Acoustic Screen Micro-Perforations Gas Evacuation
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Solution Overview
Problem
The existing method for producing acoustic protection screens for motor vehicle engines often results in surface defects such as craters on the outer face of the foam support due to poor gas evacuation during foam formation, which affects the appearance and functionality of the screen.
Innovation Solution
Incorporating micro-perforations into the reflective metal sheet allows for effective evacuation of gases during foam formation, ensuring a defect-free surface and enhanced sound absorption by allowing sound waves to pass through and be absorbed by the insulation layer and support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a reflective metallic sheet is used for thermal protection, then thermal protection is improved, but gas evacuation during foam formation is hindered causing surface defects
Solution Approach 1:
The metallic sheet is provided with micro-perforations creating a porous structure that allows gas to pass through during foam formation while maintaining the sheet's thermal reflection function. The micro-perforations enable gas evacuation without compromising the thermal protection capability of the metallic sheet.
2Temperature
If the metal sheet blocks gas evacuation, then thermal protection is maintained, but craters and surface defects occur on the foam support
Solution Approach 1:
The metallic sheet has different properties in different locations: the micro-perforations are distributed across the sheet to localize gas evacuation paths, while the bulk material maintains thermal reflection. This local differentiation allows gas to escape through specific points without compromising overall thermal protection.
3Manufacturing precision
If micro-perforations are added to the metal sheet, then gas evacuation is improved eliminating surface defects, but sound absorption may be reduced
Solution Approach 1:
The micro-perforations create a porous structure that facilitates gas evacuation during manufacturing. The porous nature also allows sound waves to pass through the metallic sheet and be absorbed by the foam support, maintaining or even enhancing sound absorption capabilities.
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 method produces a screen with a satisfactory appearance and improved sound absorption capabilities, as the micro-perforations facilitate gas evacuation and enable effective noise absorption by the foam support.
Implementation Method 1
the gases from the foam formation reaction are evacuated through the micro-perforations of the metal sheet
Implementation Method 2
inject into said second mold a precursor mixture of air porous polyurethane foam, after expansion of the foam
Implementation Method 3
provide a reflective metallic sheet for thermal protection
Implementation Method 4
compress said mat by bonding said fibers together, to form a thermal insulation layer
Implementation Method 5
the foam forms a support overmolding said layer... the support to fully play its role in sound absorption
Data Source
Figure 1~2
AI summary
The invention relates to a method comprising the following steps: providing a reflective metal thermal protection sheet (4), said sheet being provided with a plurality of micro perforations (19); providing a batt of fibres containing a thermosetting resin; superposing said sheet and said batt in a first thermocompression mould in order to form a thermal insulation layer (5) and so as to combine said sheet with said layer using said resin so as to obtain a thermal protection shell comprising said layer and said sheet; placing said shell against the upper wall (10) of a second mould, said wall being provided with out-gassing vents (11), said sheet facing toward said wall; injecting into said second mould an air-porous polyurethane foam precursor mixture, the lower wall (12) of said second mould being free of any fluidtight coating; after the foam has expanded, demoulding the screen (1) obtained, in which screen the foam forms a support (2) overmoulding said layer.