Basic Fundamentals of Extrusion and Mixing Theory

The first mechanically driven extruders for rubber and rubber-like materials were developed by Francis Shaw in 1879 in England and John Royle in 1880 in the U. S. A. For nearly 60 years the design of extruder screws remained as an art. With rapidly expanding plastic markets and rapidly rising labor and processing machinery costs, the extruder users and builders realized that only close co-ordination and cooperation among scientists, engineers, and process workers could develop an extruder which would be the most universal and economical tool in polymer processing. Between 1946 and 1953 most of the modern extrusion theory was developed. It has been proven that extrusion theory, when combined with test data and practical experience, is an extremely useful tool. Due to an abundance of empirical data and fundamental theory, extrusion technology has now grown far beyond the level of a mechanical art. At least part of the process can be described by mathematical relationships through the application of rheology, thermodynamics, and fluid dynamics theory. Important advances have been made in process control as well as in increasing output. It is significant that the technology of the rubber extruder, the parent of the plastic extruder, can even now benefit directly from these developments. The transition from hot feeding to use of cold rubber particles can be mentioned as an example.