It’s a well-known fact that many people use their microwave oven more frequently than their traditional oven, or even their cooktop. However, many consumers are confronted by the dilemma of finding an optimal place for the indispensable microwave, particularly in kitchens suffering from space constraints or where aesthetic preferences demand an uncluttered look. Sharp Electronics has provided a solution to this dilemma by designing a 30-in. freestanding range that incorporates a novel, microwave drawer in addition to a conventional oven and glass-ceramic cooktop. The Sharp Insight range was introduced earlier this year and represents Sharp’s first expansion into the arena of major appliances.

The Insight range features a sleek, high-tech, contemporary appearance to complement the technical achievement. Naturally, materials selection was critical for exterior parts that must meet a host of functional and cost requirements in addition to providing an attractive appearance. Traditionally, aesthetically critical range/oven components are manufactured using painted metals or engineering thermoplastics. For the Insight range, however, Sharp took a different direction and specified four key components to be injection molded with Bulk Molding Compound. The BMC components include the control panel frame, control panel base, the microwave drawer handle, and the oven door handle.

Fig. 1. Comparative dynamic analysis of BMC and other materials.

Aware of the many challenges associated with the heated kitchen environment, Sharp’s engineers chose BMC 400, made by Bulk Molding Compounds, West Chicago, Ill., due to the material’s high strength, stain/chemical resistance, U.L. 5-V flame rating and retention of properties at elevated temperatures. The inherently high flexural modulus associated with BMC was also important when considering end-use functionality and “implied value.” Sharp cited a correlation between rigidity and quality when considering its control and contact surfaces. The stress/strain imposed on range handles and control panels requires a stiff, heat-resistant material that can resist deflection under load.

Sharp declined to pursue traditional options for various reasons. Painted metal assemblies, although rigid, were more expensive to tool and manufacture. Metallic options also presented restrictions in design flexibility and processing methods. Engineering thermoplastic alternatives were efficient in their injection mold ability and lack of paint requirement, but demonstrated limitations in their resistance to heat and rigidity/deflection under load.

Thermoplastic materials engineered for use in kitchen/cooking conditions were more expensive (on a per pound basis) than the BMC alternative and could not match the flexural modulus (1.9 million PSI), heat deflection temperature (550 degrees F) or dynamic mechanical properties (See Fig. 1) of the BMC 400.

Sample cross-sections were injection-molded with gas assist from BMC material.

Bulk Molding Compound is a polyester-based thermosetting composite that provides a combination of properties associated with thermosets, thermoplastics and metals. BMC differs from many traditional thermosets as it can be compression molded and injection-molded, with our without gas-assist techniques.

Unlike many traditional thermoset materials where color choice was limited to black or brown, BMC can be formulated to match custom colors pallets and specified stone-like appearances. Highly resistant to impact (notched impact values in excess of 8 ft-lb./in.) the material is fiber reinforced and can be custom blended to meet the needs of the end use applications.

The company says that BMC can deliver a low-cost, pricestable alternative to metals and engineering thermoplastics because it is engineered for the most efficient use of petroleum-based resin products and is highly filled with inorganic alternatives.

The parts for the Insight project are molded by Western Plastics, Portland, Tenn.