Liquid nitrogen two-stage crushing sieve shaker and grinding and sieving control method thereof

Abstract

The application discloses a kind of liquid nitrogen two-stage crushing screening machines and its grinding screening control method, belong to the technical field of crushing screening equipment, including liquid nitrogen tank, feed bin, primary grinding bin, ball mill and screening bin;The liquid nitrogen tank is connected with primary grinding bin and ball mill respectively to supply low-temperature liquid nitrogen into primary grinding bin and ball mill by two-way independent output pipeline;The discharge end of the feed bin is communicated with the feed end of the primary grinding bin, the discharge end of the primary grinding bin is connected with the feed end of the ball mill through the communication channel, and a vertical main screening channel and a bypass return pipeline connected to the feed bin through the vertical main screening channel are arranged in the communication channel;The discharge end of the ball mill is communicated with a screening bin provided with a detachable and replaceable screen mesh.The application realizes accurate screening and closed-loop cycle re-crushing, has reasonable structure layout, strong equipment structure adaptability, excellent running stability and sealing performance, and is suitable for long-term low-temperature operation scene.

Description

Technical Field

[0001] This invention belongs to the technical field of crushing and screening equipment, specifically relating to a liquid nitrogen two-stage crushing and screening instrument and its grinding and screening control method. Background Technology

[0002] Currently, conventional material crushing and screening equipment mostly adopts room temperature mechanical crushing. For heat-sensitive, high-toughness, and high-elasticity materials, frictional heat generated during room temperature crushing can easily cause the material to heat up, deform, soften, stick together, and agglomerate. This not only results in low crushing efficiency but also seriously damages the original physical and chemical properties of the material, failing to meet the requirements of high-precision powder processing.

[0003] Existing cryogenic pulverizing equipment mostly adopts a single-stage crushing structure, achieving overall cooling solely through the introduction of liquid nitrogen into the entire chamber. This approach has several technical drawbacks: First, the uniform liquid nitrogen cooling mode for both crushing and grinding processes cannot adapt to the differentiated cryogenic process requirements of primary coarse crushing and secondary fine grinding. Insufficient cooling in the coarse crushing stage can lead to incomplete crushing, while excessive cooling in the fine grinding stage results in wasted liquid nitrogen resources. Second, traditional crushing rollers rely solely on chamber spray cooling, lacking a pre-cooling structure within the roller itself. High-temperature materials contacting the roller surface can easily cause roller sticking and blockage, resulting in poor crushing stability. Third, conventional screening channels have a single, straight-through structure, leading to poor separation efficiency between coarse and fine materials. The equipment suffers from several drawbacks. First, substandard coarse materials cannot be re-crushed stably, resulting in low screening accuracy and poor uniformity of finished particles. Second, the existing equipment lacks a targeted cold energy recovery structure, leading to the direct discharge of low-temperature nitrogen gas volatilized during crushing, resulting in significant liquid nitrogen loss and high equipment operating costs. Third, the equipment relies heavily on pipeline temperature measurement, which cannot accurately capture the actual operating temperature inside the chamber, resulting in delayed temperature control, poor temperature precision, and difficulty in maintaining a stable low-temperature crushing environment. Finally, the conventional discharge structure lacks a sealed isolation design, allowing hot and humid air from the outside to easily flow back into the equipment chamber during discharge, causing internal frost formation and material moisture regain, severely affecting the quality of the finished powder.

[0004] In summary, existing low-temperature crushing and screening equipment suffers from problems such as low temperature control accuracy, poor integration of crushing and screening, low utilization of cold energy, easy material loss, and insufficient operational stability, making it difficult to achieve integrated and efficient operation of two-stage differentiated low-temperature crushing, precise circulating screening, and closed-loop reuse of cold energy. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a liquid nitrogen two-stage crushing and screening instrument and its grinding and screening control method. It realizes differentiated low-temperature temperature control for two-stage crushing, greatly improves the material crushing quality and adaptability. It adopts a high-low staggered layered duplex channel structure to achieve precise screening and closed-loop circulation re-crushing, improves the uniformity of finished particles, has a reasonable structural layout, strong equipment structure adaptability, excellent operational stability and sealing performance, and is suitable for long-term low-temperature operation scenarios.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution: On the one hand, the present invention provides a liquid nitrogen two-stage crushing and screening machine, including a liquid nitrogen tank, a feed bin, a primary grinding bin, a ball mill, and a screening bin; The liquid nitrogen tank is equipped with two independent output pipelines that are connected to the primary grinding chamber and the ball mill respectively to supply cryogenic liquid nitrogen to the primary grinding chamber and the ball mill. The discharge end of the feed hopper is connected to the feed end of the primary grinding hopper. The discharge end of the primary grinding hopper is connected to the feed end of the ball mill through a connecting channel. The connecting channel is provided with a vertical main screening channel and a bypass return pipeline that is diverted through the vertical main screening channel and connected to the feed hopper. The discharge end of the ball mill is connected to a screening chamber equipped with a removable and replaceable screen.

[0007] Furthermore, a pair of crushing rollers rotating in opposite directions are provided inside the primary grinding chamber. Several first rollers and second rollers of different diameters are coaxially arranged on the crushing rollers along the axial direction. The first rollers between the two opposing crushing rollers are matched and correspondingly arranged with the second rollers on the corresponding crushing rollers. The crushing roller has a refrigerant channel inside its body that is connected to an independent output pipeline of the liquid nitrogen tank. The refrigerant channel has several spray holes circumferentially arranged on the outer side of the crushing roller, and the spray holes are located in the annular groove space formed between the first roller and the second roller.

[0008] Furthermore, the connecting channel is an integrated composite diversion channel structure with staggered vertical and internal and external layers. The connecting channel includes a centrally located vertical main screening channel and an eccentrically arranged bypass diversion channel. The vertical main screening channel and the bypass diversion channel are arranged in a staggered spatial interweaving layout. The inlet end of the vertical main screening channel is connected to the outlet end of the primary grinding chamber, and the outlet end of the vertical main screening channel is axially connected to the feed end of the ball mill; the bypass diversion channel is tangentially led out along the upper middle side wall of the vertical main screening channel and bends downwards before being extended and connected to the feed chamber via an external pump, so that the vertical main screening channel and the bypass diversion channel together form a double-layer staggered connection structure with upper diversion and lower independent material conveying; A funnel drop outlet is provided at the inlet end of the vertical main screening channel. A concave annular interlocking mounting groove is formed inside the vertical main screening channel. An annular screen mesh, spirally arranged from top to bottom with a transverse projection area of ​​3 / 4 to 9 / 10 of a circle, is installed on the interlocking mounting groove. An annular sealing abutment surface is provided at the bottom of the annular interlocking mounting groove. The edge of the annular screen mesh is fitted and sealed to the annular sealing abutment surface. The annular screen mesh is entirely embedded inside the annular interlocking mounting groove, with its top aligned with the funnel. The drop outlets are connected, and the vertical main screening channel is axially divided into an upstream coarse material chamber and a downstream fine material chamber. The feed inlet of the bypass diversion channel is connected to the lower part of the side wall of the upstream coarse material chamber formed by the annular screen. Only large unqualified particles intercepted by the screen are cut into the bypass diversion channel to complete the return transport. Qualified fine particles are transported directly to the ball mill along the vertical main screening channel after falling through the screen, forming an integrated screening return channel structure with high and low position partitioning, layered diversion, and staggered connection.

[0009] Furthermore, quick-lock screen clamping mechanisms are respectively provided at both ends of the vertical main screening channel of the connecting channel. The quick-lock screen clamping mechanism includes a circumferential clamp and an elastic sealing gasket. The circumferential clamp can be detachably clamped to the primary grinding chamber and the ball mill respectively, and the elastic sealing gasket abuts against the inner edge of the circumferential clamp.

[0010] Furthermore, a sample outlet is provided at the bottom of the screening chamber, and the sample outlet is equipped with a sealed material discharge valve that forms an isolation transition chamber by alternating opening and closing of upper and lower valve plates.

[0011] Furthermore, the screening chamber is equipped with a cold air return branch pipe, one end of which is connected to the upper chamber of the screening chamber, and the other end is connected back to the independent output pipeline between the liquid nitrogen tank and the primary grinding chamber.

[0012] Furthermore, flow regulating valves and temperature detection elements are respectively installed on the two independent output pipelines. The temperature detection elements respectively collect the internal temperature of the primary grinding chamber and the ball mill. The two flow regulating valves independently adjust the liquid nitrogen supply flow rate according to the detected temperature of the corresponding chamber.

[0013] Furthermore, a high-precision temperature sensor is embedded in the top wall of the primary grinding chamber and the inner side wall of the ball mill chamber.

[0014] On the other hand, the present invention provides a grinding and screening control method for a two-stage liquid nitrogen crushing and screening machine, comprising the following steps: Step S1: Liquid nitrogen is independently supplied to the primary grinding chamber and the ball mill through two independent output pipelines of the liquid nitrogen tank. The temperature of the primary grinding chamber and the ball mill chamber are collected in real time through temperature sensors on the two independent output pipelines. Step S2: Based on the preset low temperature threshold for primary crushing and low temperature threshold for fine grinding, adjust the opening of the two flow control valves accordingly. At the same time, liquid nitrogen is sprayed out through the coolant flow channel inside the crushing roller in the primary grinding chamber and the spray hole at the annular groove, so as to pre-cool the crushing roller body by immersion in the entire area and eliminate the temperature difference of the roller body. Step S3: After the temperature of the dual chambers stabilizes and reaches the standard, the material to be processed is sent from the feed hopper into the pre-cooled primary grinding chamber. The material is coarsely crushed by the interlocking structure of the first and second rollers arranged on the two sets of crushing rollers. During the coarse crushing process, liquid nitrogen is continuously added through the spray hole to maintain a low-temperature embrittlement environment during the coarse crushing process and avoid the material from heating up, sticking, and thermally degenerating. Step S4: The material coarsely crushed in the primary grinding chamber is fed into the vertical main screening channel of the connecting channel. The particle size is classified by the spiral ring screen. The large unqualified particles intercepted by the screen are collected in the upstream coarse material chamber and cut into the eccentrically arranged bypass diversion channel through the low-position feed port on the side wall. The material is then pressurized and back-transported to the feed hopper by an external pump to achieve closed-loop re-crushing. At the same time, the qualified fine particles filtered by the screen are sent directly into the ball mill along the axial direction of the vertical main screening channel. Step S5: After the qualified fine particles enter the ball mill, the coarse particles are subjected to ultra-fine grinding in a constant low-temperature environment maintained by the ball mill's independent liquid nitrogen pipeline. The grinding chamber is kept at a low temperature and stable throughout the process to ensure the low-temperature embrittlement grinding effect of the material and avoid the agglomeration and heating of fine particles. Step S6: The ultrafine material ground by the ball mill is sent into the screening chamber. The final particle size classification and screening operation is completed by the detachable and replaceable screen built into the screening chamber. At the same time, the low-temperature nitrogen gas volatilized in the upper chamber of the screening chamber is returned to the liquid nitrogen output pipeline of the primary grinding chamber through the cold gas return branch pipe for cold energy recovery and secondary utilization, reducing liquid nitrogen loss. Step S7: The qualified material after screening is temporarily stored at the bottom of the screening chamber. The pressure relief, isolation and material discharge are achieved through the isolation transition chamber structure with the upper and lower valve plates at the sampling port opening and closing alternately. The entire process prevents the backflow of hot and humid air from the outside into the equipment cavity and maintains a low temperature and sealed environment inside the whole machine. Step S8: Complete the entire automated grinding and screening process of two-stage low-temperature crushing, circulating screening, cold energy recovery, and closed discharge. Then, stop the machine and perform maintenance.

[0015] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: The liquid nitrogen two-stage crushing and screening instrument and its grinding and screening control method provided by this invention are equipped with two independent liquid nitrogen output pipelines, providing independent cooling for the primary grinding chamber and the ball mill. Combined with embedded zone temperature sensors within the chambers, the actual operating temperatures of the coarse crushing and fine grinding zones can be accurately collected. The flow regulating valves are linked to achieve independent constant temperature control of the two chambers, matching the differentiated process requirements of deep cryogenic embrittlement in the first-stage coarse crushing and constant temperature anti-agglomeration in the second-stage fine grinding. This solves the technical pain points of incomplete crushing, overheating and agglomeration in fine grinding, and waste of cooling capacity caused by the unified cooling system in traditional equipment. Simultaneously, the crushing rollers are equipped with refrigerant channels and fixed-point spray holes to achieve full-area immersion pre-cooling of the rollers, completely avoiding material sticking to the rollers and thermal deformation problems.

[0016] This invention features a unique integrated composite diversion channel with staggered upper and lower sections and internal and external layers. The vertical main screening channel enables qualified materials to pass directly for fine grinding, while the high-level tangential bypass diversion channel enables unqualified coarse materials to be returned in a closed loop for re-crushing. Combined with a spiral ring-shaped embedded sealed screen, it achieves physical zoning and layered diversion of coarse and fine materials, eliminating the problems of mixed flow of coarse and fine materials and incomplete screening. Compared with traditional straight-through screening channels, it has higher screening accuracy, better material circulation and crushing effect, and significantly improved particle size uniformity of finished powder.

[0017] A cold air return branch pipe is installed in the screening chamber to recover the low-temperature nitrogen gas volatilized in the screening chamber and guide it back to the liquid nitrogen cooling pipeline in the primary grinding chamber. This allows for the secondary utilization of waste cold energy, which changes the drawbacks of traditional equipment where low-temperature nitrogen is directly discharged into the air and liquid nitrogen is consumed in large quantities. This effectively improves the utilization rate of liquid nitrogen cooling energy, reduces the consumable costs of continuous equipment operation, and has a significant energy-saving effect.

[0018] Quick-lock sealing clamping mechanisms are installed at both ends of the main screening channel to balance the need for rapid disassembly and replacement of the screen with the airtightness of the low-temperature cavity, preventing cold leakage and external moisture intrusion and frost formation. The embedded sensor installation structure can effectively avoid equipment damage caused by material impact and accumulation, ensuring temperature measurement accuracy and equipment stability during long-term operation. The isolation transition discharge structure with alternating opening and closing of two-stage valve plates can block the backflow of external hot and humid air during the discharge process, preventing frost formation in the cavity and material moisture regain, and ensuring the stability of the finished powder quality.

[0019] The grinding and screening control method provided by this invention forms a fully closed-loop process system consisting of pre-cooling and grading regulation, primary staggered coarse crushing, staggered circulating screening, secondary fine grinding, cold energy recovery and reuse, and closed-loop discharge. Each process is logically linked, and parameters are precisely controllable, achieving standardized, automated, and refined operation of low-temperature crushing and screening, significantly improving operational efficiency and reducing manual intervention costs. Furthermore, it integrates two-stage crushing, layered screening, circulating re-crushing, intelligent temperature control, cold energy recovery, and closed-loop discharge functions into a single integrated system. Its rational structural layout and outstanding innovation make it suitable for low-temperature ultrafine grinding of various heat-sensitive and high-toughness materials, effectively solving the problems of limited processing, poor product quality, and high energy consumption associated with traditional equipment. It possesses extremely high market application value and promising prospects for promotion. Attached Figure Description

[0020] Figure 1 A three-dimensional schematic diagram of a liquid nitrogen two-stage crushing and screening instrument provided in an embodiment of the present invention. Figure 1 .

[0021] Figure 2 A three-dimensional schematic diagram of a liquid nitrogen two-stage crushing and screening instrument provided in an embodiment of the present invention. Figure 2 .

[0022] Figure 3 A three-dimensional schematic diagram of a liquid nitrogen two-stage crushing and screening instrument provided in an embodiment of the present invention. Figure 3 .

[0023] Figure 4 A three-dimensional schematic diagram of a liquid nitrogen two-stage crushing and screening instrument provided in an embodiment of the present invention. Figure 4 .

[0024] Figure 5 A schematic diagram of the communication channel provided in the embodiments of the present invention. Figure 1 .

[0025] Figure 6 A schematic diagram of the communication channel provided in the embodiments of the present invention. Figure 2 .

[0026] Figure 7 A schematic diagram of the communication channel provided in the embodiments of the present invention. Figure 3 .

[0027] Figure 8 This is a partial schematic diagram of the vertical main screening channel and the bypass diversion channel provided in an embodiment of the present invention.

[0028] Figure 9 Top view of the communication channel provided in the embodiment of the present invention Figure 1 .

[0029] Figure 10 Top view of the communication channel provided in the embodiment of the present invention Figure 2 .

[0030] Figure 11 A cross-sectional view of a connecting channel provided in an embodiment of the present invention.

[0031] Figure 12 A flowchart of a grinding and sieving control method provided in an embodiment of the present invention.

[0032] In the picture: 1. Liquid nitrogen tank; 2. Feed hopper; 3. Primary grinding hopper; 4. Ball mill; 5. Screening hopper; 6. Connecting channel; 11. Output pipeline; 21. Feed inlet; 22. Discharge end; 31. Crushing roller; 32. First roller; 33. Second roller; 34. Refrigerant flow channel; 35. Spray hole; 36. Annular groove; 51. Sample outlet; 52. Valve plate; 53. Isolation transition chamber; 54. Cold air return branch pipe; 61. Vertical main screening channel; 62. Bypass diversion channel; 63. Jacket mounting groove; 64. Annular screen; 65. Annular sealing contact surface; 66. Upstream coarse material chamber; 67. Downstream fine material chamber; 68. Funnel drop outlet; 71. Circumferential clamp; 72. Sealing gasket; 73. Pump. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0034] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention 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, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0035] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0036] like Figures 1-4 As shown in the figure, this embodiment of the invention provides a liquid nitrogen two-stage crushing and screening machine for low-temperature embrittlement-type two-stage crushing and precise closed-loop screening of heat-sensitive, high-toughness, and easily oxidized materials. The overall equipment integrates independent low-temperature temperature control of liquid nitrogen, self-pre-cooling rollers for staggered coarse crushing, staggered double-channel grading and circulating screening, closed-loop cold energy recovery, sealed discharge, and intelligent temperature control. The overall structure is compact, the working condition is stable, and the powder processing accuracy is high. It can effectively avoid problems such as thermal deformation of traditional room-temperature crushing, waste of cold energy of conventional low-temperature equipment, material mixing during screening, and moisture and frost formation at the discharge.

[0037] In this embodiment, the liquid nitrogen two-stage crushing and screening machine includes a liquid nitrogen tank 1, a feed bin 2, a primary grinding bin 3, a ball mill 4, and a screening bin 5.

[0038] The liquid nitrogen tank 1 is equipped with two independent output pipelines that are connected to the primary grinding chamber 3 and the ball mill 4 respectively to supply cryogenic liquid nitrogen to the primary grinding chamber 3 and the ball mill 4 respectively; wherein, the two output pipelines do not interfere with each other and are independently controlled.

[0039] The discharge end of the feed bin 2 is connected to the feed end of the primary grinding bin 3. The discharge end of the primary grinding bin 3 is connected to the feed end of the ball mill 4 through the connecting channel 6. The connecting channel 6 is provided with a vertical main screening channel 61 and a bypass return pipeline connected to the feed bin 2 after being diverted by the vertical main screening channel 61. The discharge end of the ball mill 4 is connected to a screening chamber 5 equipped with a removable and replaceable screen.

[0040] In this embodiment, the feed bin 2 is vertically arranged and its bottom discharge end is sealed and connected to the top feed end of the primary grinding bin 3. The material can fall steadily into the primary grinding bin 3 by its own weight to complete the first-stage low-temperature coarse crushing operation. The bottom discharge end of the primary grinding bin 3 is sealed and connected to the feed end of the ball mill 4 through a dedicated connecting channel 6. The discharge end of the ball mill 4 is further sealed and connected to the detachable screen-type screening bin 5, forming a complete material processing link from top to bottom: feeding, first-stage coarse crushing, graded screening circulation, second-stage fine grinding, and final precise screening and discharge.

[0041] like Figure 3As shown, the primary grinding chamber 3 is equipped with a pair of opposing rotating crushing rollers 31. Several first rollers 32 and second rollers 33 of alternating diameters are coaxially arranged on each crushing roller 31. The first rollers 32 between two opposing crushing rollers 31 are matched one-to-one with the second rollers 33 on their respective crushing rollers 31. Specifically, the two crushing rollers 31 have several first rollers 32 and second rollers 33 of alternating diameters evenly spaced along the axial direction. The first rollers 32 and second rollers 33 between the two sets of crushing rollers 31 are matched and engaged one-to-one, forming an alternating, step-by-step crushing structure. Compared to a uniform diameter roller grinding structure, this structure can achieve a multi-point shearing, compression, and breaking composite crushing effect on high-toughness materials, significantly improving coarse crushing efficiency and avoiding material slippage and insufficient crushing.

[0042] The crushing roller 31 has a refrigerant channel 34 inside its body, which is connected to an independent output pipe of the liquid nitrogen tank 1. The refrigerant channel 34 has several spray holes 35 circumferentially arranged along the outer side of the crushing roller 31, and these spray holes 35 are located within the annular groove 36 formed between the first roller 32 and the second roller 33. Specifically, liquid nitrogen can be sprayed outward from the spray holes 35 in the annular groove 36 through the refrigerant channel 34 inside the roller body, precisely acting on the material crushing area. This achieves full-area immersion pre-cooling of the roller body and real-time replenishment of cooling in the working area, completely solving the defects of traditional equipment such as only cooling the cavity, large temperature difference of the roller body, material sticking to the roller upon contact, and thermal deformation.

[0043] like Figures 5-11 As shown, the connecting channel 6 is an integrated composite diversion channel structure with staggered vertical and internal and external layers. The connecting channel 6 includes a centrally located vertical main screening channel 61 and an eccentrically arranged bypass diversion channel 62. The vertical main screening channel 61 and the bypass diversion channel 62 are arranged in a staggered spatial interweaving layout.

[0044] The inlet end of the vertical main screening channel 61 is connected to the outlet end of the primary grinding chamber 3, and the outlet end of the vertical main screening channel 61 is axially connected to the feed end of the ball mill 4; the bypass diversion channel 62 is tangentially led out along the upper middle side wall of the vertical main screening channel 61 and bends downwards before being extended to the feed chamber 2 via an external pump, so that the vertical main screening channel 61 and the bypass diversion channel 62 together form a double-layer staggered connection structure with upper diversion and lower independent material conveying.

[0045] Among them, the vertical main screening channel 61 is the main passage for forward material conveying. Its top inlet end is connected to the discharge end of the primary grinding chamber 3, and its bottom outlet end is axially aligned with the feed end of the ball mill 4, ensuring that qualified materials flow vertically downwards without stagnation or deviation. The bypass diversion channel 62 is tangentially led out from the upper side wall of the vertical main screening channel 61, first bends downwards at an incline, and then connects to the feed chamber 2 at the top through a detour pipeline connected to an external pump. The whole structure forms a staggered operation mode of upper diversion screening and lower direct material conveying.

[0046] A funnel-shaped drop outlet 68 is provided at the inlet end of the vertical main screening channel 61. A concave annular interlocking mounting groove 63 is formed inside the vertical main screening channel 61. An annular screen 64, spirally arranged from top to bottom with a transverse projection area of ​​3 / 4 to 9 / 10 of a circle, is provided on the interlocking mounting groove 63. An annular sealing abutment surface is provided at the bottom of the annular interlocking mounting groove 63. The edge of the annular screen 64 is fitted and sealed to the annular sealing abutment surface. The annular screen 64 is entirely embedded inside the annular interlocking mounting groove 63, with its top connected to the funnel. The bucket drop outlet 68 is connected and the vertical main screening channel 61 is axially divided into an upstream coarse material chamber 66 and a downstream fine material chamber 67. The feed inlet of the bypass diversion channel 62 is connected to the lower part of the side wall of the upstream coarse material chamber 66 formed by the annular screen 64. Only large unqualified particles intercepted by the screen are cut into the bypass diversion channel 62 to complete the return conveying. Qualified fine particles are conveyed directly to the ball mill 4 along the vertical main screening channel 61 after falling through the screen, forming an integrated screening return channel structure with high and low position partitioning, layered diversion, and staggered connection.

[0047] Quick-lock screen clamping mechanisms are respectively provided at both ends of the vertical main screening channel 61 of the connecting channel 6. The quick-lock screen clamping mechanism includes a circumferential clamp 71 and an elastic sealing gasket. The circumferential clamp 71 can be detachably clamped to the primary grinding chamber 3 and the ball mill 4 respectively. The elastic sealing gasket abuts against the inner edge of the circumferential clamp 71.

[0048] The aforementioned connecting channel 6 is detachable and quick to assemble, facilitating the rapid replacement of annular screens 64 with different mesh sizes according to the processing requirements of different material particle sizes; at the same time, the inner elastic sealing gasket tightly abuts against the gap between the clamp and the cavity, which can effectively ensure the airtightness of the entire low-temperature channel, prevent the leakage of internal cold energy and the intrusion of external hot and humid air into the channel, causing frost and material blockage, and ensure the equipment's sealing performance and operational stability under long-term low-temperature conditions.

[0049] The bottom of the screening chamber 5 is provided with a sample outlet, which is equipped with a sealed material-separating discharge valve consisting of upper and lower valve plates that alternately open and close to form an isolated transition chamber. Specifically, the bottom of the screening chamber 5 is provided with a sample outlet, and the sample outlet is equipped with a sealed material-separating discharge valve consisting of upper and lower valve plates. The two valve plates can open and close alternately to form an independent isolated transition chamber during the discharge process, realizing the operation logic of pressure relief, isolation, and step-by-step discharge. This prevents the backflow of hot and humid air from the outside into the equipment cavity, eliminates problems such as frost formation in the cavity, material moisture regain, and powder deterioration, and stably ensures the quality of the finished powder.

[0050] The screening chamber 5 is equipped with a cold gas return branch pipe 54. One end of the cold gas return branch pipe 54 is connected to the upper chamber of the screening chamber 5, and the other end is connected back to the independent output pipeline between the liquid nitrogen tank 1 and the primary grinding chamber 3. This allows all the low-temperature nitrogen gas volatilized during the operation of the screening chamber 5 to be recovered and diverted to the cooling pipeline of the primary grinding chamber 3 for secondary use, fully recovering waste cold energy, significantly improving the overall utilization rate of liquid nitrogen cooling energy, and reducing the consumable costs for continuous equipment operation.

[0051] The two independent output pipelines are respectively equipped with flow regulating valves and temperature detection elements. The temperature detection elements collect the internal temperature of the primary grinding chamber 3 and the ball mill 4. The two flow regulating valves independently adjust the liquid nitrogen supply flow rate according to the detected temperature of the corresponding chamber.

[0052] Specifically, a high-precision temperature sensor is embedded in the top wall of the primary grinding chamber 3 and the inner side wall of the ball mill 4.

[0053] Two sets of temperature sensors can accurately collect the actual operating temperature inside the primary coarse crushing chamber and the secondary fine grinding chamber in real time, and feed the temperature signal back to the control system in real time. The control system independently and in conjunction with the preset low temperature thresholds for primary crushing and fine grinding to adjust the opening of the two flow control valves, thereby achieving independent constant temperature and differentiated cooling control for the two chambers. On the other hand, the present invention provides a grinding and screening control method for a two-stage liquid nitrogen crushing and screening machine, comprising the following steps: Step S1: Liquid nitrogen is independently supplied to the primary grinding chamber 3 and the ball mill 4 through two independent output pipelines of liquid nitrogen tank 1. The temperature of the primary grinding chamber 3 and the ball mill 4 are collected in real time by temperature sensors on the two independent output pipelines. Step S2: Based on the preset low temperature threshold for primary crushing and low temperature threshold for fine grinding, adjust the opening of the two flow control valves accordingly. At the same time, liquid nitrogen is sprayed out through the coolant flow channel 34 inside the crushing roller 31 in the primary grinding chamber 3 and the spray hole 35 at the annular groove 36 to pre-cool the crushing roller 31 by immersing it in the entire roller body and eliminating the temperature difference of the roller body. Step S3: After the temperature of the dual chambers stabilizes and reaches the standard, the material to be processed is sent from the feed hopper 2 into the pre-cooled primary grinding hopper 3. The material is coarsely crushed by the interlocking structure of the first roller 32 and the second roller 33 arranged on the two sets of crushing rollers 31. During the coarse crushing process, liquid nitrogen is continuously added through the spray hole 35 to maintain a low-temperature embrittlement environment during the coarse crushing process and avoid the material from heating up, sticking, and thermally degenerating. Step S4: The material coarsely crushed in the primary grinding chamber 3 is fed into the vertical main screening channel 61 of the connecting channel 6. The particle size is classified by the spiral ring screen 64. The large unqualified particles intercepted by the screen are collected in the upstream coarse material chamber 66 and cut into the eccentrically arranged bypass diversion channel 62 through the low-position feed port on the side wall. The material is then pressurized and back-transported to the feed chamber 2 by an external pump to achieve closed-loop re-crushing. At the same time, the qualified fine particles filtered by the screen are sent straight down the vertical main screening channel 61 and directly into the ball mill 4. Step S5: After the qualified fine particles enter the ball mill 4, the ball mill 4 uses an independent liquid nitrogen pipeline to maintain a constant low temperature environment for fine grinding, which performs ultra-fine grinding on the coarse particles and keeps the grinding chamber at a stable low temperature throughout the process, ensuring the low-temperature embrittlement grinding effect of the material and avoiding the agglomeration and heating of fine particles. Step S6: The ultrafine material ground by the ball mill 4 is sent to the screening chamber 5. The final particle size classification and screening operation is completed by the detachable and replaceable screen built into the screening chamber 5. At the same time, the low temperature nitrogen gas volatilized in the upper chamber of the screening chamber 5 flows back to the liquid nitrogen output pipeline of the primary grinding chamber 3 through the cold gas return branch pipe 54 for cold energy recovery and secondary utilization, reducing liquid nitrogen loss. Step S7: The qualified material after screening is temporarily stored at the bottom of the screening chamber 5. The pressure relief, isolation and material discharge are achieved in steps through the isolation transition chamber structure of the upper and lower valve plates at the sampling port, which alternately opens and closes. The entire process prevents the backflow of hot and humid air from the outside into the equipment cavity and maintains a low temperature and sealed environment inside the whole machine. Step S8: Complete the entire automated grinding and screening process of two-stage low-temperature crushing, circulating screening, cold energy recovery, and closed discharge. Then, stop the machine, clean and maintain it.

[0054] As can be seen from the above specific implementation methods, the overall equipment structure provided by the embodiments of the present invention has a reasonable layout and clear hierarchy. The two-stage crushing conditions are independently controllable, the screening channels are layered and staggered, the material circulation is stable, the cold energy utilization rate is high, and the sealing performance is good. The supporting control method has rigorous process logic, accurate parameters, and a high degree of automation. It effectively solves the industry pain points of existing low temperature crushing equipment, such as single temperature control, poor screening accuracy, waste of cold energy, easy material deterioration, and poor operation stability. It is suitable for the fine powder processing of various heat-sensitive and high-toughness materials and has excellent practicality and promotion value.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A two-stage liquid nitrogen crushing and screening machine, characterized in that, Includes liquid nitrogen tank, feed hopper, primary grinding chamber, ball mill, and screening chamber; The liquid nitrogen tank is equipped with two independent output pipelines that are connected to the primary grinding chamber and the ball mill respectively to supply cryogenic liquid nitrogen to the primary grinding chamber and the ball mill. The discharge end of the feed hopper is connected to the feed end of the primary grinding hopper. The discharge end of the primary grinding hopper is connected to the feed end of the ball mill through a connecting channel. The connecting channel is provided with a vertical main screening channel and a bypass return pipeline that is diverted through the vertical main screening channel and connected to the feed hopper. The discharge end of the ball mill is connected to a screening chamber equipped with a removable and replaceable screen.

2. The liquid nitrogen two-stage crushing and screening machine according to claim 1, characterized in that, The primary grinding chamber is equipped with a pair of crushing rollers that rotate in opposite directions. Several first rollers and second rollers of different diameters are coaxially arranged on the crushing rollers along the axial direction. The first rollers between the two opposing crushing rollers are matched and corresponding to the second rollers on the corresponding crushing rollers. The crushing roller has a refrigerant channel inside its body that is connected to an independent output pipeline of the liquid nitrogen tank. The refrigerant channel has several spray holes circumferentially arranged on the outer side of the crushing roller, and the spray holes are located in the annular groove space formed between the first roller and the second roller.

3. The liquid nitrogen two-stage crushing and screening machine according to claim 1, characterized in that, The connecting channel is an integrated composite diversion channel structure with staggered vertical and internal and external layers. The connecting channel includes a centrally located vertical main screening channel and an eccentrically arranged bypass diversion channel. The vertical main screening channel and the bypass diversion channel are arranged in a staggered spatial layout. The inlet end of the vertical main screening channel is connected to the outlet end of the primary grinding chamber, and the outlet end of the vertical main screening channel is axially connected to the feed end of the ball mill. The bypass diversion channel is tangentially led out from the upper middle side wall of the vertical main screening channel and bends downwards before being extended and connected to the feed hopper via an external pump. This allows the vertical main screening channel and the bypass diversion channel to form a double-layer staggered connection structure with upper diversion and lower independent material conveying. A funnel drop outlet is provided at the inlet end of the vertical main screening channel. A concave annular interlocking mounting groove is formed inside the vertical main screening channel. An annular screen mesh, spirally arranged from top to bottom with a transverse projection area of ​​3 / 4 to 9 / 10 of a circle, is installed on the interlocking mounting groove. An annular sealing abutment surface is provided at the bottom of the annular interlocking mounting groove. The edge of the annular screen mesh is fitted and sealed to the annular sealing abutment surface. The annular screen mesh is entirely embedded inside the annular interlocking mounting groove, with its top aligned with the funnel. The drop outlets are connected, and the vertical main screening channel is axially divided into an upstream coarse material chamber and a downstream fine material chamber. The feed inlet of the bypass diversion channel is connected to the lower part of the side wall of the upstream coarse material chamber formed by the annular screen. Only large unqualified particles intercepted by the screen are cut into the bypass diversion channel to complete the return transport. Qualified fine particles are transported directly to the ball mill along the vertical main screening channel after falling through the screen, forming an integrated screening return channel structure with high and low position partitioning, layered diversion, and staggered connection.

4. The liquid nitrogen two-stage crushing and screening machine according to claim 1, characterized in that, Quick-lock screen clamping mechanisms are respectively installed at both ends of the vertical main screening channel of the connecting channel. The quick-lock screen clamping mechanism includes a circumferential clamp and an elastic sealing gasket. The circumferential clamp can be detachably clamped to the primary grinding chamber and the ball mill respectively, and the elastic sealing gasket abuts against the inner edge of the circumferential clamp.

5. The liquid nitrogen two-stage crushing and screening machine according to claim 1, characterized in that, The bottom of the screening chamber is provided with a sample outlet, which is equipped with a sealed material discharge valve that has two levels of valve plates that alternately open and close to form an isolation transition chamber.

6. The liquid nitrogen two-stage crushing and screening machine according to any one of claims 2 to 5, characterized in that, The screening chamber is equipped with a cold air return branch pipe. One end of the cold air return branch pipe is connected to the upper chamber of the screening chamber, and the other end is connected to the independent output pipeline between the liquid nitrogen tank and the primary grinding chamber.

7. The liquid nitrogen two-stage crushing and screening machine according to claim 6, characterized in that, The two independent output pipelines are respectively equipped with flow regulating valves and temperature detection elements. The temperature detection elements collect the temperature inside the primary grinding chamber and the ball mill, respectively. The two flow regulating valves independently adjust the liquid nitrogen supply flow rate according to the detected temperature of the corresponding chamber.

8. The liquid nitrogen two-stage crushing and screening machine according to claim 7, characterized in that, A high-precision temperature sensor is embedded in the top wall of the primary grinding chamber and the inner side wall of the ball mill chamber.

9. A grinding and screening control method for a liquid nitrogen two-stage crushing and screening machine as described in claim 8, characterized in that, Includes the following steps: Step S1: Liquid nitrogen is independently supplied to the primary grinding chamber and the ball mill through two independent output pipelines of the liquid nitrogen tank. The temperature of the primary grinding chamber and the ball mill chamber are collected in real time through temperature sensors on the two independent output pipelines. Step S2: Based on the preset low temperature threshold for primary crushing and low temperature threshold for fine grinding, adjust the opening of the two flow control valves accordingly. At the same time, liquid nitrogen is sprayed out through the coolant flow channel inside the crushing roller in the primary grinding chamber and the spray hole at the annular groove, so as to pre-cool the crushing roller body by immersion in the entire area and eliminate the temperature difference of the roller body. Step S3: After the temperature of the dual chambers stabilizes and reaches the standard, the material to be processed is sent from the feed hopper into the pre-cooled primary grinding chamber. The material is coarsely crushed by the interlocking structure of the first and second rollers arranged on the two sets of crushing rollers. During the coarse crushing process, liquid nitrogen is continuously added through the spray hole to maintain a low-temperature embrittlement environment during the coarse crushing process and avoid the material from heating up, sticking, and thermally degenerating. Step S4: The material coarsely crushed in the primary grinding chamber is fed into the vertical main screening channel of the connecting channel. The particle size is classified by the spiral ring screen. The large unqualified particles intercepted by the screen are collected in the upstream coarse material chamber and cut into the eccentrically arranged bypass diversion channel through the low-position feed port on the side wall. The material is then pressurized and back-transported to the feed hopper by an external pump to achieve closed-loop re-crushing. At the same time, the qualified fine particles filtered by the screen are sent directly into the ball mill along the axial direction of the vertical main screening channel. Step S5: After the qualified fine particles enter the ball mill, the coarse particles are subjected to ultra-fine grinding in a constant low-temperature environment maintained by the ball mill's independent liquid nitrogen pipeline. The grinding chamber is kept at a low temperature and stable throughout the process to ensure the low-temperature embrittlement grinding effect of the material and avoid the agglomeration and heating of fine particles. Step S6: The ultrafine material ground by the ball mill is sent into the screening chamber. The final particle size classification and screening operation is completed by the detachable and replaceable screen built into the screening chamber. At the same time, the low-temperature nitrogen gas volatilized in the upper chamber of the screening chamber is returned to the liquid nitrogen output pipeline of the primary grinding chamber through the cold gas return branch pipe for cold energy recovery and secondary utilization, reducing liquid nitrogen loss. Step S7: The qualified material after screening is temporarily stored at the bottom of the screening chamber. The pressure relief, isolation and material discharge are achieved through the isolation transition chamber structure with the upper and lower valve plates at the sampling port opening and closing alternately. The entire process prevents the backflow of hot and humid air from the outside into the equipment cavity and maintains a low temperature and sealed environment inside the whole machine. Step S8: Complete the entire automated grinding and screening process of two-stage low-temperature crushing, circulating screening, cold energy recovery, and closed discharge. Then, stop the machine and perform maintenance.

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