JPS6311435B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention can form a copper plating layer with good adhesion and stretchability on the surface of a welding steel wire, and in addition, reduces or eliminates the use of highly harmful chemicals in terms of plating bath composition. This invention relates to a copper plating method that aims to prevent secondary pollution. The surface of a steel wire for welding is generally plated with copper for the purpose of increasing electrical conductivity during welding and preventing rust. By the way, among the steel wires for welding, for example, 0.8
Steel wire for gas-shielded arc welding, etc. with a diameter of ~2 mmφ has an inner diameter of about twice the wire diameter and is 3 m long.
The conduit tube (stainless steel spiral tube) described above is used to send the conduit from the feeding device to the current-carrying chip, but since the conduit tube is often bent in a complicated manner during welding, the conduit tube is used to feed the steel wire for welding. The resistance is quite large. In addition, it is extremely important to maintain a constant arc length in order to obtain good welding workability.To this end, it is necessary to improve the smoothness of the copper-plated surface in order to improve the feedability of the welding steel wire. In order to obtain uniform current conduction characteristics, strong adhesion is required to prevent the steel base from being exposed due to friction and wire drawing in the feeding path. As a method for copper plating steel wire for welding, electroplating using a copper cyanide bath has traditionally been widely used, and with this method, it is relatively easy to form a copper plating layer with good adhesion and surface smoothness. can be obtained. However, since extremely harmful chemicals are used, the physical and psychological burden on workers is extremely large, and wastewater treatment to prevent pollution requires enormous equipment and maintenance costs. In addition, when manufacturing steel wire for gas shield welding, we use raw wire of about 5.5 mmφ to 0.8 to 2 mmφ (the most common is 1.2 mm
It is common to perform copper plating during the wire drawing process to the final product (φ or 1.6 mmφ), but since the copper plating layer obtained using a copper cyanide bath is hard, There are also problems such as the wire drawing process after the piercing treatment is relatively difficult and the die is subject to significant wear. Furthermore, from the viewpoint of plating speed, in electroplating using a copper cyanide bath, the plating efficiency tends to decrease as the current density increases, so in order to increase the processing speed of wire rods, the current used should be suppressed and the bath length should be increased. It is necessary to make the length significantly longer, which increases the area occupied by the equipment and also increases the amount of harmful chemicals held and the amount of liquid discharged. On the other hand, a copper displacement plating method using a copper sulfate bath is known as a copper plating method for steel plates, etc., but the plating layer obtained by this method has poor adhesion. For this reason, attempts have generally been made to form a dense copper-plated layer by adding certain chemical substances to the bath or by reducing the concentration of copper ions in the bath to suppress the deposition rate. However, even with these improvement methods, it is difficult to satisfy the high degree of adhesion required for welding steel wire, and the copper plating method of welding steel wire using a copper sulfate bath is hardly practical. It has not been. However, copper sulfate has extremely low toxicity compared to copper cyanide, so there is less danger to workers and less economic burden associated with wastewater treatment, and there is less risk of secondary pollution, making it attractive and difficult to discard. . Under the above-mentioned circumstances, the present inventors conducted research with the aim of establishing a plating method using a copper sulfate bath that would ensure adhesion and productivity comparable to copper cyanide plating method. We have been progressing. The present invention was completed as a result of such research, and consists of a method in which steel wire for welding is immersed in a copper sulfate bath for electroplating. The sulfuric acid concentration of the bath is 65 g / or less and the current density of the wire is 50 A / dm ² or more, and the wire and / or the bath are moved, and the relative speed of the wire and the bath is V (m / min). , current density C
(A/dm ² ), the copper sulfate bath temperature T (° C.), and the sulfuric acid concentration D (g/) of the copper sulfate bath so that the following equation is satisfied. V≧1/f(C-50) ² +80 However, f=4(D-T)+180 In the present invention, a steel wire with a current density in a specific range is moved in a copper sulfate bath with a bath temperature in a specific range. By electroplating while flowing the bath liquid against the direction of movement of the steel wire (if necessary, flowing it in the same direction), the amount of copper deposited due to the substitution reaction can be suppressed, and the current density of the steel wire can be controlled. By determining the relationship with the relative speed, a copper plating layer with excellent adhesion can be efficiently formed. As confirmed by the inventors through experiments,
As the current density of the steel wire increases, the formation rate of the plated layer increases and the adhesion of the plated layer improves.
This is because the amount of displacement plating decreases as the current density increases, but when the current density exceeds a certain value, the amount of displacement plating becomes approximately the same, so simply increasing the current density will cause the amount of plating to decrease. The adhesion cannot be sufficiently improved. In addition, as the current density increases, the crystal grain size of the precipitated copper increases, so
If the current density is increased too much, the adhesion of the plating layer will decrease. However, by increasing the flow rate of electrolyte (copper ions) on the cathode (steel wire) surface during the plating process, the quality of displacement plating improves and the growth of crystal grains in the electroplated area is suppressed, creating new plating nuclei on the cathode surface. is generated, and as the number of plating nuclei increases, the adhesion of the plating layer improves dramatically. In addition, in order to generate a sufficient number of plating nuclei on the surface of the steel wire despite the increase in the flow rate of the electrolyte and to grow it to a specified thickness in a short time while keeping the crystal grain size to a good level of adhesion, it is necessary to It is necessary to keep the applied current density to the minimum necessary. The easiest way to adjust the electrolyte velocity at the steel wire surface is to
A method of moving the copper sulfate bath liquid and the steel wire relative to each other can be considered, and the current density can be easily adjusted by increasing or decreasing the applied current. In addition, the allowable range of current density that can form an excellent copper plating layer varies depending on the bath temperature and sulfuric acid concentration of the copper sulfate bath, and the lower the bath temperature and the higher the sulfuric acid concentration, the higher the current density. be able to. First, the reason for setting the current density to 50 A/dm ² or more will be described. The higher the current density, the more the amount of displacement plating can be suppressed, but as shown in Figure 1, the higher the current density
When the current density is 50 A/dm ² or higher, the amount of displacement plating becomes almost equal, and in order to reduce the amount of displacement plating and improve the adhesion of the plating layer, the current density must be set to 50 A/dm ² or higher. The relationship between the amount of displacement plating and the current density in Figure 1 is expressed as the amount of displacement plating, which is the difference between the actual amount of electroplating and the amount of electroplating based on the theoretical value under the following conditions. . Plating conditions Immersion length 2m CuSO ₄・5H ₂ O 313g/ Line speed 120m/min H ₂ SO ₄ 28.4g/ Wire diameter 2.3mm Bath temperature 40°C Figure 1 shows the current density of 120A/ ^dm2 . The relationship between displacement plating amount and bath temperature is also shown. Next, the temperature of the copper sulfate bath should be kept below 50℃.
This is because the lower the bath temperature, the easier it is to obtain a dense plated layer, and if the bath temperature exceeds 50°C, it is impossible to obtain a good plated layer. This is because the quality of displacement plating and electroplating is This is because, as the bath temperature decreases, the amount of displacement plating, which has poor adhesion, increases as the bath temperature increases, as can be seen from the relationship between the amount of displacement plating and the bath temperature shown in FIG. Note that as the bath temperature becomes lower, the voltage must be increased and the amount of power consumed increases to obtain the same plated layer, so it is preferable to keep the bath temperature above room temperature. Furthermore, the reason why the sulfuric acid concentration in the copper sulfate bath is set to 65 g/or less is that the higher the sulfuric acid concentration in the bath, the higher the allowable maximum current density becomes, and accordingly the effective immersion length can be shortened. For example, if the bath temperature is 30℃ and the relative speed is constant at 100m/min, the concentration is 30g/min.
The maximum allowable current density is 110A/dm ² at a concentration of 40g/dm2, but at a concentration of 40g/dm2 ^it is 116A/dm2, and at a concentration of 45g/dm2.
119A/dm ² , 127A/d at 60g/
m ² and 95 g/m 2 , it becomes 144 A/dm ² . Therefore, in order to shorten the effective immersion length and downsize the equipment, it is preferable that the sulfuric acid concentration be as high as possible. However, the sulfuric acid concentration
If it exceeds 65g/, the drawability of the steel wire after plating will drop significantly, the steel wire surface will be easily scratched during wire drawing, and the wire drawing die will wear out significantly, so the sulfuric acid concentration must be kept below 65g/. The most preferable sulfuric acid concentration in terms of wire drawability and adhesion is 30.
~40g/. Finally, the relative velocity V between the copper sulfate bath and the steel wire
(m/min), the current density C (A/dm ² ) of the steel wire, the bath temperature T (°C) of the copper sulfate bath, and the sulfuric acid concentration D (g/) of the copper sulfate bath, as V≧1/f ( C-50) ² +80 However, the reason for setting f=4(D-T)+180 will be explained. Relative speed between plating bath and steel wire, current density,
Experiments were conducted to find the optimal electroplating conditions by varying the bath temperature of the copper sulfate bath and the sulfuric acid concentration of the copper sulfate bath. However, the relative velocity was changed by flowing the electrolyte parallel to the steel wire running direction using a reflux pump placed in the bath and adjusting the steel wire running speed. The adhesion of the copper plating layer was determined by wrapping a steel wire coated with 0.10 to 0.30% by weight around a wire rod of the same diameter, and then visually observing the peeling state of the plating layer using a 40x microscope. I decided that. As a result, the growth of crystal grains can be suppressed as the relative velocity increases, but the size of the crystal is determined by the relationship between the relative velocity and current density, but if the relative velocity is too small, the growth of crystal grains will be suppressed. It is preferable to set the relative speed to 80 m/min or more because the current density has to be suppressed and the bath length required to obtain a plated layer of a predetermined thickness is long. Incidentally, FIG. 2 shows the relationship between the relative speed and current density at which a plated layer with good adhesion can be obtained with the bath temperature and sulfuric acid concentration fixed respectively.
However, the concentration of copper sulfate (CuSO ₄ 5H ₂ O) used was
300~320g/, test wire is JIS YCW2 (2.3mm
φ). As is clear from Figure 2, when the bath temperature and sulfuric acid concentration are fixed, the relationship between the relative speed and current density that allows a plated layer with good adhesion to be obtained is V≧1/f(C-50) ² +80 (where f is a constant), and it became clear that f changes depending on the bath temperature and sulfuric acid concentration. The relationship between this f and the bath temperature and sulfuric acid concentration is f=4(DT)+180. The relationship between the relative speed of steel wire, current density, bath temperature, and sulfuric acid concentration has been explained above, but in addition to this, the amount of plating is mentioned as a major factor that controls adhesion, and as the amount of plating increases, the adhesion It tends to deteriorate. In general, it is said that in steel wire for welding, if the plating amount is 0.4% or more, the performance of the weld metal will deteriorate. In the electroplating method according to the present invention, the amount of electroplating should be at most 0.3%, allowing for a maximum of 0.10% displacement plating. Therefore, in order to establish a plating method that meets these requirements, it is necessary to consider the plating time (immersion time). The immersion time will be explained below. First, the meaning of each symbol in the formula shown below will be specified. W: Copper precipitation amount (g) t: Steel wire immersion time (seconds) I: Supply current (A) e: Current efficiency (%) M: Copper atomic weight (63.57) Z: Copper valence (2) F : Proportionality constant (96500 coulombs) G: Steel wire throughput per second (g/sec) V: Steel wire speed (m/min) R: Steel wire diameter (mm) ρ: Specific gravity of steel wire (7.833) l : Immersion length of steel wire (m) C: Current density (A/dm ² ) Amount of copper plating deposited per second W/t=I・M/Z・F・e ...[] The amount of steel wire processed is G=(100/60V)・{π(R/2・10) ² }・ρ…
…[] The current density is C=I/10・π(R/100)・l …[] The plating amount (weight%) is (W/t)/G+(W/t)×100=W/t /G×100…
...[] It can be obtained from each formula. Therefore, if we substitute the expressions [] to [] into the expression [] and rearrange it, we get
The formula holds true. Plating amount (%) =W/t/G×100=0.101・l・e・C/V・R……
[] Also, if the current efficiency (e) is 0.96%, []
From the formula, the formula [] is derived, and by further transforming the formula, the immersion time (t) can be determined from the formula []. Plating amount (%) = 0.097・l・C/V・R……[] t=60l/V=60・R/0.097・C・plating amount……[] Now, the desired electroplating amount If it is 0.3%, then
The formula [] is derived from the formula []. t=185.57・R/C...[] As is clear from the above explanation, in carrying out the present invention, the current density (C ) and immersion time (t), the amount of plating can be properly controlled, and as a result, it is possible to operate within a range that does not deteriorate adhesion in terms of the amount of plating, and welding can be used as a steel wire for welding. The quality of the parts can also be maintained. The present invention is generally constructed as described above, but the key point is to use a copper sulfate bath with bath temperature and sulfuric acid concentration in a specific range, and to calculate the relative moving speed and current density of a steel wire in a specific range of current density. By performing electroplating while properly adjusting the relationship, it is possible to efficiently form a copper plating layer with adhesion superior to that obtained using a copper cyanide bath. I decided to get it. As a result, various problems associated with the use of copper cyanide, such as risk burden, wastewater treatment, and secondary pollution, can be solved all at once. Moreover, the copper-plated layer obtained by the present invention is softer than the copper-plated layer obtained by the cyanide copper plating method, and wire drawing processing after plating is easy, with less die wear and excellent production. You can enjoy many benefits such as increased sex. Next, examples will be given to further clarify the structure and effects of the present invention. Example Copper plating was applied to the surface of carbon dioxide gas welding bare wire (JIS YCW2) with a diameter of 2.3 mm immediately after electrolytic pickling under the conditions shown in Table 1 (the plating amount was varied by varying the relative speed, current density, and immersion length). The target concentration was 0.22% by weight), and then continuous wire drawing was performed in 5 stages to 1.2 mmφ to obtain a steel wire for welding. In addition, steel wire (cathode)
The distance between the electrode and the anode is approximately 15 mm.

【table】

[Electric energy calculation method]

The weight per meter of 2.3 mmφ steel wire is 32.54 g/m, and the production amount per hour is the linear speed (liquid speed is very slow compared to the linear speed, so the relative speeds shown in Table 1 are the linear speeds as they are). ). In other words, production amount per hour = 32.54/1000 x linear velocity (m/min) x 60 (Kg/Hr) On the other hand, electric energy is calculated by dividing the value of supply current x load voltage by the above production amount per hour. Indicates the value. [Feeding resistance measurement method] A 20kg spooled wire was set in a commercially available welding wire feeding device, a 300mmφ loop was formed near the outlet of the feeding conduit cable, and a 1kg load resistance was applied to the tip of the welding torch. The force required for wire feeding was measured while feeding the wire at 8 m/min. Therefore, the values in the table include the 1 kg resistance loaded at the tip.

[Table] The plating amounts shown in Table 2 are greater than the theoretical plating amounts calculated from the current density and immersion time. This is because there is an amount of plating due to a substitution reaction. In Comparative Example 1, the current density was too low, so the adhesion was poor, and the feeding resistance as a welding wire after drawing to 1.2 mmφ also showed a high value. On the other hand, Examples 2 to 5
has good adhesion and feeding resistance due to the increase in current density and relative velocity. In Comparative Example 2, the current density was too high relative to the relative speed, so the adhesion of the electroplating itself deteriorated. Comparative Example 3 has poor adhesion and feeding properties because the relative speed is too slow. On the other hand, in Examples 5 to 7,
An example is shown in which good plating can be obtained even when the current density is increased as the relative speed increases. Examples 8 to 10 and corresponding comparative examples 4 to 6
1 and 2 show examples near the upper limit of the current density at which good adhesion can be obtained at relative speeds of 240 to 280 m/min. In this way, even if the current density becomes too high, the adhesion becomes poor, but as the sulfuric acid concentration increases, the maximum allowable current density increases. Also, the sulfuric acid concentration of Example 11 was 70
In the case of g/, the adhesion is good even at a very high current density of 300 A/dm ² , but as mentioned above, the wire drawability after plating deteriorates significantly, and it is difficult to draw the wire after plating, especially after continuous wire drawing. Not suitable for processes that require processing. Examples 12 to 14 and Comparative Examples 7 to 9 clearly demonstrate the influence of bath temperature, and Example 12 with a bath temperature of 20°C has good adhesion at a relative speed of 250 m/min and a current density of 240 A/dm ^2. , feeding resistance, but in Comparative Examples 7 to 9 in which the bath temperature was raised to 40, 50, and 60°C, a good plated layer could not be obtained even at a lower current density. Bath temperature 40, 50
Examples 13 and 14 and Comparative Examples 7 and 8 are compared in the vicinity of the allowable maximum current density at a relative speed of 240 to 270 m/min at .degree. Comparative Example 9 shows that because the bath temperature was raised too high to 60°C, it was no longer possible to obtain a good plated layer.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between current density, bath temperature and plating amount, and FIG. 2 is a graph showing the relationship between current density and relative speed which affects the adhesion of the copper plating layer.

Claims (1)

[Claims] 1. A method of electroplating by immersing a steel wire for welding in a copper sulfate bath, in which the temperature of the bath is 50°C or less, the sulfuric acid concentration of the bath is 65 g/or less, and the wire is The current density is set to 50 A/dm ² or more, the wire and/or the bath are moved, and the relative speed V (m/min) between the wire and the bath, the current density C (A/dm ² ), and the sulfuric acid are adjusted. A method for electroplating copper sulfate on steel wire for welding in such a manner that the relationship between the copper bath temperature T (° C.) and the sulfuric acid concentration D (g/) of the copper sulfate bath satisfies the following equation. V≧1/f(C-50) ² +80 However, f=4(D-T)+180