Joints and connections – Rod end to transverse side of member – Utilizing opposite sides of member
Patent
1993-04-30
1996-02-27
Knight, Anthony
Joints and connections
Rod end to transverse side of member
Utilizing opposite sides of member
403256, 403322, 403321, 451 64, F16B 3500, B27B 532, B24B 4500
Patent
active
054943680
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an improved fastener, and relates in particular, though not exclusively, to a threaded fastener suitable for fastening a grinding wheel, circular saw blade or carving disc to the spindle of a power tool.
BACKGROUND TO THE INVENTION
With a conventional threaded fastener, for example, in the form of a nut, a significant proportion of the energy required to tighten the nut on a threaded spindle of a bolt or the like, is dissipated due to friction between the nut and the surface of an object to be fastened. This means that the torque required to achieve the necessary "tightness" of the nut, (i.e. the hold-down pressure exerted by the nut on the object to be fastened), can be up to fifty percent greater than would otherwise be necessary. For this reason, special tools such as, for example, a long spanner or an adjustable torque wrench, are used to provide the torque necessary to overcome the friction and still achieve the desired hold-down-pressure. For the same reason a special tool is usually required to unfasten the nut as well.
It was hitherto thought that maximum friction is required between the nut and the fastened object in order to ensure that the nut and/or the object did not come unfastened in use. A recent discovery suggests that this may not be the case, and that provided sufficient hold-down pressure is exerted by the action of the nut against the fastened object, the nut will remain fastened due to the reactive tensioning thereof and the frictional grip on the thread of the spindle on which the nut is threaded. In many situations, the object to be fastened cannot rotate relative to the spindle, for example, because it is keyed to the spindle, so that the possibility of the nut unfastening by itself is significantly reduced anyway. However, the discovery that little or low friction is required between the nut and the fastened object to keep the nut fastened, makes it desirable to minimize such friction so that more of the torque is available to be converted to hold-down pressure.
U.S. Pat. No. 4,969,788 discloses a nut with a pressure ring of the type having a spherically shaped undersurface for engagement with a complementary shaped depression in the component to be fastened. The invention seeks to overcome problems associated with conventional slit pressure rings which are normally a separate component from the nut. A nut with a closed pressure ring connected thereto is provided, the means of connection permitting the nut and ring to rotate relative to one another about the nut axis and to shift relative to one another laterally of the nut axis. The nut and the pressure ring have confronting pressure transmitting surfaces, and at least one of the pressure transmitting surfaces is provided with a plurality of recesses for holding lubricant. This can be achieved for example by shot peening the pressure transmitting surface. According to U.S. Pat. No. 4,969,788, in this manner the shot peened pressure transmitting surface can be provided with a permanent lubricating film whereby friction between the nut and the pressure ring is not of the same magnitude as with a slit pressure ring and a debasing of the hold-down-torque during tightening of the bolt is reduced. The opposite confronting pressure transmitting surface is preferably finely turned or polished.
Presumably the lubricant employed is a liquid or viscous lubricant, for example grease, so that if the recesses in the shot peened surface are filled with the lubricant, as the nut and pressure ring are rotated relative to one another some of the lubricant in the recesses sticks to the confronting surface and is spread as a thin film between the pressure transmitting surfaces in known manner. This may prove satisfactory for a time, however after repeated use many of the recesses will be evacuated of lubricant and some of the lubricant will have been squeezed out from between the confronting surfaces so that little or no lubricant is left to form the thin film therebetween. Furthermore, liq
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