Method for moulding a green tyre in a heating press

Abstract

The invention relates to a method for moulding a green tyre (8) in a heating press (1) with a hood comprising at least two hood parts and with a container (7), which is located in one of the hood parts and contains a vulcanizing mould (6) which comprises mould parts forming the outer side of the tyre, the method comprising the following steps: - positioning a heating bladder inside the green tyre (8), - introducing a gas into the interior of the heating bladder and setting an internal pressure in the heating bladder of 0.10 bar to 0.70 bar, - closing the heating press (1) over multiple incremental movements of the hood parts (3, 4), - the first incremental movement involving closing the hood parts (3, 4) to form in the interior space of the hood a vacuum chamber (13) in which a vacuum can be created. At the same time as creating the vacuum, the differential pressure (PB) between the pressure (Pv) in the vacuum chamber (13) and the pressure (PB) in the interior of the heating bladder is set to 0.1 bar to 0.7 bar and kept there with a maximum deviation of ± 0.2 bar.

Description

[0001] Description

[0002] Method for molding a green tire into a heating press

[0003] The invention relates to a method for molding a green tire in a heating press with a hood consisting of at least two hood parts and with a container arranged in one of the hood parts, which contains a vulcanization mold having molded parts forming the outer side of the tire, with the following successive steps:

[0004] - Loading the opened heating press by placing the green tire to be vulcanized into the container,

[0005] - Positioning a heating bladder inside the green tire,

[0006] - Introducing a gas into the interior of the bladder and setting an internal pressure in the bladder of 0.10 bar to 0.70 bar,

[0007] - Closing the heating press over several partial strokes of the hood parts, whereby the hood parts are moved towards each other,

[0008] - in the first partial stroke, the hood parts are closed, forming a vacuum chamber in the interior of the hood that can be placed under vacuum,

[0009] - Removing the air within the vacuum chamber by means of a vacuum system to create a vacuum with 0.10 mbar to 950 mbar absolute pressure in the vacuum chamber.

[0010] Such a method is known, for example, from WO 2021 / 223822 A1. In the method known from this document and with the heating press known from this document, the vulcanization of a green tire takes place under vacuum. The heating press comprises a container containing a segmented vulcanization mold comprising the segments, side shells, and bead rings that shape the green tire. Heating chambers are provided for tempering the shaping parts, thus forming an external heating system. During vulcanization, the container is surrounded by a two-part, closed hood, which serves to insulate the temperature during vulcanization. A heating bladder inserted into the interior of the green tire forms an internal heating system by introducing a heating medium, for example, hot steam, under pressure into the interior of the heating bladder.Vacuum vulcanization allows a tire to be vulcanized without the need for vent valves in the vulcanization mold. The vacuum inside the hood reduces the atmospheric pressure outside the tire, creating a pressure differential between the interior of the hood and the pressure outside the hood of more than 1 bar.

[0011] To mold the green tire, the heating press is closed in two partial strokes of the hood sections. During the first partial stroke, the open end of the upper hood section is moved axially by a specific stroke in order to insert itself into the open end of the stationary lower hood section without any play. The hood sections overlap one another and are vacuum-sealed. The container and vulcanization mold remain open during this process. Before the first partial stroke, the heating bladder located in the green tire is pressurized with hot steam. This internal pressure remains unchanged or increased until the tire is molded. After the first partial stroke, the interior of the hood is placed under vacuum. During the second partial stroke, the hood is completely closed, along with the container and vulcanization mold.The internal pressure in the bladder causes the green tire to grow in the not yet closed vulcanization mold during and after the vacuum is set, so that flowable rubber material of the green tire can penetrate into the spaces between the mold parts of the vulcanization mold, the vulcanization mold is contaminated and the quality of the subsequently vulcanized tire is impaired.

[0012] The invention is based on the object of optimising the method for moulding a green tyre mentioned at the outset in such a way that undesired growth of the green tyre is prevented and contamination of the vulcanisation mould is avoided.

[0013] The stated object is achieved according to the invention in that, at the same time as the vacuum is generated in the vacuum chamber, the pressure inside the bladder is reduced in such a way that the differential pressure between the pressure in the vacuum chamber and the pressure inside the bladder is set to 0.1 bar to 0.7 and is maintained with a deviation of up to ± 0.2 bar, wherein the absolute pressure set in the bladder thus is maintained at least for the duration of reaching the minimum absolute pressure in the vacuum chamber.

[0014] The method according to the invention thus prevents the green tire from growing due to the internal bladder pressure during the critical vacuum generation phase. The internal bladder pressure is reduced and brought to a level below atmospheric pressure, thus equalizing the pressure differences. The difference between the negative pressure in the vacuum chamber and the negative pressure in the heating bladder is essentially at the level before the first partial stroke. This also ensures that the heating bladder continues to hold or fix the green tire, but without the green tire experiencing undesirable growth.

[0015] In a particularly advantageous embodiment of the invention, in a next, second partial stroke, the hood parts, the container and the vulcanization mold are closed to such an extent that the distance between the green tire and the mold parts of the vulcanization mold is reduced to approximately 1.00 mm to 2.00 mm, wherein the absolute pressure in the vacuum chamber is kept at the minimum absolute pressure and the pressure in the bladder is set such that the differential pressure between the pressure in the vacuum chamber and the pressure inside the bladder is still balanced to within + / - 0.20 bar relative to the initially set pressure. If the container and the vulcanization mold were closed completely, there is a possibility that the residual pressure in the hood would not create a sufficient vacuum and that air bubbles would remain between the tire and the mold, which would be visible on the surface of the fully vulcanized tire after vulcanization has been completed.The vulcanization mold is still slightly open, allowing the last remaining air to be removed without causing the tire to grow unevenly and without flowable rubber material creating rubber burrs by penetrating between the narrow gaps that still exist between the molded parts. It is particularly advantageous if, when / after stopping the second partial stroke, the pressure inside the heating bladder is increased to an overpressure of 0.10 bar to 1.50 bar above atmospheric pressure, while the absolute pressure in the vacuum chamber is still maintained at the minimum absolute pressure. The increase in pressure inside the heating bladder causes the tire to grow slightly to such an extent that the volume inside the vulcanization mold between the tire and the mold is reduced without causing the green tire to be pressed undesirably heavily into the vulcanization mold.The small volume also results in an absolute reduction in the remaining air volume.

[0016] In a further particularly advantageous process step for completing the forming of the tubular tire, the hood parts and, together with these, the container and the vulcanization mold are completely closed in a third partial stroke, whereby the absolute pressure in the vacuum chamber continues to be kept at the minimum absolute pressure and the pressure inside the bladder continues to be kept at the set overpressure of 0.10 bar to 1.50 bar above atmospheric pressure.

[0017] Overall, the invention ensures a gentle molding of the green tire into the heating press without damaging the green tire, whereby the process takes only a short time, in particular in the range of 30 seconds to 120 seconds.

[0018] The aforementioned reduction of the internal pressure in the bladder can be easily achieved by means of a second vacuum system.

[0019] Particularly from the beginning of the molding process up to and including the completion of the first partial stroke, it is advantageous if the pressure inside the bladder is applied or adjusted in a pulsating manner, with fluctuations of up to 0.10 bar, in order to support the escape of air between the green tire and the bladder. Further features, advantages, and details of the invention will now be described in more detail with reference to the drawing, which illustrates exemplary embodiments. In the drawings:

[0020] Fig. 1 a heating press from the prior art in the open state,

[0021] Fig. 2 the heating press from Fig. 1 in a closing phase after a first partial stroke,

[0022] Fig. 3 the heating press from Fig. 1 and Fig. 2 in closed state after a second partial stroke,

[0023] Fig. 4 is a diagram illustrating successive process phases in the molding of a green tire according to the invention into a heating press, which may be designed according to Figs. 1 to 3.

[0024] The heating press 1 shown in Figs. 1 to 3 belongs to the prior art and is a heating press as shown and described in WO 2021 / 223822 A1 and is intended for vulcanizing a green tire 8, in particular a green tire of a vehicle tire, preferably a pneumatic vehicle tire. The main components of this heating press 1 are described below, and its basic function is summarized. The heating press 1 comprises an upper press part 2, which is connected to a hood upper part 3, and a lower press part 5, which is connected to a hood lower part 4. The heating press 1 has the associated mechanisms for positioning the green tire 8 to be vulcanized, actuating the components of a vulcanization mold 6, introducing the heating media, and demolding the fully vulcanized tire.The vulcanization mold 6 is located in a container 7, which is enclosed during the vulcanization process by the hood consisting of the upper hood part 3 and the lower hood part 4. The container 7 is a conventional, state-of-the-art container which contains the

[0025] Vulcanization mold 6, here a segmented mold with a segmented ring 6a with profile elements and segmented shoes 6b as well as side shells 6c, and a locking ring 7a. A heating bladder, which is not shown, is arranged in a known manner and, before the heating press 1 is closed, is introduced into the interior of the green tire 8 positioned in the vulcanization mold 6, filled with a gas, such as a heating medium, in particular superheated steam, under pressure in order to center the green tire 8 in the mold from the inside.

[0026] The hood upper part 3 and the hood lower part 4 are designed to be airtight or vacuum-tight (Fig. 2, Fig. 3). When closed, they enclose a vacuum chamber 13 and, for this purpose, have seals 9 between the hood parts 3, 4 and a central mechanism 10. To make the closed hood consisting of the two hood parts 3 and 4 vacuum-tight, one of the seals 9 is a ring seal in the hood lower part 4.

[0027] By means of a vacuum system with a pump 11 and a vacuum tank 12, a vacuum can be generated within the closed hood, so that the otherwise usual venting valves contained in the mold surfaces of the vulcanization mold 6 can be dispensed with.

[0028] Fig. 2 shows the heating press 1 during a closing phase after a first partial stroke, with the open end of the hood upper part 3 being moved axially by a certain stroke to engage the open end of the stationary hood lower part 4 without play, with the hood parts 3 and 4 overlapping each other. The vulcanization mold 6 is open, and the hood is vacuum-sealed by the ring seal 9. To create a vacuum in the vacuum chamber 13, the connection between the vacuum tank 12 and the hood is opened.

[0029] Fig. 3 shows the heating press 1 in the closed state after a second partial stroke. After a vacuum has been created in the closed hood according to Fig. 2, the second partial stroke completely closes the vacuum-free vulcanization mold 6 and closes the connection between the vacuum tank 12 and the hood. After the tire has been vulcanized, the interior of the hood is opened via a valve, and the heating press 1 is opened to discharge the fully vulcanized tire from the vulcanization mold 6.

[0030] With reference to Figure 4, the inventive process of forming a green tire 8 until a heating press 1 is completely closed, which can basically comprise the components of the heating press 1 shown in Figures 1 to 3, will now be described. Therefore, for a better understanding of the invention, components of the heating press 1 shown in Figures 1 to 3 are mentioned in the following description, and the reference numerals assigned to them are used.

[0031] The forming process is described using successive phases 1 to 7. In Fig. 4, the time axis runs along the abscissa with time in [see], the pressure in [bar] is plotted along the left ordinate, and the distance between the upper and lower press parts in [mm] for an exemplary heating press 1 along the right. The solid line in Fig. 4 is the status line STH of the heating press 1, which has no relation to the pressure but is related to the time axis and symbolizes the current status of the heating press 1, the dash-dotted line shows the course of the pressure Pv between the hood parts 3, 4 and in the vacuum chamber 13, and the dotted line follows the course of the pressure PB inside the heating bladder.

[0032] In phase 1, the curing press 1 is open (line section a) of the status line STH), the two hood sections 3, 4 are moved apart, the green tire 8 is inserted into the open vulcanization mold 6 in a known manner, the heating bladder is located inside the green tire 8 and is pressurized from the inside by means of a gas, for example, hot steam or nitrogen, with an internal pressure of 0.10 bar to 0.70 bar (absolute), line section c), in order to fix the green tire 8. A slight pulsation of the pressure in the range of approximately 0.10 bar, symbolized by a zigzag line, supports the escape of air between the green tire 8 and the heating bladder. Outside the green tire 8 and outside the container 7 and the curing press 1, there is an atmospheric overpressure of the order of 1.00 bar, see line section b) of the dash-dotted line in phase 1.After the loader (not shown) that has been inserted into the vulcanization mold 6 with the green tire 8 has been swung out of the heating press 1, phase 2 begins. The heating press 1 is closed via a first partial stroke (analogous to Fig. 2), see the course of line section d) of the status line STH, by closing the hood parts 3, 4, so that the vacuum chamber 13 is also closed, see line section g) of the course of the status line STH. Atmospheric overpressure still prevails around the tire, see line section e) of the line Pv. The pressure PB inside the heating bladder remains at the same level as before, see line section f).

[0033] In the next phase, phase 3, the air is removed from the vacuum chamber 13 using the vacuum system. The previously existing overpressure around the green tire 8 is reduced to almost 0 bar, see line section h) of the pressure Pv line. At the same time, the pressure PB inside the bladder is reduced using another vacuum system, see line section j). In order to keep the relative overpressure inside the bladder largely constant, the pressure PB is reduced to a negative pressure relative to atmospheric pressure and until the pressure difference between the pressure Pv and the pressure PB results in a pressure PR according to the dotted line in Fig. 4, see line section i). During this time, the gas inside the bladder is removed using another vacuum system. The heating press 1 is stationary during phase 3 and is not closed any further, see horizontal line section k) of the status line STH.

[0034] In phases 1 to 3, the pressure PB inside the bladder is pulsated by up to 0.1 bar to assist the escape of air between the green tire 8 and the bladder, see jagged curve of the pressure PB.

[0035] In the subsequent phase 4, in the exemplary embodiment, there is no pulsation of the pressure PB in the heating bladder; this measure is not necessary in this phase, whereby the absolute pressure in the heating bladder is kept constant at the final pressure from phase 3, see line section n). Due to the decreasing absolute overpressure in the vacuum chamber 13 around the green tire 8, the absolute pressure in the vacuum chamber 13 (see line section m) decreases slightly further, and a constant relative overpressure is created, see line section 1) along the course of the line PR. Phase 4 lasts until the minimum absolute pressure specified by the vacuum system around the green tire 8 or in the vacuum chamber 13 is reached. The heating press 1 remains stationary during this step and does not close any further, as symbolized by the line section o) of the status line STH of the heating press 1.

[0036] In phase 5, the heating press 1 is further closed by means of a second partial stroke, see line section s) of the status line STH. This also causes the container 7 and the molded parts in the vulcanization mold 6 to close and are pushed towards the green tire 8, but only to a distance of a few millimeters, in particular 1.00 mm to 2.00 mm, between the molded parts of the vulcanization mold 6 and the green tire 8. The absolute pressure in the vacuum chamber 13 around the green tire 8 continues to be maintained at the minimum level, see line section q) in the pressure line Pv. As the volume in the vacuum chamber 13 decreases, the absolute proportion of residual air in the vacuum chamber 13 also decreases. The pressure PB in the heating bladder (see associated line section r) and the pressure PR continue to be kept constant at the level from phase 4 (see line section P).

[0037] In the next phase, phase 6, the heating press 1 stops the closing process from phase 5, see the horizontal line section w) of the status line STH of the heating press 1. At the same time, the pressure PB inside the heating bladder is increased, see line section u) in the pressure PB curve. The pressure inside the heating bladder is set to a pressure between 0.10 bar and 1.50 bar above atmospheric pressure, which creates a higher relative overpressure between the pressure PB in the heating bladder and the pressure Pv in the vacuum chamber 13 or the space around the tubular hoop 8 in the range from 1.10 bar to 2.50 bar, see line section t). The absolute pressure in the vacuum chamber 13 continues to be kept at a minimum level, see line section v) in the pressure Pv line.During this phase, the green tire 8 begins to expand slightly due to the increased relative pressure inside, while the already very small volume in the vacuum chamber 13, which may still contain residual air, becomes increasingly smaller. The vulcanization mold is still slightly open.

[0038] 6, see phase 5, allows the last remaining air to be removed without causing the tire to grow unevenly, since vulcanization mold 6 limits the maximum growth.

[0039] In the final phase of forming or closing the heating press 1 , the phase

[0040] 7, the heating press 1 is completely closed via a third partial stroke, and the closing pressure is applied to the container 7 and to hold and bring together the molded parts of the vulcanization mold 6. The heating press 1, including the container 7 and the vulcanization mold 6, is now completely closed, as shown in Fig. 3. The area around the green tire 8 remains at the minimum possible pressure level and therefore almost zero (see line section z). The pressure inside the heating bladder is still maintained at the final level from phase 6 (see line section x) of the pressure PB curve). Line section zz) in the status line STH symbolizes the third partial stroke, line section y) shows the pressure PR curve.

[0041] The duration of the phases in [see] 3 to 7 is, according to a preferred embodiment, as follows:

[0042] Phase 3: 10 to 30

[0043] Phase 4: 20 to 50

[0044] Phase 5: 5 to 15 Phase 6: 5 to 15 Phase 7: to 5

[0045] Once the container 7 has been locked, the heating process begins, typically by activating the internal heating system by further filling the bladder with the high-pressure medium, which also provides the energy for vulcanization via the internal heating system. This also presses the green tire 8 into the molding parts of the almost airless vulcanization mold 6, leaving no visible air bubbles on the tire surface.

[0046] After the vulcanization process is completed, the vacuum chamber 13 is vented, and the heating press 1 and the container 7, including the vulcanization mold 6, are opened. The vulcanized tire is released and can be unloaded.

[0047] In other designs, the heating press used for vulcanization has more than two hood parts.

[0048] List of reference symbols

[0049] 1 heating press

[0050] 2 Press upper part

[0051] 3 hood top

[0052] 4 Hood lower part 5 Press lower part

[0053] 6 Vulcanization mold

[0054] 6a Segmental ring

[0055] 6b Segment shoe

[0056] 6c side tray 7 container

[0057] 7a locking ring

[0058] 8 tires

[0059] 9 Seal

[0060] 10 Center mechanism 11 Pump

[0061] 12 Vacuum tank

[0062] 13 Hood interior a) to zz) line sections

[0063] PB Pressure in the bladder PR Differential pressure

[0064] Pv pressure around / inside the hood parts

[0065] STH status line of the heating press

Claims

Patent claims 1. A method for molding a green tire (8) into a heating press (1) with a hood comprising at least two hood parts and with a container (7) arranged in one of the hood parts, which container contains a vulcanization mold (6) having molded parts forming the outer side of the tire, comprising the following successive steps: - Loading the opened heating press (1) by placing the raw tire (8) to be vulcanized into the container (7), - Positioning a heating bladder inside the green tire (8), - Introducing a gas into the interior of the bladder and setting an internal pressure in the bladder of 0.10 bar to 0.70 bar, - closing the heating press (1) via several partial strokes of the hood parts (3, 4), whereby the hood parts (3, 4) are moved towards each other, - wherein in the first partial stroke the hood parts (3, 4) are closed to form a vacuum chamber (13) in the interior of the hood, which can be placed under vacuum, - removing the air within the vacuum chamber (13) by means of a vacuum system for generating a vacuum with 0.10 mbar to 950 mbar absolute pressure in the vacuum chamber (13), characterized in that simultaneously with the generation of the vacuum in the vacuum chamber (13) the pressure within the bladder is reduced such that the differential pressure (PB) between the pressure (Pv) in the vacuum chamber (13) and the pressure (PB) inside the bladder is set to 0.1 bar to 0.7 and is maintained with a deviation of up to ± 0.2 bar, wherein the absolute pressure (PB) set in this way in the bladder is maintained at least for the duration of the minimum absolute pressure (Pv) in the vacuum chamber (13) being reached.

2. Method according to claim 1, characterized in that in a next, second partial stroke of the hood parts (3, 4) the container (7) and the vulcanization mold (6) are closed to such an extent that the distance between the green tire (8) and the mold parts of the vulcanization mold (6) is reduced to 1.00 mm to 2.00 mm, wherein the absolute pressure (Pv) in the vacuum chamber (13) is kept at the minimum absolute pressure (PB) and the pressure inside the bladder is adjusted such that the differential pressure (PB) between the pressure (Pv) in the vacuum chamber and the pressure (PB) inside the bladder is still balanced to up to ± 0.2 bar relative to the initially set pressure.

3. Method according to claim 2, characterized in that with / after stopping the second partial stroke, the pressure (PB) inside the bladder is increased to an overpressure of 0.1 bar to 1.5 bar above atmospheric pressure, wherein the absolute pressure (Pv) in the vacuum chamber continues to be maintained at the minimum absolute pressure.

4. Method according to claim 3, characterized in that, to complete the molding of the green tire, the hood parts (3, 4) and, together with them, the container (7) and the vulcanization mold (6) are completely closed in a third partial stroke, the absolute pressure (Pv) in the vacuum chamber (13) continuing to be kept at the minimum absolute pressure and the pressure (PB) inside the heating bladder continuing to be kept at the set overpressure of 0.1 bar to 1.5 bar above atmospheric pressure.

5. Method according to one of claims 1 to 4, characterized in that the pressure (PB) inside the bladder is reduced by means of a second vacuum system.

6. Method according to one of claims 1 to 5, characterized in that at least before and immediately after the first partial stroke the pressure (PB) inside the bladder is maintained or adjusted by pulsating the pressure by up to 0.1 bar.

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