Production process of wire rod for photovoltaic industry bolt

Abstract

The invention relates to the technical field of production process optimization of fasteners for the photovoltaic industry, and discloses a production process of a wire rod for a bolt for the photovoltaic industry, which comprises the following steps: step 1, feeding inspection; step 2, primary acid pickling, water washing, phosphorization and saponification; 3, primary spheroidizing annealing is conducted, specifically, the wire rod is sequentially subjected to three-stage heating isothermal treatment, first-stage cooling isothermal treatment and variable-speed cooling treatment; 4, secondary acid pickling, water washing and lime adding; 5, rough drawing is conducted, specifically, the wire rod is preliminarily drawn into a wire rod; step 6, secondary spheroidizing annealing; step 7, process inspection; 8, third-time acid pickling, phosphorization and saponification are conducted; step 9, drawing a finished product; and 10, inspecting a finished product. According to the scheme, by optimizing the processes of acid pickling and spheroidizing links with high material loss in the traditional process, the material loss is effectively controlled and the material loss rate is reduced to 1.5-2% while the high requirement of the wire for the photovoltaic industry bolt is fully met in production, so that the material waste is remarkably reduced, and the production benefit is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optimizing the production process of fasteners for the photovoltaic industry, and specifically relates to a production process for wire rods used for bolts in the photovoltaic industry. Background Art

[0002] As one of the core pillars of the clean energy transformation, the installed capacity of photovoltaic power generation has increased exponentially in recent years. Photovoltaic bolts, as key connectors for photovoltaic brackets, components, and electrical systems, are directly related to the structural stability and full-life cycle reliability of power stations. According to statistics, a 100MW photovoltaic power station requires more than 2 million sets of bolts, and their performance requirements are stringent: they need to maintain high strength (≥8.8 grade), anti-fatigue, and stress corrosion resistance characteristics in extreme environments such as temperature differences from -40°C to 80°C, strong ultraviolet rays, and salt spray corrosion. The production process of the wire rods used for photovoltaic bolts, as raw materials, directly determines the performance and manufacturing cost of the finished products. Currently, high-carbon alloy steels (such as SCM435) and stainless steels (such as 316L) are still the mainstream materials, and SCM435 occupies approximately 65% of the market share due to controllable costs and strong strength adaptability.

[0003] However, when the existing wire rods for bolts in the photovoltaic industry are produced using conventional screw wire rods, there are problems such as high material loss rates and insufficient performance when the prepared wire rods are used to produce bolts in the photovoltaic industry. For example, the prior art CN102861782A discloses a manufacturing process for screw wire rods, which successively includes the following steps: hanging the wire rack loaded with coil wire rods into a tank filled with pickling solution; hanging the rinsed coil wire rods into a tank filled with neutralizing solution; then hanging them into a tank filled with hot lime; obtaining screw wire rods with a predetermined semi-finished product specification after drawing; placing the drawn screw wire rods in a heat treatment furnace and performing spheroidizing annealing under the protection of methanol atmosphere; repeating the first pickling step; hanging the pickled screw wire rods into a tank filled with phosphating solution; hanging them into a tank filled with saponifying solution after water rinsing; and obtaining steel wires with a predetermined finished product specification after drawing. The screw wire rods manufactured using the prior art have excellent surface quality, good brightness, strong lubricity, corrosion resistance, high cold heading performance, and high fatigue strength. However, when this process is converted to produce wire rods for bolts in the photovoltaic industry, it will affect the efficiency and cost of processing bolts in the photovoltaic industry due to high material loss rates, poor plasticity of the finished wire rods, and excessive hardness.

[0004] In view of the above contradictions, researching and developing a preparation process for wire rods used for photovoltaic bolts with a low material loss rate not only effectively makes up for the deficiencies of the prior art, but also can effectively reduce material losses, improve the plasticity and spheroidizing strength of the produced wire rods, and is of great significance for improving the efficiency of processing bolts from wire rods and reducing costs. Summary of the Invention

[0005] The present invention aims to provide a production process for wire materials used in bolts in the photovoltaic industry, so as to solve the technical problem of high material loss rate and raw material waste when producing wire materials for bolts in the photovoltaic industry in the prior art.

[0006] To achieve the above object, the present invention adopts the following technical solution: A production process for wire materials used in bolts in the photovoltaic industry, comprising the following steps:

[0007] Step 1. Incoming material inspection: Check the original chemical composition, wire diameter tolerance, metallographic structure, decarburization depth, cracks, and scratches of the material to ensure that its various technical parameters meet the product quality requirements;

[0008] Step 2. First pickling, water washing, phosphating, and saponification: Perform pickling treatment, water washing treatment, phosphating treatment, and saponification treatment on the wire rod in sequence;

[0009] Step 3. First spheroidizing annealing: Perform three-stage heating and isothermal treatment, first-stage cooling and isothermal treatment, and variable-speed cooling treatment on the wire rod in sequence;

[0010] Step 4. Second pickling, water washing, and lime treatment: Perform pickling treatment, water washing treatment, and lime treatment on the wire rod again;

[0011] Step 5. Rough drawing: Roughly draw the wire rod into wire materials;

[0012] Step 6. Second spheroidizing annealing: Perform three-stage heating and isothermal treatment, first-stage cooling and isothermal treatment, and variable-speed cooling treatment on the wire materials in sequence;

[0013] Step 7. Process inspection: Check the size, decarburization, and uniformity of the spheroidized structure of the wire materials to make them initially meet the product requirements;

[0014] Step 8. Third pickling, phosphating, and saponification: Perform pickling treatment, phosphating treatment, and saponification treatment on the wire materials in sequence;

[0015] Step 9. Finish drawing: Draw the above-mentioned wire materials according to the product size requirements to obtain finished wire materials;

[0016] Step 10. Finish product inspection: Inspect the quality of the finished wire materials, and store the qualified wire materials in the warehouse.

[0017] The principle and advantages of this solution are as follows:

[0018] 1. Compared with the prior art where the material loss rate is high and raw materials are wasted when producing wire materials for bolts in the photovoltaic industry, this solution effectively controls material loss and reduces the material loss rate to 1.5 - 2% by optimizing the pickling and spheroidizing processes with high material loss in the traditional process, thereby significantly reducing material waste and improving production efficiency.

[0019] 2. This solution effectively improves the spheroidization effect on the material surface by performing multi-stage heating isothermal, cooling isothermal, and variable-speed cooling treatments on the material during the spheroidizing annealing stage, ensuring that the prepared wire rod has excellent spheroidized structure, meeting the zero decarburization requirement. At the same time, it effectively improves the plasticity of the wire rod, fully meeting the processing requirements of bolts in the photovoltaic industry.

[0020] 3. This solution alternately performs three pickling processes and two spheroidizing treatments. After the first annealing, pickling is carried out to remove the surface carbide layer, preventing abnormal growth of carbides during the second annealing. Through two annealing processes, the distribution of carbide particles becomes more uniform, effectively improving the uniformity of deformation during cold drawing. Moreover, by alternately using three pickling processes and two annealing processes, the cold working performance is effectively improved, and the total annealing time can be effectively shortened by the two spheroidizing annealing processes, improving production efficiency.

[0021] Preferably, as an improvement, in step three, the three-stage heating isothermal treatment is as follows: The wire rod is first heated to the first temperature of 580 - 630 °C within 1 - 2 minutes and isothermally treated for 1.5 - 2 hours, then heated to the second temperature of 700 - 730 °C within 1 - 2 minutes and isothermally treated for 1 - 1.5 hours, and then heated to the third temperature of 770 - 775 °C within 0.8 - 1 hour and isothermally treated for 7 - 8 hours; the one-stage cooling isothermal treatment is: cooling to the fourth temperature of 700 - 730 °C within 1 - 2 minutes and isothermally treated for 5 - 6 hours; the variable-speed cooling treatment is: first cooling to 670 - 680 °C within 2.5 - 3 hours, then cooling to 640 - 650 °C within 1.5 - 2 hours, and finally quickly cooling to 550 - 600 °C within 1 - 2 minutes.

[0022] Technical effects: With the above settings in this solution, it is convenient to reduce the material hardness through the globular pearlite structure, improve plasticity, and reduce the cracking risk during cold drawing; it can also inhibit the net precipitation of carbides, homogenize the structure, and effectively refine the grains; during the process, the processing stress is effectively eliminated, the subsequent heat treatment deformation is reduced, and the dimensions are stabilized.

[0023] Specifically, at the first temperature gradient, the material starts to partially austenitize at the first temperature, reducing the subsequent heating thermal stress, and the isothermal treatment dissolves part of the carbides; then at the second temperature, the pearlite is transformed into austenite, and the isothermal treatment promotes the formation of carbide spheroidization nuclei; then at the third temperature, uniform austenite is formed, and the isothermal treatment dissolves the carbides fully. During this process, if the third temperature is too high, the austenite grains will become coarse, resulting in coarsening of the final carbide particles; while if the isothermal time at the third temperature is too short, the carbides will not be dissolved sufficiently, and local stress concentration is likely to occur during cold drawing.

[0024] During the subsequent cooling process to the fourth temperature, by controlling the cooling rate, the precipitation of globular carbides is effectively promoted, and isothermal treatment makes the pearlite lamellar spacing finer. If the cooling rate is too fast during this stage, flaky pearlite will be formed, causing the work hardening index to increase sharply by 50% during cold drawing of the material and reducing its processing plasticity; if the isothermal time at the fourth temperature is too long, the strength and toughness matching of the material will be reduced due to excessive aggregation of carbides.

[0025] Subsequently, through variable-speed cooling treatment, the carbide size is effectively controlled and the pearlite ratio is optimized until the reaction is terminated. In this stage, if the slow cooling stage time is too short, the fracture elongation rate during cold drawing will be affected due to insufficient growth of carbides; if the fast cooling temperature is too low, the cold working performance will be significantly reduced due to the formation of bainite structure.

[0026] Preferably, as an improvement, in step six, the third temperature of the secondary spheroidizing annealing is 750 - 765 °C.

[0027] Technical effect: With the above settings in this solution, reducing the secondary annealing temperature can slow down the austenite decomposition rate, inhibit excessive coarsening of carbides, and form finer and more uniform globular carbides, thereby improving the cutting performance and subsequent cold working performance of the material. The applicant found through long-term experiments that if the temperature of the second spheroidizing annealing is the same as that of the first spheroidizing annealing, it will lead to excessive coarsening of carbides. The large carbide particles will damage the matrix continuity and become the path for crack initiation and propagation, resulting in an increase in material brittleness and a significant reduction in material toughness.

[0028] Preferably, as an improvement, in steps two, four, and eight, before pickling, it also includes soaking the wire rod or wire in warm water at 50 - 65 °C.

[0029] Technical effect: With the above settings in this solution, when the wire surface is heated and then enters the hydrochloric acid pool, it is convenient to remove the scale on the wire rod surface more thoroughly. At the same time, because the temperature of the hot water pool can reach 50 - 65 °C, the dirt such as the oxide shell and ash on its surface can be effectively removed, improving the cleanliness of the wire rod.

[0030] Preferably, as an improvement, in steps two, four, and eight, the pickling content is as follows: first pickle in an acid solution with a concentration of 5 - 10% for 10 - 20 min, then pickle in an acid solution with a temperature of 35 - 40 °C and a concentration of 10 - 15% for 5 - 15 min, and finally pickle in an acid solution with a temperature of 35 - 40 °C and a concentration of 15 - 20% for 3 - 10 min.

[0031] Technical effect: This solution adopts staged gradient pickling, which is convenient for efficient rust removal and improves the surface cleanliness of the material. Specifically, through the concentration gradient design (5-10% → 10-15% → 15-20%), a three-stage process of "pre-reaction - main reaction - fine treatment" is formed, ensuring efficient pickling while effectively reducing the amount of hydrogen penetration and reducing the risk of hydrogen embrittlement. Moreover, in the actual process of multi-gradient pickling, it can effectively avoid over-corrosion caused by a single high-concentration acid solution and also avoid incomplete rust removal with a single low-concentration acid solution.

[0032] Preferably, as an improvement, in steps two and four, the water washing is as follows: The pickled material is subjected to four-stage water washing in a soup washing pool with a pH of 5-7, a soup washing pool with a pH of 5.5-7, a soup washing pool with a pH of 5-7, and a soup washing pool with a pH of 5.5-7 in sequence.

[0033] Technical effect: With the above settings in this solution, it is convenient to remove the influence of residual acid solution, improve the surface cleanliness, and also prevent the acid solution from entering the subsequent phosphating tank and polluting the phosphating solution. And through pH gradient control in the solution, different pH values in the four-stage water washing tank form a dynamic neutralization gradient, avoiding precipitation caused by local over-neutralization (such as the precipitation of CaCO3). Moreover, compared with single-stage water washing, four-stage countercurrent rinsing can significantly reduce the residual acid concentration. The applicant found through long-term experiments that if the number of water washing times is insufficient, hydrogen embrittlement will be caused during the cold working of the material due to the residual acid solution, reducing the material strength; and the residual acid solution will also increase the porosity of the phosphating film, thereby reducing its corrosion resistance. If the pH is too high, white flocculent precipitation (Ca(OH)2) is likely to form on the surface of the workpiece, making the phosphating film locally thinner, resulting in "crater" defects after the coating is baked and reducing the corrosion resistance. If the pH is too low, the material will rust back (Fe2O3·nH2O) after water washing, reducing the bonding force between the phosphating film and the substrate, thereby reducing the film adhesion during saponification treatment and causing the cold working lubrication to fail.

[0034] Preferably, as an improvement, in steps two and eight, the phosphating treatment is as follows: Treat in a phosphating tank at a temperature of 74-78°C, with a free acid of 7-9 Pt, a total acidity of 49-52 Pt, an acid ratio of 6-6.5, a promotion degree of 1-3 Pt, and a phosphate ratio of 0.4-0.5 for 4-6 minutes.

[0035] Technical effect: This scheme adopts the above-mentioned setting to facilitate the formation of a phosphate conversion film layer on the surface of the material. On the one hand, it protects the surface of the material, slows down the electrochemical corrosion process, and prevents the surface of the material from being oxidized by air and affecting the overall performance of the material. On the other hand, the phosphate film can block the conductivity of the metal surface and prevent the local micro-battery effect. It is suitable for parts that need insulation (such as motor silicon steel sheets). In addition, the porous structure of the phosphating film can absorb lubricants (such as saponified liquid), reduce friction resistance during metal processing, and extend the life of the mold. Specifically, compared with high-temperature phosphating at 90°C and low-temperature phosphating at 40°C, medium-temperature phosphating can balance the film formation speed and energy consumption to form a compact medium film layer; and iron-based phosphating can generate Fe3(PO4)2·8H2O and Fe2O3 composite films at this temperature to improve corrosion resistance. Limiting the free acid and combining it with the total acidity to form a stable acid ratio (6 to 6.5) can effectively control the dissolution rate of the metal matrix and the phosphating rate, effectively promote uniform crystallization, improve the crystal morphology and density of the phosphating film, and ensure the mechanical bite effect between the phosphating film and the substrate.

[0036] The applicant has found through long-term experiments that if the phosphating temperature is too high, the film layer will be too thick, which will increase the brittleness and crack easily after coating; it will also cause the evaporation of the bath liquid to intensify, and the free acid will rise faster, affecting the phosphating effect; if the phosphating temperature is too low, it will significantly reduce the film forming speed, reduce the film weight and the corrosion resistance of the film will be insufficient, and "yellow rust" (FeOOH) will easily appear, especially in the continuous production line. If the free acid is too high, it will cause "over-corrosion" due to excessive dissolution of the matrix, which will reduce the bonding strength of the film layer; it will also make the acid ratio less than 6, resulting in coarse crystals, easy to absorb oil stains, and reduce the performance of the phosphating film; if the free acid is too low, the film layer will be incomplete due to the difficulty in starting the phosphating reaction, and the stability of the bath liquid will be reduced, and zinc phosphate precipitation will be easily generated (the amount of slag will increase by 2 to 3 times). If the total acidity is too high, the film layer will be too dense due to the acid ratio>6.5, resulting in reduced adhesion, and the amount of phosphating slag will increase by 15% to 20%, blocking the spray system. If the promotion rate is too low, the phosphating film may be too thin and the corrosion resistance may be insufficient; if the promotion rate is too high, the film may be rough and the phosphating slag may increase.

[0037] Preferably, as an improvement, before the phosphating treatment, an oxalic acid treatment is also included, and the oxalic acid treatment is carried out for 3 to 5 minutes at an oxalic acid concentration of 10 to 15Pt.

[0038] Technical effect: This scheme adopts the above settings, oxalic acid and Fe 2+ , Fe 3+ , Cu 2+It forms stable complexes to remove the metal salts remaining after pickling and deeply purify the surface; it can also effectively dissolve the remaining Cr2O3 after pickling to improve the surface activity; it can also cause selective corrosion on the metal surface, and provide more active sites for the phosphating reaction through the micro-pit structure to improve the subsequent phosphating film effect. Through long-term experiments, the applicant found that if oxalic acid treatment is not adopted, the problem of blooming of the phosphating film caused by the residual pollution of metal ions will also reduce the nucleation density of the phosphating film due to insufficient surface activity, resulting in poor film layer continuity and affecting the material properties.

[0039] Preferably, as an improvement, in step four, the lime treatment is: the material is treated in a lime pool with a mass fraction of 30-40% for 2-3 minutes.

[0040] Technical effect: With the above settings in this solution, it is convenient to neutralize the acid solution remaining on the surface of the material after water washing, and avoid the remaining acid solution from continuing to react with the steel, affecting the quality and performance of the steel.

[0041] Preferably, as an improvement, in steps two and eight, the saponification treatment is: the treatment is carried out in a saponification solution with a temperature of 80-85°C, a pH of 8-9, an oil content of 0.8-1.3 Pt, and a sugar content of 1-2 Pt for 5-8 minutes.

[0042] Technical effects: With the above settings, this solution facilitates the formation of a saponification layer on the surface of the phosphating film, reducing the friction coefficient during cold working and minimizing wear. The saponification layer can seal the pores of the phosphating film, enhancing corrosion resistance. Through long-term experiments, the applicant found that the saponification temperature in this solution can accelerate the saponification reaction, enabling fatty acids to quickly combine with metal ions to form a film. If the saponification temperature is too high, the solution evaporation will intensify, the oil content will decrease, resulting in an overly thin film layer and lubrication failure. If the saponification temperature is too low, the reaction rate will slow down, leading to uneven film layer thickness, easy peeling, and scratches during cold working. The pH of the saponification solution in this solution can maintain an alkaline environment, promoting the dissociation of stearate ions (the pKa of stearic acid is approximately 5.5, and dissociation is more complete under alkaline conditions). If the pH is too high, the corrosiveness of the solution will increase, damaging the bottom layer of the phosphating film and causing coating blistering. If the pH is too low, the saponification reaction will be incomplete, resulting in a decrease in the hot water resistance of the film layer. Limiting the oil content to 0.8 - 1.3 Pt can ensure the concentration of effective lubricating components in the solution. If the oil content is too high, the solution viscosity will increase, leaving oil spots on the workpiece surface and affecting the appearance of the coating (such as gloss). If the oil content is too low, the film layer thickness will be insufficient, the friction during cold working will increase, and the die life will be shortened. By limiting the sugar content to 1 - 2 Pt in this solution, the colloidal system of the saponification solution can be stabilized through complexation. If the sugar content is too high, microorganisms will easily grow in the solution, leading to spoilage and a soaring COD value. If the sugar content is too low, the solution stability will decrease, resulting in stratification or precipitation and affecting the uniformity of the film layer. If the treatment time is too long, the brittleness of the film layer will increase due to excessive thickness, the solution consumption will also increase, and the production cost will rise. Moreover, long-term treatment at high temperatures may cause recrystallization of the film layer. If the treatment time is too short, the film layer will be incomplete, and dry friction will occur locally during cold working, generating scratches. Description of the Drawings

[0043] Figure 1 It is a graph showing the temperature change during the first spheroidizing annealing in the production process of wire rods for bolts in the photovoltaic industry according to Embodiment 1 of the present invention.

[0044] Figure 2 It is a graph showing the temperature change during the first spheroidizing annealing in the production process of wire rods for bolts in the photovoltaic industry according to Comparative Example 5 of the present invention. Detailed Embodiments

[0045] The following further elaborates on the present invention in detail with reference to embodiments, but the implementation manners of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments and experimental examples are conventional means well-known to those skilled in the art, and the materials, reagents, etc. used can all be obtained through commercial channels.

[0046] Embodiment 1

[0047] This solution provides a production process for wire rods for bolts in the photovoltaic industry, including the following steps:

[0048] Step 1. Incoming inspection: Check the original chemical composition, wire diameter tolerance, metallographic structure, decarburization depth, cracks, and scratches of the materials to ensure that their technical parameters meet the product quality requirements.

[0049] Step 2. Primary pickling, water washing, phosphating, and saponification: After soaking the wire rods in warm water at 50 - 65 °C, perform pickling treatment, water washing treatment, phosphating treatment, and saponification treatment on the wire rods in sequence. The purpose of pickling the wire rods is to remove rust. At the same time, through phosphating and saponification, a water-insoluble crystalline phosphate conversion film is deposited on the surface of the wire rods to protect the surface of the wire rods and prepare for preventing decarburization during the spheroidizing annealing process.

[0050] The content of pickling is as follows: First, pickle in acid solution with a concentration of 5 - 10% for 10 - 20 min, then pickle in acid solution with a temperature of 35 - 40 °C and a concentration of 10 - 15% for 5 - 15 min, and finally pickle in acid solution with a temperature of 35 - 40 °C and a concentration of 15 - 20% for 3 - 10 min. In this embodiment, the acid solution is specifically hydrochloric acid.

[0051] Specifically, after the wire rods enter the hydrochloric acid pool through the hot water pool, because the wire rods have been surface-heated and have a relatively high temperature, they will react violently after entering the pickling tank, generating a large amount of gas (hydrogen). The reaction equations and principles with hydrochloric acid are as follows: Fe3O4 + 8HCl = FeCl2 + 2FeCl3 + 4H2O, Fe2O3 + 6HCl = 2FeCl3 + 3H20, FeO + 2HCl = FeCL2 + H2O, Fe + 2HCl = FeCL2 + H2↑. The reaction phenomenon is that a large number of bubbles are generated on the surface of the iron, and the solution gradually turns light green.

[0052] The content of water washing is as follows: The pickled materials are subjected to four-stage water washing in a soup washing water tank with a pH of 5 - 7, a soup washing water tank with a pH of 5.5 - 7, a soup washing water tank with a pH of 5 - 7, and a soup washing water tank with a pH of 5.5 - 7 in sequence.

[0053] Before phosphating treatment, it also includes oxalic acid treatment, and the oxalic acid treatment is carried out for 3 - 5 min under the condition that the oxalic acid concentration is 10 - 15 Pt. The phosphating treatment is as follows: Treat in a phosphating tank at a temperature of 74 - 78 °C, with a free acid of 7 - 9 Pt, a total acidity of 49 - 52 Pt, an acid ratio of 6 - 6.5, a promotion degree of 1 - 3 Pt, and a phosphate radical ratio of 0.4 - 0.5 for 4 - 6 min.

[0054] The principle of the phosphating reaction is that iron reacts with phosphoric acid, releasing (hydrogen) and (ferrous ions), and the local pH decreases. It promotes the catalytic effect and the three-stage dissociation of phosphoric acid and the hydrolysis reaction of zinc dihydrogen phosphate. The reaction process is as follows:

[0055] (1) Dissolution of the metal matrix: Iron reacts with phosphoric acid, releasing H (hydrogen gas) and Fe (ferrous ions), and the local pH decreases.

[0056] (2) Promote catalytic action and the tertiary dissociation of phosphoric acid and the hydrolysis reaction of zinc dihydrogen phosphate

[0057] Promote catalysis: Fe 2+ +[O] → Fe 3+ +[R]

[0058] Dissociation of phosphoric acid:

[0059] Hydrolysis of zinc dihydrogen phosphate:

[0060] (3) Formation of the phosphating film

[0061] Formation of the phosphating film: 2Zn 2+ +Fe 2+ +2PO4 3- +4H2O = Zn2Fe(PO4)·4H2O↓

[0062] 3Zn 2+ +2PO4 3- +4H2O = Zn3(PO4)2·4H2O↓

[0063] Fe 3+ +PO4 3- = FePO4↓ (phosphating slag)

[0064] Saponification treatment: Treat for 5 - 8 min in a saponification solution at a temperature of 80 - 85 °C, pH 8 - 9, oil content 0.8 - 1.3 Pt, and sugar content 1 - 2 Pt.

[0065] During saponification, zinc stearate saponification layer is formed through the reaction of stearate in the solution and the zinc phosphate film layer, and the reaction is as follows:

[0066] Reaction: 6C 17 H 35 COONa + Zn3(PO4)2 = 3(C 17 H 35 COO)2Zn + 2Na3PO4

[0067] Step 3. Primary spheroidizing annealing: The wire rod is subjected to three-stage heating isothermal treatment, first-stage cooling isothermal treatment, and variable-speed cooling treatment in sequence; among them, the three-stage heating isothermal treatment is: the wire rod is first heated to the first temperature of 580-630°C and isothermally treated for 1.5-2 h within 1-2 min, then heated to the second temperature of 700-730°C and isothermally treated for 1-1.5 h within 1-2 min, and then heated to the third temperature of 770-775°C and isothermally treated for 7-8 h within 0.8-1 h; the first-stage cooling isothermal treatment is: cooled to the fourth temperature of 700-730°C and isothermally treated for 5-6 h within 1-2 min; the variable-speed cooling treatment is: first cooled to 670-680°C within 2.5-3 h, then cooled to 640-650 within 1.5-2 h, and finally quickly cooled to 550-600°C within 1-2 min.

[0068] Specifically, the temperature control of the primary spheroidizing treatment in this embodiment is as Figure 1 shown by the curve in. The three-stage heating isothermal treatment is: the wire rod is first heated to the first temperature of 610°C and isothermally treated for 2 h within 1 min, then heated to the second temperature of 720°C and isothermally treated for 1.5 h within 1 min, and then heated to the third temperature of 770°C and isothermally treated for 8 h within 1 h; the first-stage cooling isothermal treatment is: cooled to the fourth temperature of 720°C and isothermally treated for 6 h within 1 min; the variable-speed cooling treatment is: first cooled to 680°C within 3 h, then cooled to 650 within 2 h, and finally quickly cooled to 550°C within 1 min to terminate the reaction.

[0069] The control method of the atmosphere during annealing is as follows: Nitrogen with a small flow rate of 2 m 3 / h is turned on throughout the annealing stage. When the furnace temperature reaches First temperature Before, nitrogen with a large flow rate of 10 m 3 / h is turned on simultaneously. When the furnace temperature reaches the first temperature, 35 ml / min of methanol is turned on and the large flow rate of nitrogen is turned off; methanol is turned off when half of the holding time at the third temperature has passed, and the small flow rate of nitrogen remains unchanged before the furnace is unloaded.

[0070] Spheroidizing annealing is annealing carried out to spheroidize the carbides in steel, obtaining a structure of spherical or granular carbides uniformly distributed on the ferrite matrix. Specifically, spheroidizing annealing is mainly used for eutectoid steel and hypereutectoid steel to obtain a spheroidized structure similar to granular pearlite (since it is not necessarily eutectoid composition, it is called a spheroidized structure), thereby reducing hardness, improving machining performance, and preparing the microstructure for quenching. The spheroidized structure not only has better plasticity and toughness than the lamellar structure, but also has a slightly lower hardness. When cold-deforming a workpiece with a spheroidized structure, it is beneficial for cold forming and can also increase the service life of the cold deformation die.

[0071] Step 4: Secondary pickling, water washing, and liming: The wire rods are pickled, washed with water, and treated with lime again. The purpose of this pickling is to thoroughly pickle the oxide scale on the material surface and form a very thin lubricating layer on the surface, which is beneficial for drawing. This is to prepare for subsequent large-deformation drawing. If the pickling process is not thorough, a large number of rejects are very likely to occur during the drawing process.

[0072] Among them, the pickling and water washing steps are the same as those in Step 2. The lime treatment is as follows: The material is treated in a lime pool with a mass fraction of 30 - 40% for 2 - 3 minutes.

[0073] Step 5: Rough drawing: The wire rods are initially drawn into wire.

[0074] Specifically, in this stage, key control should be placed on scratches and abrasions on the wire surface to effectively control its surface quality. At the same time, residues, oxide scale, etc. remaining on the wire surface after surface drawing can be further removed, effectively controlling its surface quality.

[0075] Step 6: Secondary spheroidizing annealing: The wire is subjected to three-stage temperature-rising isothermal treatment, first-stage temperature-lowering isothermal treatment, and variable-speed temperature-lowering treatment in sequence. The steps in this stage are basically the same as those in the primary spheroidizing annealing in Step 3, except that the third temperature during the three-stage temperature-rising isothermal treatment is 750 - 765 °C, which is 10 - 15 °C lower than the third temperature in the primary spheroidizing annealing treatment. The main purpose of the spheroidizing annealing in this stage is to make up for the locally uncompleted spheroidization of the material during the first spheroidization, so that the material as a whole uniformly forms globular pearlite, and at the same time completely eliminates the internal stress generated during the initial drawing process.

[0076] Step 7: Process inspection: Check the dimensions, decarburization, and spheroidized structure uniformity of the wire to make it preliminarily meet the product requirements.

[0077] Specifically, in this stage, key detection should be carried out on the dimensions, decarburization, and spheroidized structure uniformity of the wire to make its spheroidization grade, wire diameter size, and decarburization depth meet the index requirements.

[0078] Step 8: Tertiary pickling, phosphating, and saponification: The wire is pickled, phosphated, and saponified in sequence.

[0079] In this stage, the pickling treatment, phosphating treatment, and saponification treatment are the same as those in Step 2.

[0080] Step 9: Finished product drawing: The above-mentioned wire is drawn according to the product size requirements to obtain the wire finished product. In this stage, key control should be placed on scratches and abrasions on the wire surface to effectively control its surface quality.

[0081] Step 10: Finished product inspection: Inspect the quality of the wire finished product, and store the qualified wire in the warehouse.

[0082] In this stage, key control should be exerted on indicators such as the surface phosphating film layer, wire diameter tolerance, coil weight, and surface scratches; in the process of finished product warehousing and storage, key control should be focused on protection, quantity, stacking to ensure standardization and safety; in the outgoing inspection, key control should be placed on ground protection, vehicle protection, and the standardization of finished product inspection reports and steel mill reports.

[0083] Specifically, taking the material of SCM435, the raw material specification of Φ6.5mm, and the product specification of Φ5.38mm as an example to illustrate the technical effects of the process of this solution. The differences in the steps and parameters of the wire production process for bolts in the photovoltaic industry in Examples 1 to 3 and Comparative Examples 1 to 7 are shown in Table 1 in detail.

[0084] Table 1 Differences in the steps and parameters of the wire production process for bolts in the photovoltaic industry in Examples 1 to 3 and Comparative Examples 1 to 7

[0085]

[0086] Experimental Example 1: Finished product detection

[0087] Perform performance tests on the wires produced by the processes in Examples 1 to 3 and Comparative Examples 1 to 7, and the results are shown in Table 2.

[0088] Table 2 Performance of the wires produced by the processes in Examples 1 to 3 and Comparative Examples 1 to 7

[0089]

[0090] Experimental data show that the wire production process for bolts in the photovoltaic industry of this solution can effectively produce wires that meet the high requirements of "zero decarburization, excellent spheroidized structure, high plasticity, and low hardness" for wires used in bolts in the photovoltaic industry (see GB / T 5953.1 - 2009). Specifically, the hardness of the wires produced by the processes of Examples 1 to 3 of this solution is 87 - 88, the tensile strength is 530 - 540 MPa, the reduction of area is 75.2 - 75.3%, the elongation is 13.2 - 13.3%, with zero carbonization and a spheroidization grade of 5, fully meeting the requirements of wires for bolts in the photovoltaic industry and being convenient for further processing into bolts for the photovoltaic industry. Moreover, by optimizing the pickling process and spheroidizing process, this solution improves the material loss rate in the pickling stage and the spheroidizing annealing stage, so that even with the combination of "three - time pickling + two - time spheroidizing annealing", the material loss rate can still be effectively reduced to 1.5 - 2%, significantly reducing material waste and improving production efficiency.

[0091] The inventor discovered during the research and development phase that the acid combination method in the acidification process, whether oxalic acid treatment is performed before phosphating, the highest temperature in the spheroidization stage (i.e., the third temperature), and the highest temperature in the second spheroidization annealing all have a significant impact on the performance of the produced wire and the overall material loss rate of the process. Specifically, if two picklings and one spheroidization annealing are used (such as Comparative Example 1), the produced wire will not be able to reach the predetermined spheroidization level due to incomplete spheroidization of some materials, which will lead to the deterioration of the plasticity and ductility of the material. If a single gradient acid solution is used for acidification (such as Comparative Example 2 and Comparative Example 3), not only is the time longer, but the material loss rate after pickling with a single gradient acid solution is greatly increased, which increases material waste and is not conducive to improving economic benefits. If there is no oxalic acid treatment before phosphating (such as comparative example 4), the surface activity will be reduced due to the metal salts remaining on the surface of the wire, thereby reducing the thickness and continuity of the phosphating film, thereby affecting the material performance; due to the insufficient thickness and continuity of the phosphating layer, more oxidized skin will be generated after the wire is spheroidized annealed, resulting in a large loss of raw materials after pickling and drawing again, thereby increasing the waste of materials. If the third temperature is too low in the first spheroidizing annealing stage (such as comparative example 5), the material hardness will be too high, the spheroidizing grade will be insufficient, and the material plasticity will be insufficient due to insufficient spheroidization, thereby failing to meet the wire requirements of the photovoltaic industry bolts. If the third temperature is too high in the first spheroidizing annealing stage (such as comparative example 6), although the spheroidizing treatment is sufficient and the material performance meets the requirements, the high temperature will cause some edges to be overburned, affecting the overall use effect of the material. If the third temperature is too high in the second spheroidizing annealing stage (such as comparative example 7), the overall performance of the material will also be affected due to excessive spheroidizing treatment.

[0092] In summary, this solution optimizes the pickling and spheroidizing processes with high material loss in the traditional process. While fully meeting the high requirements of the photovoltaic industry for bolt wire, it effectively controls material loss and reduces the material loss rate to 1.5-2%, thereby significantly reducing material waste and improving production efficiency.

[0093] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A process for producing wire for photovoltaic industry bolts, characterized by: The steps include: Step 1: Incoming material inspection: Check the original chemical composition, wire diameter tolerance, metallographic structure, decarburization depth, cracks, and scratches of the material to ensure that its various technical parameters meet the product quality requirements; Step 2: Pickling, washing, phosphating and saponifying: the wire rod is pickled, washed, phosphated and saponified in sequence; Step 3, primary spheroidizing annealing: subjecting the wire rod to three-stage heating isothermal treatment, one-stage cooling isothermal treatment and variable speed cooling treatment in sequence; Step 4: Secondary pickling, water washing and lime treatment: the wire rod is pickled, water washed and lime treated again; Step 5: Rough drawing: initially draw the wire rod into wire; Step 6: Secondary spheroidizing annealing: the wire is subjected to three-stage heating isothermal treatment, one-stage cooling isothermal treatment and variable speed cooling treatment in sequence; Step 7. Process inspection: Check the size, decarburization, and uniformity of spheroidization of the wire to make it initially meet product requirements; Step 8, three times pickling, phosphating and saponifying: the wire is pickled, phosphated and saponified in sequence; Step 9: Finished product drawing: drawing the above wire according to product size requirements to obtain finished wire products; Step 10: Finished product inspection: Inspect the quality of finished wire products and store qualified wires in warehouse.

2. A process for producing photovoltaic industry bolt wires according to claim 1, characterized in that: In step three, the three-stage heating isothermal treatment is as follows: the wire rod is first heated to a first temperature of 580-630°C within 1-2 minutes and isothermal for 1.5-2 hours, then heated to a second temperature of 700-730°C within 1-2 minutes and isothermal for 1-1.5 hours, and then heated to a third temperature of 770-775°C within 0.8-1 hour and isothermal for 7-8 hours; the first-stage cooling isothermal treatment is as follows: the wire rod is cooled to a fourth temperature of 700-730°C within 1-2 minutes and isothermal for 5-6 hours; the variable speed cooling treatment is as follows: the wire rod is first cooled to 670-680°C within 2.5-3 hours, then cooled to 640-650 within 1.5-2 hours, and finally rapidly cooled to 550-600°C within 1-2 minutes.

3. A process for producing photovoltaic industry bolt wires according to claim 2, characterized in that: In step six, the third temperature of the secondary spheroidizing annealing is 750-765°C.

4. A process for producing photovoltaic industry bolt wires according to claim 1, characterized in that: In step 2, step 4 and step 8, the process further includes soaking the wire rod or the wire material in warm water at 50 to 65° C. before pickling.

5. A process for producing photovoltaic industry bolt wires according to claim 4, characterized in that: In step 2, step 4 and step 8, the pickling contents are as follows: first pickling in an acid solution with a concentration of 5-10% for 10-20 minutes, then pickling in an acid solution with a temperature of 35-40° C. and a concentration of 10-15% for 5-15 minutes, and finally pickling in an acid solution with a temperature of 35-40° C. and a concentration of 15-20% for 3-10 minutes.

6. A process for producing photovoltaic industry bolt wires according to claim 1, characterized in that: In step 2 and step 4, the water washing is as follows: the acid-washed material is sequentially washed in four stages in a water washing tank with a pH value of 5 to 7, a water washing tank with a pH value of 5.5 to 7, a water washing tank with a pH value of 5 to 7, and a water washing tank with a pH value of 5.5 to 7.

7. A process for producing photovoltaic industry bolt wires according to claim 1, characterized in that: In step 2 and step 8, the phosphating treatment is: treating for 4 to 6 minutes in a phosphating tank with a temperature of 74 to 78°C, a free acid of 7 to 9Pt, a total acidity of 49 to 52Pt, an acid ratio of 6 to 6.5, a promotion degree of 1 to 3Pt, and a phosphate ratio of 0.4 to 0.

5.

8. A process for producing photovoltaic industry bolt wires according to claim 7, characterized in that: Before the phosphating treatment, an oxalic acid treatment is also included. The oxalic acid treatment is carried out for 3 to 5 minutes at an oxalic acid concentration of 10 to 15 Pt.

9. A process for producing photovoltaic industry bolt wires according to claim 1, characterized in that: In step 4, the lime treatment is as follows: the material is treated in a lime pool with a mass fraction of 30-40% for 2-3 minutes.

10. A process for producing photovoltaic industry bolt wires according to claim 1, characterized in that: In step 2 and step 8, the saponification treatment is: treating in a saponification solution with a temperature of 80-85° C., a pH of 8-9, a fat content of 0.8-1.3 Pt, and a sugar content of 1-2 Pt for 5-8 min.

Images