Valve Device for Injecting Gas into a Mixing Chamber of a Plastic Metering Device, and Plastic Metering Device

Abstract

The invention relates to a valve device (50) for injecting gas (4) into a mixing chamber (11) of a plastic metering device (1) in order to load at least one component (2) located in the mixing chamber (11) with the gas, comprising a pressure regulating valve (51) and a flow regulator (52), wherein an inlet (56) of the pressure regulating valve (51) is connected to an outlet (55) of the flow regulator (51), and an outlet (71) of the pressure regulating valve (51) is suitable for opening preferably directly into the mixing chamber (11). The pressure regulating valve (51) has a valve chamber (57), an actuator (58) which can be moved in the valve chamber (57), and a piston unit (59) which is coupled to the actuator (58) and by means of which an axial position of the actuator (58) can be fixed on the basis of a pressure in the valve chamber (57). The invention additionally relates to a metering device (1) for metering out a foamed and foamable plastic (5) in a discontinuous manner, comprising such a valve device (50).

Claims

1. A valve device (50) for injecting gas (4) into a mixing chamber (11) of a plastic metering device (1) for loading at least one component (2) located in the mixing chamber (11) with gas, comprising: a pressure regulating valve (51) and a flow regulator (52), wherein an inlet (56) of the pressure regulating valve (51) is connected to an outlet (55) of the flow regulator (52), and an outlet (71) of the pressure regulating valve (51) can open directly into the mixing chamber (11), wherein the pressure regulating valve (51) has a valve chamber (57), a needle (58) that can be moved in the valve chamber (57), and a piston unit (59) coupled to the needle (58), by means of which an axial position of the needle (58) can be fixed as a function of a pressure in the valve chamber (57).

2. The device (50) according to claim 1, wherein the piston unit (59) has a pressure guide piston (60) and a closing piston (61), wherein the pressure guide piston (60) serves for pressure regulation, and the closing piston (61) serves for closing the pressure regulating valve (51).

3. The valve device (50) according to claim 2, wherein a spring element is arranged between the pressure guide piston (60) and a preferably adjustable abutment (69).

4. The valve device (50) according to claim 3, wherein a spring (73) presses the closing piston (61) into a rest position in which the closing piston (61) and pressure guide piston (60) are decoupled from one another.

5. The valve device (50) according to claim 2, wherein, in a closing position of the needle (58), the closing piston (61) presses against the pressure guide piston (60), which in turn presses against the needle (58) and holds it in the closing position.

6. The valve device (50) according to claim 2, wherein the needle (58), the pressure guide piston (60), and the closing piston (61) are arranged coaxially with one another.

7. The valve device (50) according to claim 1, wherein the valve chamber (57) is delimited by a membrane (62) which is arranged between the needle (58) and the piston unit (59).

8. The valve device (50) according to claim 7, wherein the needle (58) is coupled to the piston unit (59) by magnetic force.

9. The valve device (50) according to claim 7, wherein magnets (63, 64) are arranged on two opposite sides of the membrane (62), wherein the magnetic force acts through the membrane (62).

10. The valve device (50) according to claim 7, wherein a magnet is arranged on one side of the membrane (62) and a ferromagnetic counterpart is arranged on the opposite side, wherein the magnetic force acts through the membrane (62).

11. The valve device (50) according to claim 1, wherein the actuator (58) is made of plastic.

12. The valve device (50) according to claim 1, wherein the actuator (58) is made of PEEK.

13. The valve device (50) according to claim 1, wherein a volume between the outlet (55) of the flow regulator (52) and the outlet (71) of the pressure regulating valve (51) is less than 5 cm.sup.3.

14. The valve device (50) according to claim 1, wherein a check valve (74) is provided between the outlet (55) of the flow regulator (52) and the inlet (56) of the pressure regulating valve (51).

15. The valve device (50) according to claim 1, wherein the flow regulator (52) is designed as a mass flow controller (52).

16. The valve device (50) according to claim 1, wherein the flow regulator (52) is designed as a mass flow controller (52) having a calorimetric flow meter as a measuring sensor.

17. A metering device (1) for the preferably discontinuous metering of a foamed or foamable plastic, comprising the valve device (50) according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention is explained in more detail with reference to the embodiments shown in the drawings. In the figures:

[0023] FIG. 1 shows a plastic metering device according to the invention;

[0024] FIG. 2 shows a mixing device of the plastic metering device; and

[0025] FIG. 3 shows a pressure regulating valve as part of a valve device according to the invention.

[0026] FIG. 1 schematically shows a plastic metering device which is denoted in its entirety by 1. The plastic metering device 1 serves for the preferably discontinuous metering of a plastic which is already (partially) foamed when dispensed from the plastic metering device 1, or which foams or continues to foam after dispensing.

[0027] The plastic metering device 1 comprises a mixing device 10 and a valve device 50. In the mixing device 10, a first component 2 and a second component 3 can be fed into a mixing chamber 11 in which a rotatably mounted stirrer 30 is arranged. In the mixing chamber 11, the two components 2, 3 are mixed together to form a plastic 5. For example, the first component 2 can be a mixture of polyol and water, which reacts with isocyanate as the second component 3 in the mixing chamber 11 to form polyurethane. This produces CO.sub.2, which causes the polyurethane to foam, or it can (continue to) foam after it has been metered out of the mixing chamber 11.

[0028] In addition, a gas 4 is fed to the mixing chamber 11, the quantity of which is precisely regulated by the valve device 50. For this purpose, the valve device 50 has a pressure regulating valve 51 and a flow regulator in the form of a mass flow controller 52, which are connected to one another by a connection unit 53. A pressurized expanding gas 6 is supplied to an inlet 54 of the mass flow controller 52.

[0029] The gas 4 is injected directly into a first mixing region 11a of the mixing chamber 11 and mixed or finely distributed into the first component 2 by the stirrer 30. This creates small microbubbles in the first component 2. The premixture then flows via a gap 34 into a second mixing region 11b of the mixing chamber 11. The microbubbles promote a particularly homogeneous and fine foam structure, which is described in more detail below.

[0030] An outlet 55 of the mass flow controller 52 is connected to an inlet 56 of the pressure regulating valve 51 via the connection unit 53.

[0031] FIG. 2 shows the mixing device 10 in isolation. The stirrer 30 is in this case substantially rotationally symmetrical with respect to an axis of rotation 31. The stirrer 30 is driven by a drive shaft 12, which is only partially shown. The stirrer 30 has a pin-shaped shaft connection 32 for the connection to the drive shaft 12. Preferably, the connection between the drive shaft 12 and the shaft connection 32 is a non-positive connection.

[0032] Three inlet openings are provided in the housing of the mixing device 1: for one, there is a first inlet opening 13 through which the first component 2 can be fed into the mixing chamber 11. A second inlet opening 14 for the second component 3 is provided at an axial distance from the first inlet opening 13. The axial distance between the first inlet opening and the second inlet opening 14 can be a few millimetersfor example, 3 to 20 mm.

[0033] At the same axial height as the first inlet opening 13, a gas inlet opening 15 is provided, through which the gas 4 can be injected into the mixing chamber 11. The gas 4 is preferably air (the gas can also be nitrogen or CO.sub.2).

[0034] The plastic or polyurethane foam exits the mixing chamber 11 through an outlet opening 16, which is arranged coaxially with the axis of rotation 31 and is located at an axial end 17 of the mixing chamber 11. The outlet opening 16 is formed by a nozzle 18. An inner diameter of the nozzle 18 can, for example, be 1 to 8 mm or 2 to 5 mm. A length of the nozzle 18 can be 2 to 50 mm or 30 mm. The produced plastic exits the mixing chamber 11 in an axial direction.

[0035] The stirrer 30 has a cylindrical shaft collar 33, the outer diameter of which is slightly smaller than an inner diameter of the cylindrical mixing chamber 11. The radial gap 34 between the shaft collar 33 and a mixing chamber wall 19 can be regarded as part of a throttle or flow brake, by which the mixing chamber 11 is divided into the first mixing region 11a and the second mixing region 11b.

[0036] The stirrer 30 can be moved in the axial direction (in the direction of the axis of rotation 31). FIG. 2 shows the stirrer 30 in an axial position in which an outlet gap 36 is provided between a conical stirrer tip 35 of the stirrer 30 and a funnel-shaped insert 20 which is arranged at the axial end 17 of the mixing chamber 11. As a result, it is possible for the plastic that has been produced in the mixing chamber 11 to exit the mixing device 1 through the nozzle 18. In a closed position, the conical stirrer tip 35 rests on the insert 20, thereby closing the outlet gap 36. In the closed position of the stirrer 30, the outlet opening 16 is thus closed. The axial extension of the gap between the stirrer tip 35 and the insert 20 can assume values between 0 mm (closed position) and 2.5 mm. The axial position of the stirrer 30 and/or the axial extension of the outlet gap 36 can be used to set a specific pressure in the mixing chamber 11. Means for precisely adjusting the axial position of the stirrer 30 are not shown in FIG. 2.

[0037] The axial stroke or gap (difference between the closed position and an upper end position) is dimensioned such that the shaft collar 33 and/or the flow brake is always located between the first inlet opening 13 and the second inlet opening 14 when viewed in the axial direction. As a result, the first inlet opening 13 and the gas inlet opening, which is offset by 180 in this exemplary embodiment, always open into the first mixing region 11a of the mixing chamber 11. The second inlet opening 14, however, always opens into the second mixing region 11b, regardless of the axial position of the stirrer 30.

[0038] For dividing the gas 4 and/or for mixing it with the first component 2, the stirrer 30 has first means 38 on a first axial portion 37. The first axial portion 37 of the stirrer 30 is located in the first mixing region 11a of the mixing chamber 11. The first mixing region 11a is delimited by the shaft collar 33 and a seal 21 which is inserted between the drive shaft 12 and the mixing chamber wall 19. In a second axial portion 39, which extends from the shaft collar 33 to the stirrer tip 35, second means 40 are provided for mixing a premixture, comprising the first component 2 and the gas 4, with the second component 3. The second axial portion 39 is located in the second mixing region 11b of the mixing chamber 11. The first means 38 and the second means 40 may include projections protruding radially outwards that plow through the corresponding material in the mixing chamber 11 as the stirrer 30 rotates.

[0039] Before the pressure regulating valve 51 of the valve device 50 is discussed in more detail, the operation of the mixing chamber 1 will be briefly described, focusing on the metering of the polyurethane or the polyurethane foam 5. Polyol with water as the first component 2 is fed to the first mixing region 11a through the first inlet opening 13. At the same time, air is injected into the first mixing region 11a through the gas inlet opening 15. By rotating the stirrer 30, and thus also by rotating the first means 38, the injected gas 4 is distributed into the first component 2. This creates small microbubbles of gas, which are finely distributed in the first component 2. The speed of the stirrer can be 1,000 to 6,000 rpm or 1,500 to 4,000 rpm.

[0040] Due to the pressure present in the first mixing region 11a, the premixture from the first mixing region 11a passes through the radial gap 34 into the second mixing region 11b. There, the premixture (polyol, water, microbubbles) is mixed with isocyanate (second component 3) by the second means 40. During the reaction of polyol, water, and isocyanate, CO.sub.2 is produced in addition to polyurethane. The microbubbles act as nuclei for the formation of CO.sub.2 bubbles, which form foam cells in the polyurethane. The polyurethane can be metered out of the mixing chamber 11 through the outlet opening 16. Due to the throttling effect of the flow brake and/or the radial gap 34, a (small) pressure gradient is created between the first mixing region 11a and the second mixing region 11b. The pressure gradient ensures that there is practically no flow from the second mixing region 11b into the first mixing region 11a. This prevents isocyanate or a mixture of isocyanate, polyol, and water from entering the first mixing region 11a and causing undesirable contamination there.

[0041] When a metering process is to be terminated, the stirrer 30 is moved from the position shown in FIG. 2 to the closing position in order to close the outlet opening 16. The drive shaft 12 is braked so that the stirrer 30 no longer rotates within the mixing chamber 11. The axial lowering of the stirrer tip 35 until it rests on the insert 20 and the running down of the stirrer 30 can be coordinated in such a way that the stirrer tip 35 cleans and clears the insert 20 by a residual rotation. At the same time, the valve device 50 is closed to prevent polyol from entering the valve device 50, or too much gas from accumulating in the first mixing region 11. Due to the closed valve device 51 and the closed outlet opening 16, the mixing chamber is sealed off from the environment after the metering process has ended. At the beginning of another metering process, the two components 2, 3 and the gas 4 are again fed into the mixing chamber, with the stirrer 30 rotating and axially displaced.

[0042] FIG. 3 shows the pressure regulating valve 51 on an enlarged scale. The pressure regulating valve 51 is designed as a needle valve that has a valve chamber 52, a needle 58 that can be moved in the valve chamber 52 as an actuator, and a piston unit 59 coupled to the needle 58. The piston unit 59 comprises a pressure guide piston 60 and a closing piston 61. Between the piston unit 59 and the needle 58, a membrane 62 is arranged, which defines and seals the valve chamber 57.

[0043] The coupling between the needle 58 and the piston unit 59 is achieved by two magnets 63, 64, which are designed as disc magnets made of neodymium. The magnetic force between these two magnets acts through the membrane 62. The needle 58 is firmly connected to the magnet 63 via a needle holder 65for example, by means of an adhesive connection. The magnet 64 is inserted in an intermediate piece 66, against which magnet a spherical cap 75 of the pressure guide piston 60 rests. The membrane 62 is fixed in a valve housing 68 by a threaded sleeve 67.

[0044] A coil spring 70 is arranged between the pressure guide piston 60 and an axially adjustable abutment 69 in the form of a screw sleeve and presses the pressure guide piston 60 and thus also the needle 58 to the left in the illustration in FIG. 3. The force with which the coil spring 70 presses against the pressure guide piston 60 depends upon the axial position of the screw sleeve 69. The axial position can be precisely adjusted by turning the screw sleeve 69.

[0045] If the needle 58 is moved all the way to the left, it is in a closed position in which an outlet 71 of the pressure regulating valve 51 is closed. Via the membrane 62 and the intermediate piece 66, a force opposite to the force of the coil spring 70 acts upon the pressure guide piston 60, which force depends upon the pressure in the valve chamber 57 and/or upon the pressure at the inlet 56 of the pressure regulating valve 51. If the pressure guide piston 60 is in force equilibrium, the needle 58 is not moved within the valve chamber 57. If the pressure in the valve chamber 57 drops, the force that pushes the pressure guide piston 60 to the right in the illustration in FIG. 3 also drops. Accordingly, the needle 58 is displaced to the right due to the now no longer fully compensated force of the coil spring, wherein the outlet 71 is closed and/or the flow cross-section at the outlet 71 is reduced. This causes the pressure in the valve chamber 57 to rise again, with the result that the equilibrium of forces on the pressure guide piston 60 is restored.

[0046] The closing piston 61 serves to close the outlet 71 of the pressure regulating valve 51 when a metering process on the plastic metering device 1 and thus also the supply of the gas 4 are to be terminated. In this case, the closing piston 61 is pressurized with compressed air through an air supply 72, so that the closing piston presses against the pressure guide piston 60 against the force of another coil spring 73. This overrides the otherwise prevailing balance of forces between the pressure in the valve chamber 57 and the force of the coil spring 70. The needle 58 is thus moved into the closed position and held there, independently of the pressure in the valve chamber 57. If gas 4 is to flow out of the pressure regulating valve 51 again, the compressed air supply to the closing piston 61 is terminated. The coil spring 73 then presses the closing piston back into a rest position in which the closing piston 61 exerts no force on the pressure guide piston 60.

[0047] The connection unit 53, which is arranged between the outlet 55 of the mass flow controller 52 and the inlet 56 of the pressure regulating valve 51, comprises a check valve 74 (see FIG. 1) which protects the mass flow controller 52 from an entry of the first component 2 should the pressure regulating valve 51 be damaged and unable to prevent the flow of the first component 2 through the valve chamber 57.

LIST OF REFERENCE SIGNS

[0048] 1 mixing chamber [0049] 2 first component [0050] 3 second component [0051] 4 gas [0052] 5 plastic (polyurethane foam) [0053] 6 expanding gas [0054] 10 mixing device [0055] 11 mixing chamber (11a first mixing region; 11b second mixing region) [0056] 12 drive shaft [0057] 13 first inlet opening [0058] 14 second inlet opening [0059] 15 gas inlet opening [0060] 16 outlet opening [0061] 17 axial end [0062] 18 nozzle [0063] 19 mixing chamber wall [0064] 20 insert [0065] 21 seal [0066] 30 stirrer [0067] 31 axis of rotation [0068] 32 pin-shaped shaft connection [0069] 33 shaft collar [0070] 34 radial gap [0071] 45 stirrer tip [0072] 36 outlet gap [0073] 37 first axial portion [0074] 38 first means [0075] 39 second axial portion [0076] 40 second means [0077] 50 valve device [0078] 51 pressure regulating valve [0079] 52 flow regulator/mass flow controller [0080] 53 connection unit [0081] 54 mass flow controller inlet [0082] 55 mass flow controller outlet [0083] 56 pressure regulating valve inlet [0084] 57 valve chamber [0085] 58 needle [0086] 59 piston unit [0087] 60 pressure guide piston [0088] 61 closing piston [0089] 62 membrane [0090] 63 magnet [0091] 64 magnet [0092] 65 needle holder [0093] 66 intermediate piece [0094] 67 threaded sleeve [0095] 68 valve housing [0096] 69 abutment/screw sleeve [0097] 70 coil spring [0098] 71 pressure regulating valve outlet [0099] 72 air supply [0100] 73 coil spring piston unit [0101] 74 check valve [0102] 75 spherical cap