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If we want to explain SAW (submerged type of arc welding) with a neat and proper sketch, we should know the procedure and the applications.
submerged arc welding
The welding procedure known as submerged arc welding, or SAW, involves continually feeding a tubular electrode into the weld pool in order to unite two metals by the generation of heat between the electrode and the metal.
By being buried beneath a blanket of granular flux, the region containing the molten zone and the arc receives protection from the air contaminants that could otherwise affect it.
The flux layer completely covers the region, preventing splatter, sparks, gases, and ultraviolet rays from penetrating it.
Arc creation between the wire electrode and the work piece takes place in the same way as it does during the MIG welding process.
This technique, however, has the additional benefit of shielding by the granular flux, which eliminates spatter, fumes, and UV rays as byproducts of the SAW welding process. The following items are included in the inventory of the equipment.
DC or AC current can be welded using the submerged arc welding technique.
- A source of power
- Assembly consisting of a welding torch/gun and cable
- Flux hopper and its corresponding feeding mechanism
- For use in automatic welding, a travel mechanism
The following is a list of the principal advantages offered by the SAW/Submerged Arc Welding Process:
- Excellent velocity and the highest possible deposition rate while maintaining a rapid pace.
- Outstanding quality of the weld.
- There was hardly any smoke.
- Welding that is uniform, smooth, and perfectly finished, and there is no spatter.
- Welder protection, absence of splatter, and arc flash prevention
- The process of automation is simple here.
- The electrodes were utilized very effectively.
- No manipulative skills
- Minimal metal distortion
- In windy places, it is possible to use the machine.
- There has to be no edge preparation of the material that is thinner than 12 millimeters.
Important Implementations
The procedure that is necessary for the fabrication of pipes, penstocks, boilers, structural forms, pressure vessels, railways, rotary kilns, earthmovers, cranes, girders, bridges, locomotives, and the under structures of railway coaches are referred to as "fabrications."
submerged arc process
- The automotive, aviation, and maritime construction industries, together with the nuclear power sector.
- The replacement of worn-out parts with wear-resistant alloy, as well as the reconstruction of tractor rollers, idlers, and crane pulleys.
- Appropriate for use with metals such as mild steel, medium tensile alloys, and high tensile alloys.
- Constraints imposed by SAW
The operator does not have any visibility of the welding operation. He is unable to evaluate the quality or identify any flaws.
In order to compensate for these deficiencies, various jigs, fixtures, pointers, light beams, and roller guides could be added in order to judge and improve the outcome.
It's probable that you won't always be able to pre-apply flux over the joint that needs to be welded.
It is only capable of welding in a horizontal orientation.
The minimum required thickness of the metal is 4.8 millimeters; any thickness less than this will cause the metal to catch fire.
It is important that the edges of the metal that will be welded have clean and accurate fits. It will not be feasible to place flux in edges that have an uneven shape, which may result in the edges being burned.
It's possible that the flux's quality should be a source of concern. Porosity is sometimes the result of poor quality.
Cast iron, aluminum alloy, magnesium alloy, and zinc alloy do not belong in the category of materials that can be welded using a stick welder (SAW).
The chemistry of the weld metal is difficult to manage since flux alloys have the ability to entirely transform the characteristics of low alloy steel.
The procedure is most effective when used to weld low-to-medium carbon steels, low alloy-high strength steels, tempered steels, quenched steel, and stainless steel. Experiments using submerged arc welding have been conducted on a variety of metals, including nickel alloy, copper alloy, and uranium, among others.
Problems Encountered While SAW Welding
One of the many problems is the possibility that the electrode wire will get bent when it is expelled from the nozzle and cannon.
The curve in the wire won't deposit in the spot where it's supposed to deposit because of a flaw in the design. When welding in a deep groove, the deposition will be in the wall, not the root, which will result in an incomplete root fusion. It has the potential to ensnare the flux at the base of the welding.
There is a possibility that the task of maintaining the correct size of the weld and blindly filling the weld groove will not be an easy one.
We can either overdo it by pouring an excessive amount of weld or underdo it by making a smaller deposit. This challenge can be handled by a welder who has received training.
submerged arc ppt
The cracking along the centerline is the other problem. It is possible that the exceptionally big single-pass weld will gather impurities, which will then lead to centerline cracking as the material solidifies after the weld has been completed.
This is a potential outcome when a single-pass flat fillet is performed at an angle of 45 degrees. It is possible to avoid it by making multiple passes or altering the angle by ten degrees.
The high weld hardness, which is greater than 225 Brinell, is the result of a hard weld in carbon, quick cooling, and insufficient post-weld treatment. It is possible that an excessive amount of alloy was used in the electrode.
A run out tab should be used for start and stop markings rather than directly on the product itself if the defect is going to occur at the beginning or the end of the production run.
Variables Related to Welding
The variables involved in welding are, with a few notable exceptions, comparable to those involved in the other arc welding processes.
The type of electrode and flux that we use is determined by the metal that will be welded. The size of the weld joint and the necessary current is directly related to the size of the electrode that is used.
The number of passes and bead sizes need to be taken into consideration in order to determine the joint. A weld of the same dimension can be completed using either a few or numerous passes, depending on what the metallurgy recommends.
Welds of a better and higher grade are typically deposited after multiple passes. To begin, a polarity decision needs to be made over whether or not we require the highest possible deposit rate or the greatest possible penetration.
Submerged arc welding
Submerged type of welding is an electric arc welding process in which the heat required for welding is supplied by one or more arcs between an exposed metal, one or more consumable electrodes, and a work piece.
In this method, the tip of the electrode is placed inside a special mineral powder and an arc is formed under this powder along the welding path. The arc is not visible in this method.
In the sub power system, a bare wire is used, so the wire is successively released from the special coil, and when forming an arc, it also acts as a connection intermediary.
The arc is coated with a layer of fusible flux powder which coats the molten metal and base metal near the joint and protects the molten metal from atmospheric contamination.
As the welding process progresses, in addition to each layer of weld, a layer of granular slag is also formed due to the protective powder and deposited on the molten metal.
This slag must be completely removed from the weld surface and discarded in most cases. However, there are ways to reuse or combine spent slag with fresh slag. In some cases, where the slag must be completely clean, it is not recommended to reuse the protective powder.
Since separate electrodes and powders are used in the sub-powder method, different combinations of welding powder and wire are created for specific applications. In general, there are two types of combinations for solder powder and wire:
- Alloy electrode with neutral powder
- An ordinary carbon steel electrode with alloy powder
- How to Do Powder Welding
In sub powder welding, the end of the welding wire is placed inside the lubricant. The lubricant covers the area to be welded. Before welding, a thin layer of flux powder is applied to the surface of the part. The spring moves along the connection line.
After welding, the excess powder is returned to the storage hopper. Molten metal layers remaining after welding can be easily removed.
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When the arc is completely covered by the flux layer, the heat loss is greatly reduced. This guarantees high thermal efficiency of 60%.
Under-powder welding can be done in 3 ways: semi-automatic, automatic, and automatic. In the semi-automatic method of powder welding, a manual welding gun is used.
In this method, the function of the gun is to transfer the electrodes and protective powder. The feeding of the welding wire is automatic, and the protective powder is transferred from the tank with a conical bottom to the joint site under the influence of gravity or under the pressure of air through the pipe.
In the automatic sub powder welding method, the welding is carried out without user intervention and by welding machines and automatic controllers.
The sub-powder welding method is carried out by a single machine. In this method, the user initiates the weld, monitors it, and adjusts the weld variables and weld speed. The user also decides the final welding time.
Sub-powder welding powder
Solder powders are granular mineral or metallic materials that, in sub-powder welding, perform functions such as passing along the length of the arc, forming a slag coating, carrying out slag reactions, and finally deoxygenating the melt. In fact, they play the role of coating the electrodes.
run in manual mode. The appearance of the welding powder is influenced by the chemical elements of the powder, and the grain size of the powder also plays an important role.
It should be noted that there is no general powder that can be used for most steels and gaskets, and the type of powder should be selected depending on the type of material and application.
The maximum number of amps used is usually determined by the powder used. Solder powder comes in acid, normal, and alkaline types. Solder powder is divided into pre-melted solder powder and agglomerated solder powder:
Pre-molten solder powder is obtained by melting a mixture of finely divided raw materials. The molten product undergoes a process of cooling, grinding, and filtering and reaches the desired grain size.
These seeds have high strength and density, and there is no chance that they will be crushed during processing. Premelted powders resist oxygen and hydrogen penetration and hydrogen cracking, so they can be used in open and uncovered areas and in wet areas.
Agglomerated welding powder is produced by mixing several finely divided raw materials. Viscous substances such as sodium and potassium silicates are added to the mixture, and the mixed paste is subjected to oligomerization to form fine granules.
Then this gunpowder is fired at a temperature of 600-800°C. Since the firing temperature range is below the reaction temperature of the material, deoxygenates and ferroalloys can be used.
Despite the high cost of producing oligomerized solder powder, the consumption of this solder powder during soldering is low due to the low bulk density.
Limitations of Submerged Arc Welding
Complex and expensive equipment
In some applications, this is severely limited by the flatness of the welding position because the flatness and levelness of the position are necessary to prevent flux leakage.
Solder powder can be contaminated with impurities that form pores in the solder. In some cases, it is difficult to separate the slag from the solder.
In multi-pass welding, welding slag must be removed after each pass so that it does not remain in the molten metal.
Powder welding equipment
Equipment needed to perform submerged arc welding (SAW):
- Producer
- Powder tank
- Powder nozzle
- Forceps
- Maintenance and guidance system for bare electrodes
- Clamps, robot guides, and corresponding rails
Advantages of submerged welding:
- Welding is done without smoke and radiation.
- No need for skilled welders
- High-speed welding
- High-Efficiency Electrode Deposition
- Welding with a smooth surface and no molten drop spatter
- High deposit rates
- Deep penetration weld
Applications of submerged arc welding:
The submerged arc welding process can be used in many industries and to join many metals. Due to the high deposition rate, this process is very well suited for repairing layers and surfaces.
In situations where increased surface corrosion resistance and wear resistance are required, this process is absolutely economical and reliable. Perhaps the most important advantage of the sub-powder process is its high settling rate. This method has a much higher efficiency than other common procedures.
The sub-powder process provides a high level of safety for the operator. Because there is no visible arc when welding and the operator can control the welding without wearing filter goggles or heavy protective clothing.
Another reason for the widespread use of this method is its high penetration efficiency.
The main limitation of the immersed powder method is that it is only applicable in situations where the protective powder can properly perform its function according to the wiring diagram (flat and horizontal position). Other welding situations require the use of additional equipment to properly perform this procedure.
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