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issue: November 2007 APPLIANCE European Edition

Plastic Materials
Trimming Where It Counts

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When Flymo was looking to cost-effectively produce its latest hover and roller mowers, Basell supplied an impact-modified PP grade that saved costs and production time.

A recent collaboration between Flymo and Basell allowed for the replacement of ABS with a grade of polypropylene that provided similar shrinkage properties. This gave Flymo the option to use its existing tooling and as a result, reduced costs.

The decks of Flymo lawn mowers are relatively large moldings with a number of critical features. In addition to providing structural rigidity for the body, they must also be tough enough to withstand impact from stones that may be thrown up by the mower’s blade.

Originally, these components were molded in high-impact ABS, but when outdoor appliance maker Husqvarna wanted to design a new line of Flymo-branded mowers, the company began researching alternative materials. “As with all European manufacturers, cost is a major driver in the design of the product,” says John Davies, product support manager, Husqvarna U.K. Ltd. “Designs are pushing the limits on wall thickness and the ability to fill injection mold tools.”

The challenge was finding a material that was strong enough for the deck application, but would also work with Flymo’s existing tooling. “We had proved that polypropylene (PP) was capable in this application, but the component assembled to other components and, therefore, shrinkage was very important if the product was to assemble as intended,” Davies notes. “The alternative was to produce new tooling to use PP—a very expensive option.”

The OEM found a more cost-effective solution by using a new talc-filled PP grade supplied by Basell in Frankfurt, Germany. “Basell developed grades of material that almost matched the shrinkage of the ABS,” notes Davies. “This allowed us to sample the components in the materials to assess the performance and aesthetics.” The supplier also provided technical assistance with the sampling to ensure the actual shrinkage of the components compared with the expected shrinkage.

According to Christoph Dammer, Basell’s key account manager, the secret behind the new material is a polymerization technology that enables the fine-tuning of gloss and shrinkage with adapted reinforcement. “It is a ‘drop-in grade,’ avoiding cutting new tools, and it provides performance in terms of surface appearance and mechanical properties,” Dammer tells APPLIANCE.

In addition, the material’s lower processing temperature reduces cycle time, and its recyclability helps OEMs comply with the European Directive on Waste from Electrical and Electronic Equipment (WEEE). “An all-polypropylene lawn mower would make it much easier for Flymo to satisfy the requirements of the directive, while at the same time significantly reducing costs,” Dammer says.

However, as with any switch to a new material, some compromises had to be made. “We had to sacrifice a degree of surface finish, [and] slight tooling modifications had to be made to optimize the assembly of the component,” notes Davies of Husqvarna. “As a business, it was agreed that these small compromises were worth the savings that the change of material delivered.”

Also, because of the seasonal aspect of mower production, product development took a little longer than originally expected. “Our business is very seasonal, with high levels of production between January and July. During this time, the mold tooling is not available for modification or sampling, and the business cannot accept any risk that may jeopardize production,” Davies explains.

To ensure quality, the change to PP had to undergo several trials. According to Davies, this helped build confidence that Flymo could consistently mold the components to the correct size and that the assembly of the product would not suffer due to the switch. “These trials highlighted some minor modifications which were necessary to guarantee the quality of the fit,” he says. “These actions determined that we would delay the introduction of the new material to the following season.”

Overall, Flymo is pleased with the way the project turned out and is currently working with Basell on several other development projects. “The biggest challenge was to deliver a significant cost reduction without a large investment in tooling,” Davies says. “Without the involvement and support of Basell, this would not have been possible.”

Suppliers mentioned in this article:
Basell GmbH

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