Mixing device with a pressure holding device

Abstract

The invention relates to a mixing device comprising at least one supply opening for at least one liquid and comprising at least one additional supply opening for at least one liquid curing or crosslinking agent. The liquid and/or the liquid curing or crosslinking agent is/are mixed with a gas. The mixing device also comprises a discharge opening for discharging a mixture, which can be produced in the mixing device, of the at least one liquid and the at least one liquid curing or crosslinking agent. A pressure holding device is provided for holding a specifiable pressure which is higher than the pressure at which the gas in the mixing device is foamed.

Claims

1. A mixing device comprising: at least one feed opening for at least one liquid; at least one further feed opening for at least one liquid curing or cross-linking agent, wherein the at least one liquid and/or the at least one liquid curing or cross-linking agent is or are mixed with a gas; a discharge opening for discharge of a mixture which can be produced in the mixing device and comprises the at least one liquid and the at least one liquid curing or cross-linking agent; and a pressure holding device for holding a predeterminable pressure which is greater than a pressure at which foaming-out of the gas in the mixing device occurs, wherein the pressure holding device includes an adjusting member arranged displaceably in the mixing device relative to the discharge opening, the adjusting member being configured to adjust a gap remaining between the adjusting member and the discharge opening, wherein the mixing device has a rotating agitator for mixing the at least one liquid and the at least one liquid curing or cross-linking agent, wherein the adjusting member is biased in a direction of the discharge opening by a force storage member, and wherein the agitator is adapted to be displaceable and forms the adjusting member, and wherein the force storage member is in the form of a spring.

2. A mixing device comprising: at least one feed opening for at least one liquid; at least one further feed opening for at least one liquid curing or cross-linking agent, wherein the at least one liquid and/or the at least one liquid curing or cross-linking agent is or are mixed with a gas; a discharge opening for discharge of a mixture which can be produced in the mixing device and comprises the at least one liquid and the at least one liquid curing or cross-linking agent; and a pressure holding device for holding a predeterminable pressure which is greater than a pressure at which foaming-out of the gas in the mixing device occurs, wherein the pressure holding device includes an adjusting member arranged displaceably in the mixing device relative to the discharge opening, the adjusting member being configured to adjust a gap remaining between the adjusting member and the discharge opening, wherein the mixing device has a rotating agitator for mixing the at least one liquid and the at least one liquid curing or cross-linking agent, wherein the adjusting member is biased in a direction of the discharge opening by a force storage member, and wherein the agitator is adapted to be displaceable and forms the adjusting member, wherein the mixing device further comprises a mixing chamber, the mixing chamber having the discharge opening, the agitator being arranged within the mixing chamber, and wherein the agitator is configured to be displaced by a force of the at least one liquid and the at least one liquid curing or cross-linking agent in the mixing chamber applied directly to the agitator in a direction away from the discharge opening such that the force directly displaces the agitator away from the discharge opening so as to allow the mixture to be discharged through the discharge opening, and such that the force directly determines a size of the gap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention are discussed with reference to the Figures in which:

(2) FIGS. 1a through 1c show a first embodiment of a mixing device according to the invention with different variants in detail views,

(3) FIG. 2 shows a second embodiment of a mixing device according to the invention,

(4) FIGS. 3a and 3b show an agitator illustrating forces acting on the agitator, and

(5) FIGS. 4 and 5 show detail views of further embodiments of proposed mixing devices.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(6) FIG. 1a shows a mixing device 1 having a mixing chamber 12. The Figure shows a feed opening 2 for at least one viscous liquid mixed with gas (for example polyol mixed with air) and a further feed opening 3 for at least one liquid curing or cross-linking agent (for example isocyanate), which lead into the mixing chamber 12. In this embodiment the mixing device 1 is a dynamic mixing device and includes an agitator 7 which is rotatable in the mixing chamber 12. Differently from what is described herein in addition to the liquid or instead of the liquid the liquid curing or cross-linking agent can additionally be mixed with a gasfor example air.

(7) Provided adjacent to the tip of the agitator 7 is a discharge opening 4 through which the mixture produced in the mixing chamber 12 and comprising the at least one viscous liquid mixed with gas and the liquid curing or cross-linking agent can be discharged in the direction of a nozzle 9.

(8) In the present embodiment the pressure conditions are so selected that downstream of the discharge opening 4 there is a reduction in the pressure of the mixture comprising the at least one viscous liquid mixed with gas and the liquid curing or cross-linking agent, below that pressure at which the gas foams out in the mixture so that outgassing of the gas results in expansion and thus foaming of the mixture (physical foaming).

(9) In this embodiment the pressure holding device is formed by the agitator 7 which is acted upon by way of a force storage means 8 and which is arranged spaced from the discharge opening 4 by a gap 6.

(10) To produce the mixture comprising the at least one viscous liquid mixed with gas and the liquid curing or cross-linking agent the viscous liquid which is mixed with gas and which is provided by a source 10 is introduced through the first feed opening 2 and the liquid curing or cross-linking agent which is provided by a further source 11 is introduced through the second feed opening 3, at different axial positions of the mixing device 1 which here is of an elongated configuration. Mixing of those two components takes place by means of the rotating agitator 7.

(11) In the preferred embodiment illustrated here the force storage means 8 is provided in the form of a spring which presses the agitator 7 against an end face 13 of the mixing chamber 12, that has the discharge opening 4, until sufficient force is applied to the agitator 7 by the material introduced from the sources 10 and 11, so that the agitator 7 moves away from the end face 13 and as a result a gap 6 (here an annular gap) is formed between the end face 13 and the agitator 7, whereby the mixture produced in the mixing chamber 12 can issue from the discharge opening 4. The force applied in the direction of the discharge opening 4 by the force storage means 8 is of such a magnitude that, due to the backup of the material mixture in the region of the gap 6, there is a pressure which is propagated over the mixing chamber 12 and which prevents outgassing of the gas from the mixture of the gas with the viscous liquid.

(12) If fluctuations occur in the material backup (for example as a consequence of a variation in the discharge amount, a fluctuating viscosity of the mixture, temperature fluctuations, fillers in the mixture and so forth), the position of the agitator 7 is automatically adapted relative to the discharge opening 4 so that the pressure in the mixing chamber 12 is kept substantially constant. A seal 15 (which here is shown only as acting in one direction but which can also have a sealing action in both directions) sealingly surrounds the rotating shaft 16 of the agitator 7 and seals off the mixing chamber 12 in the region of the shaft 16 of the agitator 7. The seal 15 can for example comprise Teflon and can permit smooth axial movement of the rotating shaft 16. By virtue of the fact that the shaft 16 rotates and the seal 15 causes slight friction, it is possible to achieve very fine axial positional adaptation of the agitator 7. In particular it is possible in that way to avoid unwanted pressure fluctuations due to abrupt axial displacement of the agitator 7 as a consequence of a stick-slip effect. The axial displacement of the agitator 7 is also facilitated by the rotation of the shaft 16. Preferably the seal 15 is in the form of a rotational and translational seal.

(13) In the illustrated embodiment the biasing of the force storage means 8 can be adjusted. In this example provided for that purpose is an adjusting device 5 in the form of a screw sleeve, which is adapted to act as an abutment for the spring and which is axially displaceable by a rotary movement.

(14) Unlike the illustrated situation an embodiment is also conceivable in which there is no force storage means 8 and the gap 6 between the discharge opening 4 and the agitator 7 is fixedly set. In that embodiment it is not possible to react to fluctuations in the material backup. A further embodiment (not shown) could be of such a configuration that a force storage means 8 is admittedly provided, but it is structurally biased to a predetermined degree. In this case also there cannot be any variation.

(15) FIG. 1b shows a detail view of the tip of the agitator 7 which in this embodiment is more pointed than the inclination of the end face 13 of the mixing chamber 12. As a result the tip of the agitator 7 only bears in annular relationship against the end face 13 and projects into the discharge opening 4 in order to close it off in an annular shape.

(16) FIG. 1c shows a variant of the embodiment in which the force storage means 8 is in the form of a compressed air spring. A variant is also further conceivable in which the force storage means 8 is in the form of a hydraulic piston-cylinder unit.

(17) Unlike FIGS. 1a through 1c FIG. 2 shows an embodiment in which it is not the agitator 7 that is arranged displaceably in the mixing chamber 12, but the end wall of the mixing chamber 12, in the end face 13 of which the discharge opening 4 is arranged, is displaceable relative to the agitator 7 in order once again to adjust the gap 6 between the discharge opening 4 and the agitator 7. All those variants which were shown for the embodiment of FIG. 1a are also possible for the embodiment of FIG. 2.

(18) FIG. 3a shows an agitator 7. The forces exerted on the agitator 7 by the material introduced into the mixing chamber 12 (those forces being illustrated by arrows facing towards the agitator 7) cancel each other out except for the regions A1 (sealed region of the agitator 7) and A2 (substantially pressure-less region through which the material can be discharged from the discharge opening 4). There is a pressure in the mixing chamber 12 which very substantially corresponds to the force exerted by the force storage means 8 divided by the difference between those two surfaces A1 and A2 (see FIG. 3b).

(19) FIG. 4 shows a further example of a pressure holding device for a mixing device 1 as shown in FIG. 1a and FIG. 5 shows a further example of a pressure holding device for a mixing device 1 as shown in FIG. 2. In both cases the pressure holding device is formed by an aperture 14 and an agitator 7 which is arranged spaced from the discharge opening 4 by a gap 6. The pressure which can be predetermined by these pressure holding devices can be respectively produced by the aperture 14 arranged in the region of the discharge opening 4. The dimensioning of the aperture 14, that is required for the desired pressure, can be established by trials or calculations. That permits the pressure holding device to be of a particularly simple structure, in which it is possible in particular to dispense with an adjusting device 5.

LIST OF REFERENCES

(20) 1 mixing device 2 feed opening for at least one viscous liquid mixed with gas 3 further feed opening for at least one liquid curing or cross-linking agent 4 discharge opening 5 adjusting device 6 gap 7 agitator 8 force storage means 9 nozzle 10 source for at least one viscous liquid mixed with gas 11 source for at least one liquid curing or cross-linking agent 12 mixing chamber 13 end face 14 aperture 15 seal 16 shaft