JPS61127893A - Propeller for ship - Google Patents

Abstract

PURPOSE:To improve the resistance of a propeller to cavitation erosion and corrosion by forming Cr plating of a specified thickness on the forward and backward sides of the body of the propeller. CONSTITUTION:Cr plating of >=100mum thickness is formed on the forward and backward sides of the body of a propeller for a ship so that the sides are coated entirely or partially with the plating. It is preferable that the Cr plating is composed of two or more layers. Even when the plating has fine cracks, the body of the propeller is not eroded because the plating is so thick that the cracks remain in the plating. Accordingly, the resistance to cavitation erosion is considerably improved, and the improving effect is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a marine propulsion device, and more particularly to a marine propulsion device with improved cavitation erosion resistance and corrosion resistance.

(Prior art and its problems) As is well known, marine propulsors are made of copper alloys mainly consisting of manganese bronze and aluminum bronze, and ferrous materials such as cast steel and cast iron. As marine propulsors become larger in diameter or at higher speeds, the problem of cavitation erosion occurring in the propulsors has arisen.

When cavitation erosion occurs, the roughness of the propulsion layer surface decreases, water resistance increases, propeller torque increases, and propulsion efficiency decreases. This cavitation erosion is essentially a design problem, but it is difficult to completely eliminate it with current design technology, so the occurrence of cavitation erosion is suppressed at the expense of propeller efficiency. That is the reality.

Therefore, for example, as described in Japanese Patent Application No. 59-133991, it may be possible to coat the propeller body with an ultra-high molecular weight polyethylene resin to improve cavitation erosion resistance. This marine propulsion device provides various advantages such as improved cavitation erosion resistance and corrosion resistance. However, the above marine propulsion device may require a relatively large amount of effort to manufacture.

On the other hand, since the construction efficiency is relatively good, attempts have been made to apply chrome plating to the surface of marine propellers to improve cavitation erosion resistance. The effect of improving cavitation erosion resistance is not stable and cannot be said to be sufficiently high.

The present inventors focused on the above-mentioned chromium plating and conducted various studies to find out why the improvement effect of chromium plating on cavitation erosion resistance is unstable and insufficient as described above, and the following findings were made. I got it. In other words, the chromium plating layer has congenitally minute cracks,
Erosion penetrates into the propeller body through these minute cracks, and this penetration causes further erosion.

(Means for Solving the Problems) Therefore, in the marine propulsion device of the present invention, a chromium plating layer with a thickness of 100 μm or more is formed on all or part of the forward and reverse moving surfaces of the propeller body.

In a preferred embodiment of the marine propulsion device of the present invention, the chromium plating layer is composed of two or more plating layers.

(Function) When the thickness of the chrome plating layer is set to 100 μm or more as described above, although there are fine cracks in this plating layer, the plating layer is thick enough that erosion penetrates the propeller body. It does not reach this point and remains in the plating layer. Therefore, the cavitation erosion resistance is significantly improved, and the improvement effect is also stable.

Furthermore, when the chromium plating layer is composed of two or more plating layers, erosion that extends through minute cracks will temporarily stop between the plating layers, resulting in a significant and stable improvement in cavitation erosion resistance. becomes possible. Furthermore, if two or more plating layers are used and the two lotions stop at the boundary between the top layer and the second layer as described later, the roughness will remain below the thickness of the top plating layer, and as a result, only one layer will be applied. It is possible to maintain the surface roughness after erosion rather than thickening.

(Embodiments) Next, specific embodiments of the marine propulsion device of the present invention will be described in detail with reference to the drawings.

However, for the sake of explanation, we will mainly discuss the cavitation erosion test results using test pieces, but as will be explained later, these have a good correlation with the durability test results of marine propulsion units, so it can be considered a simple test. I think that the.

First, FIG. 1 shows the change in damage weight when the thickness of the chromium plating layer was varied and tested using a magnetostrictive vibration type cavitation erosion tester using the facing method. The test conditions are as follows.

Frequency: 19KHz Amplitude: 30μm Test solution: 3% saline (25±5°C) Test time: 20
H Test piece shape = 25 frames x 25 frames x 2 cranes (thickness) Test piece material Ni-nickel aluminum bronze (JIS symbol: AJBC3) From Figure 1, when the thickness of the chrome plating layer is 100 μm or more, cavitation resistance It is clear that the erosion properties are significantly improved and the improvement effect is stable. When the thickness of the chromium plating layer is thinner than 100 μm, the cavity siding erosion loss @weight is large, and at the same time, the experimental data varies relatively widely, and the improvement effect is unstable.

Next, the reason will be explained based on FIGS. 2 to 4. In each figure, 1 is the test piece body (nickel/aluminum bronze), 2 is the chrome plating layer, and 3 is the plating layer 2.
4 indicates erosion, and (a) in each figure indicates the state before the test, and fbl indicates the state after the test. First, when the chromium plating layer 2 is thinner than 100 μm, the erosion 4 penetrates through minute cracks to the test piece main body 1, as shown in Fig. 2, and the main body 1 is significantly damaged by this penetration. . When the chromium plating layer is not thick like this, it is thought that the adjacent fine cracks are often continuous from the outermost surface to the vicinity of the boundary with the test piece body 1 when viewed three-dimensionally. In such a case, it is presumed that the above-mentioned damage progresses particularly in a short period of time (as shown near the upper limit of the shaded area in FIG. 1). On the other hand, when the chrome plating R2 is 100 μm or more, as shown in FIG. Become. Therefore, cavitation erosion resistance is significantly improved. Furthermore, in the case shown in FIG. 4, the chromium plating layer 2 is divided into a first layer 2a and a second layer 2.
In this case, the erosion 4 is formed in the first layer 2a and the second layer 2b in the plating layer 2.
Since it temporarily stops at the boundary between the two, cavitation erosion resistance can be further improved. In addition, in the case where the plating layer 2 is composed of multiple layers as described above, if the top layer is made thin, even if a part of the top layer peels off due to the erosion 4 as described above,
The surface roughness remains below the thickness of the top plating layer, and the decrease in surface roughness is less than when using only one thick layer. It has been confirmed in durability tests using small propellers that when the plating layer is thinner than 100 μm, the propulsion efficiency decreases markedly with the test time, but when the plating layer is thicker than 100 μm, the drop in propulsion efficiency is prevented, and especially when the plating layer is thinner than 100 μm, the decrease in propulsion efficiency is prevented. The results showed that the effect was remarkable in layer plating.

Although the present invention has been described in detail above, the marine propulsion device of the present invention is not limited to the above embodiments, and can be implemented with various modifications within the scope of the purpose of the present invention. .

(Effects of the Invention) The marine propulsion device of the present invention is configured as described above, and therefore the marine propulsion device of the present invention has the following effects.

■ Since cavitation erosion resistance is excellent and the occurrence of cavitation erosion is suppressed, a propulsion device can be designed without sacrificing propeller efficiency, and therefore the propulsion efficiency of ships can be increased.

■ The surface of chrome plating can be made smoother than the surface of conventional metal propellers, and because marine organisms are less likely to adhere to it, the frictional resistance between the propeller and water is reduced.

Therefore, propeller torque is reduced and propulsion efficiency can be increased.

■ The chrome plating layer has superior corrosion resistance compared to the surface of metal propellers. Therefore, corrosion of the propeller can be suppressed even when navigating in sea areas contaminated with industrial wastewater.

■ The chrome-plated surface is smoother than the surface of metal propellers, so marine life is less likely to attach to it during navigation. Therefore, the amount of propeller cleaning and polishing work performed during docking can be reduced.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the thickness of the chromium plating layer and the damage weight in the magnetostrictive vibration cavitation erosion test, Figure 2 (a) (bl to Figure 4 (a)
(bl is an explanatory diagram for explaining the progress of erosion, and Figure 2 shows the case where the chromium plating layer is thinner than 100 μm.
Figure 3 shows the case where the plating layer is 100 μm or more, and Figure 4 shows the case where the plating layer is composed of two layers. tb) shows the state after the test. 1... Test piece body, 2... Chrome plating layer, 3...
・Minute cracks existing in plating layer 2, 4... ・Erosion.

Claims (1)

[Scope of Claims] 1. A marine propulsion device, characterized in that a chromium plating layer with a thickness of 100 μm or more is formed on all or part of the forward and reverse moving surfaces of the propeller body. 2. The marine propulsion device according to claim 1, wherein the chromium plating layer is composed of two or more plating layers.