This mixer is most ideal for kneading very stiff masses. This machine consists of an open trough with an approximately semi cylindrical bottom. With in this trough two horizontal knives of roughly Z-shaped outline rotate. These knives are so placed and so shaped that the material turned up by one knife is immediately turned under by the adjacent one. These machines may be jacketed for heating or cooling, and may be closed to retain volatile solvents. This equipment finds application in Paint, Polymer and Rubber industries.