Blow film forming equipment and structural features
Blow molding equipment generally uses a single-screw extruder. From the process, the main equipment for blown film forming is extruder, head, cooling air ring, traction and coiling.
Generally, a single-screw extruder is used, and the screw diameter is -45-120 mm. The size of the crucible is determined by the thickness of the film and the size of the folding diameter. The output is affected by the two speeds of cooling and traction. The film is narrow with a small extruder, and the film is thick and wide with a large extruder.
The basic structure of the extruder includes: transmission, feeding device, barrel, screw, machine head and die. The key to the quality of the extruder is the screw structure and the aspect ratio of the screw.
The screw structure has a gradient screw, a mutant screw, and a screw with a mixture. It is suitable for all three kinds of screws of PE, and the effect of the screw with mixing is better. The length-to-diameter ratio of the screw has been limited by the mechanical processing. In the past, the long diameter of the screw was relatively short. It affected the plasticization of the plastic. First, the output was not high, and the quality was not good. Now the aspect ratio has grown to 30: 1 or more, the length to diameter ratio is long. For the production of the product, the output is high, the quality is good, and the aspect ratio is preferably 25 or more. The screw heat treatment has a long service life, preferably 38CrMnAI, which is treated by nitriding. The production capacity of the extruder is proportional to the diameter of the screw. The productivity of the extruder is proportional to the rotation speed of the extruder. The productivity of the extruder is inversely proportional to the gap between the barrel and the screw. The clearance should be less than 0.25 mm. it is good.
The types of heads used for blown film and die are mainly two types: the steering type right angle type and the horizontal direction straight type. Right angle type is divided into mandrel type, spiral mandrel type, lotus petal type, rotary type and so on. The straight-through type is divided into two types: horizontal and right-angle. This type is especially suitable for high melt viscosity and heat sensitive plastics.