A processing method of super-thin oxide film nickel-titanium wire

Abstract

The application relates to the technical field of metal materials and preparation technology thereof, in particular to a processing method of nickel-titanium wire material with an ultrathin oxide film, which has the technical scheme as follows: step 1: polishing the surface of the initial wire material to remove the surface oxide film; step 2: placing the wire material into an annealing furnace to perform atmosphere protection annealing; step 3: cold drawing the wire material, and the deformation amount of the wire material after the drawing is 30%-70%; judging whether the diameter d of the wire material is equal to the diameter D of the finished wire material, if the diameter d of the wire material is greater than the diameter D of the finished wire material, repeatedly performing step 2 and step 3, and if the diameter d of the wire material is equal to the diameter D of the finished wire material, entering step 4; step 4: placing the wire material into an annealing furnace to perform atmosphere protection annealing, so that the nickel-titanium wire material has a relatively thin oxide film, the surface smoothness is maintained, and the nickel-titanium wire material has good biocompatibility.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of metal materials and preparation thereof, and particularly relates to a processing method of nickel-titanium wire with an ultrathin oxide film. BACKGROUND

[0002] The nickel-titanium alloy has been widely applied in the field of biomedical materials due to its unique and excellent performance, such as a heart stent, a bone plate, a bone nail, and particularly an orthodontic wire made of the nickel-titanium alloy wire.

[0003] The processing method of the nickel-titanium wire in the related art mainly includes hot drawing and cold drawing; the process of the hot drawing mode comprises initial wire peeling, oxidation, fixed mold hot drawing (graphite lubrication), air annealing and acid-alkali washing, and the process of the traditional cold drawing mode specifically comprises initial wire peeling, oxidation, wire surface coating of a lubricant, fixed mold cold drawing, air annealing and alkali-acid washing; the purpose of the oxidation process is to make the wire surface obtain an oxide film to realize the lubrication effect on the subsequent drawing process.

[0004] The above two traditional processing methods of the nickel-titanium wire will generate a relatively thick oxide film on the wire surface after air annealing, and the oxide film that is too thick will result in poor performance of products such as the orthodontic wire after subsequent processes such as film plating; although the acid-alkali washing can thin the oxide film thickness on the surface of the finished wire, it will inevitably cause the surface roughness of the finished wire to be too large, and further cause the surface of the finished wire to fail to maintain good biocompatibility. SUMMARY

[0005] In order to make the nickel-titanium wire surface have a relatively thin oxide film, maintain the surface smoothness and keep the nickel-titanium wire good biocompatibility, the application provides a processing method of nickel-titanium wire with an ultrathin oxide film.

[0006] The processing method of nickel-titanium wire with an ultrathin oxide film provided by the application adopts the following technical scheme:

[0007] The processing method of nickel-titanium wire with an ultrathin oxide film comprises the following steps: step 1, polishing the surface of the initial wire to remove the surface oxide film; step 2, placing the wire into an annealing furnace for atmosphere protection annealing; step 3, cold drawing the wire, and the deformation amount of the wire after the drawing is 30% to 70%; determining whether the diameter d of the wire is equal to the diameter D of the finished wire, if the diameter d of the wire is greater than the diameter D of the finished wire, repeatedly performing step 2 and step 3 in sequence, and if the diameter d of the wire is equal to the diameter D of the finished wire, ending step 2 and step 3.

[0008] By adopting the technical scheme, the oxide film on the surface of the initial material is removed by polishing in step 1, which is beneficial to obtaining a smooth surface of the finished wire and an ultra-thin oxide film; the wire is annealed in step 2, the hardness of the wire is reduced to improve the plasticity of the wire, and the atmosphere protection annealing can greatly reduce the thickness of the oxide film on the surface of the finished wire; in addition, a thin oxide film is inevitably generated on the surface of the wire during the annealing process to replace the oxide film obtained in the oxidation process to play a role in drawing lubrication; the wire is annealed and cold-drawn for multiple times to prevent the wire from being broken due to excessive deformation; in this way, the nickel-titanium wire has a thin oxide film on the surface, and the nickel-titanium wire maintains good biocompatibility while maintaining surface smoothness.

[0009] Optionally, in step 3, the wire to be entered into the cold-drawing die is sprayed with a refrigerated lubricant, so that the cold-drawing environment temperature of the wire is-50℃ to 0℃.

[0010] By adopting the technical scheme, the lubricant plays an essential lubricating role in the cold-drawing process, and the refrigerated lubricant makes the cold-drawing temperature of the wire be at a low value, and the inside of the wire is in a martensite phase state; the nickel-titanium alloy martensite is softer and has stronger plasticity, which is beneficial to processing the finished wire with a smaller diameter; the deformation amount allowed by each cold-drawing can be increased, and the length of the wire obtained by each cold-drawing is increased; under the condition that the volume of the oxide film is constant, the thickness of the oxide film on the surface of the wire after cold-drawing is smaller, which further plays a role in reducing the thickness of the oxide film on the surface of the finished wire.

[0011] Optionally, in step 3, the wire is blown dry and the surface of the wire is wiped after cold-drawing.

[0012] By adopting the technical scheme, the surface of the wire subjected to pre-annealing is cleaner, which is beneficial to improving the surface quality of the wire after annealing and reducing the thickness of the oxide film on the surface of the wire after annealing.

[0013] Optionally, in step 3, a wire wiping device is used to blow dry and wipe the surface of the wire; the wire wiping device comprises a gas jet nozzle for blowing dry and a cotton yarn for wiping; the wire can pass through the gas jet nozzle and the cotton yarn in sequence.

[0014] Optionally, after steps 2 and 3 are completed, step 4 is set, and step 4 is: placing the wire into an annealing furnace for atmosphere protection annealing.

[0015] By adopting the technical scheme, the hardness of the finished wire is reduced to play a role in straightening; the wire with low hardness is convenient for subsequent processing of orthodontic wires and the like.

[0016] Optionally, the annealing furnace comprises a furnace body and a furnace tube arranged inside the furnace body, the furnace tube has a protective gas inlet outside the annealing furnace, and the wire rod can pass into the furnace tube and pass out from inside the furnace tube.

[0017] By adopting the technical scheme, the wire rod passes into the furnace tube from one end and passes out from the other end, the protective gas is introduced into the furnace tube through the protective gas inlet, and the on-line atmosphere annealing of the wire rod is realized.

[0018] Optionally, the two ends of the furnace body are provided with gas collection covers, the gas collection covers are communicated with gas transportation pipelines, and the two ends of the furnace tube have wire rod inlets and wire rod outlets through which the wire rod passes, and the wire rod inlets and the wire rod outlets are introduced into the corresponding gas collection covers.

[0019] By adopting the technical scheme, waste gas or toxic gas is inevitably generated during the annealing process, the waste gas is collected through the gas collection covers and the gas transportation pipelines for subsequent unified treatment, and the environmental protection performance of the annealing process is improved.

[0020] Optionally, the protective gas used in the atmosphere annealing is nitrogen, argon or acetaldehyde.

[0021] By adopting the technical scheme, the oxidation of the surface of the wire rod during the annealing process is slowed down, and the acetaldehyde can also play a certain reduction role.

[0022] Optionally, in step 2, the annealing temperature of the atmosphere annealing is 650-750 DEG C, and the annealing time is 30 s-1 min.

[0023] Optionally, in step 4, the annealing temperature of the atmosphere annealing is 400-600 DEG C, and the annealing time is 30 s-1 min.

[0024] In summary, the initial wire rod surface is polished, and the whole annealing process adopts atmosphere annealing, so that the nickel-titanium wire rod surface has a thin oxide film, the surface smoothness is maintained, and the good biocompatibility of the nickel-titanium wire rod is maintained; in addition, the wire rod to be introduced into the cold drawing die is sprayed with a refrigerated lubricant, so that the inside of the wire rod is in a martensite phase state, which is beneficial to the processing of a finished wire rod with a smaller diameter, and the deformation amount allowed by each cold drawing can be increased, and under the condition that the volume of the oxide film is certain, the thickness of the oxide film on the surface of the wire rod after cold drawing is smaller, which further plays a role in thinning the oxide film on the surface of the finished wire rod. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a flowchart of the processing method of the nickel-titanium wire rod with an ultra-thin oxide film in the present application;

[0026] Figure 2is a structural schematic diagram of the annealing furnace in the present application, and the arrow direction in the figure is the flow direction of the protective gas;

[0027] Figure 3 is a structural schematic diagram of the wire wiping device in the present application;

[0028] Figure 4 is a surface scanning electron microscope image of the finished wire in the comparative example;

[0029] Figure 5 is a surface scanning electron microscope image of the finished wire in the embodiment 1;

[0030] Figure 6 is a surface scanning electron microscope image of the finished wire in the embodiment 2.

[0031] In the figure, 1, air jet nozzle; 2, rack; 3, guide wheel; 4, cotton yarn; 5, furnace body; 6, furnace tube; 7, protective gas inlet; 8, wire feeding wheel; 9, wire collecting wheel; 10, gas collecting cover; 11, gas transportation pipeline; 12, wire inlet; 13, wire outlet. DETAILED DESCRIPTION

[0032] In the description of the present application, it should be noted that the terms "inlet", "outlet", "cold", "horizontal" and the like are all based on the relative relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the processes or modules referred to must have a specific orientation, state and operation, and therefore cannot be understood as a limitation on the present application.

[0033] The present application will be further described in detail below in combination with the drawings.

[0034] It is now defined that the wire before all the processing procedures involved in the present application are performed is the initial wire, and the wire finally expected to be obtained is the finished wire, the diameter of the finished wire meets the design size D, and the real-time size of the wire during the processing process is d.

[0035] Referring to Figure 1 The present application provides a processing method of a nickel-titanium wire with an ultra-thin oxide film, comprising the following steps: step 1: polishing, such as mechanical polishing, the initial wire to remove the relatively thick and uneven oxide film on the surface of the initial wire; the oxide film on the surface of the initial wire is too thick and has poor smoothness, and by mechanically polishing the initial wire, it is beneficial to reduce the thickness of the oxide film on the surface of the finished wire and make it obtain an oxide film with uniform texture and higher smoothness.

[0036] Step 2: on-line annealing of the mechanically polished wire through an annealing furnace, the annealing is atmosphere protection annealing, the protection gas is nitrogen, argon or acetaldehyde, the annealing temperature is controlled at 650-750℃ and the annealing time is 30s-1min. The purpose of this step is to reduce the hardness and strength of the wire, so that the plasticity of the wire is improved to meet the subsequent drawing process requirements. For the initial wire, the surface after mechanical polishing in step 1 lacks the corresponding oxide film, and this time the atmosphere protection annealing can still make the wire surface obtain a thin oxide film to play a surface lubrication role for the subsequent drawing process.

[0037] And the atmosphere protection annealing prevents the wire from contacting with a large amount of air during heating to cause the surface to produce an excessively thick oxide film, which greatly reduces the oxide film thickness of the finished wire surface compared with air annealing, and especially the acetaldehyde has reducing property, which is beneficial to make the wire surface after annealing obtain a thin oxide film.

[0038] Referring to Figure 2 , specifically, the annealing furnace includes a furnace body 5 with two open ends, a pay-off reel 8 and a take-up reel 9 respectively arranged outside the two open ends of the furnace body 5, and a furnace tube 6 fixed inside the furnace body 5. The furnace tube 6 is a three-way pipe, and the three ports are respectively a protection gas inlet 7 located outside the furnace body 5, a wire inlet 12 arranged close to the pay-off reel 8, and a wire outlet 13 arranged close to the take-up reel 9. When the wire needs to be annealed, one end of the wire wound on the pay-off reel 8 is fixed on the take-up reel 9, and the wire passes through the wire inlet 12 and the wire outlet 13 in turn. The pay-off reel 8 and the take-up reel 9 are rotated to make the wire run inside the furnace tube 6. In this process, the protection gas is transported into the furnace tube 6 through the protection gas inlet 7, and the furnace tube 6 is heated by the furnace body 5, so that the atmosphere protection annealing of the wire is realized.

[0039] Inevitably, waste gas or toxic gas is generated inside the furnace tube 6 during the annealing process. Therefore, a gas collecting hood 10 is arranged at each end of the furnace body 5, the wire inlet 12 and the wire outlet 13 are respectively connected to the corresponding gas collecting hood 10, and the two gas collecting hoods 10 are connected to a gas transportation pipeline 11. The waste gas or toxic gas generated inside the furnace tube 6 can be uniformly treated through the gas collecting hoods 10 and the gas transportation pipeline 11, thereby reducing the pollution to the atmosphere during the annealing process.

[0040] Step 3: cold drawing of the wire. The deformation amount of the wire after this cold drawing relative to the wire before this cold drawing is 30%-70%, preferably more than 40%. Further explanation: assuming that the diameter of the wire before this cold drawing is d1, and it has been assumed that the diameter of the wire after this cold drawing is d, the above deformation amount refers to the deformation amount of the radial cross-sectional area of the wire, that is,

[0041] After cold drawing, it is determined whether the diameter d of the wire at this time is equal to the diameter D of the finished wire. If the diameter d of the wire is greater than the diameter D of the finished wire, steps 2 and 3 are repeated in turn. If the diameter d of the wire is equal to the diameter D of the finished wire, steps 2 and 3 are ended and step 4 is entered.

[0042] In addition, each cold drawing is performed using a combined die, and the forming diameters of the plurality of cold drawing dies in the combined die gradually decrease in turn. The wire continuously and in turn passes through these cold drawing dies to obtain the diameter d. In addition, a nozzle capable of spraying a lubricant toward the wire is arranged at the feeding port side of each cold drawing die to play a lubricating role in cold drawing. In addition, the lubricant is refrigerated before being sprayed, so that the wire obtains a cold drawing environment in the temperature range of -50°C to 0°C during the process of passing through each cold drawing die.

[0043] The lower cold drawing environment temperature can make the inside of the wire in a martensite phase state, and the martensite phase of the nickel-titanium alloy has stronger plasticity. This makes the wire not easy to break during cold drawing in each step 3, and the wire can obtain a larger deformation to improve work efficiency. In addition, it can be understood that the volume of the oxide film on the surface of the wire after annealing in step 2 is certain, and the wire after cold drawing in step 3 can obtain a longer length and a smaller diameter. The oxide film is inevitably stretched to a greater extent, and the thickness of the oxide film can be further thinned to a greater extent. In this way, the finished wire after multiple annealing and cold drawing in the present application can obtain a smaller diameter and a surface with a thinner and more uniform oxide film compared to related art.

[0044] Referring to Figure 3 In order to ensure that the surface of the wire to be annealed each time is clean, the surface of the wire is dried and wiped after the wire completes this cold drawing in step 2 to remove impurities and residual lubricant on the surface of the wire. Specifically, a wire wiping device is arranged at the end of the discharge port of the combined die, and the wire wiping device is arranged before the process of winding the wire after cold drawing is completed. The wire wiping device includes a rack 2, a gas jet nozzle 1 arranged on the rack 2, a guide wheel 3 arranged on one side of the rack 2, and a cotton yarn 4 arranged on the rack 2.

[0045] The wire passes through the guide wheel 3, the gas jet nozzle 1, and the cotton yarn 4 in turn. The gas jet nozzle 1 can spray high-pressure gas to the wire to dry or blow off the residual lubricant on the surface of the wire. Finally, the wire is wiped by the cotton yarn 4 to obtain a clean surface, which is beneficial to improve the surface quality of the wire after annealing and further reduce the thickness of the oxide film on the surface of the wire after annealing.

[0046] Step 4: Put the wire into the annealing furnace for the last atmosphere protection annealing, i.e. the finished product annealing, to reduce the hardness of the finished product wire to play the role of straightening and facilitate subsequent processing of orthodontic wire, etc. The protective gas is nitrogen, argon or acetaldehyde, the annealing temperature is controlled at 400-600°C and the annealing time is 30s-1min, and the annealing temperature is preferably 500-550°C.

[0047] Two examples and one comparative example will be described below.

[0048] Comparative Example

[0049] The comparative example corresponds to the processing of the finished product wire in the related art. The size of the finished product wire in the comparative example is φ0.50mm. The initial wire is coated with a lubricant and then directly processed to the finished product size of φ0.50mm by cold drawing process. Subsequently, the finished product wire is subjected to atmospheric annealing, acid and alkali washing and mechanical polishing to have a relatively thin oxide film.

[0050] Reference Figure 4 After experimental measurement, the surface roughness of the finished product wire in the comparative example is 0.2μm. It is not difficult to find that there are many black areas on the surface of the wire by observing the image of the surface of the finished product wire in the comparative example, which further reflects that the surface finish of the finished product wire is poor.

[0051] Example 1

[0052] The size D of the finished product wire in this example is φ0.47mm, and the initial wire is a black wire with a size of φ0.81mm.

[0053] The black wire with a size of φ0.81mm is subjected to mechanical polishing, and then subjected to the first online annealing. The annealing temperature is 700°C, the speed of the wire collecting and releasing is 8.1m / min, and the furnace tube 6 is filled with argon during the annealing process. After the annealing is completed, the wire is subjected to low temperature cold drawing at-10°C. The sizes of the cold drawing dies in the diamond drawing die combination used during the drawing process are 0.75mm, 0.69mm and 0.62mm in sequence. The deformation after the cold drawing is 41.41%. The wire is dried and the surface is wiped. It should be noted that the annealing time of the wire can be indirectly derived from the wire collecting and releasing speed under the premise that the length of the furnace tube 6 is constant. The larger the diameter of the wire, the slower the wire collecting and releasing speed, i.e. the longer the annealing time, but the annealing time is ensured to be 30s-1min.

[0054] The φ0.62 mm wire is subjected to a second on-line annealing at 700 °C and a wire feeding and withdrawing speed of 10.6 m / min, and the annealing is also carried out in an argon atmosphere. After the annealing, the wire is subjected to a low-temperature cold drawing at -10 °C, and the sizes of the cold drawing dies in the diamond drawing assembly used in the drawing process are 0.54 mm, 0.47 mm in sequence. The deformation after the cold drawing is 42.53%, and the diameter d of the wire at this time is equal to the diameter D of the finished wire, i.e. 0.47 mm. The wire is dried and the surface of the wire is wiped.

[0055] Finally, the wire is subjected to a finished annealing at 520 °C and a wire feeding and withdrawing speed of 10 m / min, and the annealing is also carried out in an argon atmosphere. Finally, the φ0.47 mm nickel-titanium bright wire is obtained.

[0056] Reference Figure 5 After the test measurement, it is found that the surface roughness of the finished wire in Example 1 is 0.1 μm. By observing the images of the finished wires in the example and the comparative example, it is not difficult to find that the black area of the wire surface in the example is less and the surface finish is higher.

[0057] Example 2:

[0058] The size D of the finished wire in the example is φ0.50 mm, and the initial wire is a black wire with a diameter of φ1.12 mm.

[0059] The φ1.12 mm black wire is subjected to mechanical polishing, and then subjected to a first on-line annealing at 700 °C and a wire feeding and withdrawing speed of 5.9 m / min, and the annealing is carried out in a nitrogen atmosphere in the furnace tube 6. After the annealing, the wire is subjected to a low-temperature cold drawing at -10 °C, and the sizes of the cold drawing dies in the diamond drawing assembly used in the drawing process are 1.03 mm, 0.95 mm, 0.88 mm in sequence. The deformation after the cold drawing is 38.27%. The wire is dried and the surface of the wire is wiped.

[0060] The φ0.88 mm wire is subjected to a second on-line annealing at 700 °C and a wire feeding and withdrawing speed of 9.5 m / min, and the annealing is also carried out in a nitrogen atmosphere. After the annealing, the wire is subjected to a low-temperature cold drawing at -10 °C, and the sizes of the cold drawing dies in the diamond drawing assembly used in the drawing process are 0.81 mm, 0.75 mm, 0.69 mm in sequence. The deformation after the cold drawing is 38.52%. The wire is dried and the surface of the wire is wiped.

[0061] The third on-line annealing is performed on the wire with a diameter of φ0.69 mm, the annealing temperature is 700 ℃, the speed of take-up and pay-off is 9.7 m / min, and the annealing is also performed in a nitrogen atmosphere. After the annealing, the wire is cold-drawn at a low temperature of -10 ℃, the sizes of the cold-drawing dies in the combined die used in the drawing process are 0.61 mm and 0.50 mm in sequence, the deformation after the cold-drawing is 47.49%, and the diameter d of the wire at this time is equal to the diameter D of the finished wire, i.e. 0.50 mm; the wire is dried and the surface of the wire is wiped.

[0062] Finally, the finished annealing is performed on the wire, the annealing temperature is 530 ℃, the speed of take-up and pay-off is 10 m / min, and the annealing is also performed in a nitrogen atmosphere, and finally the nickel-titanium bright wire with a diameter of φ0.50 mm is obtained.

[0063] Referring to Figure 6 , the surface roughness of the finished wire in Example 2 is 0.1 μm after the test measurement, and it can be found from the observation of the images of the surfaces of the finished wires in this example and the comparative examples that the black area on the surface of the wire in this example is less and the surface finish is higher.

[0064] This specific embodiment is only an explanation of the present application, and is not a limitation of the present application, and those skilled in the art can make modifications to this embodiment without creative contribution according to the needs after reading the present specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the Patent Law.

Claims

1. A method for processing nickel-titanium wire with an ultrathin oxide film, characterized in that: Includes the following steps, Step 1: Polish the initial filament surface to remove the surface oxide film; Step 2: Place the filament material into an annealing furnace for atmosphere-protected annealing. The annealing temperature for atmosphere-protected annealing is 650℃~750℃ and the annealing time is 30s~1min. The protective gas is nitrogen, argon or acetaldehyde. Step 3: Perform cold drawing on the wire. The deformation of the wire after this drawing is 30% to 70%. Determine whether the wire diameter d is equal to the finished wire diameter D. If the wire diameter d is greater than the finished wire diameter D, repeat steps 2 and 3. If the wire diameter d is equal to the finished wire diameter D, end steps 2 and 3. During cold drawing, spray the wire that is about to enter the cold drawing die with a cooled lubricant to keep the cold drawing environment temperature of the wire at -50℃ to 0℃. Step 4: Place the filament in the annealing furnace for a final atmosphere-protected annealing, i.e., finished product annealing, to reduce the hardness of the finished filament to achieve straightening and facilitate subsequent processing of orthodontic filament. The protective gas is nitrogen, argon or acetaldehyde. The annealing temperature is controlled at 500℃~550℃ and the annealing time is 30s~1min. The annealing furnace includes a furnace body (5) and a furnace tube (6) set inside the furnace body (5). The furnace tube (6) has a protective gas inlet (7) located outside the annealing furnace. The filament can pass through the furnace tube (6) and exit from inside the furnace tube (6). Gas collection hoods (10) are set at both ends of the furnace body (5). The gas collection hoods (10) are connected to gas transport pipes (11). The two ends of the furnace tube (6) have filament inlets (12) and filament outlets (13) through which the filament can pass. The filament inlets (12) and filament outlets (13) are respectively connected to the corresponding gas collection hoods (10).

2. The processing method for nickel-titanium wire with an ultra-thin oxide film according to claim 1, characterized in that: In step 3, the surface of the cold-drawn filament is dried and wiped.

3. The processing method for nickel-titanium wire with an ultrathin oxide film according to claim 2, characterized in that: In step 3, a filament wiping device is used to dry and wipe the surface of the filament. The filament wiping device includes a jet nozzle (1) for drying and a nylon (4) for wiping. The filament can pass through the jet nozzle (1) and the nylon (4) in sequence.

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