Preparation Method of Molten Casting and Forging Composite State Electrode Roll Blank

Abstract

The present invention discloses a preparation method of a molten casting and forging composite state pole piece roll blank. The molten casting and forging composite state pole piece roll blank obtained by using this method includes a roll core and a cast and forged outer ring connected by a first molten composite transition layer. The roll core is a forged and quenched and tempered part made of alloy structural steel, and the cast and forged outer ring is a composite casting, forging and normalizing layer made of alloy tool steel. The method includes steps of obtaining a roll core with a metallographic structure of forged, quenched and tempered tempered sorbite made of alloy structural steel; smelting alloy tool steel molten steel and casting to form a liquid coating layer; cooling to form a solid coating layer; medium frequency induction heating and forging the solid coating layer and normalizing heat treatment, etc. The process of the present invention is simple, low in cost, and has excellent service performance, is suitable for large-scale industrial production and is popularized and applied in the new energy battery manufacturing industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery equipment manufacturing, and relates to the structure and materials of lithium-ion battery pole piece rollers. Specifically, it is a preparation method for a molten casting-forging composite state pole piece roller blank. Background Art

[0002] At present, the pole piece roller blanks of lithium-ion batteries at home and abroad mainly have two types: integral type and jacket-inlaid type, but both have certain defects, specifically as follows:

[0003] 1. The integral pole piece roller blank is integrally cast and forged from alloy materials and is known for its good use stability. However, the manufacturing process of this integral pole piece roller blank is complex, the production cycle is long, the equipment investment is large, and in order to ensure the internal performance and the strength and toughness of the roller neck part of the pole piece roller blank, alloy tool steel with high price is mostly selected for the material, and the material cost is extremely high.

[0004] 2. The jacket-inlaid type pole piece roller blank is made by inlaying alloy tool steel of different materials on the outer ring of an alloy structural steel roller core. Compared with the integral pole piece roller blank, the material cost is low and the equipment investment is small, but the processing cost is extremely high (the forging and machining process of the alloy tool steel outer ring is complex). Moreover, because the roller core and the outer ring use different types of alloy materials, the interfacial bonding characteristics of the two are completely different, and it is not easy to ensure the performance of the material structure of the formed intermediate transition layer. During use, under the action of contact fatigue stress, the working layer of the pole piece roller is likely to peel off, resulting in the scrapping of the entire pole piece roller. Summary of the Invention

[0005] In order to solve the above deficiencies in the prior art, the present invention aims to provide a preparation method for a molten casting-forging composite state pole piece roller blank, so as to achieve the purpose of optimizing the structure, improving the use performance, greatly reducing the cost, and improving the production efficiency.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A molten casting-forging composite state pole piece roller blank includes a roller core and a cast-forged outer ring connected by a first molten composite transition layer; wherein, the roller core is a forged and quenched and tempered part made of alloy structural steel, and the cast-forged outer ring is a composite casting-forging normalizing layer made of alloy tool steel.

[0007] As a limitation of the present invention, the metallographic structure of the alloy structural steel of the roller core is forged state quenched and tempered troostite.

[0008] As another limitation of the present invention, the cast-forged outer ring includes an intermediate layer and an outer surface layer connected by a second molten composite transition layer; wherein, the metallographic structure of the alloy tool steel of the intermediate layer is cast state tempered pearlite plus ferrite, and the metallographic structure of the alloy tool steel of the outer surface layer is forged state normalizing pearlite.

[0009] As a further limitation of the present invention, the thickness of the intermediate layer is 50 to 200 mm, the thickness of the outer surface layer is 5 to 60 mm, and the second molten composite transition layer is a boundaryless transition layer with a thickness of 1 to 20 mm between the as-cast metallographic structure and the forged metallographic structure.

[0010] As a further limitation of the present invention, the first molten composite transition layer is a boundaryless transition layer with a thickness of 1 to 20 mm formed by the mutual penetration of the roll core alloy structural steel and the intermediate layer alloy tool steel.

[0011] As a third limitation of the present invention, the alloy structural steel is a quenched and tempered structural steel with a carbon content of 0.25% to 0.55%; the alloy tool steel is a tool steel with a carbon content greater than 0.80%.

[0012] As a further limitation of the present invention, the alloy structural steel is any one of 40Cr, 42CrMo, 35SiMn, 40CrNiMo, 30CrNi2MoV, and the alloy tool steel is any one of Cr2, Cr3, Cr5, Cr8, GCr15.

[0013] The present invention also discloses a preparation method of a molten casting and forging composite state pole piece roll blank, including the following steps carried out in sequence:

[0014] S1. Place the roll core made of alloy structural steel into the casting cold mold, reserve a concentric gap of 20 to 300 mm and blow in inert protective gas for pouring;

[0015] S2. Smelt the alloy tool steel molten steel and pour it into the concentric gap of the casting cold mold to cast an alloy tool steel liquid coating layer. At this time, the outer surface of the roll core contacts the inner surface of the alloy tool steel liquid coating layer, and the two materials penetrate each other at the solid-liquid interface to form the first molten composite transition layer;

[0016] S3. After cooling the alloy tool steel liquid coating layer, form a solid coating layer of alloy tool steel with as-cast normalized pearlite;

[0017] S4. After medium-frequency induction heating and forging the solid coating layer of alloy tool steel and performing normalizing heat treatment, form a cast and forged outer ring on the outer surface of the roll core, thereby obtaining the molten casting and forging composite state pole piece roll blank as described above.

[0018] As a limitation of the present invention, in step S4, medium-frequency induction heating forging:

[0019] Heat the solid coating layer of alloy tool steel to the forging temperature range of 850 to 1200 °C by medium-frequency induction heating, and then use a free forging hammer to perform shallow high-frequency repeated forging within the forging temperature range until an outer surface layer of alloy tool steel with forged normalized pearlite is obtained; at this time, the intermediate layer between the outer surface layer and the roll core is connected to the outer surface layer through the second molten composite transition layer;

[0020] Normalizing heat treatment:

[0021] The intermediate layer and the outer surface layer are heated to the normalizing temperature by medium-frequency induction heating and then cooled statically in air, obtaining an intermediate layer of alloy tool steel with as-cast tempered pearlite plus ferrite and an outer surface layer of alloy tool steel with forged normalizing pearlite, that is, the cast-forged outer ring.

[0022] As a further limitation of the present invention, in step S4, the forging depth is 5 - 50 mm, and an outer surface layer with a thickness of 5 - 60 mm is obtained.

[0023] Due to the adoption of the above technical solutions, compared with the prior art, the beneficial effects achieved by the present invention are:

[0024] (1) From the perspective of structure and materials: The main improvement of the present invention lies in using the welding method instead of the insert sleeve method to realize the connection between the cast-forged outer ring and the roll core. During the molten casting and forging process, the two materials of the roll core alloy structural steel and the cast-forged outer ring alloy tool steel penetrate each other to form a first molten composite transition layer without a clear boundary, thereby ensuring the connection stability between the roll core and the cast-forged outer ring and effectively avoiding the defect problems of easy ring-off and working layer spalling existing in the existing insert sleeve method.

[0025] Furthermore, in the present invention, the roll core uses low-cost alloy structural steel, forming forged tempered sorbite, which has excellent resistance to alternating fatigue toughness. The cast-forged outer ring uses expensive alloy tool steel, and the outer surface layer forms forged normalizing pearlite, which has excellent wear resistance hardness and anti-fatigue pitting strength; the intermediate layer forms as-cast tempered pearlite plus ferrite, which has anti-spalling buffer performance.

[0026] In summary, the present invention optimizes the structure of the blank of the pole piece roll, improves its service performance while reducing the material cost and investment.

[0027] (2) From the perspective of the preparation process: The traditional forging technology uses a press for forging to make the whole form a forged structure. This method requires large-scale forging equipment and heating furnace equipment, and the cost is extremely high. The present invention uses medium-frequency induction local heating method, which has low energy consumption and high efficiency; uses a small-sized air pressure free forging hammer, only making the outer surface layer of the cast-forged outer ring form a forged structure, so that excellent hardness, strength and wear resistance can be obtained, and at the same time, the unforged as-cast structure can be used for pressure buffering to enhance the anti-spalling ability of the cast-forged outer ring.

[0028] To sum up, the process of the present invention is simple, the cost is low, and it has excellent service performance, suitable for large-scale industrial production and popularization and application in the new energy battery manufacturing industry. Brief Description of the Drawings

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0030] Figure 1 It is a schematic cross-sectional structure diagram of the blank of the pole piece rolling roll in Embodiment 1 of the present invention;

[0031] Figure 2 It is a schematic cross-sectional structure diagram of the casting cold mold in Embodiment 2 of the present invention;

[0032] In the figure: 1, roll core; 2, intermediate layer; 3, outer surface layer; 4, first molten composite transition layer; 5, second molten composite transition layer; 6, casting cold mold. Specific Embodiments

[0033] The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only for the purpose of illustrating and understanding the present invention, and are not used to limit the present invention.

[0034] Embodiment 1 A blank of a pole piece rolling roll in a molten casting and forging composite state

[0035] This embodiment is formed by melting and casting two different alloy materials, forming a three-layer metallographic structure, and the overall shape and specifications are exactly the same as those of the conventional pole piece rolling roll blank.

[0036] Specifically as Figure 1 shown, this embodiment includes a roll core 1 and a cast and forged outer ring connected by a first molten composite transition layer 4. Among them, the roll core 1 is a forged and quenched and tempered part made of alloy structural steel, the cast and forged outer ring is a composite casting, forging and normalizing layer made of alloy tool steel, and the first molten composite transition layer 4 is a 1-20 mm thick boundaryless transition layer formed by the mutual penetration of alloy tool steel and roll core 1 alloy structural steel when casting the cast and forged outer ring.

[0037] Furthermore, the alloy structural steel used to prepare the roll core 1 is a quenched and tempered structural steel with a carbon content of 0.25% - 0.55%, such as: 40Cr, 42CrMo, 35SiMn, 40CrNiMo, 30CrNi2MoV, etc.; the alloy tool steel used to prepare the cast and forged outer ring is a tool steel with a carbon content greater than 0.80%, such as: Cr2, Cr3, Cr5, Cr8, GCr15, etc. In this embodiment, the alloy structural steel used for the roll core 1 is 40Cr, and the alloy tool steel used for the cast and forged outer ring is Cr5.

[0038] More specifically, the metallographic structure of the roll core 1 made of alloy structural steel is forged normalized tempered sorbite. The cast and forged outer ring made of alloy tool steel includes an intermediate layer 2 and an outer surface layer 3 connected by a second molten composite transition layer 5. The intermediate layer 2 has a thickness of 50 - 200 mm, and its metallographic structure is cast tempered pearlite plus ferrite; the outer surface layer 3 has a thickness of 5 - 60 mm, and its metallographic structure is forged normalized pearlite. The second molten composite transition layer 5 is a 1 - 20 mm thick boundaryless transition layer between the cast and forged metallographic structures formed during the forging of the cast and forged outer ring.

[0039] For the preparation process of the "molten cast and forged composite state pole piece roll blank" in this embodiment, please refer to Embodiment 2 for details.

[0040] Embodiment 2 A preparation method of a molten cast and forged composite state pole piece roll blank

[0041] This embodiment is a preparation method of the "molten cast and forged composite state pole piece roll blank" in Embodiment 1, and specifically includes the following steps carried out in sequence:

[0042] S1. Place the semi-finished roll core 1 into the casting cold mold 6, reserve a concentric gap of 20 - 300 mm and blow in inert protective gas to wait for casting, as specifically shown in Figure 2 wherein, the roll core 1 is made of alloy structural steel, and its metallographic structure is forged normalized tempered sorbite. It should be noted that during actual preparation, the roll core 1 can be purchased, self-made, or other semi-finished parts of the same material can be remanufactured as the roll core 1.

[0043] S2. Smelt the alloy tool steel molten steel in an intermediate frequency induction furnace protected by bottom-blown argon gas, and pour it into the concentric gap formed in Step S1 through the casting gate of the casting cold mold 6 to cast an alloy tool steel liquid coating layer. At this time, the outer surface of the roll core 1 contacts the inner surface of the alloy tool steel liquid coating layer, and the two materials penetrate each other at the solid-liquid interface to form a 1 - 20 mm thick first molten composite transition layer 4.

[0044] S3. Cool the alloy tool steel liquid coating layer together with the casting cold mold 6 and the roll core 1 by blowing air to form an alloy tool steel solid coating layer with a cast normalized pearlite structure.

[0045] S4. After intermediate frequency induction heating and forging the alloy tool steel solid coating layer formed in Step S3, perform normalizing heat treatment to form a cast and forged outer ring on the outer surface of the roll core 1, thereby obtaining the molten cast and forged composite state pole piece roll blank as described in Embodiment 1.

[0046] Specifically, medium-frequency induction heating forging: The solid-state coating layer of alloy tool steel is heated to the forging temperature range of 850 - 1200 °C by medium-frequency induction heating, and within this forging temperature range, it is forged by a free forging hammer with shallow high-frequency repeated impact forging, with a forging depth of 5 - 50 mm, until an outer layer 3 of alloy tool steel with a forged normalized pearlite thickness of 5 - 60 mm is obtained. At this time, the intermediate layer 2 between the outer layer 3 and the roll core 1 is still in the as-cast normalized pearlite state, and the intermediate layer 2 and the outer layer 3 are connected through a second molten composite transition layer 5.

[0047] Normalizing heat treatment: After heating the intermediate layer 2 and the outer layer 3 to the normalizing temperature by medium-frequency induction heating, static air cooling is carried out, and thus an intermediate layer 2 of alloy tool steel with as-cast tempered pearlite plus ferrite and an outer layer 3 of alloy tool steel with forged normalized pearlite, that is, a cast-forged outer ring connected to the outer surface of the roll core 1, are obtained.

[0048] It should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, for those skilled in the art, they can still modify the technical solutions described in the above embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a molten casting-forging composite pole piece roll blank, characterized in that: it includes the following steps carried out in sequence: S1. Place the roll core made of alloy structural steel into the casting cold mold, reserve a concentric gap of 20 - 300 mm and blow in inert protective gas for casting; S2. Smelt the molten steel of alloy tool steel and pour it into the concentric gap of the casting cold mold to cast an alloy tool steel liquid coating layer. At this time, the outer surface of the roll core contacts the inner surface of the alloy tool steel liquid coating layer, and the two materials penetrate each other at the solid-liquid interface to form a first molten composite transition layer; S3. After cooling the alloy tool steel liquid coating layer, a solid coating layer of alloy tool steel with as-cast normalized pearlite is formed; S4. After intermediate frequency induction heating and forging the alloy tool steel solid coating layer and then performing normalizing heat treatment, a casting-forging outer ring is formed on the outer surface of the roll core, and the molten casting-forging composite pole piece roll blank is obtained; In step S4, intermediate frequency induction heating forging: Heat the alloy tool steel solid coating layer to the forging temperature range of 850 - 1200 °C by intermediate frequency induction heating, and use a free forging hammer to perform shallow high-frequency repeated forging within the forging temperature range until an outer layer of alloy tool steel with forged normalized pearlite is obtained; at this time, the intermediate layer between the outer layer and the roll core is still as-cast normalized pearlite, and the intermediate layer is connected to the outer layer through a second molten composite transition layer; Normalizing heat treatment: Heat the intermediate layer and the outer layer to the normalizing temperature by intermediate frequency induction heating and then perform static air cooling, that is, an intermediate layer of alloy tool steel with as-cast tempered pearlite plus ferrite and an outer layer of alloy tool steel with forged normalized pearlite, namely the casting-forging outer ring, are obtained.

2. The preparation method of the molten casting-forging composite pole piece roll blank according to claim 1, characterized in that: in step S4, the forging depth is 5 - 50 mm, and an outer layer with a thickness of 5 - 60 mm is obtained.

3. The preparation method of the molten casting-forging composite pole piece roll blank according to claim 1 or 2, characterized in that: the obtained molten casting-forging composite pole piece roll blank includes a roll core and a casting-forging outer ring connected by a first molten composite transition layer; wherein, the roll core is a forged and quenched and tempered part made of alloy structural steel, and the casting-forging outer ring is a composite casting, forging and normalizing layer made of alloy tool steel.

4. The preparation method of the molten casting-forging composite pole piece roll blank according to claim 3, characterized in that: the metallographic structure of the alloy structural steel of the roll core is forged quenched and tempered sorbite.

5. The preparation method of the molten casting-forging composite pole piece roll blank according to claim 4, characterized in that: the casting-forging outer ring includes an intermediate layer and an outer layer connected by a second molten composite transition layer; wherein, the metallographic structure of the alloy tool steel of the intermediate layer is as-cast tempered pearlite plus ferrite, and the metallographic structure of the alloy tool steel of the outer layer is forged normalized pearlite.

6. The preparation method of the molten casting-forging composite pole piece roll blank according to claim 5, characterized in that: the thickness of the intermediate layer is 50 - 200 mm, the thickness of the outer layer is 5 - 60 mm, and the second molten composite transition layer is a boundaryless transition layer with a thickness of 1 - 20 mm of as-cast metallographic structure and forged metallographic structure.

7. The preparation method of the molten casting and forging composite state pole piece roll blank according to claim 6, characterized in that: The first molten composite transition layer is a borderless transition layer with a thickness of 1-20 mm formed by the mutual penetration of the roll core alloy structural steel and the intermediate layer alloy tool steel.

8. The preparation method of the molten casting and forging composite state pole piece roll blank according to any one of claims 4-7, characterized in that: The alloy structural steel is a quenched and tempered structural steel with a carbon content of 0.25% to 0.55%; the alloy tool steel is a tool steel with a carbon content greater than 0.80%.

9. The preparation method of the molten casting and forging composite state pole piece roll blank according to claim 8, characterized in that: The alloy structural steel is any one of 40Cr, 42CrMo, 35SiMn, 40CrNiMo, 30CrNi2MoV, and the alloy tool steel is any one of Cr2, Cr3, Cr5, Cr8, GCr15.

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