DE2854806C2 - Device for pressing three-dimensional molded parts - Google Patents

Description

The invention relates to a device according to the preamble of claim 1.

With one from the French patent specification 21 64 533 known device is used to press two-dimensional parts. Would with a Such a device takes place the pressing of three-dimensional molded parts, the plastic would be in some areas tend to overheat or remain cool, allowing flow into others Areas would be prevented. Three-dimensional molded parts were thereby made in this state of the art Made that two-dimensional part by reheating and stretching and pulling over a Die has been converted into a three-dimensional part. However, this aftercare had one Distortion of the structure or the surface pattern of the molded part result. In addition, there will be generated internal forces which cause material fatigue and loss of shape of the molded part. The movement between the mold halves also compresses the plastic in such a way that it that an uneven pressure gradient arises on the plastic to be deformed.

In this context it should be pointed out that the term "two-dimensional" does not appear refers to those molded parts that do not have a third dimension, but to those molded parts that either have a very small third dimension or in their formation by only a small amount of the level training differ.

The object of the invention is to create a device of the type mentioned above, with the production of three-dimensional molded parts with im essentially the same wall thickness, all wall parts of the molded parts are heated to the same degree and electrical breakdowns can be avoided.

This object is achieved according to the invention by the from the characterizing part of claim I resulting features solved.

This device is used in the production of molded parts, especially three-dimensional ones Moldings suitable and uniform temperature and pressure gradients at all points of the 5 surface of the plastic material, because everywhere the electric field lines are perpendicular to the surface of the to be produced molding run. By using a compressible flow medium On one side of the patrix, even pressure is applied to the patrix, which is preferably made of There is silicone rubber, which means that pressure is applied evenly to the material to be deformed Plastic material.

The invention is explained below with reference to exemplary embodiments shown purely schematically in the drawings explained it shows

Fig. 1 is a schematic view of a known pressing tool,

Figure 2 is a schematic sectional view of a die construction according to the invention,

3 shows a cross section through a device

according to the invention with the representation of the

Press tool in the closed position below Inclusion of a compressible flow medium for

a uniform application of pressure to the pressed part,

4 shows an enlarged cross section through a Part of the in F i g. 3 illustrated construction and

F i g. 5 is a pressure-temperature-time diagram.

According to FIG. 1, the known press tool shown there consists of two tool halves 6/4 and 6ß, each of which carries a silicone rubber cushion 7/4 and TB as a die and male die. These rubber cushions TA and TB form a mold cavity for the plastic molded part 8. According to FIG. 1, the tool halves 6, 4 and 65 form electrode plates which create an electrical field via the dielectric material of the pads TA and TB. The field lines L cause uniform heating only along the horizontal areas of the plastic part 8. Along the two inclined sections of the molded part 8 there is a tendency for the plastic to overheat and for holes to be burned in in these areas. The required pressure is created by closing the electrode plates. This results in a non-uniform pressure gradient, in particular along the inclined sections SA of the plastic molded part 8.

From Fig. 1 it can also be seen that the pads TA and TB have an uneven thickness. The field lines L thus all run vertically to the electrode plates, as shown in FIG. 1.

From Figure 2, the schematic representation results in a simple embodiment of a pressing tool to create a uniform temperature gradient throughout the plastic molding 8. The crimping tool according to Figure 2 comprises two electrode plates Mi and M 2. In this embodiment, two pillows as a template or patrix be used. However, in FIG. 2 only shows a cushion 9 as a die, which rests on the electrode plate Ml on the bottom. The top-side electrode plate MX is provided with a surface which is directed towards the molded part 8 and is adapted to the desired final shape of the molded part 8. Thus, the electrode plate M 1 itself forms a surface of the mold cavity and the associated male mold.

The pillow 9 shown in Figure 2 has over the entire extension of the molded part 8 a uniform

Thickness T, therefore the heat-generating field lines L do not all run vertically, but instead all essentially perpendicular to the surface of the plastic material to be deformed. In this way, a uniform temperature gradient is created over the entire surface of the plastic molding.

The technique according to FIG. 2 can also be used for the production of plastic molded parts that deviate only slightly from the flat shape. For example, for the production of a molded part according to FIG. 1, it would be preferable to use a device which is described below in connection with FIG. With the technique according to FIG. 2, however, molded parts can be produced in which the angle A determining the deviation from the planar configuration moves in a range from 0 to 20 °. The technique according to FIG. 3 is preferred for angles greater than 20 °. This technique is also preferred when the surface requires a good impression of the tool

In Fig. 3 tool halves 10 and 12 are shown, which also each represent an upper and a lower electrode. An electromagnetic energy source 14 connects these two electrodes to establish a potential difference between these electrodes. Between the electrodes there is a mold cavity 16 in which a rubber pad 18 is located, which is fastened at the respective ends by insulating clamps 20. The lower electrode 12 forms a chamber for receiving a compressible, conductive liquid, such as mercury 22 rubber cushion 18 formed by a freely floating membrane is provided with a depressed surface 24 and can consist of silicone rubber. The pad can be made according to a variety of different known techniques using a master mold. In terms of shape and contour, this mother mold naturally corresponds to that with the device according to FIG. 1 plastic molding to be produced. The surface 28 of the upper electrode is fabricated or cast to abut the inside of the master mold. Both electrodes 10 and 12 can be made of aluminum. The upper electrode is provided with channels 3d through which a coolant, such as water or freon, flows. An actuating cylinder 32 is connected to the upper electrode 10 via a rod 33 so that this electrode can be separated from the lower electrode in order to either fill in plastic material or to remove the hardened plastic from the mold space of the tool. F i g. Figure 3 also shows a pair of guides 34 used to properly align the two electrodes with one another.

The material to be deformed can be liquid, powdery or plate-shaped. It can be inserted into the mold cavity 16 or from the outside by using one or more flow paths (not shown) m are injected through the tool into the Formhohlrautn sixteenth If plastic panels are used, the panels can be rigid or flexible, or they can be connected to other materials such as fabric or leather.

The lower electrode 12 is provided with a cooling channel 36 si Mistake. A relatively deep cavity is carved out in this electrode, through which a considerable Space for the mercury 22 is created. F i g. 3 also shows a piston 38, which within a connecting channel is slidably disposed in the electrode 12 to selectively apply pressure to the Exercise mercury. This mercury is uniform with the surface of the pad 18 in Link.

The electrodes and the pad are preferably designed so that the surfaces 28, 16 and 25 in the are essentially adapted to one another in such a way that the respective flat surface areas are parallel are arranged to each other. The liquid in the reservoir of the lower electrode is conductive so To allow electric field lines 42 to arise, soft to all areas of the plastic molded part substantially run vertically, as clearly shown in FIG. 3 can be found. In other words this means that the same potential over the entire surface 28 and along the entire surface 25 of the cushion uniform but different potential is applied as a result of these electric field lines distribution takes place uniform heating of the entire plastic molding, preceded by an extremely uniform Flow over the entire mold cavity gives the cushion 18 is a little flexible. This is how it is with the Use of a compressible liquid which is compressed by the piston 38, possible on the Surface 25 of the pad to apply an absolutely uniform pressure. This pressure is applied to the Transfer plastic molding to obtain an excellent impression on the plastic molding. The tool can be actuated by means of the cylinder 32, on the one hand to separate the tool halves or on the other hand for clamping the tool halves together. Fig.3 shows the tool in the clamped and closed position in which the cushion 18 is secured by the clamps 20 at the ends The tool halves or electrodes 10 and 12 are also fixed in any suitable manner connected with each other. Before the mold is closed, the plastic becomes liquid, powdery or Pls'.i-shaped introduced into the mold cavity 16 When the tool is closed, the mercury is already at the location shown in Fig. 3 However, the piston 38 is withdrawn enough so that at the beginning of the process by the mercury little or no pressure is transferred to the pillow.

When the tool is tightly closed, electromagnetic energy is applied to the electrodes This results in uniform heating of the plastic material. In this regard, we will now refer to the Diagram according to Fig.5 referred to, which shows two curves, namely a temperature / time curve 46 and a pressure / time curve 48. The detected temperature k & the temperature of the plastic material which was determined by a thermocouple not shown in the drawings. Of the Pressure corresponds to the pressure measured in the mold cavity.

The heat generated by the electromagnetic field is on for a period of time of 5 seconds the plastic material located in the mold cavity is applied whereby the plastic material in the liquid State is maintained. The pressure applied by piston 38 is maintained for this 5 second interval and also for an additional 5 second interval maintain. The pressure exerted by the piston 38 is increased by a relatively low, gradual

increasing pressure during the first 5 second interval controlled as shown in FIG. 5 is shown. The pressure then continues to rise and peaks z. B. on 6.5 second point in time. The pressure exerted by the piston 38 follows a curve which is essentially of curve 48 in FIG. 5 corresponds.

The silicone rubber pad 18 may have a thickness im Range from 0.635 to 0.95 cm. Since this membrane-like rubber cushion is flexible on the whole, the pressure in the mold cavity follows closely the pressure curve generated by the piston 38 is initiated.

Liquid plastics, for example plastisols, can be processed with the device.

Instead of using mercury as a liquid conductor, other liquids, including pasty liquids, can also be used. be used. In fact, it is more beneficial to use a sodium or graphite solution, as mercury vapor is poisonous. Ais other liquid Conductor a molten alloy can be used which is at about 49 "C in the liquid state is held. The liquid can be an alloy of bismuth, lead, tin, or cadmium.

If molten alloys are used instead of liquid mercury, that will Mold kept at a temperature of approximately 49 ° C. The water flowing through the channels 36 can for example be kept at a temperature of 65.5 ° C. This water is sufficient for the To cool plastic. The upper half of the tool can be kept at ambient temperature.

The pressing tool can have a square or rectangular shape, the clamps 20 run along the circumference of the tool. The clamp 20 attaches the rubber pad by means of the Tighten screws 21 (Fig. 3) on the lower half of the tool. F i g. 3 also shows the rod 33, which the upper tool half 10 connects to the cylinder 32, the rod 33 compared to the than Electrode acting upper tool half 10 is isolated by means of an insulating member 35. This isolator is necessary if the rod 33 is in any way grounded to the frame of the machine. Because at the tool half 10 a potential is applied, it is of course necessary to all grounded parts, even the guides 34 to isolate.

The cylinder 32 and the rod 33 assigned to it are for opening and closing the tool

ίο provided and also work as a clamping device after closing the mold. The cylinder 32 has an effective internal cross-section, which is large enough that the applied air pressure creates a downward force

is, which is greater than the force generated by the pressure of the liquid conductor applied to the cushion. In order to limit the lower position of the upper tool half 10, a stop 11 is provided, which consists of ciiiciVi clekiriäCn insulating material and is preferably attached to the upper tool half 10. The stop 11 limits the movement between the two tool halves. The stop 11 consists of insulating material because a voltage is applied to the tool half 10 and the corresponding potential must be isolated from all earthed parts. The cylinder 32 may also provided with a tilting or Knieh £ - _t "ilmechanismus cooperate to lock or to clamp the tool in the closed position.

The device according to FIG. Z can be used for the production of molded plastic parts with counter-curvatures. With the technique according to FIG. 3, after the production of the pressed part, a

Reverse vacuum pressure can be applied to cause the rubber cushion to open slightly. This enables the two halves of the tool to be easily separated.

For this purpose 2 sheets of drawings

Claims (2)

Claims; 1, device for pressing three-dimensional molded parts made of dielectrically heatable material, in particular made of plastic, under the action of a high-frequency capacitive alternating field with two relatively movable electrode plates made of electrically conductive material, with a die made of elastic, electrically non-conductive material on at least one electrode plate is attached, which with the opposite electrode, or a male die made of electrically non-conductive material, delimits a mold cavity and can preferably be acted upon with an electrically conductive pressure fluid, characterized in that the contours of the electrode plates (M 1, M 2 } are matched to the contour of the molded part to be produced. 2. Device according to claim 1, characterized in that that the spatial alignment of the electrode contour is achieved by the pressure fluid.