On Line / Auto Spinning In 300 Mtr. Roller Hearth Furnace To Remove Dents From Process Material
Devidas Pawar | [email protected]
Unique No.: 2015-6
Keywords: quality circles, process improvement
In 2005 the management had introduced quality circles and ThyssenKrupp (TK) best scheme to reduce on product cost. I was a member of quality circle and TK best idea evaluation committee. In quality circle our group did many improvements. This was the turning point of my life, I started thinking in a big manner and it has become my habit today. I would like to share one of my biggest improvement initiatives which always make me proud.
Since 1997 the Asia’s longest (300 Mtr.) annealing furnace is running in ThyssenKrupp. Different grades of CRNGO material is processed for annealing and insulation coating. This is a continuous process line where it stops only during furnace roller spinning process. Spinning is required to be done when the dents start appearing on the process sheet which is not acceptable for quality product. The dents on the process sheet come when there is continuous deposition of loose metal scale on ceramic rollers. For spinning process the higher thickness MS sheet of 1mm is fed by removing product sheet and the furnace temperature is also brought down to 800 °C. After this the off line spinning process is carried out to remove pickup from rollers, this complete process takes 2 hours of time. All this process is adding to the product cost. The spinning frequency varies with low to high silicon material. The average is 1.5 times per day.
Brief about the furnace; it is having total 20 zones out of which 15 numbers are heating zones where the temperature is maintained from 800 to 1200 °C and next 5 zones are Jet (air) cool zones. In heating zones there are total 60 numbers of Ceramic rolls which is driven externally by AC motors and AC drives. Zone 1 to 5 is having 6 motors each and Zone 6 to 15 is having 3 motors each. Because of high temperature the loose scale is deposited in all 60 numbers ceramic rollers and the pickup are generated over a period of hours. Then slowly it starts generating dents on process sheet which is not acceptable to the product quality. The offline spinning process is then initiated.
In 2006, I started thinking on how to avoid the Off line spinning process by doing it On line with the same process sheet. I made program logic in the PLC and started testing it in steps by taking a calculated risk. The program logic is prepared in such a way that the group motors of zone 1 to zone 15 speed is increased by few RPM with respect to the actual speed. This is done in staggered manner with fix on and off time interval between two zones. One cycle is of 8.75 minutes and is adjustable. The operator now decides the number of cycles to be run by seeing the intensity of the dents.
The On line spinning process took one year to get success / stabilize, to do the fine tuning of speed and time intervals and to get the results on different product sheets. The TK best evaluation team took another one year to study and evaluate the results as the saving was huge estimated to Rs.7 Crore per year.
