Blacksmith or forge welding.
Blacksmith welding - an ancient form of pressure welding. For nearly three millennia of humanity widely used in iron, not being able to melt, so the iron can not be used for a long time known casting and welding was invented blacksmith welding method, as if intended for iron. Prosperity and development of welding blacksmith highly facilitated by the very method of iron production, which had existed for thousands of years until the second half of XIX century.
When blacksmith welding steel is heated to transition to a plastic state, the hot metal is subjected to strong pressure in the process of forging (forging welding), rolling, extrusion, drawing, etc., should be steel heated to 1100-1300 ° C, any event above the alpha conversion -gamma.
Let us consider briefly the main processes occurring in the metal with an increase in its temperature, stopping for an example on carbon steels. As the temperature reaches a critical point Ac3 normal alpha-iron goes into gamma-iron, a good solvent carbon in large quantities. At the same cementite and pearlite steel disappear, carbon is evenly distributed over the volume of metal that goes into a homogeneous austenite. With a further increase in temperature an increase in metal grains, ie, the boundaries between the grains disappear, a few small grains coalesce into one large grain in an effort to reduce the total free surface. At this temperature, and begins welding, ie, education in the border zone of new crystal grains, borrowing material for their growth on both parts to be united, which leads to the destruction of the physical interface between the parts.
The strength of welding increases with temperature and pressure within certain limits. When excessive rise in temperature may occur the effect of superheating and melting of some metal structural components, which leads to a decrease in the strength of welded joints.
Weldability of pressure in the plastic state is very different for different metals. Has excellent welding mild steel. With increasing carbon content weldability decreases rapidly, and began with a carbon content exceeding 0.7% of poorly welded pressure. Poorly welded and many alloy steels, nonferrous metals. Cast iron is practically no pressure welded in a plastic state.
Place of welding can be heated by various heat sources. Particularly high temperatures is not required and the necessary heat can be obtained in various kilns and furnaces, heated solid, liquid or gaseous fuel. Most ordinary combustible materials by burning them with air in the furnace proper device provides sufficient heat.
The surfaces of the workpiece, even carefully peeled in advance, during the heating process is usually much oxidized, the oxide layer makes it impossible to weld. To clean the surface of the weld from oxides is necessary to resort to chemical cleaning, applying flux, forming a fusible metal oxides compounds can easily be extruded from the joint in the process of precipitation, thus allowing lead in contact with a completely clean metal surface.
When heated, iron slag were formed, whose composition varies between the oxides FeO and Fe 3 O 4 , rather refractory and melted at white heat. These oxides are basic, so for them fluxing or slagging, ie, transfer to the fusible compound, liquid at a temperature of welding should be used acidic oxides, non-volatile and quite persistent at welding. Fluxes for blacksmith welding can include: borax Na 2 B 4 O 7 , boric acid B (OH) 3 , sodium chloride NaCl, a small river or quartz sand, the battle of window glass, and mixtures thereof.
After heating and fluxing the welding operation performed precipitation. Draught causes a significant deformation of the metal surfaces along the course of his connections, mixing, and contributing to mutual diffusion of the particles of the metal parts to be united. The value of specific pressure required for deposit.
See also:
Blacksmith (Forge) Welding
Blacksmith (Forge) Welding Part 2
Induction (high frequency) Welding
Diffusion Welding
Casting or Foundry Welding
Friction Welding
Electrolytic Welding
Welding Under Water
Explosive Welding
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