Precast Shape Technology in Refractory Linings
by Paul E. Fisher, P.E.
TFL, Incorporated
____________________________________________________________________________
The design and manufacture of precast refractory shapes has become a specialized field
within the refractory industry in recent years. As the demands increase for greater refractory
lining performance and lower maintenance costs, refractory users are finding that one effective
way to achieve those goals is to incorporate a broader use of precast refractory shapes into
their lining systems. Across virtually all industries – petrochemical, steel, power generation,
metal casting and treatment, wood products, minerals processing and others - the applications
for precast shapes are limited only by the imagination, and almost invariably their use will result
in better performance and true cost savings. This article will discuss the design and
manufacture of precast refractory shapes, and the benefits to be gained in both refractory
material performance and installation logistics.
Precast Shape Design and Manufacturing
In order to realize the true benefits to be gained from the use of precast shapes, a thorough
knowledge of how the shape system will be used and
installed in the field is an absolute requirement during the
design phase. The successful design and manufacture
of a high-performance refractory shape system requires
a unique understanding of refractory materials,
manufacturing, anchoring systems, and construction
practice. Dimensional tolerances, construction
sequencing, lifting and handling capabilities at the site,
Fig 1 – Installation of precast access shapes
anchoring facilities, and the actual service demands
within the refractory lining environment are all factors that must be well known before the shape
is designed.
Precast shape manufacturing inherently requires the use of a mold or pattern to form the
shape. There are several methods for moldmaking which are routinely employed, and the type
of mold construction and materials used depends
on the size, complexity, and dimensional
tolerances required in the shape, and sometimes
the quantity of shapes required. For simplistic
shapes with loose dimensional tolerances (+/1/16”), plywood forms or metal fabricated forms
Fig 2 – Precast Headwall Shapes for Carbon
Bake Furnace
can be used. Toward the other extreme, some shapes may require extremely tight tolerances,
which require the use of a more sophisticated mold made from wood, plastic or metal. These
molds may be of the type made by a foundry pattern maker or machine shop.
Another factor in the design of a precast shape has to do with the schedule and sequencing
of the actual field installation. The shape design must take into account job accessibility, what
other lining components will already be in place when the shapes are to be installed, and how
the shape can be handled physically on the job site. Weight and lifting limitations must be
considered and planned for, as well as the type of access available into the furnace or vessel. If
necessary, lifting lugs or other fixtures can sometimes be incorporated into the shape design.
The design of the anchoring system to be used in the shape is of tremendous importance. In
addition to the normal considerations of alloy type and anchor size, the precast shape design
must also consider all alternatives for attaching the shape to the structure. Numerous methods
can be used, including threaded stud attachments through the wall, welded fixtures, or bolted
assemblies.
Perhaps most importantly, the proper refractory material must be selected to suit the
demands of the application. Factors such as the desired temperature profile through the lining,
expected mechanical stresses, potential chemical attack on the lining, erosion mechanisms, and
expansion allowance must all be understood prior to selecting a material to be used in the
precast shape.
A well-equipped precast manufacturing facility should include high-energy, large capacity
mixers, automated mixing stations with conveyors for material delivery, vibration tables, digitallycontrolled water addition, mixing time controllers, and adequate lifting capabilities for large
shapes. Firing of shapes is accomplished with a digitally-controlled furnace with burners
capable of firing to at least 1300 deg. F. In-house mold/pattern fabrication capabilities and
CAD-generated drawings for design assistance should also be expected.
Benefits from Material Property Enhancement
Regardless of how complex or sophisticated the refractory castable is that is selected for an
application, the physical properties of the material can be drastically reduced if care is not taken
during the mixing, pouring, and curing processes. Particularly with the use of more complex
refractory castables to solve specific wear issues,
installation variables become even more critical to
the performance of a lining. Unfortunately, lining
quality is often compromised by field conditions
during material placement. Project schedules,
crew skill levels, equipment availability, job cost
Fig 2 – Precast roof panels ready for shipment
pressures, or other demands can sometimes have an impact on proper refractory installation.
Improper water addition, mix time variations, over- or under-vibration, and improper curing can
drastically affect material quality. With precast shapes, cast in a controlled shop environment,
the physical properties of a castable will be more fully optimized.
Initial drying and firing of a refractory castable is a critical installation variable that can
influence lining performance. Precast shapes are typically fired in a digitally-controlled furnace
prior to shipment, ensuring that the refractory manufacturer’s recommended bake-out schedule
is closely followed. Since the shapes are fired slowly from all sides, the moisture is removed
through the entire thickness of the shape in a controlled manner. Depending on the
temperature to which the shape is fired, this can optimize the physical properties of the material
through the entire thickness of the shape, not just the hot face surface. This results in a truly
homogeneous lining. Micro-cracking within the shape, which is often introduced during field
bake-out but may go unnoticed, may also be reduced since the initial firing is more controlled.
In service, linings comprised of precast shapes often see less stresses and cracking, due to
the independent, “floating” nature of the lining. The performance of the lining can also be more
predictable, resulting in better opportunities to plan for maintenance and repairs.
Benefits from Installation Logistics
Other major benefits to be gained from the use of precast refractory shapes are related to
simplified installation and repair logistics, which can lead directly to reduced costs and shorter
down times. With the use of precast shapes, forming labor, materials, equipment costs, actual
placement time and expense, and associated costs during form removal, curing, and cleanup
are all eliminated. These costs are shifted back to the manufacturer of the shape, who can
absorb them much more efficiently when spread over his overall production capacity.
Refractory installation contractors have begun to consider precast refractory shapes much
like they do any other pre-manufactured item such as block insulation, ceramic fiber blanket,
anchors, etc. These items can be bought and then re-sold as a component of their installation
projects.
Whenever any portion of refractory repair work can be completed prior to crews being on
site, costs are automatically reduced. Installation contractors have also found that the use of
precast shapes can often give them a substantial advantage in competitive bid situations. With
the use of precast shapes, crew sizing can be minimized. Speed of installation is another
obvious benefit to both the installer and the owner, resulting in reduced costs due to shorter job
duration. Material usage is also reduced, when compared to other installation methods such as
guniting, where as much as 45% extra material is required to compensate for rebound and other
job losses. Environmental hazards such as dusting and tripping hazards associated with
equipment and hoses are also reduced substantially, if not eliminated.
Future repairs also become much more economical and quicker to accomplish. Repair
areas can often be isolated to just the immediate wear area within the boundaries of a shape.
Anchor attachment points can typically be reused. Replacement shapes, purchased early and
kept as spare parts on site, can be easily installed in a fraction of the time required for
conventional repair methods. Repairs become more of a mechanical maintenance job, rather
than a refractory installation job requiring a specialized crew and equipment.
The initial bake-out of a new refractory lining
on site can be a very expensive and timeconsuming component of a refractory repair
project. The use of precast and prefired
refractory shapes can sometimes reduce or even
Fig 3 – Precast Hearth Blocks for a car-bottom furnace
eliminate the need for an extensive initial bake-out. If an entire repair is made with a prefired
system, then normal furnace start up schedules can be used, without the fear of steam spalls or
other damage during the initial heating. Bake-out of multi-component linings, which may include
a combination of precast shapes and other materials placed in the field, can often be reduced
by the pre-firing of the castable shapes, particularly if that material would have been the critical
item determining the bake out schedule. This can have a positive impact on not only job costs,
but in reducing down time as well.
Typical precast shape applications

Burner Blocks

Pier Blocks

Manway Plugs

Checker Wall Blocks

Wall Panels

Air Grid Tiles

Burner Pipe Covers

Divider Walls

Curb Blocks

Hearth Shapes

Jambs, Lintel & Sills

Peep Sites

Delta Sections

Well Blocks

Nozzles

Impact Pads

Flue Caps

Flue Walls

Burner Ports

End Caps

Exhaust Ports

Flare Tips

Roof Sections

Spouts

Skimmer Blocks

Safety Linings

Tap Blocks

Troughs

Runners

Sleeves
Precast refractory shapes will continue to be a growing specialty in the refractory
industry in coming years. With the improved quality that can be achieved through controlled
manufacturing processes, their expanding use will play a major role in improving refractory
lining performance and reducing maintenance costs across all industries.
TFL, Incorporated is a supplier of refractory materials and related services located in Houston,
Texas, and is a leading manufacturer of custom-designed precast shapes.
Web site: www.tflhouston.com