... door structure, which is water-cooled. Its inner layer is in a dimension of 1100×680×240mm, of ... cast iron plates, which are then lined with a layer of asbestos sheets, then five layers of refractory bricks ... and outer layers, of which the inner layer is of a square hole in 75x75mm size and 150mm length, ... while the outer layer is of a round hole in 25mm diameter in 200mm length, ...