How a Tray Sealer Works: Film Feed, Gas Flush and Seal

The step-by-step sequence inside an automatic tray sealer: tray transport, gas flushing, film sealing and the checks that make the seal reliable.

The core idea of this page: a tray sealer welds a lidding film onto a rigid preformed tray in a sealing station — and the value is in what happens in that station: MAP gas flushing, vacuum or skin packaging. Choose the sealer by the sealing format (MAP, vacuum-skin or seal-only) and the tray/film you actually run, then force a witnessed seal.

For the machine landscape, see Top 5 Tray Sealers Compared and Top 10 Sealing Machine Manufacturers.

How a tray sealer works

Tray infeed and sealing station

Filled trays are fed into the machine, and each tray is positioned under a sealing head. The lidding film is drawn over the tray, and the head presses a heated seal plate onto the tray flange, welding the film to the tray rim.

MAP, vacuum and skin formats

A MAP sealer flushes the tray headspace with a protective gas before sealing, a vacuum-skin sealer evacuates the air and draws the heated film down over the product, and a seal-only sealer just welds the lid. The format is chosen by the product and shelf-life target.

Cutting and discharge

After sealing, the film is cut around the tray, and the sealed tray is discharged. The tooling — the tray cavity and seal plate — is specific to the tray size, which is why format changeover and tool cost matter.

Failure modes to design around

Seal leaks. A weak or wrinkled seal on the tray flange leaks the pack — the most common tray-sealer failure. Seal integrity must be verified on your tray and film.
Tooling mismatch. A tray that does not match the tooling seals poorly or jams. Confirm the tray dimensions and flange tolerance.
Residual oxygen. For MAP trays, a leaking seal or a poor gas flush raises residual O2 and shortens shelf life.
Changeover time. Tray size changeover involves tooling swaps; on many SKUs the changeover time is a real cost.

How to verify a tray sealer

Seal-integrity test: run a leak or burst test on sealed trays.
Residual-oxygen check: for MAP trays, measure O2 inside the pack.
Witnessed run: run your tray and film through the machine at production speed.
Changeover: time a full tray-size changeover.

Frequently asked questions

Can a tray sealer do MAP and vacuum-skin?

Many automatic tray sealers support both MAP and skin formats, but the machine must be configured for it — confirm the sealing station and gas/vacuum options.