Stock material or miscellaneous articles – Structurally defined web or sheet – Including sheet or component perpendicular to plane of web...
Reexamination Certificate
2000-03-31
2004-12-28
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including sheet or component perpendicular to plane of web...
C428S057000, C428S058000, C428S060000, C428S111000, C428S116000, C428S118000
Reexamination Certificate
active
06835436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plastic structural element comprising a plastic material and one or more inserts having length embedded in the plastic material, such that the inserts exhibit the same or different values of rigidity and/or thermal expansion coefficients compared to those of the plastic. Also within the scope of the invention is a process for manufacturing the plastic structural element and the use of the plastic structural element according to the invention.
2. Discussion of the Prior Art
Fibre-reinforced plastics are employed ever increasingly in vehicle and aircraft manufacture and in the building industry, this because of favourable material properties such as low weight, corrosion resistance, high strength and the almost unlimited possibilities regarding shape. Reinforced plastics are employed therefore e.g. in automobile manufacture for body parts such as boot lids, bonnets or aerodynamic trim (spoilers), whereby in particular glass fibre reinforced plastics (GRP), carbon fibre reinforced plastics (CRP) and aramide fibre-reinforced plastics find wide application. Since fire-resistant plastics started to be used, fibre-reinforced plastics have also been employed in areas which, because of fire risks, were previously not possible.
Assembling or fitting such plastic structural elements onto metal components or other plastic components i.e. the methods of joining, presents great problems to designers. In particular continuous fibre reinforced plastic elements cannot be joined directly to other components simply by mechanical means such as riveting or screw type connections as the difference in strength, rigidity and elasticity of the individual materials leads to local points of weakness at the joint interfaces.
Adhesive joints are often used to connect metal and reinforced plastic elements to each other. These joints, however, require very clean surfaces for adhesion and therefore often call for special surface pre-treatments. They require complicated, time-consuming work under the cleanest possible conditions. Adhesive joints often exhibit only limited strength or require very large bonding areas, which again results in restrictions in design possibilities.
Further, it is also known to integrate inserts made of metal, e.g. threaded bushes, into the plastic elements. These serve as places for joining screw type connections to other components e.g. metal structures. These inserts are, however, relatively small parts that are built into the plastic in specific regions. Often, these inserts exhibit a complex structure in order for the metal-plastic joint to achieve adequate strength. The use of such inserts is expensive and is limited to plastic castings, in particular injection moulded parts that do not contain fibre-reinforced plastics or at most only short fibres. This application is not particularly suitable for vehicle body manufacture.
Patent DE 37 21 577 C2 describes a process for manufacturing plastic sockets with a metal insert that exhibits a cylindrical cross-section and on the outside a tooth-like grooving, whereby first the plastic socket is produced, followed by introduction of the metal insert into an opening in the plastic socket, and the grooving or corrugation on the metal insert pushed into the inner wall of the opening under the application of pressure and, in addition to the application of pressure, the plastic is heated. This process is, however, not suitable for fibre-reinforced plastics, in particular for those with a high fibre content. According to DE 37 21 577 C2 processes in which the metal insert is laminated in during the production of the plastic part are unsatisfactory as the large difference between the two materials leads to discontinuities and leakage in the composite part.
EP 0 872 650 A1 also describes a metal insert which is introduced into an opening in the plastic part while the latter is heated. Also this process is not suitable for fibre-reinforced plastics and does not provide the desired strength for high load applications.
DE 41 17 167 C2 describes a metal insert which is in the form of a metal support and is completely laminated into the plastic part. So called round material sections on the metal support are provided with threaded holes and form so called threaded inserts for screw type connections. The production of such composite parts is likewise very complicated as the plastic is made up of a base laminate and an outer laminate. Furthermore, the round material sections essentially permit only the use of screw type connections.
In all of the above mentioned examples the problem of an abrupt change in stiffness and the different coefficients of thermal expansion in the two materials viz., metal and plastic are not satisfactorily solved.
Inserts of metal in plastic materials are known to suffer from the problem that both materials viz., plastic and metal exhibit very different elasticity and stiffness, as a result of which zones of weakness are formed at the interfaces. In plastics reinforced with carbon fibres (CRP) the value of the elastic modulus, hereinafter called the E-modulus, may e.g. be around four times greater than that of metallic materials e.g. aluminium. As the stiffness of the product is calculated from the E-modulus and the polar moment of inertia, a significant change in stiffness occurs at the interfaces between the two materials.
Further, because of the change in stiffness at the interface to the plastic, the large polar moment of inertia of flat, large area or strip-shaped inserts e.g. of metal, have made it impossible to embed larger and large area inserts e.g. a metal strip or metal sheet as load-bearing connecting elements in a plastic structural component.
Furthermore, as a rule metallic and plastic materials exhibit different behaviour with respect to thermal expansion i.e. they have different coefficients of thermal expansion (cubic and linear coefficients of thermal expansion). With changes in temperature this leads to stresses which may be so large that separation occurs at the interfaces between the two materials.
For the above mentioned reasons, points of weakness are formed at the joining interfaces between the plastic and the insert, considerably reducing the limits to which a structure or plastic structural element may be loaded.
In general, therefore, workshops are not equipped to produce high-quality, high-strength connections between fibre-reinforced plastics and metal inserts, for which reason it is very important to, produce plastic structural elements which already exhibit the necessary connecting points in the form of inserts for attaching metal structures or other structures using e.g. mechanical attachment means.
SUMMARY OF THE INVENTION
The object of the present invention is, therefore, to provide cost-favourable structural elements or components of plastic, in particular reinforced plastic, with connecting points in the form of inserts, in particular large area inserts and preferably of metal, by means of which in spite of the different stiffness or elasticity and thermal expansion of both materials, the connection between the plastic material of the plastic structural element and the insert exhibits high mechanical strength, load bearing capacity and durability.
That objective is achieved by way of the invention in which the plastic structural element exhibits at least one of the following features:
a) the insert is joined to the plastic material via a coupling layer of plastic, and the coupling layer produces a gradual or uniform equilibration of the E-modulus determining the stiffness and/or the coefficient of thermal expansion between the plastic material and the insert and/or
b) the embedded length of insert features one or more openings through which reinforcing fibres, fibre strands and/or textile type materials are looped and are embedded in and intimately joined to the plastic matrix of the plastic structural element and/or
c) the embedded length of insert features strips or fingers or finger-shaped projec
Faisst Dieter
Niedermeier Michael
Reif Georg
Alcan Technology & Management Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Patterson Marc
Pyon Harold
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