We have gained a lot of experience working with electric kilns including benchtop, top loading and front loading models of all ages. If you are looking to develop or refurbish your kiln we have the knowledge and products to assist you. Electric kilns are widely used in ceramics/pottery, jewellery, metalworking and glass making. Here we share some of the commonly asked questions, problems and solutions when working with electric kilns of all sizes.

How Do Electric Kilns Work?

Electric kilns come in various sizes to suit the type of product being loaded and the available electrical supply. All kilns will require a temperature controller to maintain a stable internal temperature. Older kilns may contain analogue controls, KilnSitter cones and other basic thermostatic devices. A modern kiln will come with a microprocessor based temperature controller capable of maintaining an extremely stable setpoint. Other electrical parts typically required would be solid state relays, elements and a temperature probe/thermocouple. Along with this are some important safety components including circuit breakers or fuses, isolator and overtemperature device.

Figure 1 - Small Benchtop Kiln Prior To Novus N20K48 Upgrade 

One single heating element or a number of individual elements may be used. The elements can be configured for single or three phase supplies. The number of elements and their resistance will define the total KW output of the oven. 

As the elements warm up, the air inside the kiln begins to heat and rise by convection. This action causes the air to circulate inside the kiln. The temperature of the bricks will also rise via conduction from the elements. As the process continues any materials inside the kiln will start to emit heat.

The principle of operation for the user should normally be kept as simple as possible. Turn on the kiln, check the setpoint and run a program if appropriate. The temperature controller will read the internal temperature and continue to apply power to the elements until the setpoint is reached. Different materials or heat treatments may require more advanced functions to achieve the desired end product. We recommend our N1050 and N20K48 models for the majority of kiln applications because they support Ramp & Soak programming. Although you may not need this function immediately it is wise to consider future changes in materials and temperature profiles.

A typical ramp and soak cycle might work as follows:

• Turn on the kiln
• Wait for initial setpoint to be reached
• Enter a program number
• Program executes through a number of steps or segments
• Each segment has its own target temperature and time duration
• Program ends, kiln will cool down
• Different program numbers represent alternative temperature cycles

Figure 2 - Novus N1050 Autotuning (Retrofitted To Kiln)

Considerations When Upgrading Electric Kilns

There are some important design considerations which can save downtime in future and ensure your oven runs optimally:

• Siting electrical controls - although some kilns have built in controls it is is important to consider the temperatures involved and the nature of the material being heated. For larger kilns we prefer to see a dedicated electrical control panel mounted separately to the kiln. This gives good access to the control system but helps to avoid some of the issues associated with heat and fine particles
• Choice of components - we sell Novus controllers with a 3 Year Warranty. There are many temperature controller suppliers on the market. Our main recommendation here is to use an established brand which meets CE or other internationally recognised standard. A cheap unbranded controller is not going to give many years of service and may also lead to more serious issues. The investment here is small, our N1050-PR is under £100.00+VAT and comes with Ramp & Soak programming facilities 
• Solid state relays - SSRs are an important part of the process as they are switched by the controller to apply power to the elements. This switching can occur very quickly to ensure the temperature does not overshoot. PID temperature control is covered in depth elsewhere but the role of the SSR should not be neglected. SSRs generate heat and are the number one cause of failure on the powder coating ovens we see. If the SSRs have been appropriately rated, installed and ventilated you can expect very few issues. Read on to see some of our tips for a successful oven build
• Rating of cables and components - it is crucial to consider the cable type and current rating is appropriate. This is true for all of the internal connections as well as the main supply to the oven. The use of MCBs and fuses will only be effective if some basic calculations based on the element sizes have been carried out.
• Thermocouple Type selection is important - certain temperature ranges suit different Types of thermocouple. Think about the maximum temperature you wish to operate the kiln at and make sure the thermocouple is suitable.
• Think about safety - there are some basic questions which can avoid potential dangers such as: Are all materials suitable for the temperature involved with a margin of safety? What happens if the temperature control fails and the kiln overheats? What happens if one element or SSR fails? We also recommend the use of appropriate ventilation to deal with any fumes generated

Figure 3 - Larger Front Loading Kiln Prior To N20K48 Upgrade

On the above image note the additional measures of a dedicated additional controller for overtemperature monitoring and the door limit switch. The door switch will remove power from the elements to make sure the kiln only operates with the door closed. 

Tips For Upgrading Electric Kilns

There are many mechanical design considerations when building a new kiln. Here we share our best tips for electrical design which can be applied to new or old kilns undergoing refurbishment.

1. Build a dedicated electrical enclosure to house the temperature controller, solid state relay and other electrical components. This enclosure should have a single point of electrical isolation for the kiln. If this is not possible use quality insulation and air gapping to ensure the electrical controls do not overheat
2. Ensure all cables are appropriately sized for the electrical loads required and are of the correct type for the temperatures they will be exposed to
3. Choose branded components, they don't need to be high end or leading brand. But if your kiln is going to be reliable you will need to make a modest investment
4. Dissipate heat from SSRs. Check they are oversized for the electrical load, mounted to a heat sink with thermal paste. Running a 40A SSR at full load with no heat sink is a recipe for disaster
5. Fit an overtemperature device. This can be a mechanical or electrical device that will interrupt the supply to the elements in the event of a maximum temperature being reached. This should function independently of the main temperature controller
6. Consult professionals. If you are unsure about how to wire the oven controls speak to us or find an electrician who is able to assist you. We have our own sample wiring diagrams which can be used as a starting point when planning a new build or modified controls

 

Figure 4 - Novus N1050 Prewired For Customer