Showing posts with label Induction Furnace. Show all posts
Showing posts with label Induction Furnace. Show all posts

November 30, 2008

Installation Procedure of Refractory Ramming Mass and Heating Schedule for Induction Furnace

Here is a step-by-step procedure for installation of Refractory Ramming Masses for Induction Furnace as given below:

1. Scrub all loose materials and clean the furnace.

2. Before using heat the refractory material (Ramming mass) at about 100OC to make it free from moisture. Spread the material at the furnace bottom to about 50 - 60 mm thick layer at each time. Then ram the layer uniformly using a suitable rammer. The material has to be rammed layer by layer to get maximum compaction. Before ramming, little bit poking with a rod help to drive away the air-pockets trapped within the loose refractory material spread.

3. Place the steel former on the rammed bottom. Then fix the steel iron block at the center of the steel former to get uniform thickness throughout the furnace wall.

4. For ramming the upper portion of the side-wall just above the induction coil, mix the dry refractory material with 1-1.5% Sodium Silicate solution and 3-4% water.

5. Best results can be achieved by following the heating-schedule for the furnace as mentioned hereunder -

Furnace Heating Schedule


Furnace Temperature

Rate of Heating with Holding Time

Ambient temp to 100OC

@ 30OC / hr.

Hold at 100OC.

4-6 hr depending upon the lining thickness.

100O - 800OC.

@ 50OC / hr.

Hold at 800OC.

2 - 3 hr.

800O - 1400OC.

@ 100OC / hr.

Hold at 1400OC.

4 - 6 hr.

1400OC to furnace operating temperature.

@ 100OC / hr.

October 26, 2008

Refractory Lining for Induction Furnace

The bottom structural part of Induction Furnace (Figure with details published in a separate article on Induction Furnace) on which main crucible lies is generally lined with bricks and do not require to be changed frequently. However, working face of the main crucible is lined with a suitable ramming mass. Selection of the ramming mass (R/M) entirely depends on the scrap melted (as given in the Table below) and operating parameters. The roof is lined with a suitable castable generally of High Alumina base and Low Cement Castable (LCC). The launder or spout of the furnace either is rammed or lined with refractory bricks. For side wall lining a suitable cylindrical former is essential. The former can be made either removable or consumable type. In case of consumable former the quality of the former should be compatible with the quality of the product (melt) to be produced. Generally bottom ramming is done first followed by the side wall ramming. Ramming is generally done layer-wise with the help of pneumatic rammers to ensure compaction and packing density. At the same time to avoid lamination between the layers each layer is to be scratched before putting fresh material for further ramming. The collar rim of the induction furnace crucible is made of the same refractory paste as used for constructing the crucible but with a greater addition of bonding materials & water. Then furnace heating schedule is to be followed carefully which will depend upon the furnace lining thickness, nature of ramming mass etc.


Selection of Refractories for Lining
Operation and furnace area wise chart of refractories with their Standard Specifications are given below for ready reference:
(Methods of Installation, furnace Heating Schedule etc. may be provided by the refractory vendor however, in the coming posts we shall discuss on the same also).


Furnace Operation / Area of Application
Refractory Specifications
(Std. Specfn)
Melting Mild Steel, Stainless
Steel, Manganese Steel
& Alloy Steels.
Type= Mag-Chrome R/M, MgO%= 70-85, Cr2O3%= 8-10, Sintering Temp (ST)= 800OC,Application Temp (AT)= 1750OC, Grading= 0-5 mm
Melting Cast Iron.
Type= Silica R/M, SiO2%= 97 (min),
AT= 1650OC, Grading= 0-6 mm
In the areas of Cover, Grout
of Ind Fur melting Aluminium
& its alloys.
Type= High Alumina R/M, Al2O3%= 78-80,
Fe2O3%= 1.5 (max), ST= 1100OC,
AT= 1750OC, Grading= 0-6 mm
In the areas of Cover, Top Cap, Spout/Receiver
Type= High Alumina R/M or LCC, Al2O3%= 90-92, Fe2O3%= 0.5 (max), ST= 1100OC,
AT= 1750OC, Grading= 0-6 mm
Melting Copper, Brass & Bronze
Type= Mullite base R/M, Al2O3%= 70 (min),
Fe2O3%= 0.5 (max), ST= 1100OC,
AT= 1750OC, Grading= 0-6 mm
Melting Lead, Zinc & Tin
Type= Fire clay R/M, Al2O3%= 40-45, ST= 1100OC, AT= 1650OC, Grading= 0-5 mm
Melting Cupro-Nickel alloys
Type= Spinel bonded R/M, MgO%= 70-72,
Al2O3%= 15 (min), ST= 1000OC,
AT= 1750OC, Grading= 0-5 mm
Patching between the campaigns
Type= Patching Mass, MgO%= 70-75,
Cr2O3%= 8-10, ST= 800OC,
Grading= 0-2 mm
Repairing Cover, Spout areas between the campaigns
Type= R/M or P/M, Al2O3%= 80-90,
Fe2O3%= 1 (max), ST= 1100OC, AT= 1700OC
Hot & Cold repairing of Uppercase, Inductor Lining & some Structural components
Type= LCC, Al2O3%= 60-80,
Fe2O3%= 1.5 (max)

Recent Articles

October 24, 2008

INDUCTION FURNACE

An Induction Furnace uses induction to heat a metal to its melting point which is based on the theory of Electro Magnetic Induction. Depending on their frequency (50 Hz - 250 kHz) these can be divided to three types:

  1. High Frequency
  2. Medium Frequency
  3. Low Frequency

Their capacities range from less than 1kg to 100MT, which are used for re-melting of iron & steel (steel scrap), copper, aluminium, precious metals and alloys. Even most modern foundries use this type of furnaces and now more iron foundries are replacing Cupolas with Induction Furnace to melt cast iron as the former emit lots of dust & other pollutants. The Steel making via Induction Furnace route has certain advantages & disadvantages:

Advantages of Induction Furnace


  1. It has no electrodes and electric arcs which allow productions of steel & alloys low in carbon and occluded gases without any quality problem.
  2. Low melting losses & alloying elements.
  3. High power efficiency, therefore, cost-effective.
  4. Precise control of the operating parameters.

Disadvantages of Induction Furnace


  1. Refining in Induction Furnace is not as intensive or effective as in Electric Arc Furnace (EAF).
  2. Life of Refractory lining is low as compared to EAF.
  3. Removal of S & P is limited, so selection of charges with less impurity is required.


Induction Furnaces are classified generally into two categories:

  1. Channel type induction furnace
  2. Coreless type induction furnace
Channel Type Induction Furnace design

Fig.- CHANNEL TYPE INDUCTION FURNACE

1. Channel Type Induction Furnace

These furnaces basically consist of a vessel to which one or more inductors are attached. The inductor is actually a transformer whereby the secondary winding is formed with the help of a loop of liquid metal confined in a closed refractory channel. In the furnace the energy is transformed from the power system at line frequency through a power supply to the inductor and converted into heat. One advantage of this type of furnace is that the vessel or upper case can be built in any practical size & shape to suit the application, but the disadvantage are like -
a. Power input limitation per inductor.
b. Necessity to maintain a liquid heel in the furnace always to avoid problems related to operational parameters and refractories.
For the above reasons Channel type Induction furnaces (Fig.) are treated as a receiver or holding vessel for homogenization of liquid metal with limited capability of melting.


Coreless Type Induction Furnace
Fig.- CORELESS TYPE INDUCTION FURNACE


2. Coreless Type Induction Furnace
These furnaces (Fig.) are designed like a cylindrical crucible surrounded by a power coil in which energy is supplied either directly from the network (line frequency) or through a frequency converter. The magnetic field generated by the coil carries the energy to the charge.
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=> Refractory Lining of Induction Furnaces [Read]

=> The Function of a Furnace and Kiln used in Ceramic and other Industries [Read]
=> Refractories for Reheating Furnaces [Read]
=> Refractory Resistance to Carbon Monoxide (CO) Attack [Read] 
=> Blast Furnace - Refractory Lining Pattern [Read]
=> MIDREX - The Most Widely accepted Direct Reduction (DR) Process of Ironmaking [Read]
=> COREX® : An Innovative Ironmaking Metallurgical Process [Read]
=> Iron Making in Mini Blast Furnace (MBF) [Read]
=> Use of Kyanite as Refractory Raw Material [Read]
=> HYL III and SL/RN - The two widely accepted Direct Reduction (DR) Processes of Ironmaking [Read]