Induction furnace lining materials are utilised in many parts of the world for the melting of ferrous and non-ferrous alloys in furnaces of all frequencies.
Lining materials are currently supplied for the melting of many types of alloy such as:-
CARBON STEELS STAINLESS STEELS MAGNET ALLOYS
DIE STEELS FERRO MANGANESE LOW ALLOY STEELS
MANGANESE STEELS HIGH SPEED STEELS NICKEL ALLOYS
The lining materials described are further complimented with a range of shaped materials based upon basic and high alumina materials.
LINING DESIGN
A combination of brick and rammed linings is particularly beneficial in large furnaces. This type of lining may however only be incorporated in those furnaces where the inside coil diameter is above 700 mm., and where the lining thickness is no less than 100 mm.
Lining design is largely governed by the size and configuration of a particular furnace . However where it is possible, the use of a bricked working lining is to be preferred since this allows the use of a wider range of refractory materials.
Linings based upon rammed materials, show a tendency to cracking, and this increases with furnace diameter. The use of fired brick linings in these applications goes a long way to overcoming these difficulties.
Additionally, the use of a former is not required for installation, and since the materials of a bricked lining are prefired the need for a fritting heat is eliminated.
Experience has shown that the use of a bricked working lining, backed by a dry powder, can be highly beneficial in many applications involving high capacity furnaces. Major improvements may be gained in terms of lining life and cost effectiveness.
BRICKED INDUCTION FURNACE LININGS
Bricked induction linings follow the basic installation methods utilised for all refractory structures.
Care should always be taken to ensure the use of an appropriate mortar, and that all mortar joints are of minimum thickness.
Magnesite - chrome, chrome - magnesite and magnesia spinel bricks form the working lining.
Magnesite and magnesite alumina powders form the backing lining and bottom, Phosphate bonded alumina ramming materials are used in the furnace mouth.
RAMMED INDUCTION FURNACE LININGS
Installation of the lining
Prior to installation of the furnace lining, the coil should be smoothly coated with a suitable cement, which has been thoroughly dried.
Care should be taken to ensure that there are no gaps and that all extraneous material has been removed from the furnace.
Thoroughly mix all lining material from the bag to eliminate any segregation that may have occurred during transit.
The bottom lining should be installed in layers of 75 to 100mm.thickness and spike rammed until compacted. If a vibrator is used then the surface should be spiked before new material is added. Ensure on completion that the bottom is level.
Install the lining former onto a level furnace bottom, and centralise in the furnace using wooden spacers, the placement of a suitable weight in the former is suggested to maintain stability.
Prior to installation of the sidewall material, the bottom material around the outside of the former should be spiked.
The sidewalls may now be built up by adding layers of 75 to 100mm. thickness, spiking well to allow settling and compaction between additions.
If a former vibrator is used for installation then compaction should be rapid to avoid segregation of the lining. Spiking should be carried out before additional lining material is added to the sidewalls.
The sidewall lining, on completion should be 'topped off' with a suitable refractory material. Such a material is Dycast 1600, although the addition of a bonding agent such as sodium silicate to the lining material plus a little moisture is an alternative. Whichever method is used minimal moisture additions should be made.
Vent holes should be provided at the top of the lining with a suitable rod (a welding rod is ideal), at 150mm. intervals. This will facilitate the drying of the lining.
COMMISSIONING OF THE LINING
Close attention to detail during the drying and fritting cycles will pay dividends in the life of the lining.
Careful drying allows any 'topping off' material to develop maximum strength with minimal cracking.
The fritting cycle is required to develop strength in the rammed lining material. This requires both adequate temperature and heat soak, until sufficient depth of the lining has developed into a monolith.
DRYING
Dry with a suitable heater. Alternatively drying out may be carried out with the fritting heat.
FRITTING
The charge for the fritting heat should be clean dense Turnings and large irregular pieces may lead to arcing in the charge, and should be avoided.
The charge should be slowly brought to dull red heat and held for about thirty minutes to complete drying. This time should be extended if an initial drying programme has not been carried out.
After thorough drying, the charge should be melted at a steady rate, taking care to avoid arcing between charge and former.
During the fritting cycle, the charge depth should be maintained at the maximum level, and the temperature held at the recommended fritting temperature or above, for at least one hour.
Larger furnaces may require a longer hold time at the fritting temperature
MAINTENANCE OF THE LINING
Basic linings are particularly prone to shrinkage cracking, owing to their high reversible thermal expansion, if they are allowed to cool.
In order to minimise the cracking tendency, the cooling cycle should be as slow as possible.
Areas of preferential high wear may be readily repaired using a patching material, THERMOPATCH is ideal for this application.
Furnaces which operate intermittently are best preheated to allow the lining to expand and any shrinkage cracks to close. The rate of temperature rise should be low since high rates may give rise to shelling of the fritted front face.
APPLICATION PROFILE
To enable the most suitable material to be selected for any given application, it is essential that the fullest possible information is known about the operation, particularly in terms of melting temperature and the range of alloys produced.
The application profile form below will provide the necessary information for a suitable lining recommendation.
The data requested is the minimum to enable a suitable proposal, and any additional data regarding operational parameters, particularly slag chemistry will prove invaluable.
In many instances it may be necessary for direct contact to be made with the customer so that the requirements may be fully explored, in these instances Dyson Refractories are available for discussion
Please provide the following contact information:
| Name | |
| Title | |
| Organisation | |
| Street Address 1 | |
| Street Address 2 | |
| City | |
| State/Province | |
| Zip/Postal Code | |
| Country | |
| Work Phone | |
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FURNACE OPERATIONAL DETAIL
Furnace Type
Furnace Capacity (Kg)
Furnace Diameter inside coil (mm)
Furnace Depth to bottom bricks (mm)
Power Input (Kw)
Current Frequency (KHz)
Refractory Sidewall Thickness (mm)
Refractory Bottom Thickness (mm)
Lining Former Diameter (mm)
Former Length (mm)
Does the former reach the furnace top Yes No
Is the furnace topped out with brick Yes No
Preferred Brick Size (mm)
Types of Alloy Melted
Melting Temperature (oC)
Heating Time (min)
Operation
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This page was last modified on Tuesday, June 28, 2011 10:34:27 AM
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