Our customer uses on one of their sites Vipetec ATA™ software on both paper machines for managing grade changes and monitoring efficiency. Our customers and we ourselves call them grade change libraries. These libraries have been utilized at the mill for years and, based on the customer’s needs, we have also built customer-specific calculations and functions in them that facilitate the operator’s work in grade changes. Although grade change automation is available, it only handles some of the modifications that need to be made in connection with grade changes. These other modifications and things to consider are handled by the operator based on his experience and the available information. At this point, the grade change library provides operators with a tool to quickly retrieve information and find appropriate operating parameters to perform the coming grade change. We discuss the significance of both optimal automation and expert human operators in more detail here.
“Grade change libraries have been in use on our machines for years. Utilizing them has become an essential part for our operators in performing these changes. With the help of the information produced by the grade change library, we can also monitor the functionality of the changes and take corrective action in time, if necessary,” states the Production Manager of the paper mill.
With both machines, the need to develop grade changes and maintain good functionality is generated by the large number of these changes and the resulting costs. In the first phase, already years ago, we carried out development projects on both machines, where we managed to speed up the grade changes on one machine by 35% and on the other 28%. During the project and after that, the performance of the changes has been monitored through various performance-related indicators. Through continuous monitoring, both slow and sometimes quite rapid changes in the functional performance of grade changes can be caught.
For example, two years ago, a slow decline in these changes was observed on one paper machine. The data and key figures from the grade change library were used to find out what might be causing the decline. Various calculations related to the target values of the new grade are used in grade changes. Based on the analysis of grade changes and the feedback received from the operators, the problem was traced to the calculation of target values of steam pressure of the new grade. It was then agreed to update the calculation model. As a result, we managed to improve significantly the accuracy of this calculation, with an average calculation error of more than 40% smaller compared to the previous calculation model. After the introduction of the new calculation model, the functionality of grade changes returned to the original level.
A similar situation, but with a faster decline in the grade change speed, was observed on another paper machine in the autumn of 2021. Corrective action was taken quickly. Based on the data provided by the grade change library, the measures were also aimed at improving the accuracy of steam calculation on this paper machine. In addition, there was also room for tuning in the operation of grade change automation. With the update of the steam calculation, its accuracy was again significantly improved, the calculation error was reduced by about 30% on average. Through the update of the steam calculation and the tuning of the grade change automation, the functionality of these changes was restored to a good level also on this paper machine.