3 4
by the other knife or knives, as may be the total lineal grades, the scheduler normally allows more wasted side lengths of the jobs. When the job through a knife has trim and frequently upgrades the liner weight into the been completed, another job of similar width may be next heavier paper grade to be compatible with other started to take the previous job's place; any minor width jobs. On very rare occasions, a job requiring specialist difference becomes edge trim and thus waste. If the 5 paper grade is capable of being produced by scheduling waste becomes too great, the scheduler may decide to multiple blanks across the corrugator web with minireposition his jobs on a narrower width of paper and mum side trim; such a job is known as a "self-trinimer." thus splice in a narrow paper width. It is in this narrow situation that preprints are typically
As an example, if a customer has ordered 10,000 con- used, tainers, each having a 29 inch blank width, the blanks 10
may be scheduled and run three abreast on a 99 inch Preprint Liners And Associated Problems
corrugator, using 90 inch paper. For convenience and Preprint liners are liners which have been printed in
ease of handling, one knife and stacker station may a pr0Cess prior to the corrugation process, and in a
process two of the blanks, while another knife and manner that allows the quality and complexity of the
stacker station may handle the other blank. Smce the 99 15 applied graphics md print t0 be dramatically enhanced
inch corrugator width has not been fully used, an alter- over that of prmting which takes place during conver
native is to find another slightly wider job within the sion after the corrugation process. Because such liners
same board grade combmation and with a similar over- ^mQst always feature enhanced graphics, they tend to
all lineal length to run beside the 29 mch blank or be on s ecialist ^ more unique pa ers which
blanks. For instance, a second job for 15,000 contamers, 20 m often considerabl more expensive than standard
whose blanks are 36 inches wide, with a slightly longer des Such must have the surface tex.
blank length, would give a combined width of 94 turg tQ a fme ^ ^ haye ^ ^
inches, taking into account two 29 mch blanks. With {h ^ edness necessary to provide the strucone or two inches of trim, which is always needed for . , . t . , . r., e . , , ... , , nl . , ... i_ „, tural strength component required in the finished conshrinkage and wander, 96 inch paper width may be 25 . . ° .,,r, , , r . ■ , , •j it J Ti. «• \. -j ui i v. *u tamer or to withstand the abuse of being dragged ideally used. The 36 mch wide blanks, because they are ^. , , . , ., . f.
... . , , .j , ... through the hot and cold section of an operating corru
a separate job, must be processed at the dry end with ° r"
their own knife and stacker station, however. The obvi- ° ', . ,, . , .,
ous difficulty is that one job will have been completed Pf °bvl0US Problems associated with attempting to
while the other is still running. The remainder of the 29 30 sfedule two °\moie V**TM* Jobsuon one TM *most
inch blanks will then be immediately matched with always require the preprint jobs to be run as self-tnm
another job to allow it to continue or placed back into mers" The, only exception is when a particular
the scheduling pool of outstanding work. customer places two orders which may be run simulta
The scheduler's job is thus a never-ending job of neously> which le<^e the ^ specialist papers, the
puzzling together an optimum schedule with minimum 35 graphics of which may be produced on the same roll
side trim waste, in a manner that allows the corrugator (usmS the same equipment at the same time) by the
to run continuously, and subject to a number of vari- prepnnter, which may be scheduled across the corruga
ables, including board grade, paper width, blank width, tor web width with minimum side trim waste, and
and total lineal length. Computers have automated as- whi°ri allow enough advance notice for the order to be
pects of this complex task, and have particularly al- 40 placed with the preprinter.
lowed flexibility in scheduling in order to accommodate Preprints, furthermore, often require special width customers who require "Just-in-time" delivery, small mediums and inside liners in order to fit the customer's orders and both. Such automated control also allows needs. For example, if the corrugator is of a maximum the various components of the corrugator to be more width of 99" and the width of the blank is 17", then five precisely synchronized so that production speeds of 400 45 widths, which total 85", would fit the machine. An 86" to more than 1000 feet per minute are both possible and or 87" paper width should thus be run, but those sizes practical. may not be in the normal inventory of, for instance, 90" Although there are an infinite number of possible and above. A small specialist lot of 87" medium and board grades, the industry in North America has tended inside liner would thus be required. Not only is use of to settle into using a relatively small number (three to 50 the corrugator width not maximized, but extra waste is six) of common grades in order to accommodate paper incurred as there is bound to be extra board left on some manufacturers and the trimming and scheduling prob- rolls after the job is completed. (Preprint, the most lems of the corrugated industry mentioned above. Per- expensive component, is almost always consumed tohaps the greatest number of corrugated containers, tally if possible, leaving the medium and inside narrowprobably in the range of approximately 90%, are 55 width liner rolls still containing board, which must be formed of natural kraft brown color board. Although absorbed as waste.)
the other 10% is a growing segment, it is still a small Additionally, set-up labor, time and expense usually
segment, and it comprises bleached white corrugated or make it cost-prohibitive to run less than a roll of pre
mottled white, typically on the outer surface only for print. A typical roll of preprint produces approximately
display purposes, and other specialized board grades. 60 80,000 to 100,000 square feet or around 12,000 lineal feet
The scheduler thus has far more scheduling choices of product, resulting in approximately 12,000 contain
with the popular kraft brown board grades, and the ers. At speeds of up to 1000 lineal feet per minute, the
bleached Whites, mottled whites and specialist board run may require only 20 minutes at most. Although
grades present scheduling problems. single roll preprint runs are attempted by some corruga
In order to overcome the scheduling problems pres- 65 tors, the additional settling down period encountered in
entedby the typically narrow ranges of jobs which may producing acceptable product tends to make runs of
be produced at any one time and thus scheduled with 50,000 to 100,000 containers and above (4 or more rolls)
bleached whites, mottled whites and specialist board more normal.
