|
|
Digitalfire Ceramics Technical Articles | Logged in as Level 2 access: Logout |
Oxides | Minerals | Materials | Recipes | Articles | Glossary | Hazards | Library | MDT | Pictures | Properties | Schedules | Temperatures | Tests | Troubles | Typecodes
Electric hobby kilns are certainly not up to the quality and capability of small industrial electric kilns, but if you are aware of the limitations and take precautions they are workable.
Firing an electric kiln is like using a microwave oven, right? Just slap the ware in, slam the lid, turn the switches on, and take out the beautiful ware the next day. It is that simple isn't it? Not quite!
If you are using a top loading hobby electric kiln for stoneware pottery, it is good to be aware of what you have. Compared to industrial electric kilns, you have something that is fragile, hard to control, difficult to maintain, fires unevenly, has little or no ventilation and is an energy hog! Hobby kilns are great for earthenware and slip cast ceramics that do not require tight control and they have also given many people the opportunity to get into stoneware pottery and porcelain, and even small scale manufacturing. But make no mistake, producing consistent ware will be a matter of developing a feel for what is happening inside and learning to compensate for the shortcomings of these kilns.
Consider some specific points about making these contraptions work:
Modern electric kilns have electronic controllers. This sounds impressive at first, but in some ways it is an efficient method to automate failure. The kiln still depends on the thermocouple to know what the temperature is and the elements to heat it up. Both have their limits and need maintenance and replacement regularly. A good example of the shortcoming of these controllers is the deterioration of elements: as this happens the device can no longer fire the the requested schedule, most users just ignore this truth and wonder why results are changing. Admittedly, electronic devices have the ability to control the cooling rate and soak of kilns, this is a major advance.
Mechanical sitter devices introduce more things that need maintenance and adjustment (the rod and supports bend a little with each firing). Since few people do this many times they are little more than fail-safe devices. It is actually best to use a timer and stay within earshot of the kiln as it nears completion and use manual override to finish the firing if necessary (people who do this will testify to how seldom the device shuts the kiln off at the right time).
When firing electric periodic kilns, you must get to know how to use cones properly, they are the only way to confirm what the kiln is actually doing.
Electric kilns fire very unevenly as a result of compartmentalization created by full kiln shelves that reach to nearly the edge of the kiln chamber, elements of differing efficiency, uneven distribution of ware and kiln furniture, improperly sealed lid, and lack of draft. You can improve things by having a controller that compensates zones or by setting cones to be visible in peep holes on all levels of the kiln so you do manual overrides as needed. Also, use as little kiln furniture as possible, distribute it evenly throughout the chamber, and use half shelves where practical.
It is best to fire as low as possible to minimize energy consumption and firing time. Remember, exceptionally strong ware can be made even at cone 1 and weak ware can be made at cone 12. A good approach is to develop glaze formulation and adjustment ability at your current temperature for a few years, then use this knowledge to gradually move downward. With effort, you can reduce firing temperature while increasing ware strength and going easier on your kiln.
What really matters is not how much heat the kiln produces, or even how much heat-work the cones indicate, but how much heat the ware absorbs. It is thus easy to appreciate the wisdom of placing the cones with the ware, insulating them from the shelf and away from the elements so you can be confident that they represent the ware. Remember, an electric hobby kiln has little no draft so it is very likely that center sections will not be as hot as outer areas. A large bowl or sculptural piece that fills the chamber wall-to-wall will experience the kiln's entire horizontal heat gradient. Firing slowly will ease these situations. Kiln vents create some airflow, but common sense shows that this airflow is restricted by full shelves.
In industry, the final pore water is removed quickly and evenly from ware in drying chambers that employ boiling-point temperatures and very stiff humidity controlled drafts. I'm guessing you use your kiln for this during early stages of firing! As mentioned, an electric kiln has no draft to remove pore and crystal water so temperatures can generate an extremely humid atmosphere which retards drying of thick pieces. If ware isn't dry when the really hot air starts to hit you know what happens! If possible, get a dedicated drier.
Here are a few other suggestions:
Hobby kilns are not so bad after all. Like so many other things in ceramics, limitations can be compensated for by experience and care. And if you are serious, take a look at an industrial grade kiln as soon as you can, they are amazing.
Out Bound Links
Electric Hobby Kilns: Some Recent Advances You Should Not Ignore
Electric firing is undergoing a renaissance among potters because of changing attitudes and new equi...
In Bound Links
Bubbling that occurs in clay bodies if they are ov...
|
Copyright 2003, 2008 http://digitalfire.com, All Rights Reserved |
|
INSIGHT is ceramic chemistry |