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cold-starting coreless induction melting furnaces.

by:Earlston     2020-02-07
The AFS division 8C coreless melting board induction melting furnace in Schaumburg, Illinois is designed to be used consistently.
The retained heat used continuously increases the melting time of each heat and increases the life of the refractory wall.
Occasionally, metal casters are forced (
(For economic needs or other reasons)
Limit the production operation to the extent that the melting and pouring are inconsistent, such as the melting schedule for 3 and 4 days per week.
In this case, the metal foundry personnel need to determine whether it is economically meaningful to leave the furnace full of molten metal (
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In the extension of non
The production cycle, or empty the stove and turn off the power supply.
The decision of any idle furnace must be made, and then the main factors for restarting the furnace from cold conditions include the type of furnace technology used, the impact on the furnace refractory and the establishment of the shutdown procedure.
Any decision to idle the furnace and restart from a cold state should be made after consulting the appropriate furnace manufacturer and refractory supplier.
Technical information and practical furnace technology.
When considering whether to turn off the Coreless Induction furnace for a period of time, the age and year of the melting system technology should be considered first.
Two different types of furnace technology widely used at present: line frequency (heel melt)
Application and medium and high frequency (batch melt)applications.
With very few exceptions, any furnace running at or below 200 Hz is considered an application of line frequency.
Those with a working frequency of more than 200 Hz are considered medium and high frequencies.
The basic operating difference between the two is the rate at which each coil applies power to the induction coil under different conditions.
Line frequency system needs starter block when coldstarting.
When powering on and increasing the temperature of the starter block, their magnetic and electrical properties are affected.
Due to the line frequency design features, the furnace coil is unable to obtain full power from the power supply and there may be a significant \"power drop \".
Until the furnace is filled with at least half to 2 out of 3 fully liquefied metals, the furnace power can only increase in increments for a long period of time (
Duration depends on furnace capacity and metal type).
The result is an extended cold.
The beginning cycle that requires continuous attention from melting operators (
Power tuning, tap switch, etc. ).
According to the rule of thumb, turning off the line frequency heel furnace and placing it in a cold environment is rarely advantageous
Start unless it is scheduled to be non-
Production for at least four consecutive days.
Due to the different conditions of different facilities, decisions should be made after careful evaluation of the economic impact of the shutdown, including the kilowatt hours required to maintain a low-power furnace for a long time, as well as electricity, manpower and other costs related to long cold start-up. [
Figure 1 slightly]
The more modern medium and high frequency bulk melting system is designed with solid state inverter technology, which allows the coil to completely liquidate from the power supply when it is turned on to the bathtub. (
Due to the consideration of refractory, for the stove with cold lining, full power should never be used).
These systems do not need to use a boot block and can be restarted from a cold environment using a high density return or standard charging makeup.
Or, control the gas-
Before the introduction of a cold or molten charge, the burning torch can be used to increase the temperature of the furnace and the refractory, after which full furnace power can be applied.
Medium and high frequency furnaces are good candidates for full shutdown and restart, with little regard to the time they are expected to close.
Refractory.
Restart the center problem of the stove from the cold
The starting condition is the preservation of the existing refractory lining.
Furnace refractory materials prefer a stable environment and do not respond well to thermal cycling stress.
Inappropriate cold
Start can easily lead to damage to the existing lining, so any savings from turning the furnace off will be offset by the incidental cost of subsequent restart. Cold-
Starting with the existing lining, the refractory is not required to be completely re-createdsintered.
However, it does require a re-entry of refractory
Heat at an initial rate sufficient to heat close and seal all surface cracks.
It is unwise to patch plastic or refractory materials onto cracks and think they are closed.
Before the molten metal is produced or introduced, the crack must be closed and sealed by thermal expansion.
In general, the same procedure should be used at cold start up as at full sintering until the furnace temperature reaches 1 point, 600F, where it is soaked for one to two hours.
The precise measurement of temperature must use a thermocouple. After a cold-
To begin, it is also recommended to treat the lining as a new one
Sintering lining (i. e.
Keep as low carbon as possible and as high silicon as possible, at least in the first few heats).
This can be achieved by using the gray iron return as much as possible in the initial heating.
Supplementary information on good refractory practices for initial sintering and cold
Start-up conditions can be obtained through refractory suppliers and manufacturers.
Shutdown program.
Whether the stove is run as a bulk melt or a heel melt application, two steps need to be taken when the metal production stops and the stove is emptied: 1.
Slag removal: all slag stuck to the side wall of the refractory should be removed before allowing the furnace to cool.
During the reboot, this will reduce the chance of a reboot
Molten slag is in contact with the refractory hot surface before sealing surface cracks and preventing metal fins from forming.
Use de-if Wall cleaning is impractical-
The slag flux of the final furnace before stopping the furnace. 2.
Forced air cooling: forced cooling is a good practice
Cool the stove to the ambient temperature instead of letting it cool naturally.
Forced cooling may result in a series of random cracks due to the contraction of the lining, but these cracks will be smaller and relatively easy to re-seal when restarting.
Forced cooling should be done by using a dedicated high-pressure, high-capacity centrifugal blower that directly targets the furnace cavity. The free-
Standing circulation fans that are usually seen on the melting deck and are mainly used to provide cooling air to employees are not enough (Fig. 1).
Other precautions
When performing a cold, please remember the following three thingsstart: 1.
Sliding surface material: Hot expansion and cold contraction of the liner under the cold extreme temperature gradient must be considered
Start creating.
Use of fibers or other textiles
The use of materials based on a sliding plane should be avoided because they tend to keep the lining in place and act as a constraint on the lining rather than promoting expansion.
The sliding plane is not intended as an insulating medium, but rather allows the refractory fuse to remain on the cold side of the lining and encourages the lining to move freely along the sliding plane interface.
This requires the use of a dedicated (mica-based)
Sliding surface materials should be available at any time from multiple sources. 2.
Cooling water: even if the furnace is air-cooled, the temperature of the inlet cooling water is not allowed to drop too low.
If the cooling water temperature drops below the ambient dew point at any time of the furnace air or at any time of the cold-
At the beginning, condensation is formed on the coil tube and water is introduced into the coil refractory, resulting in high ground fault potential, which will delay restart or generate an arc between the coils. 3.
Extended Low Power hold: an alternative to cold
Starting the furnace at low power is an extended hold.
When the final heat is discharged from the furnace, the cold loading is introduced into the furnace to its filling point.
At the same time, the furnace power is reduced to a point sufficient to keep and keep the furnace temperature at 1, 200F indefinitely.
When restarting, PLC-
The controlled interface is used to raise the temperature and reduce the charge to the molten bath in a preset time of five to six hours.
Although this technology relies heavily on the PLC logic adopted, except for the good
Trained and reliable melting operators, this may be a viable option for users of intermediate frequency bulk melting equipment.
Editor\'s note: The following is the first in a new series of technical columns.
[Actor tips ](
Technical information and practice)
The column will provide step-by-step instructions on how to perform tasks around the metal casting facility.
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