It has changed our way of working. Earlier our operators reacted to warp at the pre-heaters, altering temperatures to correct problems. Now we think in terms of moisture and temperature which allows us to correct warp, like edge and S-warp, which were previously impossible by controlling only the pre-heaters.
Joint development started in earnest at the end of 2014 with the delivery of Valmet IQ Moisturizers to Saica’s Viana corrugator plant in northern Spain. The initial target was to reduce warp, the deformation in the flatness of the corrugated sheet, which is one of the most severe quality destroying problems experienced in corrugated board manufacturing. Used extensively in paper production to control warp, wrinkles and heavy edges, the IQ Moisturizer is a moisturizing system with applications for moisture cross-direction profiling, warp control and smooth moisture level increase. It features an air atomized microdroplet spray nozzle to correct the warp of the combined board by reducing moisture differences in the cross direction in the top and bottom liner that cause the board to warp.
Traditionally, corrugator controls have been based on temperature reading technology. Recognizing that further improvements were possible, Saica Pack, the business division producing corrugated board within Saica Group, agreed to pool its process know-how with Valmet’s automation technology. The goal: to develop an advanced automatic quality control system for corrugators. The collaboration started by identifying the requirements of the control and the kind of measurements needed to develop the full Quality Control System (QCS). Experience with moisturizers dictated the need for accurate moisture measurements to work in the narrow confines of the corrugator as well as an accurate online warp measurement.
One of the first developments was the Valmet IQ Multipoint Moisture Measurement. Based on infra-red (IR) technology the IQ Multipoint can measure moisture content from up to nine different locations in the process. Valmet IQ Multipoint Moisture Measurement consists of measurement probes and a field box to which probes are connected with optical fibers. Depending on the installation location, there are two different types of probes that fit even the tightest spots in the machine. IQ Multipoint makes it possible for the on-line measurement of moisture at the reel stand to cope with seasonal and storage variations. Prior to gluing, it looks after optimum glue penetration and minimized warp.
Production quality is now very stable across all grades, and if we have a problem we can see it very quickly. Variability in liner moisture to the corrugator is no longer a problem. Before, we could have a wrinkle problem with a certain grade because of excessive temperature at the double backer, but now with the moisture and temperature-based control this is no longer a difficulty.
The full QCS system has been up and running in Viana since 2018. It uses a combination of moisture and temperature measurements together with the IQ Converting Moisturizer and existing heating elements. In fully automatic control, it improves gluing, reduces fluting defects or washboard, and eliminates warp in the final product. Two Valmet IQ Converting Scanners measure the final top and bottom moisture and temperature profiles before cutting, and a warp measurement before the stacker provides the warp degree feedback.
Since this first corrugator QCS, Valmet has developed the image analysis based Valmet IQ Warp Measurement (IQ Warp), which has since been successfully installed to similar systems in other Saica Group packaging converting plants.
The experience in Viana has been very positive right from the start with all the project targets met. “It has changed our way of working,” says Innovation Technology Engineer Isabel Bernad. “Before, our operators reacted to warp at the pre-heaters, altering temperatures to correct problems. Today, we think in terms of moisture and temperature which allows us to correct warp, like edge and S-warp, which were previously impossible by controlling only the pre-heaters.” Before her present position, Bernad was corrugator manager, and therefore familiar with the realities of production as well as the new technology. “We went step-by-step, first with the moisturizers under manual control to automatic operation and now with the Valmet automation controlling both moisture and pre-heat. Once the optimum values are found for each grade, the improvement in board quality and appearance is apparent; the operators don’t want to switch it off!”
Corrugator Manager Jose Manuel Melchor is very satisfied with the system. “Production quality is now very stable across all grades, and if we have a problem we can see it very quickly. Variability in liner moisture to the corrugator is no longer a problem. Before, we could have a wrinkle problem with a certain grade because of excessive temperature at the double backer, but now with the moisture and temperature-based control this is no longer a difficulty.” With up to ten product changes a day, the Valmet QCS achieves faster on-specification conditions that reduce waste. “It takes time to find the balance of moisture and temperatures for each grade, but once you have it, it is easy to replicate conditions when you next run that grade. If we see a problem with a particular stack, it is easy to look at the history of production parameters for that stack and make a change to the recipe if necessary. Some grades might need a little warp which will then flatten during storage, and in these cases the system is really useful.”
A tremendous help during this first corrugator QCS delivery is the remote connection that allows Valmet specialists in Finland to see in real-time the same screens and information that the operators and Bernad are working with. “The remote connection works really well,” says Bernad. “As this was the first corrugator QCS we follow very carefully, and Valmet is always there to help. If we have a problem, it is really quick to get assistance by email or phone because Valmet can immediately look at our data and give advice.”
Learn more: Valmet IQ for corrugated board