Over the past years, refractory metals, of which tungsten also belongs, have been widely used in various qualities. Tungsten welding has its own characteristics, which are due to the high melting point - about 3400 degrees.
Welding Features
Features of the process are due to the increased melting points of tungsten. Experts remind that the quality of tungsten welding largely depends on the purity of the metal itself. It should be as high as possible. For the procedure itself, it is necessary to prepare sources that give a sufficient concentration during heating.
Another important nuance is that, under normal temperature conditions, the compounds with tungsten obtained by welding exhibit a tendency to cracking, pronounced fragility. Therefore, prior to the start of welding with this metal, it is necessary to preheat the main raw material in advance. A temperature of +500 degrees and above is required.
If you weld individual elements, preventing their rigid bonding to each other, you can prevent the subsequent formation of cracks on the metal surface.
Occasionally, specialists make a proactive move, increasing the ductility of the welded area. For this, at the end of the heat treatment, the part is first heated to 1800 degrees, and after an hour, it is cooled using specialized furnaces.
To ensure the purity of the working elements, they are processed using electropolishing or etched with a hot mass consisting of four acids - chromic, sulfuric, hydrofluoric and nitric.
The necessary conditions
Important aspects of obtaining high-quality welds following the results of welding, especially relevant for thin-sheet structures, are as follows:
- assembly of the edge part using tungsten electrodes;
- compliance with accurate measurements;
- use of assembly and welding tools as necessary.
During tungsten welding, the electrodes must be clean. This, in turn, will improve the quality of the finished seam. Otherwise, another alloy will be formed, characterized by a lower temperature for melting, which negatively affects the quality of the weld as such.
Work with tungsten electrodes
Electrodes made of tungsten have found wide practical application. An oscillator is used to excite the arc. Moreover, the hot end must not come in contact with the filler wire or metal.
To ensure the safety of the sharpening of the used electrode and to prevent its artificial overspending, it is important to select the current strength correctly. The result will be better, the more reliable the air will be removed from the working area.
When tungsten is used for argon welding in the form of electrodes or other methods of operation, they usually turn to the use of such gases, which are characterized by sufficient inertness. We are talking about carbon dioxide or argon. Moreover, the costs of such a gas are determined by the composition of the metal and its thickness in conjunction with the selected method for welding.
During the tungsten welding process, it is important to ensure that the gas cloud covers the entire weld pool as well as the working electrode. If you need to perform welding at high speed, you will have to increase the feed rate of inert gases in advance.
Technological features of welding
When welding tungsten with each other or with other metals, when elements with a thickness of about 10 mm are joined, the direction of movement of the welding arc is always to the left. Specific cases may have their own characteristics.
So, when working with thin metals, it is important not to exceed a 60-degree angle between the burner and the working part. When it is necessary to connect individual elements with significant thickness by welding tungsten with other metals, the angle is set to 90 degrees.
If you are working with tungsten electrodes with a thin material, including when using tungsten for aluminum welding, the filler wire is placed on the side of the arc. When performing reciprocating movements, it will gradually approach the welded zone.
When work is underway with significant thickness, the wire must perform a reciprocating motion.
It is possible to work with tungsten electrodes with automatic or semi-automatic welding. In the course of such work, the angle between the electrode and the rod is strictly maintained, the direction of movement is selected.
Tungsten welding methods
In practice, tungsten welding can be performed by various methods, each of them has its own characteristic features. Most often contacted :
- to argon arc welding;
- soldering tungsten with subsequent exposure at a certain temperature;
- diffusion welding in a vacuum.
Features of argon arc welding
When performing tungsten argon arc welding with tungsten or other metals, it is important to initially take into account the tendency to crack. Therefore, initially the raw material is heated to approximately 500 degrees. It is quite possible to refuse from rigid fixing of details.
Further, to increase the ductility of the finished compounds, hourly annealing is performed under vacuum, when the temperature rises to 1800 degrees.
Not so long ago, experts developed a specialized type of tungsten powder. In its practical application, the formation of cracks on the surface does not occur, which is important.
In the conditions of an argon-filled chamber, welding of various plates and sheets with a thickness of not more than 16 mm is possible . If you are working with material with a thickness of 3.2 mm, it is important to adhere to the recommended welding speed - not more than 9 km / h.
Features of tungsten soldering, followed by a long exposure of the material at soldering temperatures
This option has much in common with argon-arc welding of tungsten. In this case, the result of the working process is the phenomenon of interdiffusion , which results in the formation of a new compound, characterized by especially high temperatures for re-melting.
Diffusion welding under vacuum
This method is especially relevant when working with extensive work surfaces of individual elements. This technique is suitable for welding tungsten with molybdenum.
By this technology , tantalum foil can be bonded. A feature of this method is that pre-heating of the feedstock is not required in advance.
Tungsten for argon welding
Work on argon welding technology is carried out using special tungsten electrodes. They can be made not only of refined metal, but also of tungsten subjected to lanthanizing or taring. The electrodes of the last two types provide not only stability, but also high quality of the welding arc.
When welding tungsten, specific grades of electrodes differ based on the presence of all kinds of additives and impurities in them. Modern experts identify the three most commonly used categories in practice.
When welding tungsten with steel, the task of the electrodes is to withstand maximum currents, preventing melting. This is due to the fact that if the tungsten itself melts, the quality of the connection will significantly decrease.
If welding is carried out under alternating current conditions, a sharp change in polarity occurs, a strong current is needed to maintain the molten end of the electrode.
Popular brands of electrodes
In practice, the following tungsten electrodes are most often used:
- From pure tungsten. They have a green color, are used when working in AC conditions. Actual for welding with aluminum, magnesium, bronze.
- From zirconium tungsten. They have a white color. They have proven themselves best under conditions of alternating current; at high current they are distinguished by excellent ignitability of the arc. Best suited for welding nickel, bronze, aluminum.
- From lanthanum tungsten. They have a golden or blue color. Relevant for welding in AC or DC conditions, contain an oxide additive. Such electrodes are suitable for spraying, welding and cutting.
Welding with copper
Against the background of the development of the modern technical industry, the need periodically arises for the manufacture of structural elements made of various materials and their combinations. Occasionally welding tungsten with copper is required. But working with any refractory metal is fraught with a number of difficulties.
For such cases, diffusion welding is usually used. It allows you to achieve the connection of various materials, including copper and tungsten.
The advantage of this technique is that it guarantees the connection of such metals, which, under other conditions, cannot be welded.
Rhenium welding
You can use a variety of elements as alloying. They are necessary for changing properties during operation with various refractory metals. It best normalizes the weldability of these rhenium metals. It best normalizes mechanical properties both with increasing and decreasing temperature during work with molybdenum and tungsten. For such cases, the lowest weldability is characteristic.
When it comes to optimal compositions, welding of tungsten with rhenium proceeds normally. The material is plastic and welds normally even at low temperature conditions.
Summary
Modern industry is characterized by active and dynamic development. This becomes the reason for more active practical application of various alloys based on tungsten and other refractory metals. But working with him is a complicated process. First of all, this is due to the complexity of the process, the complexity and, of course, the refractoriness of the feedstock.
The hardest work is carried out with alloys based on metals, classified as refractory, when they are formed by pressing.
In order to guarantee the best result, it is advisable to start welding tungsten directly only at the end of the preliminary stage - heating the metal working section to a temperature of 500 degrees.