Aerco International Inc. (Northvale, NJ) manufactures commercial water heaters and boiler systems. The company's signature product is a high-efficiency, self-descaling water heater that uses vertical stacks of helical coils that share a common steam riser and condensate return pipe. To keep field repairs and coil replacements simple and cost-effective, each independent coil set is connected to the common pipes via a threaded nut connection. The longevity of the heat exchanger is critically dependent on the integrity of these connections.

To ensure the quality of these threaded connections, Scott McGrath, a continuous improvement engineer and Six Sigma Black Belt at Aerco, incorporated a BoltFAST fastener-joint analysis software package from Sensor Products Inc. (East Hanover, NJ) as part of the company's ongoing quality inspection program.

According to McGrath, the software makes it possible for his company to confirm the upper and lower torque values and the capabilities of its connections. It also helps accurately quantify the effects of prevailing torque on the joint components created by braze in the connector threads. The program facilitates joint assembly analysis and confirms a very expensive finite element analysis performed by the company. Using software analysis, Aerco can quickly validate as many as 16 different dimensional aspects of its various threaded connection designs.

"We consider BoltFAST a mission critical tool in our quality control and new product development toolset. The knowledge derived from the program is put into action throughout Aerco," McGrath says. "Its influence extends far beyond the product design team. BoltFAST helps not only the brazing and assembly operation, but also influences materials storage and lubricant sourcing, as well as testing and inspections."

A comprehensive bolted-joint analysis software package, BoltFAST incorporates a large database of fastener and interface materials and their physical characteristics. It then uses this information to determine the fatigue endurance limit of a thread, the amount of embedding anticipated in a bolted joint and the optimal tightening torque for given friction conditions. The program determines if a bolted joint can sustain the forces acting upon it; calculates the force necessary to fracture a fastener and strip the internal and external threads; and helps determine correct tightening torque and resulting anticipated clamp force for a threaded fastener.

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