Appliance Design - August 2007 - (Page 37)

Cutaway view of a tongue-and-groove joint in a high-pressure vessel whose top and bottom glass-filled polypropylene pieces were joined using the Emabond process. The proximity of internal metal mass and delicate internal components (at right) made the assembly a challenging design for which the Emabond process proved to be a good solution. JOINING during the actual heating cycle, which typically is between 1 second to 30 seconds. Low clamping force is applied via the specially designed fixture to allow efficient transfer of melt temperature to the substrate. After joining: The Emabond material has filled the gap and the process has fused the mating parts, resulting in a polymer-to-polymer, permanent weld. The joint’s cross-section is more compact than one joined by a frictional method of assembly that typically requires broader surface area and/or flash traps. The Emabond process is a non-contact, non-violent method of assembly that is gentle on plastic parts. And it can join certain dissimilar materials, such as highly filled thermoplastics and flexible elastomers to rigid substrates. It also meets or exceeds demanding requirements such as NSF, for temperature-resistance, leakproof and pressure-tight properties, and aesthetic appearance. In addition to supplying the specialty joining materials, Emabond also supplies the equipment and control systems that manage the process. mance requirements. The conductive fillers in the material must be compatible with the thermoplastics used in the parts to be joined. The type and quantity of conductive filler also influences energy absorption and, subsequently, the amount of heat that will be generated at the bond line. Sometimes, a simple, ferromagnetic filler such as iron will be appropriate. In other cases, recently developed ceramic fillers can be used to provide more exacting control of the temperature. Applying the material as a die-cut preform, like a gasket, is one of the simplest methods from an assembly standpoint, but the material can be supplied in a variety of fashions, including extruded profiles, sheet, tape and ribbon. The material can also be co-extruded or coinjected directly onto the substrate of one of the mating parts. The Emabond engineers help OEM designers determine the optimal method for a specific application. The photo above shows an image of a tall, shear, tongue-and-groove joint that joins two glass-filled polypropylene parts to form a tank that holds liquid under high pressure. The proximity of internal metal mass and delicate internal components made the assembly a challenging design for which the Emabond process proved to be a good solution. The tongue and groove joint offers the greatest versatility, especially when leak proof and high-pressure results are required. However, joint designs can also be flat-to-flat, flat-togroove and step. Fig. 1 shows the three phases in the Emabond process: before, during, and after. Before joining: The preform is positioned in the joint. The mating parts are brought together and placed within a fixture containing a work coil that conforms to the weld line geometry. This phase is easily automated or operator initiated. During joining: The activated coil heats the Emabond material, causing the adjoining plastic surfaces to melt. Energy is only consumed Improvements The new line of solid-state RF generators with flexible power-delivery systems has advanced the technology by providing welding process control and feedback. Historically, Emabond systems used tube-type generators that operated at variable frequency ranges from 2 MHz to 8 MHz and offered limited feedback capability. The new power-delivery system accurately controls the application of energy at the bond line, and the generators are FCC compliant and CE Approved. The RF generator is programmable, and the controller provides self-diagnostics and a multitude of process control capabilities on the welding process. The immediate advantages include: 1. Precise control of energy at the bond line, including ramped power stages or pulsing of power. 2. Minimal or no heating of non-plastic components, such as metal and delicate electronics that may be near or captured within the weld line at time of assembly. 3. Flexible, moving-power application packages that can allow for spot welding and or continuous scanning of a bond line. 4. Wider overall power spectrum ranging from 1 kW to 5 kW. 5. Lower overall system cost savings. Before Joining During Joining Low Pressure Applied After Joining Copper Work Coil High Frequency Energy Emabond Material is 100% contained Precise Heat Delivery to Bond Line Produces a Structural Joint Capable of High Shear Strength Fig. 1. Sequence illustrates how the Emabond process works. www.applianceDESIGN.com applianceDESIGN August 2007 37 http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - August 2007

Contents Editorial Shipments/Forecasts News Watch A Reed Switch is Simople, yet Versatile, and Designers are Finding New Uses for this Time-Tested Technology A Novel Actuation and Sensing Technology can Register a Light Touch, but Resist Blows from a Hammer Tracing the Source of Noise is Made Easier with Noise Source Identification Methods Appliance Noise can be Annoying, but Designers have Many Material Choices to Help Rein in the Racket Nanocomposites are No Longer a Technology for the Future. These Plastic Materials are Already on the Job A New High-Strength, Low-Density Glass-Microsphere Additive can Improve Plastic Part and Molding Performance A New Electromagnetic Weld/Bonding Process Helps Ensure Long-Term Integrity of Joints in Plastic Parts Snap-Based Technology Eases Installation and Makes Products More Serviceable Two-Part Silicone Adhesives Provide a Rapid-Cure Alternative to Traditional One-Part Silicones Classified DesignMart Advertiser’s Index Association Report: GAMA

Appliance Design - August 2007

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