Blind Rivet Torsional Stiffness via Knurl Interlocking
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Solution Overview
Problem
Existing blind rivet nuts experience unacceptable twisting and torsional deformation under high mechanical loads, particularly when used with high-strength bolts, leading to excessive surface pressure and strength constraints.
Innovation Solution
Incorporating longitudinal knurls on both the elastic body and metallic sleeve to prevent rotation, along with strengthening features like flattened surfaces and radially extending ribs, which engage during the folding operation to enhance torsional stiffness and prevent deformation, and using a thermoplastic elastomeric material for the elastic body and brass or other metals for the sleeve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the blind rivet nut is designed for high strength bolts (strength class > 8.8), then the joint strength is improved, but unacceptable twisting and torsional deformation of the elastic external body member occurs
Solution Approach 1:
The patent applies local quality by providing longitudinal knurls at specific locations (in the folding zone and at the end of the blind rivet nut) rather than uniformly throughout. These localized knurl features create targeted friction zones that prevent rotation exactly where needed during the folding operation, while maintaining overall elasticity of the body member for vibration damping functionality.
Solution Approach 2:
The longitudinal knurls are pre-formed on the elastic body member before assembly. During the folding operation, these pre-formed knurls engage with corresponding knurls on the threaded sleeve, creating preliminary friction-based anti-rotation engagement that prevents twisting before it can propagate through the elastic body member.
2Device complexity
If the axial force for folding is transferred directly from the mounting bolt via the metallic threaded sleeve to the mounting member, then the folding operation is simplified, but excessive surface pressure occurs between the end face of the threaded sleeve and the bottom side of the mounting member
Solution Approach 1:
The patent applies local quality by providing an annular groove with ribs and depressions at the specific location where the fold engages during folding. This localized structural feature distributes the folding forces across multiple contact points (the ribs and depressions), preventing excessive surface pressure concentration at any single point while maintaining efficient force transfer for the folding operation.
3Object-affected harmful factors
If the elastic body member is made highly resilient for vibration damping, then the vibration damping performance is improved, but the torsional stiffness is reduced leading to unacceptable twisting under high mechanical loads
Solution Approach 1:
The patent resolves this contradiction by applying local quality through strategically placed longitudinal knurls that create localized friction-based mechanical interlocking. These knurls provide torsional stiffness exactly where rotation must be prevented (in the folding zone and at the end), while the remaining portions of the elastic body member maintain their resilience for vibration damping. The knurls act as localized stiffening elements without compromising the overall elasticity needed for vibration absorption.
Solution Approach 2:
The patent effectively creates a composite structure by combining the elastic body member with the metallic threaded sleeve through friction-based engagement of corresponding longitudinal knurls. This composite arrangement allows the elastic body to provide vibration damping while the metallic sleeve provides torsional stiffness during the folding operation, with the knurl engagement serving as the coupling mechanism between the two materially different components.
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 solution effectively prevents twisting and torsional deformation, allowing the blind rivet nut to handle high-strength bolts without unacceptable surface pressure, enhancing mechanical qualities under tensile and shear loads while providing vibration damping and noise reduction.
Implementation Method 1
the longitudinal knurls of the elastic body and the metallic sleeve which are in engagement with each other in the folding zone prior to the folding operation
Implementation Method 2
the longitudinal knurls of the sleeve cut or dig corresponding longitudinal knurls into the material of the elastic body
Implementation Method 3
These strengthening means may be formed by flattened surfaces on the outside of the elastic body within the folding zone. These measures assist in providing torsional stiffness of the elastic body.
Implementation Method 4
the deformation preventing means may comprise radially extending ribs and depressions on a side wall of an annular groove of the elastic body, the fold being urged against these ribs and depressions during the folding operation
Implementation Method 5
The elastic body is made preferably of a thermoplastic elastomeric material on a polyester base... provide for vibration dampening compensation movements and noise reduction
Data Source
AI summary
A blind rivet for a threaded joint between a support member and a mounting member consists of a body of elastic material and a sleeve of metallic material. The body is formed as a sleeve-shaped shank adapted to be inserted into a mounting hole of the support member. The shank has a mounting flange and a folding zone adapted to be folded into a fold by a folding operation. The mounting flange and the folding zone are adapted to be supported against opposite sides of said support member. The sleeve of metallic material is disposed within the body. There are provided means for preventing twisting and torsional deformation of the body.