Heating Of Billet At 1250℃
Induction heating of steel billets is to raise the billet temperature to the level where it would be plastic enough to be forged, rolled or warm formed. Induction is attractive for steel forgers, but several design and operational factors are to be taken into account. Over the past three decades, induction has become an increasingly popular choice for heating steel billets prior to forging due to its ability to create high heat intensity quickly and within a billet. That ability leads to low process cycle time with repeatable high-quality occupying minimal space on the shop floor. It is more energy efficient and inherently more environment friendly than most other heat sources for steel billets. Other advantages are
A noticeable reduction of scale
Short start-up and shut-down times
Readiness for automation with lower labor cost
Ability to heat in a protective atmosphere if required
Progressive and static heating are the two basic approaches to induction billet heating. In progressive multistage horizontal heating, billets are moved via pusher or indexing mechanism through a single coil or multi-coil horizontal induction heater. Each billet is progressively heated at predetermined positions inside of the induction heater. In static heating, the billet is placed into an induction coil for a given period of time while a set amount of power is applied until it reaches the desired heating conditions. When the heating cycle is completed, the control system checks whether the press is ready to accept the billet.
The selection of forging temperatures for plain carbon and alloy steel is based upon four major factors – carbon content, alloy composition, the temperature range for optimum plasticity, the amount of reduction. Based upon these four considerations, forging temperatures are selected such that the material has the lowest possible flow stress. Here the billet is heated at 1250 degree Celsius. Positioning and magnitude of the maximum temperature within the heated billet is a complex function of four factors – frequency, refractory, final temperature and the power distribution along the heating line.
A common approach to design of a heating line in steel production is a single power supply for several coils, with a graded number of turns and series/parallel coil circuit connection. Putting more power up-front might sound like a rule of thumb because it forces more energy into the billet at the front of the heating line, giving it more time to soak into the core of the billet. The temperature at the billet’s center can reach the forging temperature in a shorter period of time, reducing the length of coil line. To optimize induction heating performance, improve product quality, and avoid unpleasant surprises related to subsurface overheating, it is imperative that the induction system be capable of redistributing power along the line while heating the billets of different sizes and production rates.
When heating billets at nominal rates, more power should be shifted toward the beginning of the induction line. At slower rates, however when heating smaller than nominal size billets, power should be shifted toward the end of the induction line.
Normally for short billets, a hopper is used to automatically present them in a line to pinch rollers. The billets are then driven through coil one behind the other in the form of a belt on water cooled rails which reduce friction and prevent wear and tear. For long billets, single shot heating can be used. This process utilizes similar systems to bar end heating except that the whole of the billet is driven into individual coils in steel production. This is how quality metal production in India is made possible.