DE10123176C2 - Process for producing sandwich components with a cover layer and a foam-containing core layer - Google Patents

Description

The invention relates to a process for the production of sand having wichbauteilen with a cover layer and a foam the core layer, as it is based, for example, from the generic published DE 199 14 327 A1 discloses as known.

From DE 199 14 327 A1 a method is known, with the Sandwich components can be made, from a so SMC (sheet molding compound) sandwich produced Cover layers provided with an intermediate layer of foam who the. The cover layers are vorgefer in a press tool if necessary, and with the interposition of a likewise previously cut foam plate with each other under low Pressure connected to the sandwich component. Furthermore, they are in front Partial materials for the foam and the SMC cover layers, as well as release agents for simplified removal of the finished (Foam) sandwich components from the end tool mentioned.

However, the manufacturing process has several steps on and is therefore tedious, complicated, prone to failure and expensive.

The object of the invention is a process for the preparation to develop such a sandwich component, with which the Production of lightweight yet stiffer components, in particular of body parts, in the least expensive way he is possible.  

The object is achieved with a method with the Process steps of claim 1 solved.

In the method according to the invention, first one or several outer layers and other starting materials geschich tet introduced into a mold. After that, the formwork becomes closed and the starting materials are used during a Prepress time pressed together. During the pre-press time the starting materials are heated simultaneously and a propellant is particularly thermally activated. The Treibmit Tel allows at least the foaming. Gleichzei tiger to the activation of the propellant can be in an advantageous Make a crosslinking of at least one of the starting materials at least be initiated. After the pre-press time will be Forming tool up to the final value of the layer thickness of the sandwich Moved back member in Formendstellung, with the Zu return the released volume with the forming and / or expanding foam is filled and in this way formed a core layer. To here he stability heights can be used to form the core layer in addition to foam also Fa fibers, and / or other layers introduced into the mold become. Finally, all are networked in the Formendstellung finally crosslinked baren starting materials. The formwork The tool is opened and the OSS-SMC sandwich removed.

To enable the best possible surface qualities it is makes sense that in the mold first and last one each the later sandwich component on the outside at least partially limiting top layer and / or their output is inserted. This should be foamed and on first closing the outer layers and / or their starting materials ver wetting and / or hardened.

If only a high-quality surface is desired, will expedient manner in the mold only one cover layer and / or their starting materials introduced, wherein before the Foaming the curing of the top layer and / or crosslinking the starting materials of the top layer is introduced.  

In this case, it is favorable for the pre-press time (t _VP ), the reaction time of the cover layer (t _RDS ), the foaming time (t _Sch ), the reaction time of the core layer (t _RKS ) and the time until the beginning of the foaming (t _BS ) choose the following time relation:

t _VP ≦ t _RDS + t _Sch ≦ t _RKS + t _RDS ≦ t _BS .

The basis material will be the factory established in vehicle construction materials for sheet molding compound (SMC) selected in hot be processed. To the desired high To achieve rigidity and thus conventional today To exceed constructions, the sandwich component in the Type of a multilayer sandwich structure executed. This can the most common in conventional SMC components Ausfüh tion as a bivalve or heavily ribbed or swamped con attribution. Further advantages of this sandwich construction are cost savings versus double-shelled or heavily ver ribbed or pitted constructions as well as the avoidance of Sink marks.

A comparable sandwich component, which in the conventional Made of cover and core layers in single steps is not justifiable due to the high production costs. Therefore, in the inventive method, the number of Work steps reduced. At the same time is also the manufacturer ment of spatially curved components allows. Furthermore, can the recycling of components without prior material separation respectively.

Hereinafter, the invention with reference to in the drawings illustrated embodiments explained in more detail. there shows

Fig. 1 shows the manufacture of a sandwich component with an associated tool,

Fig. 2 shows the temporal procedure and

Fig. 3 shows a cross section through various sandwich components.

An OSS-SMC sandwich produced in the process according to the invention in one step (one-step sandwich) may consist of two SMC cover layers of conventional construction and a core of foamed SMC. The foam core of the OSS-SMC sandwich component is formed during the original molding process (see FIG. 1). For this purpose, the SMC mass of the core layer is added to a blowing agent which foams the core in the tool before the cross-linking of the polymer. The optionally multi-layered SMC blank is placed flat in the tool and pressed in ers th step. After completion of the flow and the mold filling takes place to achieve the desired sand wich thickness necessary foaming. Due to the foaming pressure of the core material, the outer layers remain in contact with the upper surface of the tool.

The structure of the molding formed in "One-Step" corresponds so that of a "built" sandwich, but with cover layers and core material advantageously from the same base consist of material.

However, an SMC sandwich produced by this process must not a completely flat component, but can be a geometric Structuring, such. b. have spherical curvatures.

In FIG. 2, the process sequence is shown over time. It is the three phases, pre-pressing, foaming and curing Darge presents. The travel of the tool and the pressure applied in the prepress time is recognizable. In the pre-press time, the heat energy required for the activation of a blowing agent and the crosslinking of an unsaturated polyester resin is expediently introduced into the compound.

Preferably, as starting materials for both the top layer and the core layer materials is set, based on a standard SMC and z. B. from the gat device-forming DE 199 14 327 A1 are known. The cover layer is, starting from a conventional low shrink SMC, so modifi ed that the requirements of the process are met. The core layer is based on a conventional SMC with a low glass content and contains 30 to 40 volume percent of a high proportion of recycled SMC. This makes the sandwich a monosystem that can be processed without material separation. As the blowing agent of the core layer, an alcohol is preferably used. The cycle times for processing OSS-SMC sandwich components are in the range of 180-360 s. The density of such a sandwich component is at usual Schäumra th between 0.9 and 1 g / cm ³ and can be further reduced by increasing the foaming rate. This is limited by the mechanical nature of the foam required for the respective sandwich component considered.

A good pore property resulted especially in the Ver use of alcohol as a propellant and / or in Einbrin microcapsules initially containing the propellant th.

The advantage of OSS-SMC sandwich components with regard to improving the mechanical properties is, inter alia, the production of a lightweight, rigid sandwich component. Since individual parameters do not have a clear meaningfulness, a tabular comparison of unilaterally clamped bending beams made of OSS-SMC, SMC and steel is listed below. With the same carrier dimensions and deflections, the different masses clearly show the lightweight potential of OSS-SMC. Compared to a conventional SMC, OSS-SMC is 34% lighter and 56% lighter than steel.

To the suitability of the material system and the method for Vehicle components became a demonstration component Realized that all vehicle specific requirements in the Must meet component testing. After viewing different dener commercial vehicle components, z. b. Roof, floor, back wall and door, was a front flap of a truck of the heavy class vice puts.

Contrary to the previous design, which consists of a Profilun steel structure with a SMC planking, comes the OSS-SMC version without support structure and offers thus cost and weight advantages. The add-on parts like Schar kidney, gas springs, lock traps and grille are di attached directly to the OSS-SMC stem. This component So represents a good industrial implementation of the basic technology the OSS SMC.

The direct comparison with a common component shows the high Innovation Potential of OSS-SMC Sandwich Components Regarding Lightweight construction and cost savings. Also under recycling OSS-SMC can be used both as a mono system and through Convincing use of SMC recyclate. Thus, the invention offers The process according to the invention provides good conditions for the industrial process Production of light and rigid body parts.

Claims (7)

1. A process for producing sandwich components with a cover layer and a foam-containing core layer, in which
the cover layer and further starting materials are layered in a mold,
the mold is closed,
the starting materials are pressed together during a pre-press time,
the starting materials are heated during the pre-press time,
during the pre-pressing time a blowing agent is activated in particular ther mixed,
a foam is formed with the blowing agent and at least one starting material,
after the pre-press time, the mold is retracted to the final value of the layer thickness of the sandwich component in the final mold position,
upon retraction, the released volume with it form and / or expanding foam filled and a core layer is formed, and
the mold is opened and the OSS-SMC sandwich is removed,
characterized
that in the mold first and last one later the later sandwich component on the outside at least be areal limiting limiting top layer and / or their starting materials is inserted,
that propellant is added in microcapsules,
that foamed first and then the outer layers and / or their starting materials are crosslinked and / or cured,
that in the Formendstellung all crosslinkable Ausgangsmateri alien are finally crosslinked and
that the mold is opened only after the final crosslinking of all crosslinkable starting materials. 2. A process for producing sandwich components with a cover layer and a foam-containing core layer, in which
the cover layer and further starting materials are layered in a mold,
the mold is closed,
the starting materials are pressed together during a pre-press time,
the starting materials are heated during the pre-press time,
that before the foaming the curing of the cover layer and / or the crosslinking of the starting materials of the cover layer is eingelei tet,
during the pre-pressing time a blowing agent is activated in particular ther mixed,
a foam is formed with the blowing agent and at least one starting material,
after the pre-press time, the mold is retracted to the final value of the layer thickness of the sandwich component in the final mold position,
upon retraction, the released volume with it form and / or expanding foam filled and a core layer is formed, and
the mold is opened and the OSS-SMC sandwich is removed,
characterized,
that in the Formendstellung all crosslinkable Ausgangsmateri alien are finally cross-linked, wherein
for the pre-press time (t _VP ), the reaction time of the cover layer (t _RDS ), the foaming time (t _Sch ), the reaction time of the core layer (t _RKS ) and the time until the beginning of the foaming (t _BS ) the following time relationship is selected:
t _VP ≦ t _RDS + t _Sch ≦ t _RKS + t _RDS ≦ t _BS
and
that the mold is opened only after the final crosslinking of all crosslinkable starting materials. 3. The method according to claim 1 or 2, characterized, that during the activation of the blowing agent, a crosslinking at least one of the starting materials at least initiated becomes. 4. The method according to claim 1 or 2, characterized, that in the mold a cover layer and / or their off be introduced precursors that before foaming the Här tion of the top layer and / or the crosslinking of the starting materials the cover layer is introduced. 5. The method according to claim 1 or 2, characterized, that, in addition to foam, fibers form the core layer, and / or further layers are introduced. 6. The method according to claim 1 or 2, characterized, that is used as the blowing agent alcohol. 7. The method according to claim 2, characterized, that blowing agent is added in microcapsules.