Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Having structure to restrict rotation of threaded – mating... – Comprising a thread lock
Reexamination Certificate
2000-06-30
2001-06-19
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Having structure to restrict rotation of threaded, mating...
Comprising a thread lock
C411S327000, C411S947000, C470S014000
Reexamination Certificate
active
06247884
ABSTRACT:
BACKGROUND OF THE INVENTION
The field of the invention pertains to threaded plugs for insertion in threaded boreholes such as the borescope holes formed in the metal casings of turbo-jet, fan-jet and other types of gas turbine engines used in aircraft. The borescope plugs, in particular those used in the hot section of the engine, must be corrosion resistant at high temperatures and not subject to loosening despite repeated temperature cycling when the engine is started and stopped. As a result, the borescope plugs are typically formed of high temperature refractory metal alloys that are difficult to form and therefore expensive to manufacture.
U.S. Pat. No. 2,166,686 discloses an adjusting screw for a camshaft follower. The screw is slotted and flatted at the end of the screw. The threads at the end of the screw are spaced by a relieved peripheral area from the remaining threads on the screw, and the lead of the end threads differs from the lead of the remaining threads.
U.S. Pat. No. 3,351,966 discloses a slotted fastener and method of manufacture of the threads to prevent the thread cutting or tapping effect adjacent the slot. The patent also discloses an enlarged thread area in the region of the slot to cause deformation when threaded into a threaded socket.
U.S. Pat. Nos. 4,815,276 and 5,115,636 disclose borescope plugs for double walled constructions, and U.S. Pat. No. 5,169,270 discloses a slotted plug wherein the slotted threaded portion is squeezed by the insertion tool when the plug is screwed into the threaded socket. Upon release of the tool, the plug expands to lock.
U.S. Pat. No. 5,704,748 discloses a screw having a recess intersecting the threads and a slot for a coil spring. The coil spring deflects upon mating with the threaded female member.
SUMMARY OF THE INVENTION
The new plug eliminates the present need for external capture devices or stainless steel wires through holes in the plug exterior in aircraft applications. The new plug is formed with a diametrical slot in the interior threaded end and an axial through hole. A spring unit is positioned in the through hole and slot. The spring unit is also formed with a diametrical slot that extends from the interior end of the plug well down into the post portion of the spring unit and therefore into the through hole.
The spring unit is assembled to the plug prior to heat treatment of the spring unit. Fixturing of the spring unit determines the spring rate of the unit and, in combination with the fit of the spring unit in the slot and through hole, the amount of line contact of the unit with the threads of the hole into which the plug is to be threaded. The holding torque of the plug is thereby determined.
Two alternative forms of the spring unit are disclosed. Both forms enable the plug to be easily initially threaded into the threaded borehole before the spring unit fully engages. In the first form, the spring unit is foreshortened to prevent engagement until the plug body is threaded in about a tenth of an inch or more. In the second form, the major, minor and pitch diameters are foreshortened to provide a non-standard tapered form thread as a lead-in thread that can be easily engaged by the threaded borehole.
REFERENCES:
patent: Re. 20542 (1937-10-01), Dyer
patent: 2852056 (1958-09-01), Rapata
patent: 5879116 (1999-03-01), Criswell
Deimen James M.
Moeller Manufacturing Co.
Wilson Neill
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