Tray Formers: How to Optimize for Performance

Tray former

Folding cartons are one of the most efficient ways to package products. Heiber + Schröder offers highly versatile tray formers to erect a variety of tray style cartons like chip scoops, French fry or nacho trays, Chinese takeaway boxes with web corners, trays with lid, hamburger clamshell boxes and more. Tray walls can be vertical or tapered. H+S tray formers can form trays with a 5° - 40° taper.

Achieving a consistently well-formed package during the production run implies several tasks before the gluing and folding phase, and technological improvements featured on Heiber + Schröder tray formers help you achieve the perfectly finished product.

Tray Design

If we review the folding carton manufacturing process, it all starts with the design itself. The package should be developed in a way that fulfills its four basic functions: information, visual impact, convenience, and protection. The shape and material must be evaluated to deliver structural support. The most widely used paperboard types are SBS (coated solid bleached sulfate), SUS (coated solid unbleached sulfate) and coated recycled. Other substrates are folding box board (FBB) and white lined chip board (WLC). They are coated with clay for optimum printability. Heiber + Schröder tray formers can work with paperboard ranging from 200 to 600 g/m2 and corrugated up to 1.5 mm thick.

The package dimensions affect sheet utilization rate. Cleverly laying out the blanks in the full-size paperboard sheet can save thousands in waste. Not only must the design fit the sheet, but it is restricted by the maximum blank sizes that the tray formers can process.

Cutting and Creasing

Along with the graphic design, the package has a cut and crease pattern. The cutting die extracts the package from the sheet and the creases (also called "scores") mark where the carton will be folded to take three-dimensional shape. Creases define the edges of the panels and flaps. Knowing that all paperboard is manufactured in a process where fibers are aligned in one particular direction, it makes sense to make the creases run in the same direction as these fibers ("with the grain") instead of perpendicularly ("against the grain"). Otherwise, during the forming process, the crease may break.

When designing the folding carton, the format may have glued flaps or locking corners to hold the package in shape for final use. Designers must consider that tray formers require that the glued areas do not have printing on them, for better adherence.

The actual cutting and creasing operation is done with a die, which can be setup in flat bed or rotary equipment. When the latter is used, it is usually as a final stage in the printing line. When the crease is produced, some internal delamination occurs (the different layers in the paperboard separate). And when folded in the tray former, further delamination takes place. If the crease was well done, the printed side should not show cracking, and the reverse side should have an even bulge, without crumpling. If the carton is poorly creased, the liner splits and exposes the inner layers of the paperboard.

An irregular crease has several effects on the package: it can cause the panel or flap to spring back (preventing proper adherence or folding) and reduce package compression strength as the panels and flaps will be incorrectly positioned in the tray former.

Quality control in this first stage is crucial. The edges of the printed pieces should be clean and free of debris, such as torn fibers or clumps. Loose paperboard particles would compromise the efficiency of the gluing process. 

Once the carton blanks are cut and creased, they may be sent to the packager for storage and later product filling, or they may be glued and folded for convenience, using tray formers like the CE1000 or the CE1560.

Tray Formers' First Step

Tray formers work optimally when the carton blanks are properly stacked and aligned, ensuring consistent delivery to the conveyor chain. If a blank is improperly picked or slightly rotates, it will be incorrectly glued and formed. For this purpose, Heiber + Schröder tray formers have a pre-feeder section where the carton blanks are stacked and are picked by a processor controlled, timed belt feeder. This technology is considered the best in the industry. 

Next, the make-ready process ensues. Pickup timing and carton length setup must be setup. The CE1000 and CE1560 tray formers have an automatic "teach-in" function, which recognizes the carton length from an actual sample, completing the configuration in a minute.

The conveyor chain transports the blanks to the gluing and forming stations. Heiber + Schröder tray formers have conveyor chains that are adjustable both in the running and cross directions. While the CE1000 has four, the CE1560 has six.

The Gluing Process in Tray Formers

The carton then moves forward to the gluing station. Depending on the application, the gluing technology and placement are different. 4 and 6-point glued trays are usually glued by applying the adhesive from overhead pots to diagonally folded back flaps. For example, chip scoops can be glued with top mounted glue guns. Hamburger clamshell boxes, on the contrary, use bottom mounted guns. CE1000 tray formers can also work with rotary stencils. 

The adhesive can be hot-melt or cold vinyl. If the package will have to withstand heat, it is advisable to utilize cold glue. Heiber + Schröder tray formers come with cold glue systems but have been configured with additional hot-melt equipment as well, by many of our clients.

Heiber + Schröder CE1000 tray formers have a standard cold-glue rotary stencil system which consists of 6 individually movable gluing discs with four normal and two double-width glue pots and bottles. The bottle is placed to maintain a constant glue level automatically. The glue quantity is metered by a small easy to handle thump wheel.

To build chip scoops, H+S tray formers use top mounted glue guns, moving in a lateral direction symmetrically on an oscillating shaft to create the right conical glue pattern. Each lane has two nozzles, and up to four lanes can operate simultaneously.

For hamburger clamshell boxes, the glue guns are mounted below, in a configuration of 4 nozzles per lane.

To prevent improper glue application, if one or more blanks fail to arrive, H+S tray formers automatically stop.

It is very important to ensure that the carton blanks do not skew and that the glue is applied exactly where intended. Glue splashes or squeeze-outs may prevent the package from opening properly in the filling line. 

The Forming Tower

After glue application, the carton moves to the forming tower through top and bottom belts. The tray former's conveyors position it in front of the pusher (also called mandrel or plunger), which exerts pressure on the carton against a matching cavity, making it fold along the creases with the help of metal or plastic fingers and plows. The glued flaps fall in position and are pressed for adherence.

Here, the bending force must be very precise. Heiber + Schröder tray formers utilize servo motors to a move the pusher, which is readily programmed for various tray styles and formats. The forming tools (pusher and cavity) are specific to each tray style. However, they can be modified within the machine's size range, to produce different folding carton formats.

The glued and folded cartons move along the tray former's delivery section accumulating in a shingle pattern. Each lane is individually counted and separated into corresponding batches. They are later removed for delivery to the client. 

The entire gluing and forming station is movable, on wheels, providing free access. This makes adjustment tasks easier and reduces changeover times.

Tray Former Productivity Enhancements

An additional flex-tower, allows the operator to carry out most of the setup for the next job off-line, without stopping the current batch. When the carton style changes, he/she removes the flex-tower and plugs in the new one. A single off-line unit can be shared across several H+S tray formers