25 August 2017

What’s the difference... Kilns vs. Furnace vs. Oven?

Proper heat treatment is an essential part of knife making, tool and die work, and parts fabrication. Without precise control of time and temperature, blades won’t hold their edge, and tools and parts may be too soft or too brittle for use. Buying a heat-treating kiln, oven or furnace can be a complicated process, but our job is to make it easy to navigate the decisions involved in finding the right one for your needs. Here’s some basic information to help you decide which is the best choice for your professional or hobby needs.
So, what is the difference?
For our purposes, all three of these names refer to a fireproof box that gets hot. No matter what you call it “the box” needs to have the capability to get to the desired temperature and stay there for the prescribed amount of time. It also must to have the ability to heat and cool at the prescribed rate for the particular process required. Most importantly, it must be safe and easy to operate, and last a long time. 
Kiln: associated with the manufacturing of pottery, glass or ceramic ware. These are typically fired from room temperature to a specific process temperature at a prescribed rate of increase and then allowed to cool at a controlled rate back to room temperature. The rate of increase (or decrease) during the firing and cooling stages is often of great importance. Items being fired are seldom removed from the unit while it is performing. There may be periods of time when the temperature is held during the firing but the hold time relative to the total firing time is usually insignificant. Temperatures range from 1700° F – 2350° F. 
Furnace: associated with forging or heat treating metal. These are typically HELD at a single temperature for an extended period of time. The exact rate of temperature increase during the heating stage is seldom of importance.  Items being fired are often added to or removed from the furnace when the unit is hot. There are typically long periods of time when the temperature is held during the firing, and there may be multiple cooling steps and hold times for processes including annealing, case hardening, and tempering. Temperatures range from 2000° F – 2450° F.
Oven: associated with drying or cooking, are the same as furnaces except the usage temperature range is lower. The lower temperature rating often means a large chamber can be powered with lower amperage. Temperatures range from 250° F – 900° F.
It really doesn’t matter what you call it…. As long as it does what you need it to do. From this point forward, we’re going to refer to all the options as KILNS. What you really need to know is how much space you need, what temperature do you need to get to, and how long does it need to hold at that temperature. Here is a link to a guide that you can use as a reference: The Heat-Treating Data eBook.

Now, that we have that figured out...  you need to think about:
What size do I need? A basic aspect to consider when choosing a kiln is its interior dimensions. Kilns for making knives are considerably smaller than other types of kilns because of the smaller size of the average project. Kiln size reduction helps to reduce costs as well as improve heating times. Determine the size of the largest blades you intend on creating and make sure it can fit inside your chosen kiln. It also depends on how big you want to work. There’s nothing worse than buying a kiln that you outgrow in 6 months. Think about the future and what you might grow into.

What temperatures do I need? Necessary temperatures are determined by the type of metal you work with, so make sure of your own requirements before buying a kiln. Check the above reference guide if you still have questions on heat treating temperatures.
What amperage does the kiln need 120V vs 240V and how many amps will the unit draw? Based on the size of kiln and top heat requirements, each kiln’s voltage requirements and amperage needs vary.

12-Key Controller
What type of controller do I need? A kiln controller is the brain that tell the kiln what to do, and when to do it. They range in simplicity, ease of operation, and price. Most of our heat-treating kilns have a variety of controller options that are determined by the manufacturer. Not all controllers are available through all manufacturers.

What safety features should I look for? All heat-treating kilns we sell have available door shut off devices cut power to the elements but leave the digital controller energized to resume the firing program as soon as the door has been closed. Check to see if your model has these included or if this is an add-on option.
Finally... the MOST important question. Which kiln series should I purchase?
Evenheat HT-1
The Artisan, Cubed and HT Series... The Artisan 688 is perfect for small, pocket folding blades. The Ten Cubed is larger and also designed for folding blades. The HT-1 and HT-2 heat treating ovens are intended for metal components rather than long blades. Check the electrical needs and top temps to ensure you’re getting exactly what you need as these models can vary.

KO Series... These kilns are for those needing even higher temperatures. This series has thicker wall insulation which allows the kiln to reach temperatures of up to 2400° F. The 240v requirement makes it perfect for machine shops and very ambitious hobbyists. Read more about our most popular KO heat treating oven, the KO-22.5

Evenheat KO 22.5
KF Series... These kilns have a top temperature of 2200° F but offers more capacity than the KH series. Our bestselling heat treating oven, the KF-18, has twice the interior dimensions as the KH-418 and three times that of the KH-414. Running on 240v, it’s perfect for small machine shops and the more ambitious hobbyist. The KF series represent our most popular sellers. 

KH Series... These kilns are perfect for hobbyist knifemakers working out of a residence. Running on standard North American 120v and using a standard household plug, it can be set up anywhere in the home. Despite its low weight and smaller interior chamber, KH series ovens can heat up to 2200° F. Read more about the KH-414 and KH-418 series, our most popular KH heat treating ovens. 

PMT Series… These kilns have swing doors and are available in both 120V or 240V models depending on size... from the PMT-10 to the PMT21. The PMT series is rated to 2350°F.
KM and PKM Series… These kilns have drop down doors and are available in single width or double barrel width, and are available in both 120V or 240V models depending on size. The KM-series kilns like the KM-24T are long and narrow, ideal for knives.

Last but, not least... What accessories or options do I need?

Mechanical vs. Solid State vs. Mercury Relays
Relay upgrades are another important safety and convenience item to consider. If you don’t already know, a relay is the part of the kiln that controls the power or current to the element, allowing the element to either receive current and get hot, or to interrupt the circuit thus not allowing the element to receive current and cool down. The mechanical relays, which come standard on all kilns, are what is responsible for the ubiquitous opening and closing clicking we hear while our kilns run.

ALL MECHANICAL RELAYS in U.S. kilns are virtually the same... no matter the manufacturer. 
Solid State Relay
Mechanical relays have a life of up to “X” clicks and then they fail. We know that all failures stink and that is why we recommend changing your relays every 12-24 months. If you are a heavy kiln user, you should be smart and change your relays once a year. If changing relays this is something you don't want to hassle with, you can eliminate the problem by upgrading to mercury or solid state relays and almost never (they last up to 15 years) have to change a relay again. In our opinion, it's one of the best upgrades money can buy!
Drop Door vs. Swing Door vs. Guillotine Door
Check which door is available for the kiln you choose. One door isn’t “better” than another, it just your preference for ease of access to the items inside the kiln. Drop doors facilitate the removal of items from the hot kiln so that the door does not impede access.  The drop door requires a single action of a counter-weighted hand control mounted to the left of the kiln chamber.  A safety chain prevents the door from opening too far and stressing the hinge assembly. A Guillotine door is an alternative to the drop door and slides up versus folding down. Swing doors open side to side to facilitate access to the items in the kiln.


Orton VentMaster
Downdraft Kiln Vent
This is typically used for specialty industrial heat treating processes as well as specialty burnouts for diesel engine parts, so for a hobby knife maker, this is likely not something you’ll need. Depending upon what type of metal you are heating and the ventilation of the area you are in, it may be useful to vent the kiln away from your work space due to gases produced from industrial products fired in the kiln.  As a side benefit of venting, the increased flow of atmospheric oxygen may improve reactions within the kiln.

Gas Injection Flow Meter
This is typically used for specialty industrial heat treating processes, so for a hobby knife maker, this is likely not something you’ll include in your purchase. Gas injection can be very important with heat treating metal to prevent oxygen scale from developing. Oxygen in the furnace forms a scale on the surface of knife blades and other parts during heat treating. To avoid surface scale, wrap the parts in
Glass Flow Meter
heat treating foil or inject an inert gas into the furnace. The gas displaces the oxygen. Please note that the gas may reduce heating element life. Also, gas injection does not offer better results than heat treating foil nor does gas injection prevent all scaling. The main benefit of gas injection is the savings in time over wrapping the steel in foil. The flow meter can be ordered with an optional solenoid kit, which enables you to turn the gas on or off for each segment, or stage, of the firing.

Hope we didn't overwhelm you with too much information... If you still have questions, as always... just give us a call!