Wednesday, 1 June 2016

Pre-programed Schedules - Kiln Forming Myths 24

Don’t use the pre-programed schedules that come with your kiln. 

As a universal approach, this does not stand up.  They do have the disadvantage of trying to cover all possibilities at once. This means they will fail if used uncritically. But everyone needs a place to start. 

An analogy might be the oven temperatures and times in recipes for cooking.  You have to start somewhere.  After a little experience you modify the schedule to fit the equipment you have and the material you are cooking.  This is similar to what happens with people starting in kiln forming.  Prior to the time when manufacturers began putting programs into the controllers, we all copied schedules from text books, guides and other workers.  We put them into the controller and tried them out.

I use pre-programmed schedules all the time – but they are built from my own from observations. They have been based on what others have done, writings and research, but modified by my equipment, the style of work I am doing and many other considerations as indicated in another post.

The instruction should be more about understanding what your schedule does than just dumping the pre-programed schedules.  You should know what your pre-programed schedule does. It is not enough to say “I used full fuse #1.”  You need to know what that schedule does.  You have look at the steps and temperatures and times that the schedule instructs the kiln to do.  Only in this way can you know what is working.  If it is not possible to see what the program is doing by reviewing the steps on the controller, then you need to delete it and copy a program from the glass manufacturer.  This is a reliable indicator of what will work in a wide variety of situations and can later be modified to meet your needs.

 The following are schedules for fusing and slumping.  You need to look at these and decide how you want to modify them - if at all - for your purposes.

An example of a fusing schedule

For this program, you have to decide, on the Goldilocks principle: 
  • Is the rate of advance is too fast, too slow or just right.  
  • Do I need a soak at 200C? 
  • Is the next rate of advance right? 
  • Do I need a bubble squeeze? 
  • Is the top temperature right and the soak long enough?  
  • Is the anneal soak long enough? 
  • Is the anneal rate too slow, too fast or just right?  
  • Do I need to control the rate of fall below the initial anneal cool, or just let the kiln cool naturally?

An example of a slumping schedule

Again apply the Goldilocks principle:
  • You need to think about the speed of the rate of advance. Too fast, too slow or just right?
  • Is the top temperature right? Too high, too low?
  • Is the soak too long, too short, just right?  
  • Is the annealing soak right, too short, too long?
  • Is the annealing cool too fast, too slow?

When you have thought about these things, you are well on the way to writing your own programs.