Food processor with a thermal compensator

Abstract

A mixing unit (1) comprising: a vessel (2) for containing a product to be mixed; a shaft (4) extending longitudinally inside the vessel (2) and configured for rotating around a rational axis (16) to be used for mixing the product inside the vessel (2), the shaft (4) having a first portion (5) and a second portion (6) separated from the first portion (5), wherein the mixing unit (1) further comprises a flexible member (7) connecting the first portion (5) to the second portion (6) of the shaft (4) for compensating a displacement between the first portion (5) and the second portion (6) due to thermal expansion of the vessel (2).

Description

[0001] FOOD PROCESSOR WITH A THERMAL COMPENSATOR

[0002] Technical Field

[0003] The invention relates to a mixing unit, such as a food processor, comprising a vessel, a shaft extending inside the vessel and a flexible member configured to counteract the effects of temperature changes inside the unit between the shaft and the vessel.

[0004] Background

[0005] Today it is common in many processes in the food industry to mix food products in a vessel of a mixing unit. The mixing process is usually carried out by a plurality of blades, also known as agitator blades, which are coupled to a central rotating shaft that extends longitudinally along the vessel of the mixing unit. In this way, the blades mix the food product present inside the vessel. Based on the type of product to be mixed and based on the process to which the product undergoes, the mixing unit and the corresponding components can be configured in different ways.

[0006] For example, a specific use of mixing units can involve the heating of the food product, i.e., in case of starch preparation or starch gelatinization. Accordingly, the vessel of the mixing unit can be at least partially surrounded by a heating jacket used to provide controlled heating to the content of the vessel. This jacket typically surrounds the tank and is designed to circulate a heating medium, such as steam or hot water, to maintain the desired temperature of the food product during the mixing process. The heating jacket allows for efficient heat transfer, ensuring that the food product is heated uniformly and reaches the required temperature for processing or other purposes.

[0007] However, before the entire content of the vessel is uniformly heated a thermal gradient can occur between the walls of the vessel and the innermost region of the mixing unit, i.e., the central rotating shaft, by providing heat at the region surrounding the vessel. Since the heat flows from the vessel’s walls to the central shaft, the heating depends on several factors, such as the thermal conductivity of the food product to be heated, the size of the vessel, the shaft and vessel material, and the quantity of the food product inside the vessel. In general, it is noted that in case a rapid heating of the food product is required, the initial thermal gradient between the central rotating shaft and the vessel’s walls can be significant.

[0008] Both the vessel and the central rotating shaft are usually made of metallic material. A thermal gradient between these two components can therefore cause a thermal expansion. In other words, the region of the mixing unit at lower temperature, i.e., the central rotating shaft, may undergo a smaller thermal expansion (or may not be subjected to thermal expansion at all) compared to the region of the mixing unit at higher temperature, i.e., the vessel’s walls. Since the rotating shaft is connected to the vessel at its ends, the different thermal expansion of the vessel can cause a stress action on the bearing elements and the mechanical shaft seal located at the ends of the central rotating shaft, thereby affecting the performance of the mixing unit in terms of sealing and mechanical properties.

[0009] Some solutions are present in prior art. For example, most horizontal mixing units have an external bearing arrangement at one end and an internal support bearing (slide bearing) at the other end. However, an internal bearing is seldom hygienic since it may cause wear particles into the food product. Alternatively, external bearing arrangements are employed at both ends, wherein one of the bearing arrangements is designed to allow expansion in the axial direction. In this case, the shaft seal is then also designed to allow a shaft movement in the axial direction which is, however, not a recommended hygienic solution as well. Also, known solutions provide complex arrangements of components that would lead to difficult mounting procedures of the shaft inside the vessel.

[0010] Summary

[0011] It is an object of the invention to at least partly overcome one or more of the above-identified limitations of the prior art. In particular, it is an object to provide a way for compensating the thermal expansion between the vessel and the central rotating shaft without affecting the mechanical properties of the rotating shaft and without increasing the complexity of the mounting procedure of the shaft. Also, it is an object to provide a way for compensating the thermal expansion between the vessel and the central rotating shaft that respects the hygienic requirements in food processing equipment.

[0012] To solve these objects a mixing unit is provided. The mixing unit comprises a vessel for containing a product to be mixed, a shaft extending longitudinally inside the vessel and configured for rotating around a rational axis to be used for mixing the product inside the vessel, the shaft having a first portion and a second portion separated from the first portion, wherein the mixing unit further comprises a flexible member connecting the first portion to the second portion of the shaft for compensating a displacement between the first portion and the second portion due to thermal expansion of the vessel. The mixing unit so configured is advantageous in that the thermal expansion between the vessel and the shaft is compensated by preserving the mechanical properties of the rotating shaft and in a hygienic way.

[0013] Specifically, the presence of a flexible member between two portions of the rotating shaft is advantageous in that it allows an axial displacement between the two shaft’s portions wherein however these portions are maintained rigid against shear forces and bending moment. Such a flexible member is also able to transmit the required shaft torque. Also, the simple design of the flexible member allows for an easy and quick cleaning.

[0014] It is noted that the use of such a flexible member has the additional advantage of easing the mounting procedure of the rotating shaft inside the vessel. In fact, the presence of the flexible member between two portions of the rotating shaft makes the shaft more flexible in terms of longitudinal movements, thereby compensating a lower precision in the length dimension between the shaft and the vessel. In other words, it is not necessary to manufacture a shaft being precisely dimensioned to the vessel’s length since the flexible member would compensate any dimensional length inaccuracies. Accordingly, the rotating shaft can be mounted inside the vessel with reduces efforts.

[0015] Furthermore, it is noted that the higher the temperature difference between the central rotating shaft and the inner walls of the vessel, the greater the effectiveness of the flexible element in terms of thermal expansion compensation. This occurs for instance when the food product inside the mixing unit needs to be heated in a short time so that a high quantity of external heat is provided to the vessel.

[0016] In the context of the present application, the term “flexible element” is intended as a component of the mixing unit, in particular of the rotating shaft, that is capable of undergoing a change in shape or size when subjected to external forces or conditions. This element can exhibit elasticity, plasticity, or viscoelastic behavior, allowing it to deform reversibly or irreversibly in response to mechanical, thermal, or other influences. Since the flexible element connects two portions of the central shaft, the flexibility of this element is therefore transmitted to the two portions and hence to the entire rotating shaft. For example, the flexible member is extensible along the direction of the rotational axis of the rotating shaft following the thermal expansion of the vessel.

[0017] The flexible member can be a spring element configured to change shape under load and to recover the original shape when the load is removed. In the context of the present application, “spring element” is intended as a mechanical component capable to store mechanical energy when deformed and release it when the deforming force is removed. In particular, the spring element contacts two points (i.e., nodes) that move relative to each other during the deformation process. The two points are the two portions of the central shaft. In this way, the elasticity of the flexible member, and therefore of the rotating shaft, is improved. As a matter of fact, the spring element allows a stronger elasticity of the rotating shaft in the longitudinal direction. For example, the flexible member can comprise at least a flat spring having an elongated shape.

[0018] According to one example, the flexible member can comprise a plurality of bent elements equidistantly arranged from each other, wherein each bent element connects the first portion to the second portion extending radially from the shaft. The bent element can have different shapes like a plate, a bar, a rod, a rib, etc. Importantly, the bent element can be any type of component, preferably extending longitudinally and connecting two points, that can be deformed at least partially. The bent element can be a single component or can be made of two or more parts joint together. Also, the bent element can be made of metal, such as steel. The presence of a plurality of bent elements that are equidistantly arranged from each other increases the flexibility of the flexible member. In fact, the stress action due to the thermal expansion of the vessel and acting on the two portions of the central shaft is evenly distributed across the plurality of bent elements. Furthermore, this configuration makes the flexible member easy to clean. As a matter of fact, each bent element is configured to connects the two shaft portions by extending radially from the shaft. In other words, the flexible member does not define a compact and closed structure, rather it defines an open structure, wherein the bent elements are arranged like the spokes of a wheel. In addition, since the connections between the two shaft portions is provided by bent elements, an empty space is formed between the two portions. Accordingly, the flexible member is open and easy cleanable via normal CIP procedures used in food processing equipment, thereby making the flexible member compliant with the hygienic requirements.

[0019] Since the flexible member is connected to the first and second portions of the rotating shaft, it will rotate together with the shaft and it will move inside the food product contained in the vessel of the mixing unit. In one example, each bent element might have a short edge surface having a first thickness and a large edge surface having a second thickness, the bent element moving with the short edge surface in the direction of the rotation of the shaft. In this way, the resistance of the food product to the movement of the flexible member, specifically to the movement of each bent element, is reduced. This is particularly advantageous in case of food products with high viscosity. The second thickness can be greater that the first thickness. Advantageously, the second thickness might be at least five times the first thickness. In this context, the terms “first thickness” and “second thickness” are considered the average thickness of the corresponding short and large edge surfaces of the bent element. It is noted that the ratio between the first and second thickness can be optimized based on the particular shape of the bent element and the molecular composition and physical properties of the food product. It has been proved that having at least a ratio 1 :5 between the first and second thickness is a good compromise to reduce the resistance of any type of food product with respect to the movement of the flexible member without affecting the rotational properties of the shaft. In this way, the flexible member, due to its particular configuration, can be furthermore used as an additional food agitator in a region close to the rotating shaft.

[0020] According to another example, each bent element can be flat having a first end fixed to the first portion of the shaft, a second end fixed to the second portion of the shaft and a bent part equidistant from the first end and the second end and located in the radial direction of the shaft. The bent element can therefore be configured as a flat component, e.g., a plate or a bar, starting from a first end at the first portion of the rotating shaft, extending radially from the shaft for a certain length, reaching a bent part and extending back for the same length to the second end at the second portion of the rotating shaft. In particular, each bent element has a first section extending from the first end to the bent part and a second section extending from the bent part to the second end. Since both sections extend radially from the shaft, they extend facing each other (almost parallel) with a room space (i.e., gap) therebetween. This configuration of each bent element ensures a reduced resistance of the flexible member moving inside the food product and an easy cleanability.

[0021] In one example, the bent part can have a rounded shape. This eases the manufacture of the flexible member. However, the bent part can have different shapes. For instance, the bent part can be squared, triangular, elliptical or can have any other type of possible shape connecting the two sections of the bent element. As already mentioned, the bent element can be a single component starting from the first end to the second end and bent in the middle at the bent part or can be a combination of several parts joint together. For example, the bent part can be the joint component connecting the two sections of the bent element.

[0022] In order to minimize the fluid resistance or fluid drag of the flexible member inside the food product, the two sections of the bent element can have a particular shape. According to one example, the large edge surface of each bent element, in the direction from the first end to the second end, can comprise two straight flat portions at each of the first end and the second end and two tapered flat portions at the bent part connected to the straight flat portions. In this way, each bent element can have the shape of a flat plate having a reduced width at the bent part.

[0023] In a further example, the flexible member can comprise two ring-shaped connection elements that are connected to a respective one of the first portion and the second portion of the shaft. The ring-shaped connection elements serve to join each bent element to the rotating shaft, in particular to the first and second portion of said shaft. Advantageously, the circular shape of these connections allows an evenly distribution of the bent elements extending radially from the shaft.

[0024] Specifically, in the direction from the first end to the second end of the bent element, each bent element might comprise a first straight flat portion connected to a first ring-shaped connection element at the first end, a first tapered flat portion connected to the first straight flat portion at one end and to the bent part at the other end, a second tapered flat portion connected to the bent part at one end and to a second straight flat portion at the other end, the second straight flat portion being connected to a second ring-shaped connection element at the second end of the bent element. In other words, the two sections forming each bent element can taper in the direction of the bent part, thereby affecting the fluid dynamic of the flexible member. The tapering allows for a more gradual variation in the angle of attack to the shaft along the length of the bent element, thereby reducing the formation of drag-inducing turbulences.

[0025] Therefore, the edge of one straight flat portion can form an angle a with the edge of the connected tapered flat portion, the angle a being different from zero. In order to improve the overall efficiency of the bent element in terms of fluid dynamic, the angle a can be comprised between 5 degrees and 15 degrees.

[0026] To furthermore improve the fluid dynamic of the bent element, each bent element can have a tapered rounded outline in the direction of the rotation of the shaft. As already mentioned, the bent element can have a large edge surface and a short edge surface, the bent element moving with this short edge surface in the direction of the rotation of the shaft. The short edge surface can have a tapered profile to improve the stiffness and the softness in the radial direction.

[0027] In one example, the flexible member can be located close to one end of the shaft. The rotating shaft is connected, in particular fixed, to the vessel of the mixing unit at its two ends. For this reason, a possible thermal expansion of the vessel would directly affect the central rotating shaft. Since the mechanical shaft seal and the bearings of the mixing unit are located at the ends of the shaft (usually outside the vessel), the stress action due to the thermal expansion would also affect said components. Accordingly, it is advantageous to locate the flexible member close to one end of the shaft, i.e., close to the mechanical shaft seal and bearings of the mixing unit to minimize the possible stress action applied to these components. In addition, for the mixing units having a horizontal vessel, the manway is usually located at the top of the vessel at one end, where the central shaft is connected to the internal walls of the vessel. Therefore, the position of the flexible member can be close to one end of the rotating shaft and at the manway of the vessel of the mixing unit. Specifically, the flexible member can be located at one end of the shaft below the manway of the mixing unit. In this way, the flexible member can be easily accessible from the manway for cleaning purposes.

[0028] In a further example, the flexible member can be welded to the shaft. For this purposes, the flexible member can be made of metal, such as steel, in particular stainless steel. This increases the compactness and the robustness of the flexible member that is a single element with the rotating shaft. In this way, the flexible member is a part of the rotating shaft extending radially from the rotational axis for compensating any displacement between the two portions of the shaft connected by the flexible member. To improve the welding process, the rotating shaft can be made of the same material of the flexible member.

[0029] In alternative, the flexible member can be joint to the first and second portions of the rotating shaft in a removable way, for example by means of fastening elements (i.e., threaded fasteners quick-release pins, clamping mechanisms, etc.). In this way, the flexible member can be removed from the shaft, and therefore from the vessel, for maintenance purposes such as cleaning, replacement after damage, etc.

[0030] It is noted that the vessel can comprise a heating jacket. The heating jacket serves the purpose of maintaining the desired temperature of the food product within the vessel of the mixing unit. For example, by circulating hot water, steam, or a heating medium through the jacket, the temperature of the food product can be regulated to ensure it remains within the required range for processing, storage, or other purposes.

[0031] Drawings

[0032] Embodiments of the invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which

[0033] Fig. 1 is a perspective view of a mixing unit for mixing a food product. Fog. 2A is a lateral view of a mixing unit with a portion showing the internal view of the vessel.

[0034] Fig. 2B is a cross-sectional view of the mixing unit of figure 2A along the line A- A.

[0035] Fig. 3A is a perspective view of the flexible member connected to the rotating shaft.

[0036] Fig. 3B is a front view of the flexible member of figure 3A perpendicular to the rotational axis of the shaft.

[0037] Fig. 3C is a lateral view of the flexible member of figure 3A in the direction of the rotational axis of the shaft.

[0038] Description

[0039] With reference to Fig. 1 a mixing unit 1 is illustrated. The mixing unit 1 , also known as mixer or food processor, is used for mixing a food product. The mixing unit 1 comprises a vessel 2 representing an enclosed tank configured for containing the food product to be mixed. For example, the food product can be a liquid, semi-liquid, or viscous product including one or more liquids eventually mixed with powder materials. The term “mixing” may comprise agitating, stirring, blending, and / or dissolving a powder material in a liquid. Liquid materials may include water, different fats and oils, milk, recombined milk, and sauces. Powder material may comprise raw materials such as sugar, milk powder, salt, or flour, or finished products such as instant formula, instant drinks, or dry broth.

[0040] The vessel 2 has a cylindrical shape and the mixing unit 1 is a horizontal mixer. Therefore, the vessel 2 is arranged so that the longitudinal side is arranged parallel, or almost parallel, to the ground. A horizontal mixing unit 1 is well-suited for blending food products that require a gentle mixing action. This type of mixing unit is effective for combining ingredients without damaging the texture or integrity of the food product.

[0041] The mixing unit 1 is provided with at least an opening 22, also called manway, on the top of the vessel 2. The manway 22 is a large opening with an access door that is integrated into the vessel's structure, allowing personnel to enter the interior of the vessel 2 for purposes such as cleaning, inspection, maintenance, and product removal. To provide a safe and convenient means of access, the manway 22 comprises secure locking mechanisms and sealing systems to prevent leaks and maintain hygiene standards in food processing environments.

[0042] In order to mix or blend the food product inside the vessel 2, the mixing unit 1 comprises a shaft 4 coupled to a plurality of agitator blades (not shown in the figure) that is configured to rotate around a rotational axis 16. As shown in the figure, the rotational axis 16 extends longitudinally and centrally along the vessel 2 and passes through two opposing points at the ends of the vessel 2 where mechanical shaft seals 19 are located. Also, at these two opposing points are present bearings 21 and a gearbox with bearings 20.

[0043] The mixing unit 1 also comprises a heating jacket 3 for allowing a precise temperature regulation, which is essential for various food processing tasks such as cooking, pasteurization, sterilization, and / or for maintaining specific temperatures for the production of food products. The heating jacket 3 is a shell structure surrounding the vessel 2 and is configured to circulate a heating medium such as hot water, steam or thermal oil. The heating jacket 3 can be divided into different parts comprising a bottom part, a top part, and side parts. Figure 1 schematically illustrates the side part of the heating jacket 3 and is marked with a dashed line to show that the heating jacket 3 is arranged inside the external walls of the vessel 2.

[0044] Figure 2A illustrates a lateral view of the cylindrical vessel 2 with an opened drawing portion 25 showing its internal region. From the opened drawing portion 25 it emerges that the rotating shaft 4 extends longitudinally along the vessel 2 from one end to the other end of the vessel 2 where the two mechanical shaft seals 19 are located. The rotating shaft 4 has the shape of a cylindrical rod and is divided into a first portion 5 and a second portion 6. These two portions are connected to each other by a flexible member 7. It is noted that the flexible member 7 is located close to one end of the shaft 4 connecting the vessel 2 and approximately below the manway 22.

[0045] A better illustration of the flexible member 7 relative to the rotating shaft 4 is shown in figure 2B that is a cross section of figure 2A along the line A-A. The first portion 5 is shorter than the second portion 6 and extends from one end of the vessel 2 to the flexible member 7, whereas the second portion 6 extends from the flexible member 7 to the opposing end of the vessel 2. Specifically, the first portion 5 can have a length L1 that is much shorter than the length L2 of second portion 6, for example the ratio between the length L1 of the first portion 5 and the length L2 of the second portion 6 can be 1 :16.

[0046] The flexible member 7 is welded to the two portions 5, 6 of the shaft 4 so that the first portion 5, the second portion 6 and the flexible member 7 form a single component, i.e., a single rotating element. The flexible member 7 comprises a plurality of bent elements 8 each connecting the two shaft portions 5, 6 and extending radially from the central shaft 4. The presence of these bent elements 8 allows the flexible member 7 to be deformable based on the action of applied biasing forces. Since the flexible member 7 is joint to the two portions 5, 6 of the rotating shaft 4, the flexibility provided by the bent elements impacts also on the rotating shaft 4. This is extremely useful in case of a thermal expansion due to a great temperature gradient (e.g., higher than 90°C) between the outermost region of the mixing unit 1 (i.e., the vessel 2) and the innermost region of the mixing unit 1 (i.e., the central rotating shaft 4). In fact, the difference in thermal expansion between the vessel 2 and the shaft 4 would directly impinge on the vessel-shaft connections 24.

[0047] Thermal expansion is the tendency of matter to increase in length or volume, changing its size and density, in response to an increase in temperature. The linear expansion equation is

[0048] AL = aLoAT, where

[0049] AL is the change in length of a solid material when heated or cooled, a is the linear expansion coefficient for the solid material Lo is the original length of the solid material, and AT is the change in temperature.

[0050] For example, in case of a length of 1500 mm with a thermal expansion coefficient of 0.000016 K 1 , a temperature gradient of 90 °C (from around 10°C to around 100°C) would determine a change in length of 2.16 mm.

[0051] It is noted that, in a rigid configuration as in standard mixing units, this calculated change in length cannot be simply compensated by the shaft seal 19 at the ends of the rotating shaft so that the seal 19 would be subjected to a strong stress action.

[0052] On the other hand, the deformability of the flexible member 7 can effectively compensate any thermal expansion of the vessel 2 since it would make the shaft 4 itself flexible. As a matter of fact, the two portions 5, 6 of the shaft 4 - that are connected to one end to the two opposing the vessel-shaft connections 24 and to the other end to the flexible member 7 - can react to the thermal expansion of the vessel 2 with a reciprocal displacement that is compensated by the flexible member 7 that would act as a shock absorber.

[0053] As already mentioned, to mix the food product contained in the vessel 2, the rotating shaft 4 is coupled to a plurality of agitator blades (not shown in the figure). The particular configuration of the flexible member 7 can therefore also be used as an additional agitator element, at least in the region close to the shaft 4. A preferred configuration of the flexible member 7 is illustrated in figures 3A-3C. It is noted that other configurations might be possible as will be explained below during the description of these figures.

[0054] According to figure 3A, the flexible member 7 comprises three bent elements 8. However, any number of elements 8 (e.g., at least two) can be useful for the purpose of compensating the displacement of the two shaft portions 5, 6. As shown, each bent element 8 is shaped like an elongated plate folded in two sections facing each other. However, other shapes are possible. For example, each bent element 8 can be made of one or more rods or one or more wires that are intertwined to each other in a grid shape. Also, each bent element 8 can be made as a single piece or can be the result of a combination of two or more components joint together (e.g., welded).

[0055] The flexible member 7 is connected to the first and second portions 5, 6 of the rotating shaft 4 at two ring-shaped connector elements 14’, 14”. Specifically, the flexible member 7 is connected to the first portion 5 of the shaft 4 (i.e., the short portion) at a first ring-shaped connector element 14’ and is connected to the second portion 6 of the shaft 4 (i.e., the long portion) at a second ring-shaped connector element 14”. Accordingly, by rotating the shaft 4 around the rotational axis 16 in the direction of the rotation Rs, the flexible member 7 also rotates in the same direction (i.e., Rf). The three bent elements 8 are arranged equidistantly from each other and extend radially from the shaft 4. In particular, the bent elements 8 extend along the radial direction 26 orthogonal to the axial direction 27.

[0056] As shown in the figure, each bent element 8 is flat having a first end 9 fixed to the first portion 5 of the shaft 4 (i.e. to the first ring-shaped connector element 14’), a second end 10 fixed to the second portion 6 of the shaft 4 (i.e. to the second ringshaped connector element 14”) and a bent part 11 equidistant from the first end 9 and the second end 10 and located at the maximum radial distance from the rotational axis 16 of the shaft 4. The bent part 11 has a rounded shape.

[0057] By having a plate shape, the bent element 8 has a short edge surface 17 and a large edge surface 18 (also referred to as side surface). The flexible member 7 moves with the large edge surface 18 of each bent element 8 rotating on a plane orthogonal to the axial direction 27 and rotates with the short edge surface 17 moving in the direction of the rotation of the shaft 4.

[0058] As shown in figures 3B and 3C, the short edge surface 17 has a first thickness D1 and the large edge surface 18 has a second thickness D2, wherein D2 is greater than D1. Specifically, the thickness of the large edge surface 18 (D2) is around five times (or more) the thickness of the short edge surface 17 (D1). This effects the stiffness and the softness in the radial and tortional direction. It is noted that both D1 and D2 represent an average thickness value (or the greatest value) along the bent element 8 of the short and large edge surface 17, 18, respectively.

[0059] Figure 3B is a front view of the flexible member 7 on a plane orthogonal to the axial direction 27 (i.e., to the rotational axis 16). From this figure it is clear that the outline of the large edge surface 18 of each bent element 8 has a variable width. In particular, in the direction from the ring-shaped connector element 14’, 14” to the bent part 11 , the large edge surface 18 of each bent element 8 has a straight flat portion 12’, 12” and a tapered flat portion 13’, 13” (marked with dotted boxes in the figure). The straight flat portion 12’, 12” is connected to the tapered flat portion 13’, 13”, wherein the straight flat portion 12’, 12” is also connected to one end 9, 10 of the bent element 8 and the tapered flat portion 13’, 13” is also connected to the bent part 11 .

[0060] More specifically, in the direction from the first end 9 to the second end 10 of the bent element 8, each bent element 8 comprises a first straight flat portion 12’ connected to a first ring-shaped connection element 14’ at the first end 9, and a first tapered flat portion 13’ connected to the first straight flat portion 12’ at one end and to the bent part 11 at the other end. Also, the bent element 8 comprises a second tapered flat portion 13” connected to the bent part 11 at one end and to a second straight flat portion 12” at the other end, wherein the second straight flat portion 12” is connected to a second ring-shaped connection element 14” at the second end 10 of the bent element 8. This is clearly shown in figure 3A. In other words, the bent element 8 comprises two sections facing each other. One section comprises the first end 9, the first straight flat portion 12’ and the first tapered flat portion 13’. The other section comprises the second end 10, the second straight portion 12” and the second tapered flat portion 13”. The two sections are connected by means of the bent part 11.

[0061] In particular, the width of the straight flat portion 12’, 12” can vary between D2 (i.e., the largest width) to D3 (the shortest width). The shortest width D3 is the width of the bent part 11 . Preferably, the ratio between D3 and D2 is around 1 :1.2.

[0062] As shown in figure 3B, the edge of one straight flat portion 12’, 12” forms an angle a with the edge of the connected tapered flat portion 13, 13”. The angle a is comprised between 5 degrees and 15 degrees. It is noted that this range of values is preferably advantageous for improving the fluid dynamic of the flexible member 7. However the flexible member 7 can still be used for the same purpose also with a values outside the above mentioned range, even for a=0.

[0063] With reference to figure 3C, the outline of the short edge surface 17 is shown, this figure illustrating the lateral view of the flexible member 7. The outline of the short edge surface 17 has a tapered rounded shape. In the direction from the ring-shaped connector elements 14’, 14” to the bent part 11 , the outline has a first constant width D4 that progressively shrinks until the bent part 11 is reached. Accordingly, an angle p is formed between the ring-shaped connector elements 14’, 14”, i.e., a line orthogonal to the rotating shaft 4, and the shrunk edge of the bent element 8. The angle p is comprised between 10 degrees and 20 degrees. It is noted that this range of values is preferably advantageous for improving the fluid dynamic of the flexible member 7. However the flexible member 7 can still be used for the same purpose also with p values outside the above mentioned range, even for p =0.

[0064] In the context of this application, with the term “tapered rounded shape” it is intended that the outline gets smaller until reaching an end extremity having a rounded, i.e., curved, profile. The end extremity is the bent part 11 that has a curvature radius R1. Preferably, the value of the curvature radius R1 is comprised between 10 mm and 50 mm.

[0065] For maintaining the structural stability of the flexible member 7 and at the same time to improve the fluid dynamic properties of each bent element 8, the thickness D1 of the short edge surface 17 can have a predefined value in relation to the curvature radius R of the bent part. For example, the ratio between the thickness D1 and the ratio R1 can be from 1 :1 to 1 :5.

[0066] It is noted that the compensation action of the flexible member 7 determines a movement of the bent element 8 in the axial direction 27. In other words, the displacement of the two portions 5, 6 of the rotating shaft 4 causes a relative movement of the two sections of each bent element 8 moving away from each other. Accordingly, the gap 23 formed inside the flexible member 7 between the first ringshaped connector element 14’ and the second ring-shaped connector element 14” can vary based on the bias force exerted on the portions 5, 6, of the shaft 4 due to thermal expansion. In particular, the value of D4, that is the distance between the first ringshaped connector element 14’ and the second ring-shaped connector element 14”, directly affects the efficacy of the compensation action of the flexible member 7. On the other hand, D4 is strongly related to the diameter D5 of the rotating shaft 4. As a matter of fact, a large diameter D5 requires a greater value of D4. Preferably, D4 is around twice the value of the diameter D5 (D4 = 2D5).

[0067] In addition, or as an alternative to what has been described above, the mixing unit 1 may incorporate one or more of the following embodiments. The three bent elements 8 may be arranged equidistantly and symmetrically around the rotational axis 16, each bent element 8 extending radially from the shaft 4 between a first portion 5 and a second portion 6.

[0068] The bent part 11 of each bent element 8 may be inclined by an angle p relative to the shaft axis Rs and may have a rounded contour with a radius R1 , providing flexibility and reducing stress concentration during thermal expansion.

[0069] Each bent element 8 may have an outline oriented in the direction of rotation Rf, with a leading edge defined by the edge surface 17 and a trailing edge opposite the leading edge. The side surfaces 18 of the bent elements 8 may extend between the leading edge 17 and the trailing edge and may be flat but inclined inward toward the center of the flexible member 7. Opposite side surfaces 18 may lean toward each other so that the bent element 8 has a tapered configuration when viewed in the rotation direction Rf.

[0070] The bent part 11 may be located at the maximum radial distance from the rotational axis 16 and may be positioned midway between the first end 9 and the second end 10 of the bent element 8.

[0071] The flexible member 7 may define a continuous lattice structure formed by the bent elements 8 and two ring-shaped connection elements 14’ and 14”, the ringshaped elements being coaxially arranged on the shaft 4 and providing circumferential support for the bent elements 8.

[0072] In some embodiments, the bent elements 8 may have a streamlined profile in the direction of rotation Rf to minimize resistance during mixing, and the tapered portions 13’ and 13” may converge toward the bent part 11 forming an angle a with adjacent straight portions 12’ and 12”, wherein the angle a may be between 5 degrees and 15 degrees.

[0073] The flexible member 7 may further exhibit dimensional relationships such that the large edge surface 18 has a thickness D2 greater than the thickness D1 of the short edge surface 17, wherein D2 may be at least five times D1 . Additional dimensions such as D3, D4 and D5 may define the radial and axial spacing of the bent elements 8 relative to the shaft axis Rs.

[0074] From the description above follows that, although various embodiments of the invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims.

Claims

CLAIMS1. A mixing unit (1) comprising: a vessel (2) for containing a product to be mixed; a shaft (4) extending longitudinally inside the vessel (2) and configured for rotating around a rational axis (16) to be used for mixing the product inside the vessel (2), the shaft (4) having a first portion (5) and a second portion (6) separated from the first portion (5), wherein the mixing unit (1) further comprises a flexible member (7) connecting the first portion (5) to the second portion (6) of the shaft (4) for compensating a displacement between the first portion (5) and the second portion (6) due to thermal expansion of the vessel (2).

2. Mixing unit (1) according to claim 1 , wherein the flexible member (7) is a spring element configured to change shape under load and to recover the original shape when the load is removed.

3. Mixing unit (1) according to any one of claims 1 to 2, wherein the flexible member (7) comprises a plurality of bent elements (8) equidistantly arranged from each other, wherein each bent element (8) connects the first portion (5) to the second portion (6) extending radially from the shaft (4).

4. Mixing unit (1) according to claim 3, wherein each bent element (8) has a short edge surface (17) having a first thickness (D1) and a large edge surface (18) having a second thickness (D2), the bent element (8) moving with the short edge surface (17) in the direction of the rotation of the shaft (4).

5. Mixing unit (1) according to claim 4, wherein the second thickness (D2) is greater that the first thickness (D1), wherein in particular the second thickness (D2) is at least five times the first thickness (D1).

6. Mixing unit (1) according to any one of claims 3 to 5, wherein each bent element (8) is flat having a first end (9) fixed to the first portion (5) of the shaft (4), a second end (10) fixed to the second portion (6) of the shaft (4) and a bent part (11) equidistant from the first end (9) and the second end (10) and located at the maximum radial distance from the rotational axis (16) of the shaft (4).

7. Mixing unit (1) according to claim 6, wherein the bent part (11) has a rounded shape.

8. Mixing unit (1) according to any one of claims 4 to 7, wherein the large edge surface (18) of each bent element (8) comprises two straight flat portions (12’, 12”) each located at one of the first end (9) and the second end (10), and two tapered flat portions (13’, 13”) at the bent part (11), each connected to one of the straight flat portions (12’ 12”).

9. Mixing unit (1) according to any one of claims 1 to claim 8, wherein the flexible member (7) comprises two ring-shaped connection elements (14’, 14”) that are connected to a respective one of the first portion (5) and the second portion (6) of the shaft (4).

10. Mixing unit (1) according to claims 8 and 9, wherein, in the direction from the first end (9) to the second end (10) of the bent element (8), each bent element (8) comprises a first straight flat portion (12’) connected to a first ring-shaped connection element (14’) at the first end (9), a first tapered flat portion (13’) connected to the first straight flat portion (12’) at one end and to the bent part (11) at the other end, a second tapered flat portion (13”) connected to the bent part (11) at one end and to a second straight flat portion (12”) at the other end, the second straight flat portion (12”) being connected to a second ring-shaped connection element (14”) at the second end (10) of the bent element (8).

11. Mixing unit (1) according to claim 8 or claim 10, wherein the edge of one straight flat portion (12’, 12”) forms an angle a with the edge of the connected tapered flat portion (13, 13”), wherein the angle a is different from zero, in particular comprised between 5 degrees and 15 degrees.

12. Mixing unit (1) according to any one of claims 3 to 11 , wherein each bent element (8) has a tapered rounded outline in the direction of the rotation of the shaft (4).

13. Mixing unit (1) according to any one of claims 1 to claim 12, wherein the flexible member (7) is located close to one end of the shaft (4).1714. Mixing unit (1) according to any one of claims 1 to claim 13, wherein the flexible member (7) is welded to the shaft (4).

15. Mixing unit (1) according to any one of claims 1 to claim 14, wherein the vessel (2) comprises a heating jacket (3).

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