Quality assurance on tumble dryers through plasma
Founded in Germany over 110 years ago, Miele has become the worldwide premium supplier of high-end domestic appliances. The company's wide range of electrical domestic appliances covering cooking, baking, steam cooking, refrigeration and freezing products, coffee makers, dishwashers, laundry-care machines and floor care products also includes tumble dryers. Their various plastic components are treated with Openair® plasma before inserting the seals in order to meet the high quality standards.
The seals of heat pump and condenser tumbler dryers need to adhere to such an extent that the slightest penetration of moisture is avoided even after years of use. When MIELE contracted the development of heat pump dryers several years ago, one of the objectives was aimed at minimizing the moisture losses. This objective could only be achieved by sealing the individual components which are exposed to the air stream. After comprehensive laboratory tests and fatigue testing, the manufacturer granted the release for a 2-component PUR foam. The Openair® plasma technology was integrated into the test series right from the onset of the planning and realization phase for pretreating the plastic material to be sealed.
Here, the plasma accomplishes two functions: First of all, the PP
surfaces need to be cleaned to a microfine level since they may still
have on them traces of substances such as alkali stabilizers, flame
retardants or talcum which would reduce the adhesive strength of the
foam. The second and even more important function is the strong
activation of the non-polar PP plastic material, i.e. the increase of
its surface energy. The higher this energy, the better the subsequent
wetting effect. Openair® plasma enables a rise of the surface energy
from under 30mJ/m² to over 72mJ/m², thus creating best prerequisites for
durable and long-time stable adhesion of the PUR seals to the PP
The plasma installation is equipped with both a robot-guided rotary nozzle for gentle treatment of relatively large surfaces and a static nozzle for intense treatment of complex groove geometries. The entire system runs computer controlled and fully automated. As Andreas Landeck, Project Manager of the Industrial Engineering Department at MIELE in Gütersloh comments: "Simply put, one could say – minimal maintenance effort on the one hand and full process safety on the other." The plasma installation is operated 46 weeks a year and mainly on a 3-shift basis. Approximately 12 tons of sealing material are applied to plasma pretreated surfaces in a year. By implementing the Openair® technique, the service life requirements of at least 20 years can be ensured on MIELE heat pump dryers.
Openair® plasma offers the user the following values:
- Selective pretreatment of complex groove geometries
- Environmentally friendly, residue-free cleaning of the PP surfaces
- Strong activation of the PP surfaces without the use of primers
- Long-time stable adhesion of the 2-component PUR foam seals
- Assurance of the product quality
- 100% process safety in manufacture
- Minimal maintenance effort
Miele & Cie. KG