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When heat treating bulk goods and hollow parts under defined protective gas atmosphere we recommend the usage of protective gas boxes with an additional vacuum lid. Thus the traces of oxygen in the box can be reduced by a considerable amount which improves the quality of the components accordingly. These boxes are equipped with a lid for top charging, protective gas inlet and outlet as well as a vacuum lid with rubber sealing gasket. Gas ductwork and handling while hot is the same as the protective gas boxes described on page 11. In addition, these boxes also feature a connection for a vacuum pump with a shut-off valve. After charging the box in a cold state it is brought into vacuum and afterwards flushed with protective gas. By repeating this process once or several times the results are considerably improved. After the box was flushed with protective gas the last time, the vacuum lid is removed and the box is placed into the preheated furnace. Protective gas is used for heat treatment. After the heat treatment the box is taken out of the furnace and can be cooled in air or be opened to remove the charge. The box can also be force-cooled on a cooling platform (page 20) while closed. Be sure that the protective gas flowrate is increased for this application.
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