Meaning
Electromagnetic radiation in the infrared spectrum offers an efficient method for raising the temperature of thermoplastic shapes before blowing. This process step, called infrared preform heating, prepares the amorphous resin for biaxial orientation by bringing it above its glass transition temperature. It establishes the initial temperature profile that controls how the polymer redistributes inside the mould cavity.
Energy Absorption
Different polymer resins display unique absorption bands that must match the wavelength of the emitters. During infrared preform heating, the radiation penetrates the thick plastic wall, with some energy being absorbed and some transmitted. Adjusting the air ventilation inside the oven prevents the outer skin of the preform from overheating while the inner core reaches the target temperature.
This balanced heating is essential for uniform stretching.
Process Optimization
Oven configurations use multiple rows of halogen lamps to heat distinct zones of the preform. Individual lamp power adjustments allow operators to tailor the temperature along the length of the preform. This zoning compensates for complex bottle shapes that require more material in specific areas.
Defect Mitigation
Insufficient energy input results in cold spots that resist stretching and cause thick, cloudy regions in the container wall. Conversely, excessive heating causes the resin to crystallize thermally, leading to brittle, opaque containers. Precise temperature control in this stage ensures consistent bottle quality across production runs.
