Induction Hardening Machines & Equipment. A large alternating current is driven through a coil, generating a very intense and rapidly changing magnetic field in the space within. This normally needs valve-generator set for high frequency current. With a conventional method (or if we induction hardened the entire length for that matter), there would be significantly more warpage. The heating and hardening effects are localised and the depth of hardening is controllable. The shaft is the same dimensions as example 1 (30 x 500 mm). The test trial hardening is then performed. The inductor has to be properly selected and designed for the successful induction hardening operation. The method is used for gears with modules up to 5. Two different systems – multi-frequency eddy current system (MFEC) and pulsed eddy current system (PEC) were built for measurement. In iron, hysteresis losses also contribute to some extent to the temperature rise up to curie point (768°C), above which iron is non-magnetic, i.e., above this temperature, the depth of penetration of the current increases (inverse to the frequency of the current) due to sharp decrease in magnetic permeability. The presence of alloy carbides in these steels, which are relatively more difficult to dissolve in austenite, will greatly affect the induction-hardening response of these steels. Calibration data were taken on a set of samples with known case depths. For power output normally required, around 50 kW, copper tubing of internal diameter of around 5 mm is used. The workpiece to be heated is placed within this alternating magnetic field where eddy currents are generated within the workpiece and resistance leads to Joule heating of the metal. in mm (D x L / L x W x H) Vacuum treatments 1220 x 910 x 910 Hardening and tempering in controlled atm.Ø 600 x 1000 / 850 x 550 x 600 Annealing in controlled atm. The effectiveness of these treatments depends both on surface materials properties modification and on the introduction of residual stress. This creates a moving band of heat which when quenched creates the hardened surface layer. 8.68. The above table is purely illustrative, good results can be obtained outside these ranges by balancing power densities, frequency and other practical considerations including cost which may influence the final selection, heat time and coil width. With the aid of Maxwell’s equations it can be shown that the current density decreases exponentially with depth. This phenomenon of eddy currents travelling closer to the surface of the metal bar is called ‘skin effect’ as illustrated in Fig. Power supplies for induction hardening vary in power from a few kilowatts to hundreds of kilowatts depending on the size of the component to be heated and the production method employed i.e. Spatial Manipulation Again, it’s simply a matter of applying the electrical energy in a directed manner that puts this desirable work feature in the induction hardening win column. Heat-treatment processes such as case hardening are used to prolong the service life by increasing the surface hardness and vibration resistance while maintaining a ductile, elastic microstructure at the core. Heat is produced within the surface layer of an object using a non-contact heating process based on the principles of Electromagnetic Induction. 8.61 illustrates some coil designs and the heating patterns obtained. The spheroidised pearlitic structure where carbides are present in relatively large sized spherical particles, is most difficult to austenitise in the short (induction heating) time as these large carbide particles will not dissolve easily. The resistance of the metal bar to the flow of this eddy current comes out in the form of heat (Joule heat), which also remains concentrated to the skin, or surface layers of the steel as illustrated in Fig. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. Some of the common methods used in induction hardening of gears are: 1. At the same time, the heating rate is reduced. Care must be exercised when selecting a coil face width that it is practical to construct the coil of the chosen width and that it will live at the power required for the application. Once this has been established then a variety of methods can be used to calculate the power density required, heat time and generator operating frequency. The hardening, i.e. Plagiarism Prevention 5. As soon as the part has been heated by the required induction time, the part descends by means of a hydraulic device into the quenching bath to be immersed completely. In magnetic materials, further heat is generated below the curie point due to hysteresis losses. Table 8.15 compares these temperatures for some steels. Heat is applied to the part being hardened, using an oxy- acetylene (or similar gas) flame on the surface of the steel being hardened and heating the surface above the upper critical temperature before quenching the steel in a spray of water. In traverse hardening systems the work piece is passed through the induction coil progressively and a following quench spray or ring is used. As only the tips are hardened, the wear resistance of teeth is increased but the strength remains unaffected (as the remaining body is unaffected. of measuring case depth and hardness, along with some complications and ambiguities associated withthesemeasurements.Asexpected,thesubject of induction hardening is quite complex,compris- ing electrothermal phenomena, physical effects, technological subtleties, and knowhow. In all cases the speed of traverse needs to be closely controlled and consistent as variation in speed will have an effect on the depth of hardness and the hardness value achieved. This makes induction hardening an excellent option for case hardening. Single-Shot Spin Hardening of Complete Tooth: Here also, the gear rotates and all gear teeth are heated and hardened at once. (Eddy currents are harmful in transformers as it causes useless and harmful heating. High carbon steels (1070) used for hand tools, drill and rock- bits. Allows use of Low Cost Steels such as 1045 The most popular steel utilized for parts to be induction hardened is 1045. A carbon content of 0.3–0.6 wt% C is needed for this type of hardening. When heating of an electrically conductive material for surface-hardening is done by means of induc­tion-heating, the method is known as induction-hardening. This method improves only the wear resistance of teeth surfaces without affecting other properties. This region is called ‘heat affected zone’. Hardened case depth should be adequate to provide the required gear tooth properties. Diameter : 10-100 mm, Thickness : 5-20mm; Module 1-10mm ® Hardness: 45-62 HRC, Case Depth: 1 -3 mm. A depth of 4 to 8 mm is normally sufficient to withstand crushing or squirting. All process parameters were the same for each trial. By quenching this heated layer in water, oil, or a polymer based quench, the surface layer is altered to form a martensitic structure which is harder than the base metal. It should result in high surface hardness without risk of hardening cracks and the unhardened core should give good toughness. The case hardness will allow the piece to have superior wear and strength characteristics at the surface, but allow the interior of the piece to remain flexible. Fig. The normal power input is 0.1 – 2 kW/cm2 of the heating surface. With inductive hardening, products up to 76 HRc can be hardened (depending on the type of material). c. Each shape of component requires inductor to be designed for it, and some shapes thus become difficult to be induction-hardened. Fig. In this article we will discuss about:- 1. During surface layer induction hardening, a copper coil charged with alternating current and adapted to the work piece is responsible for heating up the component. In induction-hardening, two factors are to be considered for selecting the carbon content of steels. It is many times not feasible to heat treat a component to obtain a desired microstructure before induction-hardening is done. the hardness and the hardening depth, is defined by the carbonization depth, the receptiveness and thus the hardenability of the steel, and the quenching. The coupling for stationary component is about 2-3 mm, for rotating component is 2-4 mm, and for a progressive shape is 2-5 mm. Induction Hardening Machines & Equipment. In many such cases, a double induction-hardening treatment may result in better results. It is an ideal method for gears. There are disadvantages with the single shot approach. The rapid heating drastically reduces the heating time to increase productivity of the heat treatment section. After experimentally optimizing the induction hardening process parameters for the manufacturing of the specimens, the final heat treatment depth reveals an almost identical value of about 3 mm compared to the crankshaft. Once discovered, these principles were employed over the next century or so in the design of dynamos (electrical generators and electric motors, which are variants of the same thing) and in forms of electrical transformers. 8.64 illustrates the induction-hardening response of some steels under similar conditions. Induction hardening is a hardening process in which the surface layer can be partially hardened by a local electric heating to austenitizing temperature via electromagnetic fields, by means of inductors and faster cooling down with water, up to a defined depth. Traditionally this was done using a series of graphs, complex empirical calculations and experience. Traverse methods also feature in the production of edge components, such as paper knives, leather knives, lawnmower bottom blades, and hacksaw blades. Table 8.14 illustrates some induction and flame hardenable steels. Since precise controls can be used in induction hardening, a uniform case hardened surface can be created. Depth of hardening is controlled by the parameters of the induction heating equipment, time of application and the hardenability of the material. Induction hardening covers a series of thermal heat treatment processes where a direct hardening metal, usually steel or cast iron, is heated, usually locally, by Eddy Currents generated by a water cooled copper encircling coil or shaped inductor through which alternating current is passed, followed by rapid cooling/quenching using air blast, polymer mixes or water. The need for rapid easily automated systems led to massive advances in the understanding and use of the induction hardening process and by the late 1950s many systems using motor generators and thermionic emission triode oscillators were in regular use in a vast array of industries. Induction hardening is a type of surface hardening in which a metal part is induction-heated and then quenched. Thus, normally the carbon content is kept in range 0.3 to 0.5%, which results in the hardness values of HRC 50-60, though if heat treatment is controlled properly then a carbon content as high as 0.8% (and 1.8% Cr with 0.25% Mo) is used as for rolls. The depth of hardened layer to be obtained by induction heating depends on the working conditions of the components. One of the benefits of induction hardening is the ability to selectively apply a surface hardness or case hardness to steel materials. Induction hardening of steel components improves the resistance to wear by changing and microstructure of the surface region. He further observed that if the current was kept constant, no EMF was induced in the second winding and that this current flowed in opposite directions subject to whether the current was increasing or decreasing in the circuit. Carbon and alloy steels with an equivalent carbon content in the range 0.40/0.45% are most suitable for this process.[1]. Gregory A. Fett * Dana Corp. Maumee, Ohio *Member of ASM International and member, ASM Heat Treating Society his article updates work origi-nally published in February 1985 Metal Progress, which … Flame hardening is similar to induction hardening, in that it is a surface hardening process. Download As A PDF. As there was no physical connection between the primary and secondary windings, the emf in the secondary coil was said to be induced and so Faraday's law of induction was born. By varying speed and power it is possible to create a shaft which is hardened along its whole length or just in specific areas and also to harden shafts with steps in diameter or splines. Hardening of Tooth Tips by Single-Shot Hardening Method: The spin-hardening used is simple but is used up to module 3, using high frequency current, and up to module 5, using intermediate frequency current. The darker periphery of a typical round plate, as shown in Figure 1(a), shows the ECD of a hardened sample. Normalised state also shows this but to a lesser extent. Content Guidelines 2. However in practice many selections are immediately obvious based on previous experience and practicality. In this paper, Case Hardness and ECD of induction hardened parts have been optimized using RSM, as it is mostly preferred method to solve the optimization . In induction-hardening as well as in conventional hardening, martensitic hardening is aimed and performed, but in induction heating, the austenitising time is inherently very small (few seconds compared to 1/2-2 hours), but because of very rapid heating rates during continuous heating (in induction heating), the Ac1 and Ac3 temperatures are raised and austenite is seen to form in a fraction of second at these raised temperatures. After general acceptance of the methodology for melting steel, engineers began to explore other possibilities for the use of the process. Materials: Carbon Content: Hardness-HRc: Comments : 1019: 0.15 – 0.2: 30: Typically carburized : 1035: 0.32 – 0.38: 45: Can reduce by … Symmetrically shaped components are preferred. This example emphasizes an importance for modern induction hardening systems to have a capability to effectively control not only power density during scanning but also the depth of heat generation. As the induction heating takes place, the heat is rapidly conducted from the surface to the interior. The width of the turn is dictated by the traverse speed, the available power and frequency of the generator. This is normally obtained from medium frequency current. Induction hardening is one of the most common methods to increase the hardness on the surface and near-surface layer of the components. Normally, it is used for long components with almost uniform cross sectional area. Induction hardening is generally used as a peripheral layer hardening process where the hardening depth and other parameters are manipulated through the frequency of the inductor/coil current. This can be checked from the tempering colours obtained there. 8.59. In (a) part of the figure either the component is moved continuously close to inductor, or the inductor is moved on the flat surface of component. As induction heating is quite fast, the adjacent areas are least effected. In industrial applications, where the hardness gradient is the only engineering requirement, alloy steels with carbide-forming elements should not be recommended for induction-hardening. The heating rate in the temperature range of phase trans­formation A1 to A3 for hypoeutectoid steel is about 30 to 300°C/s. Through hardening can also be obtained by induction heating. This depends on the hardenability of the material, the section thickness and the flame hardening process used. Traverse hardening is used extensively in the production of shaft type components such as axle shafts, excavator bucket pins, steering components, power tool shafts and drive shafts. Case hardening places a hard case around the entire surface of the part while induction hardening hardens only the precise pattern defined by the inductor coil. Each tooth is individually induction heated and quenched. [4], Faraday concluded that an electric current can be produced by a changing magnetic field. Prohibited Content 3. Normally the inductor goes entirely around the gear, and a quench ring concentric to gear is used. Induction hardening is one of the most common methods to increase the hardness on the surface and near-surface layer of the components. Many methods are used to provide the progressive movement through the coil and both vertical and horizontal systems are used. Induction hardening is a method for hardening the surfaces of components, usually in selected areas, by the short-time application of high-intensity heating followed by quenching. This current passes chiefly through surface layers, i.e., eddy currents are more concentrated in the surface, and decreases in strength towards the centre of the object. The depth of hardened layer to be obtained by induction heating depends on the working conditions of the components. 8.63 (b) illustrates the temperature gradient during the process, and the Ac3 temperatures for different initial micro- structure. Disclaimer 8. Flame or Induction Hardened Cases - Since no chemical change occurs in flame or induction hardening, readings must be made in the hardened or hardened and tempered condition only. Process. Engineers at Midvale Steel and The Ohio Crankshaft Company drew on this knowledge to develop the first surface hardening induction heating systems using motor generators.[5]. 8.66. i. Experimental investigation shown that for making shafts, axles or automobile components from medium carbon steel, raw material should be first normalized and then induction hardened so that uniform hardness of material can be obtained [1, 2]. Eddy currents are usefully utilised with refer­ence to the present topic of discussion, and it is precisely this current that is used to produce the induction heat. 4. Conversely, the adjustment of the electromagnetic frequency ensures precise control of hardening depth, so repeatable results are much easier to achieve. Classification of Aluminium Alloys | Metallurgy, Unconventional Machining Processes: AJM, EBM, LBM & PAM | Manufacturing, Material Properties: Alloying, Heat Treatment, Mechanical Working and Recrystallization, Design of Gating System | Casting | Manufacturing Science, Forming Process: Forming Operations of Materials | Manufacturing Science, Generative Manufacturing Process and its Types | Manufacturing Science, Types of Induction Coils for Induction-Hardening, Metallurgical Control in Induction-Hardening, Advantages and Disadvantages of Induction-Hardening. Material based on the surface layer of the components for deeper depth 4! Of heat which when quenched creates the hardened surface can be an extremely complex and involved process. 1. We induction hardened is 1045 quickly and selectively hardening the circumference of the surface-modification... About 30 to 300°C/s determined, say by metallographic method separate unit (.... 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