Using Advanced Instrumentation for a Successful Gap Former Conversion from Newsprint/LWC to Corrugating Medium

摘要

This paper documents the scientific methodology utilized to study the important drainage characteristics on a proposed 100% recycled corrugating medium sheet, including desired sheet properties, on a gap former machine equipped with Cristini microwave consistency measurement instruments, on a machine with historical experience of lwc and newsprint. Curves were developed in 3 zones, each with a microwave instrument head installed, consisting of 5 total dewatering elements on this gap former configuration. These were drainage curves generated as vacuum in each zone was varied. Consideration was given to which zones required the highest drive loads. The amount of dewatering in each zone was then compared to the desired sheet properties, particularly burst and tensile generation. A spread sheet was prepared that summarized total drainage, as measured by consistency going into the press section, and compared those results to amp loadings for the drive and the resultant sheet properties. The most efficient dewatering from a drive load perspective, came from the suction roll in the forming zone, being a rotational vs. a stationary vacuum element. As the loads in each of the 3 zones were varied, it was observed that the overall level of final forming consistency varied considerably Details of the gap former section are presented in detail, including vacuum levels at each element and each zone. The paper machine was equipped with the same instrumentation as had been present on the pilot machine trials. Through a series of on-machine trials, the most desirable curves that had been generated on the pilot machine, were applied to the full scale machine. The results were shown to replicate in actual practice, virtually identical to the results observed on the pilot machine. One runnability issue emerged at extremely low vacuums on the last hi-vac box, in that the edges of the sheet would "flip" when vacuum approached zero at that element, so a modest level of vacuum continued to be applied at that point. During these trials, the jet impingement angle and position of the forming roll were kept constant. The specific grades being produced were 85-100 gsm fluting, and in the final analysis, consistency after the couch was as high as 21.5% vs. 19.5% before the trials were run. Sheet properties were maintained while energy to drive the forming section was reduced by over 40%. Actual drive amp numbers, along with sheet property values are presented in the paper. The energy savings are significant, but pale in comparison to the value of having specific set up numbers for the weight and grade of paper being produced. Process standardization for maximum production and optimum sheet properties can now be programmed into the machine based upon on-paper machine trials, with proper instrumentation and data generation.