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Analysis of PET injection blow molding

PET raw material is a milky white or light yellow highly crystalline polymer with a smooth and shiny surface.
Analysis of PET injection blow molding

PET material properties

PET raw material is a milky white or light yellow highly crystalline polymer with a smooth and shiny surface. It has good creep resistance, fatigue resistance, abrasion resistance and dimensional stability, low wear and high hardness, and has the greatest toughness among thermoplastics: good electrical insulation performance, small temperature influence, but poor corona resistance. Non-toxic, weather-resistant, chemical resistant, low water absorption, resistant to weak acids and organic solvents, but not resistant to hot water immersion and alkali. Therefore, it is widely used in the packaging of beauty and cosmetics industries.

Mold Features

01. Depending on the project volume, the number of cavities of the preform mold ranges from one out of one to ninety-six out of one. The formwork is P20 steel with a pre-hardening process. The core, cavity, and screws are made of S136H high-strength, corrosion-resistant stainless steel. The template is completed by one processing, to ensure the concentricity of the forming hole and the guide sleeve, and to ensure the compact structure of the mold.

02. The exclusive spiral cooling water tank design for each single-core and cavity helps to shorten cycle time, improve production efficiency and save costs. The opening and closing plate adopts the bearing sliding type, which makes the prefabricated part have a reliable structure. It is a highly integrated slider, pushes plate, and ejection process. All sliding parts are inlaid with a self-lubricating copper alloy to ensure low friction efficiency and strong wear resistance.

03. Each cavity is self-locking independently to ensure high precision, reduce defects and facilitate disassembly.

04. Hot runner system: the heating temperature is uniform, it can prevent the white defects of the preform and improve the quality of plastic products.

Mould Design Points

When designing the mold, the cooling system is particularly important. The injection molding cycle of the product is shortened, the efficiency of the product is greatly improved, the size and surface effect of the product is more stable, and the quality of the product is improved. Water transport design points:

01. The front mold of the preform mold transports water, as shown in the following figure:

(1)The gate of the preform mold is independently cooled by a cooling water jacket, and the cavity is cooled by a spiral to provide good mold temperature control.

(2)The inlet and outlet of each cooling water channel need to be connected separately, not in series with each other, so as not to reduce the cooling series of the mold.

02. The preform mold core transports water, as shown in the following figure:

(1)the preform mold core adopts the water needle.

(2)from the mouth of the water to the top blowing well cooling cycle. The uniform cooling method can make the product cool quickly and improve the production efficiency and quality of the product.

Preform injection

01. Pretreatment of raw plastics

Because PET macromolecules contain lipid groups and have a certain degree of hydrophilicity, the pellets are more sensitive to water at high temperatures. When the water content exceeds the limit, the molecular weight of PET decreases during processing, and the products become colored and brittle. Due to this difficulty, the material must be dried before processing. The drying temperature is 150°C for more than 4 hours, generally 170°C for 3-4 hours. The air shot method can be used to check whether the material is completely dry.

02. Matters needing attention

(1)The recovered material should not be too large, otherwise, it is easy to “bridge” at the blanking place and affect the plasticization.

(2)If the mold temperature is not well controlled or the material temperature is not controlled properly, it is easy to cause “white fog” and opacity. The mold temperature is low and uniform, the cooling speed is fast, and the finished product is transparent with less crystallization.

stretch blow molding

01. Two-step bottle blowing method, the heating of the preform is completed by a heating oven, its temperature is automatically adjusted by manual setting, the preform is heated by a lamp in the oven, and the preform rotates while moving forward in the oven so that the preform is heated evenly.

02. The heat in the oven is controlled by the number of lamps turned on, the overall temperature setting, the power of the oven, and the heating ratio of each section. The temperature adjustment should be adjusted in conjunction with the pre-blown effect bottle.

03. After the preform is heated, it is transported to the blow mold by the transmission system of the blow molding machine for blow molding.

04. During the blow molding process, the mold is kept cool. After the blow molding is finalized, it is transferred to the transmission system to the packaging workbench to complete the packaging process.

The progress and status of the application of environmental protection materials

01. Today, when more and more attention is paid to environmental protection, marine recycled material R-PET (PCR) has been used in large quantities, from trace additions to 100% applications, and the detection and production of R-PET (PCR) materials are already available. Perfect technical system.

02. The field of PLA corn starch has also carried out multiple batches of trials and production. Due to the high cost, the current overall volume is temporarily small.

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