Introduction to manual torch brazing
Flame brazing is widespread due to its extreme flexibility and allows you to join different materials with a low investment. An element that characterizes this type of process is the level of competence of the operator who must be trained correctly in order to perform flame brazing in a workmanlike manner. This article aims to deepen the basic information on flame management to better approach this activity.
The oxyacetylene torch
Knowledge of the tools and their correct use becomes essential for deciding whether to use a flame adjustment, a torch of a specific size, rather than other variables and therefore being able to make the difference in achieving good brazing. The brazing torch, regardless of the type of gas used, consists of a handle, two regulating valves (one for the combustion gas and the other for oxygen), a lance including a nozzle or with a detachable nozzle, and two fittings hose holder with non-return valves to which the pipes are to be connected.
If a pre-mixed gas production system is used, the tap will be one, as happens with some hydrogen generators. Torches complete with flashback valves and torches with separately installed flashback valves are available on the market. The choice of one type of torch rather than another is determined by several factors such as:
- type of materials to be joint
- torch weight
- flow rate of the nozzles
- precision in flame adjustment
- torch shape
Gas for brazing
Companies and artisans who use flame brazing choose the fuel gas that best suits the specific application, also considering the costs of the gas itself, logistics management (cylinders, storage cabins, distribution systems), and obviously, safety in using the type of gas itself. When the use of the flame is occasional, on the market are available several kits that consist of a mixed gas (such as MAPP gas or other), made up of a single cylinder with a torch screwed into the head, or with two small cylinders on wheels or not on wheels, equipped with a tube torch. On the other hand, if the use is constant, oxygen is usually combined with combustible gases such as:
- natural gas,
- stored hydrogen or hydrogen from self-producer.
Users, if properly trained, usually are able to decide which gas has to be chosen based on the application and process management.
The torch must be lighted with the appropriate piezoelectric lighters, available both with electric power or manual operation: the advice is to avoid the classic gas lighter.
The next step is the adjustment of the gas nozzles: first, open the fuel gas valve gently, then slowly proceed with the opening of the oxygen until the desired flame is obtained.
It is important that the temperature of the oxyhydrogen flame allows a sufficient caloric intake to carry out fast brazing without overheating the piece too much and without producing an excessive amount of oxides.
At the same time the flame must not be too weak because if the piece is not brought to the correct working temperature of the filler material, there will be no good capillarity and therefore incomplete penetration into the joint. The ideal solution is to find a good compromise between the correct caloric intake in relation to the filler material and the two joints.
Video: flame adjustment types
The correct regulation of the gas and the flame is extensively covered in the literature and can be summarized with a concept that can generally be used for most applications.
If too much gas is added when adjusting the torch, the result will be a reducing flame otherwise, if the gas input is too low, an oxidizing flame will result.
It is important to know that the temperature of the oxy-acetylene flame is not the same in all areas of the flame. The part near the tip of the torch (dart) will be hotter and decreases as you move away from it. The part furthest from the dart is called the plume.
– Oxidizing flame
When the amount of oxygen is greater than the amount of combustible gas, the flame is defined as oxidizing. This type of flame is not recommended for brazing because it tends to oxidize the piece. It is easily recognized because the torch with this setting emits a typical hiss and the dart is very short.
– Reducing flame
The reducing flame (or carburizing flame), is obtained when the supply of fuel gas is higher than the supply of oxygen. It can be used for example when brazing aluminum. The dart is elongated with respect to the oxidizing flame.
– Neutral flame
This type of regulation is recommended in most cases and is obtained when the supply of combustible gas and oxygen is balanced. The flame is very regular, without halos.
In general, the objective of flame regulation will be to have a neutral flame.
The brazing torch and the relative system require regular maintenance and are subject to the regulation – UNI 11627:2016 Gas welding equipment – Manual gas welding, heating and cutting equipment – Periodic checks.
Keep in mind that periodic checks are essential to avoid the occurrence of accidents with possible very serious consequences for the user.
Brazing flame advantages
Flame brazing, as mentioned at the beginning, has many advantages including:
- extremely usage flexibility,
- low initial investement,
- possibility of brazing different materials such as copper, brass, steel, stainless steel, aluminum, bronze, and many others.
The limits of this type of application mainly refer to having to work with an open flame and therefore the need for specific training for the operators.
For this reason, Saldobrase offers its customers a vast series of specific training courses also in collaboration with certified companies. Upon request, it is possible to obtain certification for brazing operators and brazers according to the UNI EN ISO 13535:2012 standard. Brazing – Qualification of brazers and brazing operators.
It should be noted that for many brazing processes qualification is mandatory.