Composite Wall Septic Tank Resists Deformation
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Solution Overview
Problem
Thermoplastic septic tanks face issues with deformation under mechanical forces, buoyancy, and thermal contraction, leading to instability and higher costs compared to concrete tanks, while also being susceptible to impact damage and lacking in strength and stiffness.
Innovation Solution
A thermoplastic septic tank with a composite wall structure comprising an inner solid plastic layer, a middle closed-cell foam plastic layer for heat retention and liquid resistance, and an outer solid plastic layer for mechanical resistance, integrated through rotational molding to enhance structural integrity and resistance to deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermoplastic septic tanks are made from fully dense polymer with thicknesses in the range of one quarter to three eights of an inch, then the tanks provide adequate strength and stiffness, but the tanks are susceptible to local impact damage and deformation under mechanical forces
Solution Approach 1:
The patent applies composite materials by constructing the tank wall from multiple layers of different materials: an inner layer of dense thermoplastic polymer, a middle layer of foam plastic, and an outer layer of dense thermoplastic polymer. This composite structure provides both strength and impact resistance, as the foam layer absorbs impact energy while the dense layers provide structural integrity and stiffness.
2Stability of the object's composition
If thermoplastic septic tanks are made from fully dense polymer, then the tanks have adequate structural integrity, but the tanks exhibit undue deformation during installation and use due to buoyancy and soil pressure
Solution Approach 1:
The composite wall structure with the foam plastic middle layer provides buoyancy compensation and reduces deformation. The foam layer's lower density offsets the tank's overall buoyancy, while the multi-layer construction distributes soil pressure forces, preventing undue deformation during installation and use.
Solution Approach 2:
The patent applies local quality by creating different material properties at different locations within the wall structure. The inner and outer layers use dense thermoplastic polymer for structural integrity, while the middle foam layer provides localized buoyancy and pressure distribution, optimizing performance for specific functional requirements.
3Strength
If thermoplastic septic tanks are made from fully dense polymer, then the tanks have sufficient strength, but the tanks lack thermal insulation and lose heat from warmer wastewater to the soil
Solution Approach 1:
The composite wall structure provides thermal insulation by incorporating a foam plastic middle layer between the inner and outer dense polymer layers. The foam layer acts as a thermal barrier, reducing heat transfer from the warmer wastewater to the cooler soil, thereby minimizing energy loss while maintaining structural strength through the dense outer layers.
4Weight of moving object
If thermoplastic septic tanks are used to replace concrete tanks, then the tanks offer light weight and ease of portability, but the tanks are more costly and have lower strength under load
Solution Approach 1:
The composite wall structure achieves both light weight and high strength under load by combining materials with complementary properties. The foam plastic middle layer provides lightweight buoyancy compensation, while the dense thermoplastic polymer inner and outer layers provide structural strength and load-bearing capacity, creating a wall that is both lightweight and strong.
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 composite wall structure significantly improves the tank's resistance to mechanical forces, thermal stability, and impact resistance, while maintaining cost competitiveness with concrete tanks and ensuring compliance with vacuum tests, thereby reducing deformation and enhancing microbiological processes.
Implementation Method 1
a middle layer of closed cell foam plastic for both resisting liquid flow which penetrates the inner or outer layer
Implementation Method 2
a middle layer of closed cell foam plastic for both resisting liquid flow which penetrates the inner or outer layer and for heat retention which encourages biological processes
Implementation Method 3
a composite wall which comprises an inner layer of solid plastic for containing liquid; an outer layer made of solid plastic, for resisting external mechanical forces, and a middle layer of closed cell foam plastic
Implementation Method 4
The three layers are integrally attached at the time of formation of the tank by rotational molding
Data Source
AI summary
A septic tank or storage tank has a corrugated thermoplastic wall which has a composite layered structure. A tank wall comprises an inner layer of solid plastic for containing liquid; an outer layer made of solid plastic, for resisting external mechanical forces, and a middle layer of closed cell foam plastic for both resisting liquid flow which penetrates the inner or outer layer and for heat retention which encourages biological processes. In an embodiment, the middle layer has less than about 55 percent of the density of the inner and outer layers, and the inner layer is substantially thinner than the outer layer. The three layers are integrally attached at the time of formation of the tank by rotational molding. The tank has good resistance to mechanical forces and provides insulation.