Anti-pollution auger conveying device for lithium carbonate

Abstract

A pollution-proof auger conveyor for lithium carbonate includes an auger shaft, auger blades, and a housing. A ceramic protective sleeve is fixedly installed at the connection area between the feeding shaft section and the shaft head. The feeding shaft section, as well as the surfaces of the feeding shaft section, auger blades, and housing, are all coated with a tungsten carbide coating, ensuring that the lithium carbonate powder is in contact with the tungsten carbide coating throughout the entire conveying process. This invention completely isolates the direct friction between the metal shaft head and the housing by setting a high-purity alumina ceramic protective sleeve at the contact area of ​​the auger shaft end, preventing the generation of friction debris. Simultaneously, a tungsten carbide coating is uniformly applied to all metal surfaces in contact with the lithium carbonate powder, ensuring that the powder only comes into contact with the high-hardness, high-wear-resistant tungsten carbide coating throughout the entire conveying process, fundamentally preventing wear on the stainless steel substrate and the introduction of metal impurities. Testing shows that the magnetic foreign matter content in the lithium carbonate after conveying can be controlled below 200 ppb, and the iron impurity content ≤0.001%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of conveying, and particularly relates to a pollution-preventing auger conveying device for lithium carbonate. BACKGROUND

[0002] Battery-grade lithium carbonate is a key basic raw material for a positive electrode material of a lithium ion battery, and the purity of the battery-grade lithium carbonate directly determines the cycle life, energy density and safety performance of the battery. In the industrial production process of the lithium carbonate, powder materials need to be transferred between processes through an auger conveying device. The conveying process usually adopts a stainless steel auger blade and a shaft body, and continuous feeding is realized through a rotating propulsion mode.

[0003] Lithium carbonate powder has strong abrasive wear characteristics. In the high-speed conveying process, the surface of the stainless steel auger is continuously scoured, resulting in premature abrasive wear of the equipment. However, the auger blade and the inner wall of the inlet and outlet of the existing conveying device are usually made of stainless steel, and the hardness is low, and the service life is generally 6 to 12 months. A large amount of fine stainless steel debris generated by wear is directly mixed into the lithium carbonate material, forming magnetic metal impurities. The metal impurities can seriously damage the electrode structure, greatly shorten the cycle life of the battery, reduce the energy density, and cause safety hazards. Therefore, a conveying solution capable of inhibiting metal pollution from the source is urgently needed. SUMMARY

[0004] In view of the above problems, the present application aims to provide a pollution-preventing auger conveying device for lithium carbonate to at least partially solve the problems in the background.

[0005] The technical scheme adopted by the present application is as follows: a pollution-preventing auger conveying device for lithium carbonate is provided, which comprises: an auger shaft comprising a feeding shaft segment, a shaft head fixed to both ends of the feeding shaft segment, and a transmission shaft segment; an auger blade fixed in a spiral shape on the outer side wall of the feeding shaft segment; an outer shell arranged on the outer side of the auger blade and provided with an inlet and an outlet at both ends, respectively; wherein at least one outer wall at the connection area of the feeding shaft segment and the shaft head or the transmission shaft segment is fixedly installed with a ceramic protective sleeve, the ceramic protective sleeve is used to support the rotating movement between the auger shaft and the outer shell, and isolate the direct contact between the auger shaft and the outer shell to avoid the generation of metal debris; the feeding shaft segment, the feeding shaft segment, the auger blade and the outer shell are all coated with a tungsten carbide coating, so that the lithium carbonate powder is in contact with the tungsten carbide coating throughout the conveying process.

[0006] Furthermore, the ceramic protective sleeve includes two symmetrically distributed semi-annular sleeve bodies, which are fitted together and snapped onto the outer wall of the shaft head and / or drive shaft section. They are mechanically engaged with the dovetail groove by high-temperature adhesive bonding and fixed to the shaft head and / or drive shaft section by bolts.

[0007] Furthermore, the sleeve body includes an alumina ceramic ring with a purity of % or higher, and the sleeve body has a Mohs hardness of 9.

[0008] Furthermore, the tungsten carbide coating is a WC-12Co coating, wherein the mass percentage of tungsten carbide is 85-88% and the mass percentage of cobalt is 12-15%.

[0009] Furthermore, the tungsten carbide coating is prepared using a supersonic flame spraying process, and the coating porosity is 1 ≤ 1%.

[0010] Furthermore, the tungsten carbide coating has a Rockwell hardness of 72~75, a surface roughness Ra≤0.8μm, and a bonding strength between the tungsten carbide coating and the substrate ≥70MPa.

[0011] Furthermore, the auger blade includes a receiving surface facing the conveying direction and a backing surface opposite to the conveying direction, and the tungsten carbide coating has a greater coating thickness on the receiving surface than on the backing surface.

[0012] Furthermore, the tungsten carbide coating is applied to the circumferential region of the auger blade away from the auger shaft with a thickness greater than that applied to the region closer to the center of the auger shaft.

[0013] Furthermore, the wall thickness of the sleeve body is set to 8~12mm.

[0014] Furthermore, the interior of the outer shell has a conveying chamber for conveying lithium carbonate. After the lithium carbonate powder is conveyed through the contact between the auger shaft, auger blades and the outer shell in the conveying chamber and discharged from the outlet, the content of magnetic foreign matter in the lithium carbonate powder is ≤200ppb and the content of iron impurities is ≤0.001%.

[0015] Beneficial effects: This invention completely isolates the direct friction between the metal shaft end and the outer casing by installing a high-purity alumina ceramic protective sleeve in the contact area of ​​the auger shaft, preventing the generation of friction debris. Simultaneously, a tungsten carbide coating is uniformly applied to all metal surfaces in contact with the lithium carbonate powder, ensuring that the powder only comes into contact with the high-hardness, highly wear-resistant tungsten carbide coating throughout the entire conveying process, fundamentally eliminating wear on the stainless steel substrate and the introduction of metal impurities. Testing shows that the content of magnetic foreign matter in the lithium carbonate after conveying can be controlled below 200 ppb and the iron impurity content ≤0.001%, far superior to existing stainless steel conveying devices, effectively ensuring the high purity requirements of battery-grade lithium carbonate while reducing equipment maintenance frequency. Attached Figure Description

[0016] Figure 1 This is a three-dimensional structural schematic diagram of a pollution-proof auger conveyor device for lithium carbonate according to an embodiment of the present invention; Figure 2 A schematic diagram of the conveying auger is provided for an embodiment of the present invention; Figure 3 for Figure 2 A top-view structural diagram; Figure 4 This is a cross-sectional view of the installation of a ceramic protective sleeve on a shaft head according to an embodiment of the present invention.

[0017] Among them, 10 is the auger shaft; 11 is the feeding shaft section; 12 is the shaft head; 120 is the mounting hole; 13 is the drive shaft section; 20 is the auger blade; 201 is the material receiving surface; 202 is the material receiving surface; 30 is the outer shell; 300 is the conveying chamber; 301 is the discharge port; 40 is the ceramic protective sleeve; 400 is the screw hole; 41 is the sleeve body; 410 is the dovetail groove; and 42 is the bolt.

[0018] The accompanying drawings are provided to further understand the embodiments and form part of the specification. They are used together with the embodiments for explanation and do not constitute a limitation on the embodiments. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0020] In the description of the embodiments, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments.

[0021] like Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a pollution-proof auger conveying device for lithium carbonate, including an auger shaft 10, auger blades 20 and a housing 30.

[0022] The auger shaft 10 includes a feeding shaft section 11, and shaft heads 12 and a transmission shaft section 13 fixed at both ends of the feeding shaft section 11. The feeding shaft section 11 is the main load-bearing part of the auger, and is usually made of stainless steel round steel. Its outer diameter along the axial direction can be of constant diameter or variable diameter design.

[0023] The auger blades 20 are fixed in a spiral shape to the outer wall of the feeding shaft section 11. Specifically, they can be made by welding continuous spiral blades to the surface of the feeding shaft section 11, or by welding segmented blades together. The outer shell 30 is a cylindrical structure and is located outside the auger blades 20. Its inner diameter is slightly larger than the outer diameter of the auger blades 20, and a small gap is left between the two to ensure free rotation.

[0024] The outer casing 30 has an inlet and an outlet 301 at its two ends, respectively. The inlet is located above or to the side of one end near the drive shaft section 13, and the outlet 301 is located below the other end. The drive shaft section 13 is used to connect an external drive device (such as a motor reducer) to drive the auger shaft 10 and auger blades 20 to rotate around their own axis. Lithium carbonate powder falls from the inlet into the conveying chamber 300 inside the outer casing 30. As the auger blades 20 rotate, the powder moves axially towards the outlet 301 under the push of the auger blades 20, and is finally discharged from the outlet 301, realizing continuous quantitative conveying.

[0025] In the existing technology, the stainless steel shaft head is in direct contact with the inner ring of the bearing or the seal. Under long-term rotational friction, fine metal debris will be generated. Once these debris falls into the conveying chamber 300, they will mix with the lithium carbonate powder, thereby affecting the performance of the lithium carbonate powder.

[0026] Furthermore, at least one outer wall of the connection area between the feeding shaft section 11 and the shaft head 12 or the transmission shaft section 13 is fixedly installed with a ceramic protective sleeve 40.

[0027] Specifically, the shaft head 12 and the drive shaft section 13 typically need to mate with the bearing seat or sealing structure at the end of the housing 30, and there is relative rotational movement at this mating part. The ceramic protective sleeve 40 covers the outer cylindrical surface of the shaft head 12 or the drive shaft section 13, replacing the original metal / metal or metal / seal contact interface.

[0028] Because ceramic materials possess extremely high hardness and an extremely low coefficient of friction (with a dry friction coefficient of approximately 0.1 to 0.2 against steel), and do not contain any magnetic metallic elements, the generation of friction debris can be fundamentally avoided. Simultaneously, the outer surface of the ceramic protective sleeve 40 and corresponding parts of the outer casing 30, such as the inner ring of a bearing or a wear-resistant bushing, form a rotating support pair, ensuring the stable rotation of the auger shaft 10.

[0029] In existing technologies, when stainless steel augers transport lithium carbonate powder, the abrasive properties of the powder cause continuous generation of fine stainless steel debris on the blades and shaft surfaces. Magnetic metal impurities such as iron, chromium, and nickel from these debris directly mix into the lithium carbonate powder. Furthermore, these metal impurities can catalyze electrolyte decomposition, puncture the separator, and trigger micro-short circuits during subsequent battery manufacturing, leading to increased battery self-discharge rate, a reduction in cycle life of over 30%, and in severe cases, thermal runaway. In addition, metal impurities reduce the structural stability of the cathode material, accelerating capacity decay and making it difficult to meet the purity requirements of high-end lithium batteries, which require ≤200 ppb of magnetic foreign matter in lithium carbonate.

[0030] To further avoid the above situation, the feeding shaft section 11, as well as the surfaces of the feeding shaft section 11, the auger blades 20, and the outer casing 30, are all coated with a tungsten carbide coating, ensuring that the lithium carbonate powder is in contact with the tungsten carbide coating throughout the entire conveying process. That is, all metal substrate surfaces that may come into contact with the lithium carbonate powder (including the entire outer circumference of the feeding shaft section 11, the spiral surface and sides of the auger blades 20, and the inner wall surface of the outer casing 30) are completely covered by the tungsten carbide coating.

[0031] In this way, the powder is always in relative motion with the tungsten carbide coating during the conveying process, without directly contacting the stainless steel substrate. The hardness of the tungsten carbide coating (Rockwell hardness 72~75) is much higher than that of the stainless steel substrate (about 20~30), and it has excellent resistance to abrasive wear. It can withstand the erosion of lithium carbonate powder (Mohs hardness about 3~4) for a long time without significant wear, thus avoiding the mixing of stainless steel debris.

[0032] The tungsten carbide coating also has good corrosion resistance, preventing lithium carbonate from corroding the equipment in humid environments.

[0033] like Figure 4As shown, the ceramic protective sleeve 40 includes two symmetrically distributed semi-annular sleeve bodies 41. The sleeve bodies 41 are fitted together and clamped onto the outer wall of the shaft head 12 and / or the drive shaft section 13. Each semi-annular sleeve body 41 has a dovetail groove 410 and a corresponding dovetail tenon at its end. The two semi-annular sleeve bodies 41 can be mechanically engaged with the dovetail groove by high-temperature adhesive bonding and fixed to the shaft head 12 and / or the drive shaft section 13 by bolts 42.

[0034] In some embodiments, each semi-annular sleeve body 41 is provided with a dovetail groove 410 and a corresponding dovetail tenon at its end. The shaft head 12 is provided with a corresponding mounting hole 120. The two semi-annular sleeve bodies 41 are installed axially on the outside of the shaft head 12, and the positions of the dovetail groove 410 and the dovetail tenon are locked together. The upper part of the semi-annular sleeve body 41 is provided with a screw hole 400 at the mounting hole 120 for installing bolts 42 to fix the ceramic protective sleeve 40 to the shaft head 12.

[0035] In other embodiments, each sleeve body 41 has a semi-circular groove on its inner side that matches the outer circle of the shaft head 12. An axial dovetail groove or key can also be provided within the groove. During installation, the two semi-rings are first aligned from both sides of the shaft head 12, so that the dovetail groove 410 engages with the pre-set protrusion (or key) on the shaft head 12, preventing circumferential slippage of the sleeve body 41 relative to the shaft head 12. Then, a high-temperature resistant inorganic adhesive (operating temperature up to 300°C or higher) is applied to the mating surfaces to further fill the gaps and enhance resistance to loosening. Finally, bolts 42 are inserted into the radial lugs of the two sleeve bodies 41 and tightened to ensure the two semi-rings are tightly fitted onto the shaft head 12.

[0036] Furthermore, the sleeve body 41 includes an alumina ceramic ring made of a purity of 95% or higher, and the sleeve body 41 has a Mohs hardness of 9. High-purity alumina ceramic (alumina content ≥95%) has extremely excellent wear resistance, compressive strength and chemical stability. Its Mohs hardness of 9 is second only to diamond and cubic boron nitride, and far higher than stainless steel (approximately 5.5) and general abrasive grains.

[0037] Thus, during long-term friction with the metal or seals of the outer casing 30, alumina ceramics experience almost no wear, thus preventing the generation of ceramic debris that contaminates materials. Furthermore, alumina ceramics exhibit excellent corrosion resistance to lithium carbonate and common acidic and alkaline media, making them suitable for chemical production environments.

[0038] Furthermore, the tungsten carbide coating is a WC-12Co coating, wherein the mass percentage of tungsten carbide is 85-88% and the mass percentage of cobalt is 12-15%. Tungsten carbide (WC) is the hard phase, providing extremely high hardness and wear resistance; cobalt (Co) acts as the binder metallic phase, melting and encapsulating the tungsten carbide particles during supersonic flame spraying to form a dense coating. This ratio (cobalt content 12-15%) is called WC-12Co, a widely used high-wear-resistant coating material in industry. It achieves a good balance between hardness and toughness, and can withstand the impact and vibration during lithium carbonate transportation, preventing brittle peeling of the coating.

[0039] Furthermore, the tungsten carbide coating is prepared using a high-velocity vapor deposition (HVOF) process, resulting in a coating porosity of ≤1%. HVOF utilizes high-pressure combustion gases to heat powder to a semi-molten state and then propels it onto the workpiece surface at supersonic speeds (approximately 1000~1500 m / s). The high-speed impact causes the coating particles to deform dramatically and stack tightly, forming a dense structure with extremely low porosity. A porosity of ≤1% means that the coating has virtually no through-holes or closed pores, effectively preventing the penetration of lithium carbonate powder or moisture and acidic gases from the environment into the coating-substrate interface, thus avoiding substrate corrosion or coating blistering and peeling. Simultaneously, the low porosity also helps maintain low surface roughness and a low coefficient of friction for the coating.

[0040] Furthermore, the tungsten carbide coating has a Rockwell hardness of 72-75, a surface roughness Ra ≤ 0.8 μm, and a bonding strength ≥ 70 MPa between the coating and the substrate. A Rockwell hardness of 72-75 corresponds to a Vickers hardness of approximately 1000-1100 HV, more than five times that of ordinary stainless steel, enabling long-term resistance to abrasive wear from lithium carbonate powder. A surface roughness Ra ≤ 0.8 μm is considered semi-mirror-like, preventing powder from adhering easily to the coating surface and reducing the micro-cutting effect of the powder on the coating. A bonding strength ≥ 70 MPa means the coating will not peel off from the substrate under impact or shear, preventing coating fragments from becoming a new source of contaminants.

[0041] In some embodiments, such as Figure 3As shown, the auger blade 20 includes a receiving surface 201 facing the conveying direction and a backing surface 202 opposite to the conveying direction. The tungsten carbide coating thickness on the receiving surface 201 is greater than that on the backing surface 202. During the auger's rotation and propulsion of the powder, the receiving surface 201 directly faces the compression and scouring of the lithium carbonate powder, with powder particles impacting this surface at relatively high speeds, resulting in the most severe wear. The backing surface 202, on the other hand, is mainly subjected to slight friction from a small amount of returned powder, and its wear is far less than that of the receiving surface 201. Therefore, without affecting the overall protective effect, spraying a thicker tungsten carbide layer (e.g., 0.4~0.6 mm) on the receiving surface 201 and a thinner coating (e.g., 0.2~0.3 mm) on the backing surface 202 allows for reasonable control of the coating material usage, while avoiding stress concentration at the blade edges due to excessively thick coatings.

[0042] In other embodiments, the tungsten carbide coating is applied to the circumferential region of the auger blade 20 away from the auger shaft 10 with a greater thickness than that applied to the region closer to the center of the auger shaft 10. This is because the outer edge of the auger blade 20 has the highest linear velocity and the greatest relative velocity with the lithium carbonate powder, resulting in the strongest abrasive effect from the powder on the outer edge region. Conversely, near the root region of the auger shaft 10, the linear velocity is lower and the powder is subjected to less compression, leading to less wear. This radially differential thickness design, where the outer edge coating is thicker than the root coating, ensures a more even service life across the entire blade surface, preventing excessively rapid localized wear that could lead to downtime for maintenance.

[0043] Furthermore, the wall thickness of the sleeve body 41 is set to 8~12mm. This wall thickness has been verified through strength checks and actual working conditions: when the wall thickness is less than 8mm, the alumina ceramic ring may experience brittle fracture when subjected to radial loads (such as the eccentric force caused by the weight of the auger shaft and the pressure of the powder); a wall thickness greater than 12mm will increase the shaft end diameter, resulting in an increase in the bearing seat size of the outer shell 30, which is not conducive to compact design. The wall thickness of 8~12mm can ensure the bending strength and impact resistance of the ceramic sleeve, and is also compatible with the dimensions of conventional standard bearings and seals.

[0044] Furthermore, the outer casing 30 has a conveying chamber 300 for transporting lithium carbonate. Lithium carbonate powder is conveyed within the conveying chamber 300 through the contact between the auger shaft 10, auger blades 20, and the outer casing 30, and discharged from the outlet 301. The magnetic foreign matter content in the lithium carbonate powder is ≤200ppb, and the iron impurity content is ≤0.001%. This data is based on a sample taken from the outlet 301 after 240 hours of continuous transport of battery-grade lithium carbonate powder (D50≈10~30μm, conveying capacity 2~5 tons / hour) using a prototype with the above structure. The magnetic foreign matter content of ≤200ppb (parts per billion) is far lower than the 2000~5000ppb of traditional stainless steel auger conveying devices, and the iron impurity content of ≤0.001% (parts per million) is also far lower than the industry standard of 0.03%. This indicates that this device can eliminate metal contamination at the source and meet the stringent requirements for lithium carbonate purity in high-end lithium battery materials.

[0045] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0046] The embodiments have been described above, and such description is not restrictive. The figures shown are only one embodiment, and the actual structure is not limited to this. In short, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the inventive spirit, such design should fall within the scope of protection.

Claims

1. A contamination-resistant auger conveyor for lithium carbonate, characterized in that, include: The auger shaft (10) includes a feeding shaft section (11) and shaft heads (12) and a transmission shaft section (13) respectively fixed to both ends of the feeding shaft section (11). Screw blades (20) are spirally arranged on the outer wall of the feeding shaft section (11); The outer casing (30) is disposed on the outside of the auger blade (20); In the connection area between the feeding shaft section (11) and the shaft head (12) or the transmission shaft section (13), at least one outer wall is fixedly installed with a ceramic protective sleeve (40). The ceramic protective sleeve (40) is used to support the rotational movement between the auger shaft (10) and the outer shell (30) and to isolate the direct contact between the auger shaft (10) and the outer shell (30) to avoid the generation of metal debris. The feeding shaft section (11), as well as the surface of the feeding shaft section (11), the auger blade (20), and the outer shell (30), are all coated with a tungsten carbide coating, so that the lithium powder is in contact with the tungsten carbide coating throughout the entire process of conveying.

2. The anti-pollution auger conveyor device for lithium carbonate according to claim 1, characterized in that: The ceramic protective sleeve (40) includes two symmetrically distributed semi-annular sleeve bodies (41). The sleeve bodies (41) are fitted together and clamped on the outer wall of the shaft head (12) and / or the transmission shaft section (13). They are mechanically engaged with the dovetail groove by high-temperature adhesive bonding and fixed on the shaft head (12) and / or the transmission shaft section (13) by bolts (42).

3. The anti-pollution auger conveyor device for lithium carbonate according to claim 2, characterized in that: The sleeve body (41) includes an alumina ceramic ring with a purity of 95% or higher, and the sleeve body (41) has a Mohs hardness of 9.

4. The anti-pollution auger conveyor device for lithium carbonate according to claim 1, characterized in that: The tungsten carbide coating is a WC-12Co coating, wherein the mass percentage of tungsten carbide is 85-88% and the mass percentage of cobalt is 12-15%.

5. The anti-pollution auger conveyor device for lithium carbonate according to claim 4, characterized in that: The tungsten carbide coating is prepared using a supersonic flame spraying process, and the coating porosity is ≤1%.

6. The anti-pollution auger conveyor device for lithium carbonate according to claim 4, characterized in that: The tungsten carbide coating has a Rockwell hardness of 72~75, a surface roughness Ra≤0.8μm, and a bonding strength between the tungsten carbide coating and the substrate ≥70MPa.

7. The anti-pollution auger conveyor device for lithium carbonate according to claim 4, characterized in that: The auger blade (20) includes a receiving surface (201) facing the conveying direction and a back surface (202) opposite to the conveying direction, wherein the tungsten carbide coating is sprayed on the receiving surface (201) with a thickness greater than that on the back surface (202).

8. The anti-pollution auger conveyor device for lithium carbonate according to claim 7, characterized in that: The tungsten carbide coating is applied to the circumferential region of the auger blade (20) away from the auger shaft (10) with a thickness greater than that applied to the region near the center of the auger shaft (10).

9. The anti-pollution auger conveyor device for lithium carbonate according to claim 2, characterized in that: The wall thickness of the sleeve (41) is set to 8~12mm.

10. The anti-pollution auger conveyor for lithium carbonate according to claim 1, characterized in that: The outer shell (30) has a conveying chamber (300) for conveying lithium carbonate. The lithium carbonate powder is conveyed in the conveying chamber (300) through the contact of the auger shaft (10), auger blades (20) and the outer shell (30) and discharged from the outlet (301). The content of magnetic foreign matter in the lithium carbonate powder is ≤200ppb and the content of iron impurities is ≤0.001%.

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