Tray Shrink Packer

Overview

A tray shrink packer takes a stream of individual products, groups them into the required pack count, sets them on a corrugated tray or flat pad, wraps polyethylene shrink film around the tray and product, and runs the pack through a heat tunnel so the film shrinks tight. The result is a stable retail-ready or transport multipack such as a tray of canned drinks, bottled water or food jars. The machine sits downstream of a filler, labeller or carton sealer and upstream of a palletiser. Speed runs from about 15 packs per minute for large heavy groups up to 40 for small lightweight packs. The whole sequence is continuous, with the Main Drive keeping the infeed, wrapping and tunnel conveyors in step.

Product collation and infeed

Products arrive single file from upstream and enter the Collation Infeed. A pair of Metering Belt sections run at staged speeds to open a controlled gap between products, and a Lane Divider splits the single stream into the number of lanes the pack needs, for example three lanes of two for a six-pack. Photoelectric Product Sensor heads count the products and watch the gaps. When the lanes hold a full group, a Back Stop registers the leading row and the Group Pusher sweeps the collated group sideways onto the waiting tray. The pusher uses a profiled Pusher Bar driven by Pusher Cylinder actuators running on a Linear Guide Rail so the group transfers square and without tipping.

Tray forming

Flat blanks are held in the Tray Magazine and Former. The Blank Hopper is an inclined store with low-stack detection so an operator can top it up without stopping the line. A Suction Feeder draws one blank at a time with bellows Suction Cup heads fed by a Blower Motor, then lays it onto the forming bed. The Tray Erector folds the side and end walls up around a Former Plug using four Folding Arm sets, and a Glue Unit fires hot melt through its Glue Nozzle heads to bond the corners. The adhesive is kept liquid in the Glue Tank by a Heating Element. For pad-only formats the erector and glue stages are bypassed and the product group simply lands on a flat corrugated pad. Trays are usually B or E flute corrugated board sized to the product footprint.

Film unwind and feed

Shrink film comes off a reel held in the Film System. The reel sits on an air-expanding shaft in the Reel Cradle, and a Reel Brake regulates payout so the web does not overrun. A Dancer Arm, a spring-loaded roller carried on Coil Spring tension, absorbs the slack as the feed starts and stops, keeping web tension constant. The film runs over several Film Roller guides to the wrapping point. After the correct length is drawn for each pack, the Film Knife and Seal Bar drops: a heated Seal Wire backed by a PTFE-faced Seal Bar Body cuts the web and welds the trailing edge to the leading edge of the next pack length. The film is polyethylene shrink grade, typically 35 to 80 micron, chosen for the pack weight and the wrap pattern.

Wrapping and sealing

The Wrapping Station takes the tray and product group and draws the cut film over the top and down both sides using a curved Film Drape Plate. The two film edges meet underneath the pack, and a Side Sealer runs heated Seal Wheel elements along the overlap to fuse it into a continuous lap seal on the underside. At this stage the film is still loose, holding the group together but not yet tight. A Wrap Conveyor then carries the loosely wrapped pack into the tunnel without disturbing the open ends, which will close as the film shrinks.

Shrink heat tunnel

The Shrink Heat Tunnel is where the wrap becomes a finished pack. It is a double-skin Tunnel Housing insulated with mineral wool, with air curtains at the entry and exit to hold heat in. Inside, a Heater Bank of finned Heating Element units warms the air, and Recirculation Fan units drive that hot air across the heaters and over the pack so the film reaches shrink temperature evenly. A Tunnel Conveyor running a heat-resistant Tunnel Belt sets the dwell time, usually a few seconds, by controlling belt speed against tunnel length. Air temperature is held between roughly 140 and 220 °C by a Temperature Controller reading Temperature Sensor thermocouples in each zone. Total tunnel power is in the 24 to 48 kW range. Too little heat leaves loose film, too much scorches the film or the product, so zone control matters.

Cooling, discharge and control

Leaving the tunnel the film is hot and soft, so the Cooling and Discharge Conveyor forces ambient air down through Cooling Fan units to set the film to a tight glossy finish before the pack reaches the palletiser. The whole machine answers to the Control System. A PLC Module sequences the collation, forming, wrapping and tunnel stages, while the HMI Panel lets operators pick a recipe, watch throughput and read faults. Changeover between pack counts and tray sizes is a recipe change plus mechanical adjustment of the lane dividers, former plug and film length, typically 10 to 20 minutes. The Safety Relay drives the emergency stop circuit, and the Safety Guarding adds interlocked panels and Heat Shield covers over the hot tunnel skin to keep operators clear of moving parts and hot surfaces.