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What are the differences between blow molding and injection molding?

(1) Product Differentiation

Plastic blow molding involves shaping products using gas and requires injection processing. It is generally used for producing thicker items. Blow molding, on the other hand, is different as the products are thinner and more transparent, making any flaws more noticeable. Therefore, higher requirements are placed on blow molding in terms of material toughness and tensile properties. Injection molded products tend to be thicker and have relatively lower material requirements.


(2) Texture Differences

Blow molded products are hollow with black being a common color choice as it can conceal defects such as burrs or rough surfaces caused by the blow molding process. Due to their hollow structure, they are lightweight. Injection molded products have smoother surfaces and better texture compared to blow molded ones; they also exhibit superior flexibility and compression resistance. However, this comes at a higher cost as injection molded products tend to be priced higher than blow molded ones.

(3) Process Differences

In the blow molding process, plastic raw materials are first heated to temperatures ranging from 350-420 degrees Fahrenheit (176-215 degrees Celsius). The material is then extruded from the machine's head into a hollow tube known as a parison. The mold closes around the parison while approximately 80 psi (5.5 bar) of air is blown into it causing it to expand and take on the shape of the mold cavity. The mold is then cooled allowing the plastic to solidify. Once a set time has been reached, the mold opens up and produces the product which then goes through a trimming process that allows access to its interior.

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