Title of Invention : Device and Method of Gas Jet Atomizer with Parallel Flows for Fine Powder Production

Technical Field

[0001] This invention is considered in the technical field of powder production from melt and involves a wide range of materials such as metal powders (both ferrous and non-ferrous metals), ceramic and refractory powders, polymer material powders, etc., and especially, it enables producing powders with desired morphology (spherical and irregular), narrow and desired particle size distribution.

Background Art

[0002] Currently, there are various powder production methods, such as water atomizing, gas atomizing, centrifuge atomizing, and milling. In general, in atomizing methods, the melt is converted to fine droplets, and then the droplets are solidified and the powder is produced.

[0003] In the gas atomizing method, which is usually used to produce metal powders, gas flow is exerted to disintegrate the melt and convert it into powder. In the patents CN108274013A, CN103658667B, and CN111299601 A some designs of this method are presented which are more or less similar to each other: In a vertical system, the angular collision of gas flow with melt flow from two or more directions are used to convert metal melt to powder.

[0004] The nozzle orifice for gas atomizing in this method is circular. In patent No.

CN111299601 A, a method has been disclosed to reduce the collision bonding probability between molten droplets by direct flow, which resulted in an improved size and shape of the powder particles. In patent No.CN109482893A, to prevent particles from bonding, the atomized particles were charged which produces more regular shapes and prevents the generation of satellite powder effectively.

[0005] The current technologies are capable of producing powder within the range of 0 to 500 microns, and to achieve fine powders with a narrow particle size distribution, separation processes are required and only a small part of the produced powder mays have the intended particle size distribution. This leads to significantly increased costs of the powder production. Also, none of these methods produce completely spherical particles.

[0006] Furthermore, in current technologies, due to the placement of the melt nozzle system and the atomizer nozzle close to each other, there is a need to strictly control the temperature of the atomizing gas to prevent solidification of the melt as a result of temperature decline before atomizing.

[0007] This process is very costly and additionally, for materials with high melting points causes enormous technical issues due to high-temperature process considerations. In addition, in all of the above-mentioned patents, the atomizer is installed vertically, and it is not possible to utilize the jet atomizer horizontally. None of the aforementioned methods apply parallel gas flows for atomizing, and usually, a gas flow parallel to the melt stream in a coaxial configuration is used.

Technical Problem

[0008] Nowadays with the advancement of technology, there is an increasing demand for powders with specific particle sizes and distribution in various industries. For instance, 3D printing, which is considered as the pioneer of the third industrial revolution, requires powders with particle sizes below 50 microns in many technologies such as powder bed fusion and binder jetting. One strategy to produce powders is gas atomization.

[0009] Flowever, available methods of gas atomization create a broad particle size distribution, and therefore to obtain a powder with specific particle size and uniform distribution, various sieving steps are required that in turn incurs huge costs on the manufacturer and on the other hand, only a part of the produced powder is usable. One of the objectives of this invention is to produce powders with a narrow particle size distribution. Another objective is to reduce production costs to obtain powders with specific properties.

[0010] In many modern forming methods such as plastic and metal forming in 3D printing, or to produce plastic, metallic and ceramic parts by (MIM, CIM) and HIP methods, using powder with spherical shape and narrow particle size distribution, especially fine particle sizes are very important. This is especially the case in chemical applications where the specific surface area of the powder is important. So currently, there is an urgent need for a technology to provide these features.

[0011] Another limitation of the common atomizing methods in the world is the design of the melt nozzle and the atomizer nozzle/jet configuration in a single system which in turn results in various operational issues including limitations in the melting point of materials. So, another objective of this invention is to design and manufacture an atomizer without a technical limitation for the material melting point which allows atomizing refractory materials.

[0012] In addition, another problem of available atomizing systems is solidifying the melt flow. Indeed, the expansion of the gas at the end of the nozzle produces a cooling effect and because of the placement of the melt flow and the atomizer nozzle close to each other, solidifying of the melt flow is very likely, which in turn results in cessation of atomizing operations, reduced efficiency and difficulty in operating the powder production. Another objective of this invention is to fulfill this problem by altering the design of the atomizer nozzle and its orientation.

Solution to Problem

[0013] Basically, in the atomizing process, upon the collision of the melt flow with the surface of the gas flow, the melt flow is accelerated and disintegrated. In common gas atomizers, a gas flow passing through a circular cross-section is used and hence the contact area for the collision of the melt flow and the gas flow is limited. The higher the level of collision between the melt and the gas flow, the higher the energy transfer from the gas with high velocity and kinetic energy to the melt, resulting in more energy to disperse the melt stream and turn it into fine droplets, that are then converted to powder upon cooling.

[0014] In this invention, the boundary layer concept is used to improve the atomizing process, which implies that by increasing the boundary layers (free surface of high-pressure gas flow) in the same air volume, more uniform and finer particles are produced. For this purpose, in this invention, a high-velocity parallel gas flow nozzle (jet atomizer) has been used to convert melt into powder.

[0015] These parallel flows are used to disintegrate the melt so that the contact area between the melt flow and the gas flow is substantially increased and more energy is transferred to the melt. Upon the collision of such high-velocity gas flows with a narrow column of melt stream, fine droplets are generated from the melt, which are instantly solidified due to the system’s heat transfer, generating powder particles. In addition, these parallel flows direct the formed particles in such a way that the probability of the collision of the particles and creating satellite powders and thus enlarging the particle size is minimized, resulting in smaller and more uniform particles production.

Advantageous Effects of Invention

[0016] - Possibility of using this type of jet atomizing to produce powder from a wide range of materials, such as metal, ceramic, and polymers powders, and in general any type of material that can be melted.

[0017] - No limit on the temperature of atomizing gas (both hot and cold gases)

[0018] - Considerable reduction of production and operating costs

[0019] - Increasing the lifespan of the melt nozzle due to the reduction of erosion and the possibility of using cheap materials in its manufacturing.

[0020] - Possibility of using this invention as a horizontal and vertical atomizer

[0021] - High production efficiency of fine powder particles

[0022] - Production of micron, sub-micron and Nano-sized particles

[0023] - Production of powders with a desired and narrow particle size distribution

[0024] - Production of spherical and irregular particles by changing process parameters

[0025] - Separation of melt nozzle and gas nozzle system

[0026] - Production of refractory materials powder with a melting point of up to 3000 C.

Brief Description of Drawings

[0027] Figure 1 : Overview of the method and device

[0028] Figure 2: Melt flow path while colliding with parallel gas flows [0029] Figure 3: Different types of arrangements in parallel gas flows with different cross-sections

[0030] Figure 4: Position of the jet atomizer relative to the melt flow and the slight deviation from the horizontal direction

Description of Embodiments

[0031] Figure 1 illustrates furnace or tundish (1) for molten materials (2) in the upper part. The melt stream (3) exits from the bottom of tundish and flows towards the ground. The gas (4) passes through the gas channel (5). At the outlet of this channel, there is a component producing parallel gas flows (6) which considering the cross-section of the existing orifices, creates parallel gas flows (7).

[0032] The passage of the melt flow through the gas flows causes the melt to collide with the boundary layers of the high-velocity gas flows, and while accelerating the melt droplets, it separates the smaller droplets of the melt (8), and accordingly results in fine fragmentation of melt droplets. These ultra-fine droplets solidify by moving away from the source of production and the powder is produced.

[0033] As it is illustrated in Figure 2, compared to current methods, given the fact that the melt flow (3) is completely surrounded by the gas flows (7) due to the high- velocity gas flow and the resulting forces, the melt can’t escape without colliding with parallel gas flows. In this method, parallel flows direct the formed particles in such a way that the probability of the particles colliding with each other and creating satellite powders and so enlarging the particle size is minimized, resulting in smaller and more uniform particles.

[0034] The atomizer nozzle or the component producing parallel gas flows (6) can be a section with several orifices in different arrangements, which provides the parallel flows of the atomizing gas (7) and so, a significant increase in the boundary layer compared to a single gas flow with the same flow rate.

[0035] Figure 3 illustrates an example of cross-sectional arrangements of the gas outlets (jet atomizer) with the parallel flows along with the position of the parallel flows relative to the melt flow, which has a slight deviation from the horizontal direction and is shown with a angle (9) in figure 4. In Figure 3, several different arrangements of nozzle orifices are illustrated, but the placement of the orifices is not limited to these shapes, and examples of the proposed sections for the orifices arrangements are illustrated (top row-figure 3).

[0036] In addition, the nozzle orifices are not necessarily circular and can be square, rectangular, polygonal, and any other shape (bottom row-figure 3). As the distance and arrangements of parallel flows is adjustable during the production of the component producing parallel flows, it can be expected that the particle size distribution of the produced powder can also be adjusted.

[0037] The preference for placing the (gas jet) atomizer nozzle is horizontal and almost perpendicular to the melt stream, however, this atomizer nozzle design can be utilized in vertical atomizing systems. The nozzle and the melt stream don’t have the probability of exchanging heat before colliding with each other, which allows using cold gas in the jet.

[0038] Thus the atomizing gas can be preheated or cooled. The important point in this design is the separation of the atomizer nozzle system and the melt stream. Therefore, heat transfer and gas expansion in the nozzle does not lead to solidification of the melt stream, which increases the production efficiency and decreases production costs. In addition, due to the separation of the atomizer nozzle system and the melt nozzle, erosion in the melt nozzle is significantly reduced. As a result, the lifespan of the melt nozzle is increased and cheap materials can be used in its manufacturing, which again reduces production costs.

[0039] The slight deviation of the axis of the atomizer nozzle from 90 degrees angle with the melt flow (9) helps to control the flow of atomized particles in the atomizing chamber (Figure 4). So, in case of changing the collision angle of the melt flow with the produced gas flows (less than or more than 90 degrees) (9), other controls can be performed. This implies that considering the suction created by high-velocity gas flows, the collision angle does not have to be 90 degrees, and also supplying the melt flow can be performed from different directions. For instance, considering the suction created by high-velocity gas flows, the melt stream can be supplied or injected even from the bottom points of the gas flow.

[0040] The atomizing fluid in this invention can be air or neutral gases such as nitrogen, argon, helium, etc. An air compressor is used to generate high-velocity gas flows. Upon changing atomizing parameters such as atomizing gas type, fluid pressure and velocity, shape and diameter of parallel gas flows, melt flow diameter, and the collision angle of parallel gas flows and melt stream, the shape and size of the produced particles can be controlled. For example, by using neutral gases, it is possible to produce spherical metal powder and by using helium gas, producing particles below 20 microns with this invention is possible.

[0041] In terms of selecting a furnace for melting raw materials, the type of furnace can be chosen based on the type of the materials. For example, for melting ceramics and refractory metal alloys, plasma melting furnaces can be used, for ferrous alloys, induction furnaces, and for polymers and metals with low melting points, electric-powered and gas-powered furnaces can be used.

Examples

[0042] As it was mentioned in the technical field of the invention, this invention covers a wide range of materials including metal powders (both ferrous and non- ferrous metals), ceramic and refractory materials powders, polymer powders, etc., and additionally, this type of atomizer can be used horizontally and vertically. In the following, the use of this atomizer to produce metal powder in a horizontal atomizer is described.

[0043] A metal, which can be various ferrous or non-ferrous alloys (such as zinc, copper, silver, aluminum, etc.), is melted in a furnace (induction, arc, or flame furnace) and through a ceramic tundish, a molten stream with a diameter of 1 to 10 mm is created. Atomizing gas, which can be air or inert gas, is compressed by a compressor with an air volume of 1 to 40 cubic meters per minute and a pressure of 3 to 20 atmospheres, and through the passage from the atomizer nozzle, high-velocity parallel flows are created.

[0044] By colliding these flows with the melt flow horizontally and at an angle of approximately 90 degrees with the melt flow, melt droplets are formed and solidify in the atomizing chamber and then collected by one or more particle collection systems such as cyclones, bag filters, etc.

Industrial Applicability [0045] By using this invention, the production of various materials powder in micron, sub-micron, and Nano size, and in different morphologies of spherical, irregular, bubbles (hollow spheres), and even fibers is possible. In the following, some of the applications of these materials are mentioned.

[0046] In the field of metal powders:

- Powder metallurgy industry: Powder of various ferrous and non-ferrous alloys has a wide range of applications in the manufacture of industrial parts, especially in the manufacture of complex parts with precise dimensional control.

- New methods of manufacturing parts: New technologies for manufacturing metal parts such as additive manufacturing (3D printing), metal injection molding, and HIP require fine powders in a narrow particle size distribution.

- Welding and electrode industries: Powders of various ferrous alloys and some non- ferrous metals are considered as filler metals or energy sources.

- Military industries: Powders of some metals such as aluminum and magnesium are considered as a fuel and energy source.

- Renewable Energy Industries: Solar cells and new batteries are just examples of metal powders’ application in the field of energy.

[0047] In the field of ceramic powder:

- Rock wool and ceramic wool can be produced by this technology

- Special thermal insulation such as bubble alumina In the field of polymer powders:

- Printing toner manufacturing industry

- Wax manufacturing industry.