Clay-King.com - Home Checkout

Troubleshooting

IMPORTANT GENERAL CAUTIONS

  1. 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.
  2. Do not allow children near the kiln at anytime.
  3. Kiln surface is extremely hot and will burn you if touched.
  4. 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.
  5. Kiln should be located at least 12" from any wall.
  6. 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.
  7. Check temperatures around the kiln when it is at high fire to be sure that you are not creating an unsafe condition.
  8. Keep all flammable and combustibles away from kiln. Examples are solvents, curtains, rags, etc.
  9. Operate in a well ventilated area.
  10. 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.
  11. 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.
  12. 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.
  13. 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!
  14. Use dark glasses to view inside the kiln through the peepholes when firing.
  15. 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.
  16. Do not open the kiln lid unless the kiln is turned off and relatively cold (except for carefully controlled troubleshooting tests).
  17. Do not apply kiln wash to the brick sides, element holders or undersides of kiln shelves.
  18. 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

  1. Check element holders for possible contamination (pieces of clay, glaze, etc.) Replace any contaminated holders.
  2. Make sure bottom and shelves are coated with kiln wash.
  3. Plug up peepholes.
  4. Observe thermocouples for excessive corrosion which could lead to thermocouple failure.

MONTHLY

  1. Vacuum out kiln and element holders, repair any firebrick problems.
  2. Check temperatures around kiln (at the high end of use.)
  3. Check kiln plug and outlet box for excessive heat during firing (at the high end of use).

ANNUALLY

  1. Check element resistance.
  2. 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

  1. Check voltage to the kiln. MAKE SURE YOU ARE NOT USING A 3 PHASE KILN ON A SINGLE PHASE CIRCUIT.
  2. 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).
  3. If you have an automatic control be sure that the thermocouple is in working order (see section on controls).
  4. Make sure the On/Off Switch is turned on (if applicable to your model).
  5. 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.
  6. Infinitely Variable Zone Input Switches may have failed.
  7. 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.
  8. Check to see if Dawson Timer is set properly. (If it is at "0" the kiln will not fire.
  9. Check to see if the Dawson plunger is not locked in.
  10. 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.
  11. 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

  1. Elements age when fired and the elements increase in resistance.
  2. Switches are sometimes defective. (See section on switches).
  3. 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.
  4. 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.
  5. 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).
  6. 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.
  7. Make sure all kiln sections are plugged in (if applicable to your model). Make sure plug connection is good.
  8. 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.
  9. 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.
  10. 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.
  11. 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.
  12. 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.
  13. Trace wiring for missing or bad connections. Check wiring against wiring diagram.
  14. 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

  1. Contamination (such as glaze or kiln wash). Silica, a main ingredient of both of these, attacks the element wire.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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).
  11. 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

  1. In J Series, B Series and SQ Series kilns manufactured after January 1996 there are newer larger diameter/cross section 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?

  1. 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.
  2. If door/lid is excessively cracked or worn or has holes in it this may cause drafts in the kiln. Replace door/lid.
  3. 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.
  4. Plug up Peephole holes in the kiln to prevent drafts.
  5. 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?

  1. 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.
  2. Turn down the Infinitely Variable Zone Input Switches to a lower setting. This will moderate the amount of power going to the kiln.
  3. Check element ohms and compare with factory values.

FIREBRICK PROBLEMS

EXCESSIVE BRICK WEAR

  1. 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!
  2. 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.
  3. 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.
  4. 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

  1. Cover the bottom with kiln wash to prevent glaze from sticking to the bottom.
  2. 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

  1. 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.
  2. Repair hole as per instruction below.

BOTTOM OR TOP IS CRACKING OR FAILING

  1. Do not be concerned with small hairline cracks in the firebrick. These are normal and will close up as the brick expands when firing.
  2. Be careful not to overload the bottom.
  3. Try putting a full ceramic shelf directly on the bottom.
  4. 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.)
  5. L&L may be able to help you out with special loading systems or hearth plates. Contact factory.
  6. Mechanical shock can crack the fragile top if you let it down too quickly.
  7. Do not open kiln when hot. Heat shock will destroy the brick (just as it will your ceramic pieces.)
  8. 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

  1. Face hardener is available from L&L Kiln Mfg. Inc. Mix well before using.
  2. 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

  1. 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:

  1. 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.
  2. Access the element connections behind the element cover box(es).
  3. Disconnect the hook up wires from the element connection board. Make certain that jumpers are removed to obtain only each element value.
  4. Take ohm readings of each element separately using a digital meter.
  5. Compare against new element ohm value. L&L can provide these values.
  6. 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.
  7. 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

  1. K.W. stands for kilowatts. 1000 watts equals one kilowatt. or 1 K.W. Watts is a measure of power required by the kiln.
  2. 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.)
  3. 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.
  4. 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.
  5. 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:
  6. Volts = Amperes X Ohms
  7. Volts = Wattage / Amperes
  8. Amperes = Square Root of Watts / Ohms
  9. Amperes = Volts / Ohms
  10. Watts = Volts X Amperes
  11. Watts = (Amperes)2 X Ohms

CHECKING INPUT CONTROLS

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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

  1. Unplug kiln or turn off power at the source.
  2. Remove the switch from the kiln control panel. Leave wiring intact.
  3. 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.
  4. 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.
  5. 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.
  6. 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

  1. 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.
  2. 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.
  3. When checking fuses, also check that all fuses are the correct size and U.L class. See wiring diagrams for this information.
  4. 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.
  5. 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

  1. 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

  1. 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.
  2. Check connections at all the fuse and power terminals for evidence of overheating and/or loose connections.

IMMEDIATE FUSE BLOWING

  1. 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.
  2. 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.
  3. 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

  1. 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.
  2. Check for dust on contacts - use compressed air to blow off
  3. Check out contacts while manually opening and closing the contacts.
  4. Check power contactor coils.
  5. Check contacts on power contactors. If fused together or pitted, replace contacts or complete contactor.
  6. If above checks do not solve problem, replace contactors.
  7. 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

  1. 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

  1. 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

  1. 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.
  2. 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)
  3. 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.)
  4. 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

  1. Control is not adjusted properly.
  2. Check thermocouple for correct immersion depth. Welded end of probe should protrude at least l-l/2" into chamber.
  3. 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).
  4. Check contacts on power contactors. If fused together, replace contacts or complete contactor.

KILN TEMPERATURE OVERSHOOTS SET POINT OF AUTOMATIC CONTROL

  1. Check thermocouple for correct immersion depth. Welded end of probe should protrude at least l-l/2" into chamber.
  2. Turn down input switch settings (if you have on your kiln.) Try 75%, then 50%.
  3. Try different settings of Maximum Power. Instead of 100%, try 75%, then 50%, etc. (if available on your control.)
  4. Try faster cycle time on controller (if possible on your control)
  5. Check contacts on power contactors. If fused together, replace contacts or complete contactor.
  6. Check temperature controller indication against a known standard (a temperature calibration instrument for instance.)
  7. Check interior temperature of control panel. It should not exceed 130°F.

CHECKING CONTROLLER INDICATION AGAINST STANDARD

  1. 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.
  2. 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.
  3. 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

  1. 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.
  2. If the thermocouple itself is in good condition, trace the thermocouple extension wire circuit. Check for poor connections or broken leads.
  3. 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.
  4. 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

  1. 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).
  2. 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

  1. 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.
  2. 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.
  3. 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.
  4. Check thermocouple for correct immersion depth. Welded end of probe should protrude at least l-l/2" into chamber.
  5. 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.

*Provided by L&L Kilns

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