co2气体保护焊（CO2 gas shielded arc welding）
Section 1 brief introduction of CO2 gas shielded arc welding
CO2 gas shielded arc welding is a gas shielded arc welding using CO2 as protective gas. Referred to as CO2 welding.
CO2 welding equipment mainly welding, wire feeding mechanism and DC power supply. Welding materials mainly include welding wire and welding wire
CO2 gas. The role of the welding torch is to supply welding power, welding wire and CO2 gas to the arc. In addition, when the current is greater than 500A, the welding gun needs water cooling, so it needs a circulatory system.
The u of CO2 as a protective gas has two characteristics as follows: 1) the CO2 gas density than air, so in the flat from the CO2 gas welding torch spray of molten pool have good coverage. 2) CO2 gas will be decompod under the action of high temperature arc:
It can be en from this formula that when the CO2 gas is decompod, the volume of the product expands by half, which will be beneficial to enhance the protection effect. On the other hand, the reacti
on is endothermic reaction, the arc generated strong cooling effect of CO2 gas decomposition, is caud by arc contraction and the arc root (substance covered droplet spots to the surface area decreas, then rejected) arc stress of large droplet. The droplet at the end of the welding wire is not regular becau of the repulsive effect of the arc, and it has the repulsive transition characteristics. Therefore,
it not only affects the arc stability, but also affects the gas protection effect.
In CO2 welding, the droplet transfer form is different according to the welding wire diameter and welding specification. So people are divided into three categories according to the diameter of wire:
1) thin wire (wire diameter less than and equal to 1.2 mm) is usually welded by short circuit transition of small current and low arc voltage. At this time, the droplet at the end of the welding wire is in transition to the molten pool in the form of short circuiting contact.
(2) the wire wire diameter is 1.6 2.4mm) is mostly ud in large current and high voltage welding droplet transfer is fine droplet rejection transition, even shotdrops transition. This is a free form of transition.
3) coar wire (welding wire diameter is 2.4 - 5mm) often us high current and low voltage welding, and then the droplet transition occurs. The arc basically enters into the pit of the weld pool, and the droplet transfers in free transition form.
Compared with manual arc welding and submerged arc welding, CO2 welding has many advantages:
1) high production efficiency and energy saving. Due to the welding current density, usually 100 ~ 300A/mm2, so the arc heat concentrated, wire melting efficiency is high, the mother was the penetration depth, high welding speed, welding at the same
time do not need slag, so can significantly improve the welding efficiency and save energy.
2) low welding cost. Due to the low price of CO2 gas and welding wire, the equipment for welding before welding is not high enough, the cleaning and correcting hours after welding are less, so the cost is low.
3) small welding deformation. As the arc heat concentration, low line energy and CO2 gas has a strong
When the cooling effect, the welding workpiece heating area is small. Especially when welding thin plate, the deformation is very small.
4) the nsitivity to oil and rust is low.
5) the hydrogen content in the weld is less, so the ability to resist cold cracking of welded low alloy high strength steel is improved.
6) short circuiting welding can be done with vertical welding, backward welding and all position welding.
7) the arc visibility is good, which is beneficial to the obrvation and the welding line alignment welding. Especially in mi-automatic welding, it is easy to realize the welding of short weld and curve weld.
8) easy to operate and easy to master.
However, there are still some disadvantages:
1) compared with manual arc welding, CO2 gas shielded arc welding equipment is more complex, prone to failure, requiring higher maintenance equipment technical ability.
2) poor wind resistance, which brings some difficulties to outdoor work.
3) the arc is stronger, we must pay attention to labor protection.
4) compared with manual arc welding and submerged arc welding, the weld forming is not beautiful and the welding spatter is large.
The defects of CO2 welding can be solved by improving the technical level and improving welding equipment. And its advantages are other welding methods can not be compared, so we can think of CO2 gas shielded welding of a high efficiency, low cost energy saving welding method. So, whether it's abroad or not,
It's developing very rapidly. At prent, it has been widely ud in automobile manufacturing, locomotive and vehicle manufacturing, shipbuilding, aviation, aerospace, construction machinery, petroleum, chemical machinery, agricultural machinery and power machinery and other departments. It is mainly ud for welding low carbon steel, common low steel and low alloy high strength steel, and can also weld heat-resistant steel and stainless steel. It can be welded
with a wide thickness range and can be obtained from 0.5mm~150mm. In addition to welding, weldin
g can also be carried out, such as surfacing wear-resistant materials and corrosion resistant materials.
Second ction CO2 welding equipment
There are many kinds of CO2 welding equipment. According to the characteristics of the u can be divided into general equipment and special equipment. According to the degree of automation can be divided into mi-automatic welding and automatic welding equipment.
(-) CO2 welding process parameters and their requirements for welding equipment
The main parameters of CO2 welding include welding current, arc voltage and welding speed. In many cas, it is not enough to ensure that the parameters are not enough. Attention should also be paid to the angle of the welding torch, the position of the welding torch, the dry elongation of the welding wire and the swing characteristics of the welding gun (such as the swing frequency, the swing track, etc.). But in mi-automatic welding, the welding equipment can provide specifications, only welding current and welding voltage two process parameters, other parameters are the operator according to the process to
Seek mastery. And automatic welding is different, all the process parameters are given by the equipment. But for general automatic welding equipment, the main control parameters are welding current, arc voltage and welding speed. Other process
