10 THE DISTRIBUTOR’S LINK Laurence Claus Laurence Claus is the President of NNi Training and Consulting, Inc. He has 25 years of experience with a medium sized automotive fastener manufacturer, holding positions including Vice President of Engineering, General Manager, Director of Quality, Director of New Business Development and Applications Engineer. In 2012 he formed NNi offering technical and business training courses as well as technical consulting, expert witness and consultation work. He can be reached at 847-867-7363 or by email: Lclaus@NNiTraining.com. You can learn more about NNi at www.NNiTraining.com. A “GALLING DEVELOPMENT”- WHAT EVERY DISTRIBUTOR SHOULD KNOW ABOUT THREAD GALLING A number of year’s back I was engaged by a Midwestern distributor to review an application problem that had intermittently plagued one of their more important customers. Upon meeting with their customer, I learned the problem occurred during the assembly of a stainless steel Nylon insert lock nut to a like stainless steel screw. Although this was a sporadic problem, when it occurred the customer would experience assembly difficulties like nuts that were very hard to turn, nuts that reached installation torque levels before seating, and in the worst cases, nuts that became totally frozen (seized) in mid-run down position, often breaking the screw in torsion. Anyone that has been selling stainless steel hardware for a while may immediately recognize that this case demonstrates all the signs of thread galling. Fortunately for users, galling is usually an infrequent problem and one that can be addressed in multiple ways. However, when it occurs it is, at best, a nuisance and, at worst, a dangerous condition that could leave incompletely fastened joints vulnerable to failure. Since galling is a problem characteristic to fasteners, it is a failure that all distributors should understand and be prepared to troubleshoot with their customers. This article will provide the reader with a fundamental understanding of what galling is, the telltale signs, and ways that it can be addressed or completely eliminated when it appears. What Is Galling? So what exactly is galling? Galling, also commonly referred to as Cold Welding, is a form of adhesive wear TECHNICAL ARTICLE that occurs when material transfers from one surface to the other when they are sliding together. When parts become subject to galling, the process begins modestly at a microscopic level but quickly progressives into a worsening macro condition. It all starts when the mating surfaces that are sliding against each other begin to experience an increase in heat and friction that results in the surfaces beginning to adhere to one another. As torque continues to be applied to the turning fastener, the areas of adhesion promote tearing of the weaker metal below its surface and redepositing it on the adjacent surface. The result is a lump or ball-like deposit of material from the original surface adhered to the adjacent surface. The ASTM G40 Standard says, “Galling is a form of surface damage arising between sliding solids, distinguished by macroscopic, usually localized, roughening and creation of protrusions (e.g. Lumps) above the original surface.” [1] These newly adhered lumps then “plow into” the approaching virgin surfaces as the fastener continues to be turned onward often damaging any protective surface layer and exposing, soft, bare metal. The original lumps develop more friction and heat which progressively accelerates tearing and generates additional lumps, grows original lumps in size, or promotes additional adhesion between the surfaces until the point that the threads are completely frozen together and the fastener can no longer turn or is broken. Although this condition is theoretically possible with any material it is generally limited to softer materials, especially those which produce natural protective oxide layers. CONTINUED ON PAGE 100
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Martin Inc., is pleased to announce
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Ramco Specialties, Inc., has comple
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