I believe you all know that welding rods are necessary for electric welders.
Welding tongs can start to work after welding rods are connected.
However, do you know your welding rod model?
The use of welding rod is very particular.
The welding rod with the wrong material cannot guarantee the welding strength, so it must be polished and re-welded.
If it is large workpiece, it will be very bad. The welding place will crack, which may cause life and property safety accidents.
Therefore, we need to know how the electrode is composed?
- 1. Clamping end
- 2. Electrode coating
- 3. Welding core
- 4. Arc striking end
The surface of the electrode is coated with electrode coating.
It is a melting electrode used for shielded metal arc welding, and consists of two parts: the coating and the welding core.
The metal core covered by the coating in the electrode is called the welding core.
The welding core is generally a steel wire with a certain length and diameter.
Function of welding core
The welding core has two functions:
1. Conducting welding current and generating electric arc to convert electric energy into heat energy.
2. The welding core itself is melted as a filler metal and fused with the liquid base metal to form a weld.
When welding with electrodes, the core metal accounts for a part of the weld metal.
Therefore, the chemical composition of the welding core directly affects the quality of the weld.
Therefore, the steel wire used as the electrode core has its brand and composition specified separately.
If submerged arc automatic welding, electroslag welding, gas shielded welding, gas welding and other fusion welding methods are used as filler metal, they are called welding wires.
Related reading: Types of Welding
Welding rod coating refers to the coating layer applied on the surface of the welding core.
In the welding process, the coating is decomposed and melted to form gas and slag, which plays a role in mechanical protection, metallurgical treatment and improving process performance.
The composition of the coating includes minerals (such as marble, fluorspar, etc.), ferroalloys and metal powders (such as ferromanganese, ferrotitanium, etc.), organic substances (such as wood flour, starch, etc.), and chemical products (such as titanium dioxide, sodium silicate, etc.).
The coating of welding rod is an important factor to determine the weld quality.
Role in welding process:
1. Improve the stability of arc combustion
The bare welding rod without coating is not easy to ignite the arc.
Even if it is ignited, it cannot burn stably.
2. Protect welding pool
During welding, oxygen, nitrogen and water vapor in the air immerse into the weld, which will bring adverse effects to the weld.
It will not only form pores, but also reduce the mechanical properties of the weld, and even lead to cracks.
After the welding rod coating is melted, a large amount of gas generated will cover the arc and molten pool, which will reduce the interaction between molten metal and air.
When the weld is cooled, the melted coating forms a layer of slag, which covers the weld surface, protects the weld metal, cools it slowly, and reduces the possibility of air holes.
3. Ensure deoxidization and removal of sulfur, phosphorus and impurities of welds
Although the welding process is protected, a small amount of oxygen will inevitably enter the molten pool, which will oxidize the metal and alloy elements, burn the alloy elements, and reduce the weld quality.
Therefore, it is necessary to add reducing agents (such as manganese, silicon, titanium, aluminum, etc.) to the electrode coating to reduce the oxides that have entered the molten pool.
4. Supplement alloy elements for welds
Due to the high temperature effect of the arc, the alloy elements of the weld metal will be vaporized and burned, reducing the mechanical properties of the weld.
Therefore, appropriate alloy elements must be added to the weld through the coating to compensate for the burning loss of alloy elements and ensure or improve the mechanical properties of the weld.
For the welding of some alloy steels, it is also necessary to penetrate the alloy into the weld through the coating, so that the weld metal can be close to the base metal composition, and the mechanical properties can catch up with or even exceed the base metal.
5. Improve welding productivity and reduce spatter
The electrode coating has the effect of increasing the droplet and reducing the spatter.
The melting point of the welding rod coating is slightly lower than that of the core.
However, since the core is in the center of the arc and the temperature is high, the core melts first and the coating melts a little later.
At the same time, because the metal loss caused by spatter is reduced, the deposition coefficient is improved, and the welding productivity is also improved.
The above is the composition of welding rod, but what kind of welding rod should we choose when welding?
First of all, there is a concept that welding rods are of different types.
Let’s take a J422 electrode as an example.
See the number on the drawing?
J422 welding rod is a common name, corresponding to the international standard grade E4303.
It is an acid welding rod with titanium calcium coating.
J represents structural steel welding rod and 42 is the tensile strength of 42kg/mm2 weld metal.
Our international brand E4303 is explained as follows:
- E – electrode
- 43 – The tensile strength of the deposited metal is not less than 430Mpa.
- 0 – It represents that the welding position of the electrode is straight (“0” and “1” are suitable for all position welding, “2” are suitable for flat welding and flat fillet welding, and “4” are suitable for downward vertical welding).
- 3 – The combination of the third and fourth digits represents the type of welding current and coating
In other words
The J422 welding rod we call in China is the same as the E4303 welding rod in the world!
Take some models for example.
Model and brand comparison of common welding rods
Here’s a summary of the rough selection criteria.
The brands of commonly used welding rods are determined by the manufacturer or the industry itself, and the models are internationally used, with a wide range of types.
There are about 300 kinds of welding rods.
In the same type, different models are divided according to different characteristics.
A certain type of welding rods may have one or several varieties.
Welding rods of the same type can often have different brands in different welding rods.
Common welding rods mainly include:
1) For low carbon steel structural parts, E4303 (J422) or E5023 (J502) welding rods of titanium calcium type are generally used;
(2) Low hydrogen E4315 (J427) or E5015 (J507) welding rods shall be used for important structural parts with high requirements on plasticity, toughness and crack resistance.
When AC welding machine is used for welding, AC and DC low hydrogen E4316 (J426) or E5016 (J506) welding rods can be selected.
(3) Titanium E4313 (J421) welding rod is preferred for thin plate components with beautiful and smooth weld surface.
(4) For welding components that cannot eliminate oil rust and other dirt and require large penetration, it is better to use iron oxide E4320 (J424) welding rods.
(5) For welding components with a large number of vertical welds, if conditions permit, special welding electrodes for vertical down welding can be selected, such as E4300 (J420) welding rods.
The above are common welding rods that are distinguished according to their uses.
If the welding rods diameter is divided, the welding rods diameter depends on the thickness of the weldment.
The welding rods are generally divided into 2, 2.5, 3.2, 4, 5, 6 mm and other types according to the size of the core.
The most common types are 2.5, 3.2, and 4 mm
The approximate diameter and welding current are as follows:
|Welding rods diameter|
|Welding current (A)|
In addition, the method of selecting electrode diameter according to the thickness of weldment:
(1) The thickness of the weldment shall be ≤ 4mm, and the diameter of the selected electrode shall not exceed the thickness of the weldment.
(2) The thickness of weldment is 4~12mm, and the diameter of electrode is 3~4mm.
(3) The thickness of weldment is ＞ 12mm, and the diameter of welding rod is ≥ 4mm.
Take structural steel as an example: grade, preparation method, J XXX,
“J” representsStructural steel welding rod,
The third number represents the coating type, welding current requirements,
The first and second numbers represent the tensile strength of weld metal.
- J represents structural steel electrode;
- 50 represents that the tensile strength of weld metal is not less than 490MPa;
- 7 stands for low hydrogen electrode coating, DC.
The type of welding rod is determined according to relevant national standards and international standards.
Taking structural steel as an example, the letter “E” indicates the welding rod.
The first and second digits indicate the minimum tensile strength of the deposited metal.
The third digit indicates the welding position of the electrode,
The third and fourth digits indicate the type of welding current and coating type.
- E: Indicate welding rod;
- 43: Minimum value of tensile strength of deposited metal;
- 1: Indicating trial and full position welding;
- 5: It indicates that the electrode coating is low hydrogen sodium type, and DC reverse connection can be adopted;
The commonly used structural steel electrodes are J421, J422, J423, J424, J506 and J507.
For example, E43 series welding rods can be used to weld low carbon steel such as 20Mn and Q235 or steel with tensile strength of about 400MPa.
For welding 16Mn, 16Mng and other steels with tensile strength in the range of 500MPa, E50 series welding rods can be used (1MPa is about equal to 10kg force).
Here’s an example.
Now let’s take Q235 as an example. How should we choose a 5mm thick steel? (The data whose answers are all in the article can be queried)
First, Q235 is low carbon steel with yield strength of 235Mpa and tensile strength of 370-500Mpa.
Therefore, we can choose E43 series welding rods. Because the requirements for the workpiece are not high, we can choose E430 or E431 all position welding.
Finally, the symbol of low-carbon steel is 3 titanium calcium type coating.
Then for 5mm thick materials, we should choose the electrode with a diameter of 3.2.
Directly, for the welding rods 3.2, the current we choose is 100~130A
It is concluded that we should use E4303 welding rods with a diameter of 3.2 and a current of about 110A for welding.
Finally, I will give you a form that is easy to use if you can understand it.
Welding between the same metal materials
|Q235,10,20||J422||E4303||J422 is used for general structure, with complex shape and large rigidity.|
|J426||E4316||J426 and J427 are used for thick weldments;|
|J427||E4315||J426 and J427 are used for Q235-C and Q235D.|
|16MnR||J502||E5003||Generally, the first three types of welding rods are selected. When the requirements for weld toughness are high, the last two types of welding rods can be selected.|
|15MnVR||J506R||E5016-G||When the plate thickness is large, the first two welding rods can be selected.|
|15MnVNR||J556||E5516-G||Generally, the first three types of welding rods are selected. When the structural rigidity is small and the strength requirement is high, the last two types of welding rods can be selected.|
|18MnMoNbR||J606||E6016-D1||Large rigid thick plate structure can be used with ultra-low gas and high toughness welding rod or welding rod containing Ni;|
|J607||E6015-D1||Preheat 150~250 ℃ before welding, and conduct 250~350 ℃ post heat treatment immediately after welding or when welding is interrupted, and conduct stress relief heat treatment after welding.|
|13MnNiMoNbR||J606||E6016-D1||Preheat 150~200 ℃ before welding, and conduct nitrogen elimination treatment at 350~400 ℃ after welding.|
|R302||E5503-B2||Preheat 160~200 ℃ before welding, and conduct 675~705 ℃ tempering treatment after welding.|
|R307||E5515-B2||R302 is mainly used for cover welding.|
|12Cr1MoV||R312||E5503-B2-V||Preheat 250~300 ℃ before welding, and conduct 715~745 ℃ tempering treatment after welding.|
|R317||E5515-B2-V||R312 is mainly used for cover welding.|
|12Cr2Mo1||R402||E6000-B3||Preheat 160~200 ℃ before welding, and 675~705 ℃ tempering treatment after welding.|
|R407||E6015-B3||R402 is mainly used for cover welding.|
|16MnDR||J506RH||E5016-G||Tempering at 600~650 ℃ after welding can reduce the brittle fracture tendency of low temperature steel welding products by eliminating welding stress.|
|G202||E410-16||When the first three kinds of welding rods are used, the weldment shall be preheated at a temperature above 300C, and tempered and slowly cooled at 700 ℃ after welding.|
Welding rods are recommended for welding different steel grades
|Joint steel grade||grade||model|
|20, 20R+16Mn, 16MnRC||J427 J507||E4315 E5015|
|Q235-A+18MnMoNbR||J427 J507||E4315 E5015|
|A302 A307 A062||E309-16|
|A312 A317 A042||E309M0-16|
|Q235A, 20R,16MnR+00Cr17Ni14Mo2||A312 A317 A042||E309M0-16|