A gradient sacrificial anode coated screw for ship dissimilar metal joint

Abstract

The utility model provides a gradient sacrificial anode coating screw for ship different metal joint, including screw body, the screw body has screw head and screw rod, the outer surface of screw rod is covered with sacrificial anode protection layer, the sacrificial anode protection layer with the screw rod is through metallurgical combination or thermal spraying mode combination, the sacrificial anode protection layer sets up and is by at least two electrochemical properties different sacrificial anode material composition layer, and gradient distribution along the axial direction of screw rod. Through a kind of gradient structure's sacrificial anode coating, realize stage by stage, sequentially consume, to significantly prolong the effective protection period of screw body, improve the reliability and service life of ship connecting structure.

Description

Technical Field

[0001] This utility model relates to the field of screw technology, and in particular to a gradient sacrificial anode coated screw for dissimilar metal joining in marine applications. Background Technology

[0002] In shipbuilding, there are numerous instances of joining dissimilar metal materials, such as using high-strength steel or stainless steel bolts to connect aluminum alloy hulls or superstructures. In seawater or humid, salt-spray electrolyte environments, these different metals can form galvanic cells. The metal with the more negative electrode potential (such as aluminum) acts as the anode and corrodes more rapidly, while the metal with the more positive electrode potential (such as steel) acts as the cathode and is protected. This galvanic corrosion is one of the main causes of premature failure at ship structural connections.

[0003] Currently, the main protective measures include: 1) applying an insulating coating, but the coating is easily scratched and damaged during installation, forming a bad situation of small anode-large cathode, which accelerates local corrosion; 2) using sacrificial anode blocks for protection, but the protection range of the anode blocks is limited, and the protection current distribution is uneven for critical screw connection points, resulting in poor effectiveness; 3) using all sacrificial anode materials to manufacture screws, but their mechanical strength often cannot meet the connection requirements of critical parts.

[0004] Existing technologies also include methods for coating fastener surfaces with sacrificial anode materials. For example, Chinese patent announcement CN206072065U, published on April 5, 2017, discloses a special screw, including a screw rod and a screw head. The top of the screw rod is fixedly connected to the screw head, and a screw head cap is provided on the screw head. The surfaces of the screw rod, screw head, and screw head cap are all provided with a galvanized layer. The screw head cap is provided with an installation groove, and the central axes of the screw rod, screw head, screw head cap, and installation groove are all located on the same straight line. Three grooves are provided on the inner wall of the installation groove. This utility model has a simple structure, low cost, and strong practicality. By providing a screw rod without threads, it has a certain positioning capability and can be used to position workpieces. Compared with threaded screws, it is not easy to loosen and has strong fixation. By providing an installation groove with grooves, the screw can be installed or removed. By providing a galvanized layer, the surface of the screw is smooth, which is convenient for installation and can prevent the screw from rusting, which helps to improve the service life of the screw. The screw can perform some special connection and fixing work, is not easy to rust, and is easy to use. It provides cathodic protection by galvanizing the surface of the steel screws. However, this single zinc coating is consumed rapidly in the highly corrosive marine environment. Once the zinc layer is depleted, the internal steel screws will corrode quickly, resulting in a limited protective lifespan that cannot match the long design life of ships.

[0005] Therefore, there is an urgent need in this field for a new screw structure that can provide long-term effective electrochemical protection without affecting the mechanical properties of the screw. Utility Model Content

[0006] To address the problem of rapid consumption and insufficient protection life of single sacrificial anode coatings in existing technologies, this utility model aims to provide a gradient sacrificial anode coated screw for dissimilar metal joints in ships. Its core purpose is to achieve phased and sequential consumption of the sacrificial anode coating through a gradient structure, thereby significantly extending the effective protection cycle of the screw body and improving the reliability and service life of ship connection structures.

[0007] This utility model provides a gradient sacrificial anode coated screw for dissimilar metal joining in ships, including a screw body, the screw body having a screw head and a screw shank, the outer surface of the screw shank being coated with a sacrificial anode protective layer, the sacrificial anode protective layer being bonded to the screw shank by metallurgical bonding or thermal spraying, the sacrificial anode protective layer being configured as a layer composed of at least two sacrificial anode materials with different electrochemical properties, and being gradient distributed along the axial direction of the screw shank.

[0008] Preferably, the sacrificial anode protection layer includes an inner layer and an outer layer, the inner layer covering the surface of the screw, the outer layer covering the surface of the inner layer, and the electrode potential of the outer layer is more negative than that of the inner layer.

[0009] Preferably, the inner layer is a zinc alloy layer or an aluminum alloy layer, and the outer layer is a magnesium alloy layer or a magnesium-manganese alloy layer.

[0010] Preferably, the sacrificial anode protective layer has a three-layer structure, consisting of a first layer, a second layer, and a third layer from the inside out, with the electrode potentials of the first layer, the second layer, and the third layer becoming progressively more negative.

[0011] Preferably, the thickness of the sacrificial anode protective layer is 0.1 mm to 2.0 mm.

[0012] Preferably, the lower surface of the screw head is also covered with the sacrificial anode protective layer.

[0013] Preferably, the outer surface of the sacrificial anode protective layer is machined with threads that mate with the screw.

[0014] Preferably, the sacrificial anode protective layer is further coated with a hydrolyzable sealing coating.

[0015] Preferably, the screw body is a high-strength steel screw or a stainless steel screw.

[0016] The beneficial effects of this utility model are as follows:

[0017] 1. Gradient protection for longer lifespan: By setting a gradient sacrificial anode layer with electrode potential decreasing negative from the inside out, the outermost layer with the most negative potential is consumed first, and only after it is consumed does the innermost layer with the next most negative potential begin to be consumed. This "tiered retreat" design concept is equivalent to providing double or even multiple protections for the screw, greatly extending the overall protection lifespan and making it compatible with the ship's design overhaul cycle.

[0018] 2. Comprehensive protection and high reliability: The protective layer not only covers the screw rod but also the lower surface of the screw head, providing all-round, no-dead-angle electrochemical protection for the entire exposed surface of the screw, completely eliminating the occurrence of galvanic corrosion.

[0019] 3. Guaranteed strength and wide applicability: High-strength steel or stainless steel is used as the core material of the screw, ensuring the mechanical strength required for the connection; the soft outer sacrificial anode material provides excellent corrosion protection, achieving a perfect combination of strength and corrosion resistance, suitable for various important dissimilar metal connections in ships.

[0020] 4. Complete functions and good practicality: The threads are machined on the outside of the anode layer and a sealing coating can be selected, which not only ensures the assembly function of the screw, but also optimizes its storage and initial working condition, thereby improving the practicality and reliability of the product. Attached Figure Description

[0021] Figure 1 Front view of the first embodiment

[0022] Figure 2 This is a bottom view of the first embodiment.

[0023] Figure 3 This is a bottom view of the second embodiment.

[0024] Figure 4 This is a bottom view of the third embodiment.

[0025] Figure 5 This is a bottom view of the fourth embodiment.

[0026] The attached figures are labeled as follows: screw body 10, screw head 11, screw shank 12, sacrificial anode protective layer 13, inner layer 15, outer layer 14, third layer 18, first layer 17, second layer 16, and hydrolyzable sealing coating 19. Detailed Implementation

[0027] To further understand the features, technical means, and specific objectives and functions achieved by this utility model, the following detailed description of this utility model is provided in conjunction with specific embodiments and accompanying drawings.

[0028] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0029] For the first implementation method, please refer to Figure 1-2 As shown, this utility model provides a gradient sacrificial anode coated screw for dissimilar metal joining in marine applications, comprising a screw body 10, a screw head 11, and a screw 12. The outer surface of the screw 12 is coated with a sacrificial anode protective layer 13, which is bonded to the screw 12 by metallurgical bonding or thermal spraying. The sacrificial anode protective layer 13 is composed of at least two sacrificial anode materials with different electrochemical properties, and is distributed in a gradient along the axial direction of the screw 12. The lower surface of the screw head 11 is also coated with the sacrificial anode protective layer 13. The protective layer not only covers the screw 11 but also the lower surface of the screw head, providing all-round, comprehensive electrochemical protection for the entire exposed surface of the screw, completely eliminating galvanic corrosion. The total thickness of the sacrificial anode protective layer 13 is controlled at 0.8 mm. The outer surface of the sacrificial anode protective layer 13 is machined with threads that mate with the screw 12. These threads are replicated through precision machining to ensure good engagement performance.

[0030] The sacrificial anode protective layer 13 comprises an inner layer 15 and an outer layer 14. The inner layer 15 covers the surface of the screw 12, and the outer layer 14 covers the surface of the inner layer 15. The electrode potential of the outer layer 14 is more negative than that of the inner layer 15. The thickness of the sacrificial anode protective layer 13 is 0.1 mm to 2.0 mm. The inner layer 15 is a zinc alloy layer or an aluminum alloy layer, and the outer layer 14 is a magnesium alloy layer or a magnesium-manganese alloy layer. The electrode potential of the magnesium alloy (approximately -2.37V vs. SHE) is more negative than that of the zinc alloy (approximately -1.05V vs. SHE). Therefore, in a corrosive environment, the magnesium alloy of the outer layer 22 will preferentially act as the anode and be consumed, providing protection for the inner zinc layer and the steel screw body. After the magnesium alloy layer is exhausted, the zinc alloy inner layer 21 begins to work, continuing to provide cathodic protection for the steel screw body 1, thereby achieving two-stage gradient protection with a lifespan far exceeding that of a single zinc coating. This "tiered retreat" design concept greatly extends the overall protection life, enabling it to match the ship's design overhaul cycle.

[0031] The screw body is made of high-strength steel or stainless steel, ensuring the mechanical strength required for the connection; the outer soft sacrificial anode material provides excellent corrosion protection, achieving a perfect combination of strength and corrosion resistance, suitable for various important dissimilar metal connections in ships.

[0032] For the second implementation method, please refer to... Figure 3 As shown, based on the first embodiment, a hydrolyzable sealing coating 19 is further coated on the outside of the sacrificial anode protective layer 13. This coating may be made of wax or a specific hydrolyzable polymer material. During storage and transportation, this coating isolates oxygen and moisture, preventing unnecessary oxidation and consumption of the sacrificial anode material. When the screw is screwed into the component, the moisture in the environment causes the coating to gradually hydrolyze, exposing the active sacrificial anode surface, which then begins to provide cathodic protection.

[0033] For the third implementation method, please refer to Figure 4 As shown, the sacrificial anode protection layer 13 has a three-layer structure, consisting of a first layer 17, a second layer 16, and a third layer 18 from the inside out. The electrode potentials of the first layer 17, the second layer 16, and the third layer 18 decrease in negativeness sequentially. The thickness of the sacrificial anode protection layer 13 ranges from 0.1 mm to 2.0 mm. The lower surface of the screw head 11 is also covered with the sacrificial anode protection layer 13, and the outer surface of the sacrificial anode protection layer 13 is machined with threads to mate with the screw 12. The first layer 17 (equivalent to the inner layer) is made of aluminum alloy, the second layer 16 is made of zinc alloy, and the third layer 18 (equivalent to the outer layer) is made of magnesium alloy. The electrode potentials of the three layers decrease in negativeness sequentially (magnesium is the most negative, followed by zinc, and aluminum is relatively the most positive). During operation, the third layer of magnesium alloy is consumed first, followed by the second layer of zinc alloy, and finally the first layer of aluminum alloy. This design provides a longer stepped protection life.

[0034] For the fourth implementation method, please refer to... Figure 5 As shown, based on the third embodiment, the sacrificial anode protective layer 13 is further coated with a hydrolyzable sealing coating 19.

[0035] The above-described embodiments only illustrate four implementation methods of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A gradient sacrificial anode coated screw for dissimilar metal joining in marine applications, comprising a screw body (10) having a screw head (11) and a screw shank (12), characterized in that: The outer surface of the screw (12) is covered with a sacrificial anode protective layer (13). The sacrificial anode protective layer (13) is bonded to the screw (12) by metallurgical bonding or thermal spraying. The sacrificial anode protective layer (13) is configured to be composed of at least two sacrificial anode materials with different electrochemical properties and is distributed in a gradient along the axial direction of the screw (12).

2. The graded sacrificial anode coated screw for marine dissimilar metal joining according to claim 1, characterized in that: The sacrificial anode protection layer (13) includes an inner layer (15) and an outer layer (14). The inner layer (15) covers the surface of the screw (12), and the outer layer (14) covers the surface of the inner layer (15). The electrode potential of the outer layer (14) is more negative than that of the inner layer (15).

3. The gradient sacrificial anode coated screw for marine dissimilar metal joining according to claim 2, characterized in that: The inner layer (15) is configured as a zinc alloy layer or an aluminum alloy layer, and the outer layer (14) is configured as a magnesium alloy layer or a magnesium-manganese alloy layer.

4. The gradient sacrificial anode coated screw for marine dissimilar metal joining according to claim 1, characterized in that: The sacrificial anode protective layer (13) has a three-layer structure, consisting of a first layer (17), a second layer (16), and a third layer (18) from the inside out. The electrode potentials of the first layer (17), the second layer (16), and the third layer (18) become progressively more negative.

5. A graded sacrificial anode coated screw for marine dissimilar metal joining according to claim 4, characterized in that: The thickness of the sacrificial anode protective layer (13) is 0.1 mm to 2.0 mm.

6. A gradient sacrificial anode coated screw for marine dissimilar metal joining according to any one of claims 1 to 4, characterized in that: The lower surface of the screw head (11) is also covered with the sacrificial anode protective layer (13).

7. A gradient sacrificial anode coated screw for marine dissimilar metal joining according to any one of claims 1 to 4, characterized in that: The outer surface of the sacrificial anode protective layer (13) is machined with threads that mate with the screw (12).

8. A gradient sacrificial anode coated screw for marine dissimilar metal joining according to any one of claims 1 to 4, characterized in that: The sacrificial anode protective layer (13) is further coated with a hydrolyzable sealing coating (19).

9. A gradient sacrificial anode coated screw for marine dissimilar metal joining according to any one of claims 1 to 4, characterized in that: The screw body (10) is configured as a high-strength steel screw or a stainless steel screw.

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