Roll fed flotation/impingement air ovens and related thermoforming systems for corrugation-free heating and expanding of gas impregnated thermoplastic webs

A method for generating microcellular bubbles in a thermoplastic material, the method comprising:

• conveying a thermoplastic material impregnated with a gas, through an oven chamber, wherein the thermoplastic material is continuously conveyed through the oven chamber;
• blowing air through at least two upwardly directed nozzles and at least two downwardly directed nozzles, toward the gas impregnated material inside the oven chamber, with the blown air, heating the gas impregnated material, causing microcellular bubbles of gas in the material to nucleate and grow inside the material, while the material moves through the oven chamber, with only the blown air, suspending the material while the material moves through the oven chamber and with only the blown air, directing the material to undulate through at least two complete undulations as the material moves through the oven chamber and while microcellular bubbles nucleate and grow inside the material wherein impinging heated air streams from the at least two upwardly directed nozzles and at least two downwardly directed nozzles cause heating and uniform expansion of the gas impregnated material such that corrugation-free expansion of the gas impregnated material is enabled;
• accumulating in an enclosure of an accumulation system where the enclosure includes an interior, a first nip roller that is disposed in the interior for tensioning the gas impregnated thermoplastic material as the gas impregnated thermoplastic material moves through the oven chamber;
• heating the gas impregnated thermoplastic material in the enclosure with a heater;
• and
• advancing the gas impregnated thermoplastic material accumulated in the enclosure via another nip roller included in the interior of the enclosure.