Welding is a skilled craft that needs good experience and training. Once you have mastered that craft, you can find many ways to avoid defects that novice welders may face. Suppose you are new to the welding industry and want to weld without having faults. In that case, backing in welding is an excellent technique that provides support during the welding process, prevents burn-through welding, and gives you the best penetration. If you’re just starting welding, it’s totally understandable to be uncertain about backing weld. Before attempting it, please ensure you understand the process and what it entails.
Let’s dive deep into the topic to get the answers to most of your frequent questions.
What is Backing in welding?
Backing bars are commonly used for beveled welding joints using a metal or ceramic bar on the back side of the joint to support molten weld metal. Thus, the plate absorbs heat, and less melt thru occurs. The purpose of backing welds is to hold the weld pool, prevent leakage, and promote 100% penetration.
Before welding the joint, a backing strip or bar is welded onto the back side of the joint, but the backing must be thick enough to handle the root pass heat. A butt joint, tee joint, or outside corner joint may use on a backing bar. The backing can be removed after welding or left on to become part of the completed joint.
Temporary Backing in Welding
Leaving backing where it is used is not always desirable or necessary. For example, welded equipment or structures that are under a lot of stress should not have the support left in place.
Temporary backing can be done with ceramic or copper plates because they usually do not weld with the root. Thus, smoothly removed if supposed to be once welding is complete. The letter R is placed in the backing symbol if you want to remove the backing weld.
Permanent Backing in Welding
On the other hand, permanent backing uses metal, similar to parent metal and filler. The strip must be around 4-6mm thick and tacked in position. So the backing metal plate fuse with the joint and becomes a part of the weld.
What is the difference between back and backing welds?
A back weld is a type of weld placed on the back side of the joint after the groove weld is completed. This is often done to provide extra joint support or reinforce it.
Contrary, a backing weld is applied beforehand to the root of the groove to support and protect molten weld metal. The backing can either be removable or permanent according to the desire and demand of the workpiece and circumstances. (Source)
What is a backing strip in welding?
Backing Strip \ Backing bar
The backing strip or backing bar is an integral part of the root pass. It is fixed through tack welding at the root of the joint. It supports the molten metal from melting through, facilitates joint penetration, and protects the weld from atmospheric contamination.
The backing strip can be fused permanently with the metal being welded or can be removed later if not needed or desirable. Mostly ceramic or copper backing strips are used for temporary backing welds.
What is ceramic backing in welding?
Ceramic backings are made of a high-temperature resistant ceramic seal, a mixture of different mixed minerals like Al2O3, SiO2, Fe2O3, TiO2, etc. When the seal melts, it produces a glassy slag that forms the underside of the weld seam and seals it against air entering. Ceramic backings are available as blocks that may be stuck to the weld seam’s bottom with an adhesive edge.
The ceramic backings offer some significant advantages when it comes to welding. They work well for submerged arc welding and MAG welding with solid or metal-cored wires in the downward position. Plus, they’re perfect for positional MAG welding using rutile cored wires with fast freezing slag.
Industries like shipbuilding use ceramic backing to keep costs low. However, ceramic backing is progressively used in pressure vessel fabrication, machine construction, general steel construction, tanks, bridges, and plant engineering.
Backing in welding is a concept that is rarely known to most novice welders. Backing in welding creates a deeper penetration along the weld seam. The primary purpose of the backing is to achieve deep penetration. Besides, its goal is to support the molten weld metal, protect it from atmospheric contamination at the root, and facilitate better appearance of the weldment.
I hope this blog will be an excellent resource for anyone looking to learn more about backing in welding and will clear many perplexities about backing welds.