What's the Difference Between Single Shot Hardening and Traverse Hardening?
December 07, 2023
Hardening is a process used to increase the hardness of metals which are heated and immediately quenched. Today, when we talk about hardening, we mainly refer to case hardening with Induction Heating. Induction heating is a non-contact heating method that uses the principle of electromagnetic induction to generate heat inside the surface layer of a metal part. The benefit of induction hardening is that it can selectively harden areas of a part without affecting the overall performance of the part. There are two main methods used in the Induction Hardening of materials, especially metals. They are Single Shot Hardening and Traverse Hardening.
In the single shot quenching process, the workpiece is statically held or rotated in the induction coil, the entire area to be treated is heated simultaneously to a high temperature and rapidly cooled using a quenching medium such as water, oil, or air with the method of showering quenching or a drop quenching. The entire surface of the material is uniformly heated and quenched in a single operation. This process helps to increase the hardness and strength of the material by transforming its microstructure.
Single shots are often used where it is difficult to achieve the desired result, such as flat surface hardening of parts, edge hardening of complex shaped tools or the production of small gears.
For shaft hardening, an advantage of the single-shot method compared to the progressive transverse hardening method is production time. Additionally, using coils capable of producing longitudinal currents in the assembly rather than radial currents may be an advantage for certain complex geometries.
In the other hand, the single-shot approach also has disadvantages. It is difficult to design Coil design and a complex process. It is often necessary to use ferrite or laminated silicon steel to concentrate the magnetic field in a selected area, thereby improving the resulting hardening pattern. Another disadvantage is that more power is required due to the increased surface area heated compared to transverse methods
Traverse hardening, also known as selective or localized hardening, involves heating and quenching only specific areas of the material rather than the entire surface. This method is used when only specific parts of a component need to be hardened, while the remaining areas require different properties or characteristics. It can be achieved using various techniques such as flame hardening, induction hardening, laser hardening, or electron beam hardening. Traverse hardening provides flexibility in controlling the depth and extent of hardening, allowing precise heat treatment of specific regions of a component.
With transverse quenching hardening, the workpiece is scanned by an induction coil and a following spray quenching or drop quenching is performed. Transverse quenching is widely used in the production of shaft parts, such as axle shafts, excavator bucket pins, steering components, power tool shafts and drive shafts, etc. The component is fed through a toroidal inductor, usually a single turn. Turn width is determined by traverse speed, available power and frequency of the generator. This creates a moving hot band that forms a hardened surface layer when quenched. Depending on the requirements of the application, the quench ring can be an integral part of the following arrangement or a combination of both. By varying the speed and power, it is possible to make a shaft that is hardened along its entire length or only in specific areas, or it is possible to make a hardened shaft with diameter steps or splines. When hardening a round shaft, the part is usually rotated during machining to ensure that any variation caused by coil and component concentricity is eliminated.
To summarize, single shot hardening involves uniform heating and quenching of the entire surface, while traverse hardening selectively heats and quenches specific areas or regions of a material.
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