Moldable Plastic refractory and its application

1. Seminar and Technical Writing September 2021
Presented By: Arthita Bhattacharyya
Roll No: 919CR5008
Faculty Advisor: Dr. Debasish Sarkar
Department of Ceramic Engineering

2.  Introduction
 Monolithic Refractory
 Types of Monolithic Refractories
 History of Moldable Refractory
 Types of Moldable Refractory
 Pros & Cons of Moldable Refractory
 Raw Materials
 Particle Size Distribution
 Binders and Additives
 Role of different Binders
 Typical Specification of Moldable Refractory
 Application of Moldable Refractory

3.  Moldable plastic refractories have found wide acceptance in India
as furnace linings in steel, aluminum, power and petrochemical
industries in the last 20-25 years.
 It is especially adaptable for making quick, economical emergency
repairs due to their short setting time and good thermo-
mechanical properties in wide temperature range.
 Moldable refractory consisting of moistened aggregates is usually
rammed into place with an air & electric hammer.
 They can also be applied via gunning, resulting high installation
rate over the traditional ramming method.

4.  From the simple beginning in the early 1900’s, monolithic
refractory have evolved world-wide over the succeeding 100 years.
 With various modifications, its performance and cost effectiveness
now is at par with or superior to pre-fired refractory bricks.
 The success of monolithics has been due to significant advances
in the type and quality of binders, additives, quality and particle
size distribution of aggregates.
 Monolithic products are now designed for all installation methods
from traditional to cutting-edge, fully adapted to the specific
conditions.

5.  Depending on the installation techniques monolithics are divided
in to different categories:
 Castable refractories
 Gunning materials
 Spraycast / shotcrete products
 Refractory plastic / Moldable
 Ramming mixes
 Patch products
Large
Aggregates
Fine
Fillers
Binder &
Additives
Monolithic
Formulatio
n

6.  The first plastic refractory were simple mixtures of plastic clay and
crushed-brick grog or calcined clay furnished in a wet, moldable
form.
1920 -1940 1940 -1960 1960 -1990 1990 - 2018
1. Semi-baked, putty like
plastic firebrick.
2. Clay based plastic
refractory.
3. Phosphate bonded &
graphitic plastic.
4. Different application
technique, Advances in
additives, binders and
PSDs.
1. Introduced in boilers.
2. Different application
techniques were
adopted.
1. Experimentation with
different binders.
2. Different application
techniques were
adopted.
3. Gunning in roof of
walking beam
furnace.

7.  Based on setting:
 Heat - set - forms a bond when placed and heated to about 500 C.
 Air- set- contains aluminum sulfate which forms a crust as the refractory
dries.
 Chemically Bonded - contains phosphoric acid or an acid phosphate
which reacts with the alumina in the composition.
 Based on Form:
 Granular form- These are prepared at the proper consistency in moist
granular form, ready to use by gunning or ramming.
 Extruded form- The extruded blocks are sliced into pieces and are
rammed or poured into place with pneumatic rammer during application.

8.  Pros:
 Easy Installation at the
intricate areas in furnace,
 Less labour intensive,
 Light Weight,
 Fast dry-out and heat-up with
no need for curing or long
setting times,
 Good repair properties due to
the ability to bond to existing
fired refractory,
 Good thermo-mechanical
properties,
 Excellent thermal shock
properties.
 Cons:
 Susceptible to compaction
during storage,
 Low workability of single
component material,
 Occurrence of lamination in
lining when installed by
ramming.

9.  Alumina is the major constituent of the total composition.
 The major sources of alumina are calcined bauxite, calcined
alumina, brown fused alumina, aluminum silicates such as
kyanite, mullite and china clay.
Advantages of Mullite in place of BFA & Andalusite:
1. Mullite is a good, low cost refractory with interlocking grain structure.
2. It does not react with colloidal silica at room temperature.
3. It has little drying shrinkage and cracking tendency.
4. It shows high strength and high volume stability at high temperatures.
5. It has high thermal shock resistance owing to the low thermal expansion.
Disadvantages of Clay:
P2O5 sources react with impurities in the clay to form precipitates which destroy
the shelf life of the plastic refractory.

10. 0-0.1
0.1-1
1-3
3-5
0 10 20 30 40 50 60
Size
Range
(mm)
%
Particle Size Distribution
Moldable Ref-III
Moldable Ref-II
Moldable Ref-I
 O-1 mm dominates the particle size distribution in
moldable plastic refractory

11.  Impart strength & adherence.
 Evenly distributed in the refractory
matrix during mixing.
 Due to its acidic properties It reacts
with alumina containing raw materials
at low temperatures.
 On heating additional bonding occurs
due to formation of polymeric
phosphates.
 The phosphate bond persists until the
ceramic bond comes into effect.
Chemical Binder
• Ortho Phosphoric Acid
• Mono Aluminium Phosphate
Organic Binder
• Carboxy Mithyl Cellylose
 It serves as a plasticizer and a
lubricant to enhance thixotropic
properties.
 Helps to achieve slump
resistance in the refracttory.
 Acts as a gelling agent for
colloidal silica.

12. Sol-Gel Binder
• Colloidal Silica
Deflocculating Agent
• Sodium Hexa Meta Phosphate
 Thixotropic agent and plasticizer.
 The water based colloid surrounds the
refractory particles during mixing.
 During drying, the hydroxyl groups
(Si-OH) on the surface of the particles
generate siloxane bonds (Si-O-Si)
which results in a three dimensional
network known as gelling.
 Gelling forms a network encapsulating
the refractory particles providing
mechanical strength to the system
after drying.
 It helps to disperse the colloidal
particulate material component
of the binder and prevent
agglomeration.

13. Ortho
Phosphoric
acid
• Ortho Phosphoric Acid is
used as binder due to its
ability to provide low
temperature chemical
bonding.
• Its Lower vapour pressure
reduces stresses within a
refractory lining during heat
up and improves heat up
properties.
• Reduces drying time as the
release of moisture is
quicker.
• Creates chemical bond with
existing cement bonded
castable lining as
phosphoric acid reacts with
CaO at ambient
temperatures.
Mono
Aluminium
Phosphate
• It is prepared by the
reaction between Alumina
and phosphoric acid.
• It also provides low
temperature chemical
bonding with its
conversion to poly-
phosphate and meta-
phosphate during the heat
up.
• It has improved strength
and binding ability than
ortho phosphoric acid.
• The release of water during
drying is considerably
slower than ortho-
phosphoric acid.
Colloidal
Silica
• Provides highly permeable
structure, allows easy drying,
reduces cracks and explosive
spalling.
• Nano sized colloidal silica
particles promotes solid phase
sintering and mullite formation.
• less mixing time,
• easier installation,
• better corrosion and oxidation
resistance,
• better refractoriness,
• improved lining life and longer
shelf-life.
• Reduces phosphate migration in
the refractory mix after it is
heated to cure.
 Colloidal silica bonded
refractory shows very low
strength below its sintering
temperature (1100 C).
 It is stable at a pH of 2.7 to 3.1
or 9.0 to 9.8 and outside these
ranges, it becomes gelled and
lose thixotropy.
 Migration of phosphates into the lining after the installation results
in disruption of the moulded refractory bodies by disintegration
and macroscopic cracking.

14. Components Range (%)
Al2O3 50 - 97
SiO2 47- 2.1
Fe2O3 1.2 – 0.1
TiO2 1.5 – 2.5
CaO 0.1
Alkalies 0.1
Chemistry :
 Based on the application requirement moldable refractories are
manufactured with varying chemistry.
 Being a Al2O3 based material the Al2O3 content may vary from 50
to more than 90% to meet the desired physical properties.

15. Physical Properties 50% Al2O3 based 90% Al2O3 based
Service Temp
(Max, °F)
3000 3300
Bulk Density
(Rammed, lbs./cu.ft)
140 - 150 181 - 187
Cold Crushing Strength
(After Heating to 1500°F, lbs/sq.in)
1200-1500 3500-6000
Modulus of Rupture
(After Heating to 1500°F, lbs/sq.in)
150-200 700-1100
Linear Change,
(After Heating to 1500°F, %)
0.0 to –0.2 -0.1 to - 0.4
Physical Properties :
 Raw materials, recipe, granulometry, binders and additives play important
roles to achieve desired physical properties.
 Typical physical properties are tabulated below for 50% and 90% Al2O3
based moldable refractory.

16.  Iron & Steel Industry: 1) Reheating Furnace in mills
2) Steel Ladle Cover
3) Ignition Furnace at Sinter Plant
4) Induction Furnace
5) Foundry
 Aluminium Industry: 1) Melting & Holding Furnace
2) Induction Furnace
 Others: 1) CFBC Boilers
2) Incinerators
3) Crackers in Petrochemical industries

17. Thank You