F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
F27B5/00—Muffle furnaces; Retort furnaces; Other furnaces in which the charge is held completely isolated
F27B5/04—Muffle furnaces; Retort furnaces; Other furnaces in which the charge is held completely isolated adapted for treating the charge in vacuum or special atmosphere