Polyamide improves impeller performance

Direct-to-milled-tool process simplifies large deck mold development.

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Although there will always be a place for metals in industrial fans and fan blades, there are compelling advantages to using a reinforced engineering plastic when the manufacturing goals include reducing the cost of balanced, complex airfoil shapes; weight reduction; better corrosion resistance; and noise/vibration damping. Axial fan/impeller manufacturer Multi-Wing International A/S (Vedbaek, Denmark), founded in 1938, was on board with composite designs as early as 1958, when a cousin of the firm’s founder developed an thermoplastic axial fan concept — essentially a propeller inside a pipe that pushes air or water parallel to the impeller’s shaft. 

According to Multi-Wing’s development manager Victor Silbermann, axial fans are subjected to high speeds, undesirable natural oscillations and vibrations. Further, the fans need to absorb impact and shock energy at temperatures as low as -30°C without breaking, and perform at high temperatures as well, without excessive creep. 

The firm was on the lookout for an improved thermoplastic that could deliver the performance it needed for the circular hubs of its new mixed-flow cooling fan design for the engines of heavy construction equipment. The circular hubs fit onto the impeller axes to transfer rotational motion to the fan blades. Working in partnership with BASF AG (Ludwigshafen, Germany), Multi-Wing began trials on a new BASF long-glass fiber-reinforced polyamide formulation, trademarked Ultramid Structure LFX (B3WG10 LFX) with high weld strength and good creep resistance, for the hubs. The new, injection molded polyamide system reportedly improves resin/fiber interfacial bond strength, which results, says BASF, in a more stable fiber “skeleton.” 

Ultramid Structure LFX reportedly withstands extreme stresses and, thus, can provide protection against damage and excessive deformation of the plastic, says Silbermann, as demonstrated by high notched-impact strength test results. “In numerous tests we have found that the material can withstand extreme centrifugal forces. The stable fiber network makes it ideal for heavy loads and, therefore, a good alternative to metals in the production of our hubs.” 

Working closely with BASF throughout the development phase has enabled the company to continuously optimize its molding processes and molds, as well. Ultramid Structure LFX is easy to process, claims BASF’s Andre Schäfer, involved in applications development for engineering plastics: “We have optimized the material’s properties to such an extent that the plastic has proved a good investment in a number of client projects.”

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