Tapered Guide External Thread Member for Oblique Entry Prevention
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Solution Overview
Problem
Conventional bolts with pilots are ineffective in preventing galling and seizure due to increased length and weight, and insufficient inclination correction when the internal screw is short, leading to oblique entry issues during high-speed tightening operations.
Innovation Solution
An external thread member with a tapered guide portion and a guide screw thread on its peripheral surface, which corrects inclination through a moment acting as a fulcrum, allowing normal engagement and pitch adjustment, eliminating the need for a conventional cylindrical guide and reducing the length of the screw tip, while a cylindrical surface with the same diameter as the root diameter of the normal thread area reduces interference and tolerance for inclination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cylindrical guide is provided to correct inclination, then oblique entry is prevented, but the length and weight of the screw tip increase
Solution Approach 1:
The invention extracts the essential function of the cylindrical guide (inclination correction) and implements it through a different mechanism - the tapered guide portion with guide screw thread that corrects inclination through rotational engagement rather than through a separate cylindrical guide structure, thereby eliminating the need for excessive length
Solution Approach 2:
The invention changes the geometric parameters of the guide portion from a cylindrical shape with constant diameter to a tapered shape with varying diameter. The tapered guide portion has a smaller diameter at the tip that gradually increases toward the base, allowing it to engage and correct inclination through rotation while maintaining a compact overall length
2Reliability
If a cylindrical guide is provided to correct inclination, then oblique entry is prevented, but the weight of the screw increases
Solution Approach 1:
The invention extracts the essential function of the cylindrical guide (inclination correction) and implements it through a different mechanism - the tapered guide portion with guide screw thread that corrects inclination through rotational engagement rather than through a separate cylindrical guide structure, thereby reducing unnecessary material and weight
Solution Approach 2:
The invention merges the functions of the guide portion and the screw thread into a single integrated structure. The guide screw thread is formed directly on the tapered guide portion, combining the inclination correction function with the fastening function, thereby eliminating the need for separate heavy components
3Length of moving object
If the internal screw is short, then assembly is compact, but the cylindrical guide cannot sufficiently correct inclination
Solution Approach 1:
The invention employs a dynamic inclination correction mechanism where the tapered guide portion rotates during engagement. The rotational motion allows the guide screw thread to progressively engage and correct inclination dynamically throughout the engagement process, rather than relying on a static cylindrical guide that requires sufficient axial length
Solution Approach 2:
The tapered guide portion introduces a curved geometric profile that facilitates rotational engagement. The tapered shape creates a wedging action during rotation that effectively corrects inclination even with limited axial engagement distance, overcoming the limitation of short internal screws
4Productivity
If high-speed tightening is performed, then productivity is improved, but oblique entry and galling occur
Solution Approach 1:
The guide screw thread on the tapered guide portion performs preliminary action by engaging and correcting inclination before the main screw threads engage. This preliminary inclination correction ensures that subsequent high-speed tightening occurs with proper alignment, preventing galling and seizure while maintaining high productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively prevents oblique entry and insertion, thereby preventing galling and seizure of screw threads, even when the screw tip is short, within the defined length of an incomplete thread portion, as per JIS B 1003 standards, and reduces the occurrence of galling and seizure by adjusting the pitch and disengaging the guide screw thread.
Implementation Method 1
the diameter of the tapered guide portion increases with rotation, and the guide screw thread at the biting position is naturally disengaged from the screw thread of the internal screw, so that the inclination of the shank portion is being corrected by a moment acting thereon with an engagement portion of the transition screw thread or the complete screw thread as a fulcrum
Data Source
Figure 1
Figure 2
Figure 3(A)~3(D)
AI summary
A external thread member capable of preventing oblique entry or insertion by a short screw tip shape is provided. A external thread member including, in its shank portion (20), a normal thread area (22) in which a complete screw thread (21) to be fastened to an internal thread member is formed, a guide thread area (24) provided at a tip side of the shank portion with respect to the normal thread area (22) and in which a guide screw thread (23) having a diameter smaller than that of the complete screw thread (21) and having a same pitch is formed, and a rising area (26) in which a transition screw thread (25) gradually rising from the guide screw thread (23) to the complete screw thread (21) is formed, is characterized in that a tapered guide portion (30) with a diameter gradually decreasing toward a tip end of the shank portion is provided at a tip end side of the normal thread area (22) of the shank portion (20); the tapered guide portion (30) includes at least the guide thread area (24); the guide screw thread (23) is formed on an outer periphery of the tapered guide portion (30); and the tapered guide portion (30) has a maximum diameter equal to or smaller than an inner diameter of an internal thread and equal to or larger than a root diameter of the complete screw thread (21).