The Basics You Need to Know About Refractory Coatings

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Refractory materials are substances or minerals that have high melting points, and they are difficult to fuse except at very high temperatures. They are processed at high temperatures and are intended for high temp applications. According to the Committee C-8 if the American Society for Testing and Materials (ASTM) refractoriness has been defined as, "the capability of maintaining the desired degree of chemical and physical identity at high temperatures and in the environment and conditions of use."


Characteristics


A refractory coating on the core or mold should have the following characteristics:

  • Sufficient refractory properties to cope with the metal being poured

  • Good adhesion to the substrate to prevent spalling

  • Be permeable to minimize air entrapment

  • Be fast in drying

  • No tendency to blistering, cracking or scaling on drying

  • Good suspension and remixing properties

  • Minimize core strength degradation

  • Provide adequate protection against metal penetration

  • Good stability in storage

  • Good covering power

  • Good application properties by the method chosen

  • Leveling well and minimizing runs and teardrops 


In order for a high temp ceramic coating to achieve these characteristics, the coating must consist of:

  • Refractory filler

  • Liquid carrier

  • Suspension agents (Rheology control system)

  • Binder agent


The melting temoerature of refractory matierals is an important characteristic, showing the maximum temperature of use. It represents funamental points in phase diagrams used in high temperature chemistry, metallurgy, ceramics, etc.


When it comes to high temp ceramic coatings, refractory materials are dispersed in the binder and constitute the skelton of the coating film. The increase the viscosity, density, and hardness of the coating film in order to reduce permeabilty. 


Characteristics: cont:


Besides the characteristics that resist high tempertaures, refractory materials should exhibit other characteristics too. These include things like:

  • Suitable for particle shape, particle size, and partical size distribution

  • Chemically inert with molten metal

  • Not be readily better by molten metal

  • Not contain volatile elements that produce gas when heated

  • Heave consistent cleanliness and pH

  • Be compatible with new chemical binders as they develop


Benefits


Using refractory coatings have many benefits, including: 

  • Reduce or eliminate metal penetration

  • Reduce or prevent “burn-on”

  • Prevent erosion of sand by molten metal

  • Smoother surface finish

  • Improve overall casting quality

  • Reduced scrap

  • Lower cleaning costs


When it comes to high temp coatings, ITC 100 refractory work wonders for many applications, including kilns. The earliest known kilns date all the way back to 6,000 BCE; they were capacle of firing up to 1,652 degrees Fahrenheit (900 degrees Celsius). These refractory high temp ceramic coatings would have worked for kilns back then, and they certain do well with the kilns of today.

Justen Womack