Apparatus and method for mixing

Abstract

In a method for mixing two liquid components of a medium with the aid of a static mixer, the two components are supplied to the static mixer, are mixed therein and are subsequently dispensed from the mixer. In this respect, only one respective component is supplied to the mixer, while the other component is not supplied to the mixer.

Claims

1. A method for mixing two liquid components of a medium with the aid of a static mixer, wherein the two liquid components are supplied to the static mixer, are mixed therein and are subsequently dispensed from the static mixer as a medium, wherein only one of the two liquid components is supplied to the static mixer, while the other of the two liquid components is not supplied to the static mixer, and vice versa, the two liquid components being supplied to the static mixer in a cycled manner, the medium being dispensed in the form of droplets having the same size, with the droplets being dispensed from the static mixer in consecutive cycles after the mixing, and wherein a mixing ratio of the two liquid components is set by a number of cycles during which the respective liquid component is supplied to the static mixer.

2. The method in accordance with claim 1, wherein each of the two liquid components is pumped into the static mixer via its own pump device, with the two own pump devices being controlled independently of one another.

3. The method in accordance with claim 1, wherein the mixed medium is dispensed out of the static mixer in droplets of equal size through a metering valve which is operated at a frequency of more than 50 Hz, at least in specific time intervals.

4. The method in accordance with claim 1, wherein the two liquid components are supplied to the static mixer via a single mixing valve.

5. The method in accordance with the claim 4, wherein the mixed medium is dispensed out of the static mixer in droplets of equal size through a metering valve which is operated at a frequency of more than 50 Hz, at least in specific time intervals; and wherein the metering valve and the mixing valve are synchronized.

6. The method in accordance with claim 5, wherein the metering valve and the mixing valve are synchronized with an adjustable phase shift.

7. The method in accordance with claim 5, wherein the mixing valve is actuated between two opening strokes of the metering valve.

8. The method in accordance with claim 1, wherein the medium is dispensed out of the static mixer in droplet form; and wherein the droplet size is set by changing the pressure at which the two liquid components are introduced into the static mixer.

9. The method in accordance with claim 1, wherein the pressure at which the two liquid components are introduced into the static mixer is selected as larger than 20 bar.

10. The method in accordance with claim 1, wherein a volume of the two liquid components supplied to the static mixer is determined.

Description

(1) The present invention will be described in the following purely by way of example with reference to an advantageous embodiment and to the enclosed drawings. There are shown:

(2) FIG. 1 a schematic representation of a metering apparatus;

(3) FIG. 2 a part enlargement of FIG. 1;

(4) FIG. 3 a partly sectional view of a mixing valve;

(5) FIG. 4 a partly sectional view of a mixing apparatus; and

(6) FIG. 5 a view of the mixing apparatus of FIG. 4 with a removed mixing coil.

(7) The metering apparatus shown schematically in FIG. 1 comprises a metering valve 10 through which two-component adhesive can be jetted in droplet form. For this purpose, the metering valve 10 can be controlled at radio frequency via a valve drive 12 which is controlled by a control 14. Reference numeral 16 designates a device for the temperature control of the valve.

(8) The two components of the medium to be mixed are located in two separate reservoirs 18 and 20 and are conveyed from there into a pump device 22 from where the two components are separately supplied to a static mixer 24 having a mixing coil 26. In this respect, a mixing valve 28 is provided for the separate supply of the two components through which only a respective one component is supplied to the mixer 24, while the other component is not supplied to the mixer, and vice versa. In other words, the two components are introduced alternately into the mixer 24, but never simultaneously.

(9) A control processor 30 is provided for controlling the metering apparatus and is connected via a control line 32 to a microcontroller 34 of the mixing valve 28. The control processor 30 is furthermore connected to the microcontroller 14 of the metering valve 10 via a synchronization line. Finally, the control processor 30 is also connected via a further control line 38 to a microcontroller of a pressure regulator 40 which regulates the pump pressure for the pump device 22.

(10) The described pump apparatus has two pneumatic connectors P and R which are both connected to the pressure regulator 40 and to an adjustable pressure regulation valve 42 via which the two reservoirs 18 and 20 are pressurized by, for example, approximately 2 to 3 bar to introduce the component contained in the respective reservoir into the pump device 2.

(11) The pump device 22 will be described in more detail in the following with reference to FIG. 2.

(12) Two pump pistons 44 and 46 are provided separately for each component in the pump device 22 and can have compressed air applied to them via pneumatic valves such that they carry out consecutive pump strokes. The control of the two pump pistons 44 and 46 takes place independently of one another by a control 48. Further control electronics 50 are connected to sensors 52 and 54 which detect the respective pump stroke of a pump piston, whereby a path measurement of the pump stroke is possible and thus the volume of the pumped component can be determined.

(13) As FIG. 2 illustrates, the two reservoirs 18 and 20 are connected via a respective line and via a check valve 56 and 58 respectively to a pump space 60 or 62 respectively into which the respective pump piston 44 and 46 respectively is moved to and fro. Each component can first be introduced in this manner separately from the other from the reservoir 18 or 20 into the pump space 60 or 62 and can be pumped from there via discharge lines 64 and 66 to the mixing valve 28 (FIG. 1).

(14) The mixing valve 28 will be described in more detail in the following with reference to FIG. 3.

(15) FIG. 3 shows a partly sectional view of the mixing valve 28 which is provided with a drive 70 in the form of a piezoelectric torque block of the applicant. Two piezoelectric stacks are integrated into this drive and the drive can carry out a tilt movement about the center of gravity of the drive 70 in the direction of the double arrow with their aid.

(16) The valve drive 70 is connected to a yoke 72 whose two arms 74 and 76 act on a respective valve needle 77 and 78 which closes a valve seat 80, 82 via a valve ball connected thereto. The two valve needles 77 and 78 are each connected via adjustable plungers 84, 86 to the arms 74, 76 of the yoke 72 to set the opening stroke exactly. The supply lines 64 and 66 coming from the pump device open into the region of the respective valve seat 80, 82 so that the respective component is applied at pressure at the respective valve seat 80, 82. By actuating the valve drive 70, the yoke 72 carries out an alternating pivot movement in the direction of the double arrow, whereby the two valve seats 80 and 82 are alternately opened and closed in that the valve needles 77, 78 are alternately set against their associated valve seat 80, 82. On each opening stroke of the mixing valve, the valve needle is pressed with the valve ball fastened thereto into its open position by a spring. The two components are hereby introduced into the static mixer 24 and are mixed therein by the mixing coil 26. Only one respective component is, however, supplied to the mixer 24, while the other component is not supplied to the mixer or the other component is supplied to the mixer, while the one component is not supplied to the mixer.

(17) As FIG. 1 illustrates, the mixing valve 28 is also provided with a distance measuring device 71 by which the respective switch position of the valve can be monitored.

(18) FIG. 4 shows an enlarged and partly sectional representation of the static mixer 24 whose mixing coil 26 is surrounded by a pressure housing 27. The mixing coil 26 can be abruptly removed together with the pressure housing 27 from the static mixer 24 via a quick-release device 90, as is illustrated in FIG. 5. For this purpose, the quick-release device has a handwheel 92 which is connected via a toggle lever 93, 94 to the mixing coil 26 and to the pressure housing 27. The mixing coil 26 can thus be abruptly pulled out of the static mixer 24 together with the pressure housing 27 by rotating the handwheel 92 in the direction of the arrow shown in FIG. 4. In this position shown in FIG. 5, the supply passage 29 can also be recognized (cf. also FIG. 3) via which a component is suppliedcontrolled via the mixing valve 28. At the same time, FIGS. 4 and 5 also show a discharge passage 99 via which the medium comprising the two mixed components is supplied to the metering valve 10.

(19) The two components of the medium to be mixed is conveyed separately by the above-described mixing and metering apparatus. These pumps are each equipped with a measuring system 50, 52, 54 with whose aid the mixing ratio and the quantity removed from the respective reservoir can be determined. The pumps receive the pressurized medium in the reservoirs 18 and 20 and press it in the direction of the mixing valve 28 at approximately 20 to 60 bar. This valve is designed such that only one component can always be introduced into the mixer 24, while the valve for the other component is closed. The correct mixing ratio arises by an alternate input into the mixer. Since the quantities which are to be metered by individual droplets (dots) during jetting are extraordinarily small, a high-resolution volume measurement or a quantity measurement is only possible before the mixer with a great effort. In accordance with the invention, the volume of each component is therefore measured at the dispensed dots since the mixing valve only allows one respective component to flow in. The viscosity of the mixed product at the outlet of the mixer 24 is constant, i.e. the quantity of the dispensed dots is of an equal amount.

(20) Since a metering of the desired application structure (larger points, lines or areas) requires a large number of points in a short time, metering frequencies of more than 100 Hz are provided. In order to directly supply small quantities of the individual components in the desired mixing ratio, the mixing valve is switched over reliably and fast between two dispensed dots. It results from this that the mixing valve 28 has to switch over extremely fast and must reliably stop the one component when the other is released. The mixing ratio results by the number of dots, during which either the one component or the other component is supplied to the mixer.

(21) In the apparatus in accordance with the invention, the possible continuous mixing volume is bounded in a simple design with only two pump pistons by the stroke volume of the pump piston. However, unlimited lines can also be drawn with this arrangement since the robot by which the valve is moved can also stop in coordinated work with the metering head or can reduce to a low travel speed when the pump has to reload.

(22) Since the adhesives to be processed have comparatively short pot times of approximately 2 to 20 min, provision is made in the apparatus in accordance with the invention that metering automatically takes place into a waste disposal container on an interruption of the work procedure. At the end of work, one component is first conveyed alone through the mixer and the metering valve. The mixing coil can subsequently be abruptly drawn out of the mixer via the quick-release mechanism 90.

(23) Since the mechanical mount of the pressure housing 27 in the quick-release device 90 is of an asymmetrical design, the mixing coil cannot be inserted incorrectly. Since, furthermore, in accordance with the invention, the supply into the mixing coil is designed such that the component having the smaller portion can be mixed directly into the larger component, an insertion of the mixing coil secure against rotation is likewise of significance.