Building a structure | Welded joints
Updated: Apr 20, 2021
What is arc temperature?
Table of contents:
Many times we have seen, at a construction site there is a person holding a shield and there are sparks coming from the tool he is holding. We were told not to look directly at it but have we ever wondered what it is?
Welding is a method of fabrication that joints material by means of elevated temperatures to melt the connecting parts and cooling them together causing fusion.
Along with the two materials to be joint, there is a third element involved in welding known as filler. This filler metal forms a pool of molten metal, which when cooled forms a joint.
Along with the filler metal, another external component for welding is Flux.
During the welding operation, there are possibilities of contamination of joints due to the atmospheric conditions. Oxygen reacts with metal resulting in oxidation which could cause weaker joints. How do we prevent it? It is welding flux. It is a combination of carbonate and silicate materials used in welding processes to shield the weld from atmospheric gases. When the heat of the weld zone reaches the flux, it melts and outgasses. The gases produced, push the atmospheric gas back, preventing oxidation.
We have understood that high temperature is necessary for the material to melt causing fusion.
But how is the high temperature achieved?
There are many different energy sources that can be used for weldings such as including a gas flame (chemical), an electric arc (electrical), a laser, an electron beam, friction, and ultrasound.
The different types of welding methods are based on the combination of energy source and filler metal.
Gas welding – One of the oldest and common welding techniques is gas welding. Also know as oxyfuel welding or oxyacetylene welding, the method employees burning of acetylene and oxygen to produce a welding flame of temperature 3100 C.
Arc welding – Constant current/voltage supply is passed through the material to be joined which is close but not touching. The filler rod will have current passing through it as well, making it an electrode. When the electrode is brought close or near to the gap between the bonding materials, an electric arc is developed due to the voltage gap. The temperature of the metal rises causing it to melt. The welding region is sometimes protected by inert or semi-inert gas, known as a shielding gas, and filler material is sometimes used as well.
Laser welding – Also known as electron beam welding, a concentrated amount of electrons or laser is bombarded on the area to be welded. The rapid movement of electrons through the material causes an increase in temperature. This rise in temperature is used for welding.
Friction welding – As the name suggests, friction between two materials is used to bond the two surfaces. This is generally used with metals having lower melting temperatures and higher malleability.
Ultrasonic welding – Vibrations are produced through ultrasound passed through the material. This exposure to vibrations causes a temperature rise in the material forming a welded joint.
We have discussed types of welding based on the energy source. Along with the energy source, there can also be variations in the filler metal and electrode.
An electrode is essential in the welding process. Welding electrodes are lengths of wire that are connected with your welding machine to create an electric arc. Current passes through this wire to produce an arc, which generates a lot of heat to melt and fuse metal for welding.
The distinguished types are:
Consumable – The electrodes are consumed during the welding process, possible getting fused with a welded joint.
Non-Consumable – The electrodes are not composed during the welding process. High resistance material is used for this purpose, most commonly tungsten.
What are those sparks we see during welding?
An arc is a discharge of electrical current – just like a tiny lightning bolt. In arc welding, the parts to be welded are connected to a grounded wire, and an electrode (made of filler metal) is connected to the power supply. When the electrode is put into contact with the welding materials, then moved away, the air in between the two is ionized and electrons leap across the gap. This generates bright light and intense heat. As the arc is drawn along the join, both the tip of the electrode and the working materials become liquid and fuse together. At such high temperatures, the molten metal bubbles and spits, expelling a shower of incandescent droplets: these are the sparks you see. They can be as hot as 1300 C so be sure to stand clear!
Welding involves heating two pieces of metal so that they melt and fuse together, resulting in a very strong seam.
This requires scorching temperatures of around 5,500 degrees Celsius (9,900 degrees Fahrenheit), which are most commonly generated with an electric arc.
The intensity of current passed through material is based on the material property and the bond required.
An electrode is used to produce the electric arc required for welding.
The filler material is chosen based on the properties of the metal to be welded.
The cooling atmosphere affects the quality of the weld.
The welded joints are used widely while building any structure. But what is the degree of freedom of the joints made? To know more about the degree of freedom check our previous blog and to know more about fluid and mechanics, stay tuned with us.