Roller cleaning system with optical inspection system to prevent the formation of deposits on chill rollers
In film extrusion, many plastics form deposits on the roller surfaces during processing, which can have a negative impact on the surface quality of the film and the mass throughput. If a critical film thickness is reached, production must be stopped and the roller cleaned.
As part of the “Roll Coating Extrusion” research project, an inspection system was therefore developed for the reliable detection and quantification of roll coatings, which is coupled with a roll cleaning system. For the first time, the influence of melt and roller temperature on the formation of roller coatings over time was investigated and correlated with the resulting film properties.
As part of the project, IKV demonstrated that camera systems based on the functional principle of detecting gloss changes are suitable for the inline detection of roller coverings (Figure 1). To develop the inspection system, a line scan camera with powerful optics was therefore integrated into a laboratory smoothing unit. In this way, roller areas with or without coatings can be detected with high spatial resolution.
© IKVTo capture the entire circumference of the roller during production, the camera is triggered by a rotary encoder at reproducible angular positions. A Python algorithm combines images from the line scan camera to create an overall image that reproducibly shows the coating condition of the roller surface.
To determine the pavement growth, the gray values of the film running surface (paved) are set in relation to those of the edge area (not paved) and the roller pavement is thus quantified. The inspection system makes it possible to record the temporal and spatial formation of roller coatings with scientific accuracy and to define a technically and economically sensible time for cleaning the roller.
Extrusion tests were carried out to investigate the influence of industrially relevant parameters, such as the roller and melt temperature, on the roller coating formation of PET at a line speed of 0.3 m/s. Among other things, it was found that a reduced melt temperature (270 °C) leads to significantly faster coating formation than a higher melt temperature, especially at the start of the test.
It is hypothesized that the adhesion force between the roll coating and the roll surface increases as the temperature difference between the melt and the roll decreases, so that the resulting roll coatings increasingly remain on the roll surface instead of being carried away by the film. At higher melt temperatures, in comparison, the adhesion between the resulting roll coating and the melt predominates, which is why it is not deposited on the roll.
The project was named finalist for IGF Project of the Year in 2025
Project data and funding
Project duration: 10/2020 to 09/2022
Funding code: IGF project 21297 N via the AiF on behalf of the Federal Ministry of Economics and Climate Protection
