Self-Tapping Screw with Additional Thread for Wood Splitting
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Solution Overview
Problem
Self-drilling screws used in wood materials face challenges in minimizing the splitting effect and crack formation due to the wedge effect of conical screw tips, which reduces the durability of bolted joints.
Innovation Solution
A self-drilling screw design featuring an additional thread within the conical screw tip with a smaller pitch, larger flank angle, and lower profile height compared to the primary screw thread, which helps prevent wood splitting and crack formation, while maintaining quick screwing speed and reduced torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the screw thread extends over the conical screw tip to enable quick self-drilling, then the screwing speed is improved, but the splitting effect and crack formation in wood increase
Solution Approach 1:
The screw thread is segmented into two distinct parts: a first thread with larger pitch and profile height for rapid material displacement and feeding, and a second thread with smaller pitch and lower profile height for reduced splitting effect. This segmentation allows each thread to perform its specific function optimally without compromising the other.
Solution Approach 2:
Different regions of the screw thread have different geometric properties. The first thread portion has larger pitch and profile height suited for aggressive material displacement, while the second thread portion has smaller pitch and lower profile height suited for gentle material engagement. This local differentiation resolves the contradiction between fast screwing and reduced splitting.
2Object-affected harmful factors
If a ring with sharp edge is added within the conical screw tip to reduce splitting, then the splitting effect is reduced, but the device complexity increases
Solution Approach 1:
Instead of adding a separate ring element within the conical tip, the invention merges the splitting reduction function directly into the screw thread itself by creating a second thread with appropriate geometric parameters. This integration eliminates the need for additional components while achieving the same protective effect.
3Object-affected harmful factors
If ribs with scraping edges projecting beyond the screw tip surface are added to reduce splitting, then the splitting effect is reduced, but the screwing resistance increases
Solution Approach 1:
The invention changes the geometric parameters of the thread rather than adding projecting ribs. By reducing the pitch and profile height of the second thread, it creates a scraping effect that reduces splitting without the excessive material displacement and high screwing resistance caused by projecting ribs.
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
The additional thread effectively reduces the splitting effect and crack formation in wood, enhancing the durability of the bolted joint without increasing screwing resistance or decreasing speed.
Implementation Method 1
there is a risk that cracks may appear due to the wedge effect of the conical screw tip
Implementation Method 2
the screw thread extends over the screw shank 1, which screw thread is, for example, a chipboard thread
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a self-tapping screw comprising a cylindrical shank (1) with a conical screw tip (2) which ends in a punctiform sharp tip. The screw thread (4) starts already in the screw tip (2), at a small distance from the punctiform tip. In addition to the screw thread (4), an additional thread (5) is provided which likewise begins in the screw tip, but further down than the screw thread (4). The additional thread extends only along one to three turns and ends directly after the transition between the screw tip (4) and the cylindrical shank (1). The additional thread (5) has the same thread orientation as and a smaller pitch and a smaller thread height than the screw thread.