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Kiln Elements

In order to protect elements from the effects of harsh environments, it is very important to condition the elements by pre-oxidizing them.



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This is done by firing them to a temperature of 1922º F and soaking for seven to ten hours if possible.
The process is improved by allowing good air flow into the kiln.
Leave the peep holes open, or the kiln vent on.
If you are doing reduction firings in an electric kiln, it is important to periodically re-oxidize the elements, which makes them last longer.
The results of kiln element conditioning can be quite dramatic.
It may not have much of an affect for normal, low temperature firings, but can be very significant for harsh operating conditions.

Detecting a Broken Element

When an element burns out, it can sometimes fool a continuity tester.
A continuity tester determines if the element can carry electricity.
You can perform this test with an ohmmeter, which measures electrical resistance. You can also check continuity with a small test light available from a auto parts stores. The test light includes a battery and two lead wires.
The preferred method to check continuity is with an ohmmeter.

When an element breaks, it should no longer be able to carry electricity.
Sometimes though, a broken element will show continuity when tested with an ohmmeter or a test light, because as the element cools, the broken ends sometimes touch.
If the ends touch, electricity can still travel through the element, but when you fire the kiln, the element will produce little, if any, heat.

To test an element, find out the ohms of resistance that the element is rated for.
You can get this information from the kiln’s wiring diagram.
If an ohmmeter test gives a resistance that is close to the correct resistance, the element is not broken.
If the resistance is much higher than the rated resistance, the element could be burned out.

Testing an Element With Thermal Paper

There is another simple method of testing elements that anyone can perform.
You can use thermal fax paper cut into strips 1 inch wide and 8 1/2 inch long for this test.
A roll of fax paper is cheap and will last for hundreds of tests.
When the fax paper is exposed to heat it will turn dark.
The paper can be held by a clothespin or over the end of a pencil.

Instructions

Turn the kiln on to the high heat setting for not more than one minute.
You will hear the elements hum as they turn on.
Digital kilns will make a clicking noise which is the relays opening and closing.
UNPLUG the kiln.
OPEN the kiln.
Place an end of the fax paper strip on the element for three to five seconds.
Check the strip to see if it has turned dark.
Dark is good, no change means the element didn’t turn on.
This could be due to a burned out element, switch, relay, connector or fuse.
Repeat for each element.

If you suspect that the element is burned out even though you are still obtaining a resistance reading, check the element grooves with a flashlight when the kiln is cold. You should be able to see the break.
One of the signs that a heating element has been over fired is that the element coils begin to collapse or lie flat in the element grooves.
If you are buying a used kiln, use a small mirror to look at the elements.
If you notice collapsed coils, it is a good sign that you will need to replace the elements before firing the kiln.
After removing such an element, check out the element groove.
You may see discolored areas where the coils shorted out and melted the element wire.
These discolored spots must be removed from the groove before installing a new element.
You can dig out the melted element wire using a screwdriver.

Bulging Element

If a heating element bulges out of a sidewall firebrick groove, you should repair it as soon as possible.
Heat the element with a propane torch until the element is red hot.

Element Repair

Sometimes the biggest improvement comes from making the smallest change. When choosing a propane torch for element maintenance, the right torch makes a big difference too.
You can purchase a propane torch from a home improvement center.
Buy the type that has a push-button igniter.
When you press the button, a blue flame appears.
When you release the button, the flame goes out.
For element maintenance, do not use the older manual propane torches.
Turning them on and off is awkward.
You first have to turn a knob to start the flow of propane and then hold a match under the nozzle.

SAFETY PRECAUTIONS

Make sure the kiln is disconnected from the power before working on an element.
Use a propane torch only in an area that has good ventilation.
Clear the area of combustible materials before using the torch.
Shrinking a bulging element is easy when using the propane torch with push button igniter.
First, press the igniter and hold the flame near the bulging element.
You will see the element turn red in just a few seconds.
Then release the igniter.
Then shrink it into place with needle-nose pliers.
As the element cools, it will become stiff.
You can feel it through the pliers.
At the first sign of stiffness, press the igniter, reheat the element, and repeat the process until the element is in its groove.
Do not bend the element while it is stiff or it will break.

Element Life

There are too many variables for the wire manufacturer to be able to provide definite life expectancies for elements.
Usually as operating temperatures go up, life expectancy goes down.
Harmful atmospheres will also reduce element life.
Element wire can be damaged by some foreign materials, such as glaze splashes. Debris in element grooves can also shorten element life by reducing the element's ability to radiate heat.

The following guide has been written up by one wire manufacturer to illustrate the effect of operating temperature.
The figures are for wire temperature, the kiln temperature will be about 50º F lower.

Fahrenheit

Celsius

Percentage of Element Life

1150 2100 100
1200 2200 46
1260 2300 22
1315 2400 13
1370 2500 9


Reducing atmospheres, caused by the introduction of gas, charcoal, wood, paper or other materials will strongly affect life expectancy by impairing the oxidization of the element wire.
Foreign materials will also affect oxidization.
Steam from the kiln load will also affect element oxidization, as well as contributing to corrosion of the kilns case.
This is why ventilation during the early stages of bisque firing is so important.

How to Provide Even Heat Distribution

Kilns will naturally tend to be cool in the bottom and in the top due to heat loss through the floor and lid.
Putting an element in the floor is one way of partially addressing the problem, but this weakens the floor and the grooves tend to get filled with chunks of stuff, which reduces the element life.
It is best to install hotter elements in the top and bottom of the sidewalls because they are specially designed and proven by experience to provide even heat distribution.
In the small and medium size kilns, up to 7 cu. feet, this allows you to do away with multiple switches to adjust heat distribution.
In the larger kilns, 10 and 16 cubic feet, switches are included, which allow fine adjustment for different loads.

Repairing an Element

Ordinarily the only way to repair a burned-out element is to replace it, but when an element burns out at the connector, you may be able to install a new connector and salvage the element.
Elements rarely burn out at the connector but if it does, it is due to a loose connection, which builds up enough heat in the connector to break the element wire.
This is why it is important to securely tighten element connectors when replacing an element.
The following instructions are for kilns that use barrel connectors, but if your kiln uses a different type of connector the basic principle still applies.
If you have a burned out element and have to replace the element or connector, disconnect the kiln and remove the control panel from the kiln.
You will see two element connectors for each element in your kiln.
If the element has burned at the connector, you will usually see a bare, twisted section of element with a missing connector.
This is because the element connector falls off the broken element end.
Check to see if the burned element end has enough length so that you can install another element connector.
You will need about 1/2 inch of element length to install another connector.
If you don't, gently pull the element end with needle-nose pliers.
There is sometimes play in the element and you can feel the play as you pull the element end toward you.
If you have 1/2 inch of exposed length at the element end, you will be able to install a new element connector and salvage the element.
Do not remove the porcelain insulator located under the element.
If your kiln doesn't have a insulator, don't worry, not all kilns have porcelain insulators. Removing the insulator will give you extra element length, but the insulator is there to prevent the element from shorting out against the kiln case.
Check the element lead wire for heat damage by bending the wire.
If the insulation is brittle, replace the wire.

Element Twisting

Sometime a kiln user can repair burned out elements by twisting the broken ends together.
After unplugging the kiln, they use a small propane torch to heat the two ends to red heat and twist the wire together with pliers.
This rarely works for long, because the element has a protective oxide coating after many firings.
The oxide coating not only protects the wire from further oxidation or burning away, but it is also a good electrical insulator, so the connection made by twisting is electrically poor.
The poor connection will not conduct current very well and will get extremely hot during the firing and most likely burn out again.
On very rare occasions if you are lucky, the wire gets just hot enough to weld itself together without melting, making a good connection.
Usually the twisted joint burns out near the end of the firing when the kiln is hottest, so the user gets just one more firing out of the element.
The faulty element is then promptly forgotten until the next firing, and it is too late to call a kiln technician or replace it yourself.
These sorts of spot burn outs in elements are usually caused by poor kiln housekeeping, like not regularly vacuuming all the bits of clay and glaze that collect in the element grooves.
One little spot of glaze on an element has a fluxing action on the wire, in other words the glaze causes the wire to melt at a lower than normal temperature.
A collection of dust in the bottom of a groove can cause a overheating of an element. Both of these conditions will cause a premature failure of the element, usually with a little ball of melted wire at the point of failure.

Lots of kilns have these temporary element repairs.
The users are lucky to get one good firing every second or third attempt due to all the element failures.
You are wasting all that power just to avoid the cost of getting the kiln repaired right.
It also has another very bad side effect.
Every time the twisted element fails, it causes an electrical arc, which melts some of the element wire into the brick groove.
By the time someone is called to repair the kiln, so much element wire has melted into the brick that it has to be dug out, damaging the element groove and creating a weak spot where the element cannot not be held securely.

The moral of this story is to use only the element twist repair as a real emergency measure and be sure to call a kiln technician or any electrician to replace the faulty element or replace it yourself right after the firing.
Better yet, keep the kiln element grooves clean, and avoid the problem in the first place!

Replacing Elements

Elements will drop in power after the first couple of firings, and then be quite steady for a long time until their age catches up with them.
If a kiln's firing time is gradually getting slower and slower, it is probably the old elements which cause an abrupt slowing in firing time or with all elements working, may be your electrical supply, check with your power company.
Many people like to change all of the elements at the same time.
This is not necessary, as the new element will not affect the other elements in the kiln, unless the new element is connected in series with other elements.
In this case the older elements will tend to be worked harder, which will shorten their life even more.
If all elements are old when one element fails, it is best to change all of them, rather than face another element failure and incomplete firing in the future.
Element replacement is not difficult and most people do their own.
Below is instructions for changing the elements in a kiln.


Top Load Kilns

Disconnect the power supply to the kiln and remove wiring cover.
Make note of correct connection sequence.
Disconnect element from connector or terminal.
Straighten tail and pull out from inside kiln.
Pull coil from groove, being careful to minimize brick damage. Needle nose pliers may be helpful.
Carefully chip any foreign matter from groove, and vacuum.
Bend one element tail at 90 degrees to the coil, and insert through kiln wall.
Feed element into groove. Be sure to push coil well into the groove. Open coil slightly and bend, to suit corners.
If element is not long enough, stretch out the last few feet of the coil as necessary.
Bend second tail at 90 degrees and insert through wall.
Connect the two tails to the supply wires, and snip off excess wire.
Check condition of other element and switch connections, and tighten as required.


Front Load Kilns

Disconnect the power supply to the kiln and remove wiring cover.
Make note of correct connection sequence.
Disconnect element from connector, being careful of other element connections.
Draw the element to be replaced from inside the kiln.
Carefully chip any foreign matter from groove, and vacuum.
Element legs must lie flat and parallel. Check that the hairpin dimension is correct, allowing both legs to lie flat in their grooves.
Slide new elements into the grooves, guiding the tails through the back wall. Push the tails all the way through, with the legs lying straight in the grooves.
Prepare jumper wires and/or supply wires for reconnection.
Place the connector over the tail, and pull the tail from the end to provide tension on the coil. Tighten the connector and cut off any excess tail length.
Check condition of other element and supply connections, and tighten as required.
Here are a few more pointers that will simplify element replacement.

EXPANDING THE ELEMENT

The new replacement element for most sidewall brick grooved kiln models is bent where it fits into the corners of the firing chamber.
The element bends must fit into the back of the firebrick corners.
If the element barely fits into the corners, gently expand the distance between element coils with snap-ring pliers.
You can buy these pliers at an auto parts store.
This will prevent the element from bulging out of the grooves later.

ELEMENT CONNECTOR

If you strip the threads in an element connector, discard the connector and install a new one, because if you don't, the element will burn out at the connector.

ELEMENT ENDS

Cut off the element ends where they stick out past the element connectors.
You will have two element ends for each element that you replace.
After you install the elements, count the number of element ends to be sure that none have been left inside the kiln.
There have been cases where a discarded element end fell into the kiln sitter contact block and stops the kiln sitter from operating.
A discarded element end could also fall against wire terminals and cause a short.

Bulging Elements

This pointer is for firebrick kilns with sidewall elements also.
It does not apply to ceramic fiber kilns.
You can see heating element grooves and brick seams inside a firebrick kiln.
Most ceramic fiber kilns have embedded elements that do not use grooves.

If your kiln is new or you have just installed a new element, perform the kitchen knife test.

Do not perform this test if the element has been fired and always unplug the kiln before touching an element with anything.

KITCHEN KNIFE TEST FOR FIREBRICK KILNS WITH SIDEWALL ELEMENTS

Press the elements into their grooves by running a blunt kitchen knife, plastic comb, or any blunt object completely around each groove.
Do this before the first firing because it may not be evident to the eye whether the coil is in its groove.
If the element doesn’t lay flat in the bottom of its groove, don't be concerned as long as the element fits all the way back into each corner and doesn’t bulge outside the groove.

FIRING THE KILN TO CONE 05

When the kiln is fired to cone 05 or hotter, which is 1888º F or hotter, the elements soften to the point where they no longer support their own weight.
If they are inside the grooves, they will conform to the shape of the grooves. Sometimes, firing to cone 05 or hotter when new elements are put in your kiln, will help prevent the elements from bulging out of the grooves.

Time may be a healer, but it's a crummy beautician.



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