With so many options available in the commercial kiln and industrial oven marketplace, how do you go about determining which insulation material is ideal for your application. Is it just a matter of temperature that you need to reach? Or do you look for longevity of material? Is cost a consideration? How do you know what's what if you're just beginning to make a purchase?
We've put together a top line view of the subject; FIBER VS BRICK
Industrial kilns are built in many of configurations with one underlying tenet your unit must generate and hold heat. With that as the baseline, there are two refractory insulation materials that are used accomplish the task; fire brick and ceramic fiber. Both materials will get the job done, with pros and cons! Here's what you need to know.
Why is Brick GREAT?
Kilns and ovens built with brick will hold heat longer, period, end of statement. After accepting that fact, then we can look at the types of brick; Refractory, Insulating, and Specialty. For the sake of our conversation, we'll be discussing Insulating Brick, as that is what most commercial kilns and industrial ovens are built with. In general, the denser and the thicker the brick, the more time the brick will retain the thermal energy (heat). Only you can determine if this is positive or negative based on your needs for each project. A denser, higher-rated brick maintains temperatures better, thus utilizing less energy to do the same job. So, there is a Pro in the utilization category. This is good if you are require longer soaks, longer annealing times, and slower cool downs. The Con is that if you are trying to produce a lot of work quickly and want to turn over multiple firings (kiln cycles) in a short time, you are not going to fare so well.
Additional issues when deciding to purchase a brick kiln are durability, and cleanliness. Brick kilns are durable, but only if they stay in place and are not moved. Moving insulating brick can cause it to crack and crumble due to the porosity of the brick and its compression structure. If the unit needs to be shared by multiple departments or moved from workshop to workshop within a plant, the weight of the brick, and potential of cracking might make brick construction a poor chose.
Brick kilns are typically made in components or slabs that are cemented or mortared together, the more you move a brick kiln; the more you will weaken those seams and produce cracks, which over time could compromise the integrity of the kiln’s body. These cracks can be repaired easily, but continual breakage can be a sign of an untrained staff or a mismatch of a tool for the intended use.
Finally, an added issue is cleanliness in the workspace. Depending upon the project requirements and what your workspace necessitates keeping the project area as clean a possible can be a concern. Brick, as it ages without proper care and attention, may show fatigue and become cracked. This is due to the thermal expansion and contraction during multiple continuous heating and cooling cycles. This action causes the bricks to flake off small sand-like pieces of material which can leave debris in the workspace or on your project materials. This is prevalent on roofs of front loading units and lids on top loading units. A soft brush attachment on the shop vac with a hepa filter can help prevent some of this mess.
This chart gives a good example of the types of insulating brick used in industrial and commercial kiln production.
Why is Fiber GREAT?
In the commercial and industrial environment kilns and ovens made with ceramic fiber have been a staple because of the numerous advantages they deliver to owners and operators. Common names for Refractory Ceramic Fiber (RCF) are Unifrax, IsoFrax, FiberFrax, etc.
Let's start with the benefits of high temperature resistance; Ceramic Fiber (rigidized or raw, blanket or board form) can withstand very high temperatures, making it appropriate for higher temperature applications. When you couple this advantage with the fact that the material is lightweight and flexible, you get both of these benefits and you can have multiple configurations with less weight and more heat. A lighter kiln/oven may be necessary in buildings that have flooring load concerns, for example loft spaces, pier and beam construction, or elevated construction sheds, etc. Larger brick units may be weight prohibitive for the required size needs, whereas fiber may deliver the needed size without the weight issues.
Units made of ceramic fiber having lower thermal conductivity will heat and cool faster than brick kilns. So, the Pro is that a fiber kiln/oven is great for producing a larger volume of work more quickly. FAST turnover! Your team is not loosing time waiting for the bricks to lose their heat, because the material needs to be loaded at a cooler temperature. The Con is that if you plan to produce a lot of very thick, dense work that requires a controlled cool down, a fiber kiln may not be the best choice over brick as it will naturally cool too quickly, requiring you to use more power to keep up the temperature requirements. If you are going straight to a quench, this isn't a concern, and fiber just might be for you!
Ceramic fiber is generally resistant to chemical attack and corrosion, making it ideal for use in harsh environments. Although raw ceramic fiber is soft to the touch, it is able to be rigidized for added strength which many manufacturers do as part of the production process. Ceramic fiber is a long-lasting and durable material that can be used to build larger industrial kilns at a lowered cost. A fiber kiln will remain cleaner due to its extruded construction, and lack of joint expansion. The fiber can be easily replaced in blanket or rigid sheet/board form making a repair or rebuild less time constraining when necessary. (Due to the accumulation of Free Silica, never remove used RCF without a NIOSH approved respirator for mineral dust.)
Ceramic Fiber Board
THE BEST OF BOTH... Most manufacturers create models that have the best of both materials; brick bodies lined with fiber insulation or roofs/lids. This hybrid approach delivers the best in thermal performance as far as holding in heat without keeping so much in the unit that it will take forever to cool down. Different levels of insulation can be achieved by using different ratings of brick with different thicknesses of fiber board. The design engineers know how to get the ideal firing profile you need in the right amount of chamber space to tackle your size and weight constraints. Just ask us and we'll steer you in the right direction.
This overview of the Brick VS Fiber discussion goes hand-in-hand with other decisions you'll need to make when choosing the specifications of which industrial oven / commercial kiln is the right choice for your application and environment.
As always, feel free to reach out to our experienced team with questions or comments. We're always here to help! Give our technical team a call at (210) 446-9979 or email us at customerservice@heattreatnow.com
Firebrick Image By: SmartHouseColony
