Shielded gas arc welding is a method that significantly improves the quality of the result. This technology has several features. Before applying it, the master must familiarize himself with the basics of arc welding, which is carried out in an environment of protective gases. The features of this technology will be described below.
Features of the technique
One of the subspecies of the arc connection of metal products, workpieces is arc welding in shielding gases. GOST regulates the process during which gas is supplied to the melting point. It can be argon, oxygen, nitrogen or other varieties. There are certain features of this process.
Every welder knows that the quality of the weld depends not only on the skills of the master, but also on the conditions at the melting point. Ideally, only the electrode and filler materials should be present. If other elements get here, they can have a negative effect on welding. Because of this, the weld point will not be strong enough.
The technology of manual arc welding in shielding gas appeared back in 1920. The use of such substances allows you to make seams without slag. They are characterized by high purity, are not covered by microcracks. This method is actively used in industry when creating various elements from metal.
Special proportions of shielding gases make it possible to relieve stress in the melt zone. There are no pores, which significantly improves the quality of adhesions. The seam is getting stronger.
In industrial conditions, rods mixed with argon and carbon dioxide are used during welding. Thanks to this combination, the arc becomes constant, protecting the melt zone from drafts. This allows you to connect thin sheets of metal.
If deep melting is required, carbon dioxide and oxygen are mixed. This composition has oxidizing properties, protects the seam from porosity. There are many methods that involve the use of different gases during welding. The choice depends on the features of this process.
Welding technique
There are different modes of arc welding in a shielding gas environment. Two main techniques are applied. The first of these involves the use of melting spiers. A current flows through them, and the rod melts because of this, forming a durable seam. This material provides a strong bond.
The second method involves conducting arc welding in a shielding gas with a non-consumable electrode. In this case, the current also passes through the rod, but the material is connected due to the melting of the edges of the metal parts, blanks. The material of the electrode does not become part of the seam.
In the course of such manipulations, different gases are used:
- Inert. Such substances are odorless and colorless. Atoms there is a dense shell of electrodes. This makes them inert. Inert gases include argon, helium, etc.
- Active. Dissolve in a metal billet, reacting with it. Such media include carbon dioxide, hydrogen, nitrogen, etc.
- Combined. In certain processes, both types of gases must be used. Therefore, welding takes place in an environment of both active and inert gases.
To choose a gas environment, take into account the composition of the metal, the efficiency of the procedure itself, as well as the properties of adhesions. Other nuances may be taken into account.
During the use of inert gases, the stability of the arc increases, which allows for deep melting. Such substances are fed into the melt zone in several streams. If it runs parallel to the rod, this is the central flow. There are also side and concentric jets. Also, gas may be supplied to the movable nozzle mounted above the working medium.
It is worth noting that during arc welding, which takes place in a gas bath, the thermal parameters are acceptable for the production of the weld of the required model, quality and size.
Mode selection
To meet the requirements of GOST, arc welding in shielding gases can be carried out in different modes. For this, in most cases, the use of semi-automatic inverters is required. With the help of such equipment it becomes possible to regulate the flow of electricity, its voltage.
Inverter semiautomatic devices serve as a power source. They can differ in power, as well as options. Performance is model dependent. For most standard operations, during which welding of thick or infrequently used alloys is not required, simple apparatuses are used.
Automatic arc welding in a protective gas environment differs in a mass of parameters:
- The radius of the wire.
- Wire diameter.
- The power of electricity.
- Voltage.
- Contact feed rate.
- Gas consumption.
Existing semi-automatic modes of arc welding in shielding gases are also divided into local and general. In the first case, the shielding gas flows from the nozzle into the welding zone. This option is used more often. Using local welding, you can connect different materials, but the result may not always be satisfactory.
When using a local gas supply, air can enter the melt zone. This reduces the quality of the seam. The larger the workpiece to be welded, the worse the result will be when using this technique.
If you need to weld large parts, cameras are used in which the atmosphere is regulated. Air is pumped out of them, a vacuum is created. Further, the gas required by the technology is pumped into the chamber. Using remote control, welding is performed.
Welding preparation
To correctly perform the procedure for joining metal billets, you need to understand the essence of arc welding in shielding gas. Welding requires proper preparation. This procedure is always the same, regardless of welding technology. The edges are first given the correct geometry. This is determined by GOST 14771-76.
Mechanized shielded gas arc welding is used to completely weld the alloy, which allows you to completely connect the edges of the workpiece. There is no gap between them. If there is a certain indentation, cutting edges, welding can be done for the workpiece, the thickness of which does not exceed 11 mm.
To increase productivity in the process of automatic welding, the edges of the workpieces are cut without slopes.
After welding in carbon dioxide, it will be necessary to clean the entire plane of the seam from dirt and slag. To make pollution less significant, surfaces are treated with special compounds. Most often, these are aerosols that are sprayed onto metal. It is not necessary to wait for its drying.
During the subsequent assembly, standard spare parts are used, for example, wedges, tacks, staples, etc. The design before starting work requires a thorough inspection.
Advantages and disadvantages
Manual and automatic shielded gas arc welding has both advantages and disadvantages.
The positive qualities of this method include:
- The quality of the seam is very high. Other welding techniques cannot provide this.
- Most shielding gases are relatively inexpensive, so the welding process does not cost much. Even cheap gases provide quality protection.
- An experienced welder who previously used other methods will easily master this technology, so even a large enterprise with a large number of employees can change the specifics of maneuvers.
- The process is universal, it allows you to weld both thin and thick sheets of metal.
- High productivity, which positively affects the results of production.
- The technique is used not only for welding ferrous, but also non-ferrous metals and alloys.
- The welding process when using a gas protective bath is easily upgradeable. It can be converted from manual to automatic.
- The welding process can be adapted to all the intricacies of production.
Automatic and manual arc welding in a shielding gas environment also has certain disadvantages:
- If welding is performed in an open area, it is necessary to ensure good tightness of the chamber. Otherwise, the shielding gases may erode.
- If welding is carried out indoors, a quality ventilation system must necessarily be equipped here.
- Some types of gases are expensive (e.g. argon). This increases the cost of production, increases the cost of the entire production process.
Types of gases
Shielded gas arc welding is performed in different environments. They can be active or inert. The latter include substances such as Ar, He, and more. They do not dissolve in iron, do not react with it.
Inert gases are used for welding aluminum, titanium and other popular materials. Shielded gas arc welding with a non-consumable electrode is used for steel that is difficult to melt.
Active gases are also used during such work. But in this case, cheaper varieties are often used, for example, nitrogen, hydrogen, oxygen. One of the most popular substances that are used during welding is carbon dioxide. For the price this is the most profitable option.
The features of the gases most commonly used during the welding process are as follows:
- Argon is non-flammable and non-explosive. It provides high-quality protection of the weld from adverse external influences.
- Helium is supplied in cylinders with increased resistance to pressure, which reaches 150 atm. Gas liquefies at a very low temperature, reaching -269º.
- Carbon dioxide is a non-toxic gas that is odorless and colorless. This substance is extracted from flue gases. For this, special equipment is used.
- Oxygen is a substance that promotes combustion. It is obtained by cooling from the atmosphere.
- Hydrogen in contact with air becomes explosive. When handling such a substance, it is important to comply with all safety requirements. Gas does not have color and odor, helps ignition processes.
Features of welding in carbon dioxide, nitrogen
Shielded gas arc welding with a consumable electrode is carried out using carbon dioxide. This is the cheapest technique that is in great demand today. Under the influence of strong heating in the melting zone, CO₂ is converted into CO and O. In order to protect the surface from the oxidation reaction, silicon and manganese are present in the wire.
This also leads to some inconvenience. Silicon and manganese react with each other, forming slag. It appears on the surface of the seam, requiring removal. This is easy to accomplish. This circumstance has no effect on the quality of the weld.
Before starting work, water is removed from the cylinder, for which it is turned over. This must be done at regular intervals. If you do not perform this manipulation, the seam will become porous. Its strength properties will be low.
Shielded gas arc welding can be done with nitrogen. This technology is used for brazing copper billets or stainless steel parts. Nitrogen does not react chemically with these alloys. During welding, graphite or carbon electrodes are used. If tungsten contacts are used for these purposes, this causes them to be overused.
It is important to properly configure the equipment. It depends on the complexity of welding, the type of material and other conditions. Most often, equipment with a voltage of 150-500 A is used. It creates an arc of 22-30 V, and the gas flow in this case is 10 l / min.
Welding process
Shielded gas arc welding is an efficient technique. But in order to achieve this, the master must fulfill all the requirements put forward by the standards for this process. This technique is slightly different from other techniques that the master must necessarily take into account.
First, the metal is prepared for the welding process. When using such a technology, this procedure has a smaller effect on the result, but it must be carried out. Next, the equipment is set up in accordance with the welding parameters. The thickness and type of material are taken into account.
When the equipment is ready, the arc is ignited. In this case, the flame of the burner is scorched. Some types of welding involve preheating the workpiece. To do this, first turn on the burner, with which the metal is pretreated.
When a weld pool begins to form around the arc, wire feed begins. For this, the equipment is equipped with a special feeding device. It delivers the wire to the melt zone at a certain speed. If you need to make a long seam, this is convenient, since the arc does not have to be torn. For this, a non-meltable electrode is used, which maintains the arc for a long time.
If welding occurs when using direct current, its polarity should be reversed. This reduces the likelihood of splashing, but increases metal consumption. The deposition coefficient when using a similar technique is markedly reduced. With direct polarity, it increases by 1.5 times.
It is advisable to lead the bath from left to right (if the master is right-handed). This will show the seam formation process. Also, all actions must be performed towards yourself. The seam is created simply, from the master it is only required to guide the machine at a constant speed.
The arc breaks away from the workpiece in the opposite direction relative to the welding movement. In some cases, after such manipulation, additional heating may be required.
Equipment
Shielded gas arc welding is performed using special equipment. It uses standard power supplies and also has a voltage adjustment function.
Welding units are equipped with a wire transfer device. There are also nodes for supplying gases to the melting zone using hoses from cylinders. The welding procedure is performed at a constant high frequency current. The stability of the arc depends on the correct adjustment. The wire feed speed is also adjustable. The most popular units for carrying out such welding are:
- "Impulse 3A." It is used for welding aluminum, but the disadvantage is the small functionality of the device. It can also be used for welding ferrous metals, as well as creating ceiling joints.
- PDG-502. It is used for soldering in carbon dioxide. The device is reliable and efficient. It works from a network of both 220 V and 380 V. Electricity can be regulated from 100 A to 500 A.
- "URS 62A." It is used when welding in the field. It is mainly used for welding aluminum, but can also process titanium.
Remedies
Welding operations using gas are highly hazardous, especially when using explosive substances. Therefore, the welder must use personal protective equipment. They should cover the skin, eyes, not to allow the master to inhale harmful fumes.
Even if short-term welding is carried out in your own garage, the master must use a special mask, a respirator and heat-resistant gaiters. In this case, the work will be performed in safe mode, which also greatly affects the quality of the result.