More contact resistance heating quenching: through the electrodes will be less than 5 v voltage is added to the workpieces, the current through the large in the contact between the electrode and workpiece, and produce a lot of heat resistance, make the surface heating to the quenching temperature, then move the electrode, and surface heat is introduced into the workpiece, a rapid cooling, the purpose of quenching.
When long thing, electrode constantly moving forward, in the latter part of hardening.
This method has the advantage of simple equipment, easy operation, easy automation, minimal distortion of work piece, do not need to temper, can significantly improve the wear resistance and abrasion resistance, but the hardening layer is thinner,
The microstructure and hardness of poor uniformity.
This method is more used in cast iron surface quenching machine tool guideway, application range is not wide.
Electrolytic quenching: the workpiece in acid, alkali or salt aqueous electrolyte, artifacts to cathode, anode electrolyzer.
After direct current electrolyte by electrolysis, release oxygen in the anode, hydrogen in the workpiece.
Hydrogen gas film around the workpiece, a resistance and generate heat, heat the workpiece surface rapidly to the quenching temperature, and power outages, gas film immediately disappear, electrolyte becomes a quenching cooling medium, make the surface rapidly cooling and hardening.
Commonly used for electrolyte containing 5 -
18% aqueous solution of sodium carbonate.
Electrolytic heating method is simple, short processing time, heating time only need 5 -
10 seconds, high productivity, chilling distortion is small, suitable for the mass production of small parts
, have been used to the surface of the engine exhaust valve stem end quenching.
CNC lathe processing laser heat treatment, laser application in heat treatment research began in the early 70 s, then entered the stage of production by the laboratory research stage.
When the focus of high energy density,
Laser metal surface, the metal surface in the few seconds per thousand even rise to the quenching temperature within a few seconds.
Point due to radiation heat up so fast, too late to heat the surrounding metal, so in when they stop laser irradiation points around the metal rose from the role of the quenching cooling medium and a large amount of heat, make the light point rapidly cooling, get very fine organization, has the very high mechanical properties.
Such as high temperature to melt the metal surface, the cooling can obtain a smooth surface, after this operation is called glazing.
Laser heating can also be used to deal with the local alloying, i. e. , the workpiece is easy to wear or need a layer of wear-resistant heat-resistant parts before plating or hot metal or coated with a layer of abrasion or heat-resistant metal coating, then use laser to melt rapidly, forming wear-resisting or heat resistant alloy layer.
At the site of the need to heat a layer of chromium plating on the first, then use laser to melt rapidly, forming hard chromium heat surface of tempering, can greatly improve the service life of the workpiece and heat resistance.
Heat treatment: electron beam in the 70 s research and application.
Early continuous annealing for steelskin belt, steel wire, the energy density of up to 108 watts/cm2.
Electron beam surface hardening besides should be performed in a vacuum, other features the same as the laser.
When the electron beam bombardment metal surface bombardment by rapid heating.
Depth depends on the accelerating voltage of electron beam penetrating materials and material density.
150 kilowatts of electron beam on the surface of iron, for example, the theory of penetration depth is about 0.
On the aluminum surface can reach 0.
Electron beam bombardment surface in a very short time, the surface temperature rise rapidly, and the matrix remains cold.
When the electron beam to stop the bombardment, quickly to the heat matrix metal conduction, so that the heating surface quenching on its own.
In order to effectively & quot;
Since the cold hardening & quot;
, the volume of the workpiece and the volume of the hardened surface between should keep at least 5:1 ratio.
Surface temperature and hardening depth is also related to bombardment of time.
Heat treatment of the electron beam heating speed, austenitizing time zero point only a few seconds or less, so the surface grain size of the workpiece is very fine, hardness is higher than the general heat treatment, and has good mechanical properties.
CNC lathe processing
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