Producing high-quality PET (polyethylene terephthalate) bottles depends critically on temperature control during the blowing process. Temperature affects material flow, clarity, strength, wall thickness uniformity, and the final shape of the bottle. Below is an overview of the temperature ranges, how they are managed, and what BOHANG offers in this area.

PET Basics: Glass Transition and Crystallization

• Glass Transition Temperature (Tg): PET transitions from a rigid, glassy state into a more flexible, rubbery state around about 80 °C. Below that, the material is too stiff to stretch properly.

• Crystallization Temperature: As PET is heated further, especially under certain conditions or in hot-fill applications, parts of it can begin to crystallize. The crystallization temperature is typically somewhere in the range around 130-150 °C, depending on the grade. Crystallization changes optical and mechanical properties.

Between Tg and crystallization, PET enters what is often called a “high‐elastic” or rubbery/stretchable state. This is the window in which stretching and blowing happen efficiently.

Typical Temperature Ranges in the Stretch Blow Molding Process

1. Heating the Preform

• Preforms are first heated to a surface temperature sufficient for stretch‐blow molding. This is often in the range of 90-120 °C for standard water or beverage bottles. 

• The exact temperature depends on factors such as preform wall thickness, preform length, the molecular weight (intrinsic viscosity) of the PET resin, ambient temperature, oven design (number and strength of IR lamps), and how uniform the heating is.

2. Blow Molding Stage

• Once heated, the preform is stretched (axial and radial stretching) and blown with compressed air. The temperature must still be maintained so that material can stretch without cracking or whitening. The blow occurs while PET is in the high-elastic range between Tg (≈ 80°C) and before crystallization sets in.

• For regular bottles, this typically means blowing starts and proceeds when preform temperature is in that 90-120 °C window.

3. Hot-Fill Bottles and Higher Temperatures

• Some bottles are designed to hold hot liquids or need higher heat resistance, which requires the bottle to be partially crystallized or treated. In those cases, surface heat-setting or hot-fill treatment may require higher mold or post-blow temperatures—often 130-145 °C or more depending on the design.

• Heat setting or crystallization often follows the blowing to lock in structure, improve barrier properties or heat resistance.

Key Factors Affecting Temperature Control

• Uniform Heating: It is crucial that different zones of the preform (bottom, body, shoulder, neck) are heated to optimal and fairly uniform temperature. Disparities lead to under-blown spots, thinning, poor transparency, or distortion.

• Preform Design: Thicker walls need more time or more intense heating; longer preforms need adjustment in lamp zones. The molecular characteristics of PET also influence how it absorbs heat.

• Oven/Heating System Design: Infrared lamps are most common; some advanced systems use lasers, microwaves, or other specialized heat sources to improve energy efficiency or allow sharper temperature profiles.

• Control Monitoring: Use of IR sensors, temperature feedback systems, sometimes intelligent or automated control to maintain target temperatures. Changes in ambient temperature, lamp aging, etc., must be compensated.

Consequences of Incorrect Temperature

BOHANG Factory Capabilities & Why They Matter

To achieve precise temperature control and high quality in bottle blowing, it is essential to have reliable, well-designed machinery with good service support. BOHANG (Guangzhou Bohang Intelligent Technology Co., Ltd.) is one manufacturer worth noting.

• BOHANG designs and manufactures Automatic PET Bottle Blowing Machines, Semi-Automatic PET Bottle Blow Molding Systems, along with supporting components like molds and Manipulators.

• Being a relatively young company (established in 2021), BOHANG focuses on R&D, production, installation, and after-sales service, which means customers often benefit from newer technology and responsive support.

• BOHANG emphasizes quality assurance, fast delivery, and trustworthy service. Their product lines and factory setup include modern heating and injection/blow molding equipment, which helps in maintaining precise temperature control, uniform heating, mold quality, etc.

By using equipment from a factory like BOHANG, manufacturers gain better control over critical process parameters such as preform heating, blow timing, and post-blow finishing, all of which contribute to consistent bottle strength, clarity, and functionality.

Practical Guidelines for PET Bottle Blowing Temperature

1. Set Preform Surface Temperature Target Begin with aiming for ~ 90-110 °C for standard bottles; adjust according to preform specs.

2. Use Sensors for Feedback IR sensors for surface temperature; monitoring internal oven temperature; automatic controls help.

3. Adjust Lamp Power or Exposure Time More power or longer exposure for thick or long preforms; multiple lamp zones help.

4. Watch Ambient Conditions Heating zones are affected by shop temperature or environmental variation; consistent conditions help maintain uniformity.

5. For Hot-Fill or Specialty Bottles After blowing, apply heat setting or control mold temperature to reach ~ 130-145 °C if required for heat resistance or crystallinity.

6. Quality Checks Look for clarity, lack of haze, uniform wall thickness, proper bottom formation and no distortion in necks or shoulders.

Conclusion

The ideal temperature for PET bottle blowing lies between about 90-120 °C for standard blow molding of water or beverage bottles, while hot-fill or heat-set bottles often require higher temperatures (130-145 °C) or post-blow treatments. Controlling temperature through good machine design, uniform heating systems, feedback sensors, and reliable factory equipment is essential. BOHANG’s factory strength in modern pet bottle blowing machines, quality assurance, and full support make it a strong partner in achieving consistent, high-quality PET bottles.