Kiln Elements

Questions arise on whether old elements can become inefficient or hold a “memory” of previous firings. Old elements increase in resistance so decreasing amperage and consequently reducing the temperature that can be achieved or speed with which the kiln can reach the top temperature required. It not a "memory" of heat or temperature.

This series of blog posts will look at the nature of elements, their aging, effects of firing practices, and maintenance of the elements.

Nature of elements

A kiln element is a wire designed to have considerable resistance to electricity passing along it so creating heat.  The measurement of the amount of resistance is in units named ohms.

Most electric kiln elements are made of Kanthal A-1, a trade name of Sandvik.  This is an alloy of iron, chrome and aluminium. During the first firings the wire develops an aluminium oxide layer on its surface.  This helps protect the rest of the substance of the wire from further corrosion.

It is critical to the life of the elements to develop this aluminium oxide coating and is the reason people are told to fire their kiln clean and empty.  Any contaminants, including dust can inhibit the formation of the protective oxide locally.

The new kiln elements begin to achieve their protective coating when they reach 1000°C.  The kiln does not have to reach that temperature, just the element.  But it is advisable to fire toward 950°C at a moderate rate of about 250°C per hour and soak there for half an hour to ensure the coating is firmly in place. Your kiln may never be fired as hot again, but you will be sure the elements are properly prepared.

It is important to remember that the elements are flexible when heated initially, but after a few firings become stiff and brittle.  After the initial firings, you need to ensure the elements are still well seated in their groves.

A well-designed kiln will have the largest diameter element wire and the largest distance between the coils (runs cooler). The thicker the elements, the greater the stability and the longer the life.  When elements get above 925C they become very soft.  As they soften, the coils begin to collapse, causing the distance between the coil turns to lessen. When the distance between coil turns is small the element will overheat in those areas.

The next in this series is about the aging of elements.
Aging of elements
Firing Practices
maintenance