Moulding tool

Abstract

The invention relates to a moulding tool (11) comprising a shaping cavity (13) for producing a container from a plastics preform by stretch blow moulding, wherein the moulding tool (11) can be arranged in an open and a closed state and in the closed state forms the cavity (13), comprising a shell (15) which is made of metal and forms the cavity (13), and comprising a heating device for heating the shell using a heat source and using a heat transfer means, which transfers heat generated by the heat source to the shell (15). The heat transfer means is configured as a heat pipe which is formed by a hollow space (19) completely surrounding the shell (15).

Description

[0001] mold tool

[0002] Field of the invention

[0003] The invention relates to a molding tool according to the preamble of claim 1 and a device according to claim

[0004] State of the art

[0005] Stretch blow molds must be heated to relieve stresses in the blown container (relax) or to create additional crystals in the material that give the plastic more heat resistance, thus enabling heat-resistant containers.

[0006] Stretch blow molds are known from the state of the art, which are heated with oil and require a long time, up to several hours, to heat up to a stable temperature. Accordingly, many more hours are required for the molds to cool down again. This slow behavior is problematic because deposits form more frequently in hot molds, which must be removed from the hot mold under difficult conditions. Rapid replacement of the hot molds is also difficult. Furthermore, oil-fired operation always poses environmental and safety risks.

[0007] State-of-the-art heating systems also include heating elements and sleeves, which also require a long heating time and do not allow for quick and short-term cooling for mold cleaning or mold changing.

[0008] Object of the invention

[0009] The disadvantages of the described prior art give rise to the task of creating a blow molding tool that can be heated and cooled quickly.

[0010] Description

[0011] The stated object is achieved in a molding tool by the features recited in the characterizing portion of patent claim 1. Further developments and / or advantageous embodiments are the subject of the dependent patent claims. The invention is preferably characterized in that the heat transfer medium is designed as a heat pipe, which is formed from a hollow space completely surrounding the shell. In comparison to a heat pipe, which is uniformly tubular, the present heat pipe is formed by the large-area hollow space. The heat exchange surface formed by the entire shell surface is also much larger than a pipe cross-section. The shell can therefore be heated very quickly and evenly. The heat pipe can heat or cool, whereby the effect of the heat of condensation or evaporation can be utilized. Local heating or cooling is possible, whereby cooling or heating or cooling is possible.Hot water supply throughout an entire production plant, along with the associated energy losses and the high static demands on the piping, can be avoided.

[0012] In a particularly preferred embodiment of the invention, the shell has a wall thickness of between 1.5 and 25 mm, and preferably between 3 and 8 mm. The shell is therefore very thin-walled compared to a prior art blow mold. The shell can therefore be heated and cooled quickly because the heated or cooled metal mass is small. Due to the rapid cooling, the shell can be cleaned quickly and the required mold or shell change times are short. The shell is preferably made of aluminum. The thin wall thickness allows considerable savings in aluminum material and melting energy compared to known blow molding tools, which are rolled as an aluminum block.

[0013] It proves advantageous if the shell is manufactured using a 3D metal printing process. With a 3D metal printing process, the shell can be produced with thin walls, quickly, precisely, using very little metal, and cost-effectively.

[0014] It is advisable to provide an inlet and outlet for a heat transfer medium at the cavity. This allows the heat transfer medium to be circulated: The condensed medium is re-evaporated and fed back into the cavity.

[0015] In a particularly preferred embodiment, the heat transfer medium, water, which is present as vapor in the cavity, condenses on the shell and releases the condensation enthalpy to the shell. This allows a particularly large amount of energy to be transferred to the shell in a short time, allowing it to be heated quickly. In addition, heating is improved by the shell's large surface area compared to a pipe. Likewise, the evaporation enthalpy of the water can be used to cool the shell quickly. This makes the productivity of the blow mold according to the invention very high, also because setup times are significantly reduced compared to the prior art. In addition, water is cost-effective and not critical in production operations with regard to occupational safety and environmental protection. The water is preferably mixed with a corrosion inhibitor to prevent corrosion in the lines.The water may also contain additives to prevent deposits, as such deposits can act as undesirable insulation.

[0016] The invention is also characterized by the fact that the cavity is formed between the sleeve and a sleeve holder, and the shape of the cavity is defined by the outer shape of the sleeve and the inner shape of the sleeve holder. Therefore, a wide variety of sleeves can be inserted into the sleeve holder, since the cavity shape has no influence on the function of the heat pipe and the heat transfer medium always condenses on the comparatively cold sleeve. This is the case even if the cavity has an irregular shape.

[0017] Because the sleeve holder is designed to hold sleeves of different sizes and shapes, the molding tool can be used extremely flexibly to produce a wide variety of containers, especially bottles. This is true even though the sleeve holder is always the same. The enlargement or reduction of the cavity due to the different sleeves plays no role in the function of the heat pipe, as already explained in the last paragraph.

[0018] It has proven useful to dimension the shell holder and the shell in such a way that the heat transfer medium can be present in the cavity under positive, negative, or atmospheric pressure. This allows the condensation and boiling points to be adapted to the required production conditions by selecting the medium pressure.

[0019] The hollow blow mold and the saved metal are particularly advantageous for rapid movements, in terms of acceleration and deceleration forces, energies and the associated wear.

[0020] For cooling and cleaning the casing, the cavity can be conveniently rinsed with a cooling medium, particularly water. The cavity can also be used as a heat pipe for cooling: By utilizing the evaporation enthalpy in combination with the relatively large casing surface, the casing can be cooled particularly quickly. Cleaning with water has the advantage that cleaning can be done inline and water leaves no residue.

[0021] It is advantageous if the mold is insulated, with or without a cooling water supply. When operating very hot molds, the heat is transferred to the mold carriers and then to the entire machine or fixture. Therefore, hot molds should be insulated from the carrier, or the remaining heat should be dissipated with cooling or cold water to prevent the heat from being transferred to the rest of the machine.

[0022] A further aspect of the invention relates to a device for forming plastic preforms into plastic containers, in particular plastic bottles, comprising a movable support on which a plurality of molding tools are arranged according to the above description. Thus, a plurality of the molding tools are designed to be integrated into rotary blow molding machines or linear blow molding machines.

[0023] It is preferred if the device has a heating connection for the heat transfer medium, whereby the cavities of the molds can be supplied with the vaporized heat transfer medium. The heating connection makes it possible to centrally supply the cavities of all molds with the vaporized heat transfer medium.

[0024] Further advantages and features will become apparent from the following description of an embodiment of the invention with reference to the schematic representations. These are not to scale:

[0025] Figure 1: a sectional view of the molding tool according to the invention in a first embodiment and

[0026] Figure 2: a sectional view of the molding tool according to the invention in a second embodiment.

[0027] Figures 1 and 2 show a molding tool in a first and second embodiment, respectively, which is designated overall by the reference numeral 11. The molding tool 11 has a shaping cavity 13, in which a plastic container is bias-molded, in particular stretch-bias-molded, from a plastic preform. The plastic containers are preferably plastic bottles. The molding tool 11 can be opened and closed. The preform is placed into the open molding tool 11. After the molding tool 11 is closed, the preform is inflated to form the container, wherein the container is a negative impression of the cavity. After molding, the molding tool is opened again and the container can be removed.

[0028] The cavity 13 is formed by a shell 15 made of metal. According to the current state of the art, the shells are produced by milling the cavity into a metal block or by casting the shell. This production process is material- and energy-intensive. Furthermore, these "block shells" require a long time to heat or cool and are very heavy. These factors also have a negative impact when the shell is replaced with another one in the mold.

[0029] In contrast, the present shell 15 has a thin wall thickness. Due to its thin wall thickness, the shell 15 can preferably be manufactured using a 3D metal printing process. Such thin-walled blow mold cavities are also referred to as "shells." The wall thickness is between 1.5 and 25 mm, and preferably between 3 and 8 mm. Since the heated mass is small, the shell 15 can be heated quickly.

[0030] The thin-walled shell 15 is therefore particularly well suited to being heated by a fluid 17, in particular water. For this purpose, the mold 11 has a heating device with a heat source. The heat generated by the heat source is transferred to the shell 15 by the water as a heat transfer medium. A so-called heat pipe is provided as the heat transfer medium. The heat pipe is formed from a cavity 19 which completely surrounds the shell 15. The operating principle of a heat pipe is implemented by water evaporating and the water vapor condensing on the shell surface. As a result, the condensation enthalpy or heat is released at the shell 15. This leads to a uniform, rapid, and high heat energy transfer. In comparison to a tubular heat pipe, the present heat pipe is formed by the large-area cavity 19.The heat exchange surface formed by the entire shell surface is also much larger than a pipe cross-section.

[0031] An inlet 21 and an outlet 23 are provided on the cavity 19 to feed the steam into the cavity 19 and to drain the condensed water and return it to the cavity as steam. Since two spatially separated mold halves are present, two cavities are also required. Each of the two cavities 19 requires an inlet 21 and an outlet 23 (not shown in the figures). The condensation temperature can be adjusted as required by providing positive or negative pressure.

[0032] The sleeve 15 is held in a sleeve holder 25. The cavity 19 is formed between the sleeve 15 and the sleeve holder 25. The shape of the cavity 19 is determined by the outer shape of the sleeve and the inner shape of the sleeve holder. The sleeve holder 25 can accommodate sleeves 15 of different shapes and sizes. The shape and size of the cavity change, which is irrelevant to the effectiveness of the heat pipe, since the water vapor will always condense on the sleeve 15 regardless of its shape. Different sleeves 15 and cavities 19 with an identical sleeve holder 25 are shown in Figures 1 and 2.

[0033] A further advantage of the cavity 19 (or the heat pipe) is that it can be rinsed with a cooling medium, particularly water, for rapid cooling and cleaning of the shell. The evaporation enthalpy of the water can be used to accelerate the cooling of the shell 15. The setup times or the time required for a mold or shell change are very short due to the short cooling times and the low shell weight. Changeover between the production of a wide variety of containers, particularly bottles, can therefore be accomplished in a very short time, also because the shell holder 25 remains unchanged. The shell does not need to be removed for cleaning, but can be rinsed at short cleaning intervals. Accordingly, the molding tool 11 according to the invention has a very high productivity.

[0034] The mold 11 has an insulation 27, which can be equipped with a cooling water supply. The sleeve holder 25 is insulated and optionally supplied with cooling water to prevent the applied heat from being transferred to the rest of the machine.

[0035] The combination of a shell 15 forming the cavity with a thin wall and a cavity 19 adjoining the shell, which acts as a heat pipe, allows the shell 15 to be heated particularly quickly. The shell 15 can be cooled just as quickly. Mold changes can therefore be carried out quickly and are further simplified by the low weight of the shell 15 and a shell holder 25 designed to hold different molds or shells. Key:

[0036] 11 Forming tool

[0037] 13 Cavity

[0038] 15 Cover

[0039] 17 Fluid, water, heat transfer medium

[0040] 19 Cavity

[0041] 21 Inflow

[0042] 23 Drain

[0043] 25 cover holders

[0044] 27 Insulation

Claims

1. Forming tool (11) comprising - a forming cavity (13) for producing a container from a plastic preform by means of stretch blow molding, wherein the molding tool (11) can be arranged in an open and a closed state and forms the cavity (13) in the closed state, - a shell (15) made of metal forming the cavity (13) and - a heating device for heating the casing with a heat source and a heat transfer medium which transfers heat generated by the heat source to the casing (15), characterized in that the heat transfer medium is designed as a heat pipe which is formed from a cavity (19) completely surrounding the casing (15).

2. Molding tool according to claim 1, characterized in that the casing (15) has a wall thickness between 1.5 and 25 mm and preferably between 3 and 8 mm.

3. Molding tool according to claim 1 or 2, characterized in that the shell (15) is produced in a 3-D metal printing process.

4. Molding tool according to one of the preceding claims, characterized in that an inlet (21) and an outlet (23) for a heat transfer medium are provided on the cavity (19).

5. Molding tool according to claim 4, characterized in that the heat transfer medium is water, which is present as steam in the cavity (19), condenses on the shell (15) and releases the condensation enthalpy to the shell (15).

6. Molding tool according to one of the preceding claims, characterized in that the cavity (19) is formed between the shell (15) and a shell holder (25) and the shape of the cavity (19) is defined by the outer shape of the shell (15) and the inner shape of the shell holder (25).

7. Molding tool according to claim 6, characterized in that the sleeve holder (25) is designed to hold sleeves (11) of different sizes and shapes.

8. Molding tool according to claim 6 or 7, characterized in that the sleeve holder (25) and the sleeve (15) are dimensioned such that the heat transfer medium can be present in the cavity (19) under overpressure, underpressure or atmospheric pressure.

9. Mould according to one of the preceding claims, characterized in that the cavity (19) can be rinsed with a cooling medium, in particular water, for cooling and cleaning the casing (15).

10. Mould according to one of the preceding claims, that the mould (11) has an insulation (27) with or without a cooling water supply 11. Device for forming plastic preforms into plastic containers, in particular plastic bottles, with a movable carrier on which a plurality of forming tools (11) according to one of the preceding claims are arranged.

12. Device according to claim 11, characterized in that the device has a heating connection for the heat transfer medium (17), whereby the cavities (19) of the molds (11) can be supplied with the evaporated heat transfer medium (17).

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