The metallic hood furnaces (HBO) generate the lowest achievable operation pressures. The highest purity gas atmosphere is attained due to the vacuum capability.
The materials used in the construction are selected for the lowest vapour pressures at the highest temperatures. Heat treatment up to the highest temperatures can be achieved without harming the heating elements or insulation material. Radiation shields are used to provide thermal insulation, which are made from the same material as the heating elements, and no fibrous thermal insulation is used.
Two varieties of HBO furnaces are produced: those made using molybdenum heating elements and radiation shields are suitable for use up to 1600 °C; those made using tungsten heating elements and radiation shields are suitable for use up to 2200 °C.
Nitrogen, Argon, and Hydrogen gases are available for use in mixed or pure forms. Additional gases can be installed upon request. A slight overpressure or controlled partial pressure between 10 and 1000 mbar can be achieved. Partial pressure provides a defined gas flow through the furnace.
Due to the complete metallic design, the final vacuum level in the HBO can reach the high vacuum range and better than 5 x 10-6 mbar. Depending on the vacuum requirements, the vacuum is provided by different pumping stations. Ultrahigh vacuum options are available upon request. Gases are controlled by various dosing and controlling devices. The temperature in each of the three heating zones is individually controlled to maintain the best uniformity.