The Strengths of MIYAJI ENGINEERING GROUP, INC.
The power provided by having some of the largest seaside works in Japan
04
The Chiba Works of MIYAJI ENGINEERING GROUP, INC. (MEC) is a bridge manufacturing works that is roughly 1 kilometer long and roughly 230 meters wide, covering an area four times that of the Tokyo Dome. It has large block processing equipment and a pier for direct water transport for working on long-span bridges. This works boasts one of the highest production capacities in the industry.
1 What is large block processing equipment?
Manufactured structural components are becoming larger, and their shapes are becoming more complex due to a greater focus being placed on aesthetics. That's why in June 1989 we built a large plant capable of handling large block manufacturing.
This large plant can handle large 300-ton blocks, and it has a five-axis all-in-one CNC milling machine, so it can also perform processing for large blocks used in the main towers of long-span bridges, which require a high level of manufacturing precision. We processed the large blocks used in the main tower of the Akashi-Kaikyo Bridge, which was the world's largest suspension bridge when it was built, at this plant.
Large plant capable of handling large block manufacturing
Two 150-ton Cranes
Large plant capable of handling large block manufacturing
Two 150-ton Cranes
2 What is a large block pier for direct water transport?
The Chiba Works has a large base assembly yard with a pier that faces directly onto the sea. For large sea-spanning bridges, we can perform assembly in the assembly yard and ship the completed large blocks as-is directly over water to where the bridge will be erected, without needing to transport the blocks over land. The Chiba Works is a seaside works with facilities for directly shipping large blocks over water.
Let's look at specifically what we mean by this using the example of the roughly 100 meter tall main tower of the Kanae Bridge (Kesennuma Bay Bridge). First, the companies in the JV manufactured and painted components and then transported them to our Chiba Works. All of the blocks were then laid down on their sides at the base assembly yard, which is adjacent to the pier. The blocks were lined up and temporarily assembled in the same way as in the final bridge to confirm the overall configuration. Once the configuration was confirmed, the blocks were welded together to assemble the uppermost block (30 m/320 t), the lowermost block (65 m/890 t), and the base (200 t).
Once the base assembly of the three large blocks was completed, they were shipped directly from the pier using a crane barge. A crane barge with a 3,000 ton capacity was used to ship the main tower.
3 What does it mean to be the works with one of the highest production capacities in the industry?
The Chiba Works began full-fledged operation as a state-of-the-art works in 1983. Over forty years have passed since then, but we've constantly invested in its facilities in line with the changing times. Even now, it is one of the top works in the industry, with a steel bridge production capacity of over 30,000 tons per year.
To give a little insight into the Chiba Works, let's look at the process it uses to manufacture steel bridges.
Based on design diagrams, we create the NC machine data, welding robot data, production forms, and other production information that is needed. We also use 3D to check construction feasibility.
We use NC machines to mark the positions of cuts, holes, and component mounting positions on steel plates. Before marking, we remove rust-prevention coating from areas of the steel plates where welding is to be performed. We then use the same NC machines to perform cutting and hole-punching.
The welding of ribs (vertical ribs and stiffeners) to box girder flanges and webs is performed automatically by a welding robot system with eight articulated welding robots. Welding is performed by eight robots, which not only makes the quality of the welding more consistent, but also contributes to significant labor savings and productivity improvements. Deformation caused by welding is corrected using specialized equipment.
I-girders are fabricated by first assembling the I shape using an I assembly device and then welding it using a specialized automatic welding machine. Stiffeners are then assembled and automatically welded by a stiffener welding robot system. Almost the entire I-girder fabrication process is mechanized, automated, and performed by robots.
Box girders are assembled with the use of a crane from flanges, webs, etc. that have been assembled into panels. After assembly, the crane reverses the orientations of the blocks to make them easier to weld, and they are welded. After welding, they undergo external visual inspection and ultrasonic inspection to check the interiors of welds, ensuring that they meet designated quality standards.
Once the components are completed, they are checked to make sure that their dimensions and shapes are as specified and that it will be possible to erect them on-site without problem. This is done by assembling the blocks outdoors in the same configuration as in the final assembly (temporary assembly). Depending on the structure, 3D measurement data for individual blocks may be used to perform theoretical temporary assembly (simulated temporary assembly).
* Simulated temporary assembly using a digital camera 3D measurement system
After temporary assembly, the assembled blocks are painted. Wind, rain, and condensation can affect the quality of painting, so this process is performed in a mobile, humidity and temperature-controlled painting house.
Once painting has been completed, the blocks are transported over land by trailer or over water by a ship for transporting heavy cargo and taken to the actual worksite.
