Static mixer for a curing mixed product

[0001] This invention relates to a static mixer for mixing at least two flowable components that react on mixing to form a solidified mass.

[0002] Static mixers for the mixing of at least two flowable components are described in EP-A-0 749 776 and EP-A-0 815 929. These mixers, which are compact, deliver good mixing results, despite a simple material-saving design, and particularly in the mixing of high-viscosity substances such as sealants, two-component foams or two-components adhesives. The installed elements forming the mixer structure can be manufactured at a favorable cost by injection molding from thermoplastics so that they can be used economically for one-time use. Such a “disposable mixer” is mainly used for curing products, since the mixers can not be practically cleaned with these products.

[0003] Even if the mixing of a curing mixed product with a disposable mixer is operated continuously or quasi-continuously (for example in cycles), finite useful lives, however, result. With a continuous carrying out of the mixing under an extruding pressure that remains largely constant, i.e. with a pressure drop along the installed elements of the mixer, for example, the discharge of the mixing product noticeably reduces according to the service life. That is to say, as the service life increases, the output of the mixer decreases due to an increasing pressure drop within the mixer.

[0004] An increase in the extruding pressure only allows a relatively short extension of the mixed product discharge.

[0005] Accordingly, it is an object of the invention to provide an improved mixer for mixing at least two flowable components that react on mixing to form a solidified mass.

[0006] It is another object of the invention to increase the service life of a mixer for mixing at least two flowable components.

[0007] Briefly, the invention provides a static mixer for a curing mixed product of flowable components that react to form a solidifying mass on mixing.

[0008] The mixer includes an element that is manufactured by injection moulding and a tube for encasing the element.

[0009] The element includes a pair of parallel longitudinally disposed outer walls parallel to the longitudinal axis of the tube; a plurality of longitudinally spaced apart intermediate walls between the pair of outer walls and parallel to the longitudinal axis of the tube; a plurality of transverse walls, each transverse wall being secured to and extending between a respective one of the outer walls and a respective one of the intermediate walls; and a plurality of longitudinally spaced apart webs or floors, each web being secured to and extending perpendicularly between the outer walls.

[0010] The element has a plurality of mixing chambers disposed in rows longitudinally of the longitudinal axis of the tube and laterally of each other for receiving and mixing at least two flowable components therein. Each mixing chamber is disposed between a respective one of the outer walls, a pair of consecutively disposed transverse walls in a respective row, a pair of consecutively disposed intermediate walls and a pair of consecutively disposed webs in the respective row.

[0011] In addition, each pair of consecutively disposed intermediate walls defines a first inlet to a mixing chamber and a first outlet from the chamber and one of webs defines a second inlet to a mixing chamber with one of the transverse walls and a second outlet from the chamber with the other of the webs.

[0012] In accordance with the invention, at least one of the mixing chambers has a first corner filling forming a concave surface between one of the outer walls and one of the transverse walls for directing the flowable components towards the first outlet.

[0013] Here, the term “concave surface” means a surface which is not arched toward the interior space of the mixing chamber at any point. The surface can also be planar regionally. The concave surface is concavely curved or forms, together with the flanks of the corner of the mixing chamber, a “concave segment” in cross-section which approximately has the extent of a concavely curved curve. A small wedge-shaped corner filling provides an example for a concave surface in the sense of a secondary meaning.

[0014] At least one of the mixing chambers also has a second corner filling forming a concave surface on one of the transverse walls for directing the flowable components from the second inlet into the mixing chamber. Also, the corner fillings in one mixing chamber may be of a different size from the corner fillings in an adjacent mixing chamber.

[0015] Preferably, each of the corner fillings merges into a planar surface on the associated transverse wall in a middle third thereof.

[0016] A static mixer is known from US-A-2004/0008576 whose installed element is similar to that of the mixer in accordance with the invention, but with the corresponding corner fillings being wedge-shaped and not concave in the sense of the meaning defined above. The shape of these corner fillings is less favourable with respect to an extension of the service life. There is also a disadvantage in that the wedge-shaped corner fillings mean relatively large aggregations of wall material. Such material aggregations are unfavourable in the injection moulding of the installed element since they result in longer production cycles and thus higher manufacturing costs.

[0017] These and other objects and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

[0021] Referring to FIG. 1, the mixer element 1 of a disposable mixer is known from EP-A-0 749 776 and is manufactured by injection moulding for insertion inserted into a tube (not shown). This tube encasing the installed element 1 has an interior space with a square cross-section into which the installed element 1 fits with shape matching along a longitudinal axis 10 of the tube. (The installed element 1 and the encasing tube could also be made cylindrically: cf. FIG. 3).

[0022] Flowable components of a curing mixed product are forced through the tube and the installed element 1 from cartridges by means of pistons, with the reactive mixed product components being mixed to form a solidifying mass.

[0023] The installed element 1 has a chamber arrangement of a plurality of mixing chambers 2. The mixing chambers 2 are arranged in rows one behind the other and next to one another along the longitudinal tube axis 10 for receiving and mixing at least two flowable components therein.

[0024] Each mixing chamber 2 is delineated by a pair of parallel longitudinally disposed outer walls 6 parallel to the longitudinal axis 10, a pair of longitudinally spaced apart intermediate walls 3a,3c between the pair of outer walls 6 and parallel to the longitudinal axis 10, a pair of transverse walls 4a,4b each of which is secured to and extends between a respective one of the outer walls 6 and a respective one of the intermediate walls 3a,3b, and a pair of longitudinally spaced apart webs 3b,3d, each of which is secured to and extends perpendicularly between the outer walls 6.

[0025] Each pair of consecutively disposed intermediate walls 3a,3c defines a first inlet 5b to the mixing chamber 2 and a first outlet 5d from the chamber. One of webs 3b defines a second inlet 5a to the chamber 2 with one of the transverse walls 4a and a second outlet 5c from the chamber 2 with the other of the webs 3d.

[0026] Referring to FIG. 2, wherein like reference characters indicate like parts as above, the transport of the mixed product through the mixing chamber 2 is shown with arrows. The inlet 5a, through which a flow 12a of the mixed product enters, is located at the inlet side directly by the transverse wall 4a (see FIG. 1). The flow 12a branches into part flows 12ad and 12ac that flow off into adjacent mixing chambers through the outlets 5d and 5c.

[0027] A flow 12b enters through the second inlet 5b and is accordingly branched into part flows 12bd and 12bc which exit the mixing chamber 2 together with the part flows 12ad and 12ac.

[0028] A field of pressure gradients is created in the mixing chamber 2 on the extruding of the mixed product through the installed element 1. A velocity field of the mixed product flow is formed in accordance with the pressure gradients. The pressure gradients are the most pronounced in the region of the openings 5a, 5b, 5c and 5d, where the flow speeds are also the highest. The flow can be thought of as a bundle of flow threads. The cross-sections of the flow threads inside the mixing chamber 2 widen and, consequently, relatively low flow speeds occur there. The pressure gradients are also reduced accordingly. The reduction of the pressure gradients is location-dependent. The pressure gradients are in particular very low in corner regions that lie at a larger distance from the openings 5a, 5b, 5c and 5d. The pressure gradients practically disappear there so that the mixed product flows very slowly and practically stagnates. A reaction occurs between the mixed product components in mixing chambers in which the mixing has already progressed to a large degree. This results in an increase in the viscosity of the mixed product in the regions with a stagnating flow.

[0029] The stagnating regions increase due to this change of the viscosity so that a local immobilisation inexorably occurs. This immobilisation starts in these corner regions and expands from there into the interior region of the mixing chamber 2. The flow resistance of the installed elements 1 thereby increases. The mixing quality is also simultaneously impaired.

[0030] The fact is associated with the occurrence of the immobilisation that the mixing with the disposable mixer can only be carried out during a service life that depends on the reaction kinetics of the curing mixed product. The service life can be increased when measures are taken against the stagnation in the flowing mixed product.

[0031] Referring to FIG. 2, in accordance with the invention, the mixing chamber 2 is provided with a first corner filling 7 forming a concave surface 7a between one of the outer walls 6 and one of the transverse walls 4b′ for directing the flowable components towards the outlet 5d. As indicated, the corner is filled with wall material, indicated as a “tripod” drawn with a chain-dotted line by the transverse wall 4b. The filling of this corner, which is termed a “first corner filling 7”, sets up a concave surface 7a (in accordance with the meaning recited above) with respect to the interior space of the mixing chamber 2. As becomes vividly clear from FIG. 2, the conditions for the occurrence of stagnation are eased by the first corner filling 7, which brings about an extension of the service life.

[0032] A further measure in the form of a “second corner filling 8” additionally contributes to an extension of the service life. As shown, the transverse wall 4a is filled with wall material opposite the web 6b to form the second corner filling 8 with a concave surface 8a facing the interior space of the mixing chamber 2. The action of this second corner filling 8 is the same as that of the first corner filling 7.

[0033] The immobilisation comes into effect the more strongly, the further a mixing chamber 2 lies downstream—as long as no measure, or the same measure everywhere, is taken against this problem. It is therefore of advantage for the first and/or second corner fillings 7, 8 to be made at least partly of different size and for each corner filling 7 or 8 to be equally as large as or smaller than the corner fillings 7 or 8 following downstream.

[0034] The corner fillings 7, 8 should not form material aggregations that are too large, for which reasons were already given above. It is therefore advantageous if the following applies to the first corner filling 7 (and accordingly to the second corner filling 8): the concave surfaces 7a (or 8a) each merge at an interface line 7b into a planar surface part 4b′ (or 4a′) of the transverse wall 4b (or 4a). This interface line 7b should lie in a middle strip of the transverse wall 4b, with this strip occupying the middle third of the transverse wall 4b at its inner side.

[0035] The concave surfaces 7a or 8a are each at least approximately part of a circular cylinder. The axis of this cylinder lies in a plane standing perpendicular to the tube axis 10. The cylinder axes associated with the two corner fillings 7 and 8 are aligned perpendicular to one another.

[0036] The concave surfaces 7a and 8a each merge with a smooth course into planar surface parts 4a′ or 4b′ of the transverse walls 4a or 4b. The same applies to transitions in planes on which the outer sides 6a or 6b of the mixing chamber 2 lie.

[0037] The web 6b of the mixing chamber 2 is covered by the second corner filling 8 in the region of a zone whose area is no larger than the opening area of the inlet 5a bordering on the transverse wall 4a. This condition results from the geometry of the tool used as the mold in the injection mold device.

[0038] Referring to FIG. 3, wherein like reference characters indicate like parts as above, the mixer element may be of cylindrical shape to fit within a tube of cylindrical shape. As above the element has first and second corner fillings 7 and 8. The outer longitudinal walls 6, which form the first outer sides 6a of the mixing chambers, have a circular segment-like cross-section. The web 6b is curved. The one flank of the second corner filling 8 is therefore also curved accordingly.

[0039] When using the mixer in accordance with the invention, the mixed product of components that react to form a solidifying mass on mixing is advantageously mixed continuously or quasi-continuously with an extruding pressure that remains largely constant or varies in cycles, i.e. with a pressure drop along the installed elements 1 of the mixer. The mixing is interrupted and the mixer replaced as soon as a discharge of mixed product becomes noticeably smaller or an increase of the extruding pressure becomes necessary.

[0040] The element 1 may be constructed without the outer longitudinal walls 6 in which case the walls of the tube would take the place of the walls 6 of the element 1.

[0041] The invention thus provides an element for a static mixer that mixes at least two flowable components that react on mixing to form a solidified mass that is capable of a relatively long service life.