Extrusion blow molding of plastic hollow products - polyethylene barrel (1)
DATE：2022/12/2 9:11:08 / READ： / SOURCE：This station
Extrusion blow molding of plastic hollow products - polyethylene barrel (1)
Plastic hollow products (also called plastic containers) are a major type of plastic products, mainly including bottles, barrels, cans and boxes. These products can be produced by extrusion blow molding with an extruder, by injection blow molding with an injection molding machine, by welding and assembling with thin plates, or by rotary or hot extrusion and cold pressing.Extrusion blow molding hollow products commonly used plastics are: polyethylene, polypropylene, PVC and other resins. The molded hollow products are non-toxic, tasteless, light, corrosion resistant, sealable, beautiful and sanitary. It is widely used for packaging food, spices, chemical products, fuels and other items.
The extrusion blow molding process of plastic hollow products is relatively simple:
The main and auxiliary materials are metered and mixed according to the requirements of the material formula for the products → they can be put into the extruder after being mixed and stirred evenly → they are plasticized into a molten state and extruded from the parison die mouth → they enter the molding die and cut off the tubular molten materials → they are closed → the parison is inflated with compressed air and the products are molded → the mold is opened after being cooled and shaped → the parts and components that take out the products to complete these actions constitute the hollow plastic products extrusion blow molding machine, Its structure is shown in Figure 11-1.
In addition, there is another production mode, that is, the forming part of the extrusion molding parison and the bulging part of the parison are two independent equipment. The structure of blow molding product device is shown in Figure 11-2. It is mainly composed of a molding die in the shape of blow molded products, and the die moves to open and close
The production process of polyethylene barrel extrusion blow molding is relatively simple: the production process (Figure 11-3) is to melt the PE resin through the extruder, extrude it into a tubular parison from the mold, place it in the blow molding mold, blow it with compressed air, and obtain products with the same shape as the inner cavity of the mold after cooling and shaping.
(1) Raw materials shall be selected according to the specification and volume of the product for extrusion blow molding of polyethylene barrel: the general rule is to select low-density polyethylene with a melt flow rate (MFR) of 0.3~4g/10min for plastic barrel with smaller volume; High density polyethylene with a melt flow rate (MFR) of 0.05~1.2g/10min shall be selected for plastic drums with large volume (less than 25L); High molecular weight high-density polyethylene (HMWHDPE) shall be selected for large volume plastic drums (referring to hollow products larger than 25L).
The special PE resins for extrusion blow molding hollow products include DFDA-7143, DNDA-7145, DNDA-7146, DNDC-7148, DNDC-7150, DFDA-7340, DEX-8302, etc. produced by PetroChina Daqing Petrochemical Company. According to the requirements of product service conditions, a suitable resin brand is selected.
(2) Equipment conditions
① There are no special requirements for the structure of the extruder used for extrusion blow molding of polyethylene barrel. The general single screw extruder for extruding PE material can be used. The length diameter ratio of the screw is within the range of (20~25): 1, the compression ratio is 2~4, and the screw diameter should be determined according to the amount of material used for one-time molding of the extrusion blow molding barrel.
② Die for extruding tubular barrel blank The structure of the die for extruding tubular barrel blank is shown in Figure 11-4 and Figure 11-5.
It can be seen from Figure 11-4 that the mold structure for tubular barrel blank forming is very similar to that for plastic tube forming; The components, manufacturing materials and technical requirements of the die are also the same as those of the pipe forming die. The design can refer to the technical requirements of the die for pipe forming. The following provides several technical data required for mold design for reference during design.
a. The compression ratio is (2.5~4): 1.
b. Length of straight part of calibrating section L=about 88（ δ Is the die clearance, mm).
c. Rough estimation of the inner diameter of the die: D=D product (a is the blowing ratio).
③ Blowing hollow product forming mould The mould structure used for the forming of blowing hollow products is generally composed of two half moulds, and the opening and closing movement of the mould has horizontal movement or vertical movement; The hinge axis can also be used as the fulcrum, and the two half molds can be opened and closed along the arc line with the fulcrum axis.
In addition, for the products with concave bottom, the molding die should be designed into a three or four open structure to facilitate the smooth demoulding of the products.
Author：admin