New processing: SKZ
In windows, PVC has the edge over other materials because it can be welded, as opposed to wood or aluminium windows. However, welding can sometimes be a difficult process.
Germany’s SKZ (Süddeutsche Kunststoff-Zentrum) took on the challenge, making a long-overdue adjustment to the parameters that regulate welding machines used in heated tool butt welding for windows. The project aimed to make it more efficient and cut costs.
“High temperature welding is now possible for PVC window profiles,” says Benjamin Baudrit, joining group research manager at SKZ.
SKZ significantly lowered welding cycle times by turning up the temperature of the tool employed as well as adapting other important parameters. Each of the considered white profile types allowed a reduction of the cycle time by about 24%, along with increasing the weld strength by an average of 17%. A welding factor between 0.6 and 0.8 was achieved, which means that the welded joint has about 60 % to 80 % of the base material strength.
Profiles with outstanding weldability could even be joined up to 40% faster, while the weld quality was always ensured. Thanks to SKZ’s welding parameters, the efficiency of a window manufacturing line could be clearly increased and costs could be reduced without having to face quality losses, a higher environmental impact or additional investment.
Another type of material also attracted this company’s attention: wood-polymer composites, or WPCs, that are increasingly used in construction. For the time being, the market is focused on outdoor applications such as decking, fencing and siding. A typical WPC product is, for example, an extruded profile for decking consisting of 50% wood, 45% PVC and 5% additives.
Compared with customary inorganic fillers and reinforcing fibers, wood is less heavy, less abrasive and can be recycled. The resources are relatively cost-efficient. Thus, WPC presents a well-established alternative to tropical timber. In the long run, the use of WPC may even contribute to reduce the amount of resources coming from rainforests.
Due to the strong growth rates of WPC (especially of WPC based on PVC), SKZ recognised that joining technologies for this group of materials play a decisive role. A further increase in the production volume of WPC crucially depends on the development of technologies like suitable joining processes for the semi-finished products and their parts.
The overall aim of SKZ’s research project “Technology and Application Development for Welding Wood Plastic Composites based on PVC” deals with the weldability of commercially available WPC formulations using well known heated tool butt welding as for window profiles.
SKZ goes further: “Through ultrasound, vibration or hot plate, WPCs are also successfully weldable,” adds Baudrit.
This could open new opportunities for such composite materials for instance in windows and doors. The results of this research project can further increase the cost efficiency of the WPC products and visually enhance them thanks to positively bonded assemblies.
