Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling heat transfer with molding material
Reexamination Certificate
2001-02-13
2004-11-16
Staicovici, Stefan (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling heat transfer with molding material
C264S102000, C264S257000, C264S258000, C264S510000, C264S511000, C264S512000
Reexamination Certificate
active
06818159
ABSTRACT:
The invention relates to a process for the production of a component consisting of a fiber reinforced material, with which liquid resin is supplied to a semifinished fiber article by way of application by vacuum pressure.
Such processes are known from the state of the art and are also designated as vacuum injection processes.
Vacuum injection processes are known, for example, from U.S. Pat. No. 4,902,215, U.S. Pat. No. 5,052,906, U.S. Pat. No. 5,601,852, U.S. Pat. No. 5,439,635 or WO 94/20278.
DE 100 13 409 C1 discloses a process for the production of fiber reinforced plastic components from dry semifinished fiber composites by means of an injection process for the injection of matrix material, with which a first chamber is formed by means of a membrane permeable to gas and impermeable to matrix material and a second chamber is formed which abuts on the first chamber which is separated from the surroundings by means of a film impermeable to gas and matrix material and wherein air is drawn off from the second chamber and, as a result, matrix material from a storage vessel is drawn into the evacuated first chamber.
The object underlying the invention is to provide a process of the type specified at the outset, by means of which components of a high quality can be produced and, in particular, components with large surface areas can also be produced.
This object is accomplished in accordance with the invention, with the process specified at the outset, in that a heat curing resin is used as resin and that application by vacuum pressure and temperature are controlled such that in relation to the liquid resin the boiling point curve of the resin is not exceeded.
In accordance with the invention, heat curing resins can also be used for the production of structural components by means of a vacuum injection process. For example, the heat curing resin system Hexcel RTM6 which is authorized for aviation can be used. As a result of the use of low viscosity resins a high fiber volume content in the component can be achieved and this is, for example, between 40% and 60%. The bulk of the component can be reduced due to the high fiber volume content.
On the other hand, heat curing resins normally have a relatively low boiling pressure and so the resin can boil during the heating up due to application by vacuum pressure. The gas bubbles thereby resulting can no longer be removed from the workpiece and thus have a negative effect on the quality of the workpiece. Due to the inventive control of the application by vacuum pressure and the temperature it is possible to avoid the boiling point curve being exceeded. In accordance with the invention, structural components which are practically free from bubbles can therefore be produced with a high degree of repetition.
A separation between the structure of the semifinished fiber article (laminate structure) and impregnation of the resin can be achieved, in particular. In accordance with the invention, structural components with large surface areas can also be produced by means of a vacuum injection process without an autoclave needing to be provided. The costs of manufacturing a component may thus be reduced considerably. For example, foam cores and inserts can also be integrated in one operating procedure.
The impregnation of the semifinished fiber article itself represents a complete process which takes place in a vacuum atmosphere, i.e. is separated from the outside environment. As a result, the workplace stress is low and, in particular, it is possible for no skin contact with resin to occur.
The production of the component may also be carried out in relation to known processes with less time expended. As a result, the costs are again reduced.
It is advantageous when the application by vacuum pressure is controlled via a vacuum pump during the resin infiltration. A pumping capacity of the vacuum pump, which then has a direct effect on the vacuum pressure applied to the workpiece, may be adjusted in a selective manner. Possible losses in pressure in connecting lines and the like can be determined in a simple manner or are known and so during the resin infiltration, during which the temperature of the injected resin and the temperature of the semifinished fiber article are adjusted in a defined manner, a specific vacuum can also be set in order to avoid the resin boiling.
In order to be able to supply the resin to the semifinished fiber article in a defined manner it is particularly favorable when a distribution fabric is provided which has vacuum pressure applied to it. Flow channels are formed in the distribution fabric which serves as a flow aid and a flow of resin is generated in these channels via a pressure gradient or capillary effect. As a result, the workpiece may be impregnated with resin in a selective manner, wherein the resin flow and, in particular, resin flow fronts can be controlled.
It is favorable when the pressure following the resin infiltration is measured at a distribution fabric which serves to supply resin to the semifinished fiber article. Since the distribution fabric normally has a high permeability and covers the entire workpiece, a take-up of pressure at the distribution fabric is particularly suitable for carrying out a pressure control.
In order to measure the pressure it is advantageous when one or several pressure sensors are brought into operative connection with the distribution fabric following the resin infiltration of the workpiece. The prevailing pressure may then be determined via these pressure sensors. In order to prevent resin passing into connecting lines to the pressure sensor or sensors during the infiltration of the workpiece with resin (impregnation), the operative connection is interrupted prior to and during the resin infiltration of the workpiece. In this phase, the pressure is, in particular, adjusted via the capacity of the vacuum pump in order to avoid any boiling of the resin accordingly. Following the resin infiltration, the operative connection is again established in that a line clamp is, for example, released. The pressure at the workpiece then prevails at the pressure sensor and the vacuum can be adjusted accordingly at a given temperature with the aid of the measurement value of the pressure sensor such that no gas bubbles are formed in the resin.
In order to produce certain structural components it may be provided for the semifinished fiber article to be placed in a mold during the resin infiltration. In this respect, it is sufficient to design the mold as a one-sided form, onto which the semifinished fiber article is placed. A vacuum chamber, in which a vacuum prevails, may then be established by means of a vacuum foil which is laid over the semifinished fiber article. No specially designed autoclave has to be provided for manufacturing the structural component and, in particular, components with large surface areas can also be produced.
In order to ensure a high quality of the component it is provided, in particular, for the temperature of the mold to be controlled. As a result, the temperature of the resin during the infiltration (impregnation) can, on the one hand, be controlled in order to avoid the occurrence of boiling bubbles. On the other hand, an optimum temperature may be set for the curing of the resin after the infiltration in order to again ensure a high quality of the component in this case, as well.
To monitor the temperature it may also be provided for a plurality of temperature sensors to be arranged at a vacuum foil. The vacuum foil is arranged above the workpiece so that a measurement of temperature is also made possible in this area.
It is particularly advantageous when the temperature is adjusted with respect to the temperature dependence of the viscosity of the resin. If the viscosity is too high there is the risk of resin, which saturates the semifinished fiber article, flowing out again. If, on the other hand, the viscosity is too low, the semifinished fiber article will not be sufficiently impregnated.
A resin infiltration favorably takes place in an injection
Deutsches Zentrum fuer Luft-und Raumfahrt e.V.
Lipsitz Barry R.
McAllister Douglas M.
Staicovici Stefan
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