Foam forming technology
Today’s papermaking process uses a lot of water and energy. Using foam as a carried fluid in papermaking process has two advantages: 1) the uniformity of the material is much more uniform compared to today’s technology, water-laid forming and 2) the solids content of material after the wet-pressing is typically several percentage units higher than with water which can lead to big savings in energy consumption. With foam technology, it is possible to obtain the density range well below 100 kg/m3, which is not achievable with water. Foam technology offers several interesting options and can bring savings in energy costs and drying time.
VTT has studied the foam forming process since the late 2000’s and published tens of peer-reviewed papers and conference talks on foam technology. In NOVUM project, foam forming technology has been one of the three candidates for manufacturing electrical insulation components in a more advanced way. The trials with the laboratory scale pressing device revealed that there is a 10%-unit increase in press solids for foam formed materials compared to water-laid webs. This equals to 33% energy savings in thermal drying. However, the density level of electrical insulation components is higher than 500 kg/m3 meaning that some mechanical pressing is needed which in practice could be done in some kind of mould. All materials used in the trials are compatible with oil, which is the key requirement for electrical insulation components.
The manufacturing process of complex shapes is more challenging compared to planar web-like products. Similarly to wet-laid papermaking, foam forming is an aqueous process and during the manufacturing the carrier fluid – foam – has to be removed by means of vacuum, mechanical pressing and thermal drying. In NOVUM, VTT is currently developing a special method capable to 3D print fibrous materials. The print nozzle has been tested and some preliminary material samples produced. The second approach was to utilize sheet lamination, a technology which is quite often considered as an added manufacturing process. Sheet lamination tests were carried out by using water and foam formed handsheets and nanocellulose as an adhesive. Finally, a 3D-printed mould was used for manufacturing complex shapes from wood fibres. Several demo samples were manufactured.
Foam forming is an interesting enabling technology for various applications. By combining the competences from sustainable materials, fibre processes and manufacturing technologies including 3D printing we have taken a big step towards sustainable solutions, not only in electrical insulation materials, but also on e.g. in insulation applications.
Author: VTT/ Harri Kiiskinen