Thermoform-Fill-Seal Machine

Overview

A thermoform-fill-seal machine, also called a rollstock machine, makes a sealed package from two reels of film in one continuous run. It forms tray cavities from a heavy bottom film, indexes the trays through an open zone where they are filled, draws out the air and replaces it with a protective gas, seals a printed top film over the trays, and cuts the web into finished packs. It is the standard machine for vacuum-packed and gas-flushed food: sliced meat, cheese, fresh pasta, fish, and medical devices in formed trays.

The bottom web is pulled through the Frame and Transport by gripper chains. The Bottom Film Feed supplies the forming film, the Forming Station station shapes the trays, product is added in the Loading Zone zone, the Vacuum and Gas Station station conditions the atmosphere, the Top Film Feed adds the lid, the Sealing Station station closes the pack, and the Cutting Station station separates the packs. The Control Cabinet cabinet runs every step.

Transport and forming

Two films are involved. The bottom film is a thick forming web that becomes the rigid or semi-rigid tray; the top film is a thinner printed web that becomes the lid. The Bottom Film Feed pays the forming film into the Gripper Chain gripper chains, whose Film Gripper Clip grippers seize both edges and pull the whole web through the machine in fixed steps, so every station works on the web at the same pitch.

At the Forming Station station the Heating Frame softens the bottom film, then the web is shaped against the cooled Forming Die by vacuum and compressed air. Deep trays, up to about 120 mm, need careful heating and a plug to pre-stretch the film, or the corners thin out and leak. The Die Lift raises and lowers the die each cycle so the web can index forward between forms.

Loading and atmosphere

The formed trays then run through the open Loading Zone zone. On a manual line operators stand along the Loading Table and place product into the moving trays; on an automated line a Automatic Loader or a row of robots does it. A Load Check Camera checks each tray is loaded correctly before it reaches the seal.

Atmosphere control is what sets this machine apart from a simple tray sealer. At the Vacuum and Gas Station station the Vacuum Pump draws air out of the loaded tray, and for modified-atmosphere packing the Gas Mixer blends a protective mix, often nitrogen to displace oxygen and carbon dioxide to suppress bacteria, which the Gas Lance flushes into the tray. The Oxygen Sensor confirms residual oxygen is low enough; for fresh meat that means a few percent or less, which is what gives the long sealed shelf life.

Sealing and cutting

With the atmosphere set, the Top Film Feed lays the printed lid film over the trays, kept in register by the Registration Eye so the artwork lines up with each pack. In the Sealing Station station the heated Sealing Tool presses the lid onto the tray flange, fusing the films around every cavity at once. Seal temperature is held by a PID loop on the Seal Thermocouple, and the Seal Tool Lift lowers and raises the tool each cycle.

The Cutting Station station then frees the packs. A Cross Cutter cuts across the web between rows and a Longitudinal Slitter cuts the lanes apart, while the Trim Winder reels up the edge trim that the grippers held. The result is a stream of individual sealed packs.

Control and use

The Control Cabinet cabinet holds the PLC, the Servo Drive units that keep the transport, seal lift and cutters in step, and the Temperature Controller loops for the heating frame and seal tool. The operator sets film type, draw depth, gas mix, seal temperature and pack matrix on the HMI Touchscreen; changing pack size means swapping the form die, seal tool and cutter, which on a tool-less design takes a few minutes.

The machine indexes 8 to 20 cycles a minute, each cycle making a whole matrix of trays, so output is high. Food processors are the dominant buyers, packing fresh and cured meat, cheese, ready meals and seafood under vacuum or modified atmosphere. Medical device makers use the same machine for sterile-barrier trays. The machine's strengths are its sealed barrier, its ability to draw deep trays from plain rollstock cheaper than buying pre-made trays, and its high throughput; its cost is the tooling and the floor length the long inline layout needs.