Preparation method of ultra-long seamless mooring chain

Abstract

The invention discloses a preparation method of a super-long seamless mooring chain, during preparation, a novel additive manufacturing printer is adopted, the super-long seamless mooring chain is formed by tightly connecting n subareas, each subarea is internally provided with a front scraper, a laser, a powder bed, an ascending cylinder and a descending cylinder, and a rear scraper is arranged behind the joint of every two adjacent front scrapers; the preparation method specifically comprises the following steps: (1) designing a placement mode, making a printing file, and inputting the printing file into a printer; (2) pushing powder, paving the powder on a powder bed, and scraping the powder; (3) laser scanning and printing; and (4) circulation is carried out again until the complete high-grade super-long seamless mooring chain is printed out. According to the method, the extra-long seamless mooring chain is manufactured through additive manufacturing, the method is greatly different from a traditional production mode, and the produced mooring chain product is free of welding seams, high in strength, resistant to corrosion, quite excellent in performance, short in production process and high in manufacturing efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of mooring chain manufacturing, and more particularly to a method for preparing an extra-long seamless mooring chain. Background Art

[0002] Offshore mooring chains are crucial for maintaining the safety of marine engineering facilities and are a key component of offshore mooring and positioning systems for marine engineering equipment. They are primarily used for mooring offshore drilling platforms, deep-sea aquaculture systems, floating deep-sea wind turbines, deep-sea mooring systems, military vessels, floating production storage and offloading vessels, and other marine development facilities. Because offshore mooring chains are constantly immersed in seawater and in operation, they require not only a high degree of strength and toughness, but also resistance to seawater corrosion, fatigue, and wear. According to the 2018 edition of the Norwegian-Germanischer Lloyd standard "Offshore Mooring Chains," mooring chains are categorized by strength level into R3, R3S, R4, R4S, R5, and R6.

[0003] Currently, marine mooring chains are primarily divided into two categories: studless and studded. Studless chains are commonly used for permanent moorings. The lack of studs reduces the weight per unit strength and increases the chain's fatigue life. However, their disadvantage is that they are less convenient to operate during hoisting. Studded chains, traditionally used for MODUS and FPSOS moorings in shallower waters, have proven to be strong, reliable, and relatively easy to handle. The studs provide a stable connection between the chain links and facilitate hoisting.

[0004] Mooring chain steel is typically round steel. The traditional production process involves: scrap steel, hot-charged hot metal, electric arc furnace smelting, LF (ladle refining furnace) refining, RH (vacuum recirculating degassing furnace) degassing, bloom continuous casting, blooming, continuous rolling, steel annealing, surface peeling, ultrasonic testing, inspection, packaging, and storage. Some large-size round steel also requires die casting.

[0005] Mooring chains are manufactured after hot-rolled or forged round steel is produced. At the mooring chain processing plant, the steel is cut into the required lengths for individual links. This steel is then heated in an eddy current furnace. While still red-hot, one end is bent and attached to the entire mooring chain. The other end is then bent again. The chain is then flash welded on a welder and deburred on a deburrer. A crosspiece is placed between the links and mechanically clamped to the red-hot links before further welding. Once the chain passes flaw detection, it is sent to a heat treatment furnace for heat treatment. Tensile and break tests are then performed. Qualified chains are then ground and shot blasted before being sent to the paint shop for painting. The finished mooring chain passes inspection by the classification society before being shipped.

[0006] However, in traditional production processes, mooring chains must be welded, and there are welds at the chain link connections and crossbar connections. The chain link welds are the weak links of the entire mooring chain, and their strength, plasticity, toughness, corrosion resistance, etc. are lower than other parts.

[0007] Therefore, how to improve the performance of chain link welds in traditional production processes is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0008] In view of this, an object of the present invention is to provide a method for preparing an ultra-long seamless mooring chain to address the deficiencies in the prior art.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for preparing an ultra-long seamless mooring chain employs a novel additive manufacturing printer, which is composed of n tightly connected partitions. Each partition is equipped with a front scraper, a laser, a powder bed, a lifting cylinder, and a lowering cylinder. A rear scraper is provided behind the connection between two adjacent front scrapers.

[0011] The preparation method specifically comprises the following steps:

[0012] (1) Design the placement pattern of the mooring chain on the printer powder bed according to the type and size of the mooring chain link, create the print file, and input it into the printer;

[0013] (2) On a printer with a set program, after the mooring chain steel powder in the n rising cylinders is ejected at the same time, the n front scrapers push the powder forward and spread the powder evenly on the powder bed, and the n-1 rear scrapers follow up to scrape the powder at the same time;

[0014] (3) The front scraper and the rear scraper return to their initial positions, the laser is started, and the powder bed is scanned according to the set laser parameters to print the first layer of the mooring chain;

[0015] (4) Finally, the n descending cylinders drive the powder bed to move down one layer, and the mooring chain steel powder in the n ascending cylinders is ejected for the second time, and the powder printing process is cycled again to print the second layer, the third layer, etc., until a complete high-level ultra-long seamless mooring chain is printed.

[0016] The present invention uses additive manufacturing to manufacture ultra-long seamless mooring chains, which is significantly different from traditional production methods. The mooring chain products produced have no welds, are highly strong and corrosion-resistant, have excellent performance, a short production process, and high manufacturing efficiency.

[0017] Furthermore, the n partitions mentioned above are n independent but simultaneously printable subsystems. The number of n depends on the required length of the printed mooring chain. Ultra-long and even infinitely long can be printed in theory.

[0018] Furthermore, there are n front scrapers in total, which are the main powder spreading scrapers; there are n-1 rear scrapers in total, which are mainly used to scrape flat the raised linear powder in the gap between the two front scrapers.

[0019] Furthermore, in the above step (1), the types of mooring chain links include geared links and non-geared links; the size of the geared links is a nominal diameter of 165 to 240 mm, and the size of the non-geared links is a nominal diameter of 34 to 240 mm.

[0020] Furthermore, in the above step (1), the placement modes include serpentine and straight lines; the serpentine type is suitable for short and small chain links, and bending and coiling is used to increase the printing length; the straight line type is suitable for thick and large chain links, which cannot be bent and coiled.

[0021] Furthermore, in the above step (4), the high level includes R4, R4S, R5, R6 and the new R7; seamless means that each link of the mooring chain is formed in one step and has no welds throughout.

[0022] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The integrated additive manufacturing printing mooring chain has an extra-long chain and no welds on the chain links.

[0024] 2. The manufactured mooring chain is of high grade, high strength, good toughness and excellent corrosion resistance;

[0025] 3. The production process is short and efficient, which shortens the production cycle of the mooring chain. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of the new additive manufacturing printer;

[0027] Among them, 1-mooring chain, 2-front scraper, 3-rear scraper, 4-laser, 5-powder bed, 6-lowering cylinder, 7-raising cylinder, 8-nth partition;

[0028] Figure 2 is the particle size distribution diagram of steel powder;

[0029] Figure 3 The microscopic morphology of steel powder;

[0030] Figure 4 The following are physical pictures of cubic parts, tensile parts and impact parts;

[0031] Figure 5 Schematic diagram of the traditional manufacturing process and additive manufacturing process for mooring chains;

[0032] Figure 6 Mechanical properties of mooring chain samples under different laser powers;

[0033] Figure 7 is the impact absorbed energy of the mooring chain sample under different laser powers;

[0034] Figure 8 Impact fracture morphologies of mooring chain samples under different laser powers, where a is T2 sample, b is T4 sample, and c is T6 sample;

[0035] Figure 9 This is a physical picture of the successfully printed three-link mooring chain sample. DETAILED DESCRIPTION

[0036] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0037] Example 1

[0038] A method for preparing an ultra-long seamless mooring chain employs a novel additive manufacturing printer, which is composed of 20 independently connected but simultaneously printable partitions (subsystems). Each partition comprises a front scraper 2, a laser 4, a powder bed 5, an ascending cylinder 7, and a descending cylinder 6. A rear scraper 3 is disposed behind the junction of every two adjacent front scrapers 2.

[0039] The preparation method specifically comprises the following steps:

[0040] (1) Based on the type of the mooring chain 1 chain link being a gear chain link with a nominal diameter of 230 mm, the placement pattern of the mooring chain 1 on the printer powder bed 5 is designed to be linear, and a print file is prepared and input into the printer;

[0041] (2) On the printer with the program set, after the steel powder of the mooring chain 1 in the 20 lifting cylinders 7 is ejected at the same time, the 20 front scrapers 2 push the powder forward and evenly spread the powder on the powder bed 5. At the same time, the 19 rear scrapers 3 follow up and scrape the powder to flatten the raised linear powder in the gap between the two front scrapers 2;

[0042] (3) The front scraper 2 and the rear scraper 3 return to their initial positions, the laser 4 is started, and the powder bed 5 is scanned according to the set laser parameters to print the first layer of the mooring chain 1;

[0043] (4) Finally, the 20 descending cylinders 6 drive the powder bed 5 to move down one layer, and the steel powder of the mooring chain 1 in the 20 ascending cylinders 7 is ejected for the second time, and the powder printing process is repeated again to print the second layer, the third layer, etc., until a complete high-level R4 grade ultra-long seamless mooring chain 1 is printed. Each link is formed in one step, and there is no weld seam throughout the whole chain.

[0044] Example 2

[0045] A method for preparing an ultra-long seamless mooring chain employs a novel additive manufacturing printer, which is composed of 10 independently connected but simultaneously printable partitions (subsystems). Each partition comprises a front scraper 2, a laser 4, a powder bed 5, an ascending cylinder 7, and a descending cylinder 6. A rear scraper 3 is disposed behind the junction of every two adjacent front scrapers 2.

[0046] The preparation method specifically comprises the following steps:

[0047] (1) Based on the fact that the chain link of the mooring chain 1 is a non-gear chain link with a nominal diameter of 50 mm, the placement pattern of the mooring chain 1 on the printer powder bed 5 is designed to be a snake-shaped pattern, and a print file is prepared and input into the printer;

[0048] (2) On the printer with the program set, after the steel powder of the mooring chain 1 in the 10 lifting cylinders 7 is ejected at the same time, the 10 front scrapers 2 push the powder forward and evenly spread the powder on the powder bed 5. At the same time, the 9 rear scrapers 3 follow up and scrape the powder to flatten the raised linear powder in the gap between the two front scrapers 2;

[0049] (3) The front scraper 2 and the rear scraper 3 return to their initial positions, the laser 4 is started, and the powder bed 5 is scanned according to the set laser parameters to print the first layer of the mooring chain 1;

[0050] (4) Finally, the 10 descending cylinders 6 drive the powder bed 5 to move down one layer, and the steel powder of the mooring chain 1 in the 10 ascending cylinders 7 is ejected for the second time, and the powder printing process is repeated again to print the second layer, the third layer, etc., until a complete high-level R5 grade ultra-long seamless mooring chain 1 is printed. Each link is formed in one step and there is no weld seam throughout the whole chain.

[0051] Example 3

[0052] A method for preparing an ultra-long seamless mooring chain employs a novel additive manufacturing printer, which is composed of 25 independently connected but simultaneously printable partitions (subsystems). Each partition is provided with a front scraper 2, a laser 4, a powder bed 5, a lifting cylinder 7, and a lowering cylinder 6. A rear scraper 3 is provided behind the connection between every two adjacent front scrapers 2.

[0053] The preparation method specifically comprises the following steps:

[0054] (1) Based on the fact that the chain link of the mooring chain 1 is a non-gear chain link with a nominal diameter of 120 mm, the placement pattern of the mooring chain 1 on the printer powder bed 5 is designed to be linear, and a print file is prepared and input into the printer;

[0055] (2) On the printer with the program set, after the steel powder of the mooring chain 1 in the 25 lifting cylinders 7 is ejected at the same time, the 25 front scrapers 2 push the powder forward and evenly spread the powder on the powder bed 5. The 24 rear scrapers 3 follow up and scrape the powder to flatten the raised linear powder in the gap between the two front scrapers 2.

[0056] (3) The front scraper 2 and the rear scraper 3 return to their initial positions, the laser 4 is started, and the powder bed 5 is scanned according to the set laser parameters to print the first layer of the mooring chain 1;

[0057] (4) Finally, the 25 descending cylinders 6 drive the powder bed 5 to move down one layer, and the steel powder of the mooring chain 1 in the 25 ascending cylinders 7 is ejected for the second time, and the powder printing process is repeated again to print the second layer, the third layer, etc., until a complete high-level R7 grade ultra-long seamless mooring chain 1 is printed. Each link is formed in one step, and there is no weld seam throughout the whole chain.

[0058] Performance Testing

[0059] 1. Steel Powder Characterization

[0060] 1. Chemical composition of steel powder

[0061] In Example 1, the steel powder prepared by vacuum induction melting gas atomization (VIGA) was analyzed for chemical composition using ICP-OES and carbon-sulfur analyzer. The results are shown in Table 1.

[0062] Table 1 Chemical composition of steel powder of Example 1 (wt%)

[0063]

[0064] As can be seen from Table 1, the steel powder used in Example 1 belongs to R4 grade mooring chain steel.

[0065] 2. Particle size distribution of steel powder

[0066] In Example 1, the aerosolized raw material powder has a fine particle size. The powder particle size distribution is measured using a Malvern laser particle size analyzer, and the powder particle size distribution diagram is as follows: Figure 2 shown.

[0067] Depend on Figure 2It can be seen that the proportion of powders with a particle size of 15 to 53 μm suitable for 3D printing is the highest. The powder flowability measured by the Hall flow meter is 18.6s / 50g, and the powder bulk density measured by the Topsizer particle size analyzer is 4.16g / cm 3 .

[0068] 3. Microscopic morphology of steel powder

[0069] In Example 1, the microscopic morphology of the powder is as follows Figure 3 shown.

[0070] Depend on Figure 3 It can be seen that the powder has high sphericity and no obvious agglomeration phenomenon, which is suitable for SLM preparation of printed parts.

[0071] 2. Performance Characterization

[0072] 1. Selection of steel powder

[0073] The atomized powder was dried in a vacuum drying oven at 80°C for 6 hours. After sieving the powder through a special sieve, powder with a particle size range of 15-53μm and an average particle size of 30.3μm was selected as the raw material for the preparation of ultra-long seamless mooring chain.

[0074] 2. Experimental plan and corresponding SLM process parameters

[0075] In the experimental scheme of Example 1, the powder bed layer thickness (h) was 30 μm and the scanning distance (d) was 110 μm. The laser processing parameters included laser power (P) and scanning speed (v). The laser power was optimized in the range of 175-325 W. The scanning speed was selected as 800, 1000 and 1200 mm / s. As shown in Table 2, the parameter combinations studied and the corresponding energy density are listed. In general SLM, the laser energy density E (J / mm 3 ) is used as the evaluation index of printing parameters, and the formula is: E = P / (vhd), where P is the laser power, v is the laser scanning speed, h is the powder layer thickness, and d is the laser scanning distance.

[0076] Table 2 Experimental scheme and corresponding SLM process parameters

[0077]

[0078] 3. Printing

[0079] In the experimental scheme of Example 1, the obtained cubic pieces, tensile pieces and impact pieces are as follows Figure 4 shown.

[0080] Depend on Figure 4 It can be seen that the experimental printed parts have good molding effect, no macro cracks and pore defects, and high density.

[0081] 4. Mechanical properties

[0082] The mechanical properties data of mooring chain steel printed with different laser parameters are shown in Table 4.

[0083] Table 4 Mechanical properties of mooring chain steel under different laser parameters

[0084]

[0085]

[0086] As shown in Table 4, the tensile strength of 22MnCrNiMo steel prepared by selective laser melting is much higher than the standard 860 MPa, exceeding it by an average of more than 38%. At the same time, the changes in strength and elongation of T2 and T5 specimens are consistent with the law that the proportion of high-angle grain boundaries and low-angle grain boundaries affects performance.

[0087] Specimen T1, produced at a laser power of 175W, exhibited the highest strength, with a tensile strength of 1281MPa, a yield strength of 1121MPa, and an elongation of 6.7%. Specimen T5, produced at a laser power of 275W, exhibited the best plasticity, with an elongation of 10.2%, a tensile strength of 1175MPa, and a yield strength of 1010MPa. The elongation of the specimens first increased and then decreased with increasing laser power, while the tensile strength and yield strength showed opposite trends to the elongation.

[0088] The above experimental results show that the elongation of SLM-formed steel is slightly lower than the standard. The elongation mainly affects the plasticity of the formed part and the ductility during reprocessing. Since laser selective melting can directly produce the required shape, it does not require reprocessing and shaping of a specific shape. Therefore, the influence of elongation in the laser selective melting process is not significant.

[0089] 5. Process comparison

[0090] Comparison of the traditional manufacturing process (TM) of the mooring chain and the additive manufacturing process (AM) of Example 1 Figure 5 shown.

[0091] Depend on Figure 5It can be seen that the traditional manufacturing process of the mooring chain requires smelting-casting-rolling-bending-welding, that is, qualified molten steel is smelted in the electric furnace of the steel plant, continuously cast into round billets by ladle casting, and rolled into bars of different diameters at high temperature in the rolling mill. The bars are cut to a fixed length in the anchor chain factory and bent into rings at high temperature. The chain link interfaces are then welded together to form a whole, and finally form a mooring chain. The additive manufacturing process of Example 1 only requires smelting-atomization-additive manufacturing, that is, qualified molten steel is smelted in the electric furnace of the steel plant, atomized into powder by ladle, and formed into chain links by additive manufacturing, and finally form a mooring chain. By comparison, it can be seen that the additive manufacturing process of Example 1 does not require rolling-bending-welding, and the elongation requirement is no longer so important. The laser selective melting process for manufacturing mooring chains is of pioneering significance.

[0092] 6. Engineering stress-strain

[0093] The engineering stress-strain curves of steel samples prepared at three typical laser powers (200W, 250W, and 300W) are shown in Figure 2. Figure 6 shown.

[0094] Depend on Figure 6 It can be seen that the elongation of T4 is significantly higher than that of T2 and T6, and the maximum engineering stress of T2 is also significantly higher than that of T4 and T6.

[0095] 7. Impact performance

[0096] The impact toughness requirement of R4-grade mooring chain is greater than 50J at -20°C. The impact performance of mooring chain samples under different laser powers in the SLM process of the present invention is as follows: Figure 7 shown.

[0097] Depend on Figure 7 It can be seen that at laser powers of 175W and 200W, the impact absorbed energy of the sample was 121J and 127J, respectively, exceeding the standard requirements. From 200W to 325W, the impact absorbed energy showed a decreasing trend with increasing laser power, but the impact absorbed energy at 325W also exceeded the standard requirements. The impact energy at 200W laser power was much higher than that at 275W, which is consistent with the influence of the area ratio of lower bainite and martensite. Therefore, the impact toughness of the steel produced by the selective laser melting process meets the requirements for R4-class mooring chains.

[0098] 8. Impact fracture morphology

[0099] The impact fracture morphology of the mooring chain sample under different laser powers is as follows: Figure 8 shown.

[0100] Depend on Figure 8It can be seen that there are a large number of dimples on the impact fracture. The sample has undergone local plastic deformation during the impact process. Microscopically, the microcracks inside the material continue to expand under the action of shear stress, eventually forming small pits. The size and depth of the dimples reflect the plastic deformation ability of the material during the impact process. In areas with deep and large dimples, the material has experienced greater plastic deformation before fracture and has better impact toughness. Figure 8 The orange circled area clearly shows deep and large dimples. The number and size of pores on the cross-section of the sample with 200W laser power are significantly smaller than those of the samples with 250W and 300W laser power.

[0101] 9. Three-ring mooring chain sample

[0102] The actual picture of the three-ring mooring chain sample successfully printed in the experiment is as follows Figure 9 shown.

[0103] Depend on Figure 9 It can be seen that the mooring chain is formed in one piece without welds.

[0104] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an ultra-long seamless mooring chain, characterized in that: The preparation process uses a new additive manufacturing printer, which consists of n closely connected partitions. Each partition is equipped with a front scraper, a laser, a powder bed, a rising cylinder, and a descending cylinder. A rear scraper is set behind the connection between every two adjacent front scrapers. The preparation method specifically comprises the following steps: (1) Design the placement pattern of the mooring chain on the printer powder bed according to the type and size of the mooring chain link, create the print file, and input it into the printer; (2) On a printer with a set program, after the mooring chain steel powder in the n rising cylinders is ejected at the same time, the n front scrapers push the powder forward and spread the powder evenly on the powder bed, and the n-1 rear scrapers follow up to scrape the powder at the same time; (3) The front scraper and the rear scraper return to their initial positions, the laser is started, and the powder bed is scanned according to the set laser parameters to print the first layer of the mooring chain; (4) Finally, the n descending cylinders drive the powder bed to move down one layer, and the mooring chain steel powder in the n ascending cylinders is ejected for the second time, and the powder printing process is cycled again to print the second layer, the third layer, etc., until a complete high-level ultra-long seamless mooring chain is printed.

2. The method for preparing an ultra-long seamless mooring chain according to claim 1, characterized in that: The n partitions are n independent subsystems that can be printed simultaneously, and the number of n depends on the required length of the printed mooring chain.

3. The method for preparing an ultra-long seamless mooring chain according to claim 1, characterized in that: There are n front scrapers in total, which are the main powder spreading scrapers; there are n-1 rear scrapers in total, which are mainly used to scrape flat the raised linear powder in the gap between the two front scrapers.

4. The method for preparing an ultra-long seamless mooring chain according to claim 1, characterized in that: In step (1), the types of the mooring chain links include geared links and non-geared links; the size of the geared links is a nominal diameter of 165 to 240 mm, and the size of the non-geared links is a nominal diameter of 34 to 240 mm.

5. The method for preparing an ultra-long seamless mooring chain according to claim 1, characterized in that: In step (1), the placement mode includes a serpentine type and a straight line type; the serpentine type is suitable for short and small chain links, and bending and coiling are used to increase the printing length; the straight line type is suitable for thick and large chain links, which cannot be bent and coiled.

6. The method for preparing an ultra-long seamless mooring chain according to claim 1, characterized in that: In step (4), the high level includes R4, R4S, R5, R6 and the new R7; the seamless means that each link of the mooring chain is formed in one step and has no welds throughout.

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