How to Select the welding electrodes
Source: | Author:wenlikeji | Publish time: 2017-08-03 | 369 Views | Share:
Before you power up your machine and pick up your electrode holder, consider these basic guidelines.
Base metal type 母材类型 Tensile strength 抗拉强度Power Supply 电源Base Metal Thickness, Shape and Joint Fit-Up 母材厚度,接口形状

Stick welding is a skill that takes much practice to master, and selecting the correct electrode for the job can be equally challenging. Stick electrodes are available in a wide range of types, each of which provides different mechanical properties and operates with a specific type of welding power source. Factors you should consider when selecting a stick electrode include base metal type, joint fit-up and welding positions. Before you power up your machine and pick up your electrode holder, consider these basic guidelines.

Base metal type 母材类型

Most welding jobs require matching the composition of the welding rod to the base metal. This means that proper assessment of the base metal is important. Evaluate the metal by its appearance, magnetic properties and hardness.

Tensile strength 抗拉强度

The first two digits on welding electrodes, such as the 6011, means that it has a tensile strength of 60,000 psi. Match its tensile strength with that of the base metal.

A good example of what the strength of a weld is the rod numbers themselves. A 6011 rod using the first two digits (60XX) stands for a minimum of 60,000 pounds of tensile strength per square inch of weld. A 7018 is 70,000 pounds of tensile strength per square inch. In comparison, typical steel, which is graded A36 steel, has 36,000 pounds of tensile strength per square inch. The weld is usually two times stronger than the steel it is welding!

If you were wondering what the last two digits refer to, it’s the flux or shielding on the rod. The higher the number the more shielding, flux, and or metal is deposited. A (XX11) has a lot less coating then a (XX24).

Power Supply 电源

Most electrodes are designed to work with either AC (Alternating Current) or DC (Direct Current) power sources, and some electrodes are designed to work with both AC or DC current. The type of electrical current involved in the welding process affects the level of penetration into the base metal, with AC current generally achieving deeper penetration.

To determine the correct current type for a particular electrode, refer to the fourth digit of the AWS classification, which represents the type of coating and type of compatible welding current

Base Metal Thickness, Shape and Joint Fit-Up 母材厚度,接口形状

Thick materials require an electrode with maximum ductility and low hydrogen to prevent weld cracking. Electrodes with AWS classification numbers ending in 15, 16 or 18 provide excellent low–hydrogen properties and good toughness (high impact values) to accommodate for residual stress.

For thin materials, you will need an electrode that produces soft arcs, such as a 6013, Also, smaller diameter electrodes will provide shallow penetration to help prevent burn-through on thinner materials.

You’ll also want to assess the joint design and fit-up. If you’re working on a joint with a tight fit-up or one that is not beveled, use an electrode that provides a digging arc to ensure sufficient penetration, such as an E6010 or E6011. For materials with wide root openings, select an electrode, such as an E6012, that creates a concave weld face suitable for bridging gaps and making groove welds.

Welding Position  焊接位置

To determine what position(s) a particular electrode is qualified for, refer to the third digit in AWS classification. Here’s how you decipher the qualified electrode position:

1 = flat, horizontal, vertical and overhead

2 = flat and horizontal only

For example, a 7018 electrode can be used in the flat, horizontal, vertical and overhead positions.

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Specification and Service Conditions

Make sure to assess the conditions that the welded part will encounter throughout its service. If it will be used in high heat or low temperature environments, subjected to repetitive shock loading, a low hydrogen electrode with higher ductility will reduce the chance of weld cracking. Also, be certain to check for welding specifications if you’re working on critical applications such as pressure vessel or boiler fabrication. In most cases, these welding specifications will require you to use specific types of electrodes.

Environmental Job Conditions

To achieve the best results, you should always remove excessive mill scale, rust, moisture, paint and grease. Clean base metals help prevent porosity and increase travel speeds. If cleaning your base metal is not possible, E6010 or E6011 electrodes deliver a deep penetrating arc that has the ability to cut through contaminants.

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