Chapter 6-Extrusion Flashcards
What is extrusion?
Extrusion is used to create objects of a fixed cross section. A material is pushed through a die of the desired cross section. It can be done either hot or cold.
What materials are extruded?
Metals, polymers, ceramics, concrete , play dough and foodstuffs are usually extruded.
What is the process of extrusion?
The material is heated and loaded into the container in the press. A dummy block is then placed behind it where the ram then presses on the material to push it out of the die. After the extrusion is stretched in order to straighten it. It can then be either heat treated or cold worked.
What are the advantages of extrusion?
It is low cost compared to other molding processes. It mainly uses thermoplastics which can undergo melting and hardening. Leftover materials can also be reused which means there is no wastage. Machines operate constantly which allow 24 hour manufacturing.
What are the disadvantages?
It can be a problem predicting degree of expansion of the plastic and thus disqualifies this method for precision parts manufacturing. Also there is a limit on what kind of products it can manufacture.
Plastic soda bottles narrow at one end to accommodate a cap which normal extrusion moulding cannot achieve.
What is extrusion mainly used for?
Extrusion is mainly used for making pipes, drinking straws, curtain racks, rods and fibre. The granules melt into a liquid which is then forced through a die and is formed into a tube shape. The tube can then be printed on and cut. The pieces can then be rolled or packed together for storage. Shapes can be cut into T sections, U sections, I sections, L sections and circular sections.
What is the difference between extrusion and injection moulding?
Extrusion is a method by which molten plastic or any other material is pushed through a two-dimensional die opening. The injection moulding process is basically based on the molten die-casting method.
