Patent Publication Number: US-10773225-B2

Title: Apparatus and method for mixing components

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This claims priority to DE102016108108.6 filed May 2, 2016, which is hereby incorporated by reference in its entirety. 
     The present invention relates to an apparatus and to a method for mixing components and in particular to a dynamic mixer having a mixing chamber that has at least one first and one second inlet as well as an outlet, wherein a mixing element is rotatably arranged in the mixing chamber. 
     Known dynamic mixers of this kind have the disadvantage that the rotor separates the space in the mixing chamber such that there is a volume swept through by the rotor and a volume not swept through by the rotor within the mixing chamber. Sections are hereby created both in the region of the rotor and in the region of the mixing chamber that are not flowed through sufficiently, i.e. the medium comprising the components to be mixed is either moved too slowly at the wall of the mixing chamber due to the braking or, however, the medium is also rotated by the rotor—in particular also close to a shaft of the rotor—such that the medium only has a very low relative speed with respect to the rotor and the rotor shaft. Material can then accumulate in these regions, which in particular hardens too fast on the mixing of multicomponent adhesives. 
     It is the object of the present invention to improve a dynamic mixer such that in particular fast-hardening components can be intermixed in an improved manner in small volumes. 
     This object is satisfied by the features of claim  1  and in particular in that at least one abutment is provided in the dynamic mixer that is in particular arranged in the mixing chamber and that prevents a rotation of the mixing element by 360°. 
     In accordance with the invention, the intermixing in the mixing chamber thus does not take place by a continuous rotation by more than 360°, but rather by an enforced to and fro movement. If the abutment is provided in the mixing chamber in this context, the mixing element has to be moved against the abutment or at least toward the abutment during the to and fro movement such that the medium to be mixed is urged in the direction of the abutment, wherein the components to be mixed are blended with one another. It is necessary due to the provision of the abutment that, unlike conventional dynamic mixers, the mixing element is not moved with a continuous axial rotation in the same direction, but rather that the direction of rotation changes continuously, which promotes a good intermixing. 
     Advantageous embodiments of the present invention are described in the description, in the drawing and in the dependent claims. 
     The mixing element can be completely closed, i.e. can be configured without interruptions or openings, in a first advantageous embodiment such that it divides the mixing chamber into two mutually separate part chambers, viewed in cross-section, when it is not in one of its end positions. Two part chambers are hereby formed on each movement of the mixing element that vary their size continuously, whereby the medium can cross over from one part chamber into the other part chamber to mix. When the mixing element is in one of its end positions, one of the two part chambers is no longer present since the medium to be intermixed has been completely conveyed into the other part chamber. 
     In accordance with a further advantageous embodiment, the mixing element can have a shaft and at least one wiping vane arranged thereat. The components of the medium to be blended can be continuously wiped off the wall of the mixing chamber by such a wiping vane such that the free volume of the mixing chamber is cyclically wiped off. 
     It can be advantageous in this respect if a radial gap that extends in the axial direction and through which the medium can flow and can thereby intermix on a movement of the mixing element is provided between a radially outer end of the mixing element and a wall of the mixing chamber. The radial gap can in particular extend over the total length of the mixing chamber or over almost the total length of the mixing chamber. 
     In accordance with a further advantageous embodiment, a radial gap that extends in the axial direction and that in particular extends over the total length or over almost the total length of the mixing chamber can additionally or alternatively be provided between a shaft of the mixing element and a wall of the mixing chamber. Medium can hereby also be urged through this radial gap when the mixing element is rotated in the direction of the abutment. 
     In accordance with a further advantageous embodiment, the mixing element can at least partly not extend over the total axial length of the mixing chamber, but in particular only over approximately 85% to 99% of the length of the mixing chamber. It is ensured by this measure that the intermixed medium is no longer moved to and fro at the end of the mixing chamber and that the outlet is always open such that no appreciable pressure fluctuations occur at the outlet of the mixer. 
     In accordance with a further advantageous embodiment, a wiping vane of the mixing element can areally contact the abutment, in particular over its total area, at least in one end position of the mixing element. It is provided in this manner that the medium is displaced over a large area by the approaching surfaces of the wiping vane and of the abutment on an approach of the wiping vane toward the abutment, which promotes an intimate intermixing. 
     The wiping vane can be configured in the manner of a key bit and can have interruptions. The wiping vane can thus be formed from two or more part sections or can have openings or the like. 
     In accordance with a further advantageous embodiment, the mixing chamber can have, viewed in cross-section, a cross-section differing from the circular shape or the part-circle shape over a part section of its periphery, and in particular over its total axial length. The abutment provided in accordance with the invention can hereby be formed by the wall of the mixing chamber in that the latter has an asymmetrical and inwardly projecting cross-sectional shape. The abutment can in particular extend almost up to the mixing element such that the mixing chamber can be divided into two part chambers (except for a radial gap) by the abutment. 
     The mixing chamber can have a radius, viewed in cross-section, i.e. in a section perpendicular to the axis of rotation of the mixing element, that decreases from a maximum radius down to a minimal radius over a part section of the periphery of the mixing chamber, and in particular also over its total axial length, and then increases in size again up to the maximum radius. A wavy elevated portion that provides a good intermixing of the components in cooperation with the mixing element is hereby integrated into the mixing chamber that is circular or that is cylindrical in volume in cross-section. In a geometric aspect, the mixing chamber can have a peripheral contour, viewed in cross-section, i.e. in a section perpendicular to the axis of rotation of the mixing element, that is continuous (in a mathematical sense) and that has two inflection points. Provision is still made in this manner that no edges remain within the mixing chamber in which unmixed medium could accumulate. An abutment is nevertheless present which extends in the longitudinal direction through the mixing chamber and which the mixing element or the wiping vane can abut. 
     The mixer in accordance with the invention is particularly suitable for very quickly hardening components, for example two-component adhesives having a hardening time in the order of a few minutes, since the volume of the mixing chamber can be selected as extremely small, for example in an order of less than 20 mm 3 , in particular of less than 10 mm 3 , for example 7 mm 3 . For this reason, the mixer in accordance with the invention can also be advantageously integrated in a metering valve, and indeed such that the volume of the mixing chamber and the volume of a media channel from the outlet of the mixing chamber up to a valve seat of the metering valve takes up a volume of less than 350 mm 3 , in particular of less than 300 mm 3 , for example approximately 290 mm 3 . 
     In accordance with a further aspect of the present invention, it relates to a method for mixing two components, in particular two-component fluids, having very small hardening times. In the method, that can in particular be carried out using a mixer of the above-named kind, the two components are introduced into a mixing chamber and are mixed in the mixing chamber by a rotatable mixing element, and indeed such that the mixing element is respectively moved to and fro in the mixing chamber up to an abutment provided in the mixing chamber. It can be particularly advantageous in this respect if the two components of the medium are urged with the aid of the mixing element on every to and fro movement in opposite directions through at least one radial gap that is provided between the mixing chamber and the mixing element. The medium is preferably urged through two radial gaps when the mixing element is moved to and fro. 
    
    
     
       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: 
         FIG. 1  a perspective view through a dynamic mixer that is integrated into a housing of a metering valve; 
         FIG. 2  a longitudinal section through the arrangement of  FIG. 1 ; 
         FIG. 3  a plan view of the arrangement of  FIG. 1 ; 
         FIG. 4  a section along the line IV-IV of  FIG. 2 ; and 
         FIG. 5  a sectional view comparable with  FIG. 4 , but with the mixing element having been rotated counter-clockwise in the direction of the abutment. 
     
    
    
       FIG. 1  shows a housing  10  of a metering valve that is not shown in any more detail and that is integrated into a dynamic mixer whose outlet  12  is in communication with the metering valve (not shown) via a media channel  14 . The housing  10  of the metering valve thus also forms the housing of the dynamic mixer and a mixing chamber  16  whose cross-section can be easily recognized in  FIGS. 4 and 5  is provided in the housing  10 . The mixing chamber  16  has a first inlet  18  and a second inlet  20  into which inlets a first inlet passage  18 ′ and a second inlet passage  20 ′ open for supplying two fluid components of the medium to be mixed. It is understood that more than two inlets or also more than one outlet can also be provided. 
     A mixing element  22  that is rotatable in the mixing chamber via a shaft  24  that is guided in a socket  26  screwed in the housing  10  is provided in the mixing chamber  16  for an intimate blending of the components to be mixed in a small volume and in a short time. 
     The mixing element  22  comprises a cylindrical shaft section  28  that has a somewhat smaller diameter than a shaft section of the shaft  24  located in the socket  26  and that extends over the total length of the mixing chamber  16 . A wiping vane  30  is molded at or fastened to the outer periphery of the shaft section  28 ; it extends over approximately 90% of the axial length of the mixing chamber  16  and its radially outer end forms a radial gap A 1  extending in the axial direction with the wall of the mixing chamber ( 16 ). 
     The wiping vane  30  in the embodiment shown is continuous in the longitudinal direction, i.e. it is not interrupted, and it is connected to the shaft section  28  such hat no sharp edges are formed. The wiping vane  30  has a uniformly convexly curved surface at its radially outer jacket surface such that the medium can flow evenly through the radial gap A 1 . 
     The cross-sectional views of  FIGS. 4 and 5  illustrate that the mixing chamber  16  is not circularly symmetrical, but rather has, viewed in cross-section, a cross-section differing from the circular shape over a part section of its periphery (at the bottom in the Figures) over its total axial length in the embodiment shown (cf.  FIG. 2 ). In more precise terms, the mixing chamber  16  has, viewed in cross-section, a radius (whose center is intersected in a perpendicular manner by the axis of rotation of the shaft  24 ) that reduces from a maximum radius down to a minimal radius over a part section of the periphery of the mixing chamber and over its total axial length and then increases in size again up to the maximum radius, with the part section of the periphery extending over approximately 90°. The mixing chamber  16  thus has, viewed in cross-section, a peripheral contour or a surface line that is continuous in the geometrical sense and that has two inflection points, whereby an abutment  32  is formed within the mixing chamber  16  that is integrated into the wall of the mixing chamber and that prevents a rotation of the mixing element  22  by a complete 360°. In this respect, a second radial gap A 2  is formed between the abutment  32  and the shaft section  28  of the mixing element  22  (cf.  FIG. 2  and  FIG. 5 ); it extends in the axial direction and the wiping vane  30  can urge medium through it when the mixing element  22  moves to and fro. 
     As  FIGS. 4 and 5  illustrate, the mixing element  22  divides the mixing chamber  16 , viewed in cross-section, into two mutually separate part chambers  16   a  and  16   b  when the mixing element  22  is not in one of its two end positions. In this respect, the volume of the two part chambers  16   a  and  16   b  is the same when the mixing element  22  is in the middle position shown in  FIG. 4 . At the same time, the volume of the respective part chamber can be reduced to zero or almost zero when the mixing element  22  is in one of its two end positions. In this end position, the wiping vane  30  of the mixing element  22  contacts the abutment  32  areally and over the total axial length of the wiping vane  30  such that the medium that was previously located in the part chamber  16   a  (or  16   b ) has been completely urged through the radial gap A 2  into the respective other part chamber. If therefore, for example, the mixing element  22  is in its left end position (it is close to that position shown in  FIG. 5 ) and if the mixing element is subsequently rotated clockwise, the medium located in the maximized part chamber  16   b  is urged both through the radial gap A 1  and through the radial gap A 2  into the opening chamber  16   a  and is mixed in so doing. 
     A method for mixing two components can be carried out using the above-described dynamic mixer in which a first component and a second component are introduced through the inlet channels  18 ′ and  20 ′ into the inlet  18  and the inlet  20  of the mixing chamber  16  in that the components are pressurized. The two components are then mixed in the mixing chamber  16  by the rotatable mixing element  22  in that the mixing element  22  is respectively moved to and fro up to the abutment  32  provided in the chamber  16 . The two components introduced into the mixing chamber  16  or the medium located in the mixing chamber  16  are urged with the aid of the mixing element on each to and fro movement of the mixing element  22  in opposite directions through the first radial gap A 1  and through the second radial gap A 2  that is respectively provided between the mixing chamber and the mixing element. The to and fro movement of the mixing element  22  takes place in this respect in the embodiment shown over approximately 270°, i.e. the direction of rotation of the mixing element is constantly changed. 
     On a use of a divided mixing element or of a mixing element having interruptions, a greater turbulence can provide a greater intermixing, whereas the embodiment shown having a continuous wiping vane provides a particularly uniform wiping of the medium. 
     The drive of the mixing element can take place by a stepper motor with which the movement of the mixing element can be controlled very exactly with a changing direction of rotation. A recognition of the abutting or also of the approach to or toward the abutment can be recognized by the detection of the power consumption of the motor. It can hereby simultaneously be recognized if already hardened material has accumulated at the abutment at the housing wall. Such an increase namely produces a reduced angle of rotation that can be detected, in particular by the control of the motor. The zero position of the mixing element can furthermore be simply traveled to by the abutment. For this purpose, the motor is either moved on by a defined number of steps that is larger by at least one step than the maximum angle of rotation of the mixing element or the motor is traveled so far until an abutment is recognized with reference to the power load. 
     Alternatively, a simple electric motor can also be used for the drive and/or a distance sensor can be used that recognizes the end position or the abutment of the mixing element or measures the rotational movement of the rotor axis. 
     The above-described dynamic mixer is very well-suited for very small mixing volumes and only amounts to approximately 7 mm 3  in the embodiment shown, which amounts to a little less than 4% of the mixing volume of static mixers. The volume of the mixed medium from the inlet up to a valve seat of the metering valve (including the media channel  14 ) can also be kept extremely small, for example below 300 mm 3 .