cruise control

What is IR Comp and Why Should I Care?

The best analogy for IR Compensation is the Cruise Control on your car. When you want to keep your car speed at a specific MPH you set your cruise control. When you come to a hill your car needs more power to climb the hill so your Cruise Control gives it the right amount of gas to keep the speed constant while climbing the hill.

Most potters wheels have the same feature but it has a much less sexy name, IR Compensation. the “I” refers to current and the “R” refers to armature resistance. The adjustment is hidden in your wheels control box on the controller’s circuit board along with settings for speed control and torque. Manufacturers don’t like you messing with these settings because they are generally “tuned” to the size of your motor, pulley, belt… you get the picture.

So, to use the analogy: your wheel is the car, IR Comp. is the cruise control, Amperage is the fuel, the force you put on your wheel while throwing (especially centering) is the hill and the foot pedal is… well the foot pedal and the motor is the motor. Now I personally do not like using Cruise Control in a hilly area. That is primarily be-cause I have mostly owned small engine vehicles where I have to slam the gas pedal to the floor to get up hills and when I let cruise control try and do this it gets a little jolty (not sure if jolty is a word but I think you all know what I mean).

The bigger the engine (motor) and the smaller the hill (pressure on the wheel head), the less dramatic the joltyness (can I trademark that word?). A few more things come into play like the sophistication of the controller and the degree of IR Comp employed, but let’s get back to that later.

So, if I am driving an old VW Bug that needs a tune up and you are in a brand new 12 Cylinder engine Jaguar and we hit the same hill, I am going to slam my pedal to the floor boards while you barely have to move your foot. In other words, the adjustment is subtle because it is not putting much strain on your huge motor. This is probably why they never put cruise control on VW bugs. It would probably pop the seat right off the rails.

Okay, so what does this have to do with throwing pots? For most people, not much. For people throwing very large pots and for people throwing very thin, wide bowls at low speeds, it can be the difference between success and failure. Imagine you are dropping the walls on a 3 ft. diameter, razor thin, platter and the wheel gets a little unexpected jolt when the IR Comp kicks in.

Let’s face it, your foot pressure could be less smooth then the IR Comp so what is the solution? Buy the Jaguar with the 12 cylinder engine and never set your cruise control. In Skutt terms, get the wheel with the biggest motor you can afford and don’t worry about IR Comp because we never turn it on.

The founder of Thomas Stuart wheels, now Skutt Wheels, was a big pot potter. When he designed the wheels he specifically chose a motor that was strong enough to maintain a consistent wheel head speed, while the wheel was turning slowly, subjected to the resistance created by the weight of a lot of clay and without having to incorporate IR Comp.

So let’s get back to controllers. If you are not going to use IR Comp you are going to occasionally have to put your foot down on the gas to maintain wheel head speed. When you do this you want the power to be delivered as smoothly as possible. Think of the SSX Controller upgrade like replacing your carburetor with an electronically controlled fuel injector.

The SSX controller has more sophisticated and robust components. One of the most important of these components is it’s large capacitor. A capacitor stores energy much like a battery. Having this stored energy allows you to feather in the power when you needed it more precisely and therefor results in a smoother transition at low speeds.

For 99% of the potters out there, our 1/3 HP motor with the standard controller is perfectly satisfactory for their needs. Unless you are working with a wheel every day, making challenging pieces, you probably will not even notice the difference of any of these factors we just discussed. So, save your money for clay and just concentrate on whether you want a built-in splash pan or a removable splash pan. We will talk about that in future Blog Posts.

Share this post
Facebooktwitterpinterestlinkedintumblrmail
hot keys

Ceramic Hot Keys

hotIf you own a Skutt Kiln with a KilnMaster Controller you may only be using a fraction of the features available to you. Some of the coolest features are accessed while the kiln is firing. We call these Hot Keys. Most of these give you diagnostic information that is helpful troubleshooting your kiln or just gain better insight into the actual performance during the firing. Below is a list of the Hot Keys and their functions on newer KilnMaster Controllers (ones with green display lights):

1, 2 and 3

Skutt Ceramic Kiln Hot KeysThese keys will display the temperature reading of the corresponding thermocouple on a Zone Control Kiln. Zone Control is an optional upgrade available that places a thermocouple in each section of the kiln. This allows the controller to sense when one section of the kiln is firing too hot or too cold and make adjustments during the firing.

In a 3 section kiln, the one key will display the temperature in the top section, 2 will display the middle, and 3 will display the bottom. The controller must be configured for Zone control for these keys to work.

5

The five key will display the programmed rate of rise in degrees per hour for the active segment in the program.

7

The seven key will perform an Amp check and then continue the firing. It will temporarily stop the program, turn each relay on individually and give you the amp reading. Once all the relays have been cycled on it will continue the firing. A list of the desired amp readings for each model can be found under the Library tab on the Skutt website under troubleshooting.

Each Amp reading represents a section of the kiln starting from the top. If your kiln only has two sections the 3 reading will be zero. If one of the sections that does exist comes back with a reading of Zero, chances are likely you have a relay out. If it is reading low, it may be an indication that your one or more of the elements in that section are starting to wear out. It is a little more complicated than that so if you want a complete description on how to accurately interpret the results read the white paper on Interpreting Diagnostics under the Library Tab of the website.

8

The eight key will flash 3 decimal points representing the outputs on the control board. The outputs are what tell the relays to turn on. The one on the left will represent the top section of the kiln, the middle represents the middle section and the one on the right represents the bottom section.

This is a very complex troubleshooting tool and almost always needs to be used in conjunction with other tests to gain useful information. Most likely this test will be initiated at the request of a Skutt Technician.

0

The zero key will tell you the elapsed time since the kiln was started. This can help you estimate when to be there for the ending of the program.

View

The View key will tell you what segment of a program the controller is currently running. It will also tell you what we call the “traveling set point” and the temperature of the circuit board. The traveling set point is the temperature where the kiln is supposed to be if it were keeping up with the program.

Just because you program a kiln to fire at a particular rate to a temperature does not necessarily mean it is capable of achieving that rate. It will only do the best it can. This diagnostic feature allows you to see the actual performance. Again this feature requires advanced troubleshooting skills to extract meaningful data and will most likely be interpreted by a Skutt Technician.

The Board Temperature is a very useful in determining if your kiln room is properly ventilated. It’s kind of hard to believe that the room temperature could have much impact on the temperature of the circuit board when it is sitting so close to a kiln chamber that is 2350F, but it does.

If the board temperature reaches 160F the kiln will shutoff to avoid damaging the controller. We calculate that if the room air exceeds 100F while the kiln is firing you run the risk of getting an “E-bd” error and the kiln shutting off. Often times a fan blowing on the controller is enough to prevent this from occurring.

One last feature accessed through the view key is “skip step”. This will advance any program to the next segment in the program. To activate skip step press View then ENTER and ENTER again.

Review

Review is generally used prior to pressing Start to ensure you have entered the correct program but it can also be pressed while the kiln is firing just in case you are second guessing yourself (or someone else who may have programed the kiln).

Share this post
Facebooktwitterpinterestlinkedintumblrmail
elements

Top 5 Ways to Extend the Life of your Kiln Elements

elements Let’s face it, elements are expensive and there are plenty of things you would rather be doing on a Saturday than spending an afternoon replacing them. Unfortunately, just like the brakes on your car, you are eventually going to have to replace them. The good news is that, also just like brakes, there are a number of things you can do to extend their life. In order to better understand why we recommend certain practices it is helpful to know a little something about how elements age.

The most widely used element wire is Kanthal A-1. It is composed primarily of Iron, Cromium and Aluminum. Element life is determined by the rate at which the Aluminum oxidizes. The hotter the element temperature, the faster it oxidizes. The amount of time you spend at high temperatures (ex: slow cooling Cone 6 glazes) compounds the problem.

Whether it is a new kiln, or you have just installed new replacement elements, the first firing is critical. You will notice new elements are bright and shiny. The outside surface of the element begins to oxidize when it reaches 1832 F. The temperature of the kiln could be significantly less. The degree of temperature difference will depend on the element design, the rate at which you are firing and a number of other factors. As the element oxidizes it forms an aluminum-oxide layer around the core. The goal is to form a uniform, dense oxide layer that is well bonded to the base metal. We have found a Medium Speed, Cone 04 ConeFire program does a very good job of achieving this.

ELEMENTDEGRADATION-GRAPHICWeb

This oxide layer prevents the further oxidation of the alloy base metals by providing a barrier that resists the diffusion of oxygen into to the alloy and also prevents the diffusion of metal ions to the alloy surface. The first time you fire the element it is basically naked with nothing to protect it. If you fire the kiln empty with nothing to release damaging gases, it helps the element form a nice uniform oxide coating with minimal initial damage to the metal.

As you continue to heat and cool your kiln the element continues to expand and contract. Every time it expands and contracts, tension is formed between the the oxide coating and the base metal because they expand at slightly different rates. This forms little fissures in the oxide layer which expose the core. The exposed core then oxidizes and fill the fissures with new aluminum oxide. This both elongates the element and reduces it’s diameter.

As the core gets smaller and smaller, the resistance of the wire increases causing the element to run hotter thus compounding the problem.The net effect is a reduction in the power potential of the element.

As the element gets longer and thinner, the distance between coils becomes less. This is what is called element creep. When the distance between coil turns becomes less, the element gets hotter because the coil turns are radiating more heat on to each other. Remember that hotter is bad so this also compounds the problem.

A well designed element will ideally have the largest diameter (more core material to fill the cracks) and the largest distance between the coils (runs cooler). The heavier gauge elements also have more dimensional stability. When elements get above 1700 F they start turning into the consistency of cooked spaghetti. As they soften, the coils want to start laying down, causing the distance between the coil turns to lessen. Therefore, the thicker they are, the better they can support themselves at higher temperatures. Because of this you can also increase the distance between the coils (increase the pitch).

Okay, now that we know how elements degrade, lets look at what we can do to slow the process.

1. Choose the Right Kiln for the Job

Every kiln has a maximum temperature rating listed on the serial plate. It is the maximum temperature a kiln can achieve under “normal” conditions. This is a lot like the maximum load capacity for a pick-up truck. Just because a 1/2 ton truck is capable of hauling a bed full of gravel, it does not mean it is the best choice if you are a contractor who hauls gravel everyday, up hill, low on transmission fluid, in the Mojave Desert… you get the point. Things always last longer when you do not push them to their limits. A good example of this are 10 cu/ft kilns.

Kilns like the KM1227-3 are designed to use a common sized 50 amp plug. Manufacturers need to limit the amperage of this size model to accomodate the plug, therefore they cannot put the power into the design that they would prefer. At Skutt we offer the “PK” version of these size kilns for those people who are not restricted by this plug requirement. This would be a much better choice for artists that are consistently wanting to fire their kilns at high temperatures. One of the biggest reasons why elements last longer in more powerful kilns is because they can reach temperature faster and are not spending unnecessary time at high temperatures. If you are consistently firing to cone 6, you will be much happier with a kiln rated to cone 10

Ideally everyone would use low fire ceramics. In reality, there are a lot of characteristics (i.e crystal glazes) and properties (i.e. freeze resistant tile) that are impossible to achieve at low fire temperatures.

Cup Head System Skutt Potters Wheels

2. Keep Your Elements Clean

Road or rail vibration during shipping can cause brick dust to become airborne and settle on the elements. When you fire your kiln for he first time this dust can interfere with the creation of a good oxidation coating on the elements. It can also cause the element to run hotter as it restricts heat from escaping and burns off any combustibles. This also happens over time with just normal use. As the elements expand and contract they can loosen brick material that settle on the elements. In addition the normal dust associated with a clay studio can settle on the elements when the kiln is being loaded and unloaded. Occasionally bits of clay and glaze can fall into the element groove. These are extremely important to remove since they have the potential to completely burn through the element.

A good rule of thumb is to vacuum out your element grooves at least one a month and always vacuum out the kiln before it is fired with new elements.

3. Fire New Elements With the Kiln Empty

Just as dust is bad for the creation of a good oxide coating, so are the fumes that can emit from clay and glazes. Therefore, make sure your first firing with new elements is with the kiln chamber empty. As mentioned earlier, run a Cone 04, Medium Speed ConeFire program for best results.

4. Vent! Vent! Vent!

Even if you have the best oxide coating ever, the fumes that emit from clay and glazes can still attack the element when it expands through heating and forms cracks in the coating. Downdraft vents are your best defense against potentially harmful fumes. Downdraft vents pull the fumes from the kiln chamber before they have a chance to damage the elements. If you do not have a downdraft vent your next best option is to prop the lid a couple of inches until the kiln reaches 1000 F to allow the fumes a path to flow out of the chamber. You should also leave the top peephole out during the entire firing to handle those fumes that escape above 1000 F. Trying to reduce in your kiln will clobber their useful life and is definitely not recommended.

5. Keep the Elements Supported

We mentioned earlier that elements soften when the are heated above 1700 F (again this is the temperature of the element not the kiln chamber) and can actually droop out of a broken element groove and eventually break from elongation. Eventually this brick should be replaced but if you do not have the time you can help things by creating a little fence to hold the element in place using element pins. Usually a good time to replace brick is when it is time to replace your elements.

By following these guide lines you can easily double the life of your elements. In future blogs we will discuss the benefits of APM elements. Until then, be safe, creative and happy!

Share this post
Facebooktwitterpinterestlinkedintumblrmail