Internal mixer comprising a gas release valve

Abstract

The invention relates to an internal mixer (10) comprising a mixing chamber (12) and two mixing rotors (R1, R2), the mixing chamber comprising an inlet (14) located above the mixing rotors and an outlet (24) located below the mixing rotors, a feed hopper (16) being positioned above the inlet of the mixing chamber, the feed hopper comprising an opening (18) for loading the internal mixer with the products to be mixed, and the internal mixer comprising a ram (20), the internal mixer comprising a well (34) that passes through a wall of the mixing chamber and provides access to the upper portion (PS) of the mixing chamber, a gas release valve being fitted inside this well, the gas release valve being able to assume a closed state in which it does not allow gases to be released and an open state in which it allows gases to be released.

Description

INTERNAL MIXER INCLUDING A DEGASSING VALVE

[0001] The present invention relates to an internal mixer, for example intended for the manufacture of a rubber mixture used for the manufacture of tires.

[0002] When making a rubber compound used for tire manufacturing in an internal mixer, various gases may be released due to the increase in temperature in the mixing tank of the internal mixer.

[0003] For example, under the effect of this increase in temperature, the silicas and silanes used in the rubber mixtures used for the manufacture of tires will generate releases of water and alcohol vapors.

[0004] According to the latest developments and in order to improve certain tire performances, the quantities of silica and silane in the rubber compounds used for tire manufacturing have increased. Therefore, the rubber compounds used for tire manufacturing release more and more gases during their production in an internal mixer and these gases cause excessive pressure increases in the mixing tank of the internal mixer.

[0005] One solution to reduce pressure inside the mixing tank is to raise the internal mixer's pressure ram to create a wide opening at the mixing tank's inlet. However, this solution is not optimal.

[0006] On the one hand, to effectively vent gases before the pressure builds up in the mixing tank, it is necessary to frequently raise the pressure ram during a mixing cycle. These frequent raisings of the pressure ram reduce mixing efficiency and lead to a loss of productivity.

[0007] On the other hand, if the number of times the pressure rammer is raised is limited, the pressure increases further in the mixing tank between each rise of the pressure rammer. Therefore, the rises of the pressure ram generate sudden changes to atmospheric pressure, causing strong expansions of the gases present in the mixing tank, and these sudden expansions of the gases can cause certain quantities of products, particularly powdered products, to be expelled from the mixer and therefore lead to material losses and a loss of control over the composition of the mixture.

[0008] The present invention aims to provide a better degassing solution for internal mixers, in particular for internal mixers used for the manufacture of a rubber mixture used for the manufacture of tires.

[0009] To this end, the invention relates to an internal mixer intended for the manufacture of a rubber mixture, the internal mixer comprising a mixing tank inside which two mixing rotors are arranged, the mixing tank comprising an inlet located above the mixing rotors and an outlet located below the mixing rotors, the inlet of the mixing tank being surmounted by a feed hopper comprising an opening for introducing the products to be mixed into the internal mixer, and the internal mixer comprising a pressing ram moving in translation in the feed hopper and making it possible to press the products to be mixed onto the mixing rotors.

[0010] According to the invention, the internal mixer comprises a well passing through a wall of the mixing tank and providing access to the upper part of the mixing tank which is located above the mixing rotors, and a degassing valve is installed in this well, the valve being able to take a closed state in which it does not allow the evacuation of gases from the mixing tank and an open state in which it allows the evacuation of gases from the mixing tank.

[0011] Advantageously but not necessarily, the invention may also provide that: - the valve comprising an elongated hollow body making it possible to form a conduit for discharging gases from the mixing tank, the valve comprises a valve mounted movably at a first end of the hollow body which is located as close as possible to the internal volume of the mixing tank, - the valve is conical in shape and mounted inverted with respect to the direction of gas discharge, the largest section of the valve being located on the side of the internal volume of the mixing tank, - the valve is mounted at the end of a rod mounted to slide in translation inside the elongated hollow body and driven in translation by a jack mounted on the second end of the elongated hollow body which is located towards the outside of the mixing tank, - the internal mixer comprising a suction circuit for the gases resulting from the mixing, the degassing valve of the internal mixer is connected to this suction circuit.

[0012] The invention also relates to a mixing method using an internal mixer according to the invention, for example for producing a rubber mixture and for example for producing a rubber mixture intended for the manufacture of tires.

[0013] According to this mixing method, the degassing valve is in its closed state when one or more products are introduced into the mixing tank of the internal mixer.

[0014] Still according to this mixing process, and when the internal mixer is also equipped with a temperature sensor to provide information on the temperature inside the mixing tank, the degassing valve is brought to its open state when the temperature in the mixing tank exceeds a certain threshold, for example 80°C when the mixture produced is a rubber mixture used for the manufacture of tires.

[0015] Other characteristics and advantages of the invention will appear in the description which follows. This description, given by way of example and not as a limitation, refers to the attached drawings in which: - [Fig.l] is a schematic front and sectional view of an internal mixer according to the invention, - [Fig.2] is a detailed schematic view of the installation of a degassing valve on the mixing tank of an internal mixer according to the invention, - [Fig.3] is a schematic sectional view of a degassing valve that can be mounted on the mixing tank of an internal mixer according to the invention.

[0016] The invention relates to an internal mixer, for example intended for the manufacture of a rubber mixture used for the manufacture of tires.

[0017] Preferably, and as illustrated in Figure 1, such an internal mixer 10 comprises a mixing tank 12 inside which are arranged two mixing rotors R1, R2. The mixing tank 12 is preferably formed by two cylindrical half-tanks DC1, DC2 joined to each other and whose internal volumes communicate with each other. A rotor is installed in each of the cylindrical half-tanks DC1, DC2. The two rotors mixing rotors are preferably mounted on bearings and driven in rotation by separate motors. Preferably, the two mixing rotors are counter-rotating, i.e. driven in rotation in opposite directions.

[0018] For the purpose of producing a mixture, the mixing tank 12 comprises an inlet 14 located above the mixing rotors R1, R2. This inlet 14 of the mixing tank is surmounted by a feed hopper 16 comprising an opening 18 for introducing the products to be mixed into the internal mixer. For example, the feed hopper 16 takes the form of a vertical hollow column rising above the mixing tank 12. The feed hopper 16 is connected in a sealed manner to the inlet 14 of the mixing tank so as to form a continuous feed conduit with the inlet 14 of the mixing tank up to the mixing rotors R1, R2. For example, the feed hopper 16 and the inlet 14 of the mixing tank form a hollow parallelepiped conduit whose hollow section is parallelepiped.

[0019] For the purpose of carrying out the mixing, the internal mixer 10 comprises a pressing ram 20 moving in translation T, illustrated by a double arrow in FIG. 1, in the feed hopper 16 and making it possible to press the products to be mixed onto the mixing rotors R1, R2. When the feed hopper 16 and the inlet 14 of the mixing tank form a hollow parallelepiped conduit, the pressing ram 20 is parallelepiped. Preferably, the external dimensions of the pressing ram 20 correspond, apart from the sliding clearance, to the internal dimensions of the hollow conduit formed by the feed hopper 16 and the inlet 14 of the mixing tank. The pressing ram 20 is preferably driven in translation T in the feed hopper 16 and the inlet 14 of the mixing tank by a jack 22, for example mounted above the column formed by the feed hopper 16.

[0020] For the evacuation of the mixture produced after a mixing cycle, the internal mixer comprises an outlet 24 located under the mixing rotors R1, R2. This outlet 24 takes the form of an opening 26 provided in the bottom of the mixing tank and which can be closed using one or two flaps 28.

[0021] Like the outlet of the mixing tank, the opening 18 of the feed hopper 16 can also be closed, for example using a pivoting flap 30. This pivoting flap 30 forms an inclined face in the open position for the introduction of the products to be mixed, and it forms a vertical wall of the feed hopper when it is in the closed position, for example during a mixing cycle.

[0022] Advantageously, the mixing tank 12 is raised on a support 32 allowing a container C for receiving the mixture to be introduced under the outlet 24 of the mixing tank.

[0023] In order to allow the gases to be evacuated from the mixing tank during mixing, the internal mixer 10 comprises a well 34 passing through a wall 36 of the mixing tank 12 and giving access to the upper part PS of the mixing tank located above the mixing rotors R1, R2, and a degassing valve 38 is installed in this well 34, as shown in the detailed sectional view in FIG. 2.

[0024] Advantageously, the valve can take a closed state in which it does not allow the evacuation of gases from the mixing tank and an open state in which it allows the evacuation of gases from the mixing tank.

[0025] Preferably, the wall 36 crossed by the well 34 and in which the degassing valve 38 is installed is a side wall of the mixing tank, for example one of the side walls of the mixing tank which is located opposite the ends of the two mixing rotors R1, R2.

[0026] For example, the well 34 in which the degassing valve 38 is installed is a well provided by the manufacturer of the internal mixer 10 to receive a temperature sensor.

[0027] Preferably, the well 34 and the degassing valve 38 are cylindrical. For example, the degassing valve 38 comprises an elongated hollow body 40 making it possible to form a conduit 41 for discharging gases from the mixing tank. To allow or block the gases from escaping, and as illustrated in FIG. 3, the degassing valve 38 comprises a valve 42 mounted movably at a first end E1 of the hollow body 40 which is mounted as close as possible to the internal volume of the mixing tank 12. In more detail, the valve 42 is moved in translation at the first end E1 of the hollow body 40 between a closed position, illustrated in continuous lines in FIG. 3 and in which it closes this first end E1 of the hollow body 40, and an open position, illustrated in broken lines in FIG. 3 and in which it allows the gases to pass through this first end E1 of the hollow body 40.For this purpose, the valve 42 is mounted at the end of a rod 44 mounted to slide in translation inside the elongate hollow body 40 and driven in translation by a jack 46 mounted on the second end E2 of the elongate hollow body which is located towards the outside of the mixing tank 12.

[0028] For example, the cylinder 46 actuating the valve 42 is of the single-acting type, its return to position being ensured by a spring mounted on the rod 44 and placed in abutment.

[0029] Advantageously, the degassing valve 38 comprises an intermediate guide element 48 for guiding the rod 44 relative to the elongate hollow body 40. This intermediate guide element 48 is located approximately halfway along the length of the elongate hollow body 40 and it allows the rod 44 to be centered inside the elongate hollow body 40. This intermediate guide element 48 is perforated so as not to block the gas discharge conduit 41 formed by the elongate hollow body 40.

[0030] In order to allow the gases to be evacuated to the outside of the mixing tank 12 when the valve 42 is in the open position, the gas evacuation conduit 41 formed by the elongate hollow body 40 comprises an outlet 50 located near the second end E2 of the elongate hollow body. In the case where the internal mixer 10 comprises a suction circuit CA for the gases resulting from the mixing, the degassing valve 38 of the internal mixer is connected to this suction circuit CA via the outlet 50 of the gas evacuation conduit 41 formed by the elongate hollow body 40.

[0031] In order to prevent the mixture from entering the discharge duct 41 of the degassing valve when the valve is in the open position, the valve 42 is conical in shape and mounted in an inverted manner relative to the gas discharge direction G, the largest section of the valve 42 being located on the side of the internal volume of the mixing tank. The gas discharge direction G extends from the first end E1 of the hollow body 40 where the valve is located to the second end E2 of the hollow body 40 where the outlet 50 of the discharge duct 41 is located. Advantageously, the angle of the cone formed by the valve 42 can be adapted to best prevent the mixture from entering the discharge duct 41 of the degassing valve.

[0032] Alternatively, the valve 42 may take the form of a half-sphere mounted invertedly relative to the direction of gas discharge G, the largest section of the half-sphere being located on the side of the internal volume of the mixing tank.

[0033] For the purpose of mounting the degassing valve 38 on the mixing tank, the elongate hollow body 40 comprises means for fixing to a wall of the mixing tank. For example, the elongate hollow body 40 comprises an annular flange 54 intended to be fixed with screws to the wall of the mixing tank which receives a well 34.

[0034] Advantageously, the internal mixer comprises a second well 34 (not shown) preferably passing through another wall of the mixing tank 12, such as for example the wall opposite the wall in which the first well 34 is provided, and giving access to the upper part PS of the mixing tank located above the mixing rotors R1, R2. This second well 34 is preferably used for the installation of a temperature sensor (not shown) making it possible to provide information on the temperature inside the mixing tank 12. Advantageously, this temperature sensor is connected to the control unit controlling the operation of the degassing valve 38. Thus, the opening and closing of the valve 42 of the degassing valve 38 can be controlled as a function of the temperature measured inside the mixing tank 12.

[0035] The invention also relates to a mixing method using an internal mixer 10 equipped with a degassing valve 38 as has just been described, and which can also be equipped with a temperature sensor as has just been described.

[0036] For example, the mixing method uses an internal mixer 10 according to the invention for producing a rubber mixture.

[0037] According to this mixing method, the degassing valve is in its closed state when one or more products are introduced into the mixing tank of the internal mixer. This prevents products from entering the discharge conduit 41 of the degassing valve. Thus, the degassing valve is closed when the products to be mixed are introduced into the internal mixer before mixing is carried out, or when one or more new products are introduced into the mixture during mixing.

[0038] Still according to this mixing process, the degassing valve is brought to its open state when the temperature in the mixing tank exceeds a certain threshold, for example 80°C when the mixture produced is a rubber mixture used for the manufacture of tires. Indeed, when producing a rubber mixture comprising silica and silanes, alcohol vapors are released by the silanes contained in the mixture from this temperature of 80°C. From 100°C, water vapors are released by the mixture and more particularly by the silica contained in the mixture. Of course, under the effect of mixing and depending on the components of the mixture, other gases can be released by the mixture and must be evacuated to avoid excessive pressurization of the mixing tank and excessively violent expansions.

[0039] To protect the AC suction circuit pipes from exposure to gases at temperatures that are too high to damage them, the mixing process may also provide for the degassing valve to return to its closed state when the temperature in the mixing tank exceeds another threshold, for example 160°C.

Claims

Claims 1. Internal mixer (10) for manufacturing a rubber mixture, the internal mixer comprising a mixing tank (12) inside which two mixing rotors (R1, R2) are arranged, the mixing tank comprising an inlet (14) located above the mixing rotors and an outlet (24) located below the mixing rotors, the inlet of the mixing tank being surmounted by a feed hopper (16) comprising an opening (18) for introducing the products to be mixed into the internal mixer, and the internal mixer comprising a pressing ram (20) moving in translation in the feed hopper and making it possible to press the products to be mixed onto the mixing rotors, the internal mixer being characterized in that it comprises a well (34) passing through a wall (36) of the mixing tank and giving access to the upper part (PS) of the mixing tank which is located above the mixing rotors,and in that a degassing valve (38) is installed in this well, the degassing valve (38) being able to take a closed state in which it does not allow the evacuation of gases from the mixing tank and an open state in which it allows the evacuation of gases from the mixing tank., 2. Internal mixer according to claim 1, in which, the degassing valve (38) comprising an elongated hollow body making it possible to form a conduit for discharging gases from the mixing tank, the degassing valve (38) comprises a valve (42) mounted movably at a first end (El) of the hollow body (40) which is mounted as close as possible to the internal volume of the mixing tank.

3. Internal mixer according to claim 2, in which the valve is conical in shape and mounted in an inverted manner relative to the gas discharge direction (G), the largest section of the valve being located on the side of the internal volume of the mixing tank.

4. Internal mixer according to one of claims 2 or 3, in which the valve (42) is mounted at the end of a rod (44) mounted to slide in translation inside the elongate hollow body (40) and driven in translation by a jack (46) mounted on the second end (E2) of the elongate hollow body which is located towards the outside of the mixing tank.

5. Internal mixer according to one of the preceding claims, in which, the internal mixer comprising a suction circuit (CA) for the gases resulting from the mixing, the degassing valve of the internal mixer is connected to this suction circuit.

6. Mixing method using an internal mixer (10) according to one of claims 1 to 5.

7. Mixing method according to claim 6, wherein the internal mixer (10) is used for producing a rubber mixture such as a rubber mixture intended for the manufacture of tires.

8. A mixing method according to claim 6 or claim 7, wherein the degassing valve is in its closed state when one or more products are introduced into the mixing tank of the internal mixer.

9. Mixing method according to claim 8, wherein, the internal mixer (10) also being equipped with a temperature sensor making it possible to provide information on the temperature inside the mixing tank (12), the degassing valve is brought to its open state when the temperature in the mixing tank exceeds a certain threshold.

10. A mixing method according to claim 9, wherein the degassing valve is brought to its open state when the temperature in the mixing tank exceeds 80°C.

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