WO2003009274A1

WO2003009274A1 - Multilayer metallic sheet having acoustic insulation properties

Info

Publication number: WO2003009274A1
Application number: PCT/IT2002/000451
Authority: WO
Inventors: Sandro Fortunati
Original assignee: Sandro Fortunati
Priority date: 2001-07-16
Filing date: 2002-07-09
Publication date: 2003-01-30
Also published as: EP1410378A1; ITRM20010422A0; ITRM20010422A1

Abstract

The present invention relates to a multilayer metallic sheet having acoustic insulation properties, comprising a first metallic layer, a second metallic layer and a third metallic layer interposed between said first and second layer, and wherein said third layer is thermally constrained in the relative motion with said first and second layer by means of local re-crystallisation.

Description

"MULTILAYER METALLIC SHEET HAVING ACOUSTIC INSULATION

PROPERTIES" DESCRIPTION The present invention relates to the sector of multilayer metallic sheets with acoustic insulation properties.

Acoustic pollution presents problems that involve numerous industries, such as: construction (roofs and walls) , white goods (clothes washers, dishwashers) , household goods (aspirating hoods, appliances) , industrial goods (road and railway barriers, engines and compressors) , and transportation (land, sea, air) . The automotive industry is particularly sensitive to acoustic pollution. In this industry, the structural vibrations of engine driven vehicles are generated by different sources such as: terrain irregularities, oscillations of the engine, transmission, exhaust system masses.

In particular the exhaust system, which has an elongated and irregular shape and is positioned underneath the vehicle frame, because of the vibrations transmitted by the engine, in turn acts as a transmitter of vibrations to the passenger compartment, irradiating vibrations and hence noise and thus causing considerable annoyance. Such vibrations, and hence noisiness, are particularly severe at low speeds, as are usual in city traffic, situation in which the structure of the exhaust system if highly sensitive to noise-generating stresses. Typically, under such conditions the exhaust system is subjected to vibrations with a resonance frequency that oscillates between 12 and 20 Hz.

To contrast noise propagation, numerous methodologies and technologies have been proposed, aimed simultaneously to meet technical and economic criteria and requirements . Among the proposed solutions, the technology that provides for the use of plastic products to be applied as paints over substrates, for instance made of metallic material, is most widely used. Taking into account the considerable interest given to acoustic pollution issues in the automotive industry as well, in this particular field remarkable efforts have been expended and numerous proposed solutions have been put forth.

The patent US 5.530.213 discloses an exhaust system made of metallic material coated with a material having lesser density than the metallic material and exhibiting an irregular surface . The Japanese patent JP03160109 discloses a metallic exhaust system obtained by coupling steel and aluminium with glass or carbon fibre material .

The patent US 3.337.939 discloses an exhaust system obtained by means of an inner layer of stainless steel and an outer layer of aluminium coated with carbon steel, the two layers being separated by a third carbonisable adhesive material, like epoxy resin, such as to reduce noise transmission. The patent 4.382.487 teaches an exhaust system with an, inner portion made of enamelled steel whereon are fastened structural elements for noise abatement purposes .

Exhaust systems have also been proposed with box-like elements, with walls made with individual metallic sheet, which however have been found unsuited adequately to respond to heavy noise abatement demands .

Additional attempts to provide solutions with box-like elements with walls made with double metallic sheet have led to increased thickness and to the realisation of exhaust systems whose thickness typically is in the order of over three millimetres. Thickness increases that have obtained poor results in terms of noise abatements and have entailed a drastic and undesired increase in the weight of the exhaust system. Weight increases that contrast with the objectives of the transport vehicle industry, typically aimed at reducing fuel consumption. Considerable drawbacks have also been observed in the exhaust systems that, to reduce the thickness of the walls of the box-like elements, provide for the use of non metallic intermediate coatings, such as carbon or glass fibres. Such systems have considerable usage limitations due to their relatively low maximum working temperature, typically in the order of 100°C. Lastly, in multi-layer metallic sheets that use plastic products, as a intermediate or as a coating layer, numerous problems have been noted in terms of low weldability and poor deformability, in addition to the limitations connected with working temperatures necessarily lower than 100°C. In spite of the numerous efforts made heretofore, the known solutions comprised in the prior art exhibit the numerous drawbacks recalled above, which make their use not wholly satisfactory.

Therefore, there is a highly felt need of having available a multilayer metallic sheet with high acoustic insulation properties, reduced weight, high resistance to chemical aggressions (able to withstand strongly acidic or strongly alkaline attacks, due to typical exhaust system condensations with pH values varying from 2 to 12) and high thermal resistance (able to withstand high temperatures, exceeding 600°C) .

The present invention allows to meet this requirement, offering also the advantage of providing a multilayer metallic sheet with high formability and weldability, and reduced manufacturing costs. The subject of the present invention is a multilayer metallic sheet with acoustic insulation properties, comprising a first metallic layer, a second metallic layer and a third metallic layer interposed between said first and second layer, and in which said third layer is thermally constrained in its relative motion with respect to said first and second layer by means of local re- crystallisation. This constraint, obtained thermally, is such as to prevent the relative motion of each metallic layer with respect to the other.

The first and second metallic layers are selected among: stainless steel, carbon steel, Titanium super-alloys, Nickel super-alloys, Aluminium super-alloys.

The third layer is selected among: aluminium and its alloys, copper and its alloys, nickels and its alloys, titanium and its alloys. The first and second layer have a wall that faces the third layer with a roughness exceeding 5 μm. Measurements for assessing roughness, as is well known, are performed by means of an appropriate profilometer and normally the value provided is the one obtained by calculating the mean of the Ra measurements. Ra is the mean of the absolute values of all distances of the real profile R from the centreline in the measuring length. The ratio between the surface area that is thermally constrained, by means of local re-crystallisation, and area that is free in the relative motion of the third metallic layer with respect to the first and second metallic layer, ranges between 1 and 5%, preferably between 2.5 and 3.5%.

The thermal constraint is obtained by means of non- through welding, for instance of the laser or electrical resistance type.

The ratio between the thickness of the first layer and the thickness of the third layer ranges between 1 and 3. The ratio between the thickness of the second layer and the thickness of the third layer ranges between 1 and 3. The welded multilayer metallic sheet is then subjected to such a heat treatment as to allow to achieve a value of hardness of between 120 and 200 HV.

The multilayer metallic sheet is subjected to a flattening or heat-flattening operation, such as to allow obtaining an elongation value of less than 5%.

It is understood that the invention relates to all those products that can be used to solve acoustic pollution problems. Because of the sheer amplitude of applications, no list of possible products is provided herein, but only a few examples such as roofs, walls, covers, washers, dishwashers, sinks, aspirators and aspirating hoods, air conditioners, mufflers, cyclones, conveyers, hoppers, road and railway barriers, and many more besides. Hereafter, a few embodiments of the multilayer sheet of the present invention are provided purely by way of non limiting examples. EXAMPLE 1

An acoustically insulating metallic sheet is obtained, destined to exhaust systems for motor vehicles that comprises a first outer layer made of austenitic stainless steel with a thickness of 0.5 mm, a second outer layer made of ferrous stainless steel with a thickness of 0.3 mm and a third layer interposed between the first two, made of nickel with a thickness of 0.1 mm. The intermediate layer of Nickel, particularly suitable for high temperatures, was thermally constrained to the other two layers by means of non-through welding of the ER (electrical resistance) type.

The metallic layers used, obtained from a cold-rolling line, after the welding operation were subjected to a heat treatment in order to obtain an average hardness value of 170 HV.

Lastly, a stretch flattening operation was conducted to obtain a planar material with an elongation of 2%. The product thereby obtained was tested in an anechoic chamber and the level of irradiated vibration was measured and found to correspond to 57.2 dB in the 0-800 Hz frequency range, which is lower than the 74.1 dB of a typical single-sheet exhaust system available on the market . Relative to said product, moreover, a 50% weight reduction was recorded. In particular, a known product with a weight of 0.51 kg was compared to a proposed product according to the present invention with a weight of 0 . 24 kg . EXAMPLE 2

An acoustically insulating metallic sheet is obtained, destined to exhaust systems for motor vehicles, comprising a first outer layer made of carbon steel with a thickness of 0.6 mm, a second outer layer made of ferrous stainless steel with a thickness of 0.2 mm and a third layer interposed between the first two, made of aluminium with a thickness of 0.1 mm. The intermediate aluminium layer was thermally constrained to the other two layers by means of non- through laser welding.

The metallic layers used, obtained from a cold annealing line, after the welding operation were subjected to a heat treatment to obtain an average hardness value of 150 HV.

Lastly, a flattening operation by means of hard rolling mill was conducted to obtain a planar material with elongation of 1%. The product thereby obtained was tested in an anechoic chamber and the level of irradiated vibration was measured and found to correspond to 52 dB in the 0-800 Hz frequency range, which is lower than the 75 dB of a typical single-sheet exhaust system available on the market .

Relative to said product, moreover, a 50% weight reduction was recorded. In particular, a known product with a weight of 0.6 kg was compared to a proposed product according to the present invention with a weight of 0.3 kg.

To the products and artefacts described above, a person versed in the art, to meet additional and conditional requirements, may apply numerous additional modifications and variations, without thereby departing from the scope of protection of the present invention, as defined by the accompanying claims .

Claims

1. Multilayer metallic sheet having acoustic insulation properties, comprising a first metallic layer, a second metallic layer and a third metallic layer interposed between said first and second layer, and wherein said third layer is thermally constrained in its relative motion with respect to said first and second layer by means of local re-crystallisation.

2. Multilayer metallic sheet having acoustic insulation properties as claimed in claim 1, wherein said first and second metallic layer are selected from the group comprising: stainless steels, carbon steels, titanium super-alloys, nickel super-alloys, aluminium super- alloys .

3. Multilayer metallic sheet having acoustic insulation properties as claimed in claim 1 o 2, wherein said third metallic layer is selected from the group comprising: aluminium and its alloys, copper and its alloys, nickel and its alloys, titanium and its alloys.

4. Multilayer metallic sheet having acoustic insulation properties as claimed in any of the claims from 1 a 3, wherein said first and second layer have a wall that faces said third layer with a roughness exceeding 5 μm.

5. Multilayer metallic sheet having acoustic insulation properties as claimed in any of the claims from 1 a 4, wherein the ratio between thermally constrained surface are and area free in its relative motion ranges between 1 and 5%, and is preferably between 2.5% and 3.5%.

6. Multilayer metallic sheet having acoustic insulation properties as claimed in any of the claims from 1 a 5, wherein said thermal constraint is obtained by means of non-through welding.

7. Multilayer metallic sheet having acoustic insulation properties as claimed in any of the claims from 1 to 6, wherein said welding is of the laser type or of the electrical resistance type.

8. Multilayer metallic sheet having acoustic insulation properties as claimed in any of the previous claims, wherein said first layer has a thickness in a ratio of between 1 and 3 with respect to the thickness of said third layer.

9. Multilayer metallic sheet having acoustic insulation properties as claimed in any of the previous claims, wherein said second layer has thickness in a ratio of between 1 and 3 with respect to the thickness of said third layer.

10. Multilayer metallic sheet having acoustic insulation properties as claimed in any of the previous claims, wherein said welded sheet is subjected to a heat treatment allowing to obtain a hardness value of between 120 and 200 HV.

11. Multilayer metallic sheet having acoustic insulation properties as claimed in any of the previous claims, wherein said sheet is subjected to a flattening or stretch flattening that allows to obtain an elongation value smaller than 5%.