Low-relaxation prestressed special stainless steel strand for cable stay and its production method

Abstract

The present application relates to the field of steel strand production, especially to a low-relaxation prestressed special stainless steel cable for hoisting and its production method, including the following steps: S1, stranding: twisting a plurality of stainless steel wires together to form a strand; S2, first tensioning: performing first tensioning treatment on the twisted stainless steel strand; S3, stabilization treatment: performing heat treatment on the first tensioning treated stainless steel strand; S4, water cooling: rapidly cooling the stainless steel strand with water; S5, drying: after cooling, the stainless steel strand may need to be dried; S6, second tensioning: performing second tensioning treatment; S7, surface treatment and passivation: removing lubricant residues and passivating the surface of the strand through electrolytic citric acid solution. S8, take-up: used for winding the produced steel strand into a drum shape. The low-relaxation prestressed special stainless steel cable for hoisting produced through these steps is suitable for various engineering and application requirements, and has excellent strength, stability and excellent corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of steel strand production technology, and in particular to a low-relaxation prestressed special stainless steel strand for suspending cables and its production method. Background Technology

[0002] In recent years, with the increase in cross-river, cross-sea, and near-shore engineering projects, corrosive environments have posed challenges to the durability of prestressed steel strands, especially in seawater, high humidity and rain in the south, high temperature differences in the north, de-icing agents, and high salinity and cold environments. Currently, prestressed low-relaxation cables typically use epoxy resin-coated steel strands and hot-dip galvanized steel strands. However, these materials only temporarily alleviate corrosion resistance and encounter hard contact problems at the anchorage, leading to coating damage and accelerated localized corrosion. Furthermore, during the service life of prestressed steel strands in bridges and highways, fire risks exist. Building fires typically require two hours to extinguish, at which point the temperature of the prestressed tendons inside the prestressed concrete structure can reach nearly 400°C. Traditional prestressed steel strands deteriorate in strength and stiffness at high temperatures, and severe prestress loss occurs due to high-temperature wax deformation. This not only reduces the structural load-bearing capacity but also accelerates structural cracking and deformation, promoting the spread of high-temperature fires inward, creating a vicious cycle. The entire prestressed concrete structure may collapse quickly, causing serious safety accidents. Therefore, there is an urgent need to develop a prestressed steel strand for concrete structures that conforms to the standard GB / T5224-2014 and has characteristics such as high resistance to stress corrosion, fatigue resistance, high temperature resistance, low relaxation and high torsion. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a stainless steel wire for low-relaxation prestressed special stainless steel slings and its production method, which solves the problems existing in the prior art. The low-relaxation prestressed special stainless steel slings manufactured by this method have physical properties that meet the existing standard GB / T5224-2014 for prestressed steel strands for concrete structures, and have the characteristics of high resistance to stress corrosion, fatigue resistance, high temperature resistance, low relaxation, and high torsion.

[0005] (II) Technical Solution

[0006] To achieve the above objectives, the present invention provides the following technical solution: a stranded wire for a low-relaxation prestressed special stainless steel cable, comprising a center wire and six edge wires. The six edge wires are arranged counterclockwise on the outer edge of the center wire and are wound synchronously within the same twist pitch range to complete one round of winding, forming a stranded structure. The nominal diameter of the center wire is 5.25±0.05mm, the nominal diameter of the edge wires is 5.05±0.05mm, and the nominal diameter after twisting is 15.24mm, with an allowable deviation range between 15.09 and 15.64mm. Its physical properties meet the following requirements: tensile strength ≥1860MPa, maximum total elongation ≥2%, and stress relaxation ≤2.5%.

[0007] A special stainless steel stranded wire for low-relaxation prestressed cable and its production method are characterized by the following steps: S1 stranding, S2 first tensioning, S3 stabilization treatment, S4 water cooling, S5 drying, S6 second tensioning, S7 surface treatment, and S8 winding.

[0008] S1. Twisting: Twisting multiple stainless steel wires together to form a strand; S2. First tensioning: Performing the first tensioning treatment on the twisted stainless steel strand; S3. Stabilization treatment: Performing heat treatment on the stainless steel strand after the first tensioning treatment; S4. Water cooling: Rapidly cooling the stainless steel strand with a water cooling device; S5. Drying: Drying the stainless steel strand with a drying device; S6. Second tensioning: Performing the second tensioning treatment; S7. Surface treatment; S8. Winding: Using the method of winding the finished steel strand into a coil.

[0009] Preferably, in step S1, the production line speed of the six edge yarns during the twisting process is 15 m / min, and the production line speed of the center yarn is 15 m / min.

[0010] Preferably, during the twisting process in step S1, the twist pitch of the steel strand is set to 213mm, which is approximately 14 times the nominal diameter, with an allowable range of 205-230mm.

[0011] Preferably, during the first tensioning process in step S2, the traction pretensioning is 30-50% of the maximum force, and the tension of the traction wheel is 78-130KN.

[0012] Preferably, in step S3, the tempering temperature range of the steel strand during the stabilization treatment is 300-700℃, and the holding time is 60s.

[0013] Preferably, step S4, water cooling, includes rapid cooling to below 50°C, with the cooling time controlled within 5 seconds.

[0014] Preferably, step S5 drying includes setting the air velocity between 10m / s and 30m / s, the drying temperature between 100 and 140℃, the drying air velocity between 10m / s and 30m / s, and the drying time between 5 and 60s.

[0015] Preferably, during the second tensioning process in step S6, the traction pretensioning is 50-65% of the maximum force, and the tension of the traction wheel is 100-125KN.

[0016] Preferably, the wire release speed of the S1 twisting section is 5-60 m / min, the wire release speed of the S3 medium-frequency tempering section is 5-60 m / min, the wire release speed of the S4 water cooling section is 5-60 m / min, the wire release speed of the S7 surface treatment and passivation section is 5-60 m / min, and the wire take-up speed of the S8 section is 5-60 m / min.

[0017] (III) Beneficial Effects

[0018] Each step in this production method, including twisting speed, twist pitch, tempering temperature, cooling time, and drying parameters, is meticulously controlled to ensure that the final steel strand has excellent high-temperature resistance. The stainless steel strand produced by this method has a tensile strength ≥1860MPa, a maximum total elongation ≥2%, and a stress relaxation ≤2.5%. Its physical properties meet the requirements of the existing standard GB / T5224-2014 for prestressed steel strands for concrete structures. The steel strand described in this invention can meet the requirements for use in special stainless steel slings and has high resistance to stress corrosion, fatigue, high temperature, low relaxation, and high torsion. Detailed Implementation

[0019] This invention provides a technical solution: a low-relaxation prestressed special stainless steel cable strand and its production method, comprising the following steps:

[0020] S1. Twisting: Prepare multi-strand steel wires for twisting, including six outer edge wires and one center wire. The center wire requirements are: nominal diameter range of 5.25±0.05mm, tensile strength ≥1900MPa, and torsional performance ≥14 turns. The edge wire requirements are: nominal diameter range of 5.05±0.05mm, tensile strength ≥1920MPa, and torsional performance ≥14 turns. Prepare the center wire and outer edge wires that meet the specifications, ensuring that their diameter and performance meet the requirements. In the twisting equipment, place the six outer edge wires counterclockwise on the outer edge of the center wire. Set the twist pitch to 213mm, which is the distance of the six outer edge wires around the center wire in one revolution. The twist pitch is controlled to be 14 times the nominal diameter, with an allowable range of 205-230mm. The twisting equipment is started, and the steel wires are twisted at a twist pitch of 213mm and a speed of 5-60m / min for the edge wires and 5-60m / min for the center wire. This step is the key stage of twisting, ensuring the uniform twisting of the outer edge wires and the center wire. A certain amount of lubricant is applied to the surface of the edge wires and the center wire to reduce friction during the twisting process. During the twisting process, the six outer edge wires are wound counterclockwise around the outer edge of the center wire, twisting synchronously to form a single strand. This ensures the uniformity and stability of the steel strand. After the twisting process is completed, the twisted steel strand is fed to the next step at a speed of 5-60m / min. The feeding speed in this step affects the transmission effect of the strand and the smooth progress of subsequent processing.

[0021] It's important to note that the twist pitch refers to the distance the edge wire rotates around the center wire during the stranding process. The twist pitch directly affects the mechanical properties of stainless steel strands, including tensile strength, elongation, and bending performance. A smaller twist pitch results in a looser strand with relatively lower tensile strength but higher elongation. A larger twist pitch usually makes the strand tighter, increasing tensile strength but decreasing elongation. The twist pitch also affects the strand's relaxation properties. A smaller twist pitch may lead to greater stress relaxation, causing a significant decrease in tension after the strand is stressed. A larger twist pitch may lead to less stress relaxation, allowing the strand to maintain more stable tension under long-term stress.

[0022] S2, First Tensioning: In the first tensioning step, the twisted strand structure is fed into a dedicated tensioning device designed to apply appropriate tension to stretch the strand structure to a predetermined tension value. The traction pre-tension force for the first tensioning is 30-50% of the maximum force. Specifically, the applied tension is 30% to 50% of the maximum tension of the strand, that is, the tension applied to the strand by the traction wheel is 78-130KN.

[0023] The first tensioning step ensures that the internal structure of the stranded wire is optimized, improving its strength and stability. The tensioning process is continuous throughout the stranded wire preparation process, continuing into subsequent steps, including tempering, drying, and cooling. This continuous tensioning ensures that the stranded wire remains under tension throughout the preparation process, up to the second tensioning step. This step is characterized by continuing the tensioning process into subsequent steps to ensure that the stranded wire remains under tension throughout the preparation process, thereby optimizing its quality and performance.

[0024] S3. Stabilization Treatment: Medium-frequency tempering is a crucial step in the preparation of stainless steel strands. It is used to heat-treat the stainless steel strands after the first tensioning treatment. After the first tensioning treatment, the tensioned stainless steel strands are sent to a medium-frequency tempering device. The linear speed of the entire tempering section is controlled at 5-60 m / min. Medium-frequency tempering is accomplished by placing the stainless steel strands in a medium-frequency heating furnace. This heating process raises the temperature of the stainless steel strands to between 300℃ and 700℃. Once the target temperature is reached, the stainless steel strands are held at this temperature for 15 to 60 seconds. This holding time is to ensure uniform temperature throughout the stainless steel strands and to achieve the required microstructure. The medium-frequency tempering process helps improve the structure and properties of the stainless steel strands. During the holding process, the crystal structure of the stainless steel undergoes some adjustments to improve its strength, toughness, and stability.

[0025] S4. Water Cooling: Water cooling is used to rapidly cool the stainless steel strands that have undergone medium-frequency tempering. After the medium-frequency tempering process, the stainless steel strands that have undergone heat treatment enter the water cooling equipment and pass through the water cooling device at a linear speed of 5-60 m / min. The steel strands are immersed in cooling water and rapidly cooled to below 50°C. The cooling time is controlled within 5 seconds. The main purpose of water cooling is to rapidly cool the stainless steel strands to stabilize their microstructure and mechanical properties. Due to the high thermal conductivity of water, the strands are rapidly cooled in a short time.

[0026] S5. Drying: After the water cooling step, the stainless steel stranded wire usually contains some moisture, mainly due to residual cooling water on or inside the wire. Therefore, the stainless steel stranded wire is sent into a dedicated drying device, which includes a blower to generate hot air. The hot air generated by the blower passes through the stranded wire, effectively removing the moisture. This process aims to ensure that both the surface and interior of the stranded wire are thoroughly dried. The stranded wire enters the drying equipment via a conveyor belt to ensure that the entire surface of the stranded wire is thoroughly dried. The drying air velocity is set between 10m / s and 30m / s to ensure sufficient air circulation. The drying temperature is controlled within the range of 100-140℃ to avoid damage to the stranded wire due to excessive heat. The drying time is set to 15-20 minutes to ensure thorough removal of moisture without excessive energy consumption. During the drying process, by controlling the temperature and air velocity, the contact of the stainless steel stranded wire with oxygen can be effectively reduced, thereby slowing down the oxidation rate and helping to maintain the smoothness and corrosion resistance of the stranded wire surface.

[0027] S6. Second Tensioning: In the second tensioning step, the stainless steel strands that have already undergone drying are tensioned again to further adjust their performance and structure. The dried stainless steel strands are fed into the traction machine. The second tensioning pre-tensions 50-65% of the maximum force of the entire steel strand, that is, the tension applied to the strand by the traction wheel is 130-169KN. The second tensioning is one of the key steps in the preparation process of stainless steel strands. It is used to optimize the quality and performance of stainless steel strands through re-tensioning to ensure that they meet specific technical requirements. This step helps to make the strands have consistent performance and improve their applicability.

[0028] S7. Surface Treatment and Passivation: Lubricant residue is removed and the stranded wire surface is passivated by electrolyzing an acid solution. The purpose is to achieve two main objectives by treating the stranded wire with an electrolyzed citric acid solution:

[0029] Removing Lubricant Residue: Lubricants are commonly used in the stranding process to reduce friction and wear. However, these lubricants can leave residues on the finished stranded wire. If not removed promptly, these residues can affect the surface quality and subsequent performance of the stranded wire. Therefore, electrolytic citric acid solution effectively removes these residual lubricants in this step.

[0030] Surface passivation: Passivation refers to the formation of a dense, insoluble oxide film on the metal surface to improve its corrosion resistance. Passivation treatment using electrolytic citric acid solution can form a dense oxide film on the surface of stainless steel stranded wire, thereby improving its corrosion resistance and extending its service life.

[0031] S8. Take-up: The completed stainless steel stranded wire is fed from the previous process to the supply section of the winding equipment at a speed of 25-60m / min. The stranded wire begins to be wound on the winding equipment. After winding is completed, inspection and quality control are carried out to ensure that the wound stainless steel stranded wire meets the specifications and quality standards.

[0032] The following will describe the technical solution of the present invention clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Example 1: A low-relaxation prestressed special stainless steel strand for suspension cables and its production method, comprising the following steps:

[0034] S1. Twisting: Prepare multi-strand steel wires for twisting, including six outer edge wires and one center wire. The nominal diameter of the edge wires is 5.05mm, and the nominal diameter of the center wire is 5.25mm. In the twisting equipment, place the six outer edge wires counterclockwise on the outer edge of the center wire, and set the twist pitch to 14 times the nominal diameter, which is 212mm. Start the twisting equipment to begin twisting the steel wires at a twist pitch of 213mm and a speed of 5-60m / min for both the edge wires and the center wire. During the twisting process, the six outer edge wires are wound counterclockwise around the outer edge of the center wire, twisting synchronously to form a single strand. The twisted steel strand is then fed to the next step at a feed rate of 5-60m / min.

[0035] S2, First tensioning: The twisted strand structure is fed into a special tensioning treatment device, and the tension applied to the strand by the traction wheel is 70-130KN. This tensioning process continues until the second tensioning step.

[0036] S3. Stabilization treatment: The stainless steel strands are fed into a medium-frequency heating furnace, where the temperature is controlled at 300-700℃ and the holding time is 10-60s. The linear velocity of the entire medium-frequency tempering section is controlled at 5-60 / min.

[0037] S4. Water cooling: The steel strand is immersed in cooling water and rapidly cooled to below 50°C. The cooling time is controlled within 5-25 seconds, and the linear speed of the entire water cooling section is controlled at 5-60 m / min.

[0038] S5. Drying: The stranded wire enters the drying equipment via a conveyor belt. The drying air velocity is set at 15m / s, the drying temperature is controlled within the range of 50℃, and the drying time is set at 20-60s.

[0039] S6. Second tension: The traction wheel applies a tension of 120KN to the stranded wire, which further adjusts and improves the structure and performance of the stainless steel stranded wire.

[0040] S7. Surface treatment and passivation: The residual lubricant is removed by electrolyzing an acid solution, and the surface of the stranded wire is passivated.

[0041] S8. Take-up: The completed stainless steel stranded wire is fed to the winding equipment at a speed of 5-60m / min for winding. After winding, inspection and quality control are carried out.

[0042] Example 2: The rest is the same as Example 1, except for S3, stabilization treatment: temperature 350℃, linear velocity: 10m / min.

[0043] Example 3: The rest is the same as Example 1, except for S3, stabilization treatment: temperature 400℃, linear velocity: 10m / min.

[0044] Example 4: The rest is the same as Example 1, except for S3, stabilization treatment: temperature 450℃, linear velocity: 10m / min.

[0045] Example 5: The rest is the same as Example 1, except for S3, stabilization treatment: temperature 500℃, linear velocity: 10m / min.

[0046] Example 6: The rest is the same as Example 1, except for S3, stabilization treatment: temperature 350℃, linear velocity: 20m / min.

[0047] Example 7: The rest is the same as Example 3, except for S3, stabilization treatment: temperature 400℃, linear velocity: 20m / min.

[0048] Example 8: The rest is the same as Example 1, except for S3, stabilization treatment: temperature 450℃, linear velocity: 20m / min.

[0049] Example 9: The rest is the same as Example 1, except for S3, stabilization treatment: temperature 500℃, linear velocity: 20m / min.

[0050] Comparative Example 1: Steel strand made of commercially available high-strength carbon steel wire.

[0051] Comparative Example 2: Steel strand made of commercially available galvanized high-carbon steel wire.

[0052]

[0053]

[0054] Table 2

[0055] It should be noted that the corrosion resistance test of stainless steel stranded wire is conducted according to the method specified in the NSS neutral salt spray test of the national standard GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test".

[0056] As can be seen from the data in Table 2, the stainless steel strand produced by the present invention has significant advantages over the stainless steel strand produced by the prior art in terms of tensile strength, maximum elongation, stress relaxation resistance and corrosion resistance. In particular, the stainless steel strand produced in Example 6 has more obvious advantages. Therefore, the processing technology of the stainless steel strand in Example 6 is a preferred solution.

[0057] Through numerous experiments, the applicant discovered that the stainless steel strand produced using these steps yielded the best results. The physical properties of the prototype steel strand reached: tensile strength ≥1860MPa, maximum total elongation ≥3.5%, and stress relaxation ≤2.5%. This meets the standard of GB / T5224-2014 "Prestressed Steel Strands for Concrete Structures". The steel strand described in this invention, when applied to special stainless steel slings, can meet the requirements for sling use and possesses high resistance to stress corrosion, fatigue resistance, high temperature resistance, low relaxation, and high torsion.

[0058] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing steel strand for low-relaxation prestressed special stainless steel suspension cables, wherein the steel strand comprises one center wire and six edge wires, the six edge wires being arranged counterclockwise on the outer edge of the center wire, and they are synchronously wound within the same lay pitch range to complete one round of winding, forming a stranded structure. The nominal diameter of the center wire is in the range of 5.25±0.05mm, the nominal diameter of the edge wires is in the range of 5.05±0.05mm, and the nominal diameter after twisting is 15.24mm, with an allowable deviation range between 15.09 and 15.64mm; characterized in that... The production method includes the following steps: S1. Twisting: Six edge wires and one center wire are twisted together to form a strand; S2, First tensioning: The twisted stainless steel strands are tensioned for the first time; S3. Stabilization treatment: The stainless steel strands that have undergone the first tensioning treatment are then subjected to heat treatment. S4. Water cooling: Use a water cooling device to quickly cool the stainless steel stranded wire; S5. Drying: Use a drying device to dry the stainless steel stranded wire; S6, Second Tensioning: Perform a second tensioning process; S7. Surface treatment and passivation: The lubricant residue is removed by electrolysis of citric acid solution, and the surface of the stranded wire is passivated. S8. Winding: Used to wind the manufactured steel strand into a coil shape; During the first tensioning process in step S2, the traction pretensioning is 30-50% of the maximum force, and the tension of the traction wheel is 78-130KN; During the stabilization process in step S3, the tempering temperature range of the steel strand is 350-450℃, and the holding time is 20-120s. During the second tensioning process in step S6, the traction pretensioning is 50-65% of the maximum force, and the tension of the traction wheel is 130-169KN; The step S4 water cooling includes rapid cooling to below 50°C, with the cooling time controlled within 5 seconds. The drying step S5 includes setting the air velocity between 10m / s and 30m / s, the drying temperature between 100 and 150℃, the drying air velocity between 10m / s and 30m / s, and the drying time between 5 and 40 seconds.

2. The method for producing a low-relaxation prestressed special stainless steel cable strand according to claim 1, characterized in that, In step S1, the production line speed for the six edge yarns during the twisting process is 5-60 m / min, and the production line speed for the center yarn is 5-60 m / min.

3. The method for producing a low-relaxation prestressed special stainless steel cable strand according to claim 1, characterized in that, In step S1, the strand twisting process is set to 14 times the nominal diameter, i.e., 213 mm, with an allowable range of 205-230 mm.

4. The method for producing a low-relaxation prestressed special stainless steel cable strand according to claim 1, characterized in that, The wire release speed of the S1 twisting section is 10-60 m / min, the wire release speed of the S3 medium frequency tempering section is 10-60 m / min, the wire release speed of the S4 water cooling section is 10-60 m / min, and the wire take-up speed of the S7 section is 25-60 m / min.

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