Home| FAQ Search:Advanced|Person|Company| Type|Class Login
Quick search:
Patent number:
Patent Date:
first    back  next  last
US Patent: 3,696,412
Method and Means for Indicating Tension
Patentee:
Roger I. Swanson (exact or similar names) - Butler, PA

USPTO Classifications:
174/117F, 200/61.08, 340/668, 411/548, 73/761

Tool Categories:

Assignees:
Dake Corp. - Grand Haven, Ottawa County, MI

Manufacturer:
Not known to have been produced

Witnesses:
Unknown

Patent Dates:
Applied: Oct. 19, 1970
Granted: Oct. 03, 1972

Patent Pictures:
USPTO (New site tip)
Google Patents
Report data errors or omissions to steward Joel Havens
"Vintage Machinery" entry for Dake Corp.
Description:
Abstract

In a method and means for indicating tension on bolts, screws and the like, a plastic member of flowable material having a plurality of relatively thin copper wires embedded along each edge is utilized. The member has an annular cutout portion permitting it to be inserted between any two bearing surfaces of a threaded fastening joint with the bolt passing through the cutout portion. When the point is tightened to pre-load below yield, the plastic material flows or is extruded until the joint contacts the wire. Subsequent tightening to the desired minimum proof load will shear the wires and material to indicate that minimum proof load has been reached. The plastic strip material also serves as a lubricant to reduce the amount of torque required to reach minimum proof load and a portion is extruded into the core of the joint to act as a lock and seal. In one embodiment, the wires form a pair of leads which may be connected in an electric circuit so that when the joint is tightened to pre-load below the plastic range, there is sufficient extrusion of the plastic material to establish electrical contact between the joint and edge wires to close the electrical circuit, activating an electrical signal to indicate that pre-load has been reached. BACKGROUND OF THE INVENTION This invention relates to threaded fasteners, and, more particularly, to a fastener tension indicating system that will provide a signal at various levels of load tensioning in a threaded joint. It is well recognized that a key to a successful product is many times directly related to the success in properly tightening a threaded joint to maximum tension load. Too little or too much will in either event result in failure and the objective is lost. In addition, in mass production, material costs in the way of quantity and size of bolts, nuts, tools, etc. can often represent the difference between commercial success or failure. With the advent of power tools, many prior and existing proposals have used torque as the standard for measuring "bolt tension". Although it is theoretically feasible under ideal conditions to measure the torque applied to a fastener and thereby accurately arrive at the desirable tension, there are so many variables in actual practice such as the quality of threads, galling, foreign matter, etc. that it has proven to be unreliable as a standard for bolt tension. Where it is still used, it is common to specify bolts larger than required for the assembly and utilize less than their maximum tension. While this reduces the chances of over stressing the bolt, it also results in higher costs. With the advent of high strength bolts, and in view of the unreliability of torque as a measure of tension, the trend has been to obtain higher tensile loading in the fastener, and draw the bolt up to minimum proof load and beyond. Thus, other methods have been devised to indicate bolt tension such as strain washers, strain gauges, bolt stretch and others. However, all have proven to be too costly or impractical. SUMMARY OF THE INVENTION To achieve a successful assembled product, there are several areas of major concern. To begin with, the product must be designed to withstand the stresses and strains of the work load. Thus, an economical fastener system must be designed that will pre-stress the assembly above the work load without loosening or failing. From a commercial standpoint, an economical method and tools for assembly and inspection must be established to insure the proper pre-stressing of the assembly. Therefore, it is a principle object of this invention to provide a method and means for indicating when minimum proof load or desired bolt tension is reached in a threaded joint at a cost well below today's unreliable methods. It is also an object of this invention to provide a method and means for indicating when the joint has been tightened to pre-load before minimum proof load is reached. It is a further object of this invention to additionally provide such benefits as, the reduction of required torque to achieve proper joint tension; a seal; a bonding to resist rotation if the joint relaxes; and a method and means which is not only convenient and easy to handle by an unskilled operator, but, in fact, will reduce the amount of handling required thereby increasing overall production. For achievement of these and other objects, a tension indicating tab of flowable material is provided having a center cutout portion and means of substantially greater hardness than said material embedded along each edge. With the tab positioned between two bearing surfaces in the joint, tensile loading is provided. The tab is deformable and extrudable so that when minimum proof load is achieved, the tab is completely sheared off between the bearing surfaces. Preferably, the means embedded along each edge is comprised of a wire to provide a pair of leads connected to an electrical circuit which when closed operates an electric signal. The tab is positioned so that the wire means is partially interposed between the two bearing surfaces and when the joint is tightened to a pre-selected pre-load, the tab is partially extruded in, around and out of the joint area until electrical continuity is established between the wire means and joint thereby closing the electrical circuit to actuate the signal. Further tightening of the joint causes complete shear of the tab and wire means between the bearing surfaces thereby opening the electrical circuit to indicate minimum proof loading. The flowable characteristics of the tab acts as a lubricant thereby reducing the amount of torque required to establish a positive joint and in addition acts as a sealant and bond to resist rotation should the joint relax. To increase production and reduce handling, a plurality of tabs may be collated into a continuous strip.

Copyright © 2002-2024 - DATAMP