issue: April 2009 APPLIANCE Magazine
Expanded Online: Plastics for Compliance
Email this Article
Precertified resins help Vestel White Goods meet tough new flammability standards.
Vestel White Goods had been using halogenated flame-retardant polyamide (PA66) to mold printed circuit board (PCB) holders for its washing machines. However, recent changes to the International Electrotechnical Commission (IEC) 60335 standard for unattended household appliances made the standard more rigorous and Vestel, one of Turkey’s leading appliance manufacturers, found it needed a replacement material that could comply.
One test in particular, the Glow Wire Ignition Test (GWIT) for flammability, presented a particular challenge. The strict GWIT test is used to simulate material ignition and flammability that may come about in malfunctioning, unattended appliances. The plastic material is put in contact with a wire heated to 750°C for 30 sec. During that time, the plastic cannot ignite for more than two seconds, after which it must self-extinguish.
Vestel decided to look for a compliant material that could also solve some chronic performance issues with the PA66, particularly regarding part warpage and poor dimensional stability.
“Being a semi crystalline material, PA66 experienced warpage that led to a narrow processing window and high rates of post-molding rejects,” said Ozgur Yilmaz, head of the research and development department for Vestel washing machines. “There were also a lot of part failures—primarily due to snap fits breaking off. We wanted to find a material that not only passed the Glow Wire Ignition Test, but also provided excellent dimensional stability and low warpage to reduce scrap rates.”
Another mandate for the new material was environmental responsibility. With its corporate emphasis on environmental stewardship, Vestel wanted to be sure that the material could provide flame retardance without the use of chlorinated or brominated additives. As a global exporter, Vestel must comply with such eco regulations as the European Union (EU) Restriction of Hazardous Substances (RoHS) directive.
Sabic Innovative Plastics had already developed materials to assist appliance OEMs become compliant with the updated IEC regulations. This included a portfolio of flame-retardant materials certified by German testing organization VDE (Verband der Elektrotechnik Elektronik Informationstechnik e.V). Because the materials have already passed VDE testing for compliance with the IEC 60335 standard for unattended household appliances, appliance OEMs don’t need to spend time and resources on additional testing of plastic parts. One such material is Noryl NH6020 PPO-based resin, an amorphous material with thin-wall, halogen-free flame retardance of UL-94 V0 at 0.8 mm. It offers a ball pressure temperature (BPT) of 125°C and a comparative tracking index (CTI) value of up to 600V, depending on color. This grade is also designed to provide a good balance of flow and mechanical properties, as well as low density and a high degree of hydrolytic stability.
Vestel tried different PA66 grades with various additives, as well as a number of other materials, before it found its best solution in Noryl NH6020 resin.
“Our Noryl resin is one of the few amorphous materials that can meet the GWIT requirement for unattended appliances without compromising a BPT of 125°C and high CTI, which are also needed for live parts,” said Azam Khan, European product manager for Sabic. “Its amorphous structure and hydrolytic stability address the dimensional stability problems experienced with PA66. For design and processing, Noryl resin offers a balance of mechanical and flow properties.”
Better Dimensional Stability for More Design Freedom
By replacing unreinforced PA66 with the Noryl resin in new washing machine designs, Vestel achieved better dimensional stability and easier processing. Without part warpage, rejects and part failures were reduced to near-zero. “This improvement not only saves us money and time, but also ensures consistently high quality of the PCB holders,” noted Yilmaz.
Another benefit comes from the ability to design and mold thinner-wall parts. Vestel reduced the wall thickness of PCB holders without sacrificing the mechanical strength of the part, thus lowering its mass. Reduced part mass and lower resin density adds up to material cost savings.
Finally, avoidance of halogenated flame retardants enables Vestel to meet EU and other major regulatory requirements for environmental responsibility. This compliance allows Vestel White Goods to freely market its products around the world.
“Our customers increasingly demand non-brominated and non-chlorinated materials,” Yilmaz said, “and Noryl resin enables us to meet their needs, while ensuring flammability performance, as demonstrated by compliance with the Glow Wire Ignition Test.”
Vestel, part of Vestel Group, has total annual production of 7.5 million appliances, including washing machines, refrigerators, dishwashers, cooking appliances, and air-conditioners. Products are made under its own brand, and also as an Original Development Manufacturer (ODM) on behalf of other well-known appliance companies around the world. The company exports 75% of its production and sends appliances to more than 100 countries.