Assembly - January 2009 - (Page 74) ASSEMBLY Adhesives Dispensing Cyanoacrylates The key to cost-effective bonds with these adhesives is putting the right amount in the right place. C yanoacrylate adhesives (CA) quickly form tough and durable bonds with a wide variety of substrates including plastics, metals, ceramics and glass. Furthermore, no mixing, refrigeration or special handling—other than respecting the caustic nature of CAs—is required. improvement in dispensing systems is allowing CAs to penetrate new assembly markets, especially where cost, cure speed, precision and repeatability are paramount. What Are Cyanoacrylates? Cyanoacrylates are one-part acrylic resins that cure rapidly in the presence of moisture, in particular, the hydroxide ions that exist in water. CAs are available in a wide range of viscosities, from thin fluids to viscous gels, to meet a wide variety of specific needs. Many component assembly applications call for a CA with very low viscosity, such as a medical device that requires wicking, or capillary action, to draw the adhesive into a bonding area between mating components. One such example is an elbow being fitted and bonded onto tubing. At the other end of the spectrum, a CA in the form of a very viscous gel might be required to fill a gap, in which case the material may incorporate an agent to reduce fixturing time and ensure a cure. Gels are available that can be used to fill gaps greater than 0.01 inch without the adhesive flowing out of the gap. Various agents are also available for toughening CAs to improve peel and impact strength, and for reducing brittleness when filling gaps. In between these two extremes of viscosity are a host of other adhesive formulations for a multitude of applications including golf clubs, automotive components, appliances and electronic assemblies. CAs can be used to form a bond tough enough for the most demanding application. For Cyanoacrylate adhesives reduce cycle time in assembling fiber optic components. By Scott Beebe President Fishman Corp. Hopkinton, MA The high bond strength and rapid cure rate without the need for heat, light or catalysts have led to widespread use of CAs in a number of industries, including electronics and medical device assembly. For example, their rapid cure rate is often advantageous where fast-tack fixturing is a priority. On the other hand, they can be particularly difficult to dispense with precision and repeatability. Continuous 74 ASSEMBLY / January 2009 www.assemblymag.com http://www.assemblymag.com
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