A microwave oven comprises an oven seat (1), a cover plate (3) and a microwave generation unit which are arranged in the oven seat (1).

An oven construction includes a floor construction for the baking chamber.

An air chamber (9) connected to a furnace hearth is arranged in a center of the furnace bottom (2).

In retrofit situations an oil inlet is provided in a side wall of the drum above the bottom drum flange.

There is provided a base cover structure of a microwave oven, in which a reinforcement rib is formed at a periphery of an air intake hole of a stepped portion of a base cover in order to prevent the base cover from deformation.

A large pit gas-type heat treatment furnace comprises several gas burners (6), a furnace wall (1), a furnace bottom (2), a furnace lid (3), a flue (4), and a chimney (7).

A microwave shielding cover (2) is arranged on the upper part of the oven seat (1).

The method comprises, in part, the steps of centering a rail loader over a furnace bottom; placing the crucible on the rail loader; and moving the crucible over the crucible block in the center of the furnace bottom.