Pultrusion is a manufacturing method used to create plastics. Unlike extrusion, which molds a material by pushing it through a shaped die, pultrusion pulls strands of heated polymers through the die that gives a product its shape. While pultrusion allows for the quick creation of large and strong plastic products -- such as piping and girders -- the pultrusion method also has a few significant limitations and disadvantages.
The technique of pultrusion naturally limits the shape of materials that can be made using the process. Pultrusion can only produce materials with a cross-section of a consistent thickness. While pultrusion can quickly produce large sections of pipe or support beams, materials with more complex shapes or varying diameter over their length cannot be made using the process.
The materials that can be used in pultrusion are also limited. While an extrusion manufacturing process may use wood-based composites or aluminum, pultrusion is limited to materials that can be pulled through in strands, such as polyester and epoxy.
While pultrusion is efficient in its use of materials, the process is entirely automated and requires a constantly heated die. This constant use of heat and electricity needed to power the process makes pultrusion less energy efficient than other manufacturing methods and represents additional heating costs for the manufacturer who's using a pultrusion system. In addition, the limited types of materials that can be used in the pultrusion process are rarely recyclable.