Steel molds heating with induction Induction heating is used in several applications such as melting, annealing, welding, shrink fitting and plasma. The heat energy obtained in induction heating is given as Q = 860.R.I 2 (1) Power supplies intended for this application has to provide the necessary power, frequency and physical conditions. Investment cost of these power supplies is high, and therefore, for simple applications these induction heating systems are not preferred. Heating the steel molds used in aluminum extrusion presses is one of these simple applications. These molds are preheated up to the press temperature (450 – 500 °C) for approximately 30 minutes in resistive ovens. This process has to be repeated every morning when starting the first press and anytime when a new mold is placed. Since the mold hardness may deteriorate, it is not proper to keep the molds in these ovens for prolonged periods. Heating period may be considered as a lost time. Moreover, the energy loss is higher since the efficiency of resistive ovens is less than that of the induction ovens. There have been some work in which a metal strip was heated by using a coil placed on a yoke or inside in a pack of laminated steel (magnetic yoke.) Medium frequency has been used in these applications, and temperatures as high as 900 °C have been reached on aluminum and steel work pieces [1-4]. This work suggest a simple and cheap system utilizing the basic principles of induction heating to quickly heat the steel molds used in aluminum extrusion presses. Low power consumption is also aimed. II. METHOD Figure 1 shows the system designed for the heating process. It is connected to three-phase 50 Hz power grid. The 3-phase power transformer is rated 150 kVa, and has several taps. The balance inductor also has a tapped structure. There are also a balance capacitor and a resonance capacitor in the system. All the components are connected on the secondary of the transformer in delta. Component values are given as follows so that balance is achieved: Balance inductor, 11.74 mH, balance capacitor 863 μF, heating inductor 2.66 mH, resonance capacitor 3795 μF. The 3rd terminal of the 13-tap transformer is used. The no-load voltage at this terminal is measured to be 160 V. The winding is made by using a 15x17 mm cross-section conductor and it has 2x15 turns. This coil is placed around a core with a cross-section of 140x200 mm. The arm height is 300 mm, and the window opening is 110 mm. Two yokes with a cross-section of 140x200 mm are at the top, and the mold is placed between these two yokes. The inductor design is pictured in Figure 2. The parameters for the balance inductor are as follows: core cross-section= 120x170 mm, arm height= 310 mm, window opening= 80 mm. There are two windings with 34 turns of 10x10 mm conductor on each one. dw-inductionheating/Technology/Steel-molds-heating-with-induction-326.html
Posted on: Sun, 19 Oct 2014 01:50:30 +0000
Trending Topics
Recently Viewed Topics
© 2015