Extrusion differs from injection molding in that it is typically a continuous process. The extruder screw transports, melts and mixes a thermoplastic polymer through the barrel until the melt exits the extruder at the die. Within the die, it is formed into a shape which can be a profile, sheet, pipe or tube.
Being a continuous process, a puller or haul-off machine downstream from the extruder transports the extrudate by squeezing it lightly between two moving belts or cleats. The product moves in one side of the haul-off and exits the other side.
Once the profile or tube is pulled down the line manually by the operator and placed between the moving belts of the puller the line is now pulled continuously along the line. As it exits the puller, feet counters can enable downstream equipment to cut it to length, or spoolers can roll around product like tubing onto a reel.