Simple Solutions That Work! Issue 13

Continued on next page DEFECT PREVENTION 11 We know that most foundries, if given the choice, want something designed for their specific requirements. The one size fits all philosophy doesn’t work in most cases. Working practices shouldn’t have to adapt to suit the equipment, when the equipment can be made to suit the working practices. There have never been any hard guidelines for the castable refractory thickness, but a good rule of thumb is 10% of the top diameter. For example, if the ladle top diameter is Ø30” (Ø762mm) then the castable lining thickness should be 3” (76mm). With very large or small ladles there is some flexibility. The castable lining really needs to be at least 2” (50mm) thick for installation and integrity purposes. Likewise, at the opposite end, if the lining is up to, say, 8” thick, increasing it to 10” just to adhere to the 10% guideline is not necessary unless there is a reason for doing so. Cast refractory concrete linings initially did not always perform as well as expected, especially regarding the life of the lining and maintenance required. As many foundries at that time still used cupola melting, a common method of preheating the ladle was by filling it with the first tap from the cupola, letting it sit for 10 minutes and then pig out the metal. Leaving aside the poor efficiency of such a practice, Firebricks could cope with that sort of thermal shock treatment but castable refractories, for several reasons, could not. Clearly these new types of linings needed their own techniques when it comes to using and maintaining them. What we quickly learned was that it was important to pay much more attention to how the ladle design can be made to work with the refractory lining, especially to incorporate details that can help the ladle be turned around quickly when it comes to replacing the lining. Correct pre-heating is important to minimize casting defects and to maximize the life of the refractory, but so is ladle design. One of the drawbacks of the castable refractory is that it can require a lot of effort to be removed when it comes to the end of its working life. Detachable base sections and loose bottom plates on ladles greatly help, but it can take up to 24 hours or longer to remove and replace the lining. Often with the use of mechanical “peckers” that can damage the ladle shell. Then the new lining has to be correctly dried which can take a further 24-48 hours before the ladle can be put onto pre-heat prior to going back into operation. This assumes that all the work is done at the foundry. If you