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FLEXO Magazine : November 2008
TECHNOLOGIES & TECHNIQUES Consider the steps to produce a carton in a typical sheetfed production system. First, rolls have to be sheeted, then jogged, then printed, then jogged again, then die cut, and then sometimes hand stripped. Only then are the finished cartons ready for the gluer. Now think about a typical web-fed folding carton produc- tion system. A roll of board is put on one end of the press and finished blanks come off the other end. Let’s count the steps in the offset shop: 1 Sheeting 2 Jogging 3. Printing 4 Jogging . . . 5. Die cutting 6. Hand stripping. Now, the steps in the flexo shop: 1 Put roll on press . 2. Take finished blanks off press Intuitively, most people, even those with no printing or con- verting background, would be able to spot the more productive process. In my analyses I have discovered revenue per labor hour disparities of up to four times (400 percent) when comparing the same work through both processes. Quite simply, fewer workers can produce the same amount (or greater, as we shall soon see) of work. This is the essence of productivity. Much is made of the productivity of the 40in. sheetfed machine, perhaps the industry’s most popular size press. New machines are rated at 12,000 or even 15,000 sheets per hour. However, since printing is only one part of making a carton, these new super-pro- ducers are still hamstrung by the next operation: cutting. A 15,000 sheet press doesn’t do one much good if the die cut- ter only chews through 6,500 sheets. Of course, one can buy two or three die cutters to keep up with the fast new press, but the machines are expensive and each needs a crew to run it. These necessities put a damper on the plant’s productivity by adding labor and depreciation costs to the converter’s ledgers, when in actual fact he is endeavoring to reduce these costs. Looking now at the flexo side, the productivity of a 26in. press stacks up very favorably against the popular 40in. sheetfed sys- tem. A quick and simple calculation confirms this: Process 40in. Sheetfed Press & Flatbed Die cutter* 26in. Web Flexo with Inline Rotary Die cutter Throughput 6,500 sheets/hr* 28in. x 40in. 600 FPM 26in. web Square Area Equivalent 50,555 square feet 78,000 square feet This table, of course, represents gross theoretical throughput. These figures have to be modified to allow for makereadies, starts and stops, and all the normal things that happen on the produc- tion floor.* However, this exposes an important point—that even a fairly small web flexo press has the capacity to outproduce the venerable 40in. sheetfed machine by a wide margin. One could argue about the speed assumptions chosen for the comparison, however, experienced folding carton people will recognize the figures above as reasonable estimates. LAY ME DOWN The second major economic benefit of flexography comes from the nature of the in-line rotary die cutting process. Some might say that this is the primary benefit because the paper cost reductions are sometimes quite dramatic and fall immediately to the bottom line, hence being more visible. In any case, with pa- perboard being the largest single cost component in the making of cartons, it behooves converters to squeeze every percentage point they can out of their raw materials. A typical sheetfed layout of a reverse-tuck carton put on a rectangular sheet in the most efficient means possible will still result in waste from the gripper, nesting and edge trim. On a flexo press, the same carton is placed on a web and travels at 90 degrees to the sheet direction. There is no gripper waste (which presumes printing plate sleeves or cylinders made to the exact repeat) and there is also, and perhaps more significantly, no nesting waste. The continuously repeating pattern made possible by the rotary die allows for the most efficient use of substrate. The finite surface of the flatbed die places severe limitations on this ability to use paper efficiently. This may be equal in importance to the rotary die’s large productivity advan- tage. Certainly, we have found in our analyses that these factors combined nearly always outweigh the much higher cost of the rotary die. Recent studies support the paper savings made possible by the inline process. My own research, conducted over the last four years, confirms that. Depending on the mix of carton sizes and shapes one has to produce (which vary constantly, of course), paper savings amount to somewhere between 5 percent and 15 percent. This is chiefly due to the differences in layout described above. www. f l e x o g r a p h y. o r g NOVEMB E R 20 0 8 F LEXO 3 3