Question

In injection blow molding of plastic beverage bottles, the blowing is accomplished by

• A. hot water
• B. hot air
• C. hot oil
• D. alcohol

Hint:

Plastic bottles are blown using heated, pressurized air because it expands uniformly and does not contaminate or cool the polymer during shaping.

Answer 1

The Correct Option is B

Injection blow molding is one of the most widely used processes for producing high-quality, uniform plastic beverage bottles made of polymers such as PET (Polyethylene Terephthalate). The process consists of two main stages: injection molding of the preform and subsequent blowing of this preform to obtain the final bottle shape. In the blowing stage, it is essential to uniformly stretch the preform while it is still in a rubbery or softened condition. To achieve this, a pressurized medium must be supplied inside the hollow preform. The ideal medium must be capable of providing rapid expansion, clean operation, and precise pressure control without contaminating the plastic.

Hot air is used because it is clean, inexpensive, easily compressible, and capable of maintaining the preform at a suitable temperature during expansion. The temperature of the air prevents premature cooling and brittleness, ensuring uniform wall thickness and excellent clarity of the final product. Water or oil would interfere with the thermal balance and could cause uneven temperature distribution, poor surface finish, or contamination. Alcohol presents safety hazards due to flammability and volatility. Therefore, hot air is universally used as the blowing medium in injection blow molding.