Before
proceeding to repair your kiln it is very important to have electrical repairs
and measurements performed by an electrician or other qualified technician.
There is danger of electric shock.
Do not
allow children near the kiln at anytime.
Kiln
surface is extremely hot and will burn you if touched.
Do not
leave the kiln while firing. NO AUTOMATIC SAFETY DEVICE IS FAILPROOF! BE
ESPECIALLY CAREFUL ABOUT ATTENDING THE KILN WHILE IT IS SUPPOSED TO SHUT
OFF.
Kiln should
be located at least 12" from any wall.
The floor
should be protected from the heat if it is combustible. IMPORTANT NOTE: If
kiln overfires certain materials such as glass or glazes can reach superhot
temperatures because they become electrically conductive and can melt. This
can burn through the kiln bottom and, if there is a combustible floor, cause a
fire. Be sure to protect against this possibility.
Check
temperatures around the kiln when it is at high fire to be sure that you are
not creating an unsafe condition.
Keep all
flammable and combustibles away from kiln. Examples are solvents, curtains,
rags, etc.
Operate in
a well ventilated area.
Be sure to
use the door safety chain when loading and unloading (or servicing the kiln).
The kiln door is heavy and could cause bodily injury if it fell on you.
Do not let
the kiln's power cord or wire connection come in direct contact with the kiln
side. The kiln will melt the cord covering and potentially cause a short
circuit.
Never load
moist greenware in your kiln. The expanding steam vapor in the ware could
cause the ware to blow up, damaging your kiln interior. If this happens shut
off the kiln immediately, let it cool down and then vacuum out all element
holders to get rid of ceramic pieces that may have fallen into the
holders.
Read the
control and/or Dawson Kiln Sitter instructions as well as these and other
general instructions that come with your kiln - BEFORE OPERATING THE
KILN!
Use dark
glasses to view inside the kiln through the peepholes when firing.
Never use
an extension cord with your power cord. Locate the outlet for your kiln within
the distance required for supplied power cord. The reason for this is that the
electrical capacity of wire is a function of both its diameter and its
length.
Do not open
the kiln lid unless the kiln is turned off and relatively cold (except for
carefully controlled troubleshooting tests).
Do not
apply kiln wash to the brick sides, element holders or undersides of kiln
shelves.
Do not use
aluminum wire for hooking up kiln.
REGULAR KILN
MAINTENANCE
To keep
your kiln in top operating shape, we recommend the following minimum
housekeeping:
WEEKLY OR AFTER EACH FIRING
Check
element holders for possible contamination (pieces of clay, glaze, etc.)
Replace any contaminated holders.
Make sure
bottom and shelves are coated with kiln wash.
Plug up
peepholes.
Observe
thermocouples for excessive corrosion which could lead to thermocouple
failure.
MONTHLY
Vacuum out
kiln and element holders, repair any firebrick problems.
Check
temperatures around kiln (at the high end of use.)
Check kiln
plug and outlet box for excessive heat during firing (at the high end of
use).
ANNUALLY
Check
element resistance.
Check
operation of the Dawson Kiln Sitter or Gemini Control(s) (on the B Series).
Note in particular that the pivot point is free to move. Consider replacing
the tube assembly (especially if anything you do causes condensation of glaze
or other material.)
KILN WON'T HEAT UP AT ALL
Check
voltage to the kiln. MAKE SURE YOU ARE NOT USING A 3 PHASE KILN ON A SINGLE
PHASE CIRCUIT.
Make sure
the infinitely variable zone input switches are turned on (if included on your
kiln). There is a "click" in the "off position at "12 O’clock". Full on is the
"click" position just to the right of this (1 O’clock).
If you have
an automatic control be sure that the thermocouple is in working order (see
section on controls).
Make sure
the On/Off Switch is turned on (if applicable to your model).
Check
fuses. Make sure they are of the proper amperage and type. See wiring diagram
for details. Note that some L&L kilns have element circuit fuses.
Infinitely
Variable Zone Input Switches may have failed.
Check for
short circuits. In particular check where the elements come through the case.
Check for worn wires that may have shorted against the case.
Check to
see if Dawson Timer is set properly. (If it is at "0" the kiln will not
fire.
Check to
see if the Dawson plunger is not locked in.
Check the
door cut-off switch if there is one. In the SQ Series, G Series Kilns and some
other kilns the power contactors are shut off whenever the door is open. Power
is restored when the door is closed. If switch does not function properly,
check adjustment levers or bolts to make sure the switch is actuated when it
should be. If not, adjust properly. If the switch is actuated, but circuit
does not function properly, first make sure the wiring is correct. Pay strict
attention to whether the correct wires are connected to the proper pole of the
switch (Common, Normally Open, Normally Closed). Refer to the wiring diagrams.
Try bypassing the switch electrically which will tell you if the problem is in
the switch. If wiring is correct, repair or replace the switch.
Automatic
control (if included) indicates full upscale indication (i.e. 2400° F would be
typical) even though you know the kiln is not that hot. This indicates
thermocouple circuit failure. Some controls use some other kind of error
message (for instance "E" on the PerfectFire). Check thermocouple end. Check
thermocouple circuit.
SLOW FIRING TIME
Elements
age when fired and the elements increase in resistance.
Switches
are sometimes defective. (See section on switches).
Relays or
contactors may cause poor transfer of power to elements when they have been
used for a long period of time. Examine contacts for wear. Replace contactors
if contacts are worn or pitted.
Replacing
only one element per zone may cause an unbalance in firing. However kilns with
infinite zone switches (J Series, DaVinci Series, SQ Series) may compensate
for the unbalance with proper adjustment in the setting of the input
switch.
Use
original L&L parts for satisfactory maintenance. (Elements , in
particular, provided by other vendors may not work well in your L&L kiln.
Some of our customers have found this out the hard way and thought it was an
L&L problem. Only L&L has the proper design information to make our
elements properly).
Make sure
all elements are firing. You can do this by simply looking inside the kiln
while the elements are on. They should all be glowing a similar color red
(except on B Series kilns where elements are contoured from top to bottom).
CAUTION: In most kilns the power does not turn off when you open the lid.
Be careful not to put your hand inside the kiln while it is on. Dangerous
electric shock could result.
Make sure
all kiln sections are plugged in (if applicable to your model). Make sure plug
connection is good.
Check your
voltage. Do this at the kiln. Do this with a voltmeter. If you are not
familiar with electricity have a qualified electrician do this for you. Low
voltage will make the kiln fire considerably slower. For instance a kiln
designed for 240 volts will have 25% less power when operated on 208 volts.
Check voltage at your panel and where the kiln is connected. Check the voltage
when the kiln is firing and when it is not firing. Sometimes the high amperage
draw of the kiln will cause a voltage drop at the kiln.
Make sure
no other large electrical appliances such as a clothes dryer are on when you
are operating your kiln. This may cause a voltage drop which would slow the
kiln down.
Voltage may
vary in your area depending on season and time of day. Frequently there are
"brown outs" during the summer months in some areas. This is when the electric
utility reduces the voltage. Try firing at night after peak electrical use
hours.
Have an
electrician check your wiring. We have seen aluminum wire cause intermittent
problems with allowing enough voltage through. DO NOT USE ALUMINUM WIRING.
Make sure your wires are of the proper size and that all connections are good.
Check your circuit breaker for proper operation.
If all the
elements are firing and the kiln is still firing too slow check the amperage
draw of the kiln under a full load, i.e. with all Infinitely Variable Zone
Input Switches on 100%. See if the amperage drawn is the same as what the kiln
is rated for. See the product literature and/or data nameplate on the kiln for
the rated amperage draw. For instance, a model J230 rated for 240 volts,
Single Phase should draw 43.93 amps. If it is substantially less than the
rated amperage draw and your voltage is within 5% of the rated voltage (for
instance 230 volts for a 240 volt unit), then chances are the elements have
changed in resistance. This will require element replacement. You can check
element resistance by disconnecting the elements and checking the elements
with an ohmmeter. See your instructions or check with factory for proper
resistance.
Trace
wiring for missing or bad connections. Check wiring against wiring
diagram.
In
L&L's top loading kilns an additional bottom may be placed under the
original bottom. Also a 1" or 2" layer of ceramic fiber blanket can be
attached to the top. These measures will improve the insulation in the kiln,
thereby slowing heat loss and speeding the firing time.
ELEMENTS AND ELEMENT
PROBLEMS
FACTORS SHORTENING ELEMENT LIFE
Contamination (such as glaze or kiln wash). Silica, a main ingredient
of both of these, attacks the element wire.
Tightly
wound areas on element coils resulting from improper stretch. Have the
elements been stretched evenly? This is critical. If the element coils are
bunched up along the length of the element the element will overheat where the
coils are too close. Replacement elements are shipped unstretched and
stretching instructions are included with the elements. Also see section below
on stretching elements.
Glaze
accidentally rubbing off into holder and on element in loading kiln. If such
rub off occurs immediately vacuum thoroughly. Glaze will cause very rapid
failure.
Blow ups or
explosion of bisque ware cause small pieces of clay to be blown into holder
and element. If not immediately removed clay may melt contaminating element
and element holder. To avoid this make certain clay is very dry before firing
and, in the case of heavy handmade pieces, fire on low for a long period until
you are sure ware is dried out thoroughly. If you hear a "pop" when firing
such pieces, stop firing, cool the kiln. If blow-up has occurred, vacuum all
element grooves very thoroughly.
Firing
pieces too close to elements. We recommend at least 1-1/2" from piece to
element. Further if large flat surfaces are parallel to kiln wall.
Reducing
atmospheres will destroy elements. Do not use wood chips, oils and other
materials to generate a reducing atmosphere. A very rapid element failure may
result. NOTE: Reducing atmospheres are the opposite of oxidizing atmospheres
(plain air is an oxidizing atmosphere). The word reducing comes from the
ability of a reducing atmosphere to "reduce" oxides.
Are any
waxes, oils, carbon, fluorine, fumes present? Are you using any lead glazes?
Iron-Chrome-Aluminum elements require an oxidizing atmosphere to give
dependable service. The aluminum in the element forms a protective aluminum
oxide. Oil from tools or carbon from wax burnout will attack the element
coating. Halogens such as chlorine or fluorine will attack the elements.
Molten metals, for instance, zinc, aluminum and copper, react with iron-
chrome-aluminum elements. Moreover, these metals oxidize easily and their
oxides have an unfavorable effect on iron-chrome-aluminum. The salts of the
alkali metals, halogen salts, nitrates, silicates, and compounds of borax,
disturb the formation of oxide and are, therefore, harmful to these elements.
This is also true of the oxides of such metals as copper, lead and iron. Do
not use with free carbon. Lead oxide attacks the protective alumina oxide
coating on the element. If you are using lead glaze (or are creating any of
these other problems) be sure to use a kiln vent. Also try firing every other
load or as often as you can with a non corrosive load (such as a bisque
firing). This will help the element restore its protective alumina oxide
coating.
Excessive
soaking time will accelerate increase in element resistance. The higher the
temperature, the longer the soak, the sooner the element will decrease in
life. Usually short soaks work fine.
Are they
genuine L&L elements? There are a number of people selling "replacement
elements" for kilns. These people do not have access to the proper design
information for L&L elements. Designing an element is a complicated
process which balances such things as voltage, wire diameter, watt density,
stretch ratio, etc. It is very easy to make an element that has the same
watts as an L&L element and have nowhere near the other design
qualities that result in long element life.
If the
failure is taking place at the element end it may be twisted too tightly,
causing stress at terminal through holes. This causes local overheating at the
"through hole", and element failure. (Contact factory).
Make sure
all elements are heating. If all elements are not doing their share of the
work then the other elements will not last as long.
HEAVY
DUTY ELEMENTS
In J
Series, B Series and SQ Series kilns manufactured after January 1996 there are
newer larger diameter/crossection element holders. (The new holders fit into
the same slot that is cut in the firebrick as the older element holders).
These new holders allow the use of a new heavy duty element. The heavy duty
element is made from a larger diameter wire and features a lower watt density.
Watt density is a measure of the amount of power per square inch of element
surface. This lower watt density results in a lower element temperature for
any given kiln temperature and this results in longer element life. We have
been using this "heavy duty" design on our DaVinci kilns for over 5 years and
have found it to provide significantly longer element life. We recommend these
elements if you are having element life problems.
DOES THE KILN FIRE UNEVENLY?
Check to
make sure that door/lid is sealing properly. If door/lid is not sealing
against seal brick correctly a red glow will be visible around the door seal
when kiln is operating. Also excessive heat loss can be felt around seal. Rub
front seal high points down until no more than l/l6 of an inch gap is found at
any point along seal. Ceramic fiber gasketing material is available from
L&L for real problem kilns.
If door/lid
is excessively cracked or worn or has holes in it this may cause drafts in the
kiln. Replace door/lid.
Elements
may have differentially changed in resistance. If you have a kiln with zoning
you can usually adjust this out with the infinitely variable zone input
switches. On B Model kilns you may have to replace all elements. NOTE: B Model
kilns have contoured resistance on the elements and it is critical that you
put the elements exactly where they belong from top to bottom.
Plug up
Peephole holes in the kiln to prevent drafts.
Multi
section kilns like our "J" Econo-Kilns, "X or T" Series "DaVinci", "G" Series
Colorado and "SQ" Series Dyna-Kilns have infinite control over the input to
each section or zone. Firing chamber uniformity depends upon how a kiln may be
loaded and how the input to each zone is adjusted. Normally a kiln is on "low"
for a period of time, then set to "medium" for the next period of time, and
finally on "high" until shut-off by either Dawson kiln sitter or other control
device such as a program control. Often firing as above may end up with a
difference in temperature in various sections of the fired load or zone. To
correct this without the use of a pyrometer system requires a trial and error
method, such as using multiple cones in various zones of the kiln. After
shut-off carefully note the temperature variations and by small adjustments to
the sectional input controls when on "high" attempt to tune this difference
out. Since cones only indicate end of firing temperature one has no idea of
how the uniformity is developing as the temperature is increasing. We
recommend a TRU-VIEW multi-thermocouple pyrometer system which indicates the
temperature of each zone. (These are available from L&L). The system
includes a thermocouple located in each kiln section. A switch allows the
operator to switch from zone to zone very rapidly and thereby indicating each
zone temperature. Adjustments to the infinite control will then be indicated.
This method indicates zone temperature at all times and is also a great help
in cooling a kiln. Often a kiln should cool slowly requiring a period on "low"
heat. In such a procedure the Dawson Kiln Sitter is reset carefully to "on"
position (ignore the cone which has initially shut this kiln off) but make
absolutely certain you are on "low" heat to prevent overfiring. Do not leave
your kiln; keep checking. CAUTION: Such a procedure requires
knowing the temperature of the kiln and kiln sections and requires manual
shut-off of the kiln. Simply shut-off power manually (by turning off the
various input/zone switches) and cause the Dawson to manually shut-off by
depressing the weight of the Dawson Kiln Sitter.
DOES THE KILN HEAT TOO FAST?
Check your
voltage. Make sure you don’t have a 208 volt kiln hooked up to a 240 volt
circuit. Also some people may have high voltage like 245 volts where you
should nominally have 240 volts.
Turn down
the Infinitely Variable Zone Input Switches to a lower setting. This will
moderate the amount of power going to the kiln.
Check
element ohms and compare with factory values.
FIREBRICK
PROBLEMS
EXCESSIVE BRICK WEAR
Excessive
brick wear can be the result of various conditions. Most common is improper
curing of the brick when first fired. FOLLOW THE INSTRUCTIONS IN THE
INSTALLATION SECTION FOR THE FIRST FIRING AND CURING CYCLE!
All
insulating firebrick expands and contracts when heated and cooled. Over time
this will lead to cracking and spalling. Spalling is the continued cracking of
the brick which eventually results in large pieces of the brick falling out
from the brick section. This is a normal condition as long as the emphasis is
on eventually. Factors such as how close the kiln is operated at or near
maximum temperature, how often and how fast the kiln is cycled up to heat and
then cooled, how heavy the loads are, all figure into the brick wear equation.
There is no set rule as to how long a brick lining will last. There are some
L&L kilns which are 25 to 30 years old with the original lining still in
place. Others may have to have the lining replaced after 5 years of hard use.
Note that the type of brick we use is the same that we have always used and is
the same brick generally used in the hobby kiln industry.
Frequent
door openings when the kiln is at high temperatures can cause thermal shock,
leading to excessive cracking and spalling. Try to keep all door openings to a
minimum, unless the kiln can be cooled first.
For light
to moderate spalling, re-coat the brick with the brick hardener facing
available from the factory. This procedure can allow the brick to remain
operational.
GENERAL BOTTOM MAINTENANCE
Cover the
bottom with kiln wash to prevent glaze from sticking to the bottom.
If glaze
does get onto the bottom be sure to scrape it off. Apply kiln wash over area
that you have scraped clean.
REMOVING GLAZE SPOTS
Be sure to
remove any spots of glaze that get onto the firebrick sides. When the kiln is
heated up the glaze will remelt and potentially cause problems with the
elements.
Repair hole
as per instruction below.
BOTTOM
OR TOP IS CRACKING OR FAILING
Do not be
concerned with small hairline cracks in the firebrick. These are normal and
will close up as the brick expands when firing.
Be careful
not to overload the bottom.
Try putting
a full ceramic shelf directly on the bottom.
If you have
had several cracked bottoms try putting a piece of sheet metal on top of the
stand (L&L's larger stands have this built into them). The metal should be
stainless or aluminized steel to resist the high temperatures. (Contact
factory for a price if you need this.)
L&L may
be able to help you out with special loading systems or hearth plates. Contact
factory.
Mechanical
shock can crack the fragile top if you let it down too quickly.
Do not open
kiln when hot. Heat shock will destroy the brick (just as it will your ceramic
pieces.)
In most
L&L Kilns the bottom can be reversed once the initial inside surface has
become deteriorated over time.
APPLICATION OF HIGH TEMPERATURE BRICK HARDENER
Face
hardener is available from L&L Kiln Mfg. Inc. Mix well before
using.
To apply
the hardener first brush the surface of the brick clean to remove any loose
material or crumbling firebrick. Apply a thin coat of the brick hardener with
a soft brush over the surface of the firebrick. Do not make too thick a coat
of the hardener or it will spall off. Let the hardener dry for 24 hours and
then use. On your first firing keep the kiln on low for 3 hours minimum and
fire as slowly as possible.
REPAIRING
BRICK
A really
effective "Kiln Brick Repair Kit" is available from L&L. This includes a
special phosphate bonded cement and all the materials necessary to repair
firebrick. This includes detailed instructions on how to apply. It will repair
both large and small holes, chips and dents in the firebrick. Contact
distributor or factory for ordering information.
ELECTRICAL PROBLEMS
The following
factors and measurements will be helpful in determining certain problems and
correcting procedures. An inexpensive digital meter must be used for voltage and
ohm resistance measurements. No particular brand is recommended; but be sure to
have a meter with the proper volt range for the supply voltage, and that the ohm
meter has a 0 to 200 ohms range. A continuity tester feature is useful. Radio
Shack is a good place to find such a meter. A "Clamp-on" amprobe meter is to be
used for ampere readings.
CAUTION!
Many of these tests require working with line voltage. Only an experienced
electrician should perform these tests under these
conditions.
VOLTAGE: Take voltage reading at the kiln with the kiln on
"high" heat. Also take the voltage reading with the kiln "off" at the same
location. Compare to the nameplate voltage.
AMPERES: Check with "clamp-on" type of ammeter amprobe. Clamp
around one of the "hot" power leads going to the kiln from your power supply.
Some kilns are equipped with a flat type power cord including two power #6 wires
and a #8 ground wire. Separate one of the outside heavy gauge wires away from a
section of the cord sufficiently to allow the "clamp-on" ammeter to be properly
clamped around this "hot" cable. Take care not to penetrate the insulation
exposing the copper wire. Make sure power is off when separating. The
amperes per section can then be measured: Add readings together to obtain total
amperes and compare to the nameplate amps. The above data may indicate
the problem area. If cord supplied is of the round type you can do the above
separation on the intermediate cord that goes between the Dawson Kiln Sitter and
the instrument panel.
OHMS:
If amperes are low then the elements may require replacement. To check ohm
values follow this procedure:
Turn off
all power to the kiln. Do this at your main circuit breaker on a direct hook
up kiln (and lock out in an industrial setting) or unplug kiln if you have a
plug. THIS IS CRITICAL FOR SAFETY.
Access the
element connections behind the element cover box(es).
Disconnect
the hook up wires from the element connection board. Make certain that jumpers
are removed to obtain only each element value.
Take ohm
readings of each element separately using a digital meter.
Compare
against new element ohm value. L&L can provide these values.
Increased
ohms indicate lower power which result in increased firing time. Typically
if elements have increased by 9% in resistance then they should be
replaced.
As a crude
check it is possible to check the resistance of a whole element circuit. For
instance, if there are three elements connected together in a parallel circuit
you can check the resistance of the whole circuit without disconnecting any
elements. If you multiply the resistance that you read by the number of
elements in the parallel circuit you will get the average resistance of each
element. Be aware that this is not as good as getting a resistance reading on
each element because it does not tell you if one is high and one is low for
instance. If the elements are in series then you divide the reading by the
number of elements to get the average element
resistance. EXAMPLES: SERIES CIRCUIT: A J18 section
has two elements in series. This means that the power must travel through both
elements (i.e., if one element is broken the whole circuit is broken and
neither element will glow). A 240 volt J18 element has a nominal resistance of
10.4 ohms. Add the two resistances to get an approximate ohm reading of 20.8
for the whole section. (This could be measured at the plug). PARALLEL
CIRCUIT: A J2927 has three elements in parallel. This means that each
element can run independent of the other elements. Each element on a 240 volt
unit has a nominal resistance of 37.9 ohms. Divide this number by 3 (the
number of elements in series) to get an approximate ohm reading of 12.63 for
the whole section. (This could be measured at the plug). A J230 has two
elements in parallel. Divide the nominal element resistance of 32.7 by two to
get 16.35 at the plug. Multiply this by 3 to get the approximate ohm reading
of 113.7 ohms for a whole section. (This could be measured at the plug of the
section).
ELECTRICAL FACTS
K.W. stands
for kilowatts. 1000 watts equals one kilowatt. or 1 K.W. Watts is a measure of
power required by the kiln.
Volts:
Volts is the "pressure" of the electrical energy available. The higher the
voltage the more pressure or force with which the power is forced through the
wires. Higher voltage requires smaller wires but greater electrical
insulation. (For instance, larger fuse blocks to prevent potential short
circuits.)
Ohms: Ohms
is a measure of resistance. The higher the resistance the more power is
required to force the electrical energy through the element wires.
Amperage:
Amperage is the volume of electrical energy or current going through an
electrical system. The higher the amount (at a constant voltage), the more
K.W. or power is being used.
Ohm's Law:
Ohm's law is a statement of the mathematical relationship between watts, ohms,
amperage and volts. Several of the more common formulas are:
Volts =
Amperes X Ohms
Volts =
Wattage / Amperes
Amperes =
Square Root of Watts / Ohms
Amperes =
Volts / Ohms
Watts =
Volts X Amperes
Watts =
(Amperes)2 X Ohms
CHECKING INPUT CONTROLS
With power
on, set the input control to 100%. The temperature control (if included) must
call for heat, and door cut-off switch (if included) must be closed. At 100%
input the power should be full on. You can check this with an ammeter. Also
the pilot lights (if included) should indicate that power is on. If there are
contactors controlled by the input switch they will be energized. You should
be able to tell whether the kiln is heating up.
At lower
settings the input controls cycle the power contactors on and off. Lowest
setting allows approximately 6% (2-1/2%) on time. If the input controls are
not functioning properly, they should be replaced.
Replace any
defective switches. If element ohms are O.K. and voltage is normal then the
switches are suspect. One good way to check is to have one spare switch on
hand for effective testing.
Corroded
"spade" wire terminals can cause excess heating at the input switch which can
cause premature failure. Visual evidence of this effect may often show as a
gray area around the spade terminal or the black switch case where the plastic
has changed color from the heat.
CAUTION: When replacing switches make sure that new
"spade" slip on wire connectors replace the old ones. The old ones are usually
corroded and, when used, may cause heat that may destroy the new switch
rapidly.
REPLACING SWITCHES
Unplug kiln
or turn off power at the source.
Remove the
switch from the kiln control panel. Leave wiring intact.
Transfer
one wire at a time to the new switch so that you don't loose track of where
the wires go. If you do lose track and are uncertain that you put the wires on
correctly be sure to check the wiring diagram.
Replace
terminals on the wire, especially if there is any evidence of discoloration or
oxidation. THIS IS IMPORTANT BECAUSE OXIDATION AT THESE TERMINALS CAN CAUSE
THE SWITCH TO OVERHEAT AND FAIL.
If the
terminals do not fit snugly onto the spades on the switch take some pliers and
gently compress the female terminal so that it will be tighter on the
spade.
Replace
switch in control box making sure the top is in the correct position.
REPLACING "K" MODEL AND OTHER OLD KILN SWITCHES
The new 4
position (low/Medium/High/Off) switches used as replacements for old type
switches wire differently from the old switches. Follow instructions supplied
carefully.
CHECKING FUSES
Unplug the
kiln or disconnect power at main disconnect switch or fuse box (turn off
circuit breaker if that is the type of hook up you have.) Using a voltmeter
test the kiln to make sure there is no power coming into the kiln before
proceeding.
Check ohms
across each fuse. This should read a closed circuit (0 ohms, or very small
fraction.) A blown fuse will read a large number of ohms, or 'Overload',
indicating that the circuit is open. Some ohm meters have a continuity tester;
this tests for a closed circuit, and can be very helpful in diagnosing fuse
conditions.
When
checking fuses, also check that all fuses are the correct size and U.L class.
See wiring diagrams for this information.
If fuses
are blowing erratically, a higher ampere fuse may be necessary. Check the
surge amperes, which are the amperes that are developed when the main power is
first turned on. Replace the fuse with one of slightly higher amp capacity
than the surge amperes. Another solution is to use a slow blow time delay fuse
to prevent fuse blowing when you have a temporary power surge.
Check the
main disconnect fuses (if you have them) first, then the control circuit
fuses, then element bank and other component fuses.
DELAYED FUSE BLOWING
Premature
fuse blowing or premature circuit breaker shut-off action may be caused by
using too low a value of fuse or breaker. This would usually occur almost
immediately. If however such delayed fuse blowing or circuit breaker action
occurs after the kiln has been in operation for a long period of time without
this delayed action, then the fuse holder or circuit breaker may require
replacement. Corrosion or formation of oxides at the electrical contact points
may have occurred. Heat then generated would cause the fuse or circuit breaker
to shut-off at a lower value than its rating. Sometimes the fuse holders
become corroded or degraded over time. Check and replace if necessary.
FUSE
BLOWS AFTER KILN HAS BEEN ON FOR A WHILE
The
electrical circuit that the kiln is on may be overloaded. Check to see if
other appliances are on the same circuit and if they may have been turned on
while the kiln was firing.
Check
connections at all the fuse and power terminals for evidence of overheating
and/or loose connections.
IMMEDIATE FUSE BLOWING
If
immediate fuse blowing or circuit breaker shut off occurs this generally
indicates a short circuit. Identify problem and correct before attempting
firing. Look at all wire connections for evidence of arcing. If in doubt have
a qualified electrician examine the kiln.
A short
circuit is basically a wire path between two power lines which has little or
no resistance, thus causing an excessive amount of amperage to develop.
If a short
circuit has occurred, trace the wire path according to the wiring diagrams.
Check each connection to make sure that neighboring wires or connectors do not
touch. Also check each line to ground with an ohm meter to make sure there are
no grounded wires or connections.
POWER
CONTACTORS
Some
L&L kilns are equipped with power contactors. As time goes by these may
not transfer power very well, usually after many years of operation. If the
switches are O.K., voltage is O.K., and amperes seem O.K., the contactors may
be suspect in some cases of slow firing.
Check for
dust on contacts - use compressed air to blow off
Check out
contacts while manually opening and closing the contacts.
Check power
contactor coils.
Check
contacts on power contactors. If fused together or pitted, replace contacts or
complete contactor.
If above
checks do not solve problem, replace contactors.
With power
off, isolate the power contactor coil control circuit by removing the control
wires from it. VERY CAREFULLY, using a control voltage test lead (this can be
12 volts DC, 120,208 or 240 volts AC - check description on coil and keep in
mind that if you put the wrong voltage across the coil you could easily burn
up the coil), apply control voltage across the contactor coil. Contacts should
close. If not functioning properly, replace coil or complete contactor.
PLUG
OR OUTLET IS HOT
Either the
plug or the outlet may be defective. For instance the plug wire may be frayed,
the plug terminals may be oxidized or the socket may be oxidized. Replace
before firing. This could cause a fire!
CHECKING TEMPERATURE CONTROL RELAY OPERATION
Turn power
on. Set infinitely variable zone input controls to 100%, and control to 300°F.
set point. Hold door cutoff switch closed (if included on your kiln) and
CAREFULLY heat the thermocouple probe with a match or lighter. Power
contactors should close, and control indicator should climb to set point The
control should open the contactor just before the probe temperature reaches
set point. If temperature control does not function properly, have it repaired
or replace with a new one.
CONTROLS AND
PYROMETERS
L&L Kiln
Manufacturing Company offers program controllers such as the Dyna-Trol with
multiple thermocouple systems. Very accurate temperatures are indicated in each
zone. See separate troubleshooting instructions in the control
manuals.
ELECTRICAL NOISE IN THE CONTROL
If the
temperature indicator of the controls seems erratic; i.e. the temperature
jumps quickly from one temperature to the next by several degrees then there
is a good chance you have electrical noise being transmitted to the
control.
Check the
kiln ground. Make sure you have a good ground to the kiln. Make sure there is
only one ground to all components on the kiln (a common ground)
Make sure
no thermocouple lead wires run parallel to any power wires. The reason for
this is that the power wires will induce a very small current in the
thermocouple circuit (it does not take much to disturb this low millivolt
thermocouple circuit.)
MOVs (a
special kind of electrical noise suppresser) can be put across the contactor
coils. This suppresses the noise that the contactors cause. (Contact factory.
These are available from L&L.)
AUTOMATIC CONTROL INDICATES ERRATICALLY
Control is
not adjusted properly.
Check
thermocouple for correct immersion depth. Welded end of probe should protrude
at least l-l/2" into chamber.
If the
control had been accurate and is slowly drifting in accuracy the cause is
probably a bad thermocouple. Type K (Chromel-Alumel) thermocouples age over
time and drift in accuracy. The higher the temperature you fire at the more
quickly this will happen. Simply replace the thermocouple if this happens. If
you are firing above 2000F very often you may want to consider buying an 8
gauge Type K thermocouple or better yet our new Industrial Mullite Protection
Tube (with the 8 gauge thermocouple).
Check
contacts on power contactors. If fused together, replace contacts or complete
contactor.
KILN
TEMPERATURE OVERSHOOTS SET POINT OF AUTOMATIC CONTROL
Check
thermocouple for correct immersion depth. Welded end of probe should protrude
at least l-l/2" into chamber.
Turn down
input switch settings (if you have on your kiln.) Try 75%, then 50%.
Try
different settings of Maximum Power. Instead of 100%, try 75%, then 50%, etc.
(if available on your control.)
Try faster
cycle time on controller (if possible on your control)
Check
contacts on power contactors. If fused together, replace contacts or complete
contactor.
Check
temperature controller indication against a known standard (a temperature
calibration instrument for instance.)
Check
interior temperature of control panel. It should not exceed 130°F.
CHECKING CONTROLLER INDICATION AGAINST STANDARD
Use a
separate millivoltage source (a Fluke or Biddle calibrator is recommended) as
the input signal to the control. Remove Thermocouple lead wires to the input
terminals on the control, and attach test leads from the millivolt source.
Turn power on. Set the millivolt source to a reading of 500°F. and compare
control indication. Compare at 1000°F, 1500°F, 2000°F, and 2300°F.
The control
manufacturer's instructions specify a certain range of accuracy for the
control; compare any deviations noticed against the manufacturer's
specifications, and contact the factory or control manufacturer if there is a
problem.
Alternatively, send the control back to L&L Kiln Mfg Co.,Inc., for
calibration service. There is a nominal charge, and a shipping procedure that
must be followed. Call the factory for Return Authorization.
CHECKING THERMOCOUPLE CIRCUIT
First
inspect thermocouple weld for a good bead and no corrosion or erosion. If
there is evidence of deterioration, replace the thermocouple. IT IS WISE TO
KEEP A SPARE THERMOCOUPLE.
If the
thermocouple itself is in good condition, trace the thermocouple extension
wire circuit. Check for poor connections or broken leads.
THERMOCOUPLE POLARITY: Positive is Chromel wire which is non-magnetic.
Color of positive thermocouple lead wire is Yellow. Negative lead is Alumel
wire which is magnetic. Negative lead on thermocouple lead wire is Red.
THERE
SHOULD NEVER BE ANY OTHER METAL SUCH AS A SCREW BETWEEN THE THERMOCOUPLE WIRE
AND THE THERMOCOUPLE LEAD WIRE. IT SHOULD BE A DIRECT CONTACT. The
thermocouple lead wire is special calibrated wire for Type K thermocouples.
Using any dissimilar metal in the circuit will cause an error in the millivolt
reading from that thermocouple.
CHECKING INTERIOR TEMPERATURE OF CONTROL PANEL
The
interior temperature of the control panel where the control is located should
not exceed 125F. Check with an accurate thermometer while the kiln is
operating at its highest temperature. Pay careful attention to the critical
control components, such as the controller chassis, and any exposed circuit
boards. If you have one of the new DynaTrol controls you can press [View
Segment] and you will view the board temperature (see control instructions for
details).
You may
need to increase ventilation near the kiln or place a fan near the control
panel to cool it down.
PYROMETER OR CONTROL IS NOT ACCURATE OR READS IN REVERSE OR DOES NOT SEEM
TO INDICATE AT ALL
Sometimes
pyrometers are not as accurate as cones or other temperature measuring
devices. Usually this is not a real problem. The accuracy will not normally
vary within a particular pyrometer. We suggest calibrating the pyrometer with
an instrument of known accuracy. If you are using cones as your ultimate
reference then note at what temperature on the pyrometer the cone slumps and
mark it on the pyrometer. NOTE: All L&L pyrometers are calibrated with a
Fluke meter (traceable to the NIST) to be accurate at 2000F. At lower range of
temperatures the meters are usually off (sometimes as much as 300F). The
critical temperatures are the higher temperatures.
Check the
polarity of the thermocouple wire. THERMOCOUPLE POLARITY: Positive is Chromel
wire which is non magnetic. Color of positive thermocouple lead wire is
Yellow. Negative lead is Alumel wire which is magnetic. Negative lead on
thermocouple lead wire is Red.
Trace
thermocouple extension wire circuit, making sure that all positive leads are
connected together and all negative leads are connected together, with no
cross wiring.
Check
thermocouple for correct immersion depth. Welded end of probe should protrude
at least l-l/2" into chamber.
Sulfur will
attack Type K thermocouples. Sulfur can be in glazes, clay, oil, dirt, mortar,
some furnace cements, and some asbestos. A simple test for this is to immerse
a thermocouple with suspected contamination in a 20% hydrochloric acid
containing a few pieces of metallic zinc. If sulfur is present it can be
detected by the smell of hydrogen sulfide (a rotten egg smell). Also moistened
lead acetate paper held over the top of the test solution will turn brown or
black if sulfur is present. If you can't get rid of the sulfur problem you can
purchase a thermocouple with a protection sheath.
Troubleshooting