A marriage for performance sake: the union of good paper chemistry and sound mechanical operations can help mills live happily every after.
Performance chemicals are important to paper quality and machine performance. They enhance filler and fines retention, improve machine cleanliness, impart water holdout, control chemical and biological deposits, promote optical properties, increase strength attributes, control foam, etc. The mechanical aspects of refining, cleaning and screening, and forming affect the same properties through retention, sheet strength, formation, sheet density, sheet porosity, contaminant rejects, etc. Since these areas of chemical and mechanical influence relate so closely in their anticipated outcomes, why not marry them into common approaches for the benefits of high quality and low-cost production?
Before turning to making this marriage permanent, consider a few actual mill experiences that illustrate how these chemical and mechanical components can work for or against each other:
CASE 1. In a wet end chemistry trial on a heavy weight, coated paper machine, the objective was to increase dry strength and Scott internal bond. The wet-end trial additive was added to the thin stuck loop with an immediate move of the wet line toward the head box. The papermakers then scrambled to adjust the forming zone to accommodate the extra drainage, but they could not maintain the previously well formed sheet. This could have been the end of the evaluation. Instead, the mill people waited a few days and decided to make some adjustments to the forming board position, the clearance of the bottom slice to the forming board, the impingement angle of the stock flow, and the foil angles. On the next mill evaluation of the wet end chemistry, the papermakers could take advantage of the increased drainage to present a better-formed and drier sheet to the first press. This sheet also had a 20% increase in strength properties. Improved chemistry and machine mechanicals produced a success.
CASE 2. In another experience on a lightweight coated-two-side sheet, coating holdout was a problem. Size press penetration and coater color consumption were excessive. Paper runnability and quality were suffering. For many weeks, the papermakers tried changes in furnish, refiner plate, forming zone, sheet moisture content, size press formulation, coating color, etc., without success. Frequently, the multiple simultaneous changes did not allow tracking or trending to determine cause and effect.
After much frustration, assistance from the corporate technical staff resulted in a wet end chemistry approach to increase sheet water holdout. The approach involved holding the mechanicals in the best configuration currently known, increasing the sheet HST sizing, and an alkenyl succinic anhydride (ASA) increase with a first pass retention increase. After reaching the hold-out target, the equipment could undergo adjustment for optimum performance. This approach was successful--the internal size increased 35%, size press and tooter holdout came into the targeted range, and all sheet quality and appearance parameters improved. An additional benefit of 50 ft/min machine speed increase occurred with the retention improvements.
CASE 3. This final true example shows the best way for a chemical/mechanical marriage to work. Sheet cockles, ridges, and undulations were at an unacceptable level on a lightweight uncoated machine. A team received the task to solve the problem. This team included machine operations and people from the mill technical staff, corporate research, quality control, and field technical service.
The team identified sheet stresses and strains from micro basis weight and moisture variability as the root cause for the sheet imperfections. Combining mechanical and chemical approaches gave a marriage that resolved all the sheet imperfections. The team focused on increasing filler content, refining hardwood versus softwood, improving sheet formation, modifying machine direction/cross direction (MD/CD) tensile ratios for a more square sheet, and adjusting sheet moisture content, and improving uniformity.
The filler increase, refining changes, ratio changes, and moisture content changes all required a chemical and a mechanical approach. The team modified retention aid, starch, filler, and broke coagulants as it progressed. These chemical moves, with the mechanical aspects of refining, tensile ratio, and moisture content, provided a cause-and-affect approach that ultimately eliminated cockles, ridges, and undulations.
These are some examples of how mechanical and chemical approaches to making quality paper can work toward a common good or can oppose each other to the detriment of quality and runnability. The author would be surprised if any readers would disagree with the concept of using mechanical and chemical systems in concert to optimize machine performance. His experience is that more times than not the approach is to work mechanicals and chemicals independently in opposition of each other. How then can any mill institutionalize the successful marriage of mechanical and chemical approaches?
LEADERSHIP AND EDUCATION
Leadership and education are the keys to this successful marriage. Leadership is vital to establish an atmosphere where high quality, salable product out the door at the lowest possible cost is the only objective for the entire mill. Everyone is on the same team. The goal of the team is prime quality product at the lowest possible cost. Finger pointing, castle building, cost center competition, etc., are not allowable. All departments and individuals must unite for the common good. This principle or belief requires reinforcement and institutionalization from the top down.
When this belief system exists, employee training and education can sustain it. As shift people move from spot to spot and as technical and management personnel change jobs, new people need to understand the interactions of chemistry and mechanics, with refresher training for existing employees. This training and education must be coordinated from a central mill or corporate function so uniformity exists across all machines at all locations. Since training is frequently an initial cut in difficult times, this approach requires support from all levels of management. The experience of this author is that these dollars spent up front are well worth company support for the benefit of long-term cost savings and quality gains. S!
IN THIS ARTICLE YOU WILL LEARN:
* How chemical and mechanical approaches can be successfully "married" in a common approach to reach high quality and low cost production
* How, in one case, a task team identified sheet stresses and strains from micro basis weight and moisture variability as a root cause for sheet imperfections, leading to a solution.
* Why leadership and education are the keys to making this "marriage" work
* "Commodity, performance, or specialty chemicals?." C.A. "Kasy" King, Solutions!, August 2002, p. 42.
* "The ups and downs of specialty chemicals," C.A. "Kasy" King, Solutions!, December 2002, p. 37.
* Go to www.tappi.org and enter "Paper Chemistry" in the search engine. You will reach an archive of over 300 articles.
INTERACTING PARAMETERS AFFECTING PAPERMAKING PERFORMANCE
Consider the list of interacting parameters below as potential topics for the training and education needs of a workplace. The list is certainly not all-inclusive, and many readers will have their own list of important parameters.
Mechanical parameters: refining, cleaning, screening, water rate, HB consistency, HB pressure, hydraulic balance, slice opening, slice position and location, impingement angle, forming board type and position, breast roll box opening and position, HB profile capability, vacuums, foil box type and location, foil blade angle, forming fabric type and tension, water temperature
Chemical parameters: fiber type and percent, broke type and percent, retention aids, charge control agents, dry strength agents, wet strengths agents, sizing, fillers, dyes, deaerators, defoamers, biocides, water consumption and source, addition points, additive sequences, and dilution water source and temperature.
About the author: C.A. "Kasy" King is principal of Papermaking Process Consulting LLC, Appleton, Wisconsin, USA, and a member of the TAPPI Editorial Board. King is also secretary of the PIMA Technology Resource Management Group, which plans and implemented programs for the PIMA International Management Conference each June. He can be reached at + 1 920 991-9102, or by email at email@example.com.
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|Title Annotation:||Paper Chemistry|
|Publication:||Solutions - for People, Processes and Paper|
|Date:||Apr 1, 2003|
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