Concrete Screw With Contracting Thread Helix for Undersized Boreholes
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Solution Overview
Problem
Existing screws for concrete or masonry substrates face challenges in efficient installation, particularly when the borehole widens, as they tend to radially expand rather than contract, leading to instability during seismic situations and difficulty in undersized boreholes.
Innovation Solution
The screw design features a separate thread helix that radially contracts by displacing its crest towards the shank when driven into an undersized borehole, utilizing a thread helix receiving groove with surplus space and an accommodation cavity to facilitate this motion, allowing for easy installation and anchoring without additional force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thread helix is designed to radially expand when the shank is axially loaded (as in US 2018 0283 435 A1), then the screw maintains engagement with the borehole wall in widened boreholes, but the screw cannot be installed in undersized boreholes and requires complex groove designs with inclined flanks
Solution Approach 1:
Instead of designing the thread helix to radially expand under axial load (conventional approach), this invention inverts the behavior by designing the thread helix to radially contract. The thread helix receiving groove has a relaxation cavity that allows the thread helix to move radially inward when the shank is axially loaded, enabling installation in undersized boreholes while maintaining engagement through elastic recovery after installation
2Reliability
If the thread helix receiving groove is designed with an inclined forward flank to allow radial expansion (as in US 2018 0283 435 A1), then the thread helix can expand in widened boreholes, but the installation process becomes more complex and less productive
Solution Approach 1:
The invention changes the geometric parameters of the thread helix receiving groove by introducing a relaxation cavity with specific dimensional relationships (e.g., the cavity's radial depth and axial length are designed to accommodate the thread helix's radial contraction). This parameter change enables simple linear driving-in installation while maintaining the capability for the thread helix to adapt to borehole conditions through radial contraction and elastic recovery
3Adaptability or versatility
If the screw is designed with a separate thread helix that can radially contract, then the screw can be hammered into undersized boreholes, but additional space must be provided in the thread helix receiving groove
Solution Approach 1:
The invention applies the nesting principle by incorporating a relaxation cavity within the thread helix receiving groove. The cavity is nested within the groove structure, allowing the thread helix to move radially inward and occupy the cavity space during contraction. This nested design provides the necessary space for radial contraction without significantly increasing the overall device complexity, as the cavity is integrated into the existing groove geometry
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
This design enables efficient and productive installation by allowing the screw to be hammered into undersized boreholes, providing reliable anchoring and maintaining engagement with the borehole wall, even in seismic conditions, through the radial contraction of the thread helix.
Implementation Method 1
the crest of the thread helix of the previously unconstricted screw is displaceable towards the shank by linearly, in particular strictly-linearly, driving the shank, together with the thread helix, into an undersized borehole
Implementation Method 2
by rotation the shank, which will, due to the helical design of the thread helix, bias the thread helix radially outwards, i.e. activate the thread helix
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a screw comprising a shank, wherein a thread helix receiving groove that winds around the shank is provided in the shank, and wherein the shank has a screw tip, and further comprising a thread helix having a base and a crest, wherein the thread helix and the shank are separate parts, wherein the base of the thread helix is arranged in the thread helix receiving groove, and wherein the crest of the thread helix projects radially from the shank. According to the invention, the crest of the thread helix of the unconstricted screw is displaceable towards the shank by linearly driving the shank, together with the thread helix, into an undersized borehole in a concrete or masonry substrate. The invention also relates to a method for installing such a screw.