DE2854806A1 - COMPRESSING DEVICE AND METHOD - Google Patents

Description

HOFPMANN · ΕΙΤΪ, Ε & PARTNER

DR. ING. E. HOFFMANN (1930-1976) DIPL.-ING. W.EITLE DR. RER. NAT. K. HOFFMANN DIPL.-ING. W. LEHN

DIPL.-ING. K. FOCHSLE DR. RER. NAT. B. HANSEN ARABEILASTRASSE 4 (STERNHAUS) D-8000 MONCH EN 81 - TELEPHONE (089) 911087. TELEX 05-29619 (PATHE)

^ .31. 46.5 p / wa

CLINT, INC ₇ NATICK _r MASS. / UNITED STATES

Compression molding apparatus and method

The invention relates to an apparatus and a method for compression molding, in particular for injection molding of plastic molded parts. In particular, the invention relates on the compression molding of two-dimensional or three-dimensional parts made of plastic or similar material. The technology according to the invention can be used to manufacture parts which are used in different areas, such as in the auto industry, e.g. for the production of decorative, internal plastic parts.

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The conventional compression molding technique for the production of plastic parts includes heating the mold cavity in conjunction with closing the mold cavity around the To press plastic into the desired shape. This known technique as illustrated in Figure 1 of the application and will be discussed in detail below is appropriate for the manufacture of the aforementioned parts. These However, technology is generally only possible for the manufacture of substantially planar parts, as follows are referred to as two-dimensional parts. The term "two-dimensional parts" does not refer to parts that have no dimension, but refers to parts that either have a very small third dimension and deviate in their training by only a small amount from the level training. In the manufacture of three-dimensional Parts, and especially those that require an exact impression, are the conventional techniques not usable as it has been found that the plastic tends to burn out in some areas or still does remains cool and in this respect a flow into other areas prevented. This is because the temperature gradient across the plastic surface is not uniform. A plastic molded part, as shown in Fig. 3, is to be viewed as a three-dimensional part, which according to the until conventional techniques could only be made by reheating a two-dimensional part and Stretching and pulling is converted into a three-dimensional part via a die. However, this technique has a bias the structure or the surface pattern of the part. In addition, internal forces are generated, which cause fatigue and loss of shape of the part.

In the prior art, the plastic is moved by the movement

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pressed together between the mold halves. This creates an uneven pressure gradient on the plastic to be deformed, especially when three-dimensional parts according to FIG. 3 are to be produced.

The object of the invention is therefore to provide an improved method for the production of compression molded parts and also a to provide improved apparatus for performing the method.

This object is achieved by the method specified in detail below and characterized in the claims by a device for carrying out the method, accordingly solved the claims and the following description.

The device comprises a tool with a mold cavity for receiving the material, for example a liquid, powdery or powdery or sheet-like plastic, which possibly connected with fabric or leather, which is brought into the final shape after the compression molding process shall be. Inside the mold cavity there is a membrane-like cushion, on one side of which the deforming plastic material to form the one outer surface of the pressed part. This pillow is preferred manufactured in a master mold that has the desired impression along a surface. According to a preferred Embodiment of the invention, according to which it is desired, a uniform temperature gradient and a To provide uniform pressure, the device further comprises a compressible flow medium, which is preferably is a liquid conductor, such as mercury. This flow medium is located in the mold cavity

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Applying pressure to the other side of the pillow. A pressure device, preferably a piston, is used, to apply pressure to the liquid conductor. Finally, means are provided for applying an electromagnetic heat field to the pressing tool.

With the device described above, suitable temperature and pressure gradients arise on the surface of the Plastic material. The contact area between the liquid The head and the cushion preferably have the same contour as the indented surface of the cushion. Along this contact area there is the same potential. Likewise, the line of contact between the top electrode corresponds (Tool half) and the plastic material of the contour of the plastic material, by also the same potential along to be provided on this contact surface. Thus, as will be explained in detail later, the electrical Field lines perpendicular to the surface of the plastic to be deformed and at all points, so that over the entire Surface a uniform temperature is generated. By using a compressible flow medium on one side of the cushion, an equal pressure is applied to the cushion, which is preferably made of silicone rubber. Through this pressure is applied evenly to the Plastic material to be deformed, at all points in such a way that a perfect pressure action on the plastic material he follows.

As mentioned above, the results according to the invention Technology both a uniform compression of the plastic material and a uniform temperature gradient on the plastic material. But for the production some parts, especially parts that have little of

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deviate from the flat configuration (two-dimensional shape according to Fig. 2), the compression of the plastic material by closing the tool halves in combination with the creation of a uniform temperature gradient. This is possible because the molded cushion and the opposite Mold halves are adapted to the final shape of the compression molded part to be produced and that the cushion has a constant and uniform thickness over the entire area of the pressed part to be produced, so that the Field lines run essentially perpendicular to all surface parts of the pressed part. This will make a more uniform Temperature gradient; generated. The for the inventive method The device used is simple and inexpensive to manufacture, especially in comparison with injection molding devices.

The technology according to the invention is for the first Line heating the plastic material a high-radio frequency Field created. Because the plastic material is primarily heated, the cooling time and energy consumption are reduced reduced.

Further details, features and advantages of the invention emerge from the following description of the FIGS Drawings purely schematically illustrated embodiments. Show it:

Fig. 1 is a schematic view of a known

Press tool to represent the well-known transfer molding technique.

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

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Pig. 3 'shows a cross section through a device

According to the invention with the representation of the pressing tool in the clamped, closed Position with the inclusion of a compressible flow medium for a uniform pressurization of the pressed part,

Pig. 4 shows an enlarged cross-section through a

Part of the construction shown in Fig. 3, and

Pig. 5 a pressure-temperature diagram accordingly

the method and the device according to the invention.

According to FIG. 1, the known pressing tool shown there consists of two tool halves 6A and 6B, each of which carries a silicone rubber cushion 7A and 7B. These rubber cushions 7A and 7B form a mold cavity for the plastic pressed part 8. The complete tool construction is not shown in FIG. 1, since the tool is only shown schematically in FIG. Referring to Figure 1, the tool halves or electrodes 6A and 6B create an electric field across the dielectric material of the pads 7A and 7B. The field lines L cause uniform heating only along the horizontal areas of the plastic ^{pressed part 8. Ent 1} ing the two inclined areas of the pressed 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 electrodes 6A and 6B. This results in a non-uniform pressure gradient, in particular along the sloping one

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Areas 8A of the plastic molding 8.

From Fig. 1 it can also be seen that the cushions 7A and Fig. 7B shows an uneven thickness on iron. The field lines L, as shown in FIG. 1, all run vertically to the electrodes.

From Fig. 2 there is a schematic representation of a simple one Embodiment according to the invention for creating a uniform temperature gradient over the whole Plastic pressing part 8. The pressing tool according to FIG. 2 comprises two tool halves M1 and M2. In this embodiment two pillows can be used. However, only a cushion 9 is shown in Fig. 2, which on the bottom Tool half or electrode M2 is in contact. The upper-side tool half M1 is attached to the press part 8 directed surface provided which is adapted to the desired final shape of the pressed part 8. This is how the mold half forms M1 itself is an area of the mold cavity.

The cushion 9 shown in Fig. 2 has over the entire extent of the pressed part 8 has a uniform thickness T. Therefore, the heat-generating field lines L are not all vertical, but instead all substantially perpendicular to the surface of the plastic material to be deformed. To this Way is over the entire area of the plastic molding a uniform temperature gradient is created.

The technique according to FIG. 2 can be used for the production are used by plastic molded parts that only have a little deviate from the planar shape. For example, for the production of a pressed part according to FIG. 1, it would be closed prefer to use a method which follows

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will be described in connection with FIG. With the technique according to FIG. 2, however, pressed parts can be produced, where the angle A determining the deviation from the planar configuration is in a range from 0 to 20 ° moved. For angles greater than 20 °, the technique according to FIG. 3 is preferred. This technique is also then preferred if the surface requires a good impression of the tool.

In Fig. 3 tool halves 10 and 12 are shown, the 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 is located 18 is located, which is attached to the respective ends by insulating clips 20. The lower electrode 12 forms a chamber for receiving a compressible, preferably conductive liquid, such as mercury 22. The rubber cushion designed as a free-floating membrane 18 is provided with a depressed surface 24 and can consist of silicone rubber. The pillow can be made according to a variety of different known techniques Using a master mold can be produced. Of course, this mother shape corresponds in terms of shape and contour the plastic molding to be produced with the device according to FIG. 1. The surface 28 of the top electrode is manufactured or cast in such a way that it lies against the inside (grain-free) of the MuLLerfurru. Both electrodes 10 and can be made of aluminum. The upper electrode is provided with channels 30 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

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Electrode can be separated from the lower electrode in order to fill either plastic material or the hardened Plastic can be removed from the mold space of the tool. Fig. 1 also shows a pair of guides 34 which can be used for the correct alignment of the two electrodes to each other.

That to be formed by the method according to the invention or material to be deformed can be liquid, powdery or powdery or sheet-like. It can enter the mold cavity 16 inserted or from the outside using one or more flow paths (not shown) through the tool be injected into the mold cavity 16. When plastic sheets are used, the sheets can be rigid or flexible, or they can be connected to other materials such as fabric or leather be.

The lower electrode 12 is also provided with a cooling channel 36 Mistake. In this electrode a relatively deep cavity is carved out through which a considerable space for the mercury 22 is created. Fig. 3 also shows a piston 38, which within a connecting channel slidably disposed in the electrode 12 to selectively apply pressure to the mercury. This mercury uniformly communicates with the surface of the pad 18 .

The electrodes and the pad are preferably formed so that the outlines or areas 28, 16 and 25 are substantially are adapted to one another in such a way that the respective flat surface areas are parallel to one another are arranged. The liquid in the reservoir of the lower electrode is preferably conductive so as to be electrical

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To allow field lines 42 to arise, which run essentially perpendicular to all areas of the plastic molding, as can be clearly seen in FIG. In other words, this means that the same potential exists on the entire surface 28 and that a uniform but different potential is also applied along the entire surface 25 of the cushion. As a result of this electrical field line distribution, the entire plastic molding is heated uniformly, resulting in an extremely uniform flow over the entire mold cavity. The cushion 18 is a little flexible. As a result, when a compressible liquid is used, which is compressed by the piston 38, it is possible to apply an absolutely uniform pressure on the surface 25 of the cushion. This pressure is transferred to the plastic molding in order to achieve an excellent impression on the plastic molding. In accordance with the method according to the invention, 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 to clamp the tool halves together. Fig. 3 shows the tool in the clamped and closed position in which the pad 18 is secured by the clamps 20 at the ends. The tool halves or electrodes 10 and 12 are also fixedly connected to one another in any suitable manner. Before the tool is closed, the plastic is introduced into the mold cavity 16 in liquid, powdery or powdery or sheet form. Wen ¹ "; - the mold is closed, is are the mercury already at in Fig location shown in Figure 3, however, the piston is withdrawn enough 38, so that at the beginning of the process by the mercury only a small or no pressure on the pillow.. is transmitted.

When the tool is tightly closed, the source becomes 14

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operated optionally, vim an electromagnetic on the electrodes To apply energy. This results in uniform heating of the plastic material. In this regard reference is now made to the graph according to FIG. 5, which shows two curves, namely a temperature / time curve 46 and a pressure / time curve 48. The temperature detected may be the temperature of the plastic material, which was detected by a thermocouple not shown in the drawings. The pressure corresponds to that in the mold cavity measured pressure.

In accordance with a process operation, the the electromagnetic field generated heat for a period of 5 seconds on the plastic material in the mold cavity applied, whereby the plastic material is kept in the liquid state. The one exerted by the piston 38 Pressure is used for this 5 second interval and as well for an additional 5 second interval. The pressure exerted by the piston 38 is controlled by a relative controlled low, gradually increasing pressure during the first 5 second interval, as shown in FIG is. The pressure then continues to rise and peaks, for example, at 6.5 seconds. The one exerted by the piston 38 Pressure follows a curve which corresponds substantially to curve 48 in FIG.

The silicone rubber pad 18 can range in thickness from 6.35 to 9.5 cm (1/4 to 3/8 inch). Since this membrane-like -Rubber cushion Wed is flexible all over, the pressure follows in the mold cavity in close adaptation of the pressure curve caused by the piston 38.

It was found that using a liquid

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Plastic is preferred. Such a product is for example Plastisol.

Although mercury has been described as a type of fluid conduit for use in accordance with the invention it is understandable that other liquids, including pasty liquids, should be used in place of mercury can. In fact, it is more beneficial to have a sodium or Use graphite solution as mercury vapors are poisonous. Even though the tool is closed, the silicone rubber will of the cushion is a little porous, which allows the mercury vapors to escape from the tool can. As another liquid conductor, a molten alloy which is at about 49 ° C can be used (120 F) is kept in the liquid state. The liquid can be an alloy of bismuth, lead, tin or cadmium.

Be used when molten alloys instead of liquid mercury, it is preferred to keep the tool, as indicated above, at a temperature of about 49 ° C (120 ⁰ F). For example, the water flowing through channels 36 can be maintained at a temperature of 65.5 ° C (150 F). This water is sufficient to cool the plastic. The upper half of the tool can be kept at ambient temperature.

The pressing tool can have a square or rectangular shape, with the clamps 20 along the circumference of the Tool run. The clamp 20 places the rubber cushion on the lower tool half by means of the screws 21 (Fig. 3) fixed. Fig. 3 also shows the rod 33 which connects the upper tool half 10 with the cylinder 3 2, the rod 33 opposite the one acting as an electrode

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upper tool half 10 by means of an insulating member 35 This insulating member is necessary when the rod 33 is in any way attached to the frame of the machine is grounded. Since there is a potential at the tool half 10, it is of course necessary to remove all earthed parts, even the guides 34 to insulate.

The cylinder 32 and the rod 33 assigned to it are provided for opening and closing the tool and also function as a clamping device after the tool is closed. The cylinder 32 has an effective inner cross-section, which is large enough that a downward force is exerted by the applied air pressure is generated, which is greater than the force caused by the pressure of the liquid conductor applied to the cushion is produced. In order to limit the lower position of the upper mold half 10, a stop 11 is provided, which consists of an electrically insulating material and is preferably attached to the upper tool half 10 is. The stop 10 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 with respect to all grounded parts must be insulated. The cylinder 32 can also interact with a toggle or toggle mechanism, to lock or clamp the tool in the closed position.

The device according to FIG. 3 is also particularly useful for the HersLelluny of provided with Gegenkrümmunyen Plastic molded parts. In the past, this could Re-divide because of the difficulty of separating the tool the production of the pressed part cannot be designed in accordance with the pressing process. But with

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the technique according to FIG. 3, a vacuum reverse pressure can be applied after the production of the pressed part, to cause the rubber cushion to open easily / This enables easy separation of the two mold halves.

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Claims (1)

BLOFPMANN · EITI ^ S Ä PARTNER 2854806 PATENT LAWYERS DR. ING. E. HOFFMANN (1930-197). DIPL-ING. W.EITLE · bR. REK. NAT. K. HOFFMANN - DIPL.-1NG. W. LEHN DIPL.-1NG. K. FDCHSLE DR. RER. NAT. B. HANSEN ARABELLASTRASSE 4 (STAR HOUSE). D-8000 MDNCHEN 81 - TELEPHONE (0B9) 911087. TELEX 05-29619 (PATHE) 3.1 465 p / wa CLINT, INC., ·. NATICK, ·. I1ASS. / UNITED STATES Compression molding apparatus and method PATENT CLAIMS Device for compression molding, in particular for injection molding of plastic molded parts with a forming cavity inside Press tool for receiving a material which is brought into the shape of the pressed part to be produced, thereby g e mark eichnet that the mutually facing mold surfaces of the press tool halves (M1, M2) to the shape of the to be produced press part (8) are adapted. Device according to claim 1, characterized in that g e k e η η that a rubber pad (9) is applied to the lower half of the press tool (M2), the shape of which also matches the shape of the one to be produced Press part (8) is adapted. Device according to Claims 1 and / or 2, characterized in that there is a membrane-like space in the mold cavity (16) Form cushion (18) is arranged, on one side (25) of which the material to be formed rests, that in the mold cavity (16) compressible flow medium (22) is arranged, which rests on the other side of the cushion (18) that a Means (38) is provided to put the fluid (22) under pressure and so the material to be deformed - 2 - §09838 / 0578 ORIGINAL 2654806 to subject it to an equal pressure, and that one Device (14) is provided to in the pressing tool (10, 12) apply an electromagnetic field. 4. Apparatus according to claim 3, characterized in that that the fluid (22) is a liquid conductor. 5. Apparatus according to claim 4, characterized in that that the fluid (22) is mercury. 6. Device according to at least one of claims 3 to 5, characterized characterized in that the pressing tool is formed by at least two tool halves (10, 12) which are designed as electrodes, and that the two tool halves (10, 12) have a cavity surface (28), wherein a tool half (10) has a cavity surface (28) which is adapted to the shape of one side (24) of the cushion (18). 7. Device according to at least one of claims 3 to 6, characterized characterized in that the other tool half (12) has a cavity surface which together forms a reservoir with the cushion (18). 3. Device according to at least one of claims 3 to 7, characterized in that the fluid (22) covers substantially all of the fluid facing side of the cushion (18) is applied. 9. Apparatus according to claim 3, characterized in that that the fluid (22) is a metallic paste. 909838/0578 ΙΟ. Device according to claim 4, characterized in that that the liquid conductor is a molten alloy. ■ 11. Device according to claim 4, characterized in that that the fluid (22) is a sodium or graphite solution. 12. The device according to at least one of claims 3 to 11 characterized in that the cushion (18) faces the entire material to be deformed Surface (24) has a uniform and constant thickness. 13. Device according to at least one of claims 1 to 12, characterized in that the pressing tool has a pair of electrodes (10, 12) facing each other Has surfaces that run parallel to one another over the entire cavity. 14. Device according to at least one of claims 3 to 13, characterized in that the mutually facing surfaces of the electrodes and both surfaces of the Cushions (18) run parallel to one another over the entire cavity. 15. Method for compression molding a plastic molding under Use of a device according to claims 1 to 14, in which a material to be deformed is placed in the cavity is, characterized in that the material to be deformed is applied to one side of the cushion (18) that the flow medium (22) located on the other side of the cushion is pressurized, and that an electromagnetic field is applied to the press tool to heat the material to be deformed. 909838/057 « 2654806 16. The method according to claim 15, characterized in e t that the electromagnetic field and the pressure are applied at the same time. 17. The method according to claims 15 and / or 16, characterized in that the pressure after an interruption of the electromagnetic field is maintained. 13. The method according to at least one of claims 15 to 17, characterized in that the electromagnetic E'eld for a time interval of approximately 5 seconds and that the pressure is applied for a time interval of approximately 10 seconds. 909838/0578