DE2910227C2 - - Google Patents

Description

The present invention relates to a method for Manufacture of technical parts from thermoplastics with oriented continuous fibers, the production in usual plastomer processing machines that Reinforcing fibers in the processing tool with the Melt can be brought together and localized.

From DE-OS 25 48 751 a method for Manufacture of fiber-reinforced mold parts known thermoplastics, in which the Fibers and in a liquid or plastic state Plastic inserted into a mold cavity first, the fibers in the desired Orientation and distribution in the mold cavity fixed in position and then the plastic is injected or is pressed.

The easiest way to fix the situation those lying against each other when the tool is closed Separation surfaces of the tool used and additionally Devices for introducing the fiber web into the divided tool is provided, for example on both sides of the tool arranged conveyor elements such Transport rollers or movable across the tool Jaws.  

These measures and devices are partly to fixtures that are outside the tool are provided to fix the position Fibers.

When injecting, however, is often caused by the flow a disorder and repression of the plastic of the fibers that are also observed in a Fixation is done by devices that are outside of the tool are arranged and not too perfect reinforced parts leads. In addition there is the risk that when injecting already in positionally fixed fibers in the form increased Air pockets occur.

The object of the invention is a method for the production to indicate parts reinforced with continuous fibers, where the fibers are injected into the Injection molding compound not disordered and displaced and where air pockets are possible be avoided.

According to the invention, this object is achieved in that the continuous fibers through a through the melt flow moving guide element within the Form can be localized.

The tool is preferably sealed on the one hand through the guide element, on the other hand through an already molded part.  

The amount of fibers is determined by the number of holes and determines their diameter in the guide element.

The inventive method technical Parts with directed higher strengths, than previously in injection molding and extrusion can be achieved by adding fibers. These higher ones Strengths are when using the invention Method achieved in that as with other processes, short fibers that only without Alignment can be added, but special Areas of the finished part with directed localized Continuous fibers are reinforced. The single ones Fibers or fiber strands are installed so that them in a direction parallel to each other in the product are arranged. The fibers become during the spraying process not by the fixation outside the Tool fixed in position, but by a guide element, that is moved by the melt flow. The Reinforcing fibers are thus directly in the processing tool introduced and do not arrive first with the plasticized mass in the tool. The Reinforcing fibers are only in the processing tool brought together with the plastic melt and are located after the manufacturing process in one predefined location to directional reinforcement effects to allow for plastomer parts.

According to one embodiment, the location of the fibers different geometric shapes. After another Embodiment are using several injections performed several fiber guides. When ejecting then the fibers are not from the injection molded part  separately, but continued by means of the injection molded part. As fibers or strands in the context of The method according to the invention inter alia glass fibers and strands, and synthetic fibers and strands of various Starch used. The fibers and fiber strands can according to an embodiment with sizes and adhesion promoters. After another Embodiment are additionally with plastomers Short glass fibers are used.

For an embodiment of a production with continuous fibers reinforced parts became a rod production selected and a special injection mold developed.

The front platen of this tool has a smooth surface with no mold cavity that is centered Has sprue bushing for a bar sprue. Despite the central position of the sprue, it is an asymmetrical sprue.

It becomes a moving insert (sealing and Holding part) used to hold the continuous fibers. In the mold filling process takes place in this insert with cavity during injection molding. An insert with cavity serves against it only for holding the sprayed test specimen.

With the help of the sprayed test rod, which goes into the mold cavity is inserted after spraying, the Fiber strands tracked. In addition, a seal reached the mold space in the tool, and the fiber strands are used for the following injection molding process without additional device in the desired Longitudinally pre-fixed.  

A piston (piston with inserted fiber) was designed and built to guide the fiber. The piston is inserted into the upper mold cavity with a clearance fit. At the bottom of the piston there are holes, the location of which determines and enables the localization of the fibers. Since the piston is pushed by the inflowing melt in the direction of the mold filling flow during injection molding, no additional mechanism or drive for guiding the fibers is necessary (cf. FIG. 1). In order to prevent the fibers between the piston crown and the injection molded part from being sheared off during the ejection process, a movable insert part was built for the piston, which pushes the piston out by the ejection path during the ejection process.

The newly developed tool principle results in a workflow that is of the usual manufacture deviates from injection molded parts.

In the method according to the invention, a preferred embodiment the tool closed so far that the ejector pins are in the basic position are located. The fibers are threaded into the Piston. The piston is inserted into the tool the mold is closed and the injection molding he follows.

In this process, the piston is melted in pushed the height and guides the fibers. The injection molded part cools and freezes. The tool opens and pushed out the parts.  

This process cannot be called ejecting in the usual sense, since the parts do not fall out, but stick to the piston over the fiber strands (transfer injection molding). The piston in turn maintains its position in the guide part because the latter is advanced in the horizontal direction by the effective path of the ejector pins (cf. FIG. 2).

The injection molded part is pulled down so far until its upper part fits into the lower mold cavity. The fiber strands become automatic in this step continued. A new threading is thereby not necessary anymore. The piston moves independently In the basic position.

Only after this process you get the first one to be used partially directed reinforced part. This The process can be repeated until a new one Threading the fiber strands is necessary (e.g. Fiber tear, roving end).

A distinction must therefore be made between the continuous Production cycle and the first injection molding, where the reinforcement strands are introduced will.

The one with this tool and the workflow described Test rods produced are perfectly parallel aligned fiber strands that also the have the desired distance from the sample edge. The Separation of the test rods from the received rod happens e.g. B. by kinking, since the individual parts can only be held together via the fiber strands. After the sprue has been cut off, additional rework is required not mandatory.  

table

Measurement results

Show the measurement results shown in the table significant reinforcing effects directed by the introduced fibers.

For the test specimens reinforced with synthetic fibers tensile strength increases of up to 19% were achieved with a volume fraction of only 1.5% fibers. The However, measurement results also show that the increase in tensile strength strongly from the combination of plastic and fibers is dependent. The same applies to the Modulus of elasticity, where changes of up to 60% are achieved. Of particular note is the increase in Impact resistance of PMMA with 0.27% polyaramid fibers by 59%. As expected, the tensile strengths are included Glass fibers higher than synthetic fibers. The one with glass fibers Directionally reinforced test bars, however, show a drop in impact strength.

Embodiments of the invention are shown schematically in the attached FIGS. 1 to 4. The source flow flows against the extended ejector pin and begins to divide ( Fig. 1, point 1). The split melt flows together behind the pin and presses against the piston ( Fig. 1, point 2). The piston opposes the melt front and smoothes it. The smoothed melt front slowly pushes the piston upwards ( Fig. 1, point 3), and the piston guides the fibers. In FIG. 2, an insert part is shown for the piston guide. In Fig. 3a a closed tool with the closing tool half ( 1 ), the sealing and holding part ( 2 ), the platen ( 3 ) and the ejector ( 4 ) is shown.

The opened tool is shown in FIG. 3b.

In Fig. 4 application examples with guided fibers ( 5 ) are indicated.

Claims (3)

1. A process for the production of technical parts from thermoplastics with oriented continuous fibers, the production being carried out in conventional plastomer processing machines, the reinforcing fibers being brought together and located in the processing tool with the melt, characterized in that the continuous fibers are moved within via a guide element moved by the melt flow the shape can be localized. 2. The method according to claim 1, characterized in that that the sealing of the tool on the one hand the guide element, on the other hand by an already injection molded part. 3. The method according to claims 1 and 2, characterized in that the amount of fibers through the Number of holes and their diameter in the guide element is determined.