Tin plate for high-end food-grade dry powder and production method of tin plate

Abstract

The invention discloses a tin-plated plate for high-end food-grade dry powder and a production method of the tin-plated plate. A hot-rolled coil used by the tin-plated plate comprises the following chemical components in percentage by mass: 0.03-0.05% of C, 0.2-0.3% of Mn, 0.02-0.06% of Alt, less than or equal to 0.03% of Si, less than or equal to 0.02% of P, less than or equal to 0.02% of S, less than or equal to 0.005% of N, less than or equal to 0.03% of As, less than or equal to 0.01% of Cd + Pb and the balance of iron and inevitable impurities. The production method comprises the procedures of acid pickling, cold rolling, continuous annealing, leveling and tin plating. The thickness specification of the tin plate produced by the method is 0.21-0.25 mm, and the thickness precision is + / -2 microns; the Rockwell hardness HR30T is 59-61, the surface roughness is 0.85-1.05 [mu] m, the surface black gray grade is the first grade, and the application requirements of high-end dry powder products such as protein powder and milk powder can be met.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing, specifically relating to a high-end food-grade tin-plated sheet for dry powder and its production method. Background Technology

[0002] Tinplate has a wide range of applications in the food packaging industry. With the rapid growth in market demand for high-end dry powder products such as protein powder and milk powder, the requirements for tinplate packaging materials far exceed those for ordinary food products, specifically in the following aspects: ① Food safety red line: The risk of heavy metal (As, Cd, Pb) migration needs to be strictly controlled. Existing tinplate does not have restrictions on heavy metal content for food-grade applications, making it difficult to meet FDA and GB 4806.9-2016 standards.

[0003] ② Surface quality bottleneck: Tin-plated sheets need to be printed, stacked and transported. Black and gray residue on the surface can cause printing defects. Improper roughness can easily cause scratches or uneven ink adhesion. The industry has long faced the problem of "black and gray control and roughness balance".

[0004] ③ Poor mechanical performance stability: The tin plating layer has poor uniformity and the hardness of the tin plate fluctuates greatly, making it difficult to meet the strength requirements of high-speed can-making equipment during welding and subsequent transportation and storage, and can easily dent or crack.

[0005] ④ Pain point of dimensional accuracy: Dry powder filling has extremely high requirements for packaging weight accuracy (a deviation of more than ±1.5g may cause complaints). The thickness of the existing tin-plated plate fluctuates greatly (usually more than ±5μm), which leads to unstable can weight and affects net content control.

[0006] To address the aforementioned issues, this invention provides a tinplate solution specifically designed for high-end dry powder by optimizing raw material composition and production processes. Summary of the Invention

[0007] The purpose of this invention is to provide a high-end food-grade tin-plated sheet for dry powder and its production method, which has high food safety, excellent surface quality, high thickness precision and good mechanical properties.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-end food-grade tinplate for dry powder, wherein the chemical composition and mass percentage of the hot-rolled coil raw material used are as follows: C: 0.03%~0.05%, Mn: 0.2%~0.3%, Alt: 0.02%~0.06%, Si≤0.03%, P≤0.02%, S≤0.02%, N≤0.005%, As≤0.03%, Cd+Pb≤0.01%, with the balance being iron and unavoidable impurities.

[0009] Furthermore, the tin-plated plate of the present invention has a thickness specification of 0.21-0.25mm and an accuracy of ±2μm, which can ensure that the weight deviation of the can body is ≤0.05g, meeting the net content control requirements for dry powder filling.

[0010] Furthermore, the tinplate of the present invention has a Rockwell hardness of HR30T of 59-61, which takes into account both the welding stability of high-speed can making and the ability to prevent can collapse during transportation.

[0011] Furthermore, the surface roughness of the tin-plated sheet described in this invention is 0.85-1.05μm, which can resolve the industry contradiction between "easy to scratch" and "poor printing adhesion".

[0012] Furthermore, the surface black and gray grade of the tin-plated sheet described in this invention meets the first level of "YB / T 4951-2021 Green Design Product Evaluation Technical Specification for Tin-plated (Chromium) Sheets for Food Packaging", which can eliminate printing residue marks and improve the aesthetics of the packaging.

[0013] The production method of the high-end food-grade dry powder tin-plated sheet of the present invention includes pickling, rolling, continuous annealing, leveling and tin plating processes.

[0014] Furthermore, the pickling process described in this invention employs a push-pull pickling unit with a production speed of 100-130 m / min, and includes six pickling tanks. HCl pickling is used, and the mass concentration of HCl in pickling tanks 1-6 is 2-4%, 3-5%, 6-9%, 9-12%, 12-15%, and 16-20%, respectively.

[0015] Furthermore, the rolling process described in this invention involves using a six-roll reversible rolling mill, with 2.5-3.0mm hot-rolled coils as raw materials, rolling in 6 passes, with a cold rolling reduction rate of 90%-93%, rolling to 0.21-0.25mm, and controlling the thickness fluctuation range within ±2μm.

[0016] Furthermore, the continuous annealing process described in this invention employs a continuous annealing production line with ROA function, an annealing uniform heating temperature of 650-690℃, and a rapid cooling rate of 30-35℃ / s to ensure its resistance to aging, resulting in a hardness of 59-61HR30T after annealing.

[0017] Furthermore, the leveling process described in this invention employs a double-stand six-roll leveling machine with an elongation of 1.0%-1.5%; the No. 1 stand uses an EDM texturing roller with a roughness of 3.0-3.2μm and a pressure of 400-450 tons; the No. 2 stand uses an EDM texturing roller with a roughness of 1.4-1.6μm and a pressure of 300-350 tons.

[0018] Furthermore, the tin plating process described in this invention uses an insoluble anode tin plating production line with a tin plating amount of 2.8 / 2.8 g / m² or 2.8 / 5.6 g / m², and feeds the product into an edge cover and a blackening and ash removal machine. The tin plating speed is controlled at 330-380 m / min.

[0019] The inventive principle of this invention lies in: This invention is the first to limit the content of As to ≤0.03% and Cd+Pb to ≤0.01% in tinplate raw materials, thereby controlling the risk of heavy metal migration at the source and ensuring compliance with food contact material safety standards. Controlling the Alt content to 0.02%-0.06% ensures effective deoxidation while preventing excessive aluminum residue, thus balancing safety and processability.

[0020] This invention employs a gradient pickling process, with the HCl concentration increasing from 2-4% to 16-20%, achieving a step-by-step cleaning process of "pre-removal of floating rust → precise peeling of deep oxide scale." This avoids excessive surface roughness caused by over-pickling and solves the industry problem of "difficulty in balancing cleanliness and surface smoothness."

[0021] By using a six-roll reversible rolling mill with six passes, the reduction rate is increased to 90%-93%, and with the help of a real-time thickness monitoring system, a thickness accuracy of ±2μm is achieved. While ensuring thickness accuracy, the high reduction rate promotes uniform grain refinement and reduces performance fluctuations in the thickness direction, laying the foundation for the consistency of subsequent annealing processes.

[0022] A dual-frame differentiated leveling process is employed: Frame 1 uses an EDM texturing roller with a roughness of 3.0-3.2μm, forming uniform micro-protrusions through a relatively rough roller to improve scratch resistance; Frame 2 uses an EDM texturing roller with a roughness of 1.4-1.6μm to refine the surface texture and ensure the adhesion of printing inks. The two frames work together to achieve the target roughness of 0.85-1.05μm on the tin-plated substrate, breaking through the limitations of conventional leveling with a "single roller surface".

[0023] The tin plating process incorporates an edge shield device to eliminate current distribution differences along the board width, ensuring a tin plating uniformity deviation of ≤±3% and preventing sparks from flying during soldering due to uneven tin layer. The black ash removal machine is linked for coordinated control: at high-speed production of 330-380 m / min, mechanical wiping and electrolytic cleaning work together to ensure a first-class black ash level, resolving the industry conflict between "high-speed production and surface cleanliness."

[0024] The beneficial effects of adopting the above technical solution are as follows: (1) Food safety: The heavy metal residue is lower than the industry standard (As≤0.03%, Cd+Pb≤0.01%), which meets the requirements of FDA and GB 4806.9-2016.

[0025] (2) High surface quality: black and gray grade one, the surface roughness of the strip steel ranges from 0.85 to 1.05 μm, which significantly improves the appearance quality and scratch resistance of the packaging, and reduces the scrap rate from 1% to 0.02%.

[0026] (3) Mechanical performance stability: the uniformity deviation of the tin plating layer is ≤±3%, the hardness control range is 59-61HR30T, which increases the can making speed by 10% and reduces the welding defect rate to below 0.05%, meeting the requirements of high-speed automated production line and basically eliminating the problem of can collapse during transportation.

[0027] (4) Process adaptability: The thickness fluctuation is ±2μm, which ensures that the weight deviation of the can body is controlled within ±1.5g, thus solving the problem of complaints caused by weight fluctuations at the filling plant. Attached Figure Description

[0028] Figure 1 The surface morphology of the tin-plated sheet product in Example 1 is shown.

[0029] Figure 2 The results of surface black ash detection for the finished tin-plated sheet in Example 1 are shown. Detailed Implementation

[0030] The technical solution of the present invention will be further described in detail below through embodiments. Example 1

[0031] The raw material used for the tin-plated sheet in this embodiment is a 2.5mm thick hot-rolled coil. The chemical composition of the hot-rolled coil is: C: 0.03%, Mn: 0.21%, Alt: 0.02%, Si: 0.028%, P: 0.015%, S: 0.015%, N: 0.004%, As: 0.025%, Cd+Pb: 0.008%, with the balance being iron and unavoidable impurities.

[0032] The production method of the tin-plated sheet in this embodiment includes pickling, rolling, continuous annealing, leveling, and tin plating, as detailed below: (1) Pickling: The hot-rolled coil is fed into the push-pull pickling unit at a production speed of 100m / min. The mass concentration of HCl in pickling tanks 1-6 is 2%, 3.5%, 6.5%, 9%, 12%, and 16% respectively. There is no iron oxide scale residue on the surface after pickling.

[0033] (2) Rolling: A six-roll reversible rolling mill is used. The hot-rolled coil with a thickness of 2.5 mm is used as raw material. After six passes of rolling, the cold rolling reduction rate is controlled at 91.60%. Finally, the tin-plated plate with a thickness of 0.21 mm is rolled. The thickness accuracy of the finished product is controlled within ±2 μm.

[0034] (3) Continuous annealing: The rolled tinplate is sent to the continuous annealing production line. The annealing temperature is set to 650℃, the rapid cooling rate is 30℃ / s, and the surface Rockwell hardness after annealing is 60HR30T.

[0035] (4) Leveling: A double-stand six-roll leveling machine is used, and the leveling elongation rate is set to 1.2%. The surface roughness of the first stand EDM texturing work roll is 3.0 μm, and the leveling pressure is 450 tons. The surface roughness of the second stand EDM texturing work roll is 1.60 μm, and the leveling pressure is 300 tons. The surface roughness of the strip after leveling is 1.0 μm.

[0036] (5) Tin plating: an insoluble anode tin plating production line is used, with a tin plating amount of 2.8 / 2.8 g / m². An edge cover is used to ensure the uniformity of the tin plating amount. The tin plating speed is controlled at 380 m / min. At the same time, a black ash removal machine is used to achieve the final black ash grade of Grade 1.

[0037] The surface morphology of the tin-plated plate in this embodiment is as follows: Figure 1 As shown, by Figure 1 It can be seen that its surface roughness is uniform, which can effectively cover surface defects such as scratches and abrasions; the surface black and gray detection results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the black and gray level of the product surface meets the first level of "YB / T 4951-2021 Technical Specification for Green Design Product Evaluation: Tin-plated (chromium) Plates for Food Packaging".

[0038] Through simulated filling, the weight deviation of the empty can was within ±1g, the printing pass rate was 100%, and the welding defect rate was 0.01%. Example 2

[0039] The raw material used for the tin-plated sheet in this embodiment is a 2.75mm thick hot-rolled coil. The chemical composition of the hot-rolled coil is: C: 0.04%, Mn: 0.28%, Alt: 0.06%, Si: 0.025%, P: 0.018%, S: 0.016%, N: 0.0045%, As: 0.028%, Cd+Pb: 0.009%, with the balance being iron and unavoidable impurities.

[0040] The production method of the tin-plated sheet in this embodiment includes pickling, rolling, continuous annealing, leveling, and tin plating, as detailed below: (1) Pickling: The hot-rolled coil is fed into the push-pull pickling unit at a production speed of 110 m / min. The mass concentration of HCl in pickling tanks 1-6 is 4%, 4.5%, 7.5%, 10.5%, 13%, and 18% respectively. There is no iron oxide scale residue on the surface after pickling.

[0041] (2) Rolling: A six-roll reversible rolling mill is used. Hot-rolled coils with a thickness of 2.75 mm are used as raw materials. After six rolling passes, the cold rolling reduction rate is 91.63%, and the tinplate with a thickness of 0.23 mm is rolled. The thickness accuracy is controlled within ±2 μm.

[0042] (3) Continuous annealing: The rolled tinplate is sent to the continuous annealing production line. The annealing temperature is set to 670℃, the rapid cooling rate is 32℃ / s, and the surface Rockwell hardness after annealing is 59HR30T.

[0043] (4) Leveling: A double-stand six-roll leveling machine is used, and the leveling elongation rate is set to 1.3%. The surface roughness of the first stand EDM texturing work roll is 3.0 μm, and the leveling pressure is 400 tons. The surface roughness of the second stand EDM texturing work roll is 1.4 μm, and the leveling pressure is 350 tons. The surface roughness of the strip after leveling is 0.9 μm.

[0044] (5) Tin plating process: Use an insoluble anode tin plating production line, with a tin plating amount of 2.8 / 5.6 g / m², and put it into the edge cover to ensure the uniformity of the tin plating amount. The tin plating speed is 360 m / min. Put it into the black ash removal machine, and the surface black ash level meets the first level of "YB / T 4951-2021 Green Design Product Evaluation Technical Specification for Tin-plated (chromium) Plates for Food Packaging".

[0045] Through simulated filling, the weight deviation of the empty can was within ±1g, the printing pass rate was 100%, and the welding defect rate was 0.01%. Example 3

[0046] The raw material used for the tin-plated sheet in this embodiment is a 3.0mm thick hot-rolled coil. The chemical composition of the hot-rolled coil is: C: 0.05%, Mn: 0.29%, Alt: 0.03%, Si: 0.022%, P: 0.016%, S: 0.014%, N: 0.0042%, As: 0.026%, Cd+Pb: 0.007%, with the balance being iron and unavoidable impurities.

[0047] The production method of the tin-plated sheet in this embodiment includes pickling, rolling, continuous annealing, leveling, and tin plating, as detailed below: (1) Pickling: The hot-rolled coil is fed into the push-pull pickling unit at a production speed of 125m / min. The mass concentration of HCl in pickling tanks 1-6 is 4%, 5%, 9%, 11%, 15%, and 20% respectively. After pickling, there is no iron oxide scale residue on the surface.

[0048] (2) Rolling: A six-roll reversible rolling mill is used. The hot-rolled coil with a thickness of 3.0 mm is rolled in 6 passes with a cold rolling reduction rate of 91.67% to produce a tin-plated plate with a thickness of 0.25 mm. The thickness accuracy is controlled within ±2 μm.

[0049] (3) Continuous annealing: The annealing is fed into a continuous annealing production line with ROA function. The annealing temperature is 685℃, the rapid cooling rate is 35℃ / s, and the Rockwell hardness HR30T after annealing is 61.

[0050] (4) Leveling: a double-stand six-roll leveling machine with an elongation of 1.1%; the No. 1 stand uses an EDM texturing roller with a roughness of 3.2μm and a pressure of 430 tons; the No. 2 stand uses an EDM texturing roller with a roughness of 1.5μm and a pressure of 320 tons. The surface roughness after leveling is 0.88μm.

[0051] (5) Tin plating: The insoluble anode tin plating production line is adopted, with a tin plating amount of 2.8 / 2.8g / m². The edge cover and black ash removal machine are fed in, and the tin plating speed is 330m / min. The surface black ash level meets the first grade of "YB / T 4951-2021 Green Design Product Evaluation Technical Specification for Tin-plated (chromium) Plates for Food Packaging".

[0052] Through simulated filling, the weight deviation of the empty can was within ±1.3g, the printing pass rate was 100%, and the welding defect rate was 0.01%.

Claims

1. A tin-plated sheet for high-end food-grade dry powder, characterized in that, The chemical composition and mass percentage of the hot-rolled coil raw material used for the tinplate are as follows: C: 0.03%~0.05%, Mn: 0.2%~0.3%, Alt: 0.02%~0.06%, Si≤0.03%, P≤0.02%, S≤0.02%, N≤0.005%, As≤0.03%, Cd+Pb≤0.01%, with the balance being iron and unavoidable impurities.

2. The tin-plated sheet for high-end food-grade dry powder according to claim 1, characterized in that, The tin-plated sheet has a thickness specification of 0.21-0.25mm and a thickness accuracy of ±2μm.

3. The tin-plated sheet for high-end food-grade dry powder according to claim 1, characterized in that, The tinplate has a Rockwell hardness of HR30T of 59-61, a surface roughness of 0.85-1.05μm, and a surface black-gray grade that meets the first-class standard of "YB / T 4951-2021 Technical Specification for Green Design Product Evaluation: Tinplate (Chromium) for Food Packaging".

4. A method for producing tin-plated plates for high-end food-grade dry powder according to any one of claims 1-3, characterized in that, It includes pickling, rolling, continuous annealing, leveling and tin plating processes.

5. The method for producing tin-plated plates for high-end food-grade dry powder according to claim 4, characterized in that, The pickling process uses a push-pull pickling unit with a production speed of 100-130 m / min. It has six pickling tanks and uses HCl for pickling. The mass concentration of HCl in pickling tanks 1-6 is 2-4%, 3-5%, 6-9%, 9-12%, 12-15%, and 16-20%, respectively.

6. The method for producing tin-plated plates for high-end food-grade dry powder according to claim 4, characterized in that, The rolling process involves using a six-roll reversible rolling mill with 2.5-3.0mm hot-rolled coils as raw material, rolling in six passes with a cold rolling reduction rate of 90%-93%.

7. The method for producing tin-plated plates for high-end food-grade dry powder according to claim 4, characterized in that, The continuous annealing process adopts a continuous annealing production line with ROA function, with an annealing uniform heating temperature of 650-690℃ and a rapid cooling rate of 30-35℃ / s.

8. The method for producing tin-plated plates for high-end food-grade dry powder according to claim 4, characterized in that, The leveling process is as follows: a double-stand six-roll leveling machine is used with an elongation of 1.0%-1.5%; the No. 1 stand uses an EDM texturing roller with a roughness of 3.0-3.2μm and a pressure of 400-450 tons; the No. 2 stand uses an EDM texturing roller with a roughness of 1.4-1.6μm and a pressure of 300-350 tons.

9. The method for producing tin-plated plates for high-end food-grade dry powder according to claim 4, characterized in that, The tin plating process uses an insoluble anodic tin plating production line with a tin plating amount of 2.8 / 2.8 g / m² or 2.8 / 5.6 g / m². The tin is fed into an edge cover and a blackening and ash removal machine, and the tin plating speed is controlled at 330-380 m / min.

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