Microwaves trialled for PET bottle heating

German blow moulding machinery manufacturer Krones has unveiled a developmental microwave-based preform heating technology that it hopes may provide an energy-efficient alternative to infrared (IR) heaters.

The technique uses microwaves in place of conventional infrared or near infrared (NIR) heating equipment, which the company says provide typical efficiency levels of around 20%.

Conventional IR heating is zoned in preform heating applications to ensure that the neck, which does not require blowing, is not heated. Zoning also allows thinner sections to be exposed to less heat energy. Krones says that similar targeted heating can be realised with its microwave system.

The machine maker says microwaves can be applied in stages or over different sections of the preform, with sensors used to monitor temperature at one or more points to ensure a precise temperature profile is achieved, irrespective of any moisture in the perform. Anisotropic distribution can be used to avoid the need to rotate the preform.

The technology is still developmental and thermal distribution is still being optimised. Jochen Forsthövel, at the SKT technology centre within Krones, says it is still too early to say whether microwave heating can achieve weight savings beyond the 8.8g 500ml bottle produced using the company’s latest optimised IR radiator heating module using infra-red radiators.

Krones says a typical microwave heating arrangement applied to one of its rotary reheat stretch blow moulding machines would consist of eight compact microwave heads and 40 microwave heating units.

Although developed for PET food and beverage bottles, Krones says that EVOH, PA, PC, PMMA, PE, PP, PVC and PVA can also be microwave heated. An even wider range could be considered with suitable additive packs.