Extrusion is a first stage of thermoforming and processors should carry out the actions listed for extrusion. This section only considers the thermoforming process from sheet (either from roll or in-line).
Where pre-warming ovens are used these should be well sealed and insulated to prevent excessive heat losses. Examination with a thermal camera will quickly reveal degraded seals and areas of heat leakage. Minimising the distance between the pre-warming oven and the actual thermoformer will minimise heat losses.
Insulation and seals
Primary heating ovens should be well sealed and insulated.
Entrances and exits
Minimising the size of entrances and exits on pre-warming and primary ovens will minimise heat losses. If the sheet being warmed is only 0.5 mm thick then the entrance and exit gaps do not have to be more than 4 mm.
Thermoformer heater banks should use heating elements that match the emissivity of the heater to the absorption of the material. Heaters should be kept clean to ensure good emissivity at the right wavelength for the material. Catalytic flameless gas heaters are a new technology that can remove the need to electric heating of the sheet. Heater banks should be sealed and insulated where possible to reduce heat losses from radiation, convection and conduction.
Cooling is often a limiting factor in cycle times and the sheet temperature should be the minimum required for good forming.
Thermoforming generates a large amount of web waste that is reground and recycled. The regrinders and blowers should be linked to the thermoformer operation so that they stop operating when the thermoformer is not producing.
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