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Technical Paper


www.ireng.org


CURING, DRYING & FIRING OF REFRACTORY LININGS


W.A.J. Kastelic 1: Introduction


The integrity of refractory linings can be achieved by: • Adequate design • Clear specification • Stringent quality control


In the sequence of activities from the design to the final stage of an operating lining, the "curing, drying and firing-phase" is of utmost importance and necessitates considerable attention, in order to get what we have asked for:


"a reliable and durable refractory lining"


All (monolithic) refractory linings contain moisture, added mainly during the mixing procedure, in order to enable proper installation and achieve setting and strength.


The curing period is characterised by prevention of moisture loss from the installed material for sake of hardening and strength development;


during the drying phase all excess moisture will be evaporated, and during the firing phase controlled "fusing" of the components is achieved.


The whole procedure must take place gradually since fast evaporation, coupled with high vapour pressures, may cause ruptures. Too quick drying and firing may even destroy the bond between the individual components.


It is obvious that the curing, drying and firing-phases require proper attention from both contractor and the user, in particular user’s Operations, whilst adequate provisions must be made for it to ensure that the anticipated design is fully realised.


2: Refractory materials


This note mainly deals with monolithic refractory linings and when discussing refractory linings in general a number of expressions and classifications are used.


Monolithic refractory linings can, amongst others, be classified based on the method of installation, such as:


• cast refractory: applied by pouring, pump cast and more recent by vibration or with self-flowing properties;


Ramming mixes


Semi-dry granular ram-mixes


3 - 6 % H2 O


Chemical --


Ceramic Plastic mixes


Plastic granular mixes


5 - 8 % H2 O


Chemical --


Ceramic Plastic mixes in slices 6 - 10 % H2


Chemical --


Ceramic Table 1: Bond system and total water required for monolithic refractory materials 10 ENGINEER THE REFRACTORIES May 2018 Issue O


Dense refractory castables


4 - 18 % H2 O


Chemical Hydraulic --


Plastic refractories,


W/mKastelic Refractories Services • plastic/rammed


ramming; • gunned refractory: applied by gunning.


Depending on the way of setting/hardening the monolithic refractory materials are classified as: Hydraulically setting,


mainly containing alumina cement, which sets by means of hydration.


Chemically setting,


containing amongst others bonding agents which achieve strength development by means of chemical reactions.


generally containing a small amount of refractory clay as bonding agent.


On the basis of their nature, composition and method of installation monolithic refractory materials may require from 0 up to and over 100 %w water for mixing, placement and subsequent hardening and strength development (table 1). In the transition phase between hydraulic and ceramic bond still sufficient strength remains present, even for operation at such a temperature.


On the other hand, refractory brick constructions contain much less water Effectiveness of the bond


Bond system: Ceramic Hydraulic


Chemical (mineralogical or org.-


mineralogical)


Organic- chemical


± 50 °C


± 1000 - 1450°C


Table 2: Temperature range for various bond systems Castables


Insulating refractory castables


16 - 130 % H2


Chemical Hydraulic --


O Gun/Slinger mixes


Plastic, dense, and insulating gun mixes


5 - 40 % H2


Chemical Hydraulic Ceramic


O


>1000 °C also start of ceramic bond


Start ± 1000 °C ± 20 °C


± 200 - 500 °C


Finish


± 1200 - 1500°C


± 500 - 600°C


± 1000 - 1450°C


Condition after finish


--


>1000 °C also start of ceramic bond


> 1000 °C ceramic refractory: applied by pounding or (pneumatic)


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