Demolition hammers have to demonstrate a very high level of resilience when performing heavy-duty tasks. This applies in particular to the plastic parts used in these power tools. When plastics need to be extremely tough, DeWalt – a leading international manufacturer of professional tools – relies on Makroblend® KU2-7915 from the Bayer MaterialScience AG. This non-reinforced, impact-resistant modified blend of polycarbonate and polybutylene terephthalate (PC+PBT) is used to make handles and housing parts for a range of DeWalt demolition hammers. “Our material is used because the toughness of polyamide is stretched to the limit in this application,” explains Walter Köppchen, an expert on PC+PBT blends in the Polycarbonates Business Unit of Bayer MaterialScience. “A further advantage of our blend compared to polyamide is its high dimensional stability. This feature enables the component geometries to be converted into narrowly-defined tolerances, which is important, for example, to ensure that bearings function reliably.”
DeWalt checks the mechanical strength of the plastic parts by performing comprehensive tests based on standards, including “accident tests”, in which the hammers are dropped on their handles several times bearing their full weight. The hammer model D25980 – at 31 kilograms, one of the heaviest commercially-available electric demolition hammers on the market – demonstrates the high mechanical stresses that Makroblend® KU2-7915 can handle. Even after 30 impacts, the handle material does not fail or break.
What’s more, even at temperatures of -30 °C, the PC+PBT material remains exceptionally tough for thermoplastics, at 50 kilojoules per square meter (Charpy, ISO 179-1eA). “This means that the material can withstand high impact stress, even in sub-zero conditions,” says Köppchen.
In everyday operation, one of the thermoplastic’s key benefits is its good resistance to a number of chemicals, such as greases, oils, hand creams, solvents and sweat. Further strengths include its high heat resistance (85 °C, HDT-A) and excellent electrical insulation properties.
Bayer MaterialScience provided DeWalt with extensive support during the development and implementation of the handles and housing parts. For example, finite element calculations (FEM) were performed to analyze the handles’ behavior when subjected to vibrations, and thus establish the optimum position and geometry of the reinforcing ribs. Support was also provided with mold construction.