Patent ID: 9694534
Date: 2017-07-04
CPC Classifications: B29C,B29K,B29L

Claim:
1. A device for thermoforming a plastic film, comprising: a chamber configured to have variable internal pressure, and having an opening in a side of said chamber; an attachment system configured to attach the film around said opening, and hold a peripheral edge of the film firmly so that said film closes off and seals the chamber; a pressure control system configured to vary and control the pressure in the chamber, and cause the film held by the attachment system to deform in the chamber opening into a deformation which varies as a function of said pressure; a measurement system configured to measure a sag of the film held by the attachment system, said measurement system being arranged outside the chamber and facing the opening of said chamber; a heating system configured to heat said film held by the attachment system, and comprising a hot air blowing unit arranged to produce a stream of hot air flowing externally to the chamber and in contact with the film, wherein the blowing unit is configured to cause the stream of hot air to flow parallel to the film from a first lateral side of the opening of the chamber to a second lateral side of said opening, said second side being opposite said first side; and a ring extending around the opening of the chamber, outside said chamber, with a slanted face that is slanted relative to a midplane of the opening, and with a lower internal edge of said slanted face being arranged to come in contact with or in proximity to the film held by the attachment system, along at least a portion of the peripheral edge of said film, and with the blowing unit being arranged to produce the stream of hot air from an upper external edge of the slanted face, on the first lateral side of the chamber opening, wherein the slanted face of the ring forms an angle which is between 25° and 90° relative to an axis perpendicular to the side of the chamber, and in the midplane of the opening connecting the first and second lateral sides and wherein the slanted face of the ring is configured to guide the stream of hot air to or close to the plastic film, avoiding an area of stationary air in a recessed angle between the ring and the plastic film.