Forge Building And Lining Info FAQ
Q: How many burners do I need to heat my forge?
A: The amount of, and size of burners you need is dictated by the size of your finished forge chamber volume in cubic inches. Forge burners are not like cylinders in a car engine, meaning that more, isnt always better. If you install too many or too large of a burner in your forge it can create backpressure issues that will effect burner operation causing poor running issues. As rule of thumb, a single decent running 3/4" forge burner will heat 350 cubic inches of properly insulated forge chamber to forge welding heat.
Q: How thick does my ceramic fiber insulation need to be in my forge?
A: For most forges, 2" thick is the recommended minimum thickness. This can be achieved either by using a single layer of 2" thick ceramic fiber blanket, or using two layers of 1" thick ceramic fiber blanket. It is recommended to go with the two 1" layers, especially in smaller forges. It is easier to roll up and fit the 1" thick layers through a smaller opening. Another helpful reason to use two 1" thick layers is that it makes relining a little cheaper when it's time to do so, because you can replace just the inner most layer of blanket rather than both.
For ribbon burner forges 3" thick is the recommended thickness this can be achieved using a single 2" thick layer and a 1" layer or three 1" thick layers.
Insulating beyond 3" thick using ceramic fiber blanket isn't really needed.
Q: Can I cast my liner and skip using ceramic fiber blanket to line my forge?
A: Yes you can, however a forge with a casted liner is usually very inefficient. The liner becomes more of a heat sink much like dense firebrick and makes high temps needed for forging/forge welding much more complicated if not impossible in some instances.
Q: Can I line a forge with firebrick?
A: The answer to this question has a few answers. Yes, you can line a forge with soft insulating firebrick. I would recommend using a brick with a 2800°f temp rating.
I would not recommend using hard (dense) firebrick to line your forge. Dense firebrick is a heat sink. It will take a lot of fuel and time to heat and will not allow you to reach your forges full heating potential, and in some instances makes forge welding temps impossible. Any cost saved using this material is lost in fuel use.
Q: Can I apply castable refractory to firebrick?
A: Again this question has two answers.
You can apply castable over soft firebrick. However you can't coat hard firebrick. If your using hard split firebrick as a floor in your forge, I would urge you to make sure your bricks are accessible and replaceable as they are a comsumable and will need to be replaced as needed.
Q: Do I need to rigidize the ceramic fiber blanket in my forge?
A: The short answer is Yes.
Rigidizing the blanket does a few things. First it will help stabilize the blanket fibers. Rigidizing also firms up the blanket, making application of the refractory easier. Another helpful attribute is the waterproofing qualities rigidizing the blanket provides. A lot of castable refractories allow very little moisture in the mix, so having the wool rigidized prior to castable application will stop the wool from sucking up what little moisture there is in the mix.
All that said, Rigidizing the ceramic fiber blanket is not required before application of castable refractory.
Q: What Angle should I place my burners at?
A: Burner placement angle is a long debated subject with many schools of thought. In reality you can place your burner anywhere from 0°-90° on the shell.
In a square or rectangular forge 0°(Top dead center) is most common. Some commercially built forges enter the forge at TDC but have angled burner tubes. Bending the burner tubes on a home built forge is not needed. Using a design with a air choke that can be closed will help with the chimney effect that is caused by burners mounted in this postion, however they will still get hot at shut down of the forge. It is recommended not to use a rubber propane hose directly connected to the burners. It is far safer to use hard piping methods to a location that moves the hose connection to a location that it will not be damaged by heat from the forge.
In a round body forge, the most common placement of the burners is 15° off top dead center. This position will help relieve the chimney effect when done forging, but it is recommened to close the air choke at forge shut down.
Some round body forges use a 90° from top dead center burner placement. Bladesmiths that want to avoid hotspots in forge chamber for more even heating are most likely to choose this placement. However there are advantages to having a hotspot for certain applications.
Q: How far apart should my burners be?
A: The quick answer to this question is 3"-4" center to center placement, but you should base your burner placement on the your shell length. Example: if you have a forge shell 16" long and your insulated forge chamber volume dictates that you need (3) 1/2" burners to heat it, you would then set your burners at 4" centers to evenly space them across the length of your forge. From the end of the forge chamber you would measure over 4" and make a mark. Then from that mark, measure over another 4" and make a mark. Then from that second mark measure over another 4" and make a mark. You should now have 3 marks that are 4" apart on center. These marks represent your burner center placement.
Q: How far should my burners be inside the forge.
A: The end of your flare should be recessed into the ceramic fiber blanket a minimum of a 1/2" however 1" is better. Keeping your flare out of the forge chamber space will help it stay much cooler and last a lot longer. Also doing so will help your burners run more stabile throughout the pressure ranges. Keep in mind that flares are consumable and will need to be replaced in time so you should keep an eye on them for damage/corrosion and replace when needed.
Q: What type of regulator do I need?
A: You will need a high pressure adjustable regulator. If your running a single 1/2" burner then a 0-20 psi adjustable regulator will be fine. For two or more burners or if running a single 3/4" I would recommend using a 0-30 psi adjustable regulator. Use of a fixed psi regulator like those used for bbq's will not work for a forge burner.
Q: Should I use compression fittings to plumb my burner fuel lines.
A: While many forges are being built/sold using compression type fittings, this is not a safe practice. It is recommended to use gas rated flare fittings for all gas connections. They are self sealing and do not require the use of sealant tape or pastes.
Q: I bought a small forge inexpensive forge from an auction site and it came without any coating, do I need to coat the wool with anything?
A: Yes, you will need to coat the ceramic fiber blanket before use for a few reasons. Safety is the main reason for doing so. Free silicas are formed when ceramic fiber is superheated at or beyond 1500°f, these particulates are unsafe to inhale. The best course of action is to coat the ceramic fiber to isolate these from becoming airborne. Another reason to coat the wool is to prolong the life of your insulation. Ceramic fiber blanket is not designed for direct flame contact and will quickly degrade and fall apart when exposed to conditions within a forge chamber. It is recommended to first rigidize the wool, and then coat with either castable refractory or a refractory coating to act as a flame face within the chamber.
Q: Can I just apply rigidizer to the ceramic fiber blanket instead of using castable refractory?
A: No. You'll need to apply either a castable refractory coating or a refractory coating. Rigidizer, like ceramic fiber blanket, is not designed for direct flame contact. You must apply a flame face material. Doing so also helps protect the insulations from abrasion and use damage while using the forge.
Q: How thick do I need to apply the castable refractory?
A: A 1/4" thick coating is generally good. You can coat the bottom of your forge thicker if you like. If you do so would recommend no more than 1/4"-1/2" if your using split brick or kiln shelf floor on top of the castable. 1" thickness max if not using either.
Q: Will flux damage the castable refractory?
A: Yes. Flux will damage castable refractory. Some more than others. Greencast94 is the most flux resisant castable we carry if your going to be doing a lot of forge welding or are building a ribbon burner forge, we recommend using it to cast your floor. We do not recommend using Greencast94 to coat the sides or top of your forge. Use kastolite 30 for this instead.
Q: Im having trouble getting the castable to stick to the ceramic fiber, any tricks you can tell me?
Some castable refractory can be a pain to apply vertically or overhead horizontally. The best way to apply it is to rotate the forge as you work so that your always working with gravity, rather than against it. It's also a good practice to follow, because what happens when the forge isn't rotated, is the lower potion of the forge ends up coated thick enough, but the sides and top gets coated considerably thinner. Be sure to plan your forge build to be done in this manner
Q: I found some refractory at a big box store that says its good up to 2200°f , can I use this?
A: Unfortunately it won't hold up to conditions within a forge. Most big box store refractory is actually furnance cement. It isn,t designed to be used as a stand alone coating. What usually happens is as soon as you fire the forge, the furnace cement will bubble up and fall off in chunks. The temp rating also isnt high enough to withstand conditions within a forge. A forge will easily operate daily at or above the max temp rating of this material. Generally max temp ratings are for intermitant use. The continous use rating is much lower.
Q: I watched a youtube video where a person used plaster of paris and sand to make a homemade refractory, will this work?
A: Unfortunately, no. In a short time the plaster of paris and sand mix will fail. Plaster of paris has a max temp rating of 1200°f. While there are many videos on youtube and posts on social media showing the use of these homemade refractories, you will rarely see follow up posts showing the longevity of the material. Some will say that they have used plaster of paris and sand as refractory and say it's holding up great. But in reality, if it is holding up for them, their forge or furnace isn't getting hot enough.