Septic Tank Flange Resisting Deformation Under Soil Pressure
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Solution Overview
Problem
Large plastic septic tanks tend to deform around access openings due to inward soil pressure and weight, leading to poor fitment of lids and potential leakage, which existing technologies struggle to address effectively, especially in blow molded and rotationally molded thermoplastic tanks where material properties are isotropic.
Innovation Solution
A separately formed and structurally attached flange with a higher flexural modulus than the tank body, made from thermoplastic material with aligned chopped fiberglass fibers, is used to resist deformation and provide a secure attachment point for lids and risers, enhancing the tank's structural integrity and sealing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the tank is made with standard thermoplastic material and uniform wall thickness, then the manufacturing cost and material usage are minimized, but the tank deforms around access openings under soil pressure and vehicle loads
Solution Approach 1:
The patent applies local quality by adding a reinforcement ring specifically at the access opening location where deformation occurs, rather than strengthening the entire tank structure. This localized reinforcement provides the necessary strength to resist soil pressure and vehicle loads at the critical area while maintaining uniform wall thickness and standard thermoplastic material elsewhere, thus avoiding increased overall structural complexity
Solution Approach 2:
The reinforcement ring is constructed as a composite structure with radial and circumferential ribs that work together to resist deformation. The radial ribs provide stiffness against inward soil pressure while the circumferential ribs maintain the circular shape of the opening, creating a composite reinforcement system that effectively addresses the deformation problem without requiring complete structural redesign
2Strength
If the tank walls are heavily corrugated to increase section modulus, then the tank's load-bearing capacity is improved, but the top surface around access openings becomes prone to twisting and distortion
Solution Approach 1:
The reinforcement ring is segmented into radial ribs and circumferential ribs that are distributed around the access opening. This segmentation allows each rib to specifically address different deformation modes - radial ribs counteract inward pressure while circumferential ribs prevent twisting - thereby maintaining the flatness of the top surface without compromising the load-bearing capacity provided by the corrugated walls
3Strength
If fiberglass tanks use preferential fiber orientation to counter distortion, then deformation resistance is improved, but thermoplastic tanks cannot achieve localized property variation
Solution Approach 1:
The reinforcement ring creates a composite structure within the homogeneous thermoplastic material. The radial and circumferential ribs form a composite pattern that provides localized deformation resistance at the access opening, compensating for the inability to vary material properties in thermoplastic tanks as is possible with fiberglass tanks
4Ease of operation
If access openings are made large for maintenance access, then ease of maintenance is improved, but the structural integrity around the opening is reduced
Solution Approach 1:
The reinforcement ring provides localized structural support precisely at the access opening where the large opening creates structural weakness. The radial and circumferential ribs concentrate the reinforcement where it is most needed, allowing large openings for easy maintenance access while maintaining structural integrity to resist soil pressure and prevent deformation
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 flange significantly reduces deformation and ensures proper fitment of lids and risers, improving the tank's resistance to soil pressure and water infiltration, thereby meeting regulatory requirements and maintaining the tank's shape and functionality.
Implementation Method 1
A separately formed and structurally attached flange with a higher flexural modulus than the tank body, made from thermoplastic material with aligned chopped fiberglass fibers, is used to resist deformation
Data Source
AI summary
A plastic septic tank has a body made by rotational molding or blow molding and at least one access opening in the top. A ring flange is structurally attached to the top of the body so the bore of the flange fits the access opening. A plastic ring flange has a flexural modulus which is greater than 100,000 psi and at least twice the flexural modulus of the plastic material of the tank body. An exemplary flange is made of a plastic material which includes 5-30 weight percent glass fibers, a significant portion of which are aligned with the plane of the flange upper surface.