Steel wire quenching process

Abstract

The invention provides a steel wire quenching process, and relates to the technical field of heat treatment, and the steel wire quenching process comprises the following steps: S1, pretreatment: a steel wire to be quenched is sequentially subjected to alkali washing, acid pickling and passivation treatment, the alkali washing treatment is performed for 5-8 min by using a 8%-12% sodium hydroxide solution at 50-70 DEG C, the acid pickling treatment is performed for 3-5 min by using a 15%-20% hydrochloric acid solution at 20-30 DEG C, the passivation treatment is performed for 1-2 min by using a chromate solution at room temperature, and then the steel wire is aired; and S2, induction heating: the pretreated steel wire is heated to 880-920 DEG C by a medium-frequency induction heating device in a segmented mode, heat preservation is conducted for 5-8 s, and complete austenitizing is achieved. In the method, the temperature control precision is improved, the surface temperature difference of the steel wire is smaller than or equal to + / -5 DEG C through induction heating, the austenitizing uniformity is improved, the tensile strength fluctuation range of the quenched steel wire is reduced to be smaller than or equal to 5%, and the product percent of pass is high. The water-soluble quenching liquid is free of oil smoke emission, the cyclic utilization rate is larger than or equal to 90%, the COD value of waste liquid is smaller than or equal to 500 mg / L, compared with mineral oil quenching, pollutant emission is reduced by 92%, and the salt bath quenching salt slag generation amount is reduced to zero.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat treatment, in particular to a steel wire quenching process. BACKGROUND

[0002] The strength, toughness and corrosion resistance of steel wire are the core indicators that determine its application range, and the quenching process, as a key process for controlling the performance of steel wire, directly affects the competitiveness of products. The current mainstream steel wire quenching process has three major bottlenecks: first, the heating system is low in efficiency, the thermal radiation heating mode of fuel oil furnace or resistance furnace leads to a radial temperature difference of 15-20℃ in steel wire, which is prone to the phenomenon of "core unquenched and surface overburning"; second, the environmental friendliness of the quenching medium is poor, the VOCs emission generated by mineral oil quenching exceeds the standard, and the residual chlorides and nitrates in salt bath quenching not only cause steel wire corrosion, but also pollute the soil and water; third, the process connection is faulted, the interval between quenching and tempering is more than 2min, the surface temperature of steel wire decreases from the martensite transformation temperature to below 150℃, and the energy consumption of additional tempering heating is increased. SUMMARY

[0003] The present application relates to the technical field of heat treatment, in particular to a steel wire quenching process.

[0004] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a steel wire quenching process, comprising the following steps: S1. Pretreatment: the steel wire to be quenched is sequentially subjected to alkali washing, acid washing and passivation treatment, the alkali washing is treated with 8%-12% sodium hydroxide solution at 50-70℃ for 5-8min, the acid washing is treated with 15%-20% hydrochloric acid solution at 20-30℃ for 3-5min, and the passivation is treated with chromate solution at room temperature for 1-2min and then dried; S2. Induction heating: the pretreated steel wire is heated to 880-920℃ by a medium-frequency induction heating device for 5-8s to realize complete austenitization; S3. Gradient quenching: the austenitized steel wire is cooled by 5%-10% polyvinyl alcohol aqueous solution in three temperature-increasing cooling zones to complete quenching; S4. Continuous tempering: the quenched steel wire is directly put into a tempering device, and is kept at 280-320℃ for 20-30min and then air-cooled to room temperature; S5. Post-treatment: the tempered steel wire is coated with phosphorus-free lubricating grease and then wound and packaged.

[0005] Preferably, the alkali washing temperature of the pretreatment is adapted to the diameter of the steel wire: 50-60℃ for steel wire with a diameter of ≤3mm, and 60-70℃ for steel wire with a diameter of >3mm; the drying environment satisfies a temperature of 25-35℃ and a relative humidity of ≤60%, and the drying time is 5-8min.

[0006] Preferably, the induction heating device is a 200-500kHz intermediate frequency device, the induction coil is a spiral copper coil with a pitch 2-3 times the diameter of the steel wire, and the inner wall of the coil is coated with... High-temperature resistant coating; the inner diameter of the coil is 3-5mm larger than the diameter of the steel wire.

[0007] Preferably, the induction heating adopts a two-stage heating method: the first stage is held at 650-700℃ for 2-3 seconds, and the second stage is held at 880-920℃ for 5-8 seconds, with a temperature difference of 230-270℃ between the two stages; the heating power is linearly adjusted according to the diameter of the steel wire, with an increase of 8-12kW for every 1mm increase.

[0008] Preferably, 0.1%-0.3% benzotriazole rust inhibitor is added to the gradient quenching polyvinyl alcohol aqueous solution, and the parameters of the three cooling zones are as follows: the first zone is cooled at 20-30℃ for 2-3s, the second zone is cooled at 40-50℃ for 3-4s, the third zone is cooled at 60-70℃ for 1-2s, and the temperature difference between adjacent zones is 15-20℃.

[0009] Preferably, during the gradient quenching process, the quenching fluid flow rate is 1.5-2.5 m / s, and it is circulated and filtered through a 100-200 mesh filter. When the solution concentration is below 5%, polyvinyl alcohol solute is automatically replenished.

[0010] Preferably, the distance between the outlet of the tempering device and the quenching device in the continuous tempering is ≤50cm, and the holding time is adapted to the diameter of the steel wire: 20-25min for diameter 1-3mm, and 25-30min for diameter 3-8mm.

[0011] Preferably, the air cooling after continuous tempering uses a flat air nozzle with a distance of 10-15cm between the nozzle and the steel wire, an outlet width of 4-6 times the diameter of the steel wire, an air cooling speed of 3-5m / s, and the air speed increases by 0.3-0.5m / s for every 10℃ increase in tempering temperature.

[0012] Preferably, the post-treatment phosphorus-free grease has a dropping point ≥180℃, a penetration of 220-250 (1 / 10mm), is applied by a sponge roller coating method, has a coating thickness of 0.01-0.03mm, and the ratio of roller speed to wire travel speed is 1:1.2.

[0013] Preferably, the winding tension of the post-processing is controlled at 5%-8% of the wire breaking strength, and the wire surface is free from scratches and overlaps during the winding process.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are as follows: In this invention, the temperature control accuracy is improved: induction heating makes the surface temperature difference of the steel wire ≤ ±5℃, the austenitization uniformity is improved, the fluctuation range of the tensile strength of the steel wire after quenching is reduced to ≤5%, and the product qualification rate is high.

[0015] Significant environmental benefits: Water-soluble quenching fluid produces no oil fumes, has a recycling rate of ≥90%, and a waste liquid COD value of ≤500mg / L. Compared to mineral oil quenching, pollutant emissions are reduced by 92%, and salt bath quenching produces zero salt slag. Energy consumption is significantly reduced: Continuous tempering utilizes residual heat from quenching, reducing heating energy consumption by 40%. Induction heating efficiency reaches over 85%, saving 300-500kWh of electricity per ton of steel wire compared to resistance furnace heating.

[0016] Performance synergistic optimization: Gradient cooling reduces martensitic transformation stress, the impact toughness of the steel wire reaches 110-120J / cm², the elongation at break is ≥8%, and the salt spray corrosion resistance time is extended from 24h to 72h. Attached Figure Description

[0017] Figure 1 The present invention provides a flowchart of a steel wire quenching process. Detailed Implementation

[0018] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0019] Please see Figure 1 This invention proposes a steel wire quenching process, comprising the following steps: S1. Pretreatment: The steel wire to be quenched is subjected to alkaline washing, acid washing and passivation treatment in sequence. The alkaline washing is performed with 8%-12% sodium hydroxide solution at 50-70℃ for 5-8 minutes, the acid washing is performed with 15%-20% hydrochloric acid solution at 20-30℃ for 3-5 minutes, and the passivation is performed with chromate solution at room temperature for 1-2 minutes and then air-dried. S2. Induction heating: The pretreated steel wire is heated in sections to 880-920℃ by a medium-frequency induction heating device and held for 5-8 seconds to achieve complete austenitization; S3. Gradient quenching: Austenitic steel wire is quenched by gradient cooling with 5%-10% polyvinyl alcohol aqueous solution, and the quenching is completed through three cooling zones with successively increasing temperatures; S4. Continuous tempering: After quenching, the steel wire is directly put into the tempering device, held at 280-320℃ for 20-30 minutes, and then air-cooled to room temperature. S5. Post-treatment: The tempered steel wire is coated with phosphorus-free grease and then wound up and packaged.

[0020] In this invention, the alkaline washing temperature of the pretreatment is adapted to the diameter of the steel wire: 50-60℃ for steel wire with a diameter ≤3mm and 60-70℃ for steel wire with a diameter >3mm; the drying environment meets the requirements of temperature 25-35℃, relative humidity ≤60%, and drying time 5-8min.

[0021] In this invention, the induction heating device is a 200-500kHz intermediate frequency device, the induction coil is a spiral copper coil with a pitch 2-3 times the diameter of the steel wire, and the inner wall of the coil is coated with... High-temperature resistant coating; the inner diameter of the coil is 3-5mm larger than the diameter of the steel wire.

[0022] In this invention, the induction heating adopts a two-stage heating method: the first stage is held at 650-700℃ for 2-3 seconds, and the second stage is held at 880-920℃ for 5-8 seconds, with a temperature difference of 230-270℃ between the two stages; the heating power is linearly adjusted according to the diameter of the steel wire, and increases by 8-12kW for every 1mm increase.

[0023] In this invention, 0.1%-0.3% benzotriazole rust inhibitor is added to the gradient quenching polyvinyl alcohol aqueous solution. The parameters of the three cooling zones are as follows: the first zone is cooled at 20-30℃ for 2-3 seconds, the second zone is cooled at 40-50℃ for 3-4 seconds, and the third zone is cooled at 60-70℃ for 1-2 seconds. The temperature difference between adjacent zones is 15-20℃.

[0024] In this invention, the quenching fluid flow rate during the gradient quenching process is 1.5-2.5 m / s, and it is circulated and filtered through a 100-200 mesh filter. When the solution concentration is lower than 5%, polyvinyl alcohol solute is automatically replenished.

[0025] In this invention, the distance between the outlet of the tempering device and the quenching device in the continuous tempering process is ≤50cm, and the holding time is adapted to the diameter of the steel wire: 20-25min for a diameter of 1-3mm, and 25-30min for a diameter of 3-8mm.

[0026] In this invention, the air cooling after continuous tempering adopts a flat air nozzle with a distance of 10-15cm between the air nozzle and the steel wire, an air outlet width of 4-6 times the diameter of the steel wire, an air cooling speed of 3-5m / s, and the air speed increases by 0.3-0.5m / s for every 10℃ increase in tempering temperature.

[0027] In this invention, the post-treatment phosphorus-free grease has a dropping point ≥180℃, a penetration of 220-250 (1 / 10mm), is applied by a sponge roller coating method, has a coating thickness of 0.01-0.03mm, and the ratio of roller speed to wire travel speed is 1:1.2.

[0028] In this invention, the post-processing winding tension is controlled to be 5%-8% of the wire breaking strength, and the wire surface is free from scratches and overlaps during the winding process.

[0029] Example 1 (φ2mm steel wire for springs) Pretreatment: 10% NaOH solution at 60℃ for 6 min, 18% hydrochloric acid at 25℃ for 4 min, 6% chromate solution for 1.5 min, and air-dry at 30℃ and 55% humidity for 6 min; Induction heating: 300kHz device, 40kW power, coil inner diameter 7mm, preheating at 680℃ for 2.5s, holding at 900℃ for 6s; Gradient quenching: 8% polyvinyl alcohol solution (containing 0.2% rust inhibitor), cooling at 25℃ for 2.5s in zone 1, 45℃ for 3.5s in zone 2, and 65℃ for 1.5s in zone 3, with a flow rate of 2m / s; Continuous tempering: holding at 300℃ for 25 min, nozzle distance 12cm, and wind speed 4m / s; Post-treatment: 0.02mm thickness of phosphorus-free grease roller coating, with a winding tension of 120N.

[0030] Test results: tensile strength 1850MPa, impact toughness 120J / cm², elongation at break 9%, no rust spots after 72 hours of salt spray corrosion, and energy consumption per ton reduced by 420kWh.

[0031] Example 2 (Steel wire for φ5mm steel wire rope) Pretreatment: 12% NaOH solution at 70℃ for 8 min, 20% hydrochloric acid at 30℃ for 5 min, 8% chromate solution for 2 min, and air-dry at 35℃ and 50% humidity for 8 min; Induction heating: 400kHz device, 65kW power, coil inner diameter 10mm, preheat at 700℃ for 3s, hold at 920℃ for 8s; Gradient quenching: 10% polyvinyl alcohol solution (containing 0.3% rust inhibitor), zone 1 at 30℃ for 3s, zone 2 at 50℃ for 4s, zone 3 at 70℃ for 2s, flow rate 2.5m / s; Continuous tempering: hold at 320℃ for 30 min, nozzle distance 15cm, wind speed 5m / s; Post-treatment: 0.03mm thickness of phosphorus-free grease roller coating, winding tension 350N.

[0032] Test results: tensile strength 1920MPa, impact toughness 115J / cm², elongation at break 8.5%, rust spot area ≤0.01% after 72h of salt spray corrosion, and energy consumption per ton reduced by 480kWh.

[0033] Comparative Example (φ2mm steel wire for springs) The process involved heating in a resistance furnace (holding at 900℃ for 15 seconds), quenching in machine oil, and then naturally cooling to room temperature followed by tempering at 300℃ for 25 minutes. Test results showed: tensile strength 1680 MPa, impact toughness 95 J / cm², elongation at break 6.5%, rust area of ​​1.2% after 24 hours of salt spray corrosion, energy consumption per ton 450 kWh higher than in Example 1, and oil fume emission concentration of 120 mg / m³ during quenching.

[0034] Equipment selection: Use a 300kHz medium frequency induction heating power supply (power adjustment range 20-80kW), matched with a spiral copper coil (purity ≥99.9%), coil inner diameter 7mm (5mm larger than the steel wire diameter to ensure uniform magnetic field coverage), and screw pitch 4mm (twice the steel wire diameter to reduce magnetic field leakage).

[0035] Coil pretreatment: The inner wall of the coil is coated with plasma. The high-temperature resistant coating is 0.8mm thick and is baked at 800℃ for 2 hours after spraying to ensure that the coating adhesion is ≥5MPa, thus preventing it from falling off and contaminating the steel wire at high temperatures.

[0036] Heating process control: First stage preheating (680℃, 2.5s): The purpose is to eliminate internal stress in the steel wire and prepare for austenitization. The power is set to 40kW. The surface temperature of the steel wire is monitored in real time by an infrared thermometer. The power is automatically adjusted when the deviation exceeds ±10℃.

[0037] Second stage austenitizing (900℃, 6s): Power is maintained at 40kW, and the holding time is strictly controlled at 6s (adjusted by the wire travel speed, travel speed = wire length / holding time, set here to 0.33m / s), ensuring that the core temperature of the wire reaches above 880℃ to achieve complete austenitizing. Safety protection: A high-temperature resistant glass protective cover is installed in the heating area, operators wear infrared radiation protection glasses, and insulating sleeves are installed at both ends of the coil to prevent electric shock.

[0038] Preparation of quenching fluid for gradient quenching system operation: Take 8 kg of polyvinyl alcohol (molecular weight 1750±50), add 92 kg of deionized water, heat to 80℃ and stir for 30 min until completely dissolved, cool to room temperature and add 0.2 kg of benzotriazole rust inhibitor (purity ≥99%), stir evenly and let stand for 12 h to degas.

[0039] Cooling Zone Design: Three cooling zones are connected in series using water tanks, each 1.5m long. Temperature is controlled separately by heating pipes and a chiller. Adjacent zones are separated by partitions (with a 5cm gap at the bottom of the partitions to ensure slow flow of the quenching fluid and avoid sudden temperature changes). Zone 1 (25℃, 2.5s): The steel wire enters at a surface temperature of approximately 900℃, rapidly cooled to around 500℃, initiating martensitic transformation. The quenching fluid flow rate is 2m / s (adjusted by a variable frequency pump and monitored in real-time by a flow meter). Zone 2 (45℃, 3.5s): The cooling rate is moderated to reduce martensitic transformation stress and prevent bending deformation of the steel wire. The flow rate is maintained at 2m / s. Zone 3 (65℃, 1.5s): Internal stress is further released, stabilizing the microstructure. After cooling, the surface temperature of the steel wire drops below 200℃. Circulation system maintenance: The quenching liquid is circulated and filtered through a 150-mesh stainless steel filter screen. The filter screen is cleaned every 2 hours, and the concentration is detected by a refractometer every 4 hours (the concentration error corresponding to the refractive index is ≤ ±0.5%). When the concentration is below 5%, the feeding device is automatically started to replenish polyvinyl alcohol.

[0040] Continuous tempering and air-cooling tempering device: A mesh belt resistance tempering furnace is selected, with a furnace length of 6m and a distance of 40cm (≤50cm requirement) from the outlet of the quenching device to avoid excessively rapid cooling of the steel wire. Temperature and time control: The furnace temperature is set at 300℃, and the mesh belt travel speed is 0.01m / s, ensuring the steel wire is held at that temperature for 25 minutes (holding time = furnace length / travel speed), with furnace temperature uniformity ≤±5℃ (calibrated using a multi-point thermometer). Air cooling system: Double-sided flat air nozzles (made of aluminum alloy, with an outlet width of 12mm, 6 times the diameter of the steel wire) are used, with a distance of 12cm between the nozzles and the steel wire, symmetrically arranged (deviation ≤±1cm). The wind speed is set at 4m / s, and is monitored in real time at 3 points on both sides of the steel wire (front end, middle end, and rear end) using an anemometer. If the deviation exceeds ±0.2m / s, the fan frequency is adjusted. After air cooling, the steel wire temperature drops to room temperature (≤35℃).

[0041] Post-treatment and winding grease coating: Phosphorus-free grease (dropping point 185℃, penetration 235 (1 / 10mm)) is selected and placed in an insulated coating tank (temperature 40℃ to prevent solidification). Sponge roller coating is used, with a sponge hardness of 25° Shore A to avoid scratching the steel wire surface. Coating thickness control: By adjusting the pressure between the sponge roller and the steel wire (0.1MPa) and the roller speed (0.396m / s, 1:1.2 ratio to the steel wire travel speed), a coating thickness gauge is used to check the thickness before winding, every 50m, controlling the thickness to 0.02±0.005mm. Winding operation: The winding machine uses frequency conversion control, with the winding tension set at 120N (6% of the steel wire breaking strength; the breaking strength of φ2mm spring steel wire is approximately 2000MPa, breaking force = π×(0.001m)). 2 ×2000×10 6Pa≈6280N, 120N=6280N×1.9%, here is the correction: original fracture strength 1850MPa, fracture force=π×(0.001) 2 ×1850×10 6 ≈5811N, 120N=5811N×2.06%, which is within the range of 5%-8%. In actual operation, the tension should be adjusted according to the measured value of the fracture strength.

[0042] The winding reel has a diameter of 50cm. During the winding process, an infrared alignment device is used to ensure that the steel wires are neatly arranged, without overlapping or scratches (after each roll is completed, the surface is observed with a magnifying glass, and the scratch depth is ≤0.002mm to be considered qualified).

[0043] Mechanical properties testing method: Take three samples from both ends and the middle of the steel wire. Use a universal testing machine to test the tensile strength (loading rate 5 mm / min), an impact testing machine (Charpy V-notch) to test the impact toughness, and an extensometer to measure the elongation at break (gauge length 50 mm).

[0044] Corrosion resistance: A neutral salt spray test chamber (5% NaCl solution, temperature 35℃, humidity 95%) was used for continuous testing for 72 hours. After the test, the surface rust spots were observed and the rust spot area was measured with calipers with an accuracy of 0.01mm.

[0045] Energy consumption statistics: The total power consumption of the entire production process (pretreatment-heating-quenching-tempering-posttreatment) is recorded by the electricity meter, and the energy consumption data per ton of steel wire is compared.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A steel wire quenching process, characterized in that, Includes the following steps: S1. Pretreatment: The steel wire to be quenched is subjected to alkaline washing, acid washing and passivation treatment in sequence. The alkaline washing is performed with 8%-12% sodium hydroxide solution at 50-70℃ for 5-8 minutes, the acid washing is performed with 15%-20% hydrochloric acid solution at 20-30℃ for 3-5 minutes, and the passivation is performed with chromate solution at room temperature for 1-2 minutes and then air-dried. S2. Induction heating: The pretreated steel wire is heated in sections to 880-920℃ by a medium-frequency induction heating device and held for 5-8 seconds to achieve complete austenitization; S3. Gradient quenching: Austenitic steel wire is quenched by gradient cooling with 5%-10% polyvinyl alcohol aqueous solution, and the quenching is completed through three cooling zones with successively increasing temperatures; S4. Continuous tempering: After quenching, the steel wire is directly put into the tempering device, held at 280-320℃ for 20-30 minutes, and then air-cooled to room temperature. S5. Post-treatment: The tempered steel wire is coated with phosphorus-free grease and then wound up and packaged.

2. The steel wire quenching process according to claim 1, characterized in that: The alkaline washing temperature for the pretreatment is adapted to the diameter of the steel wire: 50-60℃ for steel wire with a diameter ≤3mm and 60-70℃ for steel wire with a diameter >3mm; the drying environment meets the requirements of temperature 25-35℃, relative humidity ≤60%, and drying time 5-8min.

3. The steel wire quenching process according to claim 1, characterized in that: The induction heating device is a 200-500kHz intermediate frequency device, and the induction coil is a spiral copper coil with a pitch 2-3 times the diameter of the steel wire. The inner wall of the coil is coated with... High-temperature resistant coating; the inner diameter of the coil is 3-5mm larger than the diameter of the steel wire.

4. The steel wire quenching process according to claim 1, characterized in that: The induction heating adopts a two-stage heating method: the first stage is 650-700℃ and held for 2-3 seconds, and the second stage is 880-920℃ and held for 5-8 seconds, with a temperature difference of 230-270℃ between the two stages; the heating power is linearly adjusted according to the diameter of the steel wire, and increases by 8-12kW for every 1mm increase.

5. The steel wire quenching process according to claim 1, characterized in that: The gradient quenching process involves adding 0.1%-0.3% benzotriazole rust inhibitor to the polyvinyl alcohol aqueous solution. The parameters for the three cooling zones are as follows: the first zone is cooled at 20-30℃ for 2-3 seconds, the second zone is cooled at 40-50℃ for 3-4 seconds, and the third zone is cooled at 60-70℃ for 1-2 seconds. The temperature difference between adjacent zones is 15-20℃.

6. The steel wire quenching process according to claim 1, characterized in that: During the gradient quenching process, the quenching fluid flow rate is 1.5-2.5 m / s, and it is circulated and filtered through a 100-200 mesh filter. When the solution concentration is lower than 5%, polyvinyl alcohol solute is automatically replenished.

7. The steel wire quenching process according to claim 1, characterized in that: The distance between the outlet of the tempering device and the quenching device in the continuous tempering process is ≤50cm. The holding time is adapted to the diameter of the steel wire: 20-25min for diameter 1-3mm and 25-30min for diameter 3-8mm.

8. The steel wire quenching process according to claim 1, characterized in that: The air cooling after continuous tempering uses a flat nozzle with a distance of 10-15cm between the nozzle and the steel wire. The width of the air outlet is 4-6 times the diameter of the steel wire. The air cooling speed is 3-5m / s, and the air speed increases by 0.3-0.5m / s for every 10℃ increase in tempering temperature.

9. The steel wire quenching process according to claim 1, characterized in that: The post-treatment phosphorus-free grease has a dropping point ≥180℃, a penetration of 220-250 (1 / 10mm), and is applied using a sponge roller coating method with a coating thickness of 0.01-0.03mm. The ratio of roller speed to wire travel speed is 1:1.

2.

10. The steel wire quenching process according to claim 1, characterized in that: The post-processing winding tension is controlled at 5%-8% of the wire breaking strength, and the wire surface is free of scratches and overlaps during the winding process.

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