Movable-Chamber Mixing Head

This invention refers to a high-pressure mixing head for mixing fluid components, in particular for mixing chemical components suitable for forming polyurethane foams which are then fed into a mold.

The mixing head of the aforesaid kind, usually comprises a body having a mixing chamber into which open out the injectors for feeding the individual components, and an outlet duct axially aligned with the mixing chamber in which a control member in the form of a movable plunger slides from a retracted position in which it allows the components to be fed into the mixing chamber, to an advanced position in which it prevents the components from entering and at the same time expelling the residual mixture remaining in the mixing chamber and in the outlet duct; a mixing head of this type is known, for example, from DE PS 2007935.

At the end of each mixing cycle, the individual components can be made to recycle towards their respective tanks by means of per se known rotating recycling valves, or slide valves, or in any other way. From a previous patent IT 21022 A/78 of the same applicant, it is also known to provide a mixing chamber, small in volume and very limited in length, arranged at right angles and in direct communication with the outlet duct in order to improve the mixing degree.

In all the known mixing heads, the disposition of the mixing chamber is fixed with respect to the outlet duct, since both are made in the body of the head or in parts connected thereto.

In such heads the mixing is achieved by means of the collision of the jets of components, in correspondence with the feed injectors, after which the flow of mixture remains substantially unchanged; in order to improve the mixing degree, it has also been suggested to use restrictors in the outlet duct, DE A-2.007934 and DE A-2.612.812, thereby involving a complex structure and complicating the functioning of the head. Moreover, on the known mixing heads, the distance between the injection nozzles depends upon the crosswise dimensions of the mixing chamber, whereas it would be desirable to keep the nozzles as close as possible for satisfactory mixing. A reduction in the crosswise dimensions of the mixing chamber however cannot be carried beyond certain limits due to the fact that it would excessively reduce the strength of the cleaning member in the chamber itself; furthermore, it would make it difficult to make component recycling channels in the cleaning member with a sufficient cross-sectional area of flow, and would introduce excessive additional pressure losses, during the recycling phases of the components which would have a negative effect during the mixing phases.

A scope of this invention is to provide a high-pressure mixing head for at least two components, of completely new design, capable of providing a high degree of mixing by simple means, which make it possible to render the disposition and the distance between the injectors independent, with respect to the mixing chamber, the dimensions and volume of which can be suitably calculated in accordance with the desired rates of flow. A further scope of the invention is to provide a mixing head, as defined, in which the recycling channels for the components are provided outside the chamber itself, and can consequently be made with suitably-sized cross sectional areas for recycling the individual components, whilst keeping pressure losses to a minimum.

A still further scope of this invention is to provide a high-pressure mixing head capable of greatly improving the degree of mixing of the components, by providing subsequent mixing areas, whilst keeping the structure and the functioning of the head extremely simple. A still further scope of this invention is to provide a mixing head, of the aforementioned type, in which it is possible to avoid any contamination whatsoever of the chemical components and/or the mixture, by the fluids actuating the hydraulic control members.

According to this invention, a high-pressure mixing head is provided, comprising a mixing chamber into which the injectors for feeding the components to be mixed may open out, and in which the chamber presents a longitudinal axis parallel to the axis of an outlet duct for the mixture, through which a cleaning member slides, the improvement consisting in the fact that the mixing chamber is formed in a slider movable in a guide channel which crosses and lies at right angles to the outlet duct, said slider being movable from a first operative position in which the chamber is disposed on one side of the outlet duct and in correspondence with the injectors of the components, and in which the outlet aperture of the chamber communicates with the outlet duct, to a second position in which the mixing chamber is axially aligned with the outlet duct and with the aforesaid cleaning member.

According to a further feature of the invention, one or more intermediate ducts may be provided in parallel, between the outlet aperture of the mixing chamber, in the first position of the slider, and the entrance of the outlet duct, which ducts are defined by peripheral walls of the slider itself and of its guide channel, thereby exploiting the high kinetic energy and speed of the flow leaving the mixing chamber in order to further improve the degree of mixing. In this connection, it is advisable to keep the length of the branched-off paths or ducts, that is to say, the stroke of the slider in the mixing chamber, very short, for example just slightly longer than the overall width of the mixing chamber, corresponding to that of the outlet duct, measured in the moving direction of the slider.

These and further features of the mixing head according to this invention will be more clearly apparent from the following description of an embodiment illustrated in the example shown in the accompanying drawings, in which:

FIG. 1 shows a longitudinal cross-sectional view, in the mixing condition;

FIG. 2 shows an enlarged cross-sectional view along the line 2--2 of FIG. 1;

FIG. 3 shows an enlarged cross-sectional view along the line 3--3 of FIG. 1;

FIG. 4 shows a side view revealing the particular shape of the slider and the two operative positions of the mixing chamber;

FIG. 5 shows a partially cutaway perspective view of the slider and of its guide channel, showing the branched-off paths of the flows which connect the movable mixing chamber to the outlet duct;

FIG. 6 shows a simplified plan view illustrating the disposition of FIG. 4;

FIG. 7 shows a longitudinal cross-sectional view similar to that of FIG. 1, with the mixing head in the component recycling condition;

FIG. 8 shows a cross-sectional view along the line 8--8 of FIG. 7;

FIGS. 9 and 10 show two cross-sectional views similar to those of FIGS. 2 and 8, for a triangular slider;

FIG. 11 shows a longitudinal cross-sectional view of a further embodiment.

The mixing head comprises a casing or body portion 1 provided internally with a channel 2 along which a slider 3 for the mixing chamber slides and is guided; as shown, the mixing chamber 4 consists of a cylindrical hole made crosswise to the slider 3, that is to say, having its longitudinal axis at right angles to the longitudinal sliding axis of the slider; the hole 4 opens at both ends and on both sides, through the walls of the slider; the side apertures 5 in the mixing chamber fit tightly to longitudinal ribs 1a of the guide channel 2, which ribs penetrate into the mixing chamber 4 and sustain the injectors 6 and 7 for the components (FIG. 2), as explained further on. Reference 8 indicates an outlet duct for the mixture which crosses the channel 2 and has the same cross-section as the chamber 3 with which it may communicate, in the condition shown in FIG. 1, through separate branched-off paths or conduits 9 and 10 defined by side walls of the slider 3 and its guide channel 2, as explained further on. Therefore, in the embodiment shown, the mixing chamber 4 presents a longitudinal axis parallel to the axis of the outlet duct 8, with which it communicates by means of branched-off ducts 9 and 10, said chamber being movable, with the slider 3, in the direction of the sliding axis of the slider itself.

The slider 3 of the mixing chamber is made to move between two operative positions, shown in FIGS. 1 and 7, by any suitable control means, for example by means of a double-acting hydraulic cylinder, or as shown, by means of two opposing single-acting hydraulic cylinders 11 and 12, in which the hydraulic control fluid is simply fed into the chamber 13, and respectively 14 of each cylinder, which is situated on the side of the piston opposite the slider 3; thus, the chamber of each cylinder 11 and 12 which is opposite the first one, is simply open to the air, thereby eliminating specific hydraulic fluid seal problems in the direction of the mixing chamber 4 and, therefore, the causes of possible contamination of the chemical components and/or of the mixture itself.

The stroke of the slider 3 may be of any length, however it is preferable to keep it as short as possible, in order to switch over extremely rapidly from one operative condition to the other; the stroke of the slider, however, in this case, must be at least slightly longer than the overall width of the outlet duct 8, and of the chamber 4, measured in the sliding direction of the slider 3.

The mixing head 1 is completed by a cleaning member, both for the mixing chamber 4 and for the outlet duct 8, in the form of a plunger 16 having the same internal diameter or the same cross-section as the chamber 4 and duct 8; the cleaning member 16 is in turn connected to the piston of a control cylinder 17 to move from a retracted position with respect to the slider 3, shown in FIG. 1, in which it allows the slider to move, to an advanced position, through the chamber 4 and the duct 8 as far as the aperture 8a of the aforesaid duct (FIG. 7). As mentioned previously, an innovatory feature of the mixing head according to this invention lies mainly in the movable disposition of the mixing chamber 4, in the slider 3, as well as in the particular conformation of the slider itself which, together with its guide channel and by means of one or more longitudinal ribs, defines one or more ducts connecting the mixing chamber 4 to the outlet duct 8.

As can be seen from the figures, the slider 3 of the mixing chamber presents a double T-shaped cross-section, the upper wings 3a and lower wings 3c of which are larger than the diameter or maximum width of the mixing chamber 4, and in which the central web 3b of the slider is smaller in transveral width, for example, equal to two thirds or half the diameter of the chamber 4, so as to define two lateral apertures 5 in the chamber 4 through which the chemical components to be mixed can be injected by means of the injectors 6 and 7 (FIG. 2). Hence, the nozzles of the injectors 6 and 7 can be arranged very closely together, at a lesser distance than the diameter of the hole 4 constituting the mixing chamber, thereby exploiting to a greater extent the high kinetic energy generated by the impact forces between the jets in order to enable them to mix together to a high degree.

The slider 3, in a position beneath the lower wing 3c, is provided with two laterally spaced longitudinal ribs 3d delimited by flat sides and bottom surfaces, in which the distance between the lateral surfaces 18 (FIG. 8) of the two ribs is equal or less than the diameter or the maximum crosswise width of the mixing chamber 4; consequently, the slider guide channel 2, in correspondence with the lower part 3d of the slider, is provided with lateral guide surfaces 19 arranged tangentially to or crossing the mixing chamber 4 and the outlet duct 8. The lower ribs 3d leading off from one end of the slider, the right one in the figures, continue half way along the mixing chamber where they form a step (FIG. 4), the concave front surface of such step defining part of the lower surface of the mixing chamber 4, which aligns with the upper surface of the outlet duct 8 when the slider is in the condition shown in FIG. 7. The longitudinal ribs 3d of the slider 3 define, moreover, a longitudinal intermediate groove 21 corresponding to a longitudinal guiding rib 22.

Separate channels 9 and 10, defined by the bottom surface and the lateral surfaces 19 and 23 of the slider guiding channel and by the lower surface of the wings 3c, are thus formed on either side of the rib 22. In this way, in the retracted condition of the mixing chamber 4, shown in FIGS. 1, 4, 5 and 6, the two parallel ducts 9, 10 are formed which define separate paths for the flow of mixture from the outlet aperture of the mixing chamber 4, which then open out on opposite sides at the entrance to the outlet duct 8.

The movable disposition of the mixing chamber 4, in the slider 3, makes it possible moreover to use separate recycling ducts 24, on the sides of the slider in order to recycle the individual components towards their respective tanks, not shown, when the mixing chamber is axially aligned with the outlet duct 8. The disposition of the recycling ducts on the sides of the slider 3, separate from the mixing chamber 4 and its cleaning member 16, and their disposition in a transversal plane, offers considerable advantages in that it is possible to dimension the recycling ducts independent of the dimensions of the mixing chamber, and to make the channels 24 of the desired width in order to reduce to a minimum any additional pressure losses; in this way, it is possible to ensure that the recycling pressure of each individual component is practically the same as the pressure required for feeding the individual components during the mixing phase.

This fact, together with the others, helps to further improve the mixing degree, especially during the initial mixing phases which are the most critical with regard to maintaining the correct stoichiometric ratios in mixing the components. Although the recycling ducts may also be orientated differently, their disposition in a plane transversal to the axis of the slider is advantageous, in that it makes it possible to reduce to a minimum the displacement of the slider necessary for switching from a component mixing phase to a recycling phase.

The mixing head according to this invention operates in the following way: assuming that the slider is in the operative position shown in FIG. 7, in which the individual components are made to recycle, and is then moved to the operative position shown in FIGS. 1, 2, 3, 4, 5 and 6, in which the mixing chamber 4 is completely retracted with respect to the duct 8, and in which the chamber 4 is in communication with the duct 8 by means of the branched-off ducts 9 and 10 defined by the walls of the slider 3 and of its guide channel. In this condition, the injectors 6 and 7 open out into the mixing chamber (FIG. 2), as their nozzles are situated at a smaller minimum distance than the width of the chamber 4 itself.

The two jets, colliding with each other at high speed, mix together thoroughly and the resulting mixture, in flowing down to the lower part of the chamber 4, separates into two different flows which are conveyed, through the branched ducts 9 and 10, on two opposing sides, tangentially to the upper end of the outlet duct 8. On arriving at this point the two flows, which still maintain high kinetic energy due to the shortness of the path, collide with each other again and, thanks also to the tangential disposition of the side walls 19, with respect to the duct 8, a swirl is generated, which gradually quietens down due to the larger cross-section of the duct 8, which creates an additional mixing effect.

In other words, the separation of the two flows and their subsequent re-mixing in the channel 8, causes all the particles of the components to mix evenly together and to combine chemically, thereby obtaining a homogenous mixture which leaves the outlet of the duct 8 in a smooth steady or laminar flow.

Upon completion of the mixing phase, the slider 3 is made to advance to the position shown in FIG. 7, in which the mixing chamber is axially aligned with the outlet duct 8 and in which the nozzles of the injectors 6 and 7 now open out into the recycling ducts 24, as shown in the cross-sectional view in FIG. 8. As the mixing chamber 4 is axially aligned with the outlet duct 8, and as the areas of their cross-sections are identical, it is possible to move forward the cleaning member plunger 16 which cleans the walls of the chamber 4 and of the duct 8, expelling all the residual mixture; this condition is shown in the cross-sectional view in FIG. 7.

The head can now be re-used for a further mixing cycle, in a way wholly identical to that previously described. In the case illustrated, the slider 3 presents a double T-shaped cross-section and two longitudinal ribs under the lower wings; the intermediate ducts connecting the chamber 4 to the outlet duct 8 are situated on the bottom of the slide guide channel 2, in correspondence with said ribs; the cross-section of the slider 3 could however be of any shape whatsoever, for example T-shaped, rectangular or triangular, with one or more longitudinal ribs, each of which defining a corresponding intermediate duct connecting the chamber 4 to the outlet duct 8, on the bottom of the slider guide channel and ending in correspondence with the mixing chamber; a differently shaped slider 3 is shown, for example, in the cross-sectional views of FIGS. 9 and 10, where the same numerical references of the previous figures refer to similar or corresponding parts. In this case, the slider 3 presents a triangular cross-section, with a single rib 3d on the lower wall, defining a single central duct 9a, as shown, for connecting the chamber 4 to the outlet duct 8, in the retracted condition of the chamber, with respect to the outlet duct itself. Although the overall cross-sectional area of the intermediate connecting duct or ducts may be of any value, such area is preferably chosen equal to or smaller than the cross sectional area of the mixing chamber 4 so that the flow of mixture maintains substantially the same speed on leaving the chamber, or is accelerated so as to create a further mixing effect along each individual intermediate duct and at the entrance of the outlet duct itself.

FIG. 11 shows a second embodiment of the movable chamber mixing head, according to this invention, in which the same numerical references indicate parts corresponding to those of FIG. 1.

In the case shown, the stroke of the slider 3 is shorter than the diameter of the mixing chamber 4, that is to say, of the outlet duct 8; consequently, the mixing chamber 4 communicates directly with the outlet duct 8 through a narrow hole 4' which can be suitably regulated by means of an adjustable stop device for interrupting the stroke of the slider 3, defined for example by a set screw 12' and relative lock nut, said screw being screwed into the rear wall of the control cylinder 12 which is situated on the same side as the injectors 6, 7 for the components to be mixed together.