Advantages and Disadvantages. Table 8.14 illustrates some induction and flame hardenable steels. Generally, the larger the depth and diameter of the material being heated, the lower the frequency required. 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. An evaluation of those patterns and their effect on gear This is normally also the distance between turns. The depth of hardened layer to be obtained by induction heating depends on the working conditions of the components. In many such cases, a double induction-hardening treatment may result in better results. 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. But when high frequency alternating current is passed through this coil, highly concentrated varying magnetic field is setup. 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. Simultaneously, inadequate spacing may cause a contact with coil, or puncture the air gap between them, and more important, may overheat the external layer. Both effective and total case must be considered to optimize shaft performance. Higher wear and fatigue resistance: Induction hardening improves wear resistance because the structure of the surface layer is altered. 8.59. 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 … This is normally obtained from medium frequency current. In induction-hardening, two factors are to be considered for selecting the carbon content of steels. UltraGlow® Induction Hardening is a form of heat treatment in which a steel or cast iron part is heated by electromagnetic induction, immediately followed by rapid cooling (quenching). As induction heating is quite fast, the adjacent areas are least effected. Flame or Induction Hardening: 4340 hardened and tempered bar can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness in excess of Rc 50. This phenomenon of eddy currents travelling closer to the surface of the metal bar is called ‘skin effect’ as illustrated in Fig. Disclaimer 8. Various probes were designed and evaluated. That is why, while designing a coil for an irregularly shaped component, care should be taken that portions closest to the coil will usually be heated at a very fast rate. Modern techniques typically use finite element analysis and Computer-aided manufacturing techniques, however as with all such methods a thorough working knowledge of the induction heating process is still required. Fig. As the frequency controls the depth of hardening, and the depth of hardening generally increases with the size of the part (see Fig. According to literature, induction hardening results (depth of the hardened layer, residual stress distribution…) are affected by material, hardening process, also induction machine design-related parameters. (Fig. The overall depth of heating is larger. 1. The workpiece weight is also the same, and the 8-ton load corresponds to 2,667 shafts. Induction tempering can be used to reduce the hardness of the components, in particular the ones which were earlier induction hardened. It can be seen from the above table that the selection of the correct equipment for any application can be extremely complex as more than one combination of power, frequency and speed can be used for a given result. This creates a “case” of martensite on the surface. Table 8.12 can be used for selecting the frequency of the current, based on hardening- depth needed, taking also into consideration equation 8.57. 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. Flame hardening is similar to induction hardening, in that it is a surface hardening process. By placing a conductive material into a strong alternating magnetic field, electric current can be made to flow in the material thereby creating heat due to the I2R losses in the material. Induction hardening is one of the classical surface-modification methods for steel products such as shafts and gears. In some … Finished bores on gears, sprockets and wheels Distortion of the bore is basically determined by the wall thickness. 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 current generated flows predominantly in the surface layer, the depth of this laye… Figure 2 shows examples of some induction hardening patterns. 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. 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. 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. Tempering of induction-hardened parts in which maximum wear resistance, or fatigue properties are desired, is not done after induction-hardening. But the starting microstructure and the composition of the steel have a far greater influence to obtain fine and homogeneous austenite during induction heating, and thus effects the choice of different induction hardening factors. One of the benefits of induction hardening is the ability to selectively apply a surface hardness or case hardness to steel materials. 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. Depth of hardening is controlled by the parameters of the induction heating equipment, time of application and the hardenability of the material. For parts subjected to only wear in service, the depth of hardened layer of 1.5 to 2 mm is normally sufficient (also for small components). An accurate design requires exact detail about each gear tooth based upon the actual profile presented Figure 1: Macroetched cross-section showing differences in induction hardened case depth due to a 350ºF preheat. Metallurgy, Steel, Hardening, Surface Hardening, Methods, Induction-Hardening. 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. As the whole part is to be uniformly heated, low frequency currents and power inputs are essential. b. By this method, it is possible to obtain differential hardness in a component. Examples of the use of induction hardening include contour or flank-only hardening of gears, ring-coil/spin hardening of smaller gears, shaft surface hardening, and local hardening of specific surfaces on components such as track pads, drive pulleys etc. without the rotation of the part as illustrated in Fig. As well as the power density and frequency, the time the material is heated for will influence the depth to which the heat will flow by conduction. Materials: Carbon Content: Hardness-HRc: Comments : 1019: 0.15 – 0.2: 30: Typically carburized : 1035: 0.32 – 0.38: 45: Can reduce by … Modern day induction heating units use the latest in semiconductor technology and digital control systems to develop a range of powers from 1 kW to many megawatts. Image Guidelines 4. 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. Induction heating systems for hardening are available in a variety of different operating frequencies typically from 1 kHz to 400 kHz. Hardened case depth should be adequate to provide the required gear tooth properties. 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. The quenching sprays may be as separate unit (Fig. Introduction to Induction-Hardening 2. In these applications, any heat generated in either the electrical or magnetic circuits was felt to be undesirable. 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. Induction hardening is a type of surface hardening in which a metal part is induction-heated and then quenched. d. Fully-automatic method for similar components is always preferred. Traverse methods also feature in the production of edge components, such as paper knives, leather knives, lawnmower bottom blades, and hacksaw blades. Induction hardening is probably the best method of hardening gears. Content Filtration 6. However in practice many selections are immediately obvious based on previous experience and practicality. Now, based on this actual result of depth of hardening, and how close this is to the desired depth, the induction-hardening factors are adjusted to obtain the exact depth. 2. Table 8.13 gives the various common power sources used for induction-hardening: Motor-generate power source is used for frequencies up to 10000 c/s. Another drawback is that much more power is required due to the increased surface area being heated compared with a traverse approach.[7]. To help you develop accurate parts and specify reasonable tolerances for hardness and case depth results, Zion Industries has created the following guidelines for the maximum surface hardness achievable using induction hardening. A large alternating current is driven through a coil, generating a very intense and rapidly changing magnetic field in the space within. However, if the alloying ele­ments are added in a steel to derive some other property, but the steel is to be induction-hardened, then it is advisable to use a relatively higher auste­nitising temperature in order to obtain a better harde­ning response. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. In reverse, if we want to have a very shallow penetration depth into the material, you will use a higher frequency. The method is used for gears with modules up to 5. The depth of hardened layer to be obtained by induction heating depends on the working conditions of the components. Depth of hardness is easily controlled. Low-alloy and medium-carbon steels with 0.4 to 0.55% C (e.g., SAE 1040, 15B41, 4140, 4340, 4150, 1552) are commonly used in induction gear hardening. Normalised state attains greater case depth than annealed state. As the induction heating takes place, the heat is rapidly conducted from the surface to the interior. If neither type of case depth is specified the total case depth is assumed. Induction Hardening Machines & Equipment. Induction-Hardening with Static Coils, or Single-Shot Hardening: This method is used for small parts having small area to be hardened so that the power output can heat it in one step such as head of a bolt. Induction hardening is a form of heat treatment in which a metal part with sufficient carbon content is heated in the induction field and then rapidly cooled. 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 quenched metal undergoes a martensitic transformation, increasing the hardness and brittleness of the part. In traverse hardening systems the work piece is passed through the induction coil progressively and a following quench spray or ring is used. This method thus improves the wear resistance as well as bending strength of the tooth. Quenched and tempered state attains maximum hardened case depth on induction hardening under similar conditions. Induction hardening however, can easily go … 8.69 illustrates some loop type and Zig-Zag type inductors to be used for surface hardening of flat components. Metallurgical Control 6. The main consideration in selecting proper operating conditions, i.e., the power, time and frequency for a given required depth of hardening is that the surface should not get overheated by the time the austenite is obtained in the required depth, or that the heating is not too slow such that the material is heated to a depth larger than specified in the time the proper austenitising temperature is reached. 8.63 (a) also illustrates that softening occurs in the region next to the hardened region parti­cularly in steel with initial structure of hardened and tempered state. Types of Induction Coils 4. The effectiveness of these treatments depends both on surface materials properties modification and on the introduction of residual stress. Thus, for induction hardening of steels, initial sorbitic structure is normally recommended. It, and setting hence, the case of shaft hardening a further advantage of heat. Of quenching-sprays, which result in local heating up a very important in. 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