Electric kiln elements…this unassuming collection of small metal coils is where the power coming from the wall is converted to heat. They are routinely subjected to extreme temperatures, strange atmospheres, and high voltage as a normal part of the firing process.   Naturally, elements will periodically wear out and need to be replaced.  But how long should they last?  How do you know when they need to be replaced?  Are all elements the same?  The answers to these questions is a bit more complicated than you might think.  In this month’s Tech Tuesday, we will begin to learn about kiln elements by discussing how your elements work.

Heat comes from resistance.

It is easy to understand that electricity flows through the wire that makes up your kiln element.  The same electricity also flows through the copper wire used inside the control box, yet they don’t get nearly as hot.  There must, therefore, be a difference in how electricity flows through different types of wire.

elec_conductor1_240

Copper is a pretty good conductor for electricity.  What that means is that electricity has a pretty easy time flowing through a wire made of copper.  With a few exceptions, Element wire is typically made of a metallic alloy called Kanthal A-1.  Unlike copper, Kanthal is highly resistive to the flow of electricity.

A good analogy is to think of it like trying to run a group of kids down a hallway in a High School:

As electricity flows through a resistor, a “sea of electrons” moves around within a lattice of other particles.  Your elements get hot because of the friction from the electrons slamming into everything as they move around.

So why do elements put out less heat over time?

Element wire naturally creates an oxide coating on its surface when it gets hot.  This coating is eaten off by the atmosphere of the kiln, and naturally replaced by the oxidizing process of the metal.  Over time, this will cause the resistance of an element to increase, as there is less conductive material for the electricity to flow through.  As the resistance increases, less heat is generated.  Lets think back to our hallway analogy.   An older element is like lining the outside edges of the hallway with walls of cinder blocks while removing the kids that were standing there. This reduces the amount of space there is for all of the kids running down the hall AND reduces the amount of friction produced since our running kids cannot run THROUGH the cinder blocks.   The overall hallway takes up the same space, and there are the same number of kids running down the hallway, but there is less room to do it in.  It is much harder (more resistance) for the same number of running kids to get down the hallway.  As time goes by, we build up the layers of cinder blocks on the outside of the hallway which continues to reduce the amount of space in the middle.  Eventually, the resistance increases to the point where we can’t get enough of our running kids down the hallway in time to do what we need them to do.  In the case of heating elements, the resistance increases to the point where we cannot produce enough heat to increase the temperature of the kiln to where we want it to be.  At that point, elements are still getting hot, just not hot enough.  They are no longer useful and need to be changed.

How can I tell when the elements actually need to be changed?

Although its not an absolutely definitive test, a visual inspection can often reveal a broken or problematic element.

Keeping good records is the first step to knowing when to start worrying about your element age.  THERE IS NO ABSOLUTE NUBMER OF FIRINGS that you will get out of a set of elements, as there are too many variables that cannot be controlled for.  A pretty good guideline to start with is the following:

If you glaze to ^04-06, you may get between 100-130 firings on a set of elements

If you glaze to ^4-6, you may get between 60-100 firings on a set of elements

If you glaze to ^8-10, you may get between 15-30 firings on a set of elements.

These numbers are an idealized, typical average and you may get greater or fewer firings out of your elements depending on your specific firing profile, clay body recipe, glaze recipe, kiln atmosphere, humidity, etc.  The low end of the range is where you should actively start testing your elements for age.

There are two main tests that I use to determine element age.  The first is a simple glow test.

The key is to have ALL the elements turn on AND STAY ON long enough for the elements to glow.  For a manual kiln, turn the switches directly to HIGH.  For a computer kiln, program a single segment profile with a rate of climb of 9999 deg F per hour to about 1500 deg F with no hold.

If you need help programming the glow test, feel free to email me the model and serial number of your kiln.  I have many programs already written up as a .pdf, and am happy to send you the instructions.

Put in all the peep hole plugs, close the lid, and start the EMPTY kiln. The element glow should happen, on most kilns, within  5-10 min.  If the glow doesn’t come until between 20-25 min, ALL the elements are firing, AND the number of firings on that set of elements falls within the above range, then you likely need new elements.

Ohms_Law_Triangle

Ohm’s Law Relationship

If you want to be absolutely sure, you can perform an element resistance test.  The resistance of a material is measured in a unit called ‘ohms’, named after the German physicist Georg Ohm.  A digital multimeter is used to measure element resistance – check the best multimeter reviews to get one.

Fluke87-V_Multimeter

The proper use of a multimeter, performing the resistance test, and the relationship between element resistance and heat output is the topic of next month’s Tech Tuesday.  As always if you have any questions, please don’t hesitate to contact us at Bracker’s Good Earth Clays.

 

 

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