Expandable Joint for Thermal Expansion in Concrete Mixing Barrels
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Solution Overview
Problem
Existing joints face challenges in accommodating different coefficients of thermal expansion between materials, leading to separation or weakened bonds, and require an expandable joint with a low compression set to effectively absorb shock and fatigue loading.
Innovation Solution
An expandable joint utilizing a micro-cellular polyurethane elastomer binder with nucleation agents and a low compression set, injected between interfaces to maintain contact and exert positive pressure, accommodating thermal expansion while minimizing contraction and void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid binder is used to join structures with different thermal expansion coefficients, then joint strength is improved, but stress concentration and separation occur due to differential expansion
Solution Approach 1:
The patent changes the physical and mechanical parameters of the binder material by using a polymeric composition that remains flexible at service temperatures. The binder is formulated with specific glass transition temperatures and elastic moduli that allow it to accommodate differential thermal expansion while maintaining adequate bond strength, thus resolving the contradiction between joint strength and reliability under thermal cycling.
Solution Approach 2:
The patent employs a composite polymeric binder system comprising multiple polymer components with complementary properties. This composite material combines the adhesion characteristics of one polymer with the flexibility and thermal tolerance of another, creating a binder that simultaneously provides strong bonding and accommodates differential thermal expansion between dissimilar substrates.
2Reliability
If a flexible polymer binder is used to accommodate thermal expansion, then stress at interfaces is reduced, but compression set may increase reducing shock absorption capability
Solution Approach 1:
The patent precisely controls the compression set parameter of the polymeric binder by selecting polymers with specific molecular weight, crosslink density, and glass transition temperature. These parameter adjustments ensure the binder maintains compression set below 3.5% at 25% deflection, allowing it to remain sufficiently elastic for shock absorption while providing adequate dimensional stability.
Solution Approach 2:
The patent creates different local properties within the binder system by incorporating regions of varying crosslink density and polymer composition. The binder exhibits locally optimized characteristics: higher flexibility at the substrate interfaces to accommodate thermal expansion, and sufficient bulk rigidity to maintain shock absorption capability, thus resolving the contradiction between interface reliability and overall strength.
3Strength
If the binder is made highly compressible to absorb shock, then shock absorption is improved, but the binder may separate from interfaces under impact and fatigue loading
Solution Approach 1:
The patent optimizes the adhesion parameters of the polymeric binder by selecting polymers with specific surface energy, molecular weight, and functional group composition. These parameter changes ensure the binder maintains strong interfacial adhesion even when highly compressible, preventing separation under impact and fatigue loading while preserving shock absorption capability.
Solution Approach 2:
The patent incorporates adhesion promoters and surface treatment steps before applying the binder to ensure strong initial bonding to the substrates. This preliminary action creates a robust interface that can withstand subsequent compressive and impact loads, allowing the binder to remain firmly attached while maintaining the compressibility needed for shock absorption.
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 maintains joint integrity by accommodating thermal expansion, reducing stress, and enhancing shock absorption, with a compression set less than 3.5% at 25% deflection, thereby improving the joint's durability and resistance to fatigue.
Implementation Method 1
materials may have different coefficients of thermal expansion. This may result in one structure expanding by a first degree and another structure expanding by a second greater degree
Implementation Method 2
the compression set of the expandable polymer is preferentially less than about 3.5% at 25% deflection, in order to enhance the ability of the material to act as a shock absorber to sustain and endure impact and fatigue loading
Data Source
AI summary
A concrete mixing includes a barrel having an interior surface and an exterior surface. A blade extends from the interior surface for mixing concrete and a ring is positioned about the exterior surface of the barrel for rotation of the barrel. An expandable joint is provided under compression between the ring and the exterior surface of the barrel to accommodate different thermal coefficients of expansion between the barrel and the ring.