Roger Smith

A Better Way To Get Things Done: Refractory Insulation

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, INSULATION TECHNICAL CONTENT, Manufacturing Heat Treat Technical Content

The faster the refractory installation, maintenance or repair, the more efficient and, by extension, profitable it is to the company, as savings fall to the bottom line. In this Technical Tuesday installment, Roger Smith, director of technical services at Plibrico Company, LLC, examines the challenges of insulation systems, taking a closer look at ultra-lightweight refractory gunite as a fast, flexible solution to controlling heat.

This informative piece was first released in Heat Treat Today’s February 2025 Air/Atmosphere Furnace Systems print edition.

Manufacturers that rely on industrial grade furnaces, boilers and incinerators to produce their quality products are always looking for ways to improve. It is how they stay relevant and, more importantly, profitable. But you don’t get better just by desiring it. You need to identify better ways to get things done and introduce risk-neutral change to current operational processes. By some estimates, inefficient processes can reduce a company’s profitability by as much as one third.

Given refractories’ importance in safeguarding an operation’s multimillion-dollar thermal-processing equipment, and to avoid unscheduled downtime, it is smart business to have a sustainable maintenance and repair process in place. When a refractory situation does arise, the more proficient the process solution the better.

Controlling the Heat

Click the image above to read Roger Smith’s column on extending the life of refractory linings.

Furnace design is largely about controlling heat to maximize energy efficiency. An energy source — whether that is gas, coal, wood or electricity — is used to heat the furnace, and the furnace lining is designed to keep that heat inside the furnace. There are other factors to be considered, such as the environment inside the furnace, whether there is any abrasion or chemical interactions, or whether the furnace maintains a steady state temperature or undergoes temperature cycles. Regardless of what considerations have to be made for the hot-face lining, an insulation package must be used to reduce fuel consumption and control the cold-face temperature.

There are a large variety of insulation packages and materials that can be used in furnace design. Insulation comes in the form of board, fiber, brick and castables. Each type of insulation comes with its own sets of considerations, such as insulation value, installation method and cost. When considering the insulation package for the vertical wall of a furnace, support must also be considered because the insulation is expected to stay where it is placed and not slump over time. There also must be a means of connecting the hot-face working lining to the furnace structure to provide support. This is accomplished with an anchoring system that connects to the furnace shell and penetrates some distance into the dense hot-face working lining.

Anchoring Systems Challenge Insulation Installations

Anchors are considered to be the bones of a refractory installation and have several functions. They hold the refractory to the wall to keep it from falling in. They also prevent wall buckling due to the internal thermal stresses created by high temperatures. And, to a lesser degree, anchors can also help support the load of the refractory weight.

The anchoring system, however, can present big challenges when installing or maintaining the insulation. In most furnace applications, anchors are first welded directly to the furnace shell. Next, the insulation package is installed and finally the working lining. With anchors sticking off the furnace shell, installing insulation can become a challenge.

Fiber insulation in the form of blanket can be pressed into the gaps between the anchors, but it is important that the insulation remains in place during the life of the furnace. Industrial furnaces tend to vibrate, either from use of combustion or exhaust blowers or other process equipment. This constant vibration can cause fiber insulation to slump and lead to hot spots in the furnace wall due to the lack of insulation.

Figure 1. Anchoring systems are installed before refractory insulation and can pose challenges.

Insulation board is rigid enough to support itself on its end and can be found in a variety of densities and thicknesses to obtain the required insulation value. However, insulation board typically comes in sheets that will have to be cut to fit around the anchors. This can result in a significant amount of manpower and a significant amount of time in a furnace installation. The downtime of an industrial furnace can be costly, which often results in tens of thousands of dollars per hour in lost profits. For this reason, companies try to minimize the time spent rebuilding a furnace. Fewer man hours on a rebuild also tends to reduce the overall cost of the project.

Ultra-lightweight refractory gunites offer a means of installing a large amount of insulation in a relatively short period of time. A gunite is a monolithic refractory castable that is pumped dry through a hose under pressure and is mixed with water at the nozzle. Once the wet castable impacts the surface, it stiffens quickly to avoid slumping and hardens as it dries. This means that the gunite could be installed over the anchors with minimal time. The installer only needs to wrap the end anchors with masking tape to keep them clean for the working lining.

Figure 2. Cold-face and heat storage/loss graph for a production furnace

Distinct Differences in Refractory Gunites

Ultra-lightweight castables are a sub-set of the lightweight castables category but with a very important difference: density. For example, the average lightweight castable with a maximum service limit of 2400°F typically has a density of about 80–90 pcf (pounds per cubic foot). By comparison, ultra-lightweight castables with a maximum service limit of 2400°F will have a density of about 25–30 pcf.

This important distinction comes into play when looking at insulation thickness and calculating cold-face temperature. At the stated densities in a furnace operating at 2000°F, it would take nearly three times more lightweight castable than an ultra lightweight castable to achieve the same cold-face temperature — making many ultra-lightweight castables perfect for insulation and most lightweight castable refractories impractical to use as part of the total insulation package.

Ultra-lightweight castables that achieve final densities of 25–30 pcf while offering service temperatures above 2400°F are available through various refractory manufacturers. One such product, Plicast Airlite 25 C/G (aka Liquid Board) from the Plibrico Company, is designed to be installed via casting or gunite using conventional gunite equipment. With low thermal conductivity and thermal-shock resistance, this material is durable and quick to install. It also has advantages over insulation board, which has a labor intensive installation process of cutting around all the welded anchors, and fiber insulation, which can experience frequent hot spots due to slumping insulation. With an ultra-lightweight, Liquid Board-type of castable, it is possible to attain required insulation values and extended lining life with the installation speed of a refractory gunite.

Working With, Not Against, the Anchoring System

Let’s consider a real-life production furnace operating at 2000°F with a simple 9-inch refractory lining consisting of six inches of dense refractory and three inches of insulation. For comparison, we will assume an ambient air temperature of 81°F and eliminate any effects of exterior wind velocity. The dense refractory working lining for these examples is Pligun Fast Track 50, a 50% alumina, 3000°F-rated refractory gunite.

As seen in Figure 2:

  • Using three inches of ceramic fiber blanket at a density of 6 pcf, a cold face temperature of 252°F can be achieved.
  • Using three inches of insulation board at a density of 26 pcf, a cold face temperature of 247°F can be achieved.
  • Using three inches of an ultra lightweight gunite such as Plicast Airlite 25 C/G with a maximum service temperature of 2500°F and assumed density of 25 pcf, a cold-face temperature of 262°F is expected.

The calculated difference in cold-face temperature between insulation board and the ultra-lightweight gunite is 15°F, but the difference in installation time savings could be multiple shifts.

Figure 3. Ultra-lightweight gunite is quickly applied over anchors with standard equipment.

The cost of downtime can be incredibly high for any manufacturer, especially since downtime can result in a series of costs and losses (both tangible and intangible), including production, labor, replacement costs, product losses and, if unexpected, reputation damage. Industry resources estimate downtime can cost thermal processing companies between $250,000 and $1 million per hour. When multiplied over several shifts, this could mean millions of dollars in downtime costs. Not to mention that labor is a major contributor to the overall cost of a refractory project. The quicker the refractory installation, the less downtime and the more profitable the company.

For example, in an approximately 750-square-foot round duct application (cylinder) with anchors already installed, on average, installation of four inches of the different insulation types can be estimated at:

  • Fiber Insulation — 137 total labor hours, or ~5.5 square feet/hour
  • Insulation board — 288 total labor hours, or ~2.6 square feet/hour
  • Ultra-light gunite/Liquid Board — 80 total labor hours, or ~9.4 square feet/hour

The quick and easy installation of the ultra-light gunite/Liquid Board represents an average estimated financial savings in downtime of between $35 million and $130 million — savings that drops directly to a company’s bottom line. The time compression of installing gunite also holds an added advantage for the insulation installer because labor hours can come with a premium price tag and can sometimes be in short supply. All of this makes the ultra-lightweight gunite solutions an excellent choice to minimize downtime and rebuild costs while meeting the furnace design criteria.

Conclusion

Manufacturers that rely on industrial-grade furnaces, boilers and incinerators to produce their quality products are constantly looking for ways to reduce costs, increase profits and improve efficiencies by looking at and introducing risk-neutral change to current processes. Maintaining efficiency and avoiding unscheduled shutdowns of heat processing equipment requires maintenance. Selecting quality materials and risk neutral installation processes that minimizes maintenance completion times can help companies become more efficient.

About the Author:

Roger M. Smith
Director of Technical Services
Plibrico Company, LLC

Roger M. Smith, a seasoned professional in the refractory industry, is the director of technical services at Plibrico Company, LLC. With a master’s degree in Ceramic Engineering from the University of Missouri — Rolla, Roger has over 15 years of experience in the processing, development and quality assurance of both traditional and advanced ceramics. He has a proven track record in developing innovative ceramic formulations, scaling up processes for commercial production, and optimizing manufacturing operations.

For more information: Visit www.plibrico.com.

This article was initially published in Industrial Heating. All content here presented is original from the author.

Find heat treating products and services when you search on Heat Treat Buyers Guide.Com

A Better Way To Get Things Done: Refractory Insulation Read More »

Maintenance Message: Extending the Service Life of Refractory Linings

/ ALUMINUM PROCESSING TECHNICAL CONTENT, GUEST COLUMN, MANUFACTURING HEAT TREAT TECH

Heat treating aluminum presents a unique concern due to the operating conditions of high temperature, chemical corrosion, mechanical abrasion, and temperature variation. Guest columnist Roger M. Smith, director of technical services at Plibrico Company, LLC, examines the critical role the refractory lining plays in the success of manufacturing aluminum, why a refractory is susceptible to cracking under extreme conditions, and how to select and prepare refractory linings to achieve a longer service life.

This informative piece was first released in Heat Treat Today’s August 2024 Automotive print edition.

A significant concern when manufacturing aluminum metal is the practical service life of the furnace. The service life is driven by the refractory lining’s ability to resist the various operating conditions within the furnace, such as high temperature, temperature variation, chemical corrosion, and mechanical abrasion. Ideally, a single refractory composition would be capable of withstanding all these conditions and readily available at a low price.
Unfortunately, this is rarely the case.

Proper refractory selection is often about finding the best balance between price, properties, and performance for the given application and operating conditions. A refractory capable of high strength and abrasion resistance is often susceptible to cracking caused by extreme temperature variations, commonly referred to as thermal shock. However, a material capable of withstanding thermal shock without catastrophic cracking may be vulnerable
to chemical corrosion. Finding the best balance of material properties for each zone in each furnace is important for maximizing the service life of a furnace.

Figure 1. Schematic showing refractory lining in an aluminum furnace

Refractory Under Attack — Requirements for Melting Aluminum

The refractory lining in an aluminum furnace (Figure 1) must endure various chemical reactions that occur while the furnace is in operation. There are three separate regions to consider: above, below, and at the melt line. Above the melt line, the refractory must withstand attack from various alkali vapors. Alkali vapors can be produced from flux used in the aluminum and from the combustion products used to heat the furnace. Below the melt line, the refractory must withstand molten aluminum. At the melt line, the region commonly referred to as the bellyband area, there is a triple point where the refractory, atmosphere, and aluminum interact.

The refractory below the melt line comes in direct contact with liquid aluminum when the furnace is in operation. This contact can create a chemical reaction zone where oxides on the surface of the refractory can be reduced, such as silica (SiO2) to form silicon. Conversely, aluminum can penetrate into the refractory lining either through the same redox reactions or through infiltration due to capillary forces.

Aluminum forms corundum (Al2O3) when it oxidizes. This results in a change of the crystal structure from face-centered cubic to hexagonal, which causes a significant volume expansion. When corundum is formed inside the refractory lining, the change in volume creates cracks, which lead to more infiltration and more cracks until the refractory lining ultimately fails.

Wetting the Refractory

One method for reducing the reaction zone is to prevent the aluminum from “wetting” the refractory (see Figure 2). A liquid’s ability to “wet” a surface is defined by the contact angle of the liquid. When the contact angle between the liquid and the surface is greater than 90 degrees, then the liquid is said to wet the surface. When the contact angle is less than 90 degrees, the liquid does not wet the surface. A liquid that does not wet the surface is analogous to water beading on a car that has been freshly waxed. When aluminum does not wet a refractory, it is not able to react with the refractory and is not able to penetrate the lining.

Figure 2. Contact angle of the liquid demonstrating wetting vs. non-wetting

Various additives can be used to reduce aluminum’s tendency to wet a refractory. Some of the most used additives include barium, boron, or fluoride. They modify the surface chemistry of the refractory and reduce aluminum’s ability to react and penetrate. Using additives such as these greatly extends the effective service life of a refractory lining.

While non-wetting additives can be beneficial to extending the service life in areas where there is contact with molten aluminum, there are no benefits when not in aluminum contact. They do not protect from alkali attacks above the melt line. They do not enhance the abrasion resistance of the material. They do not improve the thermal shock resistance of the material. Furthermore, these additives are volatile. When exposed to temperatures above 1700°F (927°C), they begin to lose their effectiveness because they chemically react with other materials in the refractory and change. The additives can also be costly, which raises the price of the refractory compared to one with the same composition but without the additive.

The presence of non-wetting additives can have some negative effects on a refractory. Tests have shown that a 1% addition of a fluoride additive in a conventional castable can reduce the hot modulus of rupture (HMOR) by as much as 30% at 2000°F (1093°C). The effect can be even more significant in a low-cement castable. The loss in hot strength is likely attributed to the formation of a glassy phase induced by the additive. Fluoride and boron are both well-known glass formers and will form a glassy phase at the grain boundaries at high temperatures, which reduces the bond strength between individual grains and the overall strength of the bulk material.

Figure 3. Refractory lining

Balancing Refractory Properties

The advantages and disadvantages of a refractory material should be considered when selecting materials for an aluminum furnace. The sidewalls of a furnace all come in direct contact with molten aluminum.

The upper sidewalls must be scraped to remove aluminum that splashes up to prevent corundum growth. The refractory selected for its sidewalls should be abrasion resistant to protect from mechanical scraping and non-wetting to protect from corundum growth. The hearth and well are submerged in aluminum, but they do not see the same level of abrasion as the sidewalls. The sub-hearth may see some molten aluminum but must also provide support, so a strong, non-wetting refractory should be used.

The door and sill will experience temperature fluctuations every time the door is opened, and they will be exposed to abrasion as the furnace is charged. Materials that are resistant to thermal shock and abrasion should be selected. The roof and superstructure need to be strong and resistant to alkali vapors. Backup insulation should be selected to reduce heat loss, but it should be of a composition that has moderate resistance to molten aluminum in case of refractory failure at the hot face.

In all these zones, the operating conditions of the specific furnace must be considered, and the balance of properties must be adjusted case-by-case. The primary failure modes must be identified, and materials should then be adjusted accordingly.

The Key to Refractory Selection

The operating conditions in an aluminum furnace require a refractory lining with different benefits in different zones. At the furnace door, the refractory can experience drastic fluctuations in temperature that can cause cracking. The upper sidewalls will develop scale that has to be scraped off, so the refractory needs to be abrasion resistant.

The lower sidewalls come in direct contact with molten aluminum and need to resist chemical attacks and aluminum penetration to avoid corundum growth. Finding a cost-effective refractory that can meet all these requirements is very difficult, but it can be done with sufficient research. Careful material selection that considers the needs and operating conditions of a particular furnace is important for maximizing the service life of a refractory lining.

About the Author:

Roger M. Smith
Director of Technical Services
Plibrico Company, LLC
Source: Plibrico

Roger Smith is a seasoned professional in the refractory industry. With a master’s degree in Ceramic Engineering from the University of Missouri – Rolla, Roger has over 15 years of experience in the processing, development, and quality assurance of both traditional and advanced ceramics. He has a proven track record in developing innovative ceramic formulations, scaling up processes for commercial production, and optimizing manufacturing operations.

For more information: Visit www.plibrico.com.

This article was initially published in Industrial Heating. All content here presented is original from the author.

Find heat treating products and services when you search on Heat Treat Buyers Guide.Com

Maintenance Message: Extending the Service Life of Refractory Linings Read More »

15 Quick Heat Treat News Items to Keep You Current

/ FEATURED NEWS, HEAT TREAT NEWS INDUSTRIES

Heat Treat Today offers News Chatter, a feature highlighting representative moves, transactions, and kudos from around the industry.

Personnel and Company Chatter

  • Roger Smith has recently been appointed Technical Manager at Plibrico Company, LLC.  Smith will be responsible for development of innovative refractory formulas, oversee product quality, and assist in identifying the best materials for refractory construction projects.
  • William “Bill” Cowell has been promoted to the position of Vice President of Operations at Advanced Heat Treat Corp. (AHT). Cowell, who has been at AHT since 1999, will oversee operations for all AHT  facilities.
  • Wirco has announced the promotion of Aaron Fisher to Vice President of our Fabrication Division. Aaron has been with Wirco for 19 years. In addition, Wirco welcomes Marco Möser as the Vice President of our Foundry Division.
  • Thomas G. Gasbarre has stepped down as Chief Executive Officer of Gasbarre Products, Inc, a position he has held since his father George Gasbarre, the founder of the company, retired in 1990. Gasbarre also announced that Tom’s son, Alex Gasbarre, has been appointed Chief Executive Officer and is now leading the development and execution of the company’s short- and long-term strategies. Heath Jenkins has been promoted and will succeed Alex as President, Press & Automation, and Manufacturing Technologies.
  • John C Plant has been appointed to serve as Chairman and Chief Executive Officer at Arconic Inc. The Board has also appointed Elmer L. Doty, a current Director, to serve as Chief Operating Officer, and Arthur D. Collins, Jr., a current Director, to serve as Lead Director. These appointments are effective immediately.
  • Xerox, based in Norwalk, Connecticut, has acquired metal additive manufacturing company Vader Systems, which will enable it to offer its customers access to low-cost metal additive manufacturing with a greater variety of metals. Based in Buffalo, New York, Vader Systems is a developer of liquid metal additive manufacturing technology.

Equipment Chatter

  • Several convection ovens were supplied to a manufacturer of small medical parts in the southern U.S. by Lucifer Furnaces. Model 42-B18 has a working chamber size of 9”H x 9”W x 18”L and heats to 1200°F.
  • A floor-standing furnace has been shipped by L&L Special Furnace Co., Inc. to a worldwide leader of high tech ceramics and associated components located in the Northeastern United States. The furnace will be used for glass components along with fiber optics and research and development. It will also be used to fill in on various thermal projects and development.
  • A Treet-All™ Box Furnace has been shipped to a Japan-based global battery manufacturing company by Lindberg/MPH.  The maximum temperature rating of this light industrial box furnace is 2050°F and has work chamber dimensions of 18” wide x 36” deep x 18” high. The Treet-All™ Light Industrial Box Furnace is suited for multiple applications, including annealing, ashing, austempering, brazing, preheating, solution treating, stress relieving, and normalizing.
  • A supplier of the aerospace industry received shipment of a Electrically Heated Horizontal Quench Solution Treat System from Wisconsin Oven Corporation. The Horizontal Quench Solution Treat System has a maximum oven operating temperature of 1,200° F and work zone dimensions of 5’4″ wide x 5’6″ long x 5’4″ high (above the rollers).
  • Chromalox, a thermal technology provider, recently contracted with Sierra Monitor Corporation  to enable cloud system connectivity on their Heat Trace solution.
  • A cabinet oven is being used to finish batch loads of metal parts at a customer’s facility. The No. 828 is a 500°F (260°C) cabinet oven from Grieve Corporation.
  • A recycling and melting group has ordered for installation a Twin-Chamber Melting Furnace TCF® from Tenova LOI Thermprocess. Italy-based Fonderie Pandolfo specializes in processing of aluminum, mainly for extrusions. The casted billets are mainly extruded in the extrusion shops of the main European extruders.

Kudos Chatter

  • Buehler, an ITW Company, and ASM International are celebrating 75 of continuous partnership in 2019. Buehler has continuously supported of the ASM World Training Center in Novelty, Ohio, through its innovations for metallography and hardness testing, solutions for the newest materials and participation in ASM International activities.
  • Pennsylvania-based Onex Inc recently completed a forge furnace refractory reline in one week.

Heat Treat Today is pleased to join in the announcements of growth and achievement throughout the industry by highlighting them here on our News Chatter page. Please send any information you feel may be of interest to manufacturers with in-house heat treat departments especially in the aerospace, automotive, medical, and energy sectors to the editor at editor@heattreattoday.com.

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