External Screw Convex Thread Structure for Lower Driving Torque
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Solution Overview
Problem
Existing self-tapping screws face issues with increased driving torque due to chip accumulation and poor foreign matter removal, especially when used with long screws or screws with adhered paint films, leading to jamming or biting problems.
Innovation Solution
An external screw member with a parallel and tapered threaded portion, featuring convex portions that gradually increase in diameter and an inclined screw driving side end face, allowing for efficient chip discharge and foreign matter removal by guiding the screw thread formation and adjusting pitches to prevent biting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the length of internal screw is increased, then the screw thread formation capability is improved, but cutting chips accumulate in the screw and driving torque increases abruptly
Solution Approach 1:
The screw thread is divided into two distinct zones: a first zone screw thread portion with standard thread height and a second zone screw thread portion with increased thread height. This segmentation allows the longer screw to form threads effectively while the increased height in the second zone creates larger spaces for chip discharge, preventing accumulation along the extended length.
Solution Approach 2:
Different portions of the screw thread are given different properties: the first zone has standard thread dimensions for initial engagement, while the second zone has increased thread height specifically to enhance chip discharge capacity. This local differentiation addresses the chip accumulation problem in longer screws without compromising overall thread formation capability.
2Object-generated harmful factors
If self-tapping screw is used to remove foreign matter from internal screw, then foreign matter removal capability is improved, but driving torque increases due to jamming or biting
Solution Approach 1:
The screw thread is designed with varying local properties: the first zone screw thread portion engages the internal screw with standard dimensions for stable threading, while the second zone screw thread portion with increased height actively removes foreign matter through its larger clearance space, preventing jamming and reducing driving torque requirements.
Solution Approach 2:
The screw is segmented into functional zones where the first zone handles thread formation and engagement, while the second zone with increased thread height specifically handles foreign matter removal. This functional segmentation allows efficient foreign matter removal without excessive driving torque.
3Object-generated harmful factors
If the thread height is increased in the second zone screw thread portion, then chip discharge is improved, but the complexity of screw thread configuration increases
Solution Approach 1:
The screw thread is segmented into two zones with a clear boundary, where the second zone has increased thread height to create larger chip discharge spaces. This segmentation improves chip discharge while maintaining relatively simple manufacturing by dividing the thread into distinct sections rather than using a continuously varying complex profile.
Data Source
AI summary
An external screw member includes a head, a shank, a parallel threaded portion, a tapered threaded portion, a screw thread, a convex portion and a screw driving side end face of the convex portion. The convex portion protruding more radially outward than the crest of the screw thread is formed in at least one of the parallel threaded portion and the tapered threaded portion over the tapered threaded portion and the parallel threaded portion. The screw driving side end face of the convex portion is configured to form an inclined plane which gradually rises from a root position of the end face at the side of the crest of the screw thread toward a crest of the convex portion in a direction opposite to a screw driving direction of the screw thread to reach the crest of the convex portion.