An extruder is a machine used in the process of extrusion, which is used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. The extruder is responsible for heating up the material and propelling it through the die to create the desired shape. Extruders can be used to create a wide variety of usable products by shaping various materials, including metals, plastics, ceramics, concrete, modeling clay, and foodstuffs. The types of extrusion equipment and their uses are widely varied, and each one is intended for a particular purpose or set of purposes. For example, plastic extruders can be used to create PVC pipe, while food extruders are used to create breakfast cereals and pre-formed snacks. Extruders can be continuous, theoretically producing indefinitely long material, or semi-continuous, producing many pieces. Extrudates are the products of extrusion and are generally called extrudates. Extruders are used in a variety of industries, including rubber processing, ceramics, and agriculture. An extruder operator is a person who sets up, operates, and maintains machinery used in the extrusion process.