Ensuring High Value and Consistency in Furnace Refractories

To obtain 'right first time' components in any production process that uses a kiln or furnace, consistency is critical. This can apply to the atmospheric content, processing temperatures, or the overall firing process. Although the quality of the furnace and kiln infrastructure itself is important to achieve this, the appropriate selection and application of refractory products used in the process are also equally significant. The products include fired refractory shapes, kiln cars, and furniture, or high-temperature insulation systems.

The Importance of Correct Material Selection

In all cases, improper product selection or material may lead to ineffective or inefficient processing, waste of process time and energy, and even reputational damage when a crucial order deadline isn't met because of an unresolved processing problem. It is not possible to tolerate the unnecessary downtime caused by the replacement of failed materials such as insulation systems. Best practice in system design and installation and material selection will be helpful to achieve optimal productivity and system uptime, based on the amount of cycles undertaken before the need to replace the systems.

At some stage it is inevitable that some products will have to be replaced, and this could be the reason that the individuals responsible to specify and purchase the kiln insulation and furnace refractories place emphasis on achieving the lowest cost unit. However, as with so many things, a product that has the lowest cost does not necessarily have the best value. Therefore determining the best solution should always be the area of focus, rather than using the cheapest product, which may have the drawback of frequent replacement.

The cost difference between a lower-grade insulation system and a superior product is trivial in comparison with the downtime cost arising from replacements of these systems. This is an area where even modest time investment or investigation of total life cycle costs can pay major dividends.

Achieving the Best Insulation System

Insulation systems are integral components that not only maintain processing temperatures but also ensure consistency throughout the kiln or furnace and uniformity of parts. They are not only critical for processing by reducing the heat loss through the top and sides of the furnace or kiln, but also ensure operator safety by maintaining the temperature of external surfaces at a safe level and reduce energy costs by retaining more heat inside. Although natural gas costs are comparatively low now, it is not possible to guarantee the same scenario in the future. Most companies are voluntarily taking measures for carbon footprint reduction regardless of any legislative requirements to do so.

In addition to ensuring minimal heat transfer, insulation systems may also be required for resisting thermal shock in applications involving rapid heating or cooling. Corrosion resistance is another key characteristic based on the application in addition to providing flexibility and physical strength. High-temperature insulation wools, like refractory ceramic fibers (Cerafiber®) Kaowool®, alkaline earth silicate fibers (Superwool® and polycrystalline fibers or combinations of high-temperature fibers and insulating firebricks or special duty castables (Kao-Tuff®, Kao- Tab®)) can be selected based on the process. Whatever may be the solution is selected, purchasers and specifiers have to take necessary measures to satisfy themselves about the consistency and quality of the materials selected, and the integrity of the production process of these products.

In these areas, inconsistency may lead to inferior performance and more frequent replacement. Instead of simply selecting a material based on its price, it is necessary to research suppliers to ensure how their processes are benchmarked between their various facilities and establish the existence of quality plans. It is essential to know what application is being made of comparative testing techniques. If the consistency of the lining material production can be proven, then it is possible to accurately predict its performance and reliability in areas such as heat transfer, which is vital in areas demanding accurate temperature control.

To minimize downtime even further, processors will prefer to use a lining material suitable for higher temperatures than what the process will use. For example, advanced polycrystalline fibers are produced by a chemical process instead of the melt and attenuation process widely utilized for other lining materials. The polycrystalline systems have extended the lifespan up to 10 years, thanks to their superior thermal and chemical stability. Although such prolonged service life is not uncommon when compared to refractory ceramic fibers, the polycrystalline systems also deliver superior performance in applications such as heat transfer.

Meeting the Unique Demands on Kiln Furniture

The story is similar in the case of kiln furniture, which has to deliver superior performance in challenging conditions, such as the effects of rapid cooling and heating. Therefore, material selection and design is highly important. Many systems made up of different materials are available for use in lower temperature processing. However, Morgan has developed a new high-performance nitrite-bonded silicon carbide material to meet the demands from within the kiln furniture industry. This novel material is capable of withstanding elevated temperatures of up to 1,500ºC (2,732ºF).

Halsic-N™ is a material from Morgan that exhibits superior strength, better refractory properties, and excellent oxidation and thermal shock resistance characteristics by combining the properties of established materials such as silicon nitride (Si3N4) and silicon carbide (SiC) in a microstructure. Setter plates, supports, and beams are the standard designs while it is also possible to fabricate components in accordance with individual customer specifications. Thermocouple protection tubes fabricated using the Halsic-N™ can be used for melting non-ferrous metals like magnesium and aluminum, thanks to its strong metal-repelling properties that ensure optimized performance and extended service life. Halsic-N™ has a flexural strength of 160 MPa and can be applied with a specially formulated coating for firing technical and porcelain ceramics.

The Shape of Things to Come?

Employing the best practice is equally as important, even in the case of fired refractory shapes. Although these products are typically used only one time and therefore, need to survive a single firing, they should also have strong thermal shock resistance characteristics to meet the requirement of subjecting to rapid heating and cooling. High-cost cast metals and superalloys are increasingly used for this purpose. Therefore, the loss of material due to failed consumables is completely unacceptable considering the involvement of the high material cost.

Material quality is also equally imperative. It is necessary to maintain the oxidization of consumable products to an absolute minimum even under high-temperature firing in order to avoid material contamination during processing, highlighting the significance of ensuring the purity of consumable products. The raw material sourcing and production processes of suppliers need to be thoroughly studied by spending adequate time in order to achieve the required material quality.

The Best Options for Inert and Vacuum Furnaces

Purchasers and designers have to consider the same factors that are necessary for ceramic furnace consumables when it comes to high-temperature inert and vacuum furnaces to address the similar challenges posed by these systems. They are ultra-high temperature furnaces with the ability to achieve temperatures up to 3000°C (5,432°F). It is extremely important to design the appropriate insulation solution of graphite or carbon felt, and graphite or carbon rigid board because the cost of these heat treating processes is an important factor in the development of cutting-edge technologies, such as semiconductor and solar products.

Many different standard materials are available to meet the specific requirements of these applications. It is possible to improve most of these materials using different methods, providing additional options for the process or furnace designers. For example, it is possible to specially design felt products to deliver extended service life or improved insulation performance.

Morgan offers a range of rigid board products, including a standard material and a low thermal conductivity material, RGB-LTC, to improve energy efficiency across a range of applications. It is possible to apply specially designed coatings for reduced friability and improved life for use in adverse conditions. The insulation purity is also an important characteristic for product performance. It is also possible to supply with different levels of purity, providing more options for designers. Selecting a specific solution to address a specific problem is essential for the purchasing company to achieve the best cost of ownership regardless of the application or requirement.

System design and product specification are not the areas where processors should feel of their own. The major manufacturers of these systems are committed to being more than just suppliers and are working in close cooperation with their customers, gaining knowledge about their individual application requirements and assisting them with system design. Based on this knowledge, they will suggest and provide the most appropriate consumables, whether they are standard products or custom-made products that need to be created on a bespoke basis. They will even collaborate with installers to ensure best design practices and to prevent problems such as poor sealing around doors, an issue that is capable of rapidly offsetting the investment made in a top-quality product. A good installer will help to ensure the optimum output that can be obtained from the product chosen. In particular, consumables should not be considered as commodities as they are critical tools without which it is not possible to achieve effective processing.

This information has been sourced, reviewed and adapted from materials provided by Morgan Advanced Materials.

For more information on this source please visit Morgan Advanced Materials.


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