GETTING TECHNICAL

58 INTERNATIONAL PAPER BOARD INDUSTRY

R egular readers of thismagazine over the years willhave noticed that most of

my articles relate to printing. Onthis occasion, I’d like to discussfolding a typical RSC (FEFCO0201). The first thing to realise isthat a box with a print defect canstill be used for packing goods, buta box with a folding defect givesproblems on a packing line. It’stherefore critically important thatboxes meet dimensionalspecifications and tolerances.

The most common boxproduced is the FEFCO 0201. It’sprobably the widest used boxdesign and the flexo folder gluer isthe most commonly used machineto produce it. But do we reallyunderstand the impact of producingthis type of box on a machine thatis not in perfect productioncondition?

In other words, when did you lastcheck the alignment of your FFG, inparticular the feeder relative to theslotting section and folding section.

Do you know how many boxes areused during set-up? Are yourcustomers happy with your foldingquality? Do you have any idea aboutthe impact on box compressionstrength when producing an RSC ona machine that is not properlyaligned? I can’t answer all thesequestions in just one article, but Ican start by giving you an insightinto what happens in relation toproducing a folded box on a FFGthat is not aligned correctly.

Let’s start by doing acontrolled test that involvesproducing an RSC in combinationwith a single colour print. Afterthat, we need to measure (using adigital camera and image analysissoftware) the boxes in differentsteps and link the data togetherto show what was happeningduring all the different productionsteps. The result will be a clearpicture of the movement of theboard and the displacement ofthe tools during the productionprocess.

WILBERT STREEFLAND LOOKSATWAYS TO ENHANCE

PRODUCTIONON THEGLUING LINE.

MRSTREEFLANDHASWORKED IN THE

CORRUGATED INDUSTRY SINCE 1992.

DURING THIS TIME, HE HASBEEN

TECHNOLOGYDEVELOPMENTMANAGER

FOR SCA PACKAGINGASWELL AS

TECHNICALMANAGERAT STORK

SCREENS. HE STARTED TECHNOLOGY

COACHINGBVBA IN FEBRUARY 2005.

GE

TTI

NG

TEC

HN

ICA

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HOW TO IMPROVETHE FOLDINGOF AN RSC

INTERNATIONAL PAPER BOARD INDUSTRY 59

GETTING TECHNICAL

The problemTo understand the problems of manufacturing an RSC, I’ve produced two drawings. What you could do is put thismagazine on your copier and copy the two images. Preferably enlarge them so that one image fits on a full A4sheet. Next, cut them out and fold them over the folding lines, as is done on the FFG. What you will notice is thatthe following image will result in a perfectly folded, flat box with no fishtailing and that the lead edge and trailedge gap are the same size.

In the next image, I simulated the box being fed skewed. If you cut it out and fold, you will see what happens.Think also about what happens in the squaring section after folding or adding side trim. It all only gets worse!After folding you will see panel misalignment and gap differences.

GETTING TECHNICAL

60 INTERNATIONAL PAPER BOARD INDUSTRY

What can you do?It all starts with doing a controlled test combiningprinting and the FFG. This makes it possible tomeasure the feeding of the board against the printingand the slotting of the board against the printing. Thenwe apply maths, which will present the results as ifthere was no printing done. We also measure the leadand trail edge gap and the fishtailing of the foldedbox.

The feeding of the board is measured in the printdirection and in cross print direction. This data willlater be used to correct the resulting gaps andfishtailing. We can do the same with the collected slotdata. The following graphs show feeding results:

Note that the skew measured on the lead edge,drive side of the board and on the drive side lead trailedge are in the same rotation direction. Remember,we did not use side trim. The cross print directionresults for the glue lap also show a misalignment thatwill affect the resulting gap.

IT’S CRITICALLY IMPORTANT THATBOXES MEET DIMENSIONALSPECIFICATIONS AND TOLERANCES.DO WE REALLY UNDERSTAND THEIMPACT OF PRODUCING A BOX ON AMACHINE THAT IS NOT IN PERFECTPRODUCTION CONDITION?

Drive Side(Glue Panel)

Operator Side(Glue Lap)

PrintDirectionLeadEdge

CrossPrintDirectionLeadEdge

PrintDirectionTrailEdge

GETTING TECHNICAL

62 INTERNATIONAL PAPER BOARD INDUSTRY

Next we measure the slot positions. The following images are the results:

Note the skew for all three slots. It differs from slot to slot. Imagine what impact this must have on the resultingfolded box. The slot depth can be measured. Here are the results for the centre slot.

The last step is to measure the folding results in terms of panel alignment (fishtailing) and gap. The followinggraph shows the panel alignment measurements (fishtailing) and how it can be corrected for the skew caused bythe feeding of the board.

LeadEdge

TrailEdge

Slot 1 (Glue Panel) Slot 2 Slot 3

Lead Edge Trail EdgeSlot 2

GETTING TECHNICAL

Note that the data corrected for the feed errorprint direction and cross print direction centre around“0”. The lead and trail edge gap was measured andcorrected for the cross print direction and printdirection feed as well as the slot position.

Notice that if we correct for the feeding andslotting error, then the gap starts to vary around itsnominal value. This indicates that all systematicfolding errors originate from how we feed the boardinto the machine and how we slot it. It is very unlikelythat this can be corrected by using a side trim knife.Best to avoid the additional waste!

RecommendationIf you want to reduce your set-up waste and improveyour folding quality, then it might be best to start bychecking the alignment of your machine, in particularthe feeding section and the slotting heads. It willprobably help you to produce boxes faster, of higherquality and with less waste. �

Wilbert Streefland can be contacted at: wilbert@tcbvba.be