Paprican Web and Roll Centre: Fixing Quality and Runnability Issues
By Pulp & Paper Canada
When paper rolls leave the mill for the pressrooms, the engineers hope that the paper quality evaluated at the mill is sufficient to predict the performance on the press. Experience shows that this is...
By Pulp & Paper Canada
When paper rolls leave the mill for the pressrooms, the engineers hope that the paper quality evaluated at the mill is sufficient to predict the performance on the press. Experience shows that this is not always the case. One of the major culprits here is bagginess. Bagginess is created when one side of the web on a printing press becomes slack and creates misregistration and wrinkles. In most cases, the engineers cannot relate the bagginess to the paper machine operation and are therefore left with no means to correct the situation. Paprican found that this kind of problem called for new tools.
Over the last few years, Paprican’s research on calendering, runnability, winding, and web stability has led, not only to the advancement of knowledge, but also to the development of new testing methods and equipment. The application of these findings has led to the inauguration of Paprican’s Web and Roll Centre (WRC). The centre is unique because its team provides a variety of means to evaluate the quality of webs and paper rolls.
The heart of the centre is certainly the Roll Testing Facility (RTF). The WRC team unwinds paper rolls on the RTF to evaluate their winding structure. Since 2002, more than 1500 rolls have been tested and analyzed this way. This impressive experience, acquired through the analysis of each roll, allows the team to relate different quality issues to the roll structure. For example, the team identified how the paper roll structure can be related to the resistance to handling. The coordinator of the service, Louise Maltais, evaluates winder adjustments to enable the mill to provide rolls that will have a better resistance to handling from the lift trucks and thus remain round. Due to the research on runnability, criteria on the maximum roll deformation can be provided so that a roll can take before it affects the runnability on the press.
Another unique feature of the RTF is the tension beam that measures the tension profile of the web precisely and with high resolution. This beam, designed by Frdric Parent and Jean Hamel, took two years to develop and has emerged as one of the most important features of the facility. The tension beam now makes it possible to identify the origins of bagginess and implement solutions to eliminate the problem. In other cases, adjustments of the moisture profile were implemented successfully. Following these fine-tuning adjustments, the edge rolls reached the same runnability as rolls produced from the centre of the machine.
The RTF now elucidates the well-known relation between web performance and roll quality that was traditionally evaluated by the operator hitting the roll with a stick. Surprisingly, the team found that the bagginess could, indeed, be related to the winding but only for some grades. This is particularly true for super-calendered and coated grades.
Also unique to the RTF is that, while the paper roll structure is evaluated, the web uniformity, stability and uniformity of the paper are also continuously evaluated. This feature adds a whole new dimension to the analysis of paper rolls and is particularly useful when the problem was not well-defined by the customer.
Another example of the WRC’s capabilities is that sometimes a better resolution is required to find the origin of the problem. The Web and Roll Centre team then turns to its TAPIO PMA (Paper Machine Analyzer). Javad Saberian specializes in running the analysis of the data from the TAPIO which can measure paper at an extremely high resolution and for bands collected in both machine direction and cross machine direction. This high resolution measurement capability and sophisticated analysis tool, supported by Paprican expertise, provides the papermaker with easily understandable and practical advice to fix the problem at the source. If required, the team combines the high resolution TAPIO measurement with other types of analysis available at the WRC.
The service of the team also extends to paper finishing like calendering. Frdric Parent, leader of the Web and Roll Centre, utilizes a roll-barring detection device that measures the calender roll shapes with extreme precision. This precision allows for identification of potential sources of deformation of the rolls. Modified grinding procedures were successful in resolving variation in the thickness of the paper. The roll-barring device was also useful to evaluate soft rolls of on-line super calender. Parent is presently working with a paper mill to evaluate if the roll-barring detection device can be used to fix barring on wet press rolls.
The work completed with the barring detection device, the RTF and the TAPIO leads to a much better understanding of how calender roll deformation could be linked to paper roll quality and uniformity. Recent work revealed that the calender was a possible source of problems at the winder, generating paper roll defects. This amplifies the benefits of having the expertise and several services regrouped.
Another key activity of the WRC team is in the evaluation of the reactivity of the sheet to a change in humidity. Andr Mnard characterizes the sheet curl and hygroexpensivity at different moisture levels using different techniques. The way the analysis is completed allows Javad Saberian, coordinator of the Dimensional Stability Analysis (DSA), to identify the origin of the instability in the paper. When completing the analysis, Saberian can identify if the curl originates from the paper machine wet end or the drying section. Recently the WRC group has worked on developing a method to test the stability of paperback books to help a mill understand how the paper and the cover affected the paperback book on the shelves of a store.
An additional service is the optimization of calender stacks. Experience and well-established calender simulation techniques allow the team to help mills find the best configuration. This service is used on a regular basis by mills to compare different options with the existing equipment, or to select new equipment required in achieving thickness targets.
In the pressroom, runnability issues in the mills can also be dealt with. Several on-press techniques are available to find the origins of the variability on the printing press and to determine what the contribution of the paper is to the variability. The WRC team also provides sophisticated statistical runnability analysis to mills identifying the most important strength properties required in obtaining the maximum runnability in the pressroom. Such studies have helped mills accomplish substantial savings on their manufacturing costs without any effect on the runnability.
These and other research results have solved web and roll quality issues for several mills through the application of successful research for optimization and troubleshooting. The WRC is an integral part of the Product Performance Research Program in Paprican, managed by Jean Hamel. To stay ahead of the needs of the industry, the centre knows that it is essential to invest in equipment improvement. For example, the Roll Testing Facility was recently modified to accept rolls of 60″ in diameter, as this might become a new standard on new printing presses. This trend will have not only a significant effect on transportation but also a serious impact on winding. Other changes will be implemented on the RTF to improve measurement on super-calendered and coated paper, and projects on studying the effects of fountain solutions on the web behaviour will be undertaken.
The WRC team is presently investigating the need for paper properties and roll structure benchmarking where a complete evaluation of the paper and roll properties would be evaluated and compared to other machines for similar grades. The team is looking at initiating this benchmarking in the fall 2006 for newsprint and, depending on demand, for fine paper later in 2007.