Soldering and brazing
Joining process in which molten solder is used with a liquidus temperature lower than the solidus temperature of the basic material(s). The molten solder moistens the surfaces of the basic material(s) and is drawn into a narrow gap between the parts to be joined during or at the end of the heating phase (or held in place there, if inserted in advance).
Note 1: These processes are commonly applied on metals; they can, however, also be applied on non-metals. The solders will always have a different chemical composition than the components to be joined.
Note 2: The processes are frequently referred to as V-joint brazing when they are applied without capillary forces.
Soldering: Joining process using solder with a liquidus temperature about 450 °C or lower.
Brazing: Joining process using solder with a liquidus temperature higher than 450 °C
Application of one or more layers of materials on the surface to achieve desired properties and/or dimensions.
Graphic classification of soldering and brazing processes
Examples for Soldering
Soft soldering, Solder joints in a heat exchanger, Induction brazing, Induction high-temperature soldering with hydrogen, Soldering of zinc coated components, Aluminium soft soldering.
Definition of Bonding
Bonding of metals is the creation of a solid joint between adherents by a synthetic material (adhesive), which hardens out by a physical-chemical reaction and joins the parts by surface adhesion as well as by inter molecular forces in the adhesive (cohesion).
Note: Adhesion is not a thermal process in contrast to welding or soldering.
Choosing the adhesion:
As during bonding the adhesion process is effected by chemical processes, the following has to be considered while choosing the adhesive.
How high is the maximum pressure on the adhesive layer. Not every adhesive has the same extension/tensile strength.
Which materials are used. There are special adhesivesof the materials, which are adapted to the chemical characteristics.
How high is the ambient temperature. Some adhesives approach their maximum extent of hardening or the highest strength only at high temperatures.
Are there other effects such as humidity, extreme solar radiation or gas atmosphere. An adhesive can thereby easily loose its adhesive strength.
The bonding area must be pre-treated before the actual bonding process.
The pre-treatments are:
Cleaning the surface (if necessary with solvent liquid) in order to remove powder, greace or other remainders.
Surface roughening by grinding or brushing in order to attach the bonding compound to the surface.
If necessary special treatment like flaming, etching or staining.
Basic Terms of Soldering Processes According to EN 14610
The soldering processes are classified according to energy carriers in EN 14610.
Physical phenomenon that makes energy required for welding available either by means of transfer to the work piece(s) or transformation in the work piece(s). The following energy carriers with their related ordinal numbers are used in the standard:
1 Solid bodies
4 Electric gas discharge
6 Movement of mass
7 Electric current
Note: When welding with solid body, liquid, gas or electric gas discharge, the energy required for welding is fed to the work piece(s) (externally); however when welding is performed by means of radiation, movement of mass or electric current, the heat energy (respectively mechanical energy in case of cold pressure welding) is generated by means of transformation of energy in the work piece.
The heat content is the decisive characteristic for solid body, liquid, and gas. Electric gas discharge and passage of current are mechanisms that feed energy of moving charge carriers to the welding zone. This is accomplished by plasma or sparks in case of electric gas discharge, by resistance heating in case of electric current at which the current is either generated on account of conductivity or by induction.
Radiation is energy conduction in terms of propagation of waves of light or from charge carriers. The decisive characteristics for movement of mass are power and displacement per time; different types of movement are translation, rotation, and oscillation.