A Locking Thread for Bolts and Nuts
Page 75
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FOR many years engineers have tried to make nuts remain tight on their bolts, and during the past 50 years many hundreds of nut-locking devices have been patented. The number of these devices proves the urgency of the Problem, and the lack of success achieved in many instances renders further efforts in this direction tubject to good-natured ridicule.
The latest development in this direction is the Dardelet self-locking screw thread. The object aimed at is autoMatically to lock the nut to its bolt simply hy the action of tightening the nut in the usual manner. The Profile of the bolt thread has, at the bottom of the groove, a gentle slope, which rises towards the end of the bolt. The profile of the nut thread has slopes of the same inclination on the crest of
the thread. When the nut is first screwed on its thread Moves freely at the bottom of the groove on the bolt. When the nut is screwed home and seated on the work the nut thread is forced up the gentle slope on the bolt thread, thus becoming wedged or jammed.
The wedging action stretches the
material of the nut, but the stretching is limited by the, approximately, square abutting faces on the sides of the threads, and it is on these faces that the load on the screw is carried. The locking action is available at any part of the threaded length of the bolt, so that exact positioning of the nut is unnecessary.
Dardelet nuts are Provided with a
form of thread which will act as a lock whichever way they are placed upon their bolts.
Severe tests for tensile strength and resistance to vibration have been made by the National Physical Laboratory, Teddington, copies of reports of which can be found in a brochure which eau be obtained from the British Dardelet Threadlock, Ltd., Chase Road, London, N.W.10.
The company has sufficient faith in the merits of this invention to warrant its building a large London factory at Gorst Road, North Acton. A recent visit to this factory. showed us that the company means to take seriously the production of Dardelet nuts and bolts, as we found large modern shops filled with the latest machines for the automatic production of bright nuts and bolts from the bar, and the forging of black bolts and nuts to receive the Dardelet form of thread. The making of black bolta and nuts is a somewhat new industry to the London district, the company relying more on the automaticity of the modern machinery they have installed than upon hand labour.