Simple Solutions That Work! Issue 17

Contact: JOHN REYNOLDS John.Reynolds@ha-group.com in figure 3 is a 20,000 lb. gas- fired reverb and had a complete refractory reline 14 months before the photo date. If properly cleaned using a good flux and procedure, the lining should have a life span of 4-7 years. This furnace was not properly cleaned and needed to be shut down for rebuild after 16 months in service. Tear out was very difficult and expensive due to the extensive corundum. WALL CLEANING FLUX These fluxes are either sodium-free or sodium-bearing. Alloy chemistry should always be reviewed before selecting which will work best for the application. A refractory lining will have a service life of 4-7 years if properly maintained. Over time the lining loses its nonwetting ability allowing aluminum and oxide to adhere to it. This commonly occurs at the metal line in a reverb furnace. Oxide growth is also affected by air infiltration, burner calibration, and furnace design. Once it’s determined that regular cleaning is not effectively removing the buildup then a wall flux should be used. Wall fluxes contain high percentages of oxidizers and fluorides and should be used as directed. APPLICATION PROCEDURE • This procedure should be done just prior to a general scheduled cleaning. • Apply the wall flux only to buildup areas. If needed, a pneumatic flux gun can be used in larger furnaces. • For best adherence, areas to be treated should be red hot. • Once applied, close the furnace door, and run up to the high fire for 10-15 minutes. • Drive to low fire and open the door. Using an appropriate tool, scrape areas treated. • After scraping the walls, a general scheduled cleaning can be done. Again, furnace cleaning is physically demanding. Furnace tenders often aggressively scrape, and chisel build-up areas after a wall flux has been applied and see very little progress. This can be discouraging and lead to discontinuing the use of the wall flux. Corundum Al2O3 takes time to get under control and is never completely removed, only kept at bay. When scraping corundum after a wall flux is applied, effort is required, but don’t overdo it. Apply before each scheduled cleaning and scrape each time. Assuming the corundum has penetrated the refractory, it's best to leave a thin layer of the oxide on the wall. Removing all the growth can result in refractory damage. Over time, the buildup will be reduced, and the use of wall flux suspended. Resume applying the wall flux when needed, a good well-trained furnace tender can make this call. Supervision should make weekly visual inspections to confirm the furnaces are cleaned correctly. Proper flux selection and good process quality control are especially important to realize the benefits in eliminating casting defects and reducing energy usage while increasing metal recovery. Applied with good process control, improved worker ergonomics, and gains in labor utilization are also key variables that are directly impacted. Fig. 3 – 20,000 lbs. Gas Fired Reverb Furnace showing extensive corundum growth. 13 BACK TO BASICS