Refractories Primer: 3 Things Every Plant Manager Should Know
If you’re new to refractories, there are a few important things to know before you begin making product selections or installation decisions.
The term “refractory” refers to a variety of materials that are non-metallic and heat resistant. Refractories are used in a number of heat processes and in different types of industrial equipment, including boilers, furnaces, ovens, kilns, gasifiers, incinerators and dryers. Not only must refractories withstand significant stress caused by heat and chemical attack, but also be able to contain substances at high temperatures.
Refractories can be a substantial investment, either in new construction or repair work. While refractory work may only be a small portion of your construction project, these materials protect your expensive equipment, keep production online, and provide personnel safety. Their value is far greater than their cost assuming the correct materials are chosen and installed properly.
Below are three facts every Plant Manager should know about refractories.
Think about the average and peak temperatures in your manufacturing processes. Refractories are used with heating applications that generate temperatures over 1000°F all the way up to approximately 3000°F.
This leads to three different classifications of refractories based on temperature:
- Normal refractory – These are typically fire clay and are used for temperatures up to 1780°F, which cover processes such as melting aluminum
- High refractory – These are typically cromite-based refractories for temperatures from 1780 – 2000° F, which cover processes like melting copper
- Super sonic refractory – These are typically zirconia-based refractories for temperatures greater than 2000°F, which cover processes like melting iron
2. Chemical Composition and Resistance
Refractories also have to be resistant to the chemicals that will be released during the manufacturing process. There are many different types of materials that can be utilized in combination with one another to create refractories that can stand up to various chemical processes.
Refractories are always going to be nonmetallic, as metallic refractories are not able to stand up to the high temperatures that most refractories must undergo. Natural materials are most commonly used, but synthetic materials can be added to the blend.
Careful consideration must be given to the chemical interaction between the refractory and the other materials being heated, since chemical breakdown in a refractory can cause catastrophic failure.
- Acidic refractories aren’t affected by acids and consist of acidic materials such as silica, alumina and fire clay. They are affected by basic materials though.
- Neutral refractories are used when the slags and atmosphere are either acidic or basic and they need to be chemically stable to both acids and bases. Alumina (Al2O3), chromia (Cr2O3) and carbon from the R203 group are typically used in neutral refractories.
- Basic refractories are used where the slags and atmosphere are basic. These are stable to alkaline materials but could react with acids. Magnesia is a very common example, along with dolomite and chrome-magnesia.
3. Size and Shape
Refractories come in many different shapes and sizes and are dependent upon how they are going to be used. Typically, refractories are going to be built using one of three different types of refractory materials:
- Bricks are going to be utilized in most furnaces
- Fiber blanks are used for linings
- Monolithic refractories are shaped depending upon how it is going to be used
Science + Art
While there’s a tremendous amount of science behind the matching of refractories to production processes and installation methods (which is discussed in more detail here), we’d like to think that there’s some art involved as well.
For example, many large companies end up with custom refractory ingredient combinations created specifically to provide the right protection for their particular application. Refractories have come a long way in the past few decades due to years of research and scientific progression, and optimizing refractory performance has become important for manufacturers’ bottom lines.
If you own a small to midsize production facility, or are a part of an engineering team for an international corporation, we can guide you through these advances and show you how to find the best solution for your refractory application.
Feel free to contact us to start a conversation.