This application claims the priority of German Patent Application No. 197 27 907.4, filed Jul. 1, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for filling cavities in workpieces or semi-finished products as well as a structural component part, especially a workpiece or semi-finished product, for mounting on or in a motor vehicle.
For purposes of sound absorption and/or improvement of the stability of motor vehicle sheet metal structures that are designed to have hollow sections, it is known to fill such cavities with foam material bodies.
A method for filling hollow bodies is known from German Patent document DE-OS 38 26 012. There, a body consisting of an open-celled foam is introduced into the cavity of the hollow body. The body is covered completely by a skin that is impermeable to gas. This skin possesses at least one opening to which a vacuum for compressing the foam body is applied when the foam body is introduced. Following its introduction into the cavity, the contracted foam body is allowed to expand by disconnecting the vacuum, so that it then fills the cavity.
Another method for filling cavities is known from German Patent document DE 40 28 895 C1 in which a foam body made of elastic and compressible plastic foam, larger than the cross section of the cavity to be filled, is mechanically compressed by a sheath made of plastic and having smaller dimensions. The compressed foam body and sheath are introduced into the cavity in the body. There, the compressed foam body is initially secured mechanically in its later position inside the cavity to be filled.
The plastic sheath that encloses the foam body is resistant only up to a certain limiting temperature, so that by heating the body cavity together with the foam body at least up to the melting point of the sheath, the compression of the foam body is eliminated so that the foam body is applied internally against the body cavity under pretension.
A support with an external metal hollow body and a core made of light material is known from German Patent document DE 42 27 393 A1, with the core having an electrically conducting layer and, beneath this layer, a jacket with a material that can be foamed by applying heat. The application of heat, which is required in any event for welding the parts of a multipartite hollow body and/or for dip painting in hot paint, is utilized for the foaming process.
A double tube with a rigid outer tube is known from German Patent document DE 40 38 979 A1, with the inner tube forming a tubular body that is deformed plastically in place and is expanded radially. The body presses an insulating jacket placed around the inner tube against the inner jacket surface of the outer tube in a sealing fashion.
Sandwich semi-finished products made of a metal/plastic composite are also known in which flat or even shaped sheets are held at a distance from one another and the space between them is filled with plastic foam. The disadvantage of such composite structures is that the plastic foam poses certain problems in recycling the body and/or the semi-finished products after the lifetime of the product has been exceeded. Material separation into metal and plastic for all practical purposes is no more possible than joint trash recycling.
It is also known that carbon foam, either by itself or placed in cavities, can be produced from a plastic foam by carbonization. This method of filling hollow chambers with foam is very expensive, however. In addition, this type of carbon foam can be produced only at high carbonization temperatures and not in painted objects. In addition, these carbon foams are not ductile.
Hence, the invention has as its purpose the improvement of a method for filling cavities in, workpieces or semi-finished products in such fashion that the cavities can be filled with foam in a simple manner. In addition, the goal of the invention includes providing a structural component part, especially a workpiece or semi-finished product, for mounting on or in a motor vehicle, whose cavities can be filled with foam in a simpler manner.
To achieve this goal, the present invention provides a method for filling hollow chambers in workpieces or semi-finished products wherein thermally foamable powdered carbon is introduced in a fixed location in the cavity of the workpiece or semi-finished product to be filled, and the powdered carbon is heated together with the workpiece or semi-finished product such that the powdered carbon swells and fills the cavity as a carbon foam, with the particles of the powdered carbon being smaller in the delivered state than after foaming. With the fixed application of powdered carbon according to the invention, the fixation of the powder in the cavity is guaranteed for foaming carbon foam, so that a foaming process is made possible without an additional mold and the intended filling of cavities with foam is achieved.
In an embodiment of the invention, the cavity to be filled with foam itself serves as the mold for the carbon foam, which is suitable especially in double-walled workpieces such as pipes and sections, i.e. in hollow chambers with sufficiently small cross sections.
In another embodiment of the invention, the powdered carbon is provided in hermetically sealed aluminum foil pouches for fixed introduction into the cavity, and the pouches filled in this manner are secured at fixed locations at suitable locations in the hollow chamber to be filled. Advantageously, the foil pouch is a folded pouch whose folds enable it to unfold and expand along with the powdered carbon when it foams, enabling adaptation of the filling material to the contour to be filled with foam. The use of plastic pouches like those known from the prior art is not possible in conjunction with powdered carbon because the high foaming temperatures of about 130.degree. C. would cause the plastic to melt prematurely and thus the fixed position of the powdered carbon would not be ensured.
In another embodiment of the invention, heating is provided by a work process that is necessary for further machining of the workpiece or semi-finished product. As a result of this measure according to the invention, the energy that would have to be expended in any event for a subsequent heating process is also utilized for the foaming process. This is especially advantageous in the embodiment in which, for filling cavities in the body, the powdered carbon is introduced into the cavities in the body-in-white phase of the body, undergoes dip painting with the body, and the foaming takes place at the same time that the dip paint is stoved.
In another embodiment of the invention, heating is performed by the normal entry into service of the workpiece. Here again, heating the workpiece that contains the hollow chamber to be filled, which would have to be done anyway, is utilized to trigger the foaming process upon the normal entry into service of the workpiece involved in this connection. This process is especially advantageous in the case of workpieces that are regularly heated to high temperatures during proper operation, for example in the embodiment of the method according to the invention in which, to fill double-walled hollow chambers of a double-walled exhaust pipe, the powdered carbon is added to the double-walled hollow chambers to be filled prior to final assembly, and the foaming takes place only when the exhaust pipe reaches its operating temperature.
As another solution to the problem that forms the basis of the invention, a structural component part is proposed according to the invention. The structural component part according to the invention, which is in particular a workpiece or semi-finished product, is provided for mounting on or in a motor vehicle and has at least one closed-off hollow chamber in which powdered carbon that can be foamed by heat is enclosed in a fixed location. The powdered carbon is heated together with the workpiece to swell the powdered carbon to form a carbon foam that fills the cavity. The particles of the powdered carbon are smaller in the delivered state than after foaming.
In an embodiment of the invention, the heat to foam the powdered carbon is provided by the entry of the structural component part into normal use.
In another embodiment of the invention, the structural component part is a double-walled, especially an exhaust-carrying pipe, with powdered carbon added directly to the double-walled hollow chamber. The foaming takes place only when the operating temperature of the pipe is reached for the first time.
In another embodiment of the invention the structural component part is a profile member (for example a side member or an A-, B-, or C-pillar for a motor vehicle body) with aluminum foil pouches containing powdered carbon that are hermetically sealed and are located at fixed positions in the (at least one) cavity.
In another preferred embodiment of the invention, the aluminum foil pouches containing the powdered carbon are added prior to or during the body-in-white phase of the body to the (at least one) cavity in order to undergo dip painting with the body, so that foaming takes place at the same time as the stoving (heating) of the dip paint.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
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