The present invention relates to a derby cone which vacuum-deposits an aluminum film on an inner surface of a panel coated with phosphors and lacquer films, and prevents aluminum particles adsorbed inside the dummy cone from being introduced into the vacuum pump, thereby extending the life and reducing the vacuum time. It is to improve the vacuum efficiency.;The present invention forms an exhaust port for discharging the air inside the lower end of one side of the auxiliary cover formed similarly to the shape of the dummy cone, and consists of a member attached to be bent and projected in a predetermined shape on the exhaust port front side.
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