Cathode Assembly PreHeater
Description
The
Electric Cathode Assembly PreHeater is designed to preheat both steel
cathode bars and carbon cathode blocks simultaneously to a predetermined
temperature in preparation for the casting of the steel bars into the
carbon cathodes. The machine works by creating a single series circuit
using the steel bars as the conductor. This is achieved by using several
clamps to connect the bars to achieve the correct electrical circuit.
When the electrical circuit is created the transformer is energised and a
large current begins to flow through the bars. This current flow in the
steel bars creates heat which increases the temperature of the bars and
indirectly increases the temperature of the blocks. The result is steel
bars which are evenly heated along the length and through the cross
section and carbon blocks which are heated in a similar fashion but at a
lesser temperature depending on the system power setting. Bar
temperatures up to 730 Degrees Celsius have been achieved in practice.
Block temperatures up to 550 Degrees Celsius are also achievable.
These bars are at 650 Degrees Celsius exiting the PreHeater on an automated trolley.
Control System
The Comtec Electric Cathode Assembly PreHeater is operated and controlled by a Red Lion HMI Touch Screen Display. The system is controlled by a Modicon M340 PLC located in the local control panel
The Touch Screen controls all the operations of the heating system in both Automatic and Manual mode and contains all the Maintenance and Information screens. Below are typical screenshots of the control system pages.
Benefits
The Comtec Electric PreHeater offers the following benefits to the Cathode Sealing Process.
Efficiency
The application of electric current directly to the steel bars means that close to 100% of the electrical energy is converted into heat in the steel bars. With careful thermal design of the movable hood it is possible to capture most of this heat inside the heating chamber so that it is used to heat the cathode blocks with minimal losses to the surroundings. This design approach ensures high efficiency conversion of electrical energy into temperature in both the steel bars and carbon cathodes.
Uniform heating
The creation of a series circuit means that all the steel bars have the same amount of current flow through them. If the steel bars have the same electrical resistance characteristics then they will all heat up at the same rate. The AC current flows through steel bars evenly over the surface and penetrates to a certain skin depth. This even distribution of current flow over the bar surface ensures an even surface temperature distribution in the bar. The electrical heating system ensures even temperature along and through the steel bars. This bar heat is transferred by radiation and convection into the carbon cathode and ensures that the surface which receives the molten cast iron is evenly heated but to a lower temperature to avoid airburn to the carbon surface.
Process Control
The system supplies assembled and heated cathode assemblies ready for casting. The time delay between the end of heating and the start of casting can be greatly reduced and is repeatable. This makes it more likely that the process parameters for the casting process are achieved. It also makes it possible to reliably alter the parameters to optimise the sealing process and improve the overall plant efficiency.
Reliability
Attention to detail has resulted in a system that is virtually maintenance free. Clamp contact faces are inspected at 3 month intervals and replaced every three years depending on frequency of use.
Fume/Emission Control
The Electric PreHeating System is designed with an inbuilt fume collection system to remove fugitive emissions resulting from the heating process. Any coatings applied to the steel bars or the carbon cathodes can create fume emissions during the heat up process. These fumes are captured by the inbuilt fume collection system which has been designed to minimise heat loss but effectively capture any fugitive emissions. The PreHeating System is electrically powered so there is no need to deal with products of combustion.
Noise
The Comtec Electric PreHeater is extremely quiet in operation and produces Leq 76 dB’A’ noise level at the operator panel when in use.