What is a Bottom Plate?

The lower edge of the box section is called the bottom plate, which is the main working part that bears positive and negative bending moments. In the reinforced concrete bridge, it must ensure the sufficient size of the tensile reinforcement required for assembly. In a prestressed reinforced concrete bridge, it needs to have a large bearing area to meet the compression requirements of the operation stage.

The treatment of water seepage cracks in the basement floor of high-rise buildings is of vital importance to the use of the basement. Once problems such as water seepage cracks occur in the basement floor, it will seriously affect the use of the basement.

The nitric acid absorption tower is mainly composed of sieve trays. The cooling water pipes coiled on the trays of each layer have a complicated structure. To ensure the flatness and levelness of the trays during assembly, the welding of the cooling coils is particularly important. Due to the large thickness of the base plate, the small diameter of the cooling water pipe, the small space between the pipes, and the difficulty in welding, the problem was solved by deep exploration and the use of deep hole welding processes. The quality of deep hole welding directly affects the quality and life of the entire equipment.

Analysis of bottom plate assembly and welding process

The original design of deep hole welding is shown in Figure 1.

Figure 1 Deep hole welding method

Because the base plate is relatively thick, heat dissipation is fast, and the joint between the pipe head and the hole is difficult, so the assembly quality cannot be guaranteed, and the welding difficulty is increased. The welding process is prone to welding defects such as shrinkage and incomplete penetration, and the welding quality cannot be Guaranteed, leaving a lot of hidden dangers. According to the characteristics of the product structure, the structure of the bottom pipe hole was changed (see Figure 2), reducing the difficulty of welding and ensuring the quality of welding.

Figure 2 Improved structure of bottom hole

Base plate welding process

1. Preparation before welding

Use a pipe beveling machine to flatten the cooling water pipe, remove burrs, and clean it with acetone; use a special tooling fixture to assemble the cooling pipe head and the bottom plate pipe hole, leaving a gap less than 0.5mm (located with a 0.5mm feeler gauge), argon The welding point is solid, and then clean the 50mm area on both sides of the weld with acetone.

2.Welding method

Using pulse automatic TIG welding.

3. Welding equipment

Automatic deep hole TIG welding equipment with tube sheet should ensure accurate positioning and easy adjustment.

4. Welding tooling

The circular groove on the back of the base plate is processed, and the circular groove cutting tool is used according to the size. The back seam protection cover is shown in Figure 3.

Figure 3 Back seam protection cover

5. Welding process

The first is welding positioning. Adjust the gap between the tip of the tungsten electrode and the inner wall of the tube. The front part of the core rod is positioned with a 19.9 mandrel, inserted into the tube hole and adjusted so that the tungsten electrode tip coincides with the center of the weld, and is fixed with the three claws of the machine head. The second is argon protection. In order to ensure the formation of the back surface, the back surface is protected by argon gas, and the flow rate is 5 ~ 14L / min. The third is the welding process, which uses single-sided welding and double-sided forming. In order to ensure the quality of welding, the welding method is one-layer welding one-layer welding.

6.Pressure test

After the bottom plate and the cooling pipe head are welded, a hydrostatic test is performed. The test pressure is 0.8 MPa and the pressure is maintained for 30 minutes. There is no leakage in the welded joint. All 768 welds are qualified and meet the welding quality requirements.

By changing the docking method of the cooling coil and the bottom tube hole, the special tooling was used for assembly and positioning. After continuous process exploration, the deep hole welding technology was mastered. The manufactured deep coil welding quality of the cooling coil is reliable, and all technical indicators meet The requirements have improved the company's processing capabilities and provided solid technical support for market development. ^[2]