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Special Focus

Don't Come Unstuck Over Folding and Gluing

by Uvan Magni, Technical Product Manager, Bobst Group North America

August-September, 2007
Designers have a poor reputation among folder-gluer operators, largely because of the choices they make when they first design a box. It doesn’t have to be this way. With a little ‘manufacturing education’, designers can make a significant, positive impact on the productivity and profitability of the box and consequently, the stress level of the operator.

The way the box is printed, processed, or diecut is certainly important to the efficiency and productivity of the production process. However, a key factor affecting profitability – box design – takes place before the box gets anywhere near the shop floor and has a significant impact on the set-up time, running speed, waste, and quality of folding and gluing.

Modifying a corner, laying varnish down over a glue flap, or choosing a particular substrate may seem inconsequential to the designer, but when the box starts in production, such choices can have a huge impact on productivity and quality. Nonetheless, when it comes to designers, perhaps gluer operators should ‘forgive them, for they know not what they do’. It’s usually not their fault, as the majority of designers never receive training on the effect of design on the folding and gluing process.

Typically, designers are focused on determining how the box will satisfy the needs of the customer and end-user in terms of strength, protection, attractiveness, and ease of use. However, it’s also important that they consider the cost of manufacturing and always aim to minimize makeready times, stoppages, and waste; maximize running speeds; and ensure the quality meets the standard. Meeting the customer’s aesthetic and structural requirements is necessary and important, but equally so is making sure the job can be manufactured efficiently and at a profit.

However, designers may be in a position to make a choice about the actual style of box they will create. The simpler the better for manufacturing, but simple may not always meet the customer’s requirements. The hierarchy of boxes dictates that, in general, as the box gets more complex so will the cost to produce it, largely because the makeready will be longer, production speeds lower, and waste percentage higher. So choosing a straight-line or crash-lock bottom style, over perhaps a four- or six-corner carton, can have a huge effect on performance. While a straight-line box may makeready in 15 minutes and run at well over a hundred thousand boxes an hour, its six-corner cousin may take an hour or two to set and run below 10,000. This is fine if the premium you can charge for the more complex box reflects the extra costs, but in today’s highly competitive packaging market, the margins on all work are being eroded. So, it’s vitally important for the designer to know where the most profit lies in terms of styles.

Carton Styles - Tricks of the Trade
Design choices made within a style also can have a massive effect on performance. One of the box types that gluer operators traditionally dislike is the tapered crash-lock bottom box, largely because that type of box generally means long, troublesome makereadies. The key ingredient to achieve from the design here is a layout that gives a good square point to feed from and a second or fourth crease that can be folded normally. Reducing the number of tapered creases that have to be folded also helps runability, as does adjusting the angle of taper so that it runs outwards, towards the base of the box.

Fishtailing is a problem that particularly affects very wide, short boxes and is common on disproportionate crash-lock bottom boxes, especially those constructed from corrugated substrates. In many designs it may be possible to change the layout to incline the second crease. This will push the top edge of the glue flap against the folded inside flap, resulting in perfect alignment of both glued panels.

On more conventional crash-lock bottom boxes, sometimes there is insufficient thickness of board at the glue flap once the box is folded. This typically results in unsatisfactory gluing. To overcome this problem, it is possible to use a special pressure belt in the delivery section of the folder-gluer. However, the best solution is to modify the outline of the glue flap to obtain a fifth thickness of board at this location and to ensure a perfectly glued box.

The growth in popularity of windowed boxes, where the consumer can see the product, means more trouble for gluer operators. Most conventional window apertures are rectangular in shape. This often leads to the carton catching as it leaves the feeder. A simple redesign of the aperture to a circular or oval profile can reduce this dramatically and therefore increase running speeds, reduce stops, and cut down on waste. Similarly, the dust flaps on straight-line boxes can catch as the box enters the feeder of the folder-gluer. Double knifing these flaps will prevent the problem, although it is good to start the cut with a straight single knife to maintain the squareness of the box once it’s made up.

Cutouts in the box, as with windows, can cause the gluer operator serious problems. Those involving right-angled projections have a tendency to cause snagging in the delivery section. The designer can help avoid this by bringing the edge of the projection back at an angle. Similarly, cutouts should be avoided if at all possible in areas where the tools of the folder-gluer will need to be applied to the blank, such as the trailing flap of a four-corner box.

Consistency in design can give folder-gluer operators some key production advantages. Operators know what to expect and can have the relevant equipment on hand (even partly made up perhaps), ready for particular profile ‘families’. This can reduce makeready times considerably. By the same token, if the designer is able to use the same or very similar profiles for different jobs, then the operator may be able to run these jobs consecutively, further maximizing makeready efficiencies.

Carton Materials

After the carton style is decided comes the choice of material. Today, this may include chipboard, kraft, solid bleached sulfate, clay-coated newsback, microflutes, ‘green’ substrates, and plastics. Each presents different challenges to the gluing process and a poorly informed decision here can have a major negative effect on gluer productivity. In the same way, the designer’s choice of finish and embellishment on the carton can have a key influence on gluer productivity. For example, certain varnishes sometimes cause feed problems or prevent effective glue application and adhesion.

While the designer may not have a direct influence on the choice of grain direction for the printing and finishing of the product, it remains a key design element. During sheet formation, fibers tend to orient themselves in the operating direction of the board-making equipment. This orientation is vitally important because the board is harder to fold across the grain (direction of fibers). To ensure the optimum productivity on the folder-gluer, the grain should be perpendicular to the running direction of the gluer.

Of course, a designer can only go so far to make the final design ‘gluer friendly’. Time, and above all the customer, will determine how much the designer will be able to adapt the design for production before it is handed over to those resourceful gluer operators. However, the more knowledge the designer has and can apply to the product before it reaches the shop floor, the more margin it will have garnered by the time it leaves.