A mixer for the preparation of ceramic mixtures for 3D printing and the method of their preparation

Abstract

The invention relates to a mixer for the preparation of ceramic mixtures for 3D printing, comprising cylindrical vessel (A) with feeding inlet (1), vessel bottom (2) and agitator (B) located in the axis of vessel (A), which consists of shaft (3) and circular dispersing disc (4) positioned on the axis of shaft (3) at vessel bottom (2), and skimmer (5) mounted laterally in relation to shaft (3) characterised in that skimmer (5) consists of skimmer blade (6) that is curved towards shaft (3), with the leading edge of skimmer blade (7) positioned in the direction of rotation of shaft (3), the leading edge of skimmer blade (7) being adjacent to the wall of vessel (A), the skimmer being mounted on shaft (3) via top crossbar (8) and scraper (9) and forming, together with the wall of shaft (3), opening (10), wherein scraper (9) is adjacent to vessel bottom (2) via scraper leading edge (12) and dispersing disc (4) is provided with teeth (11) arranged along its periphery and oriented towards feeding inlet (1) or towards vessel bottom (2). The invention also provides a method of mixing using the mixer according to the invention.

Description

[0001] A mixer for the preparation of ceramic mixtures for 3D printing and the method of their preparation

[0002] The present invention relates to a mixer for the preparation of ceramic mixtures for 3D printing and a method of the preparation of ceramic mixtures for 3D printing with the use of this mixing device.

[0003] The 3D printing technology commonly involves the use of thermoplastics such as poly lactide (PL A), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate glycol (PET-G) or thermoplastic polyurethane (TPU), as well as resins and other materials such as ceramics, wax or even chocolate, but also mixtures of these materials with additives designed to provide the 3D print with specific technical properties such as electrical conductivity, resistance to low temperatures, impact resistance, luminescence or aesthetic properties such as a specific colour or a wood-like texture. Such mixtures should demonstrate a characteristic known as ease of pumping, i.e. their consistency must allow them to be transported and extruded from the printer nozzle continuously as a homogeneous filament. They also have to be easy to incorporate, that is the mixture must be fluid enough to move within the printer tubes, but must not change in shape significantly following its ejection from the printer and under pressure from successive overlying layers, which would result in its deformation and in lower print quality. With reference to ceramic mixtures, a finished filament must demonstrate homogeneity and especially even distribution, without any lumps or air bubbles.

[0004] The mixing process is one of the most important theoretical and practical problems of the technology of generating homogeneous mixtures in various industries. In industrial practice, the achievement of a mixture made up of two or more components that is highly homogeneous, and at the same time meets all other requirements of subsequent technological process operations, is a very complex task and depends on many different factors. The most important of these factors is the selection of a suitable mixing device, which depends on a number of parameters, such as: the physico-chemical properties of materials, especially their viscosity and density, the required homogeneity of the mixture, the size of production, electric power requirements, the balance of investment and operating costs, mixing time - i.e. the total process completion time (loading, mixing, unloading, cleaning), ease of cleaning of the equipment. The choice of an agitator consists of selecting its diameter, the place of entry of the agitator's shaft into the mixing vessel and, if a rotating agitator is used, parameters such as the agitator’s diameter, blade shape, number of blades and their angle of inclination must be taken into account. Also of significance is a suitable structure of the mixing vessel, including its bottom, and the associated effects related to the interaction between the vessel and the agitator.

[0005] The mixing process is usually carried out with the use of mixing devices equipped with agitators that generate axial or radial flow. In the case of mixing in tank mixers with the use of rotating agitators, sufficient agitation of the mixed slurry is usually generated only in a limited area of the tank, which results in the occurrence of less mixed areas or stagnated areas in the mixer. In such cases, the area of intensive mixing area can be usually increased by raising the speed of rotation of the agitator, or by fitting several agitators on a single shaft. Increasing the speed of the agitator or the use of several agitators in one mixer is usually connected with higher energy consumption, which translates into lower cost-effectiveness of the process. The effects described above consequently lead to lower mixture quality and higher costs of energy needed to achieve the desired level of mixing. Especially problematic is the process of the mixing bulk materials that involves the mixing of components of various shapes, sizes and density that tend to split as a result.

[0006] Ceramic mixtures for 3D printing are made of ceramic powder, water, a powdery dispersing agent and a liquid binder, wherein the main component of the mixture is the ceramic powder of the density of at least 4 g / dm3that contributes to the high density of the mixture. The viscosity of such a mixture is approximately 3.954*105[Pa*s]. The mixture is subject to the process of mixing, following the pre-mixing of its components, for no more than minutes, after which time the thickening of the mixture, due to the activation of the binding agent, reduces the mixing efficiency until it is completely prevented by the solidification of the mixture. The mixture must therefore be prepared quickly and a high-speed agitator is required.

[0007] Known in the present art are industrial agitators with a dispersing disc and a maximum speed of 3,000 rpm, equipped with a lateral skimmer and used for the mixing of substances with high viscosity and density coefficients, but in these known solutions the skimmer rotates at a speed of a few to several revolutions per minute, typically at 12 rpm, which, in the case of the mixing of components for 3D printing, may result in the solidification of the mixture before the slurry is sufficiently mixed. The problem with these mixtures is also the settling of the slurry at the bottom of the mixing vessel, beyond the reach of the dispersing disc.

[0008] Swiss patent application CH713257 reveals a device for the preparation of mixtures for 3D printing, namely for the mixing of resin materials with dyes, which is intended to automate this process by producing multi-colour mixtures based on primary colours and with many types of resins (rigid, flexible, glossy, translucent, etc.), wherein the agitating function is performed by three turbines arranged in the mixing chamber in the form of an isosceles triangle.

[0009] The present invention relates to a mechanical mixer for the preparation of ceramic mixtures for 3D printing that consists of a vessel which incorporates a rotary mixer, equipped with a drive designed in accordance with the state of the art. The mixer consists of a cylindrical vessel with a feeding inlet, which is fed from the top and has a flat or circular vessel bottom, and an agitator located in the axis of the vessel that consists of a shaft and a circular dispersing disc mounted on the shaft axis at the bottom of the vessel, and a skimmer attached laterally to the shaft. The skimmer according to the invention consists of a skimmer blade arched towards the shaft, the skimmer blade having a leading edge that is arranged in the direction of rotation of the shaft, wherein the leading edge of the skimmer blade is adjacent to the wall of the vessel, the blade being mounted on the shaft with a top crossbar and a scraper, which form an opening together with the wall of the shaft. The scraper is adjacent to the bottom of the vessel with the leading edge of the scraper, and the dispersing disc is provided with teeth arranged along its edge and directed either towards the feeding inlet, or towards the bottom of the vessel. In one version according to the invention, the bottom of the vessel is flat and the scraper extends between the shaft and the edge of the working side of the skimmer blade, and is positioned in relation to the bottom of the vessel at a leading angle of the working side of the scraper of a = 15-25°. The teeth of the dispersing disc may have the form of rectangular flat bars, arranged along the edge of the dispersing disc at fixed distances, alternately facing towards the feeding inlet and towards the bottom of the vessel, extending at an angle of 90° in relation to the plane of the dispersing disc. These teeth can be bent into an arc centred in the centre of the dispersing disc. In both of these two versions, the teeth can be alternately offset in parallel to each other, so that the outer teeth indicate the perimeter of the dispersion disc. The above teeth arrangement, based on essential circular and rectangular shapes, facilitates the slump of high-density mixtures onto the dispersing disc and their separation from the disc, improves the durability of the device by strengthening its structure and also facilitates its cleaning, due to the absence of any kinks in the dispersing disc that could accumulate deposits or trap any lumps in the mixture.

[0010] In one version according to the invention, the top crossbar is a flat bar that extends in the direction of the movement of the skimmer, between the shaft and the edge of the working side of the skimmer blade. In this version of the invention, the top crossbar is flush with the projection of the scraper in the side view of the device and both the top crossbar and the scraper are integrated with the shaft at the base along its entire thickness. The above design of the skimmer improves its mechanical strength and its durability, in view of the high rotational speeds that the scraper is intended to achieve in the solution according to the invention.

[0011] In one version according to the invention, the leading edge of the scraper is singlechamfered on one side at an angle of 0= 15-45° to improve the take-up of the mixture from the bottom of the vessel and the removal of curds during the cleaning of the vessel.

[0012] In one version of the invention, the skimmer and the dispersing disc are mounted on the shaft using a permanent, non-separable connection to improve the durability of the device, especially in view of the fact that the skimmer and the dispersing disc according to the invention, in accordance with the method of preparing ceramic mixtures for 3D printing according to the invention, are designed to move at the same rotational speed.

[0013] In one version of the invention, the shovel of the skimmer blade forms a plane tangent to the shaft surface at its extension. In this version, the stream of slurry is guided across the entire width of the shaft by the skimmer blade shovel in such a way that the slurry stream is especially efficiently knocked off by the shaft, wherein it then slumps towards the dispersing disc, where it is re-agitated.

[0014] The method of mixing with the use of the device according to any of the versions of the invention involves the steps of filling the mixer with the mix components, processing the slurry and collecting the finished product in a manner known by the state of the art, wherein the rotational speed of the skimmer is the same as the rotational speed of the dispersing disc and in a preferable version of the invention is 2200-3600 rpm. In the device according to the invention, the processed mixture is gathered by the skimmer and its stream is directed by the skimmer blade towards the centre, where it collides with the shaft and slumps along the shaft wall towards the dispersing disc, where the mixture is further agitated. The agitator acts uniformly on the entire volume of the slurry, which results in homogeneous mixing. The liquid and powdery components are directed to the dispersing disc, wherein the dispersing disc breaks up the powder lumps and ejects the components in a radial manner, wherein they are mixed together, while the skimmer and the scraper direct the mixture towards the dispersing disc, therefore the mixing takes place in close proximity to the dispersing disc and the flow of the slurry in the mixer is considerably accelerated because of its ejection towards the centre of the vessel by the skimmer and the scraper. The skimmer and the scraper have an additional important function during the final mixing stage, when the slurry thickens and its flow is impeded, wherein they force the slurry to flow until it is completely mixed in accordance with the requirements of the technological process. The invention also enables an improvement in mixture quality in terms of its air content, because any air bubbles that may form in the mixture are broken up during the process of ejection of the slurry onto the mixer shaft.

[0015] The object of the invention is illustrated by the following examples of the invention and the drawings, in which the individual figures show

[0016] Fig. 1A A general view of the mixer

[0017] Fig. IB A frontal view of the mixer’s agitator, as seen from the working side of the skimmer blade

[0018] Fig. 2 A A top view of the mixer's agitator

[0019] Fig. 2B Detail A of Fig. IB of the drawings

[0020] Fig. 2C A cross-section of the scraper along the X-X axis as indicated in Fig.

[0021] IB of the drawings, including a section of the shaft

[0022] Fig. 3A A top view of the dispersing disc

[0023] Fig. 3B A general view of the dispersing disc

[0024] Fig. 3C Arched dispersing disc tooth

[0025] Fig. 3D Straight dispersing disc tooth

[0026] Fig. 3E A pair of dispersing disc teeth arranged with a parallel offset between each other

[0027] Fig. 4 A cross-section of the shaft with a skimmer blade along the Z-Z axis, as indicated in Fig. IB of the drawings, with a top view of the dispersing disc, wherein the arrows indicate the direction of the flow of the slurry stream in the skimmer

[0028] Example I

[0029] In this example of the invention, the mixer for the preparation of ceramic mixtures for 3D printing comprises cylindrical vessel A with feeding inlet 1, vessel bottom 2 and agitator B located in the axis of vessel A, which consists of shaft 3 and circular dispersing disc 4 positioned on the axis of shaft 3 at vessel bottom 2, and skimmer 5 mounted laterally in relation to shaft 3, wherein skimmer 5 consists of skimmer blade 6 that is curved towards shaft 3 with a radius of r = 100 mm and with the leading edge of skimmer blade 7 positioned in the direction of rotation of shaft 3, the leading edge of skimmer blade 7 being adjacent to the wall of vessel A, skimmer 5 being mounted on shaft 3 via top crossbar 8 and scraper 9 and forming, together with the wall of shaft 3, opening 10. Scraper 9 is adjacent to vessel bottom 2 via scraper leading edge 12. Dispersing disc 4 is provided along its periphery with teeth 11 facing either towards feeding inlet 1, or towards vessel bottom 2.. The bottom of vessel 2 is flat and scraper 9 extends between shaft 3 and the edge of the working side of skimmer blade 6, and is positioned in relation to vessel bottom 2 at a leading angle of the working side of the scraper of a = 19°. Dispersing disc 4 is provided with 24 identical teeth arranged along its periphery, which have the form of rectangular flat bars alternately oriented at 90° with respect to the plane of dispersing disc 4 towards feeding inlet 1 and towards vessel bottom 2. Top crossbar 8 has the form of a flat bar that extends in the direction of rotation of shaft 3, between shaft 3 and the edge of the working side of skimmer blade 6. Scraper leading edge 12 is single-chamfered on one side at an angle of 0= 15-45°. Skimmer 5 and dispersing disc 4 are mounted on shaft 3 via a permanent, non-separable connection. Skimmer blade shovel 12 forms a plane that is tangent to the surface of shaft 3 at its extension.

[0030] Example II

[0031] The invention in accordance with example I, with the exception that dispersing disc 4 is provided along its periphery with 24 teeth alternately oriented at an angle of 90° with respect to the plane of dispersing disc 4 towards feeding inlet 1 and towards vessel bottom 2, wherein teeth 11 are alternately a rectangular flat bar, or a rectangular flat bar longitudinally curved in an arc that is centred in the centre of dispersing disc 4. In another version of this invention teeth 11 are alternately offset in parallel against each other.

[0032] Example III

[0033] In an example of the method according to the invention, a ceramic mixture for 3D printing is prepared using ceramic powder, water, a dispersing agent and a binding agent, which includes the mixing these ingredients using a device in accordance with Example I following their pre-mixing for 9.5 minutes, wherein the rotational speed of skimmer 5 is the same as the rotational speed of dispersing disc 4 and equals 3000 rpm.

[0034] List of designations

[0035] A vessel

[0036] B agitator

[0037] 1 feeding inlet

[0038] 2 vessel bottom

[0039] 3 shaft

[0040] 4 dispersing disc

[0041] 5 skimmer

[0042] 6 skimmer blade

[0043] 7 skimmer blade leading edge

[0044] 8 top crossbar

[0045] 9 scraper

[0046] 10 opening

[0047] 11 teeth

[0048] 12 scraper leading edge

[0049] 13 skimmer blade shovel a leading angle of the working side of scraper

[0050] P chamfer angle of the scraper leading edge x-x, z-z axes of cross-sections

Claims

Claims1. A mixer for the preparation of ceramic mixtures for 3D printing comprising cylindrical vessel (A) with feeding inlet (1), vessel bottom (2) and agitator (B) located in the axis of vessel (A), which consists of shaft (3) and circular dispersing disc (4) positioned on the axis of shaft (3) at vessel bottom (2), and skimmer (5) mounted laterally in relation to shaft (3), characterised in that skimmer (5) consists of skimmer blade (6) that is curved towards shaft (3), with leading edge of skimmer blade (7) oriented in the direction of rotation of shaft (3), the leading edge of skimmer blade (7) being adjacent to the wall of vessel (A), and is mounted on shaft (3) via top crossbar (8) and scraper (9) and forms, together with the wall of shaft (3), opening (10), wherein scraper (9) is adjacent to vessel bottom (2) via scraper leading edge (12) and dispersing disc (4) is provided with teeth (11) arranged along its periphery and oriented towards feeding inlet (1) or towards vessel bottom (2).

2. Mixer according to claim 1, characterised in that vessel bottom (2) is flat and scraper (9) extends between shaft (3) and the edge of the working side of skimmer blade (6), and is positioned in relation to vessel bottom (2) at a leading angle of the working side of the scraper of a = 15-25°.

3. Mixer according to claim 1 or 2, characterised in that at least one tooth (11) is a rectangular flat bar.

4. Mixer according to claim 1 or 2, characterised in that at least one tooth (11) is a rectangular flat bar longitudinally curved into an arc centred in the centre of dispersing disc (4).

5. Mixer according to claim 4, characterized in that teeth (11) are alternately offset in parallel to each other.

6. Mixer according to any one of the preceding claims, characterised in that top crossbar (8) is a flat bar extending in the direction of rotation of shaft (3), between shaft (3) and the edge of the working side of skimmer blade (6).

7. Mixer according to any one of the preceding claims, characterized in that the leading edge of scraper (12) is single-chamfered on one side at an angle of 0 = 15- 45°.

8. Mixer according to any one of the preceding claims, characterised in that skimmer (5) and dispersing disc (4) are mounted on shaft (3) via a permanent, non-separable connection.

9. Mixer according to any one of the preceding claims, characterised in that skimmer blade shovel (13) forms a plane that is tangent to the surface of shaft (3) at its extension.

10. Mixing method with the use of device according to any one of the preceding claims, characterized in that the rotational speedof skimmer (5) is the same as the rotational speed of dispersing disc (4).

11. Mixing method according to claim 10, characterised in that the rotational speed of skimmer (5) and dispersing disc (4) equals 2200-3600 rpm.

12. Mixing method according to claim 11, characterised in that the rotational speed of skimmer (5) and dispersing disc (4) equals 3000 rpm.

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