Welding is a vital fabrication process that helps in the formation of continuous structures, whether it is practical or impractical to form such structures. Applying a welding tool like backing to join the parent materials ensures the structure’s integrity. So, what is backing in welding?
Backing in welding involves placing materials at or near the root joint to shield and support molten weld metal. It facilitates complete joint penetration, and various materials can be used as a backing piece.
This article looks at ceramic backing in welding and what backing in welding is. I also discuss the differences between back welds and backing welds.
What Is Ceramic Backing in Welding?
Ceramic backing in welding is simply using ceramic as a backing to support and shield molten weld metal. Ceramic backings consist of sealed, high-temperature resistant ceramic from several mineral mixes, including SiO2, Al2O3, TiO2, Fe2O3, etc. In the weld pool, these backings are chemically neutral.
When a ceramic backing melts, it produces a glassy slag that pools under the weld seam, sealing it against air entering. Ceramic backings come as single ceramic segments or blocks, and the blocks are about 2 cm long on a flexible aluminum foil with an adhesive edge.
The adhesive edge of the blocks allows them to be attached to the underside of the weld seam. Ceramic backing segments are about 10 to 15 cm long and placed in metallic rails. These rails are then joined to the workpiece with magnets or other fixtures.
Uses and Advantages of Ceramic Backing
- Ceramic backings turn a two-side welding process into a single-side process easily.
- One-sided welding at a construction site can often be done inside the component to avoid weather interference.
- They are moisture-resistant, and thus, suitable for outdoor welding.
- It is widely used for Metal Inert Gas (MIG) weld backing because it doesn’t fuse itself to the workpiece during welding and is easy to remove.
- Dense ceramics with low moisture content are great for welding fine-grained, high-strength steels requiring weld metals with very low hydrogen content.
- Root runs welded with ceramic backing usually have a lower incidence of pores, slag inclusions, insufficient penetration, restart errors, and undercut.
- They provide economic advantages for Metal Active Gas (MAG) welding and submerged arc welding with metal-corded or solid wires in the downward position.
- Using ceramic backing in one-sided welding increases the process reliability when root runs have to be notch-free, such as stress corrosion or dynamic loading.
Although ceramic backing tapes are often used to help support roots of weld metals, there are concerns with using them during Tungsten Inert Gas (TIG) welding. They have a welding point of 1,800ºC, and temperatures in TIG welding go up to 6,000ºC.
What Is Backing in Welding?
Backing is a material applied at the root of a weld joint to support and shield molten weld metal. It prevents the molten metal from dripping through the open root (a burn-through) and facilitates a complete joint penetration. Full penetration means 100% of the base metal’s thickness is fused by the weld.
Asbestos, a piece of metal, or other fireproof material can serve as a backing. Backing bars or materials are placed at both sides of a joint or adjacent to the root joint in electro gas and electro slag welding, and they must be thick enough to withstand the heat of the root pass.
You may place a steel backing bar before completing the groove weld with continuous/discontinuous tack welds or fillets. Tee joints, outside corner joints, and butt joints use a backing strip.
Copper strips and ceramic backings may be taken off after welding, whereas cofferdam or void space closing welds may be left on the finished weld, and the letter R is placed on the backing symbol if the backing should be removed.
Some reasons for removing a backing strip from a weld are:
- Backings can be sources of stress concentration.
- A backing strip can act as an aperture to collect moisture, promoting rust.
- It can also prevent a weldment (completely welded joint) from bending under a uniform load, and it will break if it cannot bend uniformly.
Temporary or removable backing may come from a ceramic substance or copper – materials that don’t fuse to the root and are easily removed after the welding process is completed.
Permanent backing usually comprises a base metal similar to the parent metal being welded, and it fuses to the root of the weld to become permanent. They do not come off easily.
A single-sided multi-process weld made without backing can address the different materials it’s made from differently. For example, a weld with a TIG root and MMA fill has the TIG classed as a weld without backing, but the MMA fill is classed as one made with backing.
What Is the Difference Between Back and Backing Welds?
Fabrication and engineering drawings have welding symbols that describe the size and type of weld and other important information. If a welder doesn’t know the symbols, they cannot do their job correctly.
The American Welding Society came up with a system in 1929 for indicating welding requirements. The back weld and backing symbols use the same symbols, and many welders confuse them.
The two main differences between back welds and backing in welding are their functions and application times. Outlined below are the differences:
- A backing weld involves using a metal strip or ceramic plate on the joint backside (usually beveled) to avoid too much melt-through and to absorb some of the heat. In contrast, a back weld or back gouging is the process of cutting a groove in the backside of an already welded joint.
- Back gouging removes discontinuities of the root pass and ensures 100% joint fusion at the root, and backing aids complete joint penetration.
- A backing weld is placed at the joint root before welding, while a back weld is placed on the joint’s backside after the groove is welded.
If the properties of the root pass metal are not desirable to the finished weld, back gouging can help remove it. Although it is impossible to memorize all the symbols, you can know as much as you need for your work with practice.
