JPH11302895A - Plating method of inner surface of cylindrical body and cylindrical body with its inner surface plated - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plating method of the inner surface of a cylindrical body capable of forming a plated layer whose film thickens is changed in the axial direction by one time plating treatment. SOLUTION: A plating method comprises a step in which the shape of an anode 24 so that the inside diameter of a plated cylindrical body 22 is the same in the axial direction is decided, a step to obtain the calculated value of current density through a finite element method, a step to calculate the current efficiency from the calculated value of the current density and the experimental value of the plated film thickness and a step to obtain the predicted value of the plated film thickness from the calculated value of the current density and the calculated value of the current efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for plating inside a cylinder, such as a weapon barrel, a cylindrical engine component, or a reaction cylinder, as a protective layer on a cylinder inner surface, and a cylinder having an inner surface plated. In particular, a plating layer whose film thickness changes in the axial direction of the cylindrical body is formed.

[0002]

2. Description of the Related Art In general, in a weapon barrel, etc., in addition to a large thermal load and sliding friction with a bullet band of a bullet, corrosion and wear occur, so that the life of a cylinder such as a weapon barrel is extended. A protective layer is provided on the inner surface of the cylinder. In this case, it is known that electrolytic chromium plating is suitable as the protective layer.

For example, in a large-diameter weapon barrel disclosed in Japanese Patent Application Laid-Open No. 7-167590, a loading chamber, which is a place where the barrel of the barrel is filled, is connected to the loading chamber, and a gun which receives a large thermal load. A chromium plating layer having a thickness of 100 to 200 μm is provided in a region of the diameter portion. However, in this method, the chrome plating layer is provided only on the caliber portion of the muzzle that receives a large thermal load, but the muzzle portion, which is the front region of the weapon barrel that receives a large mechanical shock, Since the protective layer is not provided, there is a problem that the barrel life is short against sliding friction with a bullet, abrasion, and corrosion due to use environment.

For this reason, not only the gun barrel portion which receives a large thermal load but also the muzzle portion needs to be protected from sliding friction with the bullet band of the bullet, abrasion, corrosion due to the use environment, etc. It is necessary to provide a chromium plating layer over the entire area. At this time, if a chromium plating layer having a thickness of 100 to 200 μm is uniformly provided over the entire inner surface of the barrel, the protective layer often peels off at the muzzle side. FIG.
According to the peel test shown in FIG. 11, the results show that the thinner the plating film, the greater the peel resistance of the film, as shown in FIG. Need to be thinner. For this reason, it is necessary to increase the thickness of the chromium plating layer in the muzzle portion receiving a large thermal load, and to reduce the thickness of the chrome plating layer in the muzzle portion receiving a mechanical impact.

As shown in FIGS. 12 and 13, there is a plating method in which a plating film thickness is changed in an axial direction on the inner surface of a cylinder of a barrel. First, as shown in FIG. 12, a thick chromium plating layer 5 is formed on the loading chamber and a muzzle diameter portion continuous with the loading chamber, and then, as shown in FIG. Form.

However, in such a cylindrical inner surface plating method, since two plating anodes 6 and 10 are prepared and plating is performed twice, the setup change operation is the same as the ordinary plating operation.
There is a problem that it takes twice as long. In a region where the thickness of the chrome plating layer 5 changes from the thickness of the chrome plating layer 5 to the thickness of the thin chrome plating layer 9, the shape of the anode 6 is changed from a large diameter to a small diameter.
For example, in the case of a straight tapered shape, the applied plating layer does not have a uniform inner diameter of the gun barrel, so that a step of flattening by machining after plating is further required.

For this reason, as shown in FIG. 14, there is a method of combining two anodes 13 and 14 having different sizes to perform plating at one time. However, the anode 13,
14 has a problem in that the anode structure and the current circuit are complicated and the cost is high, since they are connected by the conducting wires 7 and 11, respectively. If the anode shape is linearly tapered from a large diameter to a small diameter in a region where the thickness changes from a thick chromium plating layer to a thin plating layer, the inner diameter of the gun barrel will not be uniform, and the machine will not be machined after plating. There is a problem that a step of flattening by processing is required.

[0008]

SUMMARY OF THE INVENTION According to the present invention, when the plating film thickness on the inner surface of the cylinder is changed, the plating on the inner surface of the cylinder in which the plating layer is applied has the same diameter by a single plating operation. It is an object of the present invention to provide a method and a cylindrical body whose inner surface is plated. It is another object of the present invention to provide a plating method for the inner surface of a cylinder, which can simplify the plating operation without performing machining or the like after plating, and to provide a cylinder having an inner surface plated. Still another object of the present invention is to provide a plating method for an inner surface of a cylinder in which a plating film is unlikely to be peeled off, and a cylinder having an inner surface plated.

[0009]

Means for Solving the Problems In the present invention, claim 1 is provided.
The described invention provides an anode (2) extending in the axial direction of the cylindrical body (22).
4, 25), the anodes (24, 25) and the cylinder (22) are immersed in a plating solution, and a current is passed between the anodes (24, 25) and the cylinder (22). (22)
This is a plating method for the inner surface of a cylinder in which plating with different film thicknesses is performed in the axial direction on the inner surface, and by calculating the current density calculation value obtained by the finite element method, the predicted coating film thickness is calculated to determine the optimal anode shape. It is characterized in that it is determined.

According to a second aspect of the present invention, an anode (24, 25) extending in the axial direction of the cylinder (22) is arranged, and the anode (24, 25) and the cylinder (22) are placed in a plating solution. A plating method for the inner surface of a cylinder for applying plating having different film thicknesses in the axial direction on the inner surface of the cylinder by immersing and applying a current between the anodes (24, 25) and the cylinder (22). Calculating a current density calculation value of the cylinder (22) by a method; and calculating current efficiency from the current density calculation value and an experimental value of the plating film thickness at each axial position of the cylinder (22). A step of obtaining a plating thickness prediction value from the relationship between the current density calculation value and the current efficiency calculation value, and a step of determining an anode shape whose inner diameter is uniform at each axial position from the plating thickness prediction value. Is characterized by consisting of

According to a third aspect of the present invention, there is provided the method for plating the inner surface of the cylinder according to the second aspect, wherein after determining the diameter of the anode on the thick plating layer side and the diameter of the anode on the thin plating layer side of the cylinder (22),
A region where the thickness changes from a thick plating layer to a thin plating layer is divided into n parts (n: an integer) in the axial direction, and the anode diameter at each of the divided positions is variously changed to create a finite element method analysis model. Is calculated, and the anode diameter is determined so that the predicted value of the plating film thickness becomes the set cylinder inner diameter.

According to a fourth aspect of the present invention, there is provided the method for plating the inner surface of a cylinder according to any one of the first to third aspects,
The step of obtaining the estimated plating film thickness includes: (1) applying a temporary potential to the cathode and anode, which are actual boundary conditions; and (2) current density (i = −κ · ∂) by the finite element method.
(3) obtaining an average current density on the cathode surface (total current amount / cathode surface area) from the total current amount which is an actual plating application condition; and (4)
Adjusting the potentials of the cathode and the anode such that the current density i by the finite element method becomes the average current density;
(5) obtaining a current density distribution on the cathode surface;
(6) a step of obtaining a current efficiency when a current density calculation value and a plating film thickness experimental value are obtained at the adjusted potential; and (7) a step corresponding to each axial position of the cylindrical body (22). Calculating a current efficiency at each position in the axial direction from the relationship between the current density and the current efficiency and calculating a predicted value of the plating film thickness at each position in the axial direction.

According to a fifth aspect of the present invention, there is provided the method for plating the inner surface of the cylinder according to the fourth aspect, wherein the step of determining an anode shape such that the plated inner diameter has the same diameter at each axial position. (1) setting the outer diameter of the anode shape to a fixed value for the anode diameter on the side of the thick plating layer; and (2)
(3) creating a finite element method analysis model for each of the anodes; and (4) plating film thickness prediction values for each model. Calculating the area from the thick plating layer to the thin plating layer by dividing the area into n parts (n: integer) in the axial direction, and (5) making the plating film thickness at each of the divided positions equal to the set cylindrical inner diameter. And (6) determining the anode shape by selecting an anode diameter that is a cylindrical inner diameter for each n.

According to a sixth aspect of the present invention, there is provided the method for plating the inner surface of a cylinder according to any one of the first to fifth aspects, wherein the cylinder (22) is a cylinder. Claim 7
According to a preferred embodiment of the present invention, in the method for plating the inner surface of a cylinder according to any one of claims 1 to 6, the plating is chrome plating. The invention according to claim 8 is the first invention.
The plating is performed by the plating method for the inner surface of the cylinder according to any one of the above-mentioned items. According to a ninth aspect of the present invention, there is provided a cylindrical body whose inner surface is plated according to the eighth aspect, wherein the cylindrical body (22) is a cylindrical weapon barrel.

(Function) From the experimental value of the plating film thickness and the current density calculated value obtained by the finite element method, a predicted value of the plating film thickness is determined, and the optimum anode shape is determined. Plating can be applied to the shape. Specifically, a step of obtaining a current density calculation value by a finite element method, a step of calculating a current efficiency from a current density calculation value and an experimental value of a plating film thickness, and a relationship between the current density calculation value and the current efficiency calculation value An optimum anode shape is determined by a step of obtaining a predicted plating film thickness value and a step of determining an anode shape in which the inner surface of the cylinder has the same diameter at each position in the axial direction. As described above, the optimum thickness of the plating film is obtained by calculating the current density by the finite element method by applying the relational expression between the current efficiency and the current density by applying the plating film thickness. Can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a chromium plating method according to an embodiment of the present invention, showing a linear tapered anode in which the anode diameter is changed linearly. FIG. FIG. 6 is a cross-sectional view showing a multi-step tapered anode changed to a negative electrode.

As shown in FIG. 1, the cylinder on which the plating is performed is a cylinder 22. The inner surface 23 of the cylinder 22 has a small-diameter portion 23a disposed at the front end and a large-diameter portion 23c disposed at the rear end. Is provided, and a diameter changing portion 23b whose diameter changes smoothly from the small diameter portion 23a to the large diameter portion 23c is provided in the middle. The small diameter portion 23a is a portion where the thin chrome plating layer 21 is formed, and the large diameter portion 23c is a portion where the thick chrome plating layer 20 is formed. An anode 24 extending in the axial direction of the cylinder 22 is disposed on the axis of the cylinder 22, and the cylinder 22 and the anode 24 are immersed in a plating solution, and a current is passed between the cylinder 22 and the anode 24, Plating is applied to the inner surface of the cylinder 22.

In FIGS. 1 and 2, the shape of the anode corresponding to the region A (hereinafter, region A) where the thick chromium plating layer 20 changes to the thin chromium plating layer 21 in the cylinder 22 having different inner diameters of the inner surface 23 of the cylinder. It is shown. As shown in FIG. 1, the anode 24 is provided with a linear tapered portion 24a corresponding to the region A. As shown in FIG.
5 is provided with a continuous multi-step portion 25a that continuously changes in multiple steps corresponding to the region A. The continuous multi-step portion 25a is formed such that the diameter of the anode 25 changes from the thick chromium plating layer 20 to the thin chromium plating layer 21 outwardly. The anodes 24 and 25 are connected to a current source via an electric lead (not shown). Similarly, the cylinder 22 is also connected to a current source by an electric conductor (not shown), and functions as a cathode during plating.
In this embodiment, the anode 24 whose anode shape changes in a linear taper shape is shown in FIG. 1, and the anode 25 whose anode shape changes continuously and in multiple steps is disclosed in FIG. The shape corresponding to A is not limited to this, is not continuous, and is changed stepwise, or
It is also possible to change the shape like an arc portion such as a concave or convex parabola, a circle, or an ellipse.

Next, a method for obtaining the predicted value of the plating film thickness will be described in detail below. The plating film thickness has a relationship represented by the following equation with the current density and the current efficiency.

[0020]

## EQU1 ## Plating film thickness = Current efficiency × Current density × Electrification time (1)

First, an experiment was performed under the same conditions as in the actual plating operation, with the plating bath composition, plating bath temperature, and pretreatment conditions.
Obtain the experimental value of plating film thickness. From the experimental value of the plating film thickness and the current density calculation value calculated based on the shape, (1)
The current efficiency is obtained by the following equation obtained by modifying the equation.

[0022]

[Equation 2] (Current efficiency) = (Plating film thickness) / {(Current density) × (Electrification time)} (2)

The current density can be solved by giving a boundary condition to the following Laplace equation using the portion of the plating bath 26 surrounded by the anode 23 and the inner cylindrical surface 23 serving as the cathode as an analysis region.

[0024]

３ ² φ = 0 (Laplace equation, φ: potential) Equation (3) φ = Va, Vc (boundary condition, Va: anode potential, Vc:
Cathode potential) i = −κ∂φ / ∂n (i: current density at cathode, κ: electrical conductivity (reciprocal of electrical resistance), n: unit normal of cathode surface, ∂φ / ∂n: cathode Strength of the surface)

The above equation can be solved by the finite element method. A method for obtaining the current density i based on the boundary conditions of the finite element method is shown in the flowchart of FIG. Appropriate potentials Vc and Va are given to a cathode (for example, 0 V) and an anode (for example, 3 V) which are actual boundary conditions (S1), and a current density (i = -κκφ / ∂n) is obtained by a finite element method. ) (S
2).

Here, the average current density on the cathode surface (total current amount / cathode surface area) is determined from the total current amount, which is the actual plating application condition (S3), and the current density i by the finite element method is The potentials of the cathode and the anode are adjusted so as to obtain the current density (S4). The potential is adjusted so that the calculated value of the current density on the side of the thick chromium plating layer is equal to the average current density during construction. On the thick chrome plating layer side, the current density i was made uniform, that is, on the construction, the total current amount was calculated so that the current density i on the thick chrome plating layer side was constant. I have.

FIG. 3 is a finite element mesh division diagram of an axisymmetric two-dimensional model having the plating bath 26 in FIG. 1 as an analysis region. Such calculation is performed for various anode shapes to search for a shape in which the diameter of the inner surface of the cylinder becomes uniform as shown in FIG.

A method for determining the current density will be described with reference to FIGS. FIG. 8 shows the relationship between the axial position x of the cylinder when the current density calculation value i by the finite element method and the plating film thickness experiment value t by the actual experiment are obtained. FIG. 9 shows the relationship between the current density calculated value i and the plated film thickness experimental value t corresponding to each position x in the axial direction and the current efficiency η obtained by substituting the calculated value into the above equation (2). FIG. 5 shows the relationship between the current density i and the current efficiency η by increasing the number of samples. As described above, the current efficiency η is obtained by substituting the current density calculation value i and the plating film thickness experimental value t into the equation (2), and the gradient of the appropriate current density i−current efficiency η is determined by a large number of samples. Ask (S
6) Substituting the current density value i and the current efficiency η obtained in FIG. 5 into the equation (2) again, and calculating a plating film thickness predicted value (S7). In this way, the anode film shape is determined by obtaining the plating film thickness prediction value.

In order to make the inner surface of the cylinder a uniform inner diameter, the anode shape is specifically determined as follows. First, the outer diameter of the anode shape is set so that the plating film thickness required for the thick chromium plating layer side and the thin chromium plating layer side is as shown in FIG.
Are determined according to the flowchart shown in FIG. In step f1, the diameter on the side of the thick chromium plating layer is set to a fixed value based on the experiments so far.

In step f2, a finite element method analysis model is created by variously changing the anode diameter on the thin chromium plating layer side. At this time, the region A where the thick chromium plating layer changes to the thin chromium plating layer has a linear taper shape in which the anode diameter of the thick chromium plating layer side and the anode diameter of the thin chrome plating layer side are linearly connected. In step f3, an analysis mesh as shown in FIG. 3 is created for each model.

In step f4, for each model, the anode diameter on the thick chrome plating layer side and the anode diameter on the thin chrome plating layer side are determined. In step 5, the region changing from the thick chromium plating layer to the thin chromium plating layer is n
Divide (n: integer). A finite element method analysis model is created by variously changing the anode diameter at each of the divided positions, the plating film thickness is calculated, and the anode diameter is selected so that the estimated plating film thickness becomes the set cylinder inner diameter ( (Fig. 4). The number of divisions n for n division is determined by examining the variation of the inner diameter in the axial direction based on the film thickness prediction value according to the dimensional tolerance of the inner diameter of the cylinder.

As shown in FIG. 4, for example, an example is shown in which the area A is divided into five in the axial direction and the anode diameter of the first division is selected. Assuming that the line of the base, that is, the cylindrical inner surface 23 is a dotted line B, the anode diameter is 107, 108, 109, 110, 111 m.
From the state of change in the A region when it is changed to m, it is optimal to select the anode diameter whose inner surface of the cylinder whose film thickness changes little from the thickest chrome plating layer to the thin chrome plating layer is almost the same diameter. Find the diameter. In this example, in the first division, the diameter of the anode is 109 mm, which is the optimum diameter. (Step f6) In the present embodiment, only the cylinder 22 is described as the cylinder, but the present invention is not limited to the cylinder, and any cylinder may be used. Even in the case of a cylindrical body, an anode having an optimal shape can be obtained by applying the finite element method. Further, the plating is not limited to chromium plating, and the protection layer may be formed by plating other than chromium such as nickel depending on the use.

(Specific Example) Next, a case where the chrome plating method for the inner surface of the cylinder according to the present embodiment is applied to a weapon barrel will be described. In FIG. 1, the right side of the cylinder 22 is a portion on the loading chamber side of the weapon barrel, the plating bath 26 portion is a loading chamber, and a gun caliber portion continuous to the loading chamber of the weapon barrel is indicated by an area A. Before chrome plating, be sure to use cylinder 2
2 is performed. After degreasing, under the following conditions, cylinder 2
2 and the anode 24, a chromium plating layer having a different thickness is formed on the inner surface 23 of the cylinder. The working conditions of the chrome plating are as follows. Bath temperature: 55-68 ° C (actually temperature is controlled to be constant by adjusting the temperature to 62 ° C, 68 ° C, etc.) Current density: 20 A / dm ² (dm = 0.1 m) Plating solution: CrO ₃ / H ₂ SO ₄ (CrO ₃ : chromic acid concentration 200 g / l, H ₂ SO ₄ : sulfuric acid concentration 5 g / l) Current efficiency: Conditions are determined based on plating time and film thickness data.

[0034]

As described above, according to the present invention, an optimum anode shape is determined by calculating a plating film thickness prediction value based on a current density calculation value obtained by the finite element method. A plating layer having a different thickness in the axial direction can be formed by a single plating operation. This eliminates the need for machining or the like after the plating process as in the related art, so that the processing operation can be greatly simplified and reduced. Also,
Since a plating layer having a different film thickness can be formed at one time, there is no need to overlap the plating layers, so that the plating does not peel off as in the related art, and has sufficient durability as a protective layer.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a linear tapered anode in which a diameter of an anode is linearly changed in a chromium plating method according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a multi-step tapered anode in which the diameter of the anode is changed in multiple steps in the chromium plating method according to the embodiment of the present invention.

3 is an axially symmetric 2 in which a plating bath portion of FIG. 1 is an analysis region.
FIG. 3 is a finite element method mesh division diagram of a dimensional model.

FIG. 4 is a relationship diagram for estimating an axial position in a cylinder and an optimum diameter at an inner diameter of the cylinder.

FIG. 5 is a diagram showing a relationship between current density and current efficiency.

FIG. 6 is a diagram showing a flowchart for calculating a film thickness prediction value from a current density calculation value.

FIG. 7 is a diagram showing a flowchart for determining an anode shape by selecting an anode diameter at each position in the axial direction.

FIG. 8 is a diagram showing a relationship between a calculated value of current density and an experimental value of plating film thickness at each position in the axial direction.

FIG. 9 is a diagram showing a relationship between current density and current efficiency obtained by calculation.

FIG. 10 is a view showing a chromium plating film peeling test method.

FIG. 11 is a diagram showing a relationship between a chromium plating film thickness and a peeled area.

FIG. 12 is a cross-sectional view showing a case where a chromium plating layer is provided on a part of a cylinder in a first stage in a conventional method for changing a plating film thickness in an axial direction.

13 is a cross-sectional view showing a case where a chromium plating layer is provided on a part of the cylinder and then a chromium plating layer is provided on the entire surface of the cylinder in the second stage in the method of FIG.

FIG. 14 is a cross-sectional view for explaining a method in which a chromium plating layer can be applied at one time in another conventional method for changing the plating film thickness in the axial direction.

[Explanation of symbols]

 Reference Signs List 20 thick chrome plating layer 21 thin chrome plating layer 22 cylinder (cylindrical body) 23 inner surface of cylinder 23a small diameter portion 23b diameter change portion 23c large diameter portion 24 anode 24a linear taper portion 25 anode 25a continuous multi-step portion 26 plating bath A thick plating layer Area changing from thin to thin plating layer

Claims (9)

[Claims] An anode (24, 25) extending in the axial direction of a cylinder (22) is arranged, and the anode (24, 25) and the cylinder (22) are immersed in a plating solution to form an anode (24, 25). 2
5) A plating method for the inner surface of a cylinder in which plating with different film thicknesses is performed in the axial direction on the inner surface of the cylinder (22) by applying a current between the cylinder and the cylinder (22), which is obtained by a finite element method. A plating method for an inner surface of a cylinder, wherein an optimum anode shape is determined by calculating a plating film thickness prediction value based on a current density calculation value. 2. An anode (24, 25) extending in the axial direction of the cylinder (22) is arranged, and the anode (24, 25) and the cylinder (22) are immersed in a plating solution to form an anode (24). ,
25) A plating method for an inner surface of a cylinder, in which plating between the inner surface of the cylinder and a film having a different thickness is applied to the inner surface of the cylinder by applying a current between the cylinder (22) and the cylinder (22) by a finite element method. Calculating a current density calculated from the calculated current density and an experimental value of the plating film thickness at each axial position of the cylindrical body (22); From the relationship between the calculated efficiency values, a step of obtaining a plating film thickness prediction value; and, from the plating film thickness prediction value, a step of determining an anode shape whose inner diameter is uniform at each position in the axial direction. The plating method for the inner surface of the cylinder. 3. The method for plating the inner surface of a cylinder according to claim 2, wherein a thicker plating layer side anode diameter and a thinner plating layer side anode diameter of the cylinder (22) are determined, and then the thicker plating layer is thinned. A region changing into a layer is divided into n parts (n: integer) in the axial direction, an anode diameter at each of the divided positions is variously changed, a finite element method analysis model is created, a plating film thickness is calculated, and a plating film is formed. A plating method for an inner surface of a cylinder, wherein an anode diameter is determined such that a predicted thickness value becomes a set cylinder inner diameter. 4. The plating method for an inner surface of a cylinder according to any one of claims 1 to 3, wherein the step of obtaining the predicted value of the plating film thickness comprises: (1) a cathode, which is an actual boundary condition; Applying a temporary potential to the anode; (2) obtaining a current density (i = -κ∂φ / ∂n) by the finite element method; and (3) obtaining a total current amount which is an actual plating condition. Calculating the average current density on the cathode surface (total current amount / cathode surface area); and (4) adjusting the potentials of the cathode and anode such that the current density i by the finite element method becomes the average current density. (5) calculating the current density distribution on the cathode surface; (6) calculating the current efficiency from the calculated current density value and the plating film thickness experimental value at the adjusted potential; Find the current efficiency at the position Calculating a predicted plating film thickness at a position. 5. The plating method for an inner surface of a cylinder according to claim 4, comprising a step of determining an anode shape in which the inner surface of the cylinder has the same diameter at each position in the axial direction from the predicted plating film thickness. (1) setting the anode diameter on the thick plating layer side as a fixed value; (2) creating models with variously varying anode diameters on the thin plating layer side; Creating a finite element method analysis model, and (4) calculating a plating film thickness prediction value for each model, and dividing an area where a thick plating layer changes into a thin plating layer into n parts in the axial direction (n: integer) ) And (5)
A step of selecting an anode diameter which becomes a cylindrical inner diameter in which a plating film thickness at each of the divided positions is set; and (6) for each n,
Determining the shape of the anode by selecting the diameter of the anode as the inner diameter of the cylinder. 6. The plating method for an inner surface of a cylinder according to claim 1, wherein the cylinder (22) is a cylinder. 7. The plating method for an inner surface of a cylinder according to claim 1, wherein the plating is chrome plating. 8. A tubular body whose inner surface is plated by the plating method according to any one of claims 1 to 7. 9. The cylindrical body whose inner surface is plated according to claim 8, wherein the cylindrical body (22) is a cylindrical weapon barrel. .