The upper film is positioned above the thermoformed containers and is then thermo-welded to protect the product from ambient air. The product is therefore skin packaged or packaged in a modified atmosphere. In both cases, vacuum is necessary.

A film is advanced over a forming die and heat and vacuum are used to form a food container (thermoforming). After a quick cool, food is loaded into the containers and advanced to sealing dies where evacuation and the upper film is heat sealed to the container.

Rollstock Packaging:

A gas flushing for modified atmosphere may also be incorporated prior to heat-sealing of the container. 

Typical pump range is single stage 40 to 2,000 m3/h including blowers. The small pumps are used for the thermoforming process. Some machines use three pumps – blower stage for fast pump speed and a large fore-pump for exhausting too. This is used for evacuation of package. Also, a small SOGEVAC is used first for the forming of trays or pouches. Leybold products sold include SCREWLINE, SOGEVAC and RUVAC.

Typical pumping system:

central vacuum system made of rotary vane pumps or dry pumps.

Thermoforming

Pump temperature

High

Heavy duty operation (cycles)

High

Dust / Powder / Particules

Low

Moisture

Low
Tray-sealing

Pump temperature

High

Heavy duty operation (cycles)

High

Dust / Powder / Particules

Low

Moisture

Medium