LU101898B1 - Method and device for producing an object by rotational molding - Google Patents

Abstract

The invention relates to a method for producing an object by means of rotational molding, in which a rotational molding mold composed of several rotational molding parts is rotated in order to deposit plastic powder or plastic granules made of a thermoplastic plastic material, previously filled into the interior of the rotational molding mold, on the inner wall of the rotational molding mold to effect. A film consisting of the thermoplastic material, which has a constant thickness DF over its entire surface, is arranged self-supporting and thermally uninsulated in relation to the rotational mold between two rotational mold parts of the rotational mold in such a way that the interior space is divided through the film into at least a first partial interior space, the one having a first inner wall portion of the inner wall, and a second partial interior space having a second inner wall portion of the inner wall is divided.

Description

29.06.2020 002A0021LU 1 lu101898 Description Title: Method and device for producing an object by rotational molding Cause rotational mold filled plastic powder or plastic granules of a thermoplastic plastic material on the inner wall of the rotational mold. The invention also relates to a rotary device system.

In order to produce objects by means of rotational molding, it is usual to fill a raw material into a rotational molding mold and then to rotate the rotational molding mold with the aim of depositing the raw material on the inner wall of the rotational molding mold.

In order to be able to produce rotation-moulded objects from plastics, it is necessary to rotate a rotation-moulding mold charged with raw material and to heat it up to such a high temperature that the mostly powdery or granular, in particular microgranular, raw material melts during the rotation process and adheres to the Inner wall of the mold attached. The rotational movement must not take place exclusively around a single axis of rotation; rather it is necessary to rotate the mold in at least two dimensions. ; It is known to divide the interior of a rotational mold with a separating device into two sub-interiors to one-piece

06/29/2020 002A0021LU 2 lu101898 to produce objects that consist of two parts made of different materials or different colored materials. For this purpose, different or differently colored raw materials are filled into the partial interiors before the rotation process. However, in practice, dividing the rotary casting mold into part interiors using a separating device is problematic, time-consuming and often leads to defective end products. US Pat. No. 6,383,437 B1 discloses a mold for rotational molding that consists of two mold parts. A plate-shaped partition is inserted into the mold, which divides the mold into two halves. In addition, blades are arranged on the partition wall, which further subdivide the interior. Molding material of different colors, which is melted during rotation, is inserted into the cavities separated by the partition wall. After the partition wall has been removed, a third mold material has to be inserted and another rotation process has to be carried out in a complex manner in order to connect the mold parts created during the first rotation process to one another, which is very complex, and in particular time-consuming.

From WO 81/02994 it is known to have a mold cavity with a | Divide separator into several parts. The separating device can be a plate or a film, but this reference points out that using a plate causes fewer problems. When using foil, it is imperative that the foil held by the rotational mold be additionally supported or protected from heat, for example with an additional layer of aluminum foil. However, the introduction of additional supports and/or thermal insulation makes the process particularly complex.

GB 2489591 A also points out that a thermal insulation material must be used in order to seal a film that

29.06.2020 002A0021LU 3 lu101898 to protect the interior of the rotational mold.

In addition, a plastic material is selected for the film that has a higher melting point than the plastic powder or plastic granulate that is filled into the interior spaces of the parts and is intended to accumulate on the wall of the rotational mold.

The inclusion of additional | However, thermal insulation makes the process disadvantageously expensive.

In addition, it has been shown that the connecting section of the sections of the manufactured object created in the different partial interior spaces is disadvantageously often less mechanically resilient than the remaining sections of the manufactured object.

It is therefore the object of the present invention to specify a method that can be carried out simply and efficiently, with which one-piece objects can be produced in a single rotational molding process, which have at least two sections that are reliably connected to one another.

The object is achieved by a method, which is characterized in that a film consisting of the thermoplastic material, which has a constant thickness Dr over its entire surface, is arranged self-supporting and thermally uninsulated with respect to the rotational mold between two rotational mold parts of the rotational mold in such a way that the interior space is divided by the film into at least a first partial interior space, which has a first inner wall portion of the inner wall, and a second partial interior space, which has a second inner wall portion of the inner wall.

It is another object of the present invention to provide a rotary device system for carrying out the above.

specify procedure.

29.06.2020 002A0021LU 4 lu101898 This object is achieved by a rotation device system with at least one rotation device and with at least one rotation mold composed of several rotation mold parts and with a clamping device which is designed to attach a film, in particular directly, to one of the rotation mold parts.

In a manner according to the invention, it was recognized that it is possible to produce an object by rotational molding with a subdivided interior of the rotational mold, in which the connection between the sections of the manufactured object created in different partial interior spaces can be subjected to just as much stability and strength as in the sections outside of the Link.

This is achieved by using a film to divide the interior of the rotational mold, which consists of the same thermoplastic material as the plastic powder or plastic granulate introduced into the partial interiors of the rotational mold to manufacture the object and which preferably has a special thickness (for this more below). The use of such a slide is described in | 20 Surprisingly and according to the invention, uninsulated (i.e. without thermal protection of the film) and self-supporting (i.e. in particular without additional mechanical support for the film) is possible, which considerably simplifies the entire production process of a molded part compared to the methods known from the prior art and in particular accelerated.

In particular, the film can advantageously be attached to the rotational mold before the rotation process, preferably with a clamping device, in such a way that the film is not directly mechanically supported on any other part apart from at least one of the rotational mold parts (and possibly on the clamping device) at the start of the rotation process .

In that regard, in the interior of the rotational mold no

06/29/2020 002A0021LU lu101898 Support arranged to support the film. In addition, no thermal insulation for insulating the foil is placed in the interior of the rotational mold. In particular, the film can be in direct contact with the thermally conductive material (in particular metal or metal alloy) of the rotational mold without thermal insulation. Also, the rotational mold does not require a thermally insulating section for the foil and preferably does not have such a section.

It is particularly advantageous if the following applies to the thickness Dr of the film in millimeters: Dest 2, where D is the average wall thickness of the object to be produced in millimeters and Q is the area of the film within the rotational mold in square millimeters and h is the height of the object to be produced in millimeters and x is a value between 5 and 15. The value x can advantageously be 10 in particular. Mathematically, x has the unit: [Vmm]. For example, for the production of a circular-cylindrical plant pot with a diameter of 500 mm and a height of 500 mm and an average wall thickness of 2 mm, a film can advantageously be used according to the invention that has a thickness of approx. 0.16 mm, with x the value 10 was assumed.

With such a thickness Dr, it is guaranteed that the film creates a particularly good and in particular mechanically highly resilient connection of the parts of the manufactured object that have arisen in the partial interior spaces, because the film is created during the rotation process in which the rotary casting mold is heated when the wall is created of the item to be manufactured melts with it. In addition, according to the invention, with such a thickness, Dr

29.06.2020 002A0021LU 6 lu101898 ensures that the film (despite the lack of thermal insulation and despite the lack of additional support) neither tears prematurely during the rotation process nor exerts excessive inward forces on the wall of the object to be produced due to heat-related shrinkage .

Advantageously, especially since no thermal insulation is used, the foil can be attached in such a way that it is in direct contact with the rotationally molded parts. In particular, it can advantageously be provided that no thermal insulation is arranged between the film and the rotationally molded parts. In a particularly advantageous embodiment that can be carried out particularly quickly, the film is attached to one of the rotational molding parts by means of at least one holding element, in particular by means of a clamping device (preferably operable without tools), before the rotational molding mold is closed by placing at least one other rotational molding part on it. In particular, the film can be arranged in such a way that it completely spans the opening of the rotational molding part.

The holding element, in particular as a clamping device, is preferably designed in such a way that the film can be attached without tools and/or can be released again without tools.

In a particularly advantageous embodiment, the clamping device is designed to be able to fasten the film to one of the rotational mold parts, in particular exclusively to a single one of the rotational mold parts, in such a way that the interior of the rotational mold through the film opens into at least a first part of the interior, which is a first part of the inner wall of the Has inner wall, and a second part interior, which has a second inner wall portion of the inner wall, is divided.

29.06.2020 002A0021LU 7 lu101898 Alternatively or additionally, the clamping device can be designed to be able to attach the film to the rotational molding part in such a way that it covers an opening of the rotational molding part, in particular completely.

There are no fundamental restrictions with regard to the thermoplastic synthetic material. In particular, it has been shown that the formula given above for the thickness Dr of the film can be used for all thermoplastic materials that are usually used in rotational molding, in particular in spherical rotational molding, in particular for the standard thermoplates PE-LD, PE-HD, PE-LLD, PP, is applicable. The use of POM, PA 6, PET, PBT, PPA, TPE, SPS, PEK or PPS is also possible, with the formula given above for the thickness Dr of the film being applicable to advantage. Particularly good results are achieved when the thermoplastic material is polyethylene, in particular LD-PE. In a particular embodiment of the method according to the invention, a plastic powder or plastic granulate made of the thermoplastic material is filled into the first partial interior space and a plastic powder or plastic granulate made of the thermoplastic synthetic material is filled into the second partial interior space, with the in the first partial interior space The plastic powder or plastic granulate that is filled in has a different color than the plastic powder or plastic granulate that is filled into the second partial interior. In this way it is possible to produce one-piece articles that have sections | have different colors. Alternatively or additionally, it is also possible, for example, that in the | first partial interior, a plastic powder or plastic granulate is filled from the thermoplastic material and that in the | second partial interior from a plastic powder or plastic granules

29.06.2020 002A0021LU 8 lu101898 is filled with the thermoplastic material, with the plastic powder or plastic granules filled into the first partial interior being mixed with other particles, in particular differently colored color particles, than the plastic powder or plastic granules filled into the second partial interior .

It is also possible in this way, for example, to produce one-piece objects which have sections of different colors.

In order to produce an object that has the same wall thickness largely everywhere, the quotient of the volume of the plastic powder or plastic granulate filled into the first partial interior and the area of the first inner wall portion should be just as large as the quotient of the volume of the second partial interior filled plastic powder or plastic granules and the surface of the second inner wall portion.

However, it is also advantageously possible to select the volumes in such a way that the quotient of the volume of the plastic powder or plastic granules filled into the first partial interior and the area of the first inner wall portion is different from the quotient of the volume of the Part interior filled plastic powder or plastic granules and the surface of the second inner wall portion.

In this way, objects with different wall thicknesses can be produced.

For example, a planter can be produced that has a greater wall thickness in the lower half, which is naturally more heavily mechanically stressed during use, than in the upper half, which is naturally less mechanically stressed during use.

In this way, raw material and (in terms of the manufactured item) weight can be advantageously saved.

In a particularly quick and efficient execution of the

29.06.2020 002A0021LU 9 lu101898 method according to the invention, a plastic powder or plastic granulate made of the thermoplastic plastic material is filled into a first of the rotationally molded parts, which at least partially surrounds the first partial interior. For this purpose, the first rotationally molded part is preferably aligned in such a way that the opening is directed upwards. After the plastic powder or the plastic granulate has been filled in, the opening of the first rotationally molded part is covered with the foil. This can advantageously be done in that the film by means of at least one holding element (which can preferably be operated without tools), in particular a clamping device, on | attached to the first rotomolded part. After that, the plastic powder or plastic granulate made of the thermoplastic material intended for the second partial interior is placed on the film and the second rotational mold part is placed on the first rotational mold part to form the rotational mold part. The rotation process can then begin, in which the rotational mold rotates and at the same time is heated.

As already mentioned, the film is preferably attached to the first rotationally molded part by means of at least one holding element, in particular by means of a clamping device, before the plastic powder or plastic granulate made of the thermoplastic material intended for the second partial interior is placed on the film. In particular, the clamping device can have at least one spring or spring clip. This way the slide before the | quickly and reliably attached to the first rotomolded mold part (and preferably only to the first rotomolded mold part) during the rotational process and quickly and reliably detached from the first rotomolded mold part after the rotational process. Attaching the film to only one of the

29.06.2020 002A0021LU 10 lu101898 The advantage of rotational molding is that time can be saved and a larger number of objects can be produced per unit of time.

Of course, it is also possible to attach the film in a different way, but the method described above can be carried out particularly quickly and reliably.

The attachment of plastic to the first inner wall portion and the attachment of plastic to the second inner wall portion occurs simultaneously during the same rotation process in which the rotational mold is rotated and heated to a temperature above the melting temperature of the thermoplastic plastic material. The film melts into the wall of the object to be produced and, due to its small thickness, cannot be seen with the naked eye on the finished end product; not even if the film has a different color than the plastic powder or plastic granulate used.

However, the use of a film that has a different color than the plastic powder or plastic granules used offers the particular advantage of providing the manufactured products with information that is invisible to the end user and that later | can be read, for example, by a microscopic and/or chemical examination. For example, the color of the foil used can be assigned to a production year, so that a later microscopic and/or chemical examination | the year of manufacture of an item can be determined retrospectively. A specific manufacturer can also be assigned to the color of the film, for example. Whether the respective product has to be destroyed for the microscopic and/or chemical examination depends on the shape and the thermoplastic material used.

29.06.2020 002A0021LU 11 lu101898 In a particularly flexible embodiment, the rotation device of the rotation device system has a sphere in which the rotational mold is arranged or can be arranged, and a drive device for driving a rotational movement of the sphere. In particular, the sphere can have openings through which hot air for heating and cold air for subsequent cooling can be blown onto the rotational mold during a rotation process.

An object which has been produced using the method according to the invention is particularly advantageous and in particular mechanically stable. In particular, the object can be a planter or a lampshade or a liquid tank. However, there are no fundamental restrictions on the items that can be produced. The subject of the invention is shown schematically and by way of example in the drawing and is described below with reference to the figures, elements which are the same or have the same effect are usually provided with the same reference symbols, even in different exemplary embodiments. 1 shows an embodiment of a rotation device system according to the invention during the execution of a first step of an embodiment of the method according to the invention, FIG. 2 shows the embodiment of a rotation device system according to the invention during the execution of a second step of the method,

29.06.2020 002A0021LU 12 lu101898 FIG. 3 shows the exemplary embodiment of a rotation device system according to the invention during the execution of a third step of the method, and FIG. 4 shows the exemplary embodiment of a rotation device system according to the invention during a rotation process. Fig. 1 shows an embodiment of a rotary device system according to the invention. The rotary device system includes a rotary device 1 and a rotary mold 4 that can be assembled from a first rotary mold part 2 and a second rotary mold part 3. In the example shown, the rotary mold 4 is designed to produce a plant container. However, there are no fundamental restrictions with regard to the type of object to be produced.

A clamping device 5 is arranged on the upper peripheral edge of the first rotationally molded part 2 , which has several clamping elements and is designed to fasten a film 12 (not shown in this figure) directly to the first rotationally molded part 2 .

The rotary device system also has a ball 6 . The ball 6 consists of a first hemisphere 7 and a second hemisphere 8, which can be releasably connected to one another. The first rotationally molded part 2 is fastened in the first hemisphere 7 by means of first springs 9 , while the second rotationally molded part 3 is fastened in the second hemisphere 8 by means of second springs 10 . As FIG. 1 shows, the second hemisphere 8 together with the second rotational mold part 3 can be lifted off the first hemisphere 7 and the first rotational mold part 2 .

29.06.2020 002A0021LU 13 lu101898 Plastic powder or plastic granulate 11 made of a thermoplastic material is filled into the first rotationally molded part 2 .

Then, in a second step, a film 12 consisting of the thermoplastic material, which has a constant thickness Dr over its entire surface, is self-supporting and thermally uninsulated relative to the rotational mold and is attached to the first rotational mold part 2 by means of the clamping device 5 in such a way that it closes the opening of the first rotational molding part 2 completely spanned, which is shown in Figure 2.

The first rotational mold part 2 and the film 12 then surround a first partial interior space 19 of the rotational mold 4. Then, in a third step, the plastic powder or Plastic granules 13 made of the thermoplastic material are placed on the film 12 (which is shown in FIG. 3) and the second rotational mold part 3 is placed on the first rotational mold part 2 to form the rotational mold 4 and the ball 4 is closed.

The rotation process can then begin, which is shown in FIG.

During the rotation process, the rotational mold is rotated and heated at the same time.

The plastic powder or plastic granules 11 filled into the first partial interior space 19 can have a different color than the plastic powder or plastic granules 13 filled into the second partial interior space 21. In this way it is possible to produce a one-piece object which has sections of different colors.

Alternatively, the plastic powder or plastic granules 11 filled into the first partial interior space 19 can be mixed with other particles, in particular differently colored color particles, than the plastic powder or plastic granules 13 filled into the second partial interior space 21. This is also the case for example, it is possible to produce a one-piece article that has portions of different colors.

29.06.2020 002A0021LU 14 lu101898 Alternatively or additionally, it is also possible to select the amounts of plastic powder or plastic granules 11, 13 such that sections of the object are created in the partial interior spaces that differ in terms of their wall thicknesses.

The rotation device 1 has a receptacle for the ball 6 in which the rotation mold 4 is arranged. The ball 6 is driven to rotate by means of a drive device 14 . The drive device 14 includes a drive motor 15 which drives a drive wheel 16 to rotate about a horizontal axis. The drive wheel 16 is in frictional contact with the outside of the ball 6 and drives it to rotate. The entire drive device 14 can be rotated about a vertical axis with a further drive device 17 in order to be able to change the orientation of the axis of rotation about which the ball 6 rotates, in particular continuously. The ball 6 is held in position during its rotation by means of laterally arranged rolling balls 18 . The interior of the rotary casting mold 4 is divided by the self-supporting and thermally uninsulated film 12, in particular with respect to the rotary casting mold 4, into the first partial interior 19, which has a first inner wall portion 20 of the inner wall of the rotary casting mold 4, and the second partial interior 21, which has a second inner wall portion 22 has the inner wall of the rotational mold 4 divided.

During the rotation process, the plastic powder or plastic granules 11, 13 from the thermoplastic plastic material previously filled into the interior of the rotational mold melt when they come into contact with the inner wall of the heated rotational mold and deposits on the first inner wall portion 20 and on the second Inner wall portion 22. The film 12 melts into the resulting wall of the object to be manufactured.

29.06.2020 002A0021LU 15 lu101898 After the rotation process, the second hemisphere 8 and the second rotational mold part 3 are separated again from the first hemisphere 7 and the first rotational mold part 2 so that the one-piece object produced (not shown) can be removed.

Remnants of the foil protruding from the wall of the object can be easily separated.

29.06.2020 002A0021LU 16 lu101898 List of reference symbols: 1 rotation device 2 first rotational mold part 3 second rotational mold part 4 rotational mold 5 clamping device 6 ball 7 first hemisphere 8 second hemisphere 9 first springs 10 second springs 11 plastic powder or plastic granules 12 foil 13 plastic powder or plastic granules 14 drive device 15 drive motor | 16 drive wheel 17 further drive device | 20 18 Rolkugeln 19 First partial interior First inner wall portion 21 Second partial interior 22 Second inner wall portion fo Hv

Claims (19)

06/29/2020 | 002A0021LU 17 lu101898 patent claims 1. A method for producing an object by means of rotational molding, in which a rotational mold (4) composed of several rotational mold parts (2, 3) is rotated in order to accumulate plastic powder or plastic granules previously filled into the interior of the rotational mold (4). (11, 13) made of a thermoplastic material on the inner wall of the rotational mold (4), characterized in that a film (12) consisting of the thermoplastic | Plastic material, which has a constant thickness Dr over its entire surface, is arranged freely and thermally uninsulated in relation to the rotational mold (4) between two rotational mold parts (2, 3) of the rotational mold (4) in such a way that the interior space is blocked by the film (12) in at least a first partial interior (19), which has a first inner wall portion (20) of the inner wall, and a second partial interior (21), which has a second inner wall portion (22) of the inner wall. 2. The method according to claim 1, characterized in that the thickness Dr of the foil (12) in millimeters applies: Dr=} 2, where D is the average wall thickness of the object to be produced in millimeters and Q is the area of the foil (12) within the rotational mold (4) in square millimeters and h is the height of the article to be made in millimeters and x is a value between 5 and 15. | 06/29/2020 002A0021LU 18lu101898 3. The method according to claim 1 or 2, characterized in that the film (12) is attached in such a way that it is in direct contact with the rotationally molded mold parts (2, 3). 4. The method according to any one of claims 1 to 3, characterized in that no thermal insulation is arranged between the film (12) and the rotationally molded parts (2, 3). 5. The method according to any one of claims 1 to 4, characterized in that the thermoplastic material is polyethylene, in particular LD-PE. 6. The method according to any one of claims 1 to 5, characterized in that a plastic powder or plastic granulate (11) made of the thermoplastic material is filled into the first partial interior (19) and that in the second partial interior (21) a plastic - Powder or plastic granulate (13) made of the thermoplastic material is filled in, with the plastic powder or plastic granulate (11) filled into the first partial interior space (19) having a different color than that into the second partial interior space (21) filled plastic powder or plastic granules (13). 7. The method according to any one of claims 1 to 6, characterized | characterized in that a plastic powder or plastic granulate (11) made of the thermoplastic material is filled into the first partial interior (19) and that a plastic powder or plastic granulate (13) made of the thermoplastic material is poured into the second partial interior (21). Plastic material is filled in, with the plastic powder or plastic granules (11) filled into the first part of the interior (19) being admixed with other particles, in particular color particles of a different colour, 29.06.2020 002A0021LU 19 lu101898 as the plastic powder or plastic granules (13) filled into the second part of the interior (21). 8. The method as claimed in one of claims 1 to 7, characterized in that the quotient of the volume of the plastic powder or plastic granules (11) filled into the first partial interior (19) and the area of the first inner wall portion (20) is different on the quotient of the volume of the plastic powder or plastic granulate (13) filled into the second partial interior (21) and the area of the second inner wall portion (22). 9. The method as claimed in one of claims 1 to 8, characterized in that a plastic powder or plastic granules ( 11) is filled in from the thermoplastic plastic material, and that an opening of the first rotationally molded part (2) is then covered with the film (12) and that the plastic powder or plastic granulate (13) intended for the second part interior (21) is then made of the thermoplastic material is placed on the film (12) and that the second rotational mold part (3) is then placed on the first rotational mold part (2) to form the rotational mold (4). 10. The method according to claim 9, characterized in that the film (12) is attached to the first rotationally molded part (2) by means of at least one holding element, in particular by means of a clamping device (5), before the plastic intended for the second partial interior (21). - Powder or plastic granulate (13) from the thermoplastic material is placed on the film (12). ZOO 06/29/2020 002A0021LU 20lu101898 11. The method according to any one of claims 1 to 10, characterized in that the rotational mold (4) is heated during a rotation process to a temperature above the melting temperature of the thermoplastic material. | 12. The method according to any one of claims 1 to 11, characterized in that the rotational mold (4) is arranged in a rotatably mounted ball (6) which is rotated during the rotation process. 13. An object produced using a method according to any one of claims 1 to 12. 14. Object according to claim 13, characterized in that the object is a planter or a lampshade or is a liquid tank. 15. Rotation device system with at least one rotation device (1) and with at least one rotation casting mold (4) composed of several rotation casting mold parts (2, 3) and with a clamping device (5) which is designed to clamp a film (12), in particular directly, on a of the rotational molding parts (2, 3), in particular exclusively on one of the rotational molding parts (2, 3). 16. Rotation device system according to claim 15, characterized in that the clamping device (5) can be operated without tools. 17. Rotational device system according to claim 15 or 16, characterized in that the clamping device (5) is designed to fasten the film (12) to the rotationally molded part (2, 3) in such a way that it forms an opening in the rotationally molded part (2, 3). covers. 06/29/2020 002A0021LU 21lu101898 18. Rotation device system according to one of claims 15 to 17, characterized in that the clamping device (5) is designed to fasten the film (12) to the rotational mold part (2, 3) in such a way that the interior of the rotational mold (4) the film (12) is divided into at least a first partial interior (19), which has a first inner wall portion (20) of the inner wall, and a second partial interior (21), which has a second inner wall portion (22) of the inner wall. 19. Rotation device system according to one of claims 15 to 18, characterized in that the rotation device (1) has a ball (6) in which the rotational mold (4) is arranged or can be arranged, and at least one drive device (14) for driving a rotational movement the ball (6).