Plastic Manhole Cover Trough with Molded Webs and Reinforcement Grid
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Solution Overview
Problem
Conventional manhole covers face challenges in manufacturing complexity, material usage, and durability, with steel troughs requiring extensive work and material for attachment of rotary locks and lifting devices, and concrete troughs experiencing abrasion and fragmentation over time.
Innovation Solution
A manhole cover with a trough-shaped lower part made of glass fiber reinforced plastic, featuring molded webs for a positive connection with concrete or mortar, and reinforcement grids to absorb loads and prevent cracking, manufactured using injection molding for simplified production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a steel trough-shaped lower part is used, then strength and load-bearing capacity are improved, but manufacturing complexity and labor expenditure increase due to the need to secure receiving chambers and lifting devices before pouring concrete
Solution Approach 1:
The receiving chambers for rotary locks and lifting devices are integrated directly into the trough-shaped lower part as molded-in features, eliminating the need for separate components and their complex assembly. The trough is designed with recesses and attachment points built-in, combining multiple functions into a single molded component.
Solution Approach 2:
The receiving chambers and lifting device mounting points are pre-formed during the injection molding process of the trough, rather than requiring subsequent assembly operations. This preliminary formation of attachment features simplifies the overall manufacturing process and reduces labor requirements.
2Quantity of substance
If the trough-shaped lower part is made solely of concrete, then material costs are reduced, but durability deteriorates due to abrasion and fragmentation of unframed edges
Solution Approach 1:
The manhole cover combines two materials with complementary properties: a plastic trough providing structural integrity and abrasion resistance, and concrete filling providing compressive strength and cost-effectiveness. This composite structure leverages the advantages of both materials while mitigating their individual weaknesses.
Solution Approach 2:
Different materials are used in different regions of the manhole cover where needed: plastic for the trough walls that require abrasion resistance, and concrete for the filling that requires compressive strength. The receiving chambers and lifting devices are also locally positioned at specific areas requiring enhanced durability.
3Ease of manufacture
If the trough is made of plastic with concrete filling, then ease of manufacture is improved through injection molding, but water ingress risk increases due to potential gaps between concrete and trough
Solution Approach 1:
The corners of the trough are designed with rounded transitions rather than sharp angles, creating a continuous curved surface that prevents gap formation between the concrete filling and plastic trough. This geometric optimization ensures complete concrete coverage and eliminates water ingress pathways.
Solution Approach 2:
The molded webs act as intermediary structural elements that extend into the concrete filling, creating a mechanical interlock that prevents gap formation. These webs serve as a transition zone that ensures intimate contact between the plastic trough and concrete, eliminating spaces where water could penetrate.
4Stability of the object's composition
If reinforcement grids are added to the trough, then cracking resistance is improved, but device complexity increases
Solution Approach 1:
The lower reinforcement grid is integrated into the trough structure through molded-in attachment points, combining the reinforcement system with the trough as a unified component. This integration eliminates separate assembly steps while providing effective crack prevention.
Data Source
Figure 1
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AI summary
The application relates to a manhole cover with a trough-shaped lower part (5) having a base (12) and a circumferential rim (13), wherein the trough-shaped lower part (5) is made of plastic and is provided on the base (12) and on the rim (13) with numerous molded, intersecting ribs (14,15), wherein at least one lower reinforcing grid (23) is fixed in the trough-shaped lower part (5), and wherein the trough-shaped lower part (5) is filled with concrete or mortar.