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Visual Tension Bolt Measurement Disclosure Number: IPCOM000246466D
Publication Date: 2016-Jun-09
Document File: 2 page(s) / 52K

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The Prior Art Database


Described is a visual tension bolt measurement method.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

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Visual Tension Bolt Measurement

Torque wrenches are typically used when installing bolts to a pre-set, desired value. To assure that the bolt is secure, a certain amount of bolt tension is required. Unfortunately, torque wrenches may only be accurate to +/- 30% due to unknown variations of the coefficient of friction. Torque is the force required to rotate a bolt or nut and is often confused with bolt tension in the shaft. Equations to convert torque to bolt axial tension depend on the mating materials, the coefficient of friction, whether or not a lubricant is utilized, etc. Factors affecting this coefficient include the material and size of the bolt, nut and washer, type of plating, surface smoothness, machining accuracy, corrosion or wear on the threads, presence and type of thread lubricant, the number of times a bolt has been previously tightened, and many other factors. In complex assemblies where there are many fasteners employed, it is very time consuming to use a torque wrench to sequentially check each individual fastener for proper tension.

    Fastener manufacturers often provide torque specifications for tightening various bolts to establish a required tension. However, these torque specs are only accurate for one coefficient of friction and, thus, cannot account for inevitable changes in friction. Worse, even these potentially misleading specs are often not available in field applications or their use is impractical or poorly administered. Moreover, a torque wrench is not always available (e.g., in field applications).

    It would be very useful if one could specifically adjust a mechanochromic polymer to change color at various tension extension levels to correlate to proper elongation required for higher strength bolts. For instance, a standa...