- Last Updated: Thursday, 19 June 2014 19:43
Kiln Maintenance Checklist
by Jim Skutt
Establishing a kiln maintenance check list is easy. Determining how often it is required is the challenge as usage can vary, depending on the program. But for art educators, “back to school” seems to be an obvious and ideal time as many items are probably best evaluated annually. Once the school year begins, time becomes very precious as you focus on other objectives. Doing your kiln maintenance homework now will save you time and perhaps budget dollars down the road.
Control and Shutoff Devices: The most important part of any kiln is the shutoff device. In a kiln equipped with a Dawson Kiln-Sitter it is called the shutoff tube (Photo 2) and in a digital kiln it is called a thermocouple (Photo 1). It is imperative these devices are always in good working order. The way to check them is to use pyrometric cones on the shelves and to study the results to make sure these devices are providing the correct amount of heatwork to the ceramic pieces.
Digital kilns: The Thermocouple or temperature probe is the single most important component in the kiln control circuit, the reason for this is simple, GIGO, garbage in… garbage out. If the temperature signal sent to the circuit board is flawed from the start the controller has no possible way of giving you a good firing. We always recommend using pyrometric cones to detect thermocouple drift as soon as it starts, but we know that advice is a bit like getting that oil change every 3,000 miles. At a minimum you should keep a spare on hand and replace the probe once a year just to insure it won’t be the cause of a bad firing.
- Kiln-Sitter Kilns: Just like the thermocouple is the sensor in a digital kiln, the Shut-Off Tube is the sensor on a KS kiln. Generally you will get many years of use out of the shut-off tube, but it makes the "replace it" list because people don’t view it as a replacement item. If your kiln is 3 or more years old and you fire it every day and you haven’t changed the shut-off tube, your are probably due.
- Digital kilns: The Thermocouple or temperature probe is the single most important component in the kiln control circuit, the reason for this is simple, GIGO, garbage in… garbage out. If the temperature signal sent to the circuit board is flawed from the start the controller has no possible way of giving you a good firing. We always recommend using pyrometric cones to detect thermocouple drift as soon as it starts, but we know that advice is a bit like getting that oil change every 3,000 miles. At a minimum you should keep a spare on hand and replace the probe once a year just to insure it won’t be the cause of a bad firing.
Power Switching Components: Again there are 2 main types: relays are used in the digital kilns, switches are used in Kiln-Sitter type kilns.
- Relays: the electrically actuated switches that turn your kiln elements ON and OFF should be replaced on bi-annual basis. Some people have found their relays last much longer than that, others would recommend annual replacement to be safe. This is largely a factor of how many times you fire your kiln each week. If you are firing every day of the week I think it is prudent to change the relays once a year. However if you only fire every other day, you should be fine to change them every 2 years.
- Switches: also like the relays the switches in your KS kiln may need to be replaced over the years, so it is difficult to say exactly when switches will need to be replaced, but I’d put them on the same schedule as the shut-off tube assembly mentioned above.
- Vacuum Interior of Kiln: Any large pieces of debris on the heating elements can melt and cause the element to fail in that spot. Therefore it is important to keep the kiln chamber free of debris by vacuuming with a HEPA filter equipped vacuum cleaner.
- Plug & Receptacles: The power plug and wall receptacle combination is worth checking every year. All that is involved is to pull the kiln plug out of the wall receptacle and look at the prongs on the plug. If they appear bright brass color you are in good shape, if on the other hand they are dark and brownish or black you should replace both the kiln plug and the wall receptacle immediately. This repair should only be performed by a qualified kiln repairperson. One way to keep your plug and wall receptacle in good shape is to add one step to your pre-firing checklist: make sure the plug is fully engaged with the wall receptacle before each firing by pushing the plug into the receptacle. Don’t pull it out to first, just push the plug into the wall receptacle and make sure any gap has been removed. By doing that one thing you will prevent trouble before it every starts.
- Heating Elements: People always want to know when to replace their elements. This seems to be one of the most confounding maintenance items for kilnowners. Since a set of elements is relatively expensive I can only comment on when the elements will definitely need to be replaced. No matter what your maintenance schedule is, or the last time you replaced elements, we know one thing for sure: tired elements is the number 2 cause for long or stalled out firings (Err1 on the display for you digital kiln users out there. Low voltage is the #1 cause). It might be excessive to suggest you to change them every year - if you are infrequently firing you won’t need to. But the whole point of this article is to keep your kiln running year after year and to minimize the down time. The best I can do is to tell to do one of the following: 1) replace them every year whether or not they need it, just to be safe or 2) keep a detailed log of the firing times and when they start to increase schedule a time to have them replaced in the near future.
Bands & Lid Hardware: The mechanical strength of the kiln comes from the bricks and the stainless steel bands that compress these bricks. It is very important to tighten the bands at least once a year to insure the bricks stay where we’ve put them. Use a screwdriver (see photo), but also hold the body of the gear clamp with pliers to prevent you from twisting the band as you tighten. Any screws that have rusted or corroded should be replaced.
- Down-Draft Vent Systems (if installed): The vent system also requires some inspection, testing and usually some minor repairs to the ductwork. I am talking about downdraft vent systems especially in the airflow testing through the kiln. The short version is to close the kiln up just like you would when firing with a downdraft vent, then light a match or cigarette lighter so the flame is just above one of the ¼” intake holes in the lid. The flame should be pulled down into the hole. If it is not then there may be a problem with the ductwork or the vent itself and further investigation is required to insure proper ventilation of your studio. Note: a corroded fan impeller inside the vent housing can be a cause excessive vibration – cleaning or replacement will fix the problem. It is also very important to inspect your 4” or 6” ductwork for any holes or leaks. If you are using a downdraft vent and you smell fumes in the studio you should be looking for leaks in the ductwork. When you have located a suspect seam or hole the quickest way to seal it is with… you guessed it, duct tape (this is what the stuff was made to do). Wisconsin residents take note, the last time we checked a second power vent is required at the discharge end of the vent ductwork to maintain negative pressure for the entire length of the ductwork.
Here are additional sources of information:
- 10 Hot Kiln Tips - by David Gamble http://www.skutt.com/pdf/articles/10HotKilnTips.pdf
- Kiln Firing Tips http://www.skutt.com/pdf/firingtips.pdf
- Kiln Maintenance http://www.skutt.com/pdf/Maintainence.pdf
- Prepping Your Kiln video http://www.skutt.com/video/3_Preping.html
- General video index http://www.skutt.com/video/index.html
Kilns aren’t that different from people, we all age at different rates, but with a little work we can slow the rate. It reminds me of George Burn’s quote “If I would have known I’d live this long I would have taken better care of myself”. Good luck n the coming school year and keep those kilns firing.