Copper fitting 5/16 solder union with Obus valve cap

Types of torch welding: soft soldering and hard solderingIn this article you will see everything you need to know to perform welds on copper pipes or other metals using a torch, very useful if you want to repair a copper pipe leak or if you want to install a radiator, a sink, etc. Soldering copper or other metals with a torch consists of joining copper parts with the help of a second metal that melts between them. The melting temperature of the filler metal rod must be lower than that of the copper or metal to be welded. The piece to be welded does not melt, therefore it is not a fusion welding of the base material. This type of welding is used when you want to join different materials, or those that have poor weldability and high resistance is not required. It is the easiest welding technique to perform, even for DIY beginners. There are two types of welding regarding the melting temperature of the filler material: soft soldering and hard soldering. Soft soldering requires reaching temperatures below 450°C, while hard soldering uses temperatures above 450°C. For example, filler materials made of silver and copper require temperatures of 600°C and 900°C. The higher the melting temperature of the filler material, the greater the strength of the joint. In electronics, the filler material consists of 60% tin and 40% lead and the temperature required for its fusion is only 190°C. Previously with lead pipes, a large proportion of lead was used in the filler material, but nowadays with copper piping it has been eliminated from the filler material, replaced by copper and a higher proportion of tin. The filler material used in hard soldering is generally an alloy of copper, copper phosphate and zinc, or copper and silver. The melting point is between 600°C and 880°C. Alloys with a high proportion of silver (40%) are recommended for making high mechanical strength welds and are those used for copper and brass gas pipe joints. Brass is used for joining steel parts. The filler metal or flux is used with a flux, which is responsible for removing impurities from the joining surface and also oxides so that the flux adheres well. Selection of the appropriate torch depending on the type of welding to be performedThe soldering lamp: is powered by a butane or butane/propane cartridge. It is ideal for performing soft soldering (with tin wire). Soldering torch: is powered by butane or propane gas cylinders and provides a larger flame, usually come with various nozzles for different applications. This torch is suitable for welding different metals and alloys: tin, copper, brass, aluminum and zinc. Its use is not recommended for ferrous metals as it offers low mechanical strength in joints. Bi-gas torch: is powered by an LPG or acetylene cartridge, mixed with oxygen at pressure, coming from another tank. It is ideal for performing hard soldering of large diameter pipes and also for ferrous metals. Professionals usually use this type of torch for all hard soldering as it greatly facilitates their work since it provides a higher temperature. Selection of filler metal or flux The choice of filler metal will depend on the type of material to be welded and the strength required for the joint and will influence the type of torch to use. The more resistant the filler material, the higher its melting temperature. Type of welding Mechanical strength Application Soft soldering (tin) Weak: 5 kg/mm2 Installation of faucets, extension of water lines. Hard soldering (copper/phosphorus) 50 kg/mm2 Cold and hot water pipes, radiators, water circuits. Copper/silver 6% and 20% 60 kg/mm2 Facilitates professionals in achieving resistant and watertight joints. The silver content helps to rotate the pieces while they are being welded ensuring good sealing. Copper/silver 40% 40 kg/mm2 Copper pipe for gas. Procedure for torch welding You must prepare the material to be welded very well, sanding the two surfaces to be joined with sandpaper. Then, with a soft cloth we remove the dust and finally with a brush. We apply the flux at the joint that will receive the filler metal and fit the pieces in their final position. The pieces to be welded must be held (if necessary) with pliers since copper and its alloys are good heat conductors. If you are going to weld against a wall, there are special fireproof fabrics to isolate the wall from the torch flame. As we have seen for home DIY, the torch used can be a refillable