BATCH ANNEALING PROCESS
It is the process in which batches of cold strips which are placed on the base and enclosed by inner cover and then covered by the furnace.This is different processes for annealing of cold rolled steel.
For this process overhead crane is used for loading of base and moving of equipment.
Basic equipment required for the annealing of strips are as follows:
- base unit provide with re circulation fan
- protective ,gas tight cylindrical cover
- heating furnace or heating bell.
- cooling bell or hood.
At this stage number of cold rolled steel coils are placed one above the other over the work base.
These coils are separated by the convector plates. After loading of coils in the base unit the interior cover is placed over the base and protective gas is circulated in the enclosure.
After this heating bell or heating furnace is placed over the cover. during this process the burners of heating furnace start to provide heat to the interior cover and it heats the circulating protective gas. heat from the interior cover is passed to the coils inner and upper surface through convector plates .And the coils get heated by convector plates from circulating protective gas and radiation between coil and interior cover. The furnace brings the charge to the desired temperature.
Cylindrical coil over the work base called charge.
The temperature to which the cold rolled coils or strips are heated dependent on the chemical and Mechanical properties of coils or strips.
After this steel coils reached at particular temperature, where soaking process takes place.
During the batch annealing process there is formation of new strain free crystals (grains) which replaces all deformed crystals of the cold worked material. Takes place at a temperature known as re crystallization temperature. it takes place temperature at 550 deg C.
After this heat treatment process , heating furnace is removed that means end of heating.
cooling is performed by removing of heating furnace or heating bell Over the base leaving the interior cover to maintain the protective atmosphere.
And then cooled furnace is placed over the base, blower will started eject the heat to the air and left to desired temperature.
After reached to desired temperature it will undergoes water cooling process.
In the end coils ejected from the base with new strain free crystals structure on the surface.It is the different processes for annealing of cold rolled steel.
CONTINUOUS ANNEALING PROCESS
Continuous annealing line is defined as process which contains all the steps of cleaning ,cooling,heating, refining in single line. the over all time required for the process is shortened.It is more demanding requirements in steel mechanical properties.It is also the different processes for annealing of cold rolled steel.
The continous annealing line has many advantages:
- more productivity in shortened time
- corrosion resistance , better shape with exceptional smoothness
- can operate easily
- suitability for coating material.
- increased in ductility and removal of strains that lead to failure.
During this process at first stage the coil is placed in the un coiler. due to continuous line process there is two un coiler. after this the head end of new coil is joined with the tail end of previous coil with the help of welding. due to this joining the movement of continuous line remain maintained.
For this continuous process accumulators or loopers are provided.
- entry accumulators
- exit accumulators
Accumulators are used to provide the storage areas between static steel coils and continuous strip running through the furnace or heat treatment section.
As the un coiler is stopped ,replaced with the new coil and both the coils welded together during
This time the entry accumulators unwinds to provide the continuous coil or we can say entry accumulator consists of two parallel set of rolls, as the starting stage entry accumulator move apart at some particular distance to hold more coil for the continuous process and the accumulators supplies the coil to the furnace or heat treatment section.
The coil goes through multi stages of annealing process consists of pre heating, heating ,holding ,rapid and Slow cooling, over ageing and finally cooling.
Then coil go through skin pass process and set required material properties, Pass through oiling machine for surface protection.
Finally at the end during shearing operation , the exit accumulator winds up while the full coil is unloaded at the exit.
During the whole process the temperature is depend upon the chemical and mechanical properties of coils.
so above two are different processes for annealing of cold rolled steel.
EFFECT OF HEAT TREATMENT ON METAL
Varying in the rate of cooling (quenching) of the metal controls grain size and grain patterns.
Grain characteristics are controlled to produce different levels of hardness and tensile strength.
Hardness and tensile strength increase in heat-treated steel toughness and ductility decrease.
It is used to produces compressive and tensile stresses.
Stresses are minimized by using heat sink welding and annealing.
Softens steel and improves ductility
Relieves internal stresses caused by previous processes
Refines grain structure
Advantages of batch annealing process
- operating cost is low
- product quality is good
- good productions rates
- less capital investment