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Inside Iowa State
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September 12, 2003

Detecting the problem

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by Anne Krapfl
As Brian Larson can attest, the solution lies in a correct assessment of the problem.

Last spring, Larson, a program manager for the Iowa Demonstration Laboratory, the outreach arm of Iowa State's Center for Nondestructive Evaluation and one of four divisions in IPRT Company Assistance, was approached by engineers from Gits Manufacturing Co. of Creston.

A popular Gits product is a butterfly valve for exhaust gas recirculation on heavy trucks. Changing the material of the shaft to a more wear-resistant -- but more brittle -- alloy had created cracking problems.

Gits engineers believed their assembly employees were cracking the shaft when they pressed a pin through the valve shaft, and they sought a non-destructive evaluation (NDE) technique to test the assembled valves prior to shipment. Larson's team, which specializes in sharing NDE technology with industry, developed an ultrasonic inspection technique to detect cracks in the valves.

When Larson visited Gits' Creston plant to help implement the ultrasonic testing, he noted employees using a dye-in-oil penetrant to visually check new valves for cracks as they arrived from the supplier. (Dye in an oily solution seeps into defects and then bleeds back out after the excess solution is removed from the surface of a valve.) Larson suggested a more sensitive visual check in which a special dye in the oil glows under ultraviolet light. This new inspection technique detected tiny cracks in nearly all the new shafts, leading to the conclusion that a faulty drilling process was the real source of the problem.

Gits officials continue to use the florescent inspection idea and are working with their supplier to correct the drilling problem. Gits project engineer Neil Wohlenhaus said a redesign of the valve shaft is the long-term solution, but the assistance from Iowa State resulted in more than $200,000 in inventory savings for Gits.

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