Conventional Refractory Castables by Casting

CONVENTIONAL REFRACTORY CASTABLES BY CASTING DESIGN AND INSTALLATION MANUAL

Thermal Ceramics 

TABLE OF CONTENTS A. Preface Introduction B. Refractory Castables by Casting 1. General 1.1 Dense Castables 1.2 Lightweight Castables 1.3 Gunning Castables 1.4 Special Purpose Castables 2. Pre-Installation 2.1 Storage 2.2 Surface Preparation Prior to Refractory Placement 2.3 Formwork 2.4 Anchors 3. Installation 3.1 Water 3.2 Temperature 3.3 Mixing 3.4 Placement 3.5 Multilayer Linings 3.6 Joints 3.7 Finishing 3.8 Curing 4. Firing List of Figures Figure 1 Proper Bag Storage Figure 2 Formwork Figure 3 Paddle Mixer Figure 4 Shaking Needles Figure 5 Ball in Hand Test Figure 6 Standard Vibrator Figure 7 Vibrating Behind Forms Figure 8 Multilayer Linings Figure 9 Consruction Joints Figure 10 Expansion Joints Figure 11 Finishing Figure 12 Cast with Forms in Place Figure 13 Spraying with Curing Compound

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DESIGN & INSTALLATION MANUAL CONVENTIONAL REFRACTORY CASTALBES BY CASTING

1 . G ENE RA L

INTRODUCTION

Over the past 75 years, Thermal Ceramics has proven to be a world leader in solving heat intensive problems. In addition to manufacturing ceramic fiber, brick and fired shape products, a wide range of refractory monolithic products are available. From lightweight, highly insulating materials to dense, high strength products, Thermal Ceramics has a refractory castable to meet the needs of the customer. All industries are serviced with these products, including ferrous, non-ferrous, chemical, utility and ceramic related markets. The Thermal Ceramic operation in Augusta, Georgia has been certified to ISO 9002 standards for refractory monolithic production. At this facility, both raw materials and finished products are routinely tested to make sure they meet a demanding quality level. An experienced staff of refractory specialists is on hand at Thermal Ceramics to assist you in product selection, system design, and installation techniques. This Design and Installation Manual is intended to give the designers, installers and users of Thermal Ceramics monolithic products a broad range of information guidelines on the particular topic. Any questions or comments regarding this manual should be addressed to your local Thermal Ceramics representative.

Castable refractories are classified into 4 major groups – dense castables, lightweight castables, gunning castables and special purpose castables. 1.1 Dense Castables Dense castables are designed for strength, abrasion and erosion resistance and are primarily used as the working hot face. 1.2 Lightweight Castables Lightweight castables are used primarily for their thermal insulating properties behind dense castables, or in certain conditions as working hot face linings. Their inherent low density significantly reduces structural loading. 1.3 Gunning Castables Gunning castables are modified versions of the above castables allowing them to be effectively placed using pneumatic guns. Some grades are dual purpose allowing both casting and gunning without change. Installation of gunning grade castables is discussed in the procedures titled “Refractory Castables by Gunning” (M 148). 1.4 Special Purpose Castables This grouping covers the modern range of low cement castables and castables with less conventional binders and are discussed in other procedures. This procedure, “Conventional Refractory Castables by Casting,” covers the installation of dense and lightweight castables (groups 1.1 and 1.2 of the above) by casting. 2. PRE-INSTALLATION 2.1 Storage Castables should be stored in a dry, well-ventilated area and held off the floor on pallets (Figure 1). If stored outside, the bags must be protected from rain or dripping water by a fixed cover. Storage temperature is not a consideration as long as the castable is in the desired temperature range prior to casting (See Section 3.2). If the bags are further protected by plastic sheeting, ensure that there is sufficient ventilation underneath the plastic sheet to prevent water from condensing on the bags. Avoid storing in areas of high humidity. Pallets should not be stacked more than three high when in storage. This should be reduced to two pallets when storing lightweight castables. This is to prevent the consolidation and caking of material on the bottom rows of the pallet.

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Where refractory concrete is to be cast in tall vertical sections, the formwork should generally have a height of not more than 48 inches, with provision for additional sections to be mounted rapidly to ensure the continuous casting of panels between designated joints.

Figure 1 - Proper Bag Storage

Most Thermal Ceramics castables have a finite shelf life called a “nominal shelf life.” When quoting shelf life, a period of one year is used. Product that is older than the nominal shelf life should be checked for setting properties prior to use. Signs of aging are longer setting times and reduced strengths. All bags have the date of manufacture printed on them to aid in determining the age of the material. Always use the oldest materials first and, if aged beyond the nominal shelf life, have the material tested before use. The work surface shall be substantially free of dust, scale, oil, water, dirt and loose foreign material and should be cleaned if necessary. 2.3 Formwork  Formwork should be constructed from strong materials that resist water absorption (Figure 2). Generally 3¼4 inch plywood or steel forms are favored for this job because of their inherent strength and non-absorbent nature. The surface of the formwork must be lightly but thoroughly oiled or greased to facilitate removal from the face of the casting. The surface of the formwork should be uniform and smooth to give a good surface finish to the casting. It also aids in formwork release. Formwork must be as watertight as possible with all joints and holes sealed. The use of vibrators during casting will cause liquids and fines to “bleed” through cracks in the formwork. This liquid will be rich in cement and can leave a weakly bonded material adjacent to the leaking joint causing detrimental results. December 2002

Figure 2 - Formwork

2.4 Anchors Both ceramic and metallic anchors are appropriate for use with conventional castable refractories. This subject is treated in a separate procedure, “Anchoring of Monolithic Refractories” (M 150). 3. INSTALLATION 3.1 Water The water used for mixing should be clean and of drinkable quality – potable water. Since the amount of water added to the castable does more to affect the properties than any other factor, it must be accurately measured. Water amounts are shown on the back of the monolithic bags, but these are intended as a guide only. Actual amounts will depend upon field conditions and should adhere to that recommended on the manufacturer’s data sheet. This may only be varied at the manufacturer’s representative’s direct instruction. 3.2 Temperature Ambient conditions as well as casting water and material temperatures can significantly affect the setting time of castables. In very cold conditions, the bags should be kept in warm storage, though not less than 60°F, for at least 48 hours before use.

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DESIGN & INSTALLATION MANUAL CONVENTIONAL REFRACTORY CASTALBES BY CASTING

The ideal temperature of mixed castables lies between 60°F - 80°F. When cast in place until thoroughly dried, the castable and environment preferably should not fall below 50°F and certainly not below 40°F as the castable will take longer to set. If the castable freezes before the hydraulic set is completed, the ultimate strength of the material can be reduced by 50% or more. Therefore, until the cast material is fired, freezing conditions must be avoided.

can be placed within 20 minutes from the start of mixing and do not combine different types of material. Add one half to three quarters of the mixing water to the mixer and begin its operation. Then add the castable in full bag lots. After the mix becomes uniform in color, the remainder of the water is added in small increments to bring the mix to the correct consistency. Do not use more than the recommended amount of water without direct authorization from the manufacturer’s representative.

Figure 3 - Paddle Mixer

In very hot weather, the bags should be kept in cool storage and the outer steel shell and formwork cooled with water sprays. When spraying, care needs to be taken to ensure that no cooling water seeps into the casting cavity. If it does, it must be dried before casting commences. Cool water should be used for mixing. At high temperatures, the time available to place the material is dramatically shortened; e.g. at 100°F the working time can be as little as two minutes. 3.3 Mixing Mixing combines the dry materials and water into a homogenous mass. Mixing must be done in a paddle type or continuous augur type mixer of sufficient capacity to ensure thorough mixing (Figure 3). Small cement drum type mixers generally do not have enough energy to get thorough mixing. The level of dry product in the mixer must not be above the center paddle shaft. Paddle type mixers incorporate rotating shafts with paddles attached. The paddles, which put a high level of work energy into the mixing operation, must be made of steel and have no more than 3¼4 inch clearance from the mixer walls. They assure a rapid, thorough mix and virtually clean themselves from batch to batch. The mixer and tools used in casting must be clean. Some substances like lime or portland cement found in dirty mixers can cause flash setting or otherwise lower the ultimate strength of the castable. The mixer should also be washed periodically during the course of mixing to prevent buildup of material. Do not mix more material than December 2002

Figure 4 - Shaking Needles

When using a bottom discharge mixer, discharge at least two buckets of product from the mixer to clear the gate. This material can be immediately returned to the mixer and re-mixed. The discharge gate should be cleaned out after every mix to prevent buildup of old material in this region. If stainless steel fibers are to be added to the castable, they should be added after all the refractory and water has been added to the mixer. The fibers should be introduced by sprinkling them into the mixer or preferably by shaking them through a wire basket (Figure 4). If the fibers are already contained in the castable, the water addition should be made on the basis of the powder weight, not the bag weight. The weight of fibers present in the mix needs to be subtracted from the bag weight before calculating the casting water needed. Care needs to be taken here since the addition of fibers will cause a lowering of the mix fluidity. NO EXTRA WATER needs to be added to compensate for this loss in fluidity. Lightweight castables should be mixed for approximately six minutes and dense castables for a minimum of three minutes when using a paddle mixer. Excess mixing generates heat causing a decrease in the setting time, while

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Figure 5 - Ball In Hand Test

Figure 6 - Standard Vibrator

insufficient mixing will result in a non-homogenous batch and reduce the strength.

Vibrate (or rod) until the material has settled. The surface should have a wet appearance and air bubbles rising to the surface will cease. Best results are achieved by inserting the poker to a depth of no greater than 12-16 inches, keeping it vertical, and letting the vibrator move slowly through the castable mass. DO NOT force the vibrator through the material as this will cause pockets of air to be left behind. The vibrator head size should be suited to the size of the section being cast - generally a 1 2 inch diameter head is used for large casts, while a 2-2  /  1 1-1  / 2 inch diameter head can be used in smaller casts. Smaller vibrators require a higher VPM rating. When

The “ball in hand” test is a useful guide to proper casting consistency. Tossed one to two inches in the air, a ball of properly mixed castable should adapt to the shape of the hand when it is caught. The ball should not flow through the fingers or break apart. Breaking may indicate insufficient water in the mix. Flowing through the fingers may indicate that the mix is too wet. In contrast insulating castables are wetter and thus will slightly flow through the hand when thrown in the air and caught. This test is unsuitable for the thixotropic, vibratory cast, low cement materials. 3.4 Placement The work of placement of the mixed refractory castable covers several functions: • To position and consolidate freshly mixed material within 20 minutes of it leaving the mixer • To work in a manner which minimizes material segregation • To fill all voids, particularly around obstructions and in corners and to eliminate all air bubbles. Once application has started, it should proceed without interruption until the lining of the part or section concerned is completed. Consolidation of dense castables is done by means of a medium to high frequency vibrator, applied either internally or externally. High frequency is desirable as a lower water content can then be used, causing an increase in strength, density and abrasion resistance. A poker type vibrator (internal) gives maximum strength and densification in the finished casting and assists flow around anchors and into recesses. Insulating castables should be lightly vibrated with a medium frequency vibrator or rodded into place.

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Figure 7 - Vibrating Behind Forms

removing, the vibrator should be drawn upwards very slowly through the castable so it does not leave any holes or channels behind. The mix is too stiff if holes are left behind. When vibrating around anchors and other obstructions, add fresh material from one side and allow the vibrator to feed the material around and under the obstruction to avoid the formation of air pockets (Figure 7). For deep cavities requiring successive layers of castable mix, the poker should pass through the freshly added mix into the previously cast material to ensure a homogenous lining free of laminations.

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DESIGN & INSTALLATION MANUAL CONVENTIONAL REFRACTORY CASTALBES BY CASTING

It is important to note that over vibration will tend to segregate water from the mix, weakening the cast and should thus be avoided. 3.5 Multilayer Linings Where an insulating lining has previously been installed, if possible, the lining should be coated with an impermeable membrane to prevent premature moisture loss from the fresh castable into the insulating layer. The membrane used should burn out at low temperature when the drying cycle is started. Alternatively, the back-up layer may be dampened prior to casting by lightly spraying with water.

you require it, rather than leaving the castable to stress relieve itself in a random crack pattern. For expansion joints, adjacent panels are separated and offset during installation by materials such as cardboard or plastic that will burn out during firing and leave a gap, or by high temperature materials such as ceramic fiber which remain in the gap, but have some degree of recov ery after compression.

Figure 10 - Expansion Joints

3.7 Finishing

Figure 8 - Multilayer Linings

3.6 Joints The two types of joints used in casting are construction  joints and expansion joints.

When finishing the exposed surface of the refractory casting to the necessary level or shape, it is important to avoid excessive troweling of the surface. This draws water to the surface and produces a fine finish of cementrich segregated material which is easily dislodged under alternate heating and cooling. It also seals the surface retarding the escape of moisture during dry-out.

Construction joints (Figure 9) are designed to break the  job up into conveniently sized panels. Adjoining panels are cast up against each other without leaving any gaps using the set face of previously cast sections as the formwork edge. Panels are generally 10-15 ft2. This size can generally absorb stresses without cracking. The construction joint can be regarded as placing a crack where

Figure 11 - Finishing

3.8 Curing Curing prevents the premature loss of moisture from freshly cast refractory concrete during the chemical changes associated with hydration of the calcium aluminate binder. When mixed with water, an exothermic hydration reaction takes place that drives off water at an early stage.

Figure 9 - Construction Joints

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Loss of water from the surface of the cast before the cement is fully hydrated results in a weaker cast. To prevent this, various methods of moist curing can be used. Thermal Ceramics

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Formwork should be left in place for a minimum of 24 hours and exposed refractory concrete either lightly sprayed with water, covered with plastic sheeting, or sprayed with a concrete curing compound. The concrete curing compound forms an impermeable membrane to prevent moisture loss during curing but will burn out at low temperatures during firing.

it should be sprayed or brushed with Kao-Seal™ surface coating to resist the onset of alkali hydrolysis attack. 4 . FIRING Detailed firing schedules are separate from this procedure. They are available from any Thermal Ceramics office or representative. Notice: Some of the products described in this literature contain  Refractory Ceramic Fiber (RCF) and/or crystalline silica (cristobalite or quartz). Based on experimental animal  data, the International Agency for Research on Cancer  (IARC) has classified RCF, along with fibrous glasswool  and mineral wool, as a possible human carcinogen  (Group2B) and respirable crystalline silica as a probable  human carcinogen (Group 2A).

Figure 12 - Cast with Forms in Place

The lower the ambient temperature, the longer the curing time required for proper strength generation. External heating (using a small space heater or similar) may be required to keep the ambient temperature high enough for effective curing (and also casting).

To reduce the potential risk of health effects, Thermal  Ceramics recommends engineering controls and safe  work practices be followed by product users. Contact the  Thermal C eramics P roduct St ewardship Group (1-800-  722-5681) to request detailed information contained in its  MSDSs and product literature and videos.

After the initial 24-hour moist cure, formwork can be stripped away, being careful not to damage the lining as this could possibly occur. A further 24 hours drying is generally allowed before the lining is fired to further increase the final strength.

Figure 13 - Spraying with Curing Compound

If the freshly placed castable is not scheduled to be thoroughly dried (above 500°F) or fired for an extended period of time, then under certain conditions, alkali hydrolysis may result. Alkali hydrolysis is a gradual deteriorating process that begins by attacking the castable surface and continues into the interior. Insulating castables are more susceptible due to their porosity, particularly in a warm, humid environment. Unless the castable can be heated,

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For further information, contact your nearest Thermal Ceramics technical sales office. You may also fax us toll-free at 1-800-KAOWOOL, or write to Thermal Ceramics, P. O. Box 923, Dept. 140, Augusta, GA 30903. Global Headquarters Thermal Ceramics Global L'Européen - Bât. C 2, rue Joseph Monier 92859 Rueil-Malmaison Cedex, France T: +33 (0)1 47 16 22 23 F: +33 (0)1 47 16 22 40 E-mail: [email protected]

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