Analysis of Welding Process of Work Roller Roller Platform of Nangang 4700 Rolling Mill

1. Overview

With the continuous advancement of the global machinery industry, various fields of steel material processing have experienced significant growth, including casting, forging, and riveting. The use of welded structures has become increasingly prevalent in industries such as aerospace, mining equipment, metallurgical systems, and large-scale hydropower, thermal power, and nuclear power equipment. Compared to other metal structures, welded components offer several advantages: they can reduce structural weight, improve product quality, are typically made from rolled steel with strong overload resistance and impact capacity, and help save manufacturing time, resources, and energy. This paper focuses on analyzing the welding process of the work roll changer platform used in the Nangang 4700 rolling mill. The welding structure of this platform differs from previous designs, particularly in the slope and bottom design. The overall forming concept is illustrated in Figure 1. In earlier platforms, the bottom and inclined surfaces were constructed using steel plate welding, as shown in Figure 2. The bottom plate was exceptionally wide and long, as depicted in Figure 3. Additionally, the platform features four lifting ears located in each corner, positioned beneath the top plate. These structural elements create specific challenges for assembly and welding, which will be discussed in detail below.

2. Tailor Welding Position and Groove Form

As shown in Figure 3, the width of the steel plate used is 3,720 mm, exceeding the standard width of 3,000 mm. This makes it impossible to use a single sheet directly. Moreover, the bottom plate is different from those previously produced by our company. Due to limitations in our factory’s equipment and aging machinery, it is difficult to form the steel plate as a whole. Therefore, the bottom plate must be divided into three sections for tailor welding. The positioning of these welds is shown in Figure 3, and the size of each section depends on the incoming steel plate dimensions.

Figure 3

Once the welding position is determined, the groove form at the joint must also be considered. According to the German Westmark standard, full penetration welds are required for plates or profiles, and these must undergo ultrasonic or X-ray inspection, along with surface crack detection to ensure quality. Additionally, carbon arc gouging is necessary to remove the root of the weld, with a depth of 10–15 mm. As a result, the groove form for the tailored weld is shown in Figure 4.

3. Welding Process Analysis

From Figure 1, it is clear that the presence of bearing plates and side ribs beneath the lifting lugs affects the welding process. If assembled all at once, some welds may be difficult to access or complete properly. Previously, the lifting lugs were placed outside the platform, allowing for secondary assembly and welding. However, in this case, we decided on three stages of assembly and welding: first, the bottom plate, wing plate, and ribs are assembled and fully welded; then the top plate is reloaded, and finally, the lifting lugs and small side ribs are installed. This approach facilitates the joining of flaps and allows for the welding of ribbed plates. The groove form of the rib was adjusted from a K-shaped groove in the original design to a single-sided V-groove, and the welding was performed on the outer side. In summary, the design of welded structures must meet practicality, safety, manufacturability, and cost-effectiveness requirements. When developing the welding process, it is essential to consider both the assembly configuration and the specific form of the joint openings.

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