Appliance Design - January 2009 - (Page 32)

PLASTICS & PLASTIC PARTS Fig. 6. Part design resulting from rotational draft method. Fig. 7. Part design resulting from planar draft method. is “planar drafting,” which requires a separate step from the rotation that creates the basic part. In this case, each half of the end surface is drafted separately in a plane angled away from the parting line. (See Fig. 7.) The key difference between these two approaches is what happens as the drafted surface approaches the parting line. Rotational draft leaves the end face of the dowel nearly vertical at the parting line, while planar draft keeps the same degree of draft at every point on the end faces of the dowel. Dodging the draft While drafting is the key to simplicity of design, ease of molding, and cost control, sometimes a part demands a surface parallel to the direction of mold opening. Probably the most common reason not to draft a surface is to make it fit with other parts of a finished product. Fig. 8 shows a bracket that bolts to a machine. If the mating face were drafted, the top face would tilt at an angle, which is unacceptable for this application. In such a situation, the feature can be formed using a cam-driven side action in a mold. Side actions are typically used to form undercuts that could not be molded in a simple two-part mold. But because cams move perpendicular to the direction of primary mold opening, they can also be used to produce surfaces that are undrafted in relation to the A- and B-side mold halves. In other words, if the surface cannot be drafted, allowing the part to move away from the mold as Customers everywhere depend on our igniters. No matter where you are, from the North Pole to the South Seas, Saint-Gobain has an igniter to meet your needs. Our igniters deliver dependable performance in gas appliances of every description, from furnaces and boilers to ranges, cooktops, and dryers. Made with a state-of-the-art ceramic, our igniters offer physical and thermal strength, electrical stability, easy handling, and simple installation. They are available in virtually every voltage, including 12V, 24V, 120V, and 240V. Slotless MINI-IGNITER™ CRYSTAR® Igniter For more information about Saint-Gobain Igniter Products – makers of the original Norton Igniter – call us at 603-673-2681 or visit us at www.igniterproducts.saint-gobain.com. After all, when it comes to reliability, our igniters beat the others cold. AD12074StGobain.indd 32 applianceDESIGN 1 January 2009 11/16/07 9:17:17 AM www.applianceDESIGN.com http://www.igniterproducts.saint-gobain.com http://www.igniterproducts.saint-gobain.com http://www.appliancedesign.com

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Appliance Design - January 2009 Contents Editorial Shipments/Forecasts News Watch Supplier Spotlights Commercial Appliances Plastics & Parts Electronics Motors Design Marts Association Report: NAFEM Advertiser’s Index

Appliance Design - January 2009

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