Cold welding: types and features
The term “cold welding” refers immediately to two ways of joining materials, which, in fact, have nothing in common with each other. Therefore, you should immediately clarify which method is being discussed. The first method is the compounding of metals by pressure, without the characteristic stage of melting. In addition, the term “cold welding” is used when special epoxy glue is used for work. This method is used to connect both homogeneous and dissimilar materials.
Cold welding using a special epoxy mixture is so named because the resulting seam is very durable. The junction can be processed by any mechanical method (drilling, grinding) without risk of damage. Cold welding is universal - for all types of materials, and special, designed for durable bonding of metals and alloys. It is used for minor repair of machine parts, restoration of small fragments, repair of broken threads, etc.Since the glue line is sealed, it can be used to seal cracks in pipes and boats.
Cold metal welding
This method of connection was known at the dawn of mankind, in the Bronze Age. But despite this, they really became interested in cold welding only in the middle of the 20th century. A characteristic feature of this method is the absence of the melting phase of the metal, all work takes place without preheating, at room temperature. An interesting fact: scientists have repeatedly tried to explain the mechanism of action of this process, put forward, for example, hypotheses about recrystallization or the energy field, but they all could not withstand any criticism. The currently accepted theory is as follows: all metal atoms are connected by a special metal bond, and if the distance between two blanks is less than 300 angstroms, they form a common electron cloud that will keep them together. However, the formation of this bond can be prevented by metal oxides present on the surface and the air gap. Therefore, they are squeezed out of the working area by various methods - deformation by a punch, running, compression, shear.Cold welding is used to join soft metals: alloys of copper, aluminum, gold, silver. This method is widely used in electrical engineering.
This process is designed to connect dissimilar and homogeneous metals, mainly rods with a circular cross section. Unlike cold welding, with which friction welding is sometimes confused, there is a phase of material melting, but it occurs not due to forced heating of the working area, but by converting mechanical energy into heat energy. The rods are fixed opposite each other, rotated, and due to inertial forces, their ends are melted, after which a fast draft is produced.
All these types of permanent connections have a common feature: if initially they were developed as an alternative to the usual welding process and were used quite rarely, then today they are used everywhere.