“Mixing head”

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TECHNICAL FIELD

This invention is applied to the food industry.

In particular, the invention relates to a mixing head and is applied for example in the pastry industry to obtain emulsified and aerated creams. Even more in particular, the mixing head according to this invention is applied in continuously operating mixing apparatuses.

Furthermore, the invention relates to a mixing method which can be actuated in continuously operating mixing apparatuses.

PRIOR ART

Mixing heads, known for example from the document JP-H02 144136, are designed to emulsify creams and to aerate them, in order to obtain the desired final specific weight. A cream is fed to the mixing head, optionally adding further ingredients, to be emulsified and aerated also by introducing air or another gas, for example nitrogen. The mixing takes place as a result of the joint action of a suitably configured rotor/stator system. In particular, while the rotor rotates in the stator, the respective series of alternating blades generates a variable passageway within which the cream passes that then undergoes a continuous mixing and an intimate mixing of the components and the gaseous part.

The coupling between the rotor and stator provides a dynamic mechanical seal for isolating the mixing chamber. As is known, this seal comprises a stator portion and a rotor portion kept in mutual contact by a helical spring which encircles the rotating shaft on which the rotor is mounted and which pushes the rotor portion against the stator portion.

Because it is located within the mixing chamber, the useful life of the seal depends on the products being processed. In particular, products with a high content of sugar strongly stress the seal which within little time, generally a month, presents the first leaks and must be replaced.

In fact during the processing, the sugar grains reduce in size and thus the sugar can easily infiltrate between the surfaces in contact. In the case where the temperature in the mixing chamber is such as to dissolve the sugar, the drawbacks given by this infiltration are limited. But in the case where the temperature of the product drops and/or the process is interrupted, the infiltrated sugar solidifies, thereby reducing the performance of the spring and the sealing members (O-ring) and acting as an abrasive component in the moment when the processing is resumed.

SUMMARY

In this context, the technical task underlying the present invention is to provide a mixing head, in particular for continuously operating mixing apparatuses, and a mixing method which obviate at least some of the drawbacks in the prior art as described above.

In particular, an object of the present invention is to provide a mixing head and method capable of improving the useful life of the seal interposed between the rotor and stator.

A further object of the present invention is to limit the friction and to improve the operation of this seal.

The technical task set and the objects specified are substantially attained by a mixing head and method, comprising the technical characteristics as set out in one or more of the accompanying claims. The dependent claims correspond to further advantageous aspects of the invention.

It should be highlighted that this summary introduces, in simplified form, a selection of concepts which will be further elaborated in the detailed description given below.

In particular, in accordance with a first aspect, the present invention relates to a mixing head adapted to be used for continuously operating mixing apparatuses. The mixing head comprises a rotor/stator system in which a sealing device is interposed between the rotor and the stator, this sealing device having an axially fixed rotor portion and a stator portion kept in contact with the rotor portion by means of a pushing action operated axially thereon by a pushing device.

The applicant considers that the provision of the pushing device so as to make it active on the stator portion improves the useful life of the sealing device interposed between the rotor and stator, avoiding leaks and infiltrations. In particular, the pushing device is no longer arranged inside the mixing chamber in contact with the substance being processed.

In accordance with a second aspect, the present invention relates to a mixing method which can be actuated in continuously operating mixing apparatuses. The mixing method provides preparing a mixing chamber comprising a rotor/stator system and introducing a cream to be mixed into the mixing chamber, driving the rotor in rotation. It is also envisaged to inject air under pressure into a duct opening to the outside and placed in fluid connection with a sealing device interposed between the rotor and stator and to detect possible leaks by measuring the pressure inside said duct and thus detecting the variations with respect to the pressure of the injected air. The Applicant believes that the early detection of leaks and infiltrations allows carrying out the necessary checks and appropriate replacements, avoiding damaging further components of the mixing head.

In one or more of the aspects specified, the present invention can comprise one or more of the following features.

Preferably an outer casing surrounds the mixing chamber which extends along an axis and comprises at least one processing portion. The rotor is arranged inside the processing portion of the mixing chamber and is mounted on a rotating shaft arranged with the rotation axis coinciding with the axis that passes through the outer casing. The stator is solidly constrained to the outer casing, has an annular shape around the axis and encircles the rotor in a radially external position thereto at least at the processing portion of the mixing chamber. The rotor portion of the sealing device encircles the rotating shaft, is solidly constrained to the rotor in rotation about the axis and is mounted in a fixed position along the axis itself.

The stator portion of the sealing device encircles the rotating shaft and is slidingly mounted along the axis relative to the outer casing.

The rotor portion and the stator portion respectively have an annular rotor surface and an annular stator surface arranged transversely relative to the axis and encircling the rotating shaft.

The pushing device is active on the stator portion in axial thrust to maintain the annular stator surface in contact with the annular rotor surface.

Preferably the pushing device comprises at least one elastic element operatively interposed between the stator portion and the outer casing.

Still more preferably the elastic element is interposed between the stator portion and a stop ring encircling the rotating shaft and mounted in a fixed position along the axis.

The elastic element preferably has a preload for example equal to 1 mm. Preferably the pushing device comprises a plurality of elastic elements, preferably helical springs, distributed angularly around the axis and the rotating shaft in such a way as to obtain a uniform distribution of the load. Still more preferably the elastic elements are interposed between the stator portion and a stop ring encircling the rotating shaft and mounted in a fixed position along the axis.

The elastic elements preferably have a preload for example equal to 1 mm. Preferably a bushing solidly constrained to the outer casing partially houses the stator portion slidably along the axis. Preferably the stop ring is fixed axially and angularly inside the bushing so as to simplify the assembly of the sealing device.

Preferably the pushing device is arranged in a housing volume separated from the mixing chamber so as to preserve the structure and mechanical characteristics thereof. The annular stator surface in contact with the annular rotor surface is arranged inside the mixing chamber. Preferably the bushing internally defines the housing volume and comprises sealing gaskets that separate the mixing chamber from the housing volume. Preferably the outer casing has one or more ducts placed in fluid connection with the sealing device and exiting outside the mixing head in order to detect any leaks. Still more preferably a lower duct is provided leading into a lower portion of the mixing head and/or an upper duct leading into an upper portion of the mixing head. The lower duct receives by gravity and lets any leaks exit that are thus visually shown to an operator of the mixing head. The upper duct is connected to a source of compressed air and has a pressure gauge configured to detect differences in pressure in the upper duct itself due to leaks and infiltrations.

Preferably the rotor portion comprises an annular rotor body having the annular rotor surface and a fixing sleeve fixed to a front surface of the rotor and encircling the rotating shaft. The fixing sleeve and the annular rotor body are mutually connected for example by means of a tubular body arranged radially external thereto.

Preferably a sealing gasket is interposed between the fixing sleeve and the front surface of the rotor so as to prevent infiltrations.

Preferably a contact portion of the annular rotor surface and the annular stator surface has radial dimensions comprised between 89 millimetres and 95 millimetres, preferably 95 millimetres.

Preferably the annular rotor surface and the annular stator surface have a coating of silicon carbide SiC obtained through the surface treatment of laying silicon carbide SiC so as to increase the mechanical and thermal hardness and resistance to wear thereof, and therefore improve the seal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will become more apparent from the following indicative, and hence non-limiting, description of a preferred, but not exclusive, embodiment of a mixing head. This description will be set out below with reference to the appended drawings, which are provided solely for indicative and therefore non-limiting purposes, in which:

- figure 1 schematically shows a sectional view of a mixing head;

- figure 2 schematically shows a sectional view of a portion of the mixing head of figure 1 according to the line ll-ll of figure 5;

- figure 3 shows the enlarged detail III of figure 2;

- figure 4 shows a perspective view of some components of the head of figure 1 , assembled to each other;

- figure 5 shows a front view of the components of figure 4, with an indication of the planes of section ll-ll of figure 2;

- figure 6 shows a transversal section view of the outer casing of the mixing head according to the line VI-VI of figure 1 .

DETAILED DESCRIPTION

The present invention relates to a mixing head.

With reference to the figures, the number 1 generally indicates a mixing head, preferably adapted to continuously operating mixing apparatuses. The other numerical references refer to technical features of the invention which, barring indications otherwise or evident structural incompatibilities, the person skilled in the art will know how to apply to all the variant embodiments described.

Any modifications or variants which, in the light of the description, are evident to the person skilled in the art, must be considered to fall within the scope of protection established by the present invention, according to considerations of technical equivalence.

The mixing head 1 comprises an outer casing 2 surrounding at least one mixing chamber 3.

The mixing chamber 3 extends along an axis "X". As for example illustrated in figure 3, the mixing chamber 3 has an inlet portion 3a, a processing portion 3b and an outlet portion 3c arranged in sequence along the axis "X". The inlet portion 3a preferably has tapered shape, which narrows away from the processing portion 3b, and is placed in communication with the exterior through a supply duct, not illustrated. Preferably the supply duct is arranged radially relative to the axis "X".

The processing portion 3b has a substantially cylindrical shape around the axis "X".

The outlet portion 3c preferably has tapered shape, which narrows away from the processing portion 3b, and is placed in communication with the exterior through an outlet duct 5 through which the emulsified and aerated cream is sent to the subsequent processing. Preferably the outlet duct 5 is arranged coaxially to the axis "X".

The outer casing 2 has a gap 6 arranged at least partially around the mixing chamber 3. Preferably the gap 6 has an annular shape around the axis "X". The gap 6 is adapted to receive a fluid, for example water, adapted to carry out the thermal stabilisation function. The fluid is introduced and extracted in the gap with continuity by means of a circulation system, for example by means of a hydraulic pump. To control the mixing parameters, the fluid is introduced in the gap 6 at a controlled temperature.

The number 7 indicates a stator solidly constrained to the outer casing 2 and laterally delimiting the processing portion 3b of the mixing chamber 3. The stator 7 has an annular shape around the axis "X" and preferably defines a delimiting inner side wall of the gap 6. In other words, the gap 6 is arranged around the stator 7 and in a radially external position thereto.

In accordance with a possible embodiment, the stator 7 has a plurality of annular stator mixing portions 8 distributed along the axis "X" at a radially internal surface of the stator 7. Each annular stator mixing portion 8 comprises a plurality of stator blades 9 distributed circumferentially around the axis“X” and extending in a centripetal direction from the radially internal surface of the stator 7. Preferably each stator blade 9 has a radial shape. The number 10 indicates a rotor arranged inside the processing portion 3b of the mixing chamber 3 and rotating around a rotation axis coinciding with the axis "X" of the mixing chamber 3.

The rotor 10 has a cylindrical shape around the axis "X" and is encircled by the stator 7 arranged at a radially external position with respect thereto at the processing portion 3b of the mixing chamber 3.

In accordance with a possible embodiment, the rotor 10 has a plurality of annular rotor mixing portions 1 1 distributed along the axis "X" at a radially external surface of the rotor 10.

Each annular stator mixing portion 1 1 comprises a plurality of rotor blades

12 distributed circumferentially around the axis “X” and extending in a centrifugal direction from the radially external surface of the rotor 10. Preferably each rotor blade 12 has a radial shape.

The annular rotor mixing portions 1 1 are arranged in an alternating manner with the annular stator mixing portions 8 along the axis "X" and meshing with them.

The rotor 10 is mounted on a rotating shaft 13, also arranged with a rotation axis coinciding with the axis "X" of the mixing chamber 3. The rotating shaft

13 passes through the outer casing 2.

The rotating shaft 13 can be mounted on bearings 14 housed in a support 15 preferably created as an appendage of the outer casing 2.

Advantageously the mixing head 1 comprises a sealing device 16 operatively interposed between the rotor 10 and the stator 7, in particular the outer casing 2.

The sealing device 16 comprises a rotor portion 17 operatively associated with the rotor 10 and encircling the rotating shaft 13.

The rotor portion 17 is solidly constrained to the rotor 10 in rotation about the axis“X” and is mounted in a fixed position along the axis itself.

In accordance with a possible embodiment, the rotor portion 17 comprises an annular rotor body 18 which has an annular rotor surface 19 arranged transversely with respect to the axis "X" and encircling the rotating shaft 13. Preferably the annular rotor surface 19 has a coating of silicon carbide SiC obtained through the surface treatment of laying silicon carbide SiC.

Advantageously, silicon carbide SiC is a ceramic material with excellent resistance to abrasion, corrosion and thermal shock. Even more advantageously, silicon carbide SiC has excellent thermal conductivity (and therefore low thermal expansion) and extreme resistance to acids and bases.

In addition, silicon carbide SiC is used in the food industry because it is not capable of generating toxicological issues.

Preferably the rotor portion 17 comprises a fixing sleeve 20 fixed to a front surface 10a of the rotor 10 and encircling the rotating shaft 13. Even more preferably a sealing gasket 20a is interposed between the fixing sleeve 20 and the front surface 10a of the rotor 10. More precisely, the sealing gasket 20a is preferably arranged on a surface of the fixing sleeve 20 orthogonal relative to the axis of rotation "X" of the rotating shaft 13, rather than on a surface parallel to the axis of rotation "X". Still more precisely, the sealing gasket 20a is arranged along the outermost perimeter of the fixing sleeve 20, so as to prevent even the slightest infiltration between the sleeve itself and the surface 10a of the rotor 10.

In this way, the sealing gasket 20a arranged in a corresponding housing that receives it in a stable manner, advantageously also prevents a possible deposit of product being processed inside the same housing in which it is positioned, thereby avoiding the proliferation of bacterial flora.

The fixing sleeve 20 and the annular rotor body 18 are mutually connected for example by means of a tubular body 21 arranged radially external thereto.

The sealing device 16 comprises a stator portion 22 operatively associated with the stator 7 and encircling the rotating shaft 13.

The stator portion 22 is slidably mounted along the axis "X", i.e. in the axial direction, relative to the outer casing 2 on which it is mounted. The stator portion 22 has an annular stator surface 23 arranged transversely relative to the axis "X" and encircling the rotating shaft 13. Preferably the annular stator surface 23 has a coating of silicon carbide SiC obtained through the surface treatment of laying silicon carbide SiC.

The number 24 comprehensively indicates a pushing device acting on the stator portion 22 in axial thrust to maintain the annular stator surface 23 in contact with the annular rotor surface 19.

In accordance with one aspect of the present invention, the annular stator surface 23 in contact with the annular rotor surface 19 are arranged inside the mixing chamber 3.

Preferably, the annular stator surface 23 in contact with the annular rotor surface 19 are arranged inside the inlet portion 3a and are immersed in the product being processed.

In other words, at least the inlet portion 3a (like the entire mixing chamber 3) does not define a cooling circuit with a specific cooling liquid, but is filled by the same product being processed.

For example, preferably the working speeds of the rotor 10 are relatively low (comprised between 120 and 180 rpm) and therefore the possible heat created in the friction between the annular stator surface 23 and the annular rotor surface 19 is irrelevant both as regards the maintenance of the working temperature and as regards the possible transfer of the heat generated to the product in transit in the unit of time.

In still other words, preferably the product in transit in the mixing chamber 3 also acts as a lubricant between the annular stator surface 23 and the annular rotor surface 19.

In accordance with another aspect of the present invention, the pushing device 24 is arranged in a housing volume "V" separated from the mixing chamber 3.

A contact portion of the annular rotor surface 19 and the annular stator surface 23 has radial dimensions comprised between 81 millimetres and 87 millimetres, preferably 87 millimetres, so as to have a smaller friction surface and therefore a reduction of the heat generated.

The pushing device 24 can comprise at least one elastic element operatively interposed between the stator portion and the outer casing. Preferably the pushing device comprises a plurality of elastic elements 25, preferably helical springs, distributed angularly around the axis“X” and the rotating shaft 13.

The springs preferably have a preload for example equal to 1 mm and work in pushing force to maintain the annular stator surface 23 in contact with the annular rotor surface 19 and ensure the seal.

Preferably the elastic elements 25 are axially interposed between the stator portion 22 and a stop ring 26 encircling the rotating shaft 13 and mounted in a fixed position along the axis“X”.

For example, a bushing 27 can be provided, solidly constrained to the outer casing 2, inside which it partially houses the stator portion 22 axially slidable relative to the bushing.

Moreover, the bushing 27 houses the stop ring 26 which is axially and angularly fixed inside the bushing itself.

For example the stop ring 26 is angularly fixed inside the bushing 27 by means of shape couplings constituted by radial protrusions 28 and seats 29 adapted to receive the radial protrusions and extending in the axial direction. The shape coupling prevents slipping off axis and maintains the stop ring 26 centred.

For example the stop ring 26 is axially fixed inside the bushing 27 by means of a fixing pin 30 radially inserted between the bushing 27 and the stop ring 26. In this way the stop ring is axially locked at least in the direction opposite the stator portion 22.

Preferably the bushing 27 internally defines the housing volume“V” and comprises sealing gaskets 31 that separate the mixing chamber 3 from the housing volume“V”. In accordance with a possible embodiment which may not provide the sealing device 16 and the pushing device 24 in the embodiments described above, the outer casing 2 can have one or more ducts 32 placed in fluid connection with the sealing device, and in particular with the coupling between the annular rotor surface 19 and the annular stator surface 23 and exiting outside the mixing head.

Preferably, as better illustrated in figure 6, at least one lower duct 33 is provided leading into a lower portion of the mixing head and/or an upper duct 34 leading into an upper portion of the mixing head.

The lower duct 33 receives by gravity and lets any leaks exit that are thus visually shown to an operator of the mixing head.

The upper duct 34 is connected to a source 35 of compressed air and has a pressure gauge 36 configured to detect differences in pressure in the upper duct 34 itself due to leaks and infiltrations.

In addition to the above, in general the components of the mixing head have chamfered edges so as to improve the hygiene of the mixing head itself.

In use, the mixing head 1 allows actuating a mixing method in which the cream to be mixed is introduced into the mixing chamber 3 and the rotor 10 is driven in rotation.

The mixing takes place continuously, emulsifying and aerating the cream following the rotor/stator interaction and optionally further introducing a gas, for example nitrogen, in the inlet portion of the mixing chamber. The mixed cream then proceeds in output from the mixing chamber.

During the mixing, air under pressure is injected into the upper duct 34 and the pressure is measured inside the upper duct 34, thereby detecting the variations (generally increasing) relative to the pressure of the injected air, indicating leaks in the mixing chamber 3.

A visual or sound alarm system can be operatively associated with the pressure gauge 36 to highlight possible leaks.