Stock material or miscellaneous articles – Hollow or container type article
Reexamination Certificate
2000-02-04
2004-06-29
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
C264S257000, C264S258000, C264S511000, C264S571000, C425S143000
Reexamination Certificate
active
06756090
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to apparatus and a method for the molding of a load-bearing element made of reinforced thermoplastic, and to one such load-bearing element.
The present invention relates to the technical fields of thermoforming of so-called sandwich elements, and the blow-molding of hollow bodies made of reinforced thermoplastic. The present invention uses thermoplastic layers in a material charge as a plastic membrane which, upon internal pressurization or external vacuum generation, is non-permeable. With the aid of pneumatics and/or hydraulics, the plastic membrane provides a molding force, in the direction towards the internal surfaces of a molding tool, on reinforcement material which lies between the plastic membrane and the internal walls of the molding tool. By heating the thermoplastic matrix material, either before or during molding, to a temperature exceeding the softening temperature, a material charge can be molded and consolidated inside the molding tool in order to provide a load-bearing element made of reinforced thermoplastic.
Load-bearing elements according to the present invention are advantageously used for load-bearing components in vehicles, but they can also be used for other applications where low weight and high rigidity are required.
BACKGROUND OF THE INVENTION
At present, it is normal for load-bearing components, such as for motor vehicles, to be made from fiber-reinforced thermoplastics. In this connection, use is often made of so-called GMT technology, which involves a material charge with reinforcement material and thermoplastic matrix material being molded by compression molding during heating (thermoforming) in a two-part molding tool.
According to the prior art such a molding tool comprises a number of tool components which can be maneuvered so that the molding tool can be opened and closed. The tool components of the molding tool are additionally arranged so as to be able to apply an external compression force on the material charge which is located inside a cavity inside the molding tool. Moreover, the tool components are provided with guide pins or the like for achieving a good fit between the tool components during compression.
During compression molding, according to the prior art, the thermoplastic matrix material is preheated, with the aid of separate heating means, to the softening temperature or melt temperature of the thermoplastic matrix material.
In the prior art, the material charge sometimes has the form of a so-called preform, which is produced in a separate stage. The preform can be produced, for example, by coating a preforming screen, having a shape which is approximately similar to the final component, with cut roving or other glass fiber material and a suitable binder for holding the reinforcement in place. A precondition of GMT technology is that a thermoplastic matrix material is also present.
The previously known GMT technology requires the use of molding tools which, for example with the aid of hydraulic means, exert a pressure from outside onto the material layers which are to be molded. GMT technology uses a fairly large amount of energy and is less well suited for the manufacture of objects having the lowest possible weight.
Another previously known technique for the molding of components which comprise thermoplastics is blow-molding. In this connection, the raw material is plasticized in an extruder and is formed into a tubular blank which is engaged over a blow nozzle and enclosed in a mold consisting of two concave halves, after which the raw material is blown up and pressed against the cooled walls of the mold cavity and set. This technique has previously been used for the production of light thermoplastic hollow bodies without reinforcement, which hollow bodies therefore have a relatively low degree of wall rigidity.
Thus, a first object of the present invention is to make available an arrangement for molding a load-bearing element of reinforced thermoplastic in an energy-saving manner.
SUMMARY OF THE INVENTION
In accordance with the present invention, this and other objects have now been realized by the invention of apparatus for molding a load-bearing element comprising reinforced thermoplastic material provided from a material charge comprising at least one layer of thermoplastic matrix material comprising a non-permeable plastic membrane having a predetermined softening temperature and a reinforcement material, the apparatus comprising a molding tool including a first molding surface and a second molding surface whereby when the first and second molding surfaces are juxtaposed in a closed molding position at least one internal cavity having dimensions corresponding to the load-bearing element is formed therebetween, means for urging the first and second molding surfaces into the closed molding position, heating means for heating the matrix material to a temperature above the predetermined softening temperature, and matrix material molding means for providing a pressure or vacuum force for urging the matrix material against at least one of the first and second molding surfaces with the reinforcement material therebetween to thereby urge the reinforcement material against the at least one of the first and second molding surfaces to mold and consolidate the material charge. In a preferred embodiment, the matrix material molding means provides the force by pneumatic or hydraulic pressure.
In accordance with one embodiment of the apparatus of the present invention, the matrix material molding means provides the force in the form of a pneumatic vacuum.
In accordance with another embodiment of the apparatus of the present invention, the first and second molding surfaces are juxtaposed to provide a molding force onto selected areas of the material charge when in the closed molding position.
In accordance with another embodiment of the apparatus of the present invention, the apparatus includes cooling means disposed within the molding tool. In another embodiment, the apparatus includes heating means disposed within the molding tool.
In accordance with another embodiment of the apparatus of the present invention, at least one of the first and second molding surfaces includes compressing means for compressing predetermined regions of the material charge so as to provide a plurality of internal cavities between the predetermined regions and to provide compressed regions of the material charge including the non-permeable plastic membrane.
In accordance with the present invention, a method has also been devised for molding a load-bearing element comprising providing a molding tool including a first molding surface and a second molding surface forming a closed molding position when the first and second molding surfaces are juxtaposed against each other, introducing a material charge between the first and second molding surfaces comprising at least one layer of thermoplastic matrix material comprising a non-permeable plastic membrane having a predetermined softening temperature and a reinforcement material, with the reinforcement material disposed between the thermoplastic matrix material and at least one of the first and second molding surfaces, molding the material charge between the first and second molding surfaces with areas of the thermoplastic matrix material clamped within the molding tool to provide a seal, heating the material charge to an elevated temperature exceeding the predetermined softening temperature, providing pressure or vacuum force for urging the matrix material against the at least one of the first and second molding surfaces with the reinforcement material therebetween to mold and consolidate the material charge, and cooling the load-bearing element to a temperature below the predetermined softening temperature.
In accordance with one embodiment of the present invention, the at least one layer of thermoplastic matrix material and the reinforcement material are separate layers, whereby during providing of the pressure or vacuum force the at least one layer of therm
Lerner David Littenberg Krumholz & Mentlik LLP
Nolan Sandra M.
Volvo Personvagnar AB
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