Dowel with Radially Movable Spreading Elements and Anti-Twist Ribs
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Solution Overview
Problem
Existing dowels for fastening frame elements to masonry often twist during screwing, especially with longer lengths, due to inadequate anti-rotation mechanisms and interference from spreading elements during insertion.
Innovation Solution
A dowel design featuring a cylindrical sleeve with radially movable spreading elements that are initially flush with the sleeve interior, which fold inwards during insertion, and an anti-twist device such as narrow ribs on the sleeve and spreading elements to minimize rotation, along with a tapered tip and impact protection for easy installation and reduced counter-torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If spreading elements are arranged radially on the dowel sleeve, then anchoring strength is improved, but insertion is hindered due to interference with the hole wall
Solution Approach 1:
The spreading elements are designed to be radially movable rather than fixed, allowing them to dynamically adjust their position. During insertion, they remain retracted to minimize interference, and during anchoring, they spread radially to engage the hole wall, thus resolving the contradiction between insertion ease and anchoring strength
Solution Approach 2:
The dowel sleeve is segmented into multiple spreading elements that can move independently. This segmentation allows each element to be optimized for its specific function - remaining compact during insertion and expanding for anchoring, thereby achieving both easy insertion and strong anchoring
2Length of moving object
If the dowel sleeve is made longer to increase fastening capability, then fastening capability is improved, but tendency to twist during screwing increases
Solution Approach 1:
Anti-twist ribs are pre-formed on the dowel sleeve surface before insertion. These ribs engage with the hole wall during insertion and continue to provide anti-rotation support during screwing, preventing the dowel from twisting even when made longer for increased fastening capability
Solution Approach 2:
The anti-twist ribs create an asymmetric surface geometry on the otherwise cylindrical dowel sleeve. This asymmetry provides mechanical engagement with the hole wall that resists rotational forces, allowing the dowel to be made longer without increasing its tendency to twist during screwing
3Strength
If spreading elements are made to protrude radially for better anchoring, then anchoring strength is improved, but insertion interference increases
Solution Approach 1:
The spreading elements transition from a retracted state during insertion to an extended state during anchoring. This dynamic behavior allows them to minimize insertion interference by staying flush with the dowel surface during insertion, then provide enhanced anchoring strength when radially extended during the spreading phase
Data Source
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AI summary
A dowel contains a sleeve with a tapered tip. The sleeve is not expandable. Its wall contains numerous radially movable expansion elements, which, in the dowel's normal state (i.e., after its manufacture), project outwards so that their inner surfaces, facing the interior of the sleeve, are flush with the sleeve wall. When the dowel is inserted through a hole in a frame into a drilled hole, the expansion elements fold inwards at the points where they encounter resistance.