Blow molding equipment generally uses a single screw extruder. From the process, it can be known that the main equipment for blown film forming are extruder, head, cooling air ring, traction and winding.

1. Extruder:

Generally, a single screw extruder is used. The diameter of the screw is Φ45-120mm, and the size of Φ is determined by the thickness of the film and the size of the folded diameter. The output is affected by the two speeds of cooling and traction. Small extruder with narrow film and large extruder with thick and wide film.

The basic structure of the extruder includes: transmission device, feeding device, barrel, screw, 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 includes gradient screw, abrupt screw, and screw with mixing diagram. For PE blown film flame retardants, all three screws are suitable, and the screw with mixing diagram is better. The length-to-diameter ratio of the screw was relatively short due to mechanical processing in the past. It affected plasticization of plastics. First, the output was not high, and secondly, the quality was not good. Now the length-to-diameter ratio has grown to 30: More than 1, the aspect ratio is long. For product production, the output is high and the quality is good. The aspect ratio should be above 25. The screw heat treatment has a good service life and long life, preferably 38CrMnAI, after nitriding treatment. The production capacity of the extruder is proportional to the diameter of the screw. The production capacity of the extruder is proportional to the speed of the extruder. The production capacity of the extruder is inversely proportional to the gap between the barrel and the screw. The gap should be below 0.25mm. it is good.

2.The head and die are used for blown film.The main types of head are the turning right-angle type and the horizontal straight-through type.

class. Right-angle type is divided into mandrel type, spiral mandrel type, lotus petal type, rotary type and so on. Through type is divided into two types of horizontal and right angle, this type is particularly suitable for large melt viscosity and heat-sensitive plastic.

2.1 Mandrel-type machine head advantages: The machine head has less material and is not easy to be overheated and decomposed. It is suitable for processing PVC. The structure is simple, easy to manufacture and easy to operate. The material flow is slow, and it is easy to produce uneven thickness.

2.2 Spiral mandrel head advantages: good mechanical strength, stability, not easy to tilt and center, the thickness of the film is uniform; disadvantages: large volume, unreasonable design, resulting in more film seams, and easy to reduce the mechanical strength of the film.

2.3 Lotus petal-type machine head advantages: simple structure, convenient processing, low cost, easy operation and cleaning; disadvantages: more stitches, easy to reduce product strength.

2.4 Advantages of the central feeding head: The film thickness is relatively uniform, and it is not easy to produce the phenomenon of centering. It is suitable for processing PE, PP, PA. Disadvantages: There are more materials in the machine, more stitches, and inconvenient operation.

2.5 Advantages of the rotary head: the film thickness is uniform, and it is not easy to cause the phenomenon of centering. It can make the film that is not in the local part be scattered on the roll, making the curled film flat, easy to print, and high quality. Disadvantage: the structure is more complicated , The cost is higher.

3.1 Relationship between die clearance and film thickness Die clearance mm Film thickness mm 0.5-0.75 0.075 or less 0.75-1.25

0.075-0.3 Note: The die clearance on the table above

For the production of LDPE, the gap is larger for the production of HDPE.

3.2 The relationship between the die diameter and the tube diameter and the inflation ratio.

3.3 Die head diameter, film tube folding diameter, and inflation ratio check table. The inflation ratio is the ratio of the film bubble diameter to the die diameter. For LDPE film, it is better to control it at about 1: 2.5. Blowing ratio--the ratio of the diameter of the film tube to the diameter of the machine head δ = h / rb, that is r = h / δb r--the degree of inflation δ--the thickness of the film h--the die gap b--folding for the drafting speed Width = DΠ / 2

3.4 Die head heat, depending on the size of the die head, generally requires CM2 is 2-3WV.

3.5 Inflation ratio is generally controlled within a certain range. If the inflation ratio is too small, the strength of the product is not uniform in the vertical and horizontal directions. If the inflation ratio is too large, it is difficult to operate. -2.5 is suitable for HDPE. Generally between 3-5 is suitable for PP film. Controlling between 1.5-2.5 is suitable for PA film. Controlling between 1.5-2.5 is suitable for PVC film. Controlling is 1.5- Between 3 is appropriate.