Overjacketing and tubing extrusion are highly preferred processes for extruding a range of plastic materials. The overjacketing extrusion process is discussed here. In the process of wire coating, the bare wire or some bundles of jacketed wires, filaments, etc. are pulled through the die's center, which is similar to the tubing die. The different materials that are used here, depends on the application. Basically, an insulated wire is a tube (thin walled) that is formed around bare wire.
For coating a wire, there are mainly two different kinds of extrusion tooling used. These are called "pressure" tooling or "jacketing" tooling. The selection of the type of tooling to be used depends on the fact that whether the specific application needs intimate contact or if it needs polymer adhesion to the wire or not. In case there is the requirement of an intimate contact or adhesion, pressure tooling is used or else, jacketing tooling is selected.
Jacketing Tooling vs Pressure Tooling
Jacketing tooling differs with pressure tooling on the parameter of pin's position with respect to the die. In case of jacketing tooling, the pin is extended all the way and flushed with die. Upon feeding the bare wire through the pin, it does not directly makes contact with molten polymer unless it leaves the die. In pressure tooling, the pin's end is retracted in the crosshead, where it contacts with polymer at a higher pressure.
The process of tubing extrusion or extruded tubing process is used to manufacture products like medical tubing and drinking straws. This process is exactly similar to the process of regular extrusion, until the stage of die. To extrude the hollow sections, a pin or mandrel is placed inside the die and in various cases, positive pressure is applied through the pin onto the internal cavities.
For specialty applications, it is required to make tubings with a number of lumens or holes. For such applications, tooling is created with the placement of more than one pin in die's center for the production of required number of lumens. In large number of cases, the pins are available with air pressure from a range of sources. This way, it becomes easy to adjust individual lumen sizes with the adjustment of pressure to the individual pins.