DE69308260T2 - Mixing device for highly viscous substances - Google Patents

Abstract

An appropriate device for mixing substances which have a high viscosity, comprising one or two mixing rollers (13) rotating about vertical axes, which can be raised and lowered into and out of a rotating cylindrical drum (3) with a vertical axis, containing the substances to be mixed, and which can be moved in radial direction, and driving means (5, 10, 15) for actuating the movements of the mixing rollers and of the drum so that the mixing rollers, which are first of all raised to make it possible to instal the drum (3) containing the substances to be mixed, enter the drum (3) in an approximately central position while being immersed into the substances to be mixed, and then they produce the mixing by the combined action of their own rotation and the rotation of the drum (3), while moving, during this operation, closer to the walls of the drum, so as to subject the substances to be mixed to crushing, rolling and drawing in all the regions of the drum (3); finally, the mixing rollers (13) again adopt a substantially central position and are raised out of the drum (3) to allow it to be moved away and at the same time are cleaned by cleaning devices (16).

Description

This invention relates to a device suitable for mixing substances having a high viscosity. A particularly significant, but non-limiting example of substances with which the device according to the invention is suitable for mixing are printing inks for offset printing, to which special reference is made in the following description.

For certain printing operations it is necessary to mix, in precise proportions, several inks of different colours. The dosing of the inks to be mixed is carried out by means of special devices, such as in particular that according to European patent application EP-A-0 538 926. After the different inks have been poured into a drum in the desired proportions, they must be mixed in an extremely precise manner. This operation encounters difficulties mainly due to the high viscosity and adhesiveness of the inks. According to the known method, this operation is carried out by means of mixing devices which use a mixing element in the form of butterflies which rotate within the mass of inks to be mixed, or by means of mixers of the kneading machines type used in bread making, or by means of other devices which, however, do not provide such a high yield in this operation and which, after use, present great problems for cleaning them, which is carried out manually with considerable difficulty. Another problem that occurs with printing inks is that contact with atmospheric oxygen causes them to undergo oxidation, resulting in solidified layers and persistent bubbles, which subsequently have a detrimental effect. In certain cases, this problem is solved by Enclosing the mixing device and the drums in which the mixing operation is carried out in an airtight enclosure, applying a vacuum and then introducing an inert gas such as nitrogen. However, due to the shape of the known mixing devices, it is not at all advantageous to encapsulate them in airtight covers, in many cases it is not possible to do this and a further operation would have to be added; causing the materials to pass through inside a three-drum refining machine to displace the air which has entered during the mixing operation.

These difficulties, which typically occur when mixing printing inks of different colors, or even just a part of these difficulties, also occur when mixing other materials that have a high viscosity, such as in the production of high-viscosity printing inks when powdered pigments are dispersed in the varnish or clear coat.

From the document FR-A-1 465 170 a mixing device is known, with at least one mixing roller, with means for supporting the mixing roller, which can be rotated by means of the same about a vertical axis and can be lowered and raised in and out of a cylindrical barrel containing the substances to be mixed, as well as moved radially within the cylindrical barrel, with means for supporting the cylindrical barrel, which can be rotated by means of the same about a vertical axis, and with a motor device for driving the movements of the mixing roller and the barrel, the whole being designed in such a way that the mixing roller and the barrel are set in rotation, that the mixing roller, which is initially raised so that the barrel containing the substances to be mixed can be inserted, is lowered in such a way that it penetrates approximately into the middle of the barrel and immerses itself in the substances to be mixed, that the mixing process then takes place by the combined effect of the rotational movement of the mixing roller and the rotational movement of the barrel, the mixing roller moving during this process moves in the circumferential direction and approaches the wall of the barrel so that the materials to be mixed are pressed, rolled and stretched in all areas of the barrel, and that finally, the mixing roller returns to the approximately central position and is lifted out of the barrel in this position, which can then be carried away. This device corresponds to the preamble of patent claim 1.

One of the main aims of this invention is to provide a mixing device that works with a high output and therefore in relatively short periods of time, achieving a complete degree of mixing even with materials that have a high viscosity and adhesiveness, such as in particular the inks for offset printing. Another aim is to provide a device that can be cleaned by means of simple operations and that is suitable for mechanization, at least to a large extent. Another aim is to provide a device that has a shape that does not cause great problems in enclosing the active parts in an environment outside the atmosphere, in those cases in which this requirement arises. Yet another aim of the invention is to provide a device that, by its very nature, tends to work so as to expel air contained in the materials.

These objects are achieved according to this invention by a device of the type specified, mainly in that the device also has a cleaning device which is operatively connected to the mixing roller in order to remove at least the majority of the material still adhering to the mixing roller when the latter is lifted out of the mixed materials.

In this device a mixing operation takes place by the effects of rolling and stretching, in the same way as those devices carried out in a known manner by means of the three-cylinder machines for the production of viscous inks, with a high yield and by achieving a perfect mixture in a relatively short period of time and with a relatively reduced energy consumption, as well as an effective action of expelling the air possibly trapped in the treated materials. At the same time, the simple shape of the mixing elements, formed by one or more rollers, allows to effect a cleaning according to the invention, which simultaneously with the lifting out at the end of the operation by means of simple cleaning devices using a wiping blade or an air blade nozzle arranged around the mixing rollers, the rollers, when they arrive in their upper position, already being cleaned to a large extent and only a thin film or veil of material to be removed remaining.

Preferably, the device comprises a container which is arranged near the working position and is intended for the barrel and contains a solvent or a detergent into which the mixing roller can be lowered after the mixing process. The container can also contain cleaning devices, such as brushes or the like.

This method of cleaning the rollers can be improved and the operations for cleaning the mixing elements can be substantially mechanised, although in certain cases other simple cleaning operations must be carried out manually.

Furthermore, the simple shape of the mixing elements and the possibility of supporting them on a plate which, during the mixing process, rests on an upper edge of the drum containing the substances to be mixed, makes it possible to easily create a seal between the plate and the drum and therefore to create a negative pressure inside the drum and to provide the possibility of introducing inert gas.

In one embodiment, the device comprises a single mixing roller, the diameter of which preferably corresponds to approximately half the diameter of the barrel containing the substances to be mixed.

In another embodiment, the device also comprises a second mixing roller which is parallel to the first roller and supported at a variable distance therefrom, whereby during the working process the distance between the two rollers is also reduced, whereby the The materials to be mixed are also subjected to rolling and stretching in the area between the two mixing rollers.

The invention also relates to the mixing process effected by the mixing device according to the invention.

These and other features, objects and advantages of the invention will become clear from the following description of an embodiment given by way of non-limiting example with reference to the accompanying drawings, in which:

Fig. 1 is a plan view of a mixing device according to the invention, with the upper part thereof removed according to the line I-I of Fig. 2;

Fig. 2 shows a longitudinal vertical section of the same, taken along the line II-II of Fig. 1;

Fig. 3 shows a transverse vertical section of the same, taken along the line III-III of Fig. 1;

Fig. 4 is a view from the bottom of the central region of a barrel suitable for cooperation with the mixing device according to the invention; and

Fig. 5 shows a sectional view taken along the dashed line V-V of Fig. 4.

The device according to the invention includes a support frame 1 provided with means, such as a roller conveyor 2, for moving the drums 3 containing the substances to be mixed. A rotating platform 4, driven by a motor 5 by means of a gear 6, is provided for supporting the drum 3, on which the working operation is carried out by setting it in rotation.

Above the inlet area of the barrel 3, the support structure 1 is provided with longitudinal guides 7 for supporting a movable frame comprising a plate 8 resting on the inlet area of the barrel 3 and comprising columns 9 at the upper end on which a motor assembly 10 is installed. The motor assembly 10 is operatively connected to vertical screws 11 cooperating with internal threads of a bracket 12 supporting the mixer elements, in this way the bracket can be raised to the position shown in Fig. 2 by means of dashed lines at 12' and lowered to the working position shown by solid lines.

In the embodiment shown in the drawings, two mixing elements are present and they are formed by two parallel rollers 13 with a relatively reduced diameter. However, as shown by the dot-dash lines in Fig. 2, the pair of rollers 13 can also be replaced by a single mixing roller 13'. In this case, the single roller preferably has a relatively large diameter, e.g. half the inner diameter of the barrel 3. The following description refers to the embodiment with two mixing rollers 13, but it is clear to a person skilled in the art how the arrangements can be simplified in the case when a single mixing roller 13' is used, as well as it is also possible that more than two mixing rollers are used.

Each mixing roller 13 is rotatably supported by a trolley 14 which moves transversely on the support plate 12. The transverse movements of each trolley 14 are driven by a motor means (not shown) which can be constituted by an electric motor or a hydraulic or pneumatic cylinder to move the corresponding mixing roller 13 radially in relation to the barrel 3 and in relation to the other mixing roller 13. On the trolleys 14 are installed motor assemblies 15 which are connected to the mixing rollers 13 for driving their effective rotation.

Under the support plate 8, a cleaning device 16 (Fig. 2) is mounted around the mixing rollers 13, which is formed by a wiper blade and/or by a nozzle, which is suitable for blowing out an air blade, e.g. according to Italian patent application No. TO 91 A 000 791. Finally, near the working position of the barrel 3, e.g. behind it (Fig. 2), a washing tank 17 is installed for the final cleaning of the mixing rollers.

The device described operates as follows. While the mixing rollers are in their raised position (which the drawings show only by dashed lines as support 12' and motor 15') closely centered with respect to the rotary platform 4, a drum 3 containing the materials to be mixed is raised along the roller conveyor 2 up to the rotary platform 4 and the latter is set in rotation by the motor 5. If necessary, a seal is made between the support plate 8 and the inlet area of the drum 3 to allow oxygen to be led out and an inert gas to be introduced into the drum 3. The mixing rollers 13, set in rotation by the respective motors 15, are then lowered into the drum 3 and into the materials to be mixed by lowering the support 12 by means of the motor 10 and the screws 11. The rollers 13, as they rotate, draw in the materials to be mixed due to their viscosity, and in the area between the two rollers 13 these materials are subjected to rolling and stretching, whereby a particularly precise mixing takes place. A similar process takes place between the mixing roller which is located closer to the wall of the barrel 3 and the wall itself. Furthermore, during this operation the mixing rollers 13 are moved by means of the load drives 14 in the radial direction with respect to the rotating barrel, whereby all areas of the materials to be mixed contained in the barrel are reached by the mixing process, and the effect of compression, rolling and stretching which takes place between a mixing roller and the barrel wall increases as the distance between these parts is reduced. This phenomenon is particularly important when only a single roller 13 is used. If, on the other hand, two mixing rollers 13 are used, the mutual distance between these rollers can be regulated and kept constant at a preferred value, or preferably it is also reduced during the working process by bringing the rollers closer together in order to increase their effect, as this process progresses. The radial displacement of the mixing rollers may take place only once, or may be repeated two or more times by periodically moving the rollers in a repeated manner towards the center.

When the mixture obtained is considered sufficient, the rollers 13 are brought back to a substantially central position, the rotation of the barrel 3 can be stopped and the mixing rollers 13 are withdrawn from the now mixed materials by lifting the support 12 by means of the motor 10 and the screws 11. During this lifting, the cleaning device 16 is activated, e.g. by bringing it closer to the mixing rollers, and the cleaning device removes from the mixing rollers 13 during their passage most of the adhering viscous material, causing it to fall downwards into the barrel 3. The central position of the rollers 13 during this working stage ensures that the materials dripping from the rollers are collected by the barrel 3 without polluting the surrounding environment. In this way, the mixing rollers arrive in their raised position in a noticeably cleaned state, although they are not yet completely cleaned.

While the treated barrel 3 is removed and a new barrel is placed on the platform 4, the support plate with all the elements supported by it is moved along the guides 7 until the mixing rollers 13 are placed above the tank 17 containing a solvent or detergent and, if necessary, some cleaning means such as brushes or the like, and the mixing rollers 13 are lowered into this tank. In this way, their cleaning can be brought to a significant level by mechanical means, which may be definitive, but in any case further manual cleaning, if necessary, will be very easy. The rollers are then brought back to their initial position for a new working cycle.

Emptying the mixed substances from the barrel 3 is usually carried out by inserting a piston 18 (Fig. 5) from the top into the barrel 3 and opening an outlet which is designed as a cylindrical bore in the bottom of the barrel 3. During this operation, the stream passing through a simple bore of the barrel can easily incorporate or retain gas bases which are subsequently detrimental. In order to obtain in the best way the results of the precise operation made possible by the device according to the invention, it is possible to use an improved barrel. An example of a barrel (not claimed) incorporating an improvement is shown in Figs. 4 and 5.

The bottom 19 of the improved barrel 3 has a large opening at its lower end which is normally closed by a conical or flat valve 20 urged by a spring 21. When pressure is exerted on the material contained in the barrel 3 by means of the piston 18, the force of the spring 21 is overcome and the valve 20 opens slightly, thus allowing the material contained in the barrel 3 to escape. Therefore, the opening through which the viscous material flows is in the form of a thin slit, and the high cutting stresses to which the viscous material is subjected in passing through this slit cause any gas bubbles that may be present to burst. In this way, the mixed materials, which are discharged in the form of a lamellar nozzle, can be removed from the barrel in the best condition for their use or further processing, e.g. for packaging.

It is understandable that the properties of the various viscous materials to be mixed as well as their amounts may vary greatly and in connection with this the structural and working parameters of the device according to the invention should be selected in a suitable manner. Thus, the diameter of the mixing rollers should be selected as a function of the barrels to be treated, the number of mixing rollers installed and the properties of the materials to be treated. The number of rollers used (one or more) depends both on the difficulty of the mixing process by the materials to be treated and on the time allowed for the working process. The angular velocities and the directions of rotation (equal or opposite) of the barrel and the mixing roller or rollers can be modified. to obtain the best results and for this purpose it is advantageous that the motors driving the components are provided with a suitable control device.

Claims (11)

1. Device for mixing substances that have a high viscosity 1 with at least one mixing roller (13), with means (7-12) for holding the mixing roller (13), which can be rotated about a vertical axis with the aid of the same and can be lowered and raised into and out of a cylindrical barrel (3) containing the substances to be mixed, as well as moved radially within the cylindrical barrel (3), with means (4) for holding the cylindrical barrel (3), which can be rotated about a vertical axis with the aid of the same, and with drive means (5, 10, 15) for driving the movements of the mixing roller (13) and the barrel (3), the whole being designed in such a way that the mixing roller (13) and the barrel (3) are set in rotation, that the mixing roller (13), which is initially raised so that the barrel (3) containing the substances to be mixed can be inserted, is lowered in such a way that it penetrates approximately into the middle of the barrel (3) and into the the mixing process is then carried out by the combined effect of the rotary movement of the mixing roller (13) and the rotary movement of the barrel (3), the mixing roller moving in the circumferential direction during this process and approaching the wall of the barrel (3) so that the materials to be mixed are pressed together, rolled and stretched in all areas of the barrel (3), and finally the mixing roller (13) returns to the approximately central position and is lifted out of the barrel (3) in this position, which can thus be carried away, characterized in that the device also has a cleaning device (16) which is operatively connected to the mixing roller (13) in order to remove at least most of the material still adhering to the mixing roller (13) when the latter is lifted out of the mixed material. 2. Mixing device according to claim 1, characterized in that a tub (17) is provided which is arranged near the working position provided for the barrel (3) and contains a solvent or a detergent, wherein the mixing roller can be lowered into this tub after the mixing process. 3. Mixing device according to claim 2, characterized in that the tub (16) contains additional cleaning agents such as brushes or the like. 4. Mixing device according to claim 1, characterized in that a support frame (1), a conveyor (2) carried by the support frame (1) for the barrels (3) containing the substances to be treated, a turntable (4) for the barrel (3) during treatment, a support plate (8) supported on the support frame (1) and resting on the inlet area of the barrel (3) and a console (12) which can be moved by drive means (10, 11) in a direction perpendicular to the support plate (8), and at least one carriage (14) arranged on the console (12) which carries at least one mixing roller (13), as well as drive means (10, 15) are provided which serve to drive the mixing roller (13) and for the horizontal movement of the carriage (14). 5. Mixing device according to claim 2 and 4, characterized in that means (7) are also provided for displacing the support plate (8) in a horizontal direction perpendicular to the direction of movement of the carriage (14) from and to the tank containing the solvent or the detergent. 6. Mixing device according to claim 4, characterized in that at least part (10) of the drive means consist of electric motors which drive actuating screws (11). 7. Mixing device according to claim 4, characterized in that sealing means are arranged between the support plate (8) and the inlet area of the barrel (3). 8. Mixing device according to any one of the preceding claims, characterized in that in one embodiment thereof a single mixing roller (13') is provided, the diameter of which preferably corresponds to approximately half the diameter of the barrel (3) containing the substances to be mixed. 9. Mixing device according to any one of claims 1 to 7, characterized in that in one embodiment thereof at least one second mixing roller (13) is provided, which runs parallel to the first mixing roller and is arranged at a variable distance from the same. 10. Method for mixing substances that have a high viscosity, with a device that has at least one mixing roller (13), means (7-12) for holding the mixing roller (13), which can be rotated about a vertical axis with the aid of the same and can be lowered and raised into and out of a cylindrical barrel (3) containing the substances to be mixed, as well as moved radially within the cylindrical barrel (3), means (4) for holding the cylindrical barrel (3), which can be rotated about a vertical axis with the aid of the same, and drive means (5, 10, 15) for driving the movements of the mixing roller (13) and the barrel (3), whereby the mixing roller (13) and the barrel (3) are set in rotation, the mixing roller (13), which is initially raised so that the barrel (3) containing the substances to be mixed can be inserted, is lowered so that it is approximately penetrates into the middle of the barrel (3) and immerses itself in the materials to be mixed, and then the mixing process takes place by the combined effect of the rotary movement of the mixing roller (13) and the rotary movement of the barrel (3), the mixing roller moving in the circumferential direction during this process and thereby approaching the wall of the barrel (3) so that the materials to be mixed are pressed, rolled and stretched in all areas of the barrel (3), and that finally the mixing roller (13) returns to the approximately central position and in this position is lifted out of the barrel (3), which can thus be carried away, characterized in that the mixing roller (13), while it is lifted out after each mixing process, is cleaned by a cleaning device (16). 11. Method according to claim 10, characterized in that the mixing roller (13) is thoroughly cleaned in a tub (17) which contains a solvent or a detergent and possibly additional cleaning agents.