Ishida weigher enables fixed-weight packing

WEIGHING fish is not as easy as it seems, and one to know it is Deutsche See Fischmanufaktur. Germany's seafood market leader has switched to a weighing solution that meets its fixed-weight pack requirements.

The seafood company, whose Gourmet range comprises salmon, cod, and snapper fish pieces weighing between 155g and 175g each, requires two large fresh fish fillets for its fixed-weight pack without straying too far from the overall weight target.

The company has been using manual static weighing, which was slow and caused overweight because the pack's fillet allocation was decided by the worker handling the machine. The classic multihead weigher does not present a solution either. Even if two fish pieces got into any one weighing hopper, the contents cannot be used to achieve an accurate weighment. Further, it is difficult to move large fresh fish pieces across metal surfaces, onto which pieces could get stuck.

Ishida Europe's answer to the problem is a complete integrated packing line featuring a special 14-head screwfeeder weigher with scraper hoppers. The new system boasts a speed of 30 packs per minute, equivalent to nine tonnes of packaged fish per two-shift day. It has rotating metal spirals to thrust the fragile and sticky fillets into the hoppers.

The weigher uses three different approaches to get single fillets into as many weigh hoppers as possible whilst preventing any weigh hopper from having more than one fillet at a time. The fillets are placed by operators in the segmented conveyor, which moves the fish pieces to the top of the weigher. From here the fillets are transferred to a rotating funnel that deposits them into the screwfeeder troughs one at a time. Upon sensing the arrival of a fillet, the load cell or weight sensor in each pool hopper switches off the rotating screw in the corresponding trough until the pieces have been moved to a weigh hopper or one of the booster hoppers, which are located directly underneath the weigh hoppers and store products that have been weighed.

A timing hopper collects the fillets, enabling complete weighments to be dropped into the same section of a short segmented conveyor. The hopper also delivers the fillets to operators for placing into twin thermoformed trays. The pieces are then sealed under a modified atmosphere, labelled, and deep frozen.

The Ishida design raises the probability of finding a fillet combination very close to the target weight with the help of its 14 booster hoppers. These allow the system's on-board computer to choose from up to 28 different fillets during each weighment. Ishida's unique Anti Floor Vibration system further improves accuracy by sampling ambient factory vibration and subsequently adjusting the weigh signal to cancel it out.

To ensure safety and prevent contamination, the ascending conveyor has special drip trays that prevent liquids and product fragments generated during processing from entering the weigher. The embossed metal surfaces that receive the fish fillets dropped by the rotating funnel adopt a geometry designed specifically to ensure that each fillet arriving at the screw will move in the same direction as the screw itself. This, in turn, generates a gentle forward motion toward the hoppers without crushing the fish pieces. The scraper gates on the hoppers have a grill made up of rounded bars. This design is meant to prevent the fillet from sticking onto the hoppers by ensuring that only parts of each fillet come in contact with the surface of the gate.

According to Deutsche See technical manager Bernd Schröder, "Extensive tests were run to choose screws that are best suited for handling our fish fillets. Ishida have been faithfully at our side all along.  The technical support has been excellent."

Rods fitted to the DC aid gentle transfer of salmon fillets