Ferro Magnetic Stirrer Coils
M/s YEL Pune developed New FMS Coils for continuous casting for Big Steel Plants.
FMS process is defined by a rotative stirring in the continuous casting mould FMS. By acting right from the start of the solidification, this process is able to control the soundness of the first solidified shell, as well as the cleanliness of the subsurface zone. The process appears as the only stirring method to consider when the surface quality of the products must be controlled.
A stirrer located in the secondary cooling zone creates an equiaxed structure in the liquid pool. The width of the equiaxed zone mainly depends on the width of the pool at the structure is desired, the width of the pool at the stirring level. So, if a large equiaxed structure is desired, the S. Stirrer should be located as high as possible along the strand sometimes just below the mould.
The stirrers are designed in order to provide a rotative or a linear stirring movement, rotative stirrers are more suitable for small sizes, linear stirrers are more suitable for big sizes.
FMS applied for casting of medium carbon steels, low-alloyed steels and stainless steels.
FMS PROCESSES:
The continuous casing of some difficult grades for instance bearing steels raises specific metallurgical problems. The segregation control requires a complete combination of the 3 types of stirrers per strand:
M-FMS removes the superheat and initiates the equiaxed solidification.
S-FMS refines the size of the crystals,
F-FMS reduces the final level of segregation.
Ferro Magnetic Process on the surface and subsurface quality.
The surface and the subsurface area of the strand are formed inside the mould, so that only FMS can control the soundness of the shell Two major effects are observed by stirring a better cleanliness of the metal and a reduction of the porosity resulting form the gas evolution during solidification.
• Surface and subsurface cleanliness
In case of conventional CC process, non-metallic inclusions enter with molten steel into the mold.
When the molten steel rotates in the mould non metallic inclusions are centrifugated towards the center of the mold and washed away from the solidification front as shown in Figure 3.
• The rotation of the metal continues by inertia below the mold, so the washing effect of stirring is retained along 1or 2 meters along the strand depending on the casting conditions. As a result the subsurface of the product contains less inclusions. In curved mold machines, the location of the inside radius inclusion band is shifted to a deeper distance from the outer surface. In some cases, this inclusion band can be almost eliminated
We manufacturing Ferro magnetic stirrer < 100 up to 500 KVA from quality non ageing rust, dustless steel with copper winding insulated by kapton coating having extra high insulation regesterence and heat conduction. During manufacturing components of stirrer under goes various tests.Which increase reliability in operation of stirrer from 2 to 10 hertz = i.e.Stirrer synchronous = 120 to 600 RPM S/S Containers are tested at 15 kg per cm/ 2
Design Technology of FMS
Ferro Principles
We distinguish between rotative and linear stirrers. Both are acting according to the princi0ple of an electrical asynchronous AC- motor.
A rotative stirrer acts like the stator of an electrical AC motor. It is fed by a three phases or sometimes two-phase electrical power supply and creates a rotating magnetic field within its pole gap as illustrated in Figure23. This rotating magnetic field induces a torque in the liquid steel of the billet or bloom passing through the stirrer. The liquid steel consequently acts as the rotor of an AC motor and rotates around the axis of the cast product in a plane perpendicular to the casting direction.
A linear stirrer can be understood as the transformation of cylindrical inductor, which has been cut open on one side and unrolled to a flat size. One obtains a stator creating a traveling magnetic field. This traveling magnetic field induces a force in the liquid steel which points in the liquid steel which points in the traveling direction.
• Choice of rotative or linear stirrers
There is a basic difference between rotative and linear stirrers: The rotative stirrer induces axial-symmetrical forces creating a torque over the whole section of the liquid pool whatever the size of the liquid pool is and even if the strand is not centered inside the stirrer. It follows that all the forces induced within the whole section of the liquid pool and consequently the full power induced inside the liquid pool contribute to the rotation of the liquid steel.
• Performance of stirrers
The performance of a stirrer is given by the effective stirring force acting on the luquid steel and by the effective stirring power induced inside the liquid steel. Both have to be above a minimum value in order to produce the required metallurgical improvements. The performance of a stirrer are the magnetic flux produced by the stirrer and the frequency of the electrical power feeding. Increase of the magnetic flux always increase of the magnetic flux always increase the performance.
• Design parameters of FMS
The stirrer surrounds the copper mold and induces a rotating magnetic field since the magnetic field must cross the copper walls, the stirrer is operated at low frequency 2 to 10 Hz depending on the mold size and the copper thickness) All pieces between the copper mold and the stirrer inner surface must be made with non-magnetic stainless steel.