Application of plasma welding system in stainless steel welded pipe

Automatic welding process and supporting special equipment can greatly improve product quality, increase production efficiency, reduce manufacturing costs, and improve working conditions of workers. However, domestic and domestic welded pipe production lines are still in a relatively backward state. Since China does not have a good stainless steel welded pipe welding system, most manufacturers use manual arc welding and manual argon arc welding. Both welding methods use stainless steel welded tubes.

The production line has many disadvantages: 1. The preparation cost of the groove before welding is high; 2. The welding efficiency is slow; 3. Due to manual operation, the welding quality is not guaranteed, and the product qualification rate is low; 4. The heat input is large and the workpiece is deformed. Big. In contrast, plasma welding, due to energy concentration and no slotting, can achieve double-sided molding of 8mm stainless steel single-sided welding, greatly reducing the preparation work before welding, ensuring quality and improving efficiency.

1. The principle of plasma arc generation

The plasma arc is ionized to produce high-temperature ionized gas, and is mechanically compressed by the water-cooled nozzle to form a plasma arc from the small hole in the center of the nozzle. The energy density can reach 105-106 W / cm2, which is higher than free arc (about 105). Below W / cm2), its temperature can reach 18000-24000K, also higher than free arc (5000-8000K). The basic principle of plasma arc welding process.

2. Advantages of plasma welding process

(1) Strong penetration, no need to open the groove thickness below 8mm, greatly reducing the preparation time before welding.

(2) The arc energy is concentrated, the welding heat affected zone is small, and the welding deformation is small.

(3) The welding speed is fast, and the plasma is reduced by 4-5 times compared with manual argon arc welding.

(4) Excellent repeatability.

(5) The rigidity of the arc post, adopting the small hole effect, can realize stable single-sided welding and double-sided molding.

3. Brief introduction of plasma welding equipment

Plasma welding equipment includes welding power source welding gun mop cover dedicated cooling water tank pneumatic system

3.1 Welding power supply

The welding power supply adopts new technology digital inverter power supply, which can work normally under the condition that the network voltage fluctuates by 20%. It is particularly suitable for China's basic national conditions; digital power system has fast response, high control accuracy and stable performance; it is adjusted separately to ensure dimensional stability. In the welded pipe industry, we choose the power supply model DC-P400, which has a rated current of 400A and a 60% duty cycle at 20 ° C.

3.2 Plasma torch generates a plasma arc during plasma welding and the tool used for welding is called a plasma torch. As shown in Figure 5. The structure, manufacturing accuracy and manufacturing process of the welding torch all affect the performance of the plasma torch and also determine the difficulty of the plasma welding process. The cooling capacity of the welding torch is also an important indicator to measure the quality of the plasma torch. For the torch nozzle, the tungsten clamp must be sufficiently cooled. In plasma welding, tungsten must be concentric with the nozzle. For a good plasma torch, the amount of retraction can be adjusted freely.

4. Application of plasma welding system in stainless steel welded pipe

The length of the pressure tube produced in this industry is generally 6000mm. The material is austenitic stainless steel, such as 304 (l), 316 (l), 321, etc., thickness ≥ 3mm, diameter ≥ Φ 133mm, weld quality requires beautiful appearance, X-ray secondary inspection is qualified. The process we use is 3-8mm plasma single-sided welding double-sided molding;> 8mm open Y-shaped groove, leaving 5-6mm blunt edges, using plasma welding primer, argon arc welding or plasma cover, also used for submerged arc cover .

Replacing the traditional manual welding method with plasma automatic welding stainless steel welded pipe can not only greatly reduce the manufacturing cost, but also improve the welding quality and production efficiency, and help to improve the backward performance of China's existing stainless steel welded pipe production line. For the rapid development of China's petroleum and chemical industries. Electric construction and other industries provide large-diameter welded pipes, which has accelerated the technological and equipment innovation of the welded pipe industry and increased the output of welded pipes.