Causes and elimination of welding spatter in CO2 welding process, molten metal particles and slag often occur to fly around the phenomenon.
The spatter pattern of CO2 welding is shown. It can be seen that there are three kinds of splash, one is caused by short circuit, the other is caused by gas precipitation, and the third is caused by free transition. In the late formation of droplet short circuit.
The Metal Bridge is formed in the later period of the droplet short-circuit. It is also called normal short-circuit spatter because of the spatter caused by electric explosion. This spatter is very small in the case of low current, and the amount of spatter is also small, as shown in figure A. When the current is large, a transient short-circuit often occurs, that is, the formation of liquid metal bridge in the early stage of the short-circuit, often causing a larger electrical explosion spatter, as shown in Figure B.
When the current is high, the inductance of the circuit is small, and once the short circuit is easy to cause a strong splash of molten droplets and molten pool. In high current, thick wire and low voltage conditions, often for submerged arc welding, once a short-circuit, often the molten steel will be rushed out of the pool and the formation of spatter, as shown in Figure D.
The short circuit between the welding wire and the molten pool will be caused if the starting arc or feeding wire is too fast, then the welding wire may break and cause flying.
Welding caused by metallurgical factors, in the molten pool and droplets filled with CO2(or CO) gas, due to internal pressure caused by gas escape or explosion, often accompanied by spatter, such as figure F and G. In the free transition, because of the contraction of the CO2 arc, the arc concentrated on the bottom of the droplet and caused the droplet to deviate from the wire axis, when the droplet falls off, the droplet flies off in a rotating form or the thin neck between the droplet and the welding wire explodes with a large current, thus resulting in the spatter form in figures H and K.
The cause of spatter in CO2 welding and the measures to reduce spatter are one of the main technical problems in CO2 welding. There are two main ways to produce spatter, one is caused by electrical explosion of short-circuit bridge, the other is caused by metallurgical factors.
The former Soviet scholar binchuk experiment found that when the short-circuit bridge through a large current, the short-circuit bridge will overheat explosion, and produce a splash. Its energy is accumulated in 100 ~ 150 US time before the explosion.
This kind of electrical explosion spatter occurs between the wire and the droplet in the normal short circuit (short circuit time & GT. 2MS) . When the bridge is broken, a large amount of liquid is pushed into the molten pool, and only a few tiny droplet becomes the spatter.
The splash is usually small at the peak value of the short-circuit current; conversely, the splash is large at the peak value.
In the case of instantaneous short-circuit (short-circuit time 2MS) , the short-circuit bridge takes place between the molten drop and the molten pool. When the bridge overheats and explodes, the explosive force throws the molten metal into all directions, and often produces the splash of larger particles, which is easy to adhere to the surface of the workpiece and difficult to remove, and even destroy the surface finish of the workpiece.
Obviously, the way to reduce the spatter of electric explosion should first avoid instantaneous short-circuit, that is, in the early period of short-circuit, reduce the current (such as to suppress the rise speed of short-circuit current) .
Secondly, the peak current of normal short circuit is reduced. It is often to reduce the rise rate of short-circuit current, short-circuit current in the short-circuit later quickly reduced, and rely on the metal surface tension pull off the bridge, then will achieve no splash transition.
Another kind of spatter, caused by gas escape or even explosion, is often related to the characteristics of the welding metallurgical process. To reduce the use of deoxidation welding wire, should contain enough silicon, manganese elements, high requirements can also be used with aluminum and titanium welding wire. They inhibit the formation of CO gas. In addition, attention should be paid to welding wire and workpiece surface cleaning, rust and oil removal.
