Abstract:
The issues of low efficiency, high safety risks, and long construction cycles during the installation of steel casting brackets for tilted dual-shaft rudder systems in the ship assembly stage. Taking the segmented dual-shaft rudder system of a certain Ro-Ro ship as the research object, we analyzed its precision control standards and requirements. We proposed a precision quality control method for pre-installing steel casting brackets during the segmented construction stage and implemented it during the construction process. The implementation results indicate that this precision quality control method can fully meet the operational requirements of the ship’s main engine in the later stages, significantly improving ship production and construction efficiency, shortening the shipbuilding cycle, and improving the construction working environment.
1. Introduction
The steel casting brackets for ship shaft rudder systems are typically installed during the hull assembly stage. This method is difficult to implement, results in low work efficiency, has a long construction period, and involves high-altitude operations, posing significant safety risks. Currently, many domestic shipyards lack experience when building long-shaft engineering vessels for the first time and have weak precision control awareness, leading to multiple repairs [1].
To address this, this paper takes a certain Ro-Ro ship as the research object. Firstly, combining the precision control characteristics of the dual-shaft rudder system segments, we moved forward the pre-installation of the dual-shaft rudder system steel casting brackets to the segmented construction stage. Secondly, starting from the splicing of the shaft system steel castings, we adopted three-dimensional detection technology to control the precision of pre-installation at various key points to ensure efficient and precise installation of the ship’s shaft rudder system.
2. Formulation of Precision Control Plan for Pre-installation of Steel Castings for Shaft Rudder Systems
The brackets for the shaft system of a certain Ro-Ro ship are all installed on the outside of the hull. There are six shaft system steel castings at the stern used to fix the main engine rotating shaft and two rudder system steel castings used to fix the rudder rotating shaft. The shaft system steel castings are installed on six segments: two stern castings on the ED11P/S segments, two “I”-shaped single-arm brackets on the AG02C segment, and two “V”-shaped double-arm brackets on the AG03C segment; the two rudder sleeves of the rudder system steel castings are installed on the AG01C segment.
2.1 Precision of Pre-installation
To ensure the installation precision of the shaft rudder system during the assembly stage and the normal operation of the main engine shaft system, the concentricity of the shaft holes of the shaft and rudder system steel castings must be controlled within a range of 2 mm.
2.2 Construction Environment
Due to the extremely high precision requirements for the pre-installation of shaft rudder system steel castings, the construction environment also has high demands. To ensure that the ambient temperatures during measurement are basically the same, thereby ensuring measurement accuracy, the environment for splicing and pre-installation of steel castings must be indoors.
2.3 Positioning Scheme
Before pre-installing the shaft rudder system steel castings, a positioning scheme must be formulated to clarify the anti-deformation addition and positioning scheme for each step in the positioning process of the eight steel castings. The specific content is as follows:
Table 1: Positioning Requirements for Steel Castings of Various Segments
| Segment | Positioning Direction | Positioning Requirements | Allowable Error Range |
|---|---|---|---|
| ED11P/S (2 stern castings) | Front-to-back | Based on the distance between the front end face of the steel casting shaft hole and the tail end face of the segment, positioned with an error of 0-3 mm | ±3 mm (for positioning) |
| Left-to-right | The concentricity of the stern casting shaft hole is positioned at 0 mm, with an allowable error range of ±1 mm | ±1 mm | |
| Height | Based on the center of the shaft hole, add 3-5 mm of anti-deformation in the height direction | – | |
| AG02C (2 “I”-shaped single-arm brackets) | Front-to-back | Positioned based on the front end face of the steel casting, with a 4 mm anti-deformation addition towards the bow when ensuring the single-arm frame structure aligns with the ribs | – |
| Left-to-right | The concentricity is positioned at 0 mm based on the center of the shaft hole, with an allowable error range of ±1 mm | ±1 mm | |
| Height | Based on the center of the shaft hole, add 3-5 mm of anti-deformation in the height direction | – | |
| AG03C (2 “V”-shaped double-arm brackets) | Front-to-back | Positioned based on the tail end face of the steel casting, with a 5 mm anti-deformation addition towards the stern when ensuring the double-arm frame structure aligns with the ribs | – |
| Left-to-right | The center of the steel casting is positioned 5 mm towards the side of the hull | – | |
| Height | Based on the center of the shaft hole, add 5 mm of anti-deformation in the height direction and position at a height of +5 mm | – | |
| AG01C (2 rudder sleeves) | Front-to-back | Positioned based on the position of the rudder hole center in the segment, with positioning of 0-1 mm | – |
| Left-to-right | Positioned based on the center of the rudder hole at 0 mm | 0 mm (fixed positioning) | |
| Height | Based on the lower opening of the rudder sleeve as the positioning benchmark, with an addition of 3-5 mm of anti-deformation | – |
3. Implementation of Precision Control Plan for Segmented Pre-installation of Steel Castings
3.1 Precision Control for Assembly and Splicing of Steel Castings
The “I”-shaped single-arm bracket and “V”-shaped double-arm bracket steel casting shafts are assembled by splicing multiple steel castings on a horizontal iron platform jig. To ensure the splicing precision quality, the following are the precision control requirements for the shaft frame splicing:
Table 2: Precision Control Requirements for Shaft Frame Splicing
| Requirement | Details |
|---|---|
| Drawing benchmarks | Draw the center benchmark of the steel casting shaft hole and the splicing positioning benchmark on the platform. |
| Hoisting and positioning | After the steel casting is hoisted onto the jig, a plumb line should ensure that the concentricity of the steel casting placement shaft hole is 1 mm and coincides with the center and splicing seam position on the platform. |
| Welding method | Adopt symmetrical welding. First, apply the bottom weld of the butt joint, then perform symmetrical welding by two people. Monitor in real-time whether the bracket deforms during welding, and adjust the welding sequence if deformation occurs. |
| Post-welding measurement | After welding is completed, measure the shaft hole and upper opening dimensions after the steel casting has completely cooled to ensure that the splicing precision of the steel casting is controlled within 2 mm. |
3.2 Precision Control for Stern Casting Tube Splicing
The stern casting tube is assembled by splicing steel castings and steel pipes. The specific splicing precision control method is as follows:
Table 3: Precision Control Method for Stern Casting Tube Splicing
| Requirement | Details |
|---|---|
| Assembly and positioning | During the assembly and positioning stage, connect two steel casting cylinder bodies with one steel pipe. When positioning the splice, add a 2-3 mm contraction allowance for each butt weld. During the cylinder body splicing process, place a 2-3 mm high welding anti-deformation allowance in the middle of the first and second butt weld positions for weld gap contraction and deformation control in the height direction during welding. |
| Concentricity detection | After the cylinder body splicing is formed, move the concentricity position detection points inside the cylinder body to the outer surface of the steel casting tube body, and make six detection marking points. Use a 3D total station to replace the traditional steel wire method for concentricity detection. |
| Welding process monitoring | During the welding of steel castings, detect the points on the outer side of the tube body, analyze the changes in cylinder straightness, and guide the adjustment of the welding sequence on-site based on the straightness change data to ensure that the concentricity of the stern casting tube after welding is controlled within a 1.5 mm error range. |
3.3 Precision Control for Rudder Sleeve Pre-installation
The two rudder pedestals on segment AG01C are located on two curved assemblies. The precision quality of the rudder pedestal positioning directly affects the rudder sleeve positioning consequently, the entire rudder system positioning. To ensure the pre-installation precision of the rudder sleeves, during the rudder sleeve positioning phase, anti-deformation amounts are added according to the rudder sleeve positioning scheme. By tracking the welding process data, measurements and observations are taken of the height-direction data changes of the rudder pedestal and rudder sleeve, as well as the concentricity changes in the forward-backward and left-right directions. These measurement data variations are used to guide the welding sequence during the on-site construction process, ensuring that the concentricity precision of the rudder pedestal is controlled within ±1 mm.
During the pre-installation control of the “I” and “V”-shaped steel castings segments, special considerations are given to the high precision requirements of the shaft and rudder system. It is necessary to ensure that the pre-installation of the steel castings is carried out only after all welding of the segment hull structure is completed.
(1) Selection of Positioning Benchmarks. After the welding of the hull structure of segments AG02C and AG03C is completed, a three-dimensional total station is utilized to conduct a complete measurement of the overall precision of the segments, clarifying the benchmarks for the positioning of the “I” and “V”-shaped steel castings on the segments in the forward-backward, left-right, and up-down directions.
(2) Positioning of Steel Castings. The steel castings are lifted and placed at the corresponding positions on the segment structure. Crosshair markings are set at the front and rear end faces of the steel casting bore, serving as positioning detection points for the steel casting shaft bracket. Utilizing three-dimensional detection technology, the steel castings are positioned according to the pre-installation positioning scheme. After the positioning data meets the requirements, assembly welding of the steel castings is performed.
(3) Welding of Steel Castings. Clamps are used to fix the connection between the steel castings and the structure, and spot welding is employed to secure the steel castings at strong structural locations, ensuring that the welding length between the hull’s strong structure and the end of the “V”-shaped steel casting is no less than 500 mm. Symmetrical welding is adopted during the welding process to control the welding sequence and prevent axis offset. During welding, the welding of outer plates and decks is completed before the welding of internal components. Meanwhile, the precision of the steel casting center is monitored in real-time using a three-dimensional total station measurement method, with data detection conducted at a frequency of once every hour. Adjustments to the welding sequence are made on-site based on data changes.
Due to the unique structure of the “V”-shaped steel casting on segment AG03C, there is a tendency for it to deflect towards the ship’s side after welding. To ensure that the relative spacing and forward-backward direction errors of the bore centers of the two “V”-shaped steel castings are controlled within standard ranges after welding, the first steel casting on the port side is welded first. After the welding of the first “V”-shaped steel casting is completed, positioning and anti-deformation amounts are added for the second “V”-shaped bracket based on actual changes. During the welding process, the concentricity precision of both steel castings should be taken into account to ensure that the dual bore concentricity error is within ±1 mm.
In summary, the precision control measures implemented during the pre-installation of the rudder sleeves and steel castings ensure the accurate installation of the shaft and rudder system, which is crucial for the smooth operation of the ship. These precision control methods provide a solid technical foundation for the pre-installation of shaft and rudder system segments of other ship types and have obtained valuable data and experience.