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Flux-cored arc welding
From Wikipedia, the free encyclopedia
FCAW wire feeder
Flux-cored arc welding (FCAW or FCA) is a semi-automatic or automatic arc welding process. FCAW requires a continuously-fed consumable tubular electrode containing a flux and a constant-voltage or, less commonly, a constant-currentwelding power supply. An externally supplied shielding gas is sometimes used, but often the flux itself is relied upon to generate the necessary protection from the atmosphere, producing both gaseous protection and liquid slag protecting the weld. The process is widely used in construction because of its high welding speed and portability.
FCAW was first developed in the early 1950s as an alternative to shielded metal arc welding (SMAW). The advantage of FCAW over SMAW is that the use of the stick electrodes used in SMAW is unnecessary. This helped FCAW to overcome many of the restrictions associated with SMAW.
One type of FCAW requires no shielding gas. This is made possible by the flux core in the tubular consumable electrode. However, this core contains more than just flux, it also contains various ingredients that when exposed to the high temperatures of welding generate a shielding gas for protecting the arc. This type of FCAW is attractive because it is portable and generally has good penetration into the base metal. Also, windy conditions need not be considered. Some disadvantages are that this process can produce excessive, noxious smoke (making it difficult to see the weld pool); As with all welding processes, the proper electrode must be chosen to obtain the required mechanical properties. Operator skill is a major factor as improper electrode manipulation or machine setup can cause porosity.

A drawing of FCAW at the weld point
Another type of FCAW uses a shielding gas that must be supplied by an external supply. This is known informally as "dual shield" welding. This type of FCAW was developed primarily for welding structural steels. In fact, since it uses both a flux-cored electrode and an external shielding gas, one might say that it is a combination of gas metal (GMAW) and flux-cored arc welding (FCAW). This particular style of FCAW is preferable for welding thicker and out-of-position metals. The slag created by the flux is also easy to remove. The main advantages of this process is that in a closed shop environment, it generally produces welds of better and more consistent mechanical properties, with fewer weld defects than either the SMAW or GMAW processes. In practice it also allows a higher production rate, since the operator does not need to stop periodically to fetch a new electrode, as is the case in SMAW. However, like GMAW, it cannot be used in a windy environment as the loss of the shielding gas from air flow will produce porosity in the weld.
Process variables[edit]
  • Wire feed speed (and current)
  • Arc voltage
  • Electrode extension
  • Travel speed and angle
  • Electrode angles
  • Electrode wire type
  • Shielding gas composition (if required)
  • Reverse polarity (Electrode Positive) is used for FCAW Gas-Shielded wire, Straight polarity (Electrode Negative) is used for self shielded FCAW
Advantages and applications[edit]
  • FCAW may be an "all-position" process with the right filler metals (the consumable electrode)
  • No shielding gas needed with some wires making it suitable for outdoor welding and/or windy conditions
  • A high-deposition rate process (speed at which the filler metal is applied) in the 1G/1F/2F
  • Some "high-speed" (e.g., automotive) applications
  • As compared to SMAW and GTAW, there is less skill required for operators.
  • Less precleaning of metal required
  • Metallurgical benefits from the flux such as the weld metal being protected initially from external factors until the slag is chipped away
  • Porosity chances very low
Used on the following alloys:
  • Mild and low alloy steels
  • Stainless steels
  • Some high nickel alloys
  • Some wearfacing/surfacing alloys
Of course, all of the usual issues that occur in welding can occur in FCAW such as incomplete fusion between base metals, slag inclusion (non-metallic inclusions), and cracks in the welds. But there are a few concerns that come up with FCAW that are worth taking special note of:
  • Melted contact tip – when the contact tip actually contacts the base metal, fusing the two and melting the hole on the end
  • Irregular wire feed – typically a mechanical problem
  • Porosity – the gases (specifically those from the flux-core) don’t escape the welded area before the metal hardens, leaving holes in the welded metal

FCAW Flux Cored Arc Welding

Home  Welding Processes  FCAW Flux Cored Arc Welding

Information and Guides About FCAW

Slag peeling from Flux Cores Arc Weld in the vertical up position
Flux core arc welding was introduced in the 1950’s. Technically the introduction of this process was not new. It was just a new type of an electrode that can be used on a MIG welding machine. Flux cored arc welding is a process similar to MIG welding. Both processes using continues wire feeds, and similar equipment. The power supply for a FCAW, and a MIG welder, are the same machine. They are both considered semi automatic processes, and have a very high production rate.
The main difference between flux cored arc welding and MIG welding is the way the electrode is shielded from the air. Flux cored arc welding just like the name implies, has a hollow wire with flux in the center, similar to the candy called “pixy sticks”. Just as the name states, a “Flux Core”. The main difference between MIG welding and flux core arc welding is, FCAW gets its shielding from the flux core, and this allows the operator to weld outdoors where it is windy. It’s like a SMAW welding electrode turned inside out! MIG welding gets its shielding from a bottle of gas which has serious drawbacks, when welding outdoors, or in drafty conditions.

Flux Cored Arc Welding Production

Cruise ship Oasis of the Seas. This was the wave deflector installation project. The ship is over 25 stories high and was the largest in the World at the time.
Flux cored arc welding is the most productive of the manual welding processes! When comparing MIG welding to flux core arc welding, there is a huge gap in production, in the amount of weld per hour. A MIG welder can typically produce 5 to 8 pounds of weld per hour, versus a FCAW welder packing 25 plus pounds of weld per hour. On top of that flux core welding can weld 1/2″ plates in a single pass with full penetration on both sides. Flux core arc welding for this reason is primarily used in the shipbuilding industry. Ships are made of heavy plate, and have endless amounts of welding that needs to be done. Flux core welding produces high quality welds, fast, and even when in windy conditions.

Weldability of Metals

Welding with flux cored electrodes has some serious cons when it comes to the weldability of metals. So far, FCAW has been perfected on most carbon steels, cast iron, nickel based alloys, and some stainless steels. Unfortunately most non ferrous exotic metals cannot be welded and that includes aluminum. On the upside for most hobbyists the flux core electrode may be an excellent choice for general garage work, because if used in a MIG welder there is no shielding gas required on some electrodes.

How Flux Cored Arc Welding Works

Flux cored arc welding just like MIG welding requires three main ingredients, electricity, filler metal, and a form of shielding from the air. Just like MIG welding, flux core welding works by feeding an electrode continuously to the joint. First the welder squeezes the trigger, and then the wire feeder begins to feed the electrode to the joint, at the same time the electrode gets electrically charged. Once the electrode hits the metal joint, the electricity short circuits, and heats up the electrode till the electrode begins to melt. Once the electrode begins to melt, the metal also starts to melt, and then both of them start to create a puddle. This puddle at the same time melts the flux core, creating a shield from air, and at the same time produces a slag that protects the weld from contamination.

FCAW Self-Shielding vs. Dual Shield

Flux cored arc welding comes in two types of shielding. The first difference is in the electrode itself, it is a tubular wire with a shielding powder in the center. In technical terms this is called “Self-Shielding” or sometimes branded “Inner Shield”. The second is the same type of electrode, but another ingredient is added. A bottle of gas is used in addition to the flux core shielding. The technical term for this is “Dual Shield”. In the case of dual shielding, you have a powder flux in the center of the electrode and an external shielding gas protecting the weld area.

FCAW Voltage Type – Welding Polarity – Power Supply

A flux cored welding power supply is also a MIG welding power supply, they are the same machine. That is a “Constant Voltage Power Supply”. Constant voltage power supplies keep the voltage near, or at the same level. Unlike a TIG, or Stick welder, that keeps the amperage consistent. In the flux cored welder the amperage is changed with the wire feed speed. The faster the wire feeds, the more contact the electrode has, producing more amperage, and heat.
The voltage type used is D/C direct current like the type current produced by a battery. The polarity used in industrial flux core arc welding is typically D/C electrode (+) positive. This means that the handle is the positive side of the circuit, or the electricity flows from the metal to the welding handle. This is typical when larger electrodes are used. When welding with smaller electrodes and sheet metals, the polarity is changed to D/C electrode (-) negative.
The main difference between FCAW, and a MIG welder’s are, flux cored arc welding power supplies are available with, much, more, power! Basically they are an extremely powerful MIG welder! Some flux core arc welders come with the capabilities of running over an extremely hot, 1000 plus amps! That is where they leave MIG welding in the dust for production.


Shielding Gases for FCAW

In the case of dual shielding being used with a flux cored electrode the choices of shielding gasses are limited.

C25 flux core dual shield gas
The choices are as follows:
CO2 – Carbon dioxide
Ar – Argon
CO2 / Ar – A mixture of the two
Ar / Ox – A mixture of the two
CO2 by itself produces the deepest penetrating weld but has some drawbacks. The mechanical properties of the weld are not the best due to fact the flux in the wire reacts with the shielding gas. Others drawbacks are, it produces a lot of spatter, and the arc is stiff and not as stable as it can be.
Argon by itself will also weld with a flux cored electrode, but just like CO2, it reacts not favorable with the flux. Both Argon and Carbon dioxide can make a decent looking weld if used by themselves. What the weld looks like versus the actually quality of the weld are two different stories.
The most common gases used for dual shield FCAW are a mixture of Carbon Dioxide and Argon or Argon and Oxygen. The most popular is C25 / 25% Carbon Dioxide and 75% Argon. This gas produces a stable arc, less spatter, and allows more of a spray transfer of metal. I recently used this mixture when taking my 3G flux cored arc welding certification. In some other cases a mixture of Argon and Oxygen may be used. Oxygen in small percentages stabilizes the weld arc and improves the mechanical properties of the weld.
Ultimately if using dual shield it’s always best to read the electrodes manufactures recommendations or ask you gas supplier for the proper gas.


FCAW Electrode Types

flux core label 71t 1
The electrodes used for flux cored welding are almost visually the same as a MIG welding electrode. The difference is that flux cored electrodes are tubular, or a hollow tube with flux in the center. MIG welding electrodes are solid metal.
Flux cored electrodes come in standard sizes. Some are the same size as most MIG welding electrodes but others are comparable to the thickness of a stick welding electrode.
Here are some of the more popular sizes for standard industrial applications:

As with most electrodes there is a standard classification code or designation code, on the spool they come on. To understand the classifications better it is important to know some basics about where the classification codes are different.
A somewhat common flux cored welding electrode is the “E71T – 1”. As with all electrodes the numbers and letters all mean something. There identifications are as follows.
  • E – Stands for electrode.
  • 7 – Stands for the minimum amount of tensile strength. In this case it is 70,000 lbs of tensile strength per square inch of weld. The way this number is figured is by adding four zeros to the number.
  • 1– Stands for the position that this electrode can be welded in. There are only two designations and they are “0” for flat and horizontal welding, then there is “1” for all position welding.
  • T – Stands for a tubular electrode. When “T” is used it is always assumed it is a flux cored electrode.
  • 1 – The last is the shielding flux type designations.
As a note with all flux cored electrodes they need to be stored in a dry place. Otherwise the may pick up moisture and this will cause major weld defects.


Flux Cored Welding Transfer Types

When welding with a flux cored electrode there are two metal transfer types used! The transfer types are Spray Transfer and Globular. Spray transfer is the most commonly used. Just like the name states the metal from the electrode gets heated up to the point that it literally sprays the filler metal to the joint. Globular transfer heats up the electrode hot enough for globs of metal to drip off of the electrode to the weld joint. What separates the two transfer types are, voltage settings, wire speed, and the gasses used, if any.

Flux Cored Arc Welding Joint preparation

Joint preparation for flux core is not as critical as with MIG welding. FCAW can typically burn through mill scale and minor rust. In many cases when the metal is cut with a torch, it can be welded as-is, with no additional cleaning. For the shipbuilding industry this is a huge savings in labor cost. In addition to easy joint preparation, beveled groove joints can be narrower for metals ½ inch or thinner, and they can be welded in a single pass with full penetration on both sides.

Ceramic Backing Tape

Commonly in the ship building industry many joints are welded from a single side using a ceramic backing tape. The ceramic backing tape is like a mold to pour metal in, but in this case the electrode will fill that mold. When ceramic backing tape is used it allows for full joint preparation and outstanding weld quality. This in return gives full control of the shape and penetration of the back side of the weld. Once the weld is finished, the ceramic tape is simply peeled off, and thrown away. The pictures below are of the first time I used ceramic backing tape on a 3G weld joint. It’s real easy as long as you keep the arc in the puddle!
Hàn điểm hàn FCAW
Quy trình hàn hồ quang hàn FCAW
Thông tin và hướng dẫn về FCAW
Slag peeling từ Flux Cores Arc Weld ở vị trí đứng lên
Hàn hồ quang nguyên chất được giới thiệu vào những năm 1950. Về mặt kỹ thuật việc giới thiệu quá trình này không phải là mới. Nó chỉ là một loại điện cực mới có thể được sử dụng trên một máy hàn MIG. Hàn hồ quang luồng thông là một quá trình tương tự với hàn MIG. Cả hai quá trình sử dụng nguồn cấp dữ liệu dây chuyền liên tục, và các thiết bị tương tự. Việc cung cấp điện cho một FCAW, và một máy hàn MIG, là cùng một máy. Cả hai đều được coi là bán tự động quy trình, và có một tỷ lệ sản xuất rất cao.
Sự khác biệt chính giữa hàn hồ quang luồng thông và hàn MIG là cách mà điện cực được bảo vệ khỏi không khí. Phép hàn hồ quang luồng tuôn chảy giống như tên của nó, có một dây rỗng với thông lượng ở giữa, tương tự như kẹo gọi là "gậy xám". Giống như tên gọi, một "Flux Core". Sự khác biệt chính giữa hàn MIG và hàn hồ quang nguyên tử là, FCAW được che chắn từ lõi lưu thông, và điều này cho phép các nhà điều hành để hàn bên ngoài nơi có gió. Nó giống như một điện cực hàn SMAW quay ra bên trong! MIG hàn được che chắn của nó từ một chai khí có những hạn chế nghiêm trọng, khi hàn ngoài trời, hoặc trong điều kiện dám.

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