Bài 7 của loạt bài về kết cấu của Bảo tàng Edo Tokyo

This document is a page from a Japanese technical journal, Journal of Structural Construction Engineering (Volume 1, Issue 1, 1994), detailing a specific welding system for steel construction.

• Welding Method: The text describes using a consumable nozzle electro-slag welding process for site construction to simplify equipment needs.

• System Components: The system utilizes a steel-backed backing plate on one side and a water-cooled steel backing plate on the other, eliminating the need to raise or lower the welding machine body.

• Welding Equipment: The welding power supply requires a capacity of roughly 600A to 1000A, and the setup includes a welding machine, wire reel, and vertical/horizontal adjustment devices.

• Procedure Details: The document outlines procedures for managing root gaps (set to 25mm), preventing misalignment to avoid slag leaks, and performing preheating to approximately 50°C to remove moisture.

Translation

• Header: Journal of Structural Construction Engineering, Volume 1, Issue 1 (March 1994)

• Section 6.2 Welding System: For on-site construction, this project used consumable nozzle electroslag welding to simplify the equipment as much as possible, with one side of the backing material made of steel and the other side a water-cooled steel backing plate. This method melts the steel electrode nozzle simultaneously with the wire, eliminating the need to raise or lower the welding machine body, allowing the steel backing plate to be tightly fixed from the beginning, and simplifying the equipment and operation. Table 2 shows the welding equipment and materials. As the welding power source usage is high, a capacity of about 600A to 1000A is required. The wire feeding control method uses a voltage control system, and for operational purposes, it consists of a control box and an operation box equipped with switches, current, and voltage meters necessary for direct operation.

• Figure 11: Example of field joints for large columns and beams

• Figure 12: Groove shape and backing plate installation status

• Section 6.3 Working Procedure: The main work procedures are shown below. Due to assembly errors, the established root gap may become narrower than set. In such cases, an arc may occur between the base metal or the backing plate, causing welding defects, or the molten metal in the slag pool may not convect sufficiently, causing lack of fusion. Therefore, the groove spacing was made as close to the designated spacing as possible. In particular, it is difficult to adjust the groove spacing after the erection is completed, so construction was carried out while checking the groove condition during erection. Also, if the groove misalignment is large, it causes slag leakage and undercutting, so the misalignment was kept to 1mm or less. If moisture enters during welding, it boils in the slag pool, blowing up the molten slag and deteriorating the welding appearance and fusion. Therefore, moisture on the groove surface was thoroughly removed before starting welding. Also, preheating is not necessary for electroslag welding, which has a large heat input, but preheating to about 50°C was performed for the purpose of cleaning and moisture removal. The quality of the installation of the start tab, end tab, and copper backing plate causes molten metal leakage and welding defects, so careful installation was performed. The copper backing plate was securely installed using fixing jigs and wedges.

• Table 3: Welding conditions are shown in Table 3. For the welding start part, preheating tends to improve fusion for thick plates, so the start part was preheated to about 60°C. The welding time was about 2 to 3 hours, during which the copper backing plates were replaced in sequence. After welding was completed, the start tab was removed. Since the end tab is provided at the upper flange groove part, it interferes with the welding of the upper flange along with the slag in the groove part. Therefore, the slag inside the upper flange groove was removed with an arc air gouge.

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