Corrugated Cardboard Production Quality Defects Related to Heat Transfer
The increased market demand for lighter weight corrugated board poses unique challenges for older machines that were primarily designed for larger flutes sizes using heavier liner and fluting mediums.
Specifically, production of lightweight board can cause operational issues at the single facer and hot plate/double backer sections of the corrugator, these issues are primarily related to the inability of the system to turndown in temperature without flooding these sections.
The smaller flutes and lighter medium/liner require a lower steam temperature at these sections to prevent delamination, bursting, fluff outs, warp, and curl quality defects. However, by lowering the steam pressure, hot plate and single facer sections may flood, resulting in further problems related to the loss of heat transfer.
The above-mentioned quality defects may also be attributed to the mechanical setup of the machine (i.e. problems at the glue applicator/pressure roll). In these instances, this issue will largely remain constant even when moving up to a large flute run, while heat transfer related issues may subside in such an instance.
OEM steam systems typically offer limited control overheat transfer into the liner and fluting mediums other than by medium wrap or speed adjustment. Systems with such limited control can only really be designed to work well for one board combination. OEM control systems are set up to run on combined board temperature; the steam system needs to be able to deliver the required temperature being called out and needs to be able to responds accordingly
Where a site is producing large variations in board combinations, lightweight runs suffer from not enough turndown, in this situation, the site can reduce wrap, speed up if possible, and/or apply an excess of glue to act as a heat sink, which is not ideal as it not only adds an excess of weight but the added excess is a waste of glue. This makes it even harder to run good flat board.
At the other end with heavyweight production getting enough heat into the mediums while maintaining a respectable production speed can be an issue. Further, a key related complication is roll flooding, which is a combination of rotary joint and syphon design quality and steam system design flexibility.
All is not lost though, steam systems can be modernized, in fact, even a partial rebuild can be a revelation to the end-user in terms of performance and control. Key benefits of modernizing your OEM steam system can be summarized as:
- Improved board quality through reliable and consistent temperature control and elimination of board delamination, bursting, fluff out, warp, and curl quality defects, where these defects are attributed to heat transfer.
- Accurate, precise, and repeatable temperature control, resulting in increased profitability because of stable lightweight production runs.
- Reduction in reject board rates (waste) attributed to high section surface temperatures.
- Reduced maintenance burden, improved H&S, and hygiene via the elimination of vessel pits.
- Energy efficiency by operating at lower pressures and temperatures.