What Is Gas Tungsten Arc Welding?

Tungsten arc welding is often called TIG welding, which is an arc welding method that generates heat between non-consumable electrodes and the work; the electrode rod, the bath, the arc and the work near the heated area are all in a gas state. Protection from atmospheric contamination. This protection is supplied by a gas or mixed gas stream, which must provide full protection, because even a very small amount of air contamination can contaminate the weld bead.

Tungsten arc welding is used

This welding method is due to

Tungsten arc welding can be divided into manual tungsten arc welding and

Tungsten arc welding is suitable for manual or automatic operation, and can be used for continuous welding and intermittent welding (sometimes called '

1) gas control requirements: gas is required to come first and then go,

Tungsten arc welding can be applied to metal welding in a wide range of thicknesses. This method is very suitable for welding objects under 3mm thick, because the arc generates intense and concentrated heat, which results in high welding speed. Multi-pass welding can be used welding.

Although the base metal thickness of 6.25mm or more, other welding methods are usually used. However, high-quality thick weldments are required to use tungsten arc welding for multilayer welding. For example, in the manufacture of 8m diameter rocket motors and 15mm thick shells, tungsten-argon arc welding uses filler metal for longitudinal and circumferential multi-pass welding. Although for this thick metal, this welding method is slower, but because

Preventing complex shapes using automatic methods requires manual welding. Manual operation is used for welding on irregularly shaped objects that require short welding passes, or welding in difficult to reach (inaccessible) areas. Manual operation is also suitable for full-position welding.

Automatic equipment can use curved and straight surface welding. For example, a special sine wave welding of the corrugated titanium poles to the component parts. For this sine wave welding, a mechanical guide unit is designed to follow the metal template to guide the welding gun. For example, the manual operation of this welding is extremely difficult to control.

Because in tungsten arc welding, the heat is generated between the pole and the work, and the edges of the work are melted and must be cleaned and joined together when the weld bead solidifies.

In order to obtain a good quality bead by tungsten arc welding, basically all surfaces to be welded and adjacent areas must be cleaned, and if molten metal is used, it must also be cleaned.

Another basic requirement is that the assembly of the component parts to be welded must be firmly maintained in the correct relevant position. When the assembly method is demanding, and the work is thin and the shape is complicated. The equipment to be used when not using molten metal welding or automatic welding.

"Current" is the most important operating condition in the control of any welding operation, because it is related to the depth of penetration, welding speed, welding speed and quality of the bead; basically, there are three welding currents to choose from: ( a) DC positive polarity, (b) DC reverse polarity, (c) AC (d).

Tungsten arc welding machines include: (a) Transformer --- rectifier type, DC output. (B) Transformer type, AC output (c) Power-driven generator-electric motor drive. (Only for ac output), or engine drive (for ac or dc output).

Transformer and rectifier welding machines have several advantages over power-driven generators: low initial cost, no current drop during warm-up, quiet operation, low maintenance and operating costs, no rotating parts, low power input during standstill, The advantage of an engine-driven generator is that it can be used in areas where electricity is supplied.

Welding torches for tungsten argon arc welding by hand must be solid, lightweight, and fully insulated. There must be a handle for pressure and transport of protective gas to the arc area, and a collet, chuck or other means to firmly press the tungsten electrode. The rod and guides the welding current to the electrode rod. The welding torch combination generally includes various cables, hoses and connecting parts that connect the welding torch to the power supply, gas and water. The entire system must be airtight. Leakage at the Chinese joint of the hose will cause a large loss of protective gas, and the molten pool cannot be fully protected. Air suction into the gas system is often the main problem. Careful maintenance is required to ensure airtight gas. system.

Tungsten arc welding torches have different sizes and types, ranging from light to three pounds to almost one pound. The size of the welding torch varies depending on the maximum welding current that can be used, and electrode rods of different sizes and The angles of different types and sizes of nozzles, electrode rods and handles also vary with different welding guns. The most common angle is about 120 °, but it is also a 90 ° head angle welding torch, and even an angle-adjustable welding gun. Some torches have auxiliary switches and gas valves in their handles.

The main difference between TIG welding torches is air-cooled and water-cooled. Because most of the cooling by air cooling is provided by gas shielded welding. Therefore, the correct statement should be that GAS-COOLED real air cooling is only radiated to the surrounding air. On the other hand, some cooling of the water-cooled welding torch is provided by the protective gas, but others are supplemented by water circulating through the welding torch. .

Air-cooled welding torches are usually light weight, small and solid, and cheaper than water-cooled welding torches. However, they are generally limited to welding currents below about 125 amps, and are normally used for welding thin plates with low usage. Where the operating temperature of the tungsten electrode rod is higher than that in a water-cooled welding torch, and because of this, when using a pure tungsten electrode rod or welding near the rated current capacity, tungsten particles will fall off and fall into the molten pool. in.

Water-cooled welding torches are designed for continuous high-current welding. They can be used for continuous operation at welding currents up to 200 amps. Some are designed for maximum welding currents of 500 amps. They are heavier and more expensive than air-cooled welding torches.

The welding torch connects the water pipe and related joints. Generally, the cable carrying the electric current to the electrode rod by the electric welding machine is enclosed in the outlet pipe of the water cooling water (see Figure 3). This can provide cooling of the cable and allow the use of small cables. Diameter, light-weight and windable wires, sometimes including mating parts and flow switches and fuses. Water leaks in the welding torch or the gas system contains moisture, which can contaminate the bead and cause irregular operation.

Swing rolling welding method:

1) Select the size of the magnetic nozzle of the welding torch according to the size of the groove and the welding material. The magnetic nozzle is the support point for rocking and rolling;

2) Pre-hot spot welding with arc after high-frequency arc initiation. The magnetic nozzle is constantly oscillated by the operator's wrist. The magnetic nozzle is closely attached to the groove surface, and is rolled from the left to the right along the center of the weld, swinging forward and backward Movement, decay current until arc quenching after shrinking of molten pool ^[1]

Harmful factors of argon arc welding

There are three aspects of the harmful factors of argon arc welding affecting the human body:

(1) Thorium in radioactive thorium tungsten electrode is a radioactive element, but the radiation dose of thorium tungsten electrode in tungsten arc welding is very small, within the allowable range, the harm is not great. If radioactive gas or particles enter the human body as an internal radiation source, it will seriously affect physical health.

(2) High-frequency electromagnetic field When high-frequency arc initiation is used, the intensity of the high-frequency electromagnetic field is between 60 and 110V / m, which is several times higher than the reference sanitary standard (20V / m). But because the time is short, it has little effect on the human body. If the arc starts frequently, or the high-frequency oscillator is used as an arc-stabilizing device in the welding process, high-frequency electromagnetic fields can become one of the harmful factors.

(3) Hazardous gas-When argon arc welding of ozone and nitrogen oxides, the arc column temperature is high. The intensity of ultraviolet radiation is much greater than that of ordinary arc welding, so a large amount of ozone and oxynitride are generated during the welding process; especially the concentration of ozone is far beyond the reference sanitary standard. If no effective ventilation measures are taken, these gases have a great impact on human health and are the most important harmful factors of argon arc welding.

Security measures

(1) Ventilation measures The argon arc welding work site should be well ventilated to discharge harmful gases and soot. In addition to the ventilation of the workshop, several axial fans can be installed to exhaust air in places where the welding work is heavy and the welding machine is concentrated.

In addition, local ventilation measures can also be used to remove harmful gases around the arc, such as the use of open-arc fume hoods, fume extraction torches, and small portable fans.

(2) Radiation protection measures use cerium tungsten electrodes with extremely low radiation doses as much as possible. When processing thorium tungsten and cerium tungsten electrodes, sealed or exhausted grinding wheels should be used for grinding. Operators should wear personal protective equipment such as masks and gloves. Wash their hands and faces after processing. Rhenium and cerium tungsten electrodes should be stored in aluminum boxes.

(3) High-frequency protection measures In order to prevent and weaken the influence of high-frequency electromagnetic fields, the measures taken are:

1) The workpiece is well grounded, and the torch cable and ground wire should be shielded with metal braided wire;

2) reduce the frequency appropriately;

3) Try not to use a high-frequency oscillator as an arc stabilization device, and reduce the high-frequency electrical time.

4) Other personal protective measures When argon arc welding, due to the strong effect of ozone and ultraviolet rays, it is advisable to wear non-cotton work clothes (such as acid-resistant cloth, silk cloth, etc.). In the case of welding in the container and local ventilation cannot be used, personal protective measures such as air supply helmets, air supply masks or gas masks can be used ^[1] .