JP4877548B2 - Chrome plating equipment - Google Patents

Description

  The present invention relates to a chromium plating apparatus for depositing a hard chromium layer on a workpiece surface using a pulse current.

  It has been conventionally known that a chromium layer having no crack can be formed by performing so-called pulse plating using a pulse current (see, for example, Patent Document 1). However, according to the conventional general pulse plating method, even if there is no crack in the chromium layer after the plating treatment, if a thermal history is received, a large crack (macro crack) may be generated in the chromium layer, and the thermal history is received. The application to parts had to give up.

  Therefore, Patent Document 2 discloses a chromium plating method in which chromium plating is performed while adjusting a pulse waveform of a pulse current in a plating bath, and a compressive residual stress of 100 MPa or more is applied to the chromium layer. According to this method, the compressive residual stress applied to the chromium layer acts so as to suppress the generation of new cracks, and good corrosion resistance is maintained even after a thermal history.

  By the way, the electroplating process includes a continuous process in which a workpiece is continuously flowed in a processing tank and a batch process in which a plurality of workpieces are placed in a processing tank and processed in a batch manner. To perform production, batch processing is advantageous. However, when chromium plating is performed in a batch process by the method described in Patent Document 2, there is considerable variation in the compressive residual stress of the resulting chromium layer even within the same processing lot, and the above-described compression residual of 100 MPa or more. It was difficult to stably obtain a workpiece (part) that satisfies the stress.

  For this reason, Patent Document 3 proposes that the waveform of the pulse current supplied to each workpiece is made uniform regardless of the workpiece by adjusting the inductance of the wiring from the pulse power supply to each workpiece. According to this, it is possible to energize with the pulse current applied to each workpiece being made close to each other, and it is possible to minimize the variation in compressive residual stress between the workpieces.

Japanese Patent Laid-Open No. 3-207884 JP 2000-199095 A JP 2006-126820 A

  On the other hand, according to experiments by the present inventors, when the compressive residual stress of the chromium layer is 150 MPa (−150 MPa), macrocracks are generated in the chromium layer by heat treatment at 250 ° C. × 2 h, whereas 240 MPa or more. It is confirmed that no macro cracks are generated in the chromium layer even when a heat treatment of 400 ° C. × 2 h is applied at a compressive residual stress of −240 MPa or less. For this reason, in order to stabilize the chromium layer against the thermal history, it is important to stably obtain a higher compressive residual stress. In addition to the invention described in Patent Document 2, the Patent Document 3 is also cited. In the invention described in (2), there is no guarantee that a high compressive residual stress such as 240 MPa or higher, preferably 250 MPa or higher, can be obtained stably, and further improvement has been desired.

  The present invention has been made in view of the technical background described above, and the object of the present invention is to provide a chromium plating apparatus that can stably apply higher compressive residual stress to the chromium layer. It is in.

  While the present inventors are diligently studying means for applying a higher compressive residual stress to the chromium layer, the reciprocal inductance of the wiring from the pulse power source to each workpiece is adjusted with the cross-sectional shape, length, interval, etc. of the wiring. It has been found that it is effective to make it as small as possible, and that it is effective to make the rise and fall times of the pulse current as short as possible. Furthermore, if the reciprocal inductance of the wiring from the pulse power supply to each workpiece is made extremely small, or if the rise and fall times of the pulse current are made extremely short, undershoot and overshoot are likely to occur in the pulse waveform, which is rather high compression. It has also been found that it may be difficult to obtain residual stress.

  The present invention has been made on the basis of the above knowledge, and the first invention is that a plurality of workpieces are immersed in a chromium plating bath, and a chromium layer having a compressive residual stress is applied to the workpiece surface using a pulse current. In the chromium plating apparatus to be deposited, the reciprocal inductance of the wiring from the pulse power source to each workpiece is set to a predetermined value of 6.8 μH or less, preferably a predetermined value in the range of 0.5 to 6.8 μH.

  The second invention is a chromium plating apparatus in which a plurality of workpieces are immersed in a chromium plating bath and a chromium layer having a compressive residual stress is deposited on the workpiece surface using a pulse current. The total of the down time is set to a predetermined value of 0.38 ms or less, preferably a predetermined value in the range of 0.04 to 0.38 ms.

  In the first and second inventions described above, the compressive residual stress of the chromium layer is not particularly limited, but the chromium layer having a high compressive residual stress of 250 MPa or more is deposited. it can.

  According to the chromium plating apparatus according to the present invention, the reciprocal inductance of the wiring from the pulse power source to each workpiece, or the total of the rise and fall times of the pulse current is within a predetermined range, so that higher compression is achieved for each workpiece. It is possible to stably deposit a chromium layer having a residual stress, for example, a compressive residual stress of 250 MPa or more, which greatly contributes to an improvement in heat resistance of the chromium plated component.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
FIG. 1 shows a first embodiment of a chromium plating apparatus according to the present invention. This chromium plating apparatus 1 has a batch processing tank 2 made of an electrically insulating material containing a plating bath containing an organic sulfonic acid, and immerses ten workpieces W (W1 to W10) in the chromium plating bath. A chromium layer having a desired compressive residual stress is deposited on the surface of the workpiece W using the pulse current of the pulse power supply 3. In the batch processing tank 2, a plurality of cylindrical anode electrodes Y (anodes) corresponding to the workpieces W are arranged in a row at predetermined intervals. A cathode electrode K is arranged above each of the plurality of anode electrodes Y, and a workpiece W is held below the cathode electrode K. The workpiece W is inserted into the anode electrode Y and is opposed to the inner peripheral wall of the anode electrode Y.

  Hereinafter, the plurality of anode electrodes Y are appropriately referred to as first, second,..., Tenth anode electrodes Y1, Y2,. The plurality of cathode electrodes K are appropriately referred to as first, second,..., Tenth cathode electrodes K1, K2,.

  As shown in FIGS. 1A and 1C, the anode electrode Y is connected to a plate-like anode holder 6 via hook members 5 arranged at equal intervals. The anode holding body 6 is connected to the positive electrode terminal 3a of the pulse power source 3 via the anode-side bus bar 7 (hereinafter, the connecting portion is referred to as a feeding point 8) at the center thereof. The anode-side bus bar 7 has one end connected to the substantially L-shaped plate-like anode-side bus bar main body 9 whose one end is connected to the positive electrode terminal 3 a of the pulse power source 3, and the other end of the anode-side bus bar main body 9. The anode-side bus bar extension plate 10 is connected to the feeding point 8 of the anode holder 6 at the other end of the anode-side bus bar extension plate 10.

  As shown in FIGS. 1B and 1C, the cathode electrode K is connected to a plate-like cathode holder 15 disposed above the batch processing tank 2. The cathode holding body 15 is connected to the negative electrode terminal 3b of the pulse power source 3 via the cathode side bus bar 16 at both ends thereof. The cathode side bus bar 16 has a substantially L-shaped plate-like cathode side bus bar body 17 whose one end is connected to the negative electrode terminal 3 b of the pulse power source 3, and a substantially U shape connected to the other end of the cathode side bus bar body 17. Cathode-side busbar extension 18. The cathode-side busbar extension 18 includes a plate-like extension body 19 and orthogonal plates connected perpendicularly to both ends of the extension body 19 (hereinafter, for convenience, the left-hand side of FIG. The right side of FIG. 1 is referred to as a second orthogonal plate 21), and the first and second orthogonal plates 20, 21 are respectively connected to the end of the cathode holder 15.

  The anode side bus bar main body 9 and the cathode side bus bar main body 17 are arranged so as to be close to each other as much as possible through the insulating member 22, and the inductance is reduced as the current flows in the reverse direction. ing. Further, the first orthogonal plate 20 side portion of the extension portion main body 19 is joined to the other end portion side of the cathode side bus bar main body 17 via an insulating member 23.

  The current supplied from the pulse power source 3 is fed to the feeding point 8 through the anode-side bus bar 7, passes through the anode holder 6, and the anode electrode Y (first and second) disposed in the batch processing tank 2. ,... Are fed to the tenth anode electrodes Y1, Y2,. Further, the current forms a plating layer on each workpiece W through the plating solution, and flows through the workpiece W to the cathode electrodes K (first, second,..., Tenth cathode electrodes K1, K2,... K10), and the cathode. It returns to the pulse power source 3 through the side bus bar 16. In the process of current flowing in this way, the current fed to the feeding point 8 is diverted from the feeding point 8 to each anode electrode Y and flows to each workpiece W. Then, the current flowing through each workpiece W flows toward both ends of the cathode holder 15.

  Focusing on the fact that current flows in the manner as described above, in this embodiment, the portion between the adjacent anode electrodes Y (the wiring portion between the adjacent anode electrodes Y in the anode holding body 6, the hook member 5 is the target). ) And the inductance of the arrangement portion between the adjacent cathode electrodes K (the wiring portion between the adjacent cathode electrodes K in the cathode holder 15 is a target) (in this embodiment, 0.075). μH).

  The inductance of the electrode is composed of a self-inductance and a mutual inductance, and the self-inductance is determined by its material (magnetic permeability) and shape (length, thickness; cross-sectional area), and the mutual inductance is an electrode adjacent to these. It is known that the distance between them affects. In this embodiment, the elements for determining the inductance and the influence matters are adjusted, and each inductance is set to an equivalent value.

  Also, the inductance inside the pulse power source 3, the inductance of the wiring from the pulse power source 3 to the fifth and sixth anode electrodes Y5 and Y6, and the inductance of the wiring from the pulse power source 3 to the first and tenth cathode electrodes K1, K10 Is set to a predetermined value in the range of 0.5 to 6.8 μH.

  In the first embodiment, the chromium plating apparatus 1 is used to immerse the workpiece W in a plating bath containing an organic sulfonic acid and perform a plating process using a pulse current (hereinafter referred to as a pulse plating process). ). Here, the current pattern as shown in FIG. 2 is adopted as the condition of the pulse plating treatment.

  In FIG. 2, the pulse current waveform alternates between the maximum current density IU and the minimum current density IL, and is held at the maximum current density IU and the minimum current density IL for a predetermined time T1, T2. . Although the minimum current density IL is set to zero (off) here, it is needless to say that the minimum current density IL may be set to any value between the maximum current density IU and zero. Also, the holding times T1 and T2 may be set to the same value or different values.

  In the first embodiment, first, the maximum current density IU and the minimum current density IL (here, IL = 0) and the holding times T1 and T2 held at these current densities are set to appropriate values. Then, a pulse plating process is performed to deposit a crack-free chromium layer S having a desired compressive residual stress on the surface of the steel base material (work W) M as shown in FIG. Here, the chromium layer S is formed to have a compressive residual stress of 250 MPa or more. Thus, since the reciprocal inductance of the wiring from the pulse power supply 3 to each workpiece W1 to W10 is set to a predetermined value in the range of 0.5 to 6.8 μH, the pulse waveform of the current supplied to each workpiece W1 to W10 is one. Thus, the above-described high level of compressive residual stress can be obtained for all the workpieces W1 to W10.

  Since the chrome-plated part obtained in this way is provided with the crack-free chrome layer S, the medium causing the corrosion does not reach the metal base of the steel base material M, and the desired corrosion resistance is ensured. Moreover, since the chromium layer S has a high compressive residual stress, no new cracks are generated even after a thermal history, and excellent corrosion resistance is maintained.

  In the first embodiment, the case where the inductance of the wiring between the adjacent anode electrodes Y and the inductance of the wiring between the adjacent cathode electrodes K is sufficiently small is set as an example. Although an example in which an equal pulse current flows through W is taken as an example, the present invention may be configured as shown in FIG. 4 (second embodiment).

  The chrome plating apparatus 1 ′ according to the second embodiment is configured so that the anode holder 6 has fifth and sixth anode electrodes Y 5 and Y 6 [corresponding to the power feeding point 8 (connecting portion with the pulse power source 3)]. The inductance of the wiring between the electrodes is set to be larger by changing the cross-sectional area (thickness) as they are separated (that is, at the end side). Further, as the cathode holder 15 is separated from the first and tenth cathode electrodes K1 and K10 (corresponding to the connecting portion with the pulse power source 3) (that is, becomes the central portion), the cross-sectional area (thickness) Is set so that the inductance of the wiring between the electrodes increases.

  In the second embodiment, the pulse currents flowing to the workpiece W close to the power feeding point 8 and each workpiece W separated from the power feeding point 8 are overlapped including rising and falling. Therefore, the same pulse current is supplied, the plating process can be performed equally, and the quality can be made even more uniform.

Using chrome plating equipment 1 shown in Fig. 1, 10 steel bars (diameter 12.5mm, length 350mm, plating length 300mm) made of JIS S45C were used as test materials, chromic acid 290 g / L, sulfate radical 4.2 g / L, organic sulfonic acid 12g / L component chrome plating bath, bath temperature 70 ℃, maximum current density IU = 200 A / dm ² , minimum current density IL = 0 A / dm ² (Figure 2), pulse plating was performed on the surface of the specimen under the conditions of holding time (on time) T1 = 0.9 ms at the maximum current density IU and holding time (off time) T2 = 0.5 ms at the minimum current density IL. A chromium layer S (FIG. 3) having a thickness of about 15 μm was formed.

  Also, the inductance inside the pulse power source 3, the inductance of the wiring from the pulse power source 3 to the fifth and sixth anode electrodes Y5 and Y6, and the inductance of the wiring from the pulse power source 3 to the first and tenth cathode electrodes K1, K10 The total inductance (round-trip inductance) is 6.8μH (A), 6.0μH (B), 5.2μH (C), 3.6μH (D), 2.7μH (E), 1.9μH (F), 1.1μH ( G), 0.7 μH (H), 0.5 μH (I) and 8.4 μH (Z).

  Corresponding to the setting of the reciprocal inductance as described above, as shown in FIG. 5, the calculation for obtaining the pulse current flowing through the workpiece W was performed using a simulation model corresponding to the equivalent circuit of the chromium plating apparatus 1. By this calculation, the results shown in FIGS. 6A to E and FIGS. 7F to I and Z were obtained. In the figure, U represents the waveform of the pulse current flowing through the workpiece W near the power feeding point 8, and V represents the waveform of the pulse current flowing through the workpiece W separated from the power feeding point 8.

  From the results shown in FIGS. 6 and 7, the waveform U of the pulse current flowing through the workpiece W close to the feeding point 8 and the waveform V of the pulse current flowing through the workpiece W separated from the feeding point 8 are slightly shifted at the rise and fall. However, there is no significant difference between the two pulse waveforms, and it has become clear that substantially the same pulse current is supplied to each workpiece W.

  Further, as the reciprocal inductance becomes smaller, both the rise time and the fall time tend to be shorter. When the reciprocal inductance is in the range of 0.5 to 6.8 μH, the total rise and fall time is shortened to 0.04 to 0.39 ms. However, as the reciprocal inductance becomes smaller, the tendency of overshoot (at the time of rise) and undershoot (at the time of fall) becomes stronger, so the lower limit of the reciprocal inductance is 0.5 μH, and the total rise / fall time is 0.04ms is the limit. When the reciprocal inductance is set to 8.4 μH (Z: comparative example), although the overshoot and undershoot are slight, the pulse waveform has a total rise / fall time exceeding 0.40 ms.

  Using the chrome plating apparatus 1 'shown in FIG. 4, the same 10 steel bars (steel bars No. 1 to 10) as in Example 1 were used as test materials, and pulse plating was performed under the same plating conditions as in Example 1. A chromium layer S (FIG. 3) having a thickness of about 15 μm was formed on the surface of the test material.

  Here, the inductance of the wiring between the fourth and fifth anode electrodes Y4 and Y5 is 0.03 μH, the inductance of the wiring between the third and fourth anode electrodes Y3 and Y4 is 0.06 μH, and the second and third anode electrodes Y2 and Y2, respectively. The inductance of the wiring between Y3 is 0.09 μH, the inductance of the wiring between the first and second anode electrodes Y1 and Y2 is 0.12 μH, and the inductance of the wiring between the sixth and seventh anode electrodes Y6 and Y7 is 0.03 μH. The inductance of the wiring between the seventh and eighth anode electrodes Y7 and Y8 is 0.06 μH, the inductance of the wiring between the eighth and ninth anode electrodes Y8 and Y9 is 0.09 μH, and between the ninth and tenth anode electrodes Y9 and Y10 The wiring inductance is set to 0.12 μH.

  The inductance of the wiring between the first and second cathode electrodes K1 and K2 is 0.03 μH, the inductance of the wiring between the second and third cathode electrodes K2 and K3 is 0.06 μH, and the third and fourth cathode electrodes K3 and K4. The wiring inductance between the ninth and tenth cathode electrodes K9 and K10 is 0.03 μH, and the wiring inductance between the fourth and fifth cathode electrodes K4 and K5 is 0.12 μH. The inductance of the wiring between the eighth and ninth cathode electrodes K8 and K9 is 0.06 μH, the inductance of the wiring between the seventh and eighth cathode electrodes K7 and K8 is 0.09 μH, and between the sixth and seventh cathode electrodes K6 and K7. The wiring inductance is 0.12μH.

  On the other hand, the inductance inside the pulse power supply 3, the inductance of the wiring from the pulse power supply 3 to the fifth and sixth anode electrodes Y5, Y6, and the inductance of the wiring from the pulse power supply 3 to the first and tenth cathode electrodes K1, K10 The same as in Example 1, the reciprocal inductance is 6.8 μH (A), 6.0 μH (B), 5.2 μH (C), 3.6 μH (D), 2.7 μH (E), 1.9 μH (F), 1.1 μH (G), 0.7 μH (H), 0.5 μH (I) and 8.4 μH (Z) were set.

  Corresponding to the setting of the reciprocal inductance as described above, the pulse current flowing through the workpiece W using a simulation model corresponding to the equivalent circuit of the chrome plating apparatus 1 ′ substantially the same as that shown in FIG. The operation for obtaining was performed. By this calculation, the results shown in FIGS. 8A to E and FIGS. 9F to I and Z were obtained. In the figure, U represents the waveform of the pulse current flowing through the workpiece W near the power feeding point 8, and V represents the waveform of the pulse current flowing through the workpiece W separated from the power feeding point 8.

  From the results shown in FIGS. 8 and 9, the waveform U of the pulse current flowing in the work W near the power supply point 8 and the waveform V of the pulse current flowing in the work W separated from the power supply point 8 overlap including the rise and fall. Thus, it is clear that substantially the same pulse current is supplied to each workpiece W.

  Further, as the reciprocal inductance becomes smaller, both the rise time and the fall time tend to be shorter. When the reciprocal inductance is in the range of 0.5 to 6.8 μH, the total rise and fall time is shortened to 0.04 to 0.39 ms. Further, even when the reciprocal inductance is reduced, overshoot (at the time of rising) and undershoot (at the time of falling) are not caused. When the reciprocal inductance is set to 8.4 μH (Z: comparative example), the pulse waveform has a total rise / fall time exceeding 0.40 ms.

[Test example]
For each sample obtained in Examples 1 and 2, the residual stress of the chromium layer S was measured. Residual stress was measured using the “X-ray stress measurement method” disclosed in “Non-destructive Inspection” Vol. 37, No. 8, pp. 636-642 edited by Japan Nondestructive Inspection Association.

  FIG. 10 shows the residual stress obtained for each sample of Example 1 organized by reciprocal inductance. In the figure, the residual stress is divided into a maximum value and a minimum value, and the same applies to the following figures. From the results shown in FIG. 10, the compressive residual stress tends to increase as the reciprocal inductance decreases, and a high compressive residual stress of 250 MPa or higher (−250 MPa or lower) is obtained at a reciprocal inductance of about 6.8 μH or lower. However, the minimum value of the compressive residual stress (maximum residual stress) tends to be rather small when the reciprocal inductance is about 1.0 μH or less. This is presumably because if the reciprocal inductance is too small, the tendency of overshoot and undershoot to occur in the pulse waveform becomes strong (see FIG. 7). However, even when the reciprocal inductance is about 0.5 μH, a compressive residual stress of about 250 MPa is obtained. Therefore, when a high compressive residual stress of 250 MPa or more is desired, the reciprocal inductance is a predetermined value in the range of 0.5 to 6.8 μH. It turns out that it is desirable to set to.

  FIG. 11 shows the residual stress obtained for each sample of Example 2 organized by reciprocal inductance. From the results shown in FIG. 10, the compressive residual stress tends to increase as the reciprocal inductance decreases, and a high compressive residual stress of 250 MPa or higher (−250 MPa or lower) is obtained at a reciprocal inductance of about 6.8 μH or lower. In each sample of Example 2, the minimum value (maximum residual stress) of the compressive residual stress is not reduced even when the reciprocal inductance is about 1.0 μH or less. Therefore, it is desired to obtain a high compressive residual stress of 250 MPa or more. In some cases, it is desirable to set the reciprocal inductance to a predetermined value in the range of 6.8 μH or less.

  FIG. 12 shows the residual stress obtained for each sample of Example 1 organized by the sum of the rise and fall times of the pulse waveform. From the results shown in FIG. 11, the compressive residual stress tends to increase as the total value of the rise / fall time decreases, and the total value of the rise / fall time is about 0.38 ms and is higher than 250 MPa (−250 MPa). Compressive residual stress is obtained. However, the minimum value of the compressive residual stress (maximum residual stress) tends to be rather small when the total value of the rise and fall times is about 0.08 ms or less. This is presumably because if the total value of the rise and fall times is too small, the pulse waveform tends to cause overshoot and undershoot (see FIG. 7). However, even when the total rise / fall time is about 0.05 ms, a compressive residual stress of about 250 MPa is obtained. Therefore, when a high compressive residual stress of 250 MPa or more is desired, the rise / fall time of It can be seen that it is desirable to set the total value to a predetermined value in the range of 0.05 to 0.38 ms.

  FIG. 12 shows the residual stress obtained for each sample of Example 2 organized by the sum of the rise and fall times of the pulse waveform. From the results shown in FIG. 12, the compressive residual stress tends to increase as the total value of the rise / fall time decreases, and the total value of the rise / fall time is about 0.38 ms or less and 250 MPa (−250 MPa or less). High compressive residual stress is obtained. Further, in each sample of Example 2, the minimum value (maximum residual stress) of the compressive residual stress is not reduced when the total value of the rise and fall times is about 0.08 ms or less, and therefore, a high value of 250 MPa or more. When it is desired to obtain the compressive residual stress, it can be seen that it is desirable to set the total value of the rise and fall times to a predetermined value in the range of 0.38 ms or less.

It is a figure which shows typically the chromium plating apparatus which concerns on the 1st Embodiment of this invention, (A) is the plane sectional drawing, (B) is front sectional drawing, (C) is side sectional drawing. It is a graph which shows an example of the waveform of the pulse current in the chromium plating method which concerns on the chromium plating apparatus of FIG. It is a schematic diagram which shows the state of the surface layer part of the chromium plating components obtained by the chromium plating method which concerns on the chromium plating apparatus of FIG. It is a figure which shows typically the chromium plating apparatus which concerns on the 2nd Embodiment of this invention, (A) is the plane sectional drawing, (B) is a front sectional view. It is a circuit diagram which shows the simulation model of the chromium plating apparatus of FIG. 1, FIG. FIG. 3 is a waveform diagram for each of the magnitudes (A) to (E) of the reciprocal inductance, showing calculation results obtained by the simulation model of the chromium plating apparatus of FIG. 1. The calculation result obtained by the simulation model of the chromium plating apparatus of FIG. 1 is shown, and is a waveform diagram for each of the magnitudes (F) to (I) and (Z) of the reciprocal inductance. FIG. 5 is a waveform diagram for each of the magnitudes (A) to (E) of the reciprocal inductance, showing calculation results obtained by the simulation model of the chromium plating apparatus of FIG. 4. The calculation result obtained by the simulation model of the chromium plating apparatus of FIG. 4 is shown, and is a waveform diagram for each of the magnitudes (F) to (I) and (Z) of the reciprocal inductance. It is a graph which arrange | positions and shows the measurement result of the residual stress about each sample obtained in Example 1 of this invention by arranging with a reciprocal inductance. It is a graph which arrange | positions and shows the measurement result of the residual stress about each sample obtained in Example 2 of this invention in order by a reciprocal inductance. It is a graph which arrange | positions and shows the measurement result of the residual stress about each sample obtained in Example 1 of this invention with the total value of rise / fall time. It is a graph which arrange | positions and shows the measurement result of the residual stress about each sample obtained in Example 2 of this invention with the total value of rise / fall time.

Explanation of symbols

1,1 'chrome plating equipment 3 pulse power supply 6 anode holder 8 feeding point 15 cathode holder Y anode electrode K cathode electrode W workpiece

Claims (6)

  5. In a chromium plating apparatus in which a plurality of workpieces are immersed in a chromium plating bath and a chromium layer having compressive residual stress is deposited on the workpiece surface using a pulse current, the reciprocal inductance of the wiring from the pulse power supply to each workpiece is 6. A chromium plating apparatus, which is set to a predetermined value of 8 μH or less.   The chromium plating apparatus according to claim 1, wherein the lower limit of the reciprocal inductance is set to 0.5 µH.   The chromium plating apparatus according to claim 1 or 2, wherein a chromium layer having a compressive residual stress of 250 MPa or more is deposited on the work surface.   In a chromium plating apparatus in which a plurality of workpieces are immersed in a chromium plating bath and a chromium layer having a compressive residual stress is deposited on the workpiece surface using a pulse current, the total rise / fall time of the pulse waveform is 0.38 ms. A chromium plating apparatus characterized by being set to the following predetermined value.   The chromium plating apparatus according to claim 4, wherein the lower limit of the total rise and fall times of the pulse waveform is set to 0.04 ms.   6. The chromium plating apparatus according to claim 4 or 5, wherein a chromium layer having a compressive residual stress of 250 MPa or more is deposited on the work surface.

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