Patent Application
20080075912
The invention relates to a shielding component, in particular a heat shield, in which an insulating layer is at least partially used.
Shielding components of this type are known in the most varied embodiments and are widely used especially in automotive engineering. Components designed as heat shields are intended to keep away the heat from engines and their components, such as turbochargers, catalytic converters, etc., which has been released by radiation and/or convection. Since the parts to be shielded which are under consideration constitute not only heat sources, but are also noise sources, in addition to heat insulation, favorable acoustic shielding behavior is also extremely important.
To meet these requirements, it has already been proposed in DE 41 37 706 A1, that an acoustically transmitting metallic carrier as a cover layer be provided as the sound-absorbing heat insulation for a shielding component, with an insulating material located on the carrier in the form of an insulating layer. The insulating material in the known solution is a solid, formed from quartz sand, with a grain diameter of approximately 0.8 to 2 mm. The quartz sand material can be easily placed in existing impressions of the carrier and can be enclosed by the metallic carrier; due to the use of the solid, the known solution, however, has a high weight, and to the extent the shielding part is designed as a multilayer design, there is increased production effort in addition to production costs.
Comparable solutions are also shown in DE 102 53 508 B3 which, as the insulating layer between sheet metal plates, which are designed as cover layers, uses highly dispersed silicic acid which is incompressible like quartz sand, and ensures high heat insulation, and in DE 42 11 409 A1 which as the heat insulating and noise-damping layer as the liner for internal combustion engines of motor vehicle uses glass fiber inserts which among other things are provided with mineral fillers, such as quartz sand or basalt wool.
On the basis of this prior art, the object of the invention is to improve the known solutions while retaining their advantages, specifically to ensure good acoustic and heat absorption, such that at low production costs a lightweight design for the shielding component can be accomplished. This object is achieved by a shielding component with the features of claim 1 in its entirety.
In that, according to the characterizing part of claim 1, the insulating layer is formed from a cellular structure, it is designed with the formation of a combination of interacting individual cells, the individual “cell walls” stiffening the overall structure, that is to say, the shielding component as a whole, and the spaces between the “cell walls” made as cavities being used to reduce the weight of the shielding component so that it can be made as a lightweight component. The cellular structure moreover has clearly improved acoustic and vibration damping compared to a solid insulating layer, for example built from dense materials, fiber composite materials or solid mineral beds, such as quartz sand. The internal cellular structure of the shielding component reduces the density with a simultaneous increase of the tensile and compressive strength values. The cellular structure of the shielding component also allows increased absorption of deformation energy; this in turn benefits deformation behavior in operation of the shielding component.
The respective cellular structure used as an inherently stable layer as a rule can form the shielding component; in one preferred configuration it is, however, provided that the respective insulating layer extends at least partially along at least one cover layer in order in this way to protect the cellular structure, which may be prone to abrasion, against mechanical damage. It has furthermore proven especially advantageous to form the cellular structure from an open-cell foam, a hollow sphere structure, a honeycomb structure or a screen printed structure. With these cellular structures, insulating layers of geometrically complex shape can be produced so that almost no limits are imposed on the mechanical configuration of the shielding components; this enters into consideration when the shielding material made as a heat shield directly at the site of heat formation must follow complex three-dimensional outside geometries, as are dictated for example by the configuration of an engine block, turbocharger or catalytic converter.
For the purposes of an optimized lightweight design with still high strength values, it has proven favorable to use a metal foam for the insulating layer. For purposes of a sandwich construction, it has in turn proven especially favorable to use for the foam an open-pore structure which ensures a large amount of elasticity with simultaneous stability especially when cyclic bending stresses or the like occur.
Other advantageous configurations of the shielding component according to the invention are the subject matter of the other dependent claims.
The shielding component according to the invention will be detailed below using different embodiments as shown in the drawings. The figures are schematic and are not drawn to scale.
The embodiment of the shielding component shown in
The flanged fastening situation in question is shown in
Essentially this hollow sphere structure could also be obtained by way of a ceramic material, the use of metals for the hollow sphere structure, however, having the advantage that the structure is compressible up to a certain degree. Additionally, the combination of hollow spheres which has been built up in this way is mechanically and thermally stable and resists abrasive influences. Thus it is also possible, by omitting the sheet metal cover layer 10, to make and use the illustrated structure 14 of hollow sphere as an insulating layer directly for a heat shield by means of forming. Precisely by means of the combination of the sheet metal cover layer 10 with the insulating layer 14, the insulating layer 14 is thus protected against abrasive influences, and in particular with a thin execution of the insulating layer 14 the cover layer 10 contributes to stabilization of the entire heat shield and facilitates installation of the heat shield in the interior of the vehicle, such as the engine compartment or the like.
In addition to the indicated structure of hollow spheres or the like, which can be built up from a hollow honeycomb structure or the like, the insulating layer 14 can be a metal foam, in particular in the form of an open-cell foam. In addition to the metal foam, a composite foam using thermally stable plastic materials can also be used for the insulating layer 14, as can ceramic foams which must be sintered for their production, and in contrast to the metal foams which are preferably used, do not exhibit elastically resilient stretching or compressive behavior, this being inherently desirable so that the shielding component or heat shield under thermal stress can reversibly expand under the influence of heat as required.
To obtain a metal foam, for example a process for producing porous metal bodies can be used, as is disclosed by DE 40 18 360 C1. In the known process, first a mixture of a metal powder and a gas-releasing propellant powder is produced. Then this mixture is formed hot compacted into a semifinished product at a temperature at which joining of the metal powder particles takes place primarily by diffusion and at a pressure which is selected to be of such a magnitude as to counteract decomposition of the propellant. The hot compacting is done until the metal particles are tightly joined among one another and in this respect constitute a gas-tight closing-off for the gas particles of the propellant. The semifinished article produced in this way is then heated to a temperature above the decomposition temperature of the propellant and then the body foamed in this way is cooled. The propellants can be metal hydrides, such as titanium hydride or carbonates, but also easily vaporizing substances in the form of pulverized organic substances. Metals here are in particular pure aluminum powder, but also copper powder and the like. Details on production can be found in the indicated patent.
Another process for producing steel foam, in particular in the form of aluminum and nickel foams, is the so-called SlipReactionFoamSinter (SRSS) process, the foaming taking place by a chemical reaction at room temperature. In the process, first the metal powder and the dispersant are mixed, with the formation of a laminar silicate, depending on the alloy content of the metal powder a propellant in the form of a very finely reactive metal powder, for example in the form of carbonyl iron, being added. The concentrated phosphoric acid is added to the solvent, water and/or alcohol, the acid dissociating in the water. A type of slip-like suspension is thus formed in which two reactions proceed in parallel, specifically on the one hand hydrogen gas bubbles forming in the chemical reaction and between the reactive metal particles and the acid and causing direct foaming of the slip, and furthermore a metal phosphate forms which assumes the task of the binder and stabilizes the foam structure. The green compact obtained in this way is then sintered with reduction of the atmosphere to form an open-pore metal foam (see in this context also DE 197 16 514 C1).
Furthermore, the open-cell foam can in turn be obtained by a coating process of polymer foams using metal powder, such as iron powder. This production process then corresponds in turn to a process for producing the respective hollow sphere structure using the subsequent unbending and sintering. In this connection, the materials preferably used are steel or alloys based on nickel, cobalt, and titanium. Likewise intermetallic compounds can be used. The open-cell or open-pore foams produced in this way in addition to high permeability have a large specific surface and accordingly a high degree of heat dissipation capacity. This open pore foam can be made to have large pores or small ones. The open porosity leads to a low rough weight for the foam material and accordingly to a low weight for the entire shielding component. As a result of the pore structure a corresponding metal foam is also elastically resilient and thus can analogously balance thermally induced changes in length or volume. Moreover, in this way a very compressively stiff, loadable, integral article for the respectively desired shielding component results.
An individual cell for a pertinent open-pore foam is shown with its pores 20 and the cell walls 22 which border the pores in
Another possibility for obtaining the desired cellular structure as a hollow structure in the form of a honeycomb structure as shown in
The honeycomb structure as shown in
The cavities (pores) formed by the cellular structure of the insulating layers 14 can moreover be provided with other filler materials, such as fiber materials, solids and the like. In this way, further adaptations to thermal circumstances can be created and/or the indicated structure can be further stiffened.
Using cellular insulating layers for shielding components such as heat shields, in addition to very good thermal insulation and outstanding noise absorption, due to the high energy absorption capacity, good mechanical damping relative to vibrations and impacts is achieved so that a heat shield which has been designed in this way can be considered very durable for later use.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 039 756.8 | Aug 2006 | DE | national |
