to provide a plurality of locking portions in said plastic material, the one end of said arm having a hinge pin hole provided with a synthetic resin bushing integrally formed with said engineering plastic material by an injection molding, said bushing being placed beside said metal core;
• a stopper engaged with said notched fixing portion of the arm for limiting a full opening position of a door;
• a bracket mounted on said door support frame and hinged to said pin hole of the arm, thus to hinge said arm to said door support frame;
• and
• a locking unit penetrated by said arm and locked to one of said locking portions of the arm, said locking unit being mounted on said door and comprising a locking body and a cover covering the locking body, both said locking body and said cover being made of an engineering plastic material, said locking body receiving at least one fixing nut and at least one roller unit having a locking roller slidably contacting said arm for moving said locking unit into different locking portions along said arm with said roller unit having elastic means for urging the roller unit against the arm such that the locking roller maintains tight contact with the arm independent of arm thickness.