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issue: November 2007 APPLIANCE European Edition

Plastic Materials
A Flexible Solution

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by Lisa Bonnema, Senior Editor

As appliance design becomes increasingly important, manufacturers are turning to plastic suppliers for materials that are both durable and flexible.

Aesthetics and function were key design components for the plastic handle of a new kettle from UK-based Kenwood. The company chose the traditional “kitchen white” as the handle colour to evoke a feeling of cleanliness, but that meant it also had to be easy to keep clean. Using a Santoprene TPV material from ExxonMobil, Kenwood decided to produce a smooth grip instead of a textured grip after in-house tests that proved a smooth grip would be easier to clean.

Most manufacturers will agree that one of the main benefits that plastic materials can offer is versatility. That advantage is perhaps more relevant now than ever. New technologies are enabling materials that are durable enough to replace metal, but can also provide design flexibility and a variety of aesthetic options. And let’s not forget about the cost advantages.

Sybill Kraemer, global market segment manager for Santoprene-brand thermoplastic vulcanizates (TPVs) at ExxonMobil Chemical, confirms that highly functional plastic parts are moving from “function only” to “function and aesthetics.” Case in point: a kettle introduced by Kenwood, a kitchen appliance manufacturer based in Kenwood, UK. The company wanted to develop a kettle that was both reliable and stylish by creating a smooth, white soft-touch handle that incorporated an integrally molded button operating a novel “seesaw” lid.

After researching several materials, Kenwood chose a TPV from ExxonMobil for the soft-touch grip and “sealed-in” membrane covering the lid-release button on the handle. Darren Prosser, Kenwood project manager, explains: “Santoprene TPV was selected for the grip because it could provide a tactile surface, and for the membrane covering the lid-release button because of its functional performance, which is particularly important when the kettle gets hot.”

According to Kraemer of Houston, TX, U.S.–based ExxonMobil, the material can deliver equal or better performance at a significantly lower cost than thermoset rubbers. “They provide improved chemical, heat, and sealing performance and can be processed on existing thermoplastics extrusion and coextrusion, injection and coinjection molding, blow molding, or overmolding equipment,” she tells APPLIANCE.

The material is also designed to offer creative flexibility. “A number of Santoprene-brand TPV grades bond to multiple substrates, especially engineering thermoplastics, eliminating the need for adhesives, bonding agents, and physical or mechanical interlocks,” Kraemer says. “As well as enhancing design opportunities, combining different materials in this way can provide improved functionality, part consolidation for easier assembly, and reduced costs. These grades can also be easily coloured for additional creative design opportunities.”

Pliable Achievements

One of the major benefits of plastics is the ability to find new applications, according to Gunes Celik, appliances segment leader, Europe, of Sabic Innovative Plastics, located in Istanbul, Turkey. “The advancement and transfer of existing plastics technology from one industry to another is mapping the route for appliance designers to access new aesthetic possibilities and economies without compromising on application performance,” he explains.

Over the years, Celik says that many plastic applications have required the use of a coating or finish to meet end-user requirements for aesthetic or functional properties. “The coatings used on plastics have generally been liquid, as these allowed the coatings to achieve good adhesion results, together with other key coating properties, without requiring high cure temperatures,” he explains. “As industry sought to improve the coating process for plastics, developments in areas such as conductive primers, which allowed further coats to be applied using electrostatic processes, opened the way to further benefits. This, in turn, led to an interest in the application of powder coatings onto plastic materials.”

While the majority of plastics today do not have the necessary resistance to powder-coating cure temperatures, Celik says that the perceived advantages of powder coating have driven the development of conductive plastics, which are able to be used in several applications where powder coating has become the norm. “These plastic substrates are designed for the direct application of powder coatings to the surface with no pretreatments or preprocessing steps, ultimately giving the coater the option to hang plastic substrates next to metal substrates on a powder coating line,” Celik says.

Tough as Metal

One material that is replacing metal is vinyl, according to Roger Steller, senior applications development engineer, Vinyl Compounds at PolyOne Corp. “Washer doors on front-loading washers and pedestal storage units are now being made with vinyl instead of steel, allowing for greater design flexibility,” he says. “Work-surface boards made with vinyl result in a chemical-resistant workspace across the top of the washer and dryer.”

Steller adds that the time and cost involved to tool a vinyl part compared with stamped metal is significantly less. “In addition, vinyl can be molded to create complex angles and curved surfaces—design features that are extremely difficult to achieve with stamped metal,” he says.

PolyOne, based in Avon Lake, OH, U.S., with sales facilities and plants located throughout Europe, is also seeing appliance companies use vinyl in modular consoles and internal parts such as circuit board housings. “As more appliances incorporate digital electronics, vinyl can be used in many parts where ultra-high-heat-performance plastics were once required,” Steller tells APPLIANCE. “Vinyl can also be used to manufacture snap-in-place compo- nents, which allows faster and more-economical assembly.

Another advancement Celik notes is the use of engineering materials in place of traditional materials like metals, thanks to new and increasing capabilities, heat resistance, and mechanical strength. In fact, the undisputable durability of metal has motivated plastic suppliers to work harder at developing high-performance materials that are just as durable, and more cost-effective than their robust competitor.

That was certainly the strategy behind a new detergent-resistant, glass-reinforced polypropylene (PP) from Borealis AG. The Austrian supplier developed its GB266WG material to be lightweight and durable, allowing it to withstand the aggressive environment found inside white goods and making it an effective alternative to steel parts such as dishwasher frames. “All appliance producers are interested in switching from metal to plastic, if possible,” says Werner Posch, project manager at Borealis in Linz, Austria. “Polypropylene and polyethylene are the preferred materials because of the excellent detergent resistance. However, this requires development in respect to the cleaning agents and…the combination of stabilization and polymer needs to be considered.”

According to the company, the performance of its new PP material can be attributed to a novel stabilization system that enhances the lifetime of important structural components. It prevents the additional ageing effects of light, oxygen, and usage-induced wear and tear, such as loss of strength, stiffness or flexibility, discolouration, scratching, or loss of gloss. “We added the performance of different stabilizers to find the right formulation that works against the oxidation effect,” Posch tells APPLIANCE.

The PP material also helps reduce the amount of energy required during appliance usage. “The reduced thermal conductivity of our material in comparison with metals creates a reduced required amount of energy to hold the temperature during the cleaning process,” Posch explains. Also, because the thermal conductivity is decreased, he
says the filler, which acts as an absorber, will decrease the acoustic transmission.

The material was created to be used in both washing machine and dishwasher applications, allowing OEMs to potentially reduce their inventory of materials by using the same PP for both appliances. Additionally, by decreasing thermal and acoustic transmission, it minimizes the need for separate insulation materials, further lowering production costs for appliance manufacturers.

In addition, the lightweight features of the PP make it easier to handle and transport than traditional steel materials. Other features include high stiffness and low heat extension, ensuring a watertight connection between components such as a PP-dishwasher frame and connecting steel parts.

From Material to Market

No matter what material is being used, there is one truth that spans all of appliance production—speed to market. “Product development is happening at an ever-increasing pace,” confirms Kevin Crystal, senior quality engineer at Protomold in Maple Plain, MN, U.S. “OEMs require prototypes faster, and require real molded parts earlier in the cycle.”

In response to customer demand, the global supplier says it has developed ways to make real molded parts in as fast as one day, and in standard delivery of three weeks. The company also claims that it can quickly incorporate more functionality into plastic components. Complex parts can be molded in three weeks or less, with as many as four side actions per part.

When designing its Bosch TWK8SL1 water kettle, BSH Bosch und Siemens Hausgerate was seeking a tough, high-performance plastic that could withstand the appliance’s repeated cycles of cold and boiling heat. The German appliance company also wanted the material to be compatible with use in electrical components and comply with the latest standards for electrical appliances.

After testing a number of materials, BSH chose Lexan EXL resin from Sabic Innovative Plastics (formerly known as GE Plastics). “This material proved its temperature resistance by successfully completing 12,000 heating and cooling cycles, its durability easily surpassing that of the closest competitive material, which survived only 7500 test cycles, by a wide margin,” says Gunes Celik, appliances segment leader, Europe, at Sabic. “Furthermore, Lexan EXL resin showed its resistance to common decalcifiers, as well as outstanding hydrolytic stability compared with standard polycarbonates.”

According to Celik, the material builds on the strength of standard Lexan polycarbonate resin, with even greater impact performance under extreme conditions such as low-temperature ductility or notch-sensitive designs. “A copolymer of polycarbonate (PC) and polysiloxane, the combined properties of Lexan EXL resin represent a significant upgrade to conventional PC and PC-blend materials available in the marketplace today,” he tells APPLIANCE. “The siloxane component provides extreme low-temperature ductility and because silicone is relatively unaffected by heat or humidity, these materials retain their properties for a longer time than standard polycarbonate resins when exposed to these conditions.”

Much of the increase in speed is due to advancements in online quoting which help automate the process of supplying plastic parts. Customers can upload a 3-D CAD model of a specific plastic part, and a quote is automatically generated. “From our perspective, it is all about speed,” notes Brad Cleveland, Protomold CEO. “We concentrate on being fast, and our customers figure out how to take advantage of it.”

Instead of getting products to market faster, Cleveland says some OEMs are using the time savings to perfect product designs. “It might take them just as long to get to market, but they have iterated 10 times instead of twice, so their risk is dramatically lower,” he explains.

Another option for appliance OEMs is to use the time savings to manufacture several different versions of a product in the same amount of time it used to take to develop one design. “It’s almost like mass-customization,” Cleveland says. “They can use our very-low-cost tool and very quick response time, and go to market with 10 products in parallel rather than one, and each one of those products is just slightly different.”

Michael Rhoads, national sales manager, Foams Business Unit of Saint-Gobain High-Performance Materials (Granville, NY, U.S.), adds that time to market can often be decreased by simply doing things right the first time. “We are focused on helping OEMs pick the correct part in the beginning of the design phase,” he says. “There are many products that will work in an application. However, it is important not to overengineer solutions.”

Rhoads says that because of the rapid design phase, he often encounters situations in which OEM engineers are using materials because they have worked in the past. “This is a very safe approach, but you often end up with a material that is overengineered for applications,” he explains.

Of course, product development isn’t the only area where speed is important. Krauss-Maffei (München, Germany) introduced its In-Line RotoCore system to offer appliance companies an efficient and flexible method of producing plastic parts. The company’s latest refrigerator forming cabinet fixture is engineered to accommodate manufacturers whose multiple model changes dictate the necessity for a quick-core-change option.

The equipment uses “top-down” technology, where the foam core is indexed down into the refrigerator cabinet while it is lying on the back-support table. The rotary quick-core-change system is a stand-alone unit, located in front of the cabinet- forming fixture rather than on top of it, as is the case with more-traditional core-change designs. The foam core transfers from the fixture to the core-change unit via an in-line linear rail system and a motorized load/unload arm. After a foam core is placed into the core-change rotary unit, the rotary unit indexes the next selected model’s core into the load (or “down”) position. The linear rail system then guides the selected core into the fixture as the motorized load/unload arm moves the newly selected core into place.

According to the supplier, the system’s core-change table can be designed to accommodate up to four different models during production, depending on customer needs. The end result is a reduction in the production downtime associated with typical tooling change-out procedures on standard fixture designs.

Adaptable Advantages

Whether on the design table or on the production floor, today’s suppliers know that above all, plastic materials and equipment must be able to adapt to the needs of their customers. “The design and manufacture of next-generation appliances must navigate their way between
increasing market demands, costs, and regulatory mandates,” says
Celik of Sabic Innovative Plastics.

Posch of Borealis adds: “This industry is forced to reduce complex production methods by cheaper solutions. Plastics fulfill this and also offer lots of other advantages in comparison with metals. The important point is to support the customer with the right design proposals and material properties to help create the right solution for him.” 

Suppliers mentioned in this article:
PolyOne Corp.
GE Plastics

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