high tech castables by casting - usa

HIGH TECHNOLOGY CASTABLES BY CASTING

DESIGN AND INSTALLATION MANUAL

Thermal Ceramics

TABLE OF CONTENTSA. Preface

Introduction 3B. High Technology Castables by Casting1. General 4

2. Pre-Installation 42.1 Storage 42.2 Surface Preparation Prior to Refractory Placement 42.3 Formwork 42.4 Anchors 5

3. Installation3.1 Water 53.2 Temperature 53.3 Mixing 53.4 Placement 63.5 Multilayer Linings 73.6 Joints 73.7 Finishing 73.8 Curing 8

4. Firing 8List of Figures

Figure 1 Proper Bag Storage 4Figure 2 Formwork 4Figure 3 Paddle Mixer 5Figure 4 Typical Large Paddle Mixer 6Figure 5 Continuous Mixer 6Figure 6 High Frequency Vibrator 6Figure 7 Multilayer Linings 7Figure 8 Construction Joints 7Figure 9 Expansion Joints 7Figure 10 Finishing 7Figure 11 Cast with Forms in Pace 8Figure 12 Spraying With Curing Compound 8

December 2002 Thermal Ceramics Page 2

INTRODUCTION

Over the past 75 years, Thermal Ceramics has provento be a world leader in solving heat intensive problems.

In addition to manufacturing ceramic fiber, brick andfired shape products, a wide range of refractory mono-lithic products are available. From lightweight, highlyinsulating materials to dense, high strength products,Thermal Ceramics has a refractory castable to meetthe needs of the customer. All industries are servicedwith these products, including ferrous, non-ferrous,chemical, utility and ceramic related markets.

The Thermal Ceramic operation in Augusta, Georgiahas been certified to ISO 9002 standards for refracto-ry monolithic production. At this facility, both raw mate-rials and finished products are routinely tested to makesure they meet a demanding quality level.

An experienced staff of refractory specialists is onhand at Thermal Ceramics to assist you in productselection, system design, and installation techniques.This Design and Installation Manual is intended to givethe designers, installers and users of ThermalCeramics monolithic products a broad range of infor-mation guidelines on the particular topic. Any ques-tions or comments regarding this manual should beaddressed to your local Thermal Ceramics represen-tative.

DESIGN & INSTALLATION MANUALHIGH TECHNOLOGY CASTALBES BY CASTING



1. GENERAL

High technology castables, such as Kaocrete

249C/250C and the Kaocrete HPM grades have limecontents of 1-3%. High densities and strengths areachieved in these low cement products by careful grainsizing and the use of additives to reduce the water need-ed to cast.

2. PRE-INSTALLATION

2.1 Storage

High technology 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 ordripping water by a fixed cover. Storage temperature isnot a consideration as long as the castable is in thedesired temperature range prior to casting (See Section3.2). If the bags are further protected by plastic sheeting,ensure there is sufficient ventilation underneath the plas-tic sheet to prevent water from condensing on the bags.Avoid storing in areas of high humidity. Pallets should notbe stacked more than three high when in storage to pre-vent the consolidation and caking of material on the bot-tom rows of the pallets.

The high technology castables have a finite shelf lifecalled a nominal shelf life. When quoting shelf life, aperiod of nine months is used. Product that is older thanthe nominal shelf life should be checked for setting prop-erties prior to use. Signs of aging are longer setting timesand reduced strength. All bags have the date of manu-facture printed on them to aid in determining the age ofthe material. Always use the oldest materials first and, if

aged beyond the nominal shelf life, have the materialtested before use.

2.2 Preparation Prior to Refractory Placement

The work surface shall be substantially free of dust,scale, oil, water, dirt and loose foreign material andshould be cleaned by sandblasting if necessary.

2.3 Formwork

Formwork should be constructed from strong materialsthat resist water absorption (Figure 2). Generally 34inch plywood or steel forms are favored for this jobbecause of their inherent strength and non-absorbentnature.

The surface of the formwork must be lightly and thor-oughly oiled or greased to facilitate removal from the faceof the casting. The surface of the formwork should be uni-form and smooth to give a good surface finish to the cast-ing. It also aids in formwork release.

Formwork must be as watertight as possible, so all jointsand holes must be sealed. The use of vibrators duringcasting will cause liquids and fines to bleed throughcracks in the formwork. These liquids will be rich in fineparticles and can thus leave a weakly bonded materialadjacent to the leaking joint with detrimental results.

Where refractory concrete is to be cast vertically, theformwork should have a height of not more than 48 inch-es with provision for additional sections to be mountedrapidly to ensure the continuous casting of panelsbetween designated joints.

Figure 1 - Proper Bag Storage

Figure 2 - Formwork

2.4 Anchors

Both ceramic and metallic anchors are appropriate foruse with high technology castable refractories. This sub-ject is treated in a separate procedure, Anchoring ofMonolithic Refractories (M150).

3. INSTALLATION

3.1 Water

The water used for mixing should be clean and of drink-able quality - potable water. Since the amount of wateradded to the castable does more to affect the propertiesthan any other factor, it must be accurately measured.

Water amounts are shown on the back of the monolithicbags, but these are intended as a guide only. Actualamounts will depend upon field conditions and shouldstrictly adhere to that recommended on the manufactur-ers data sheet (since the strength of high technologycastables are especially sensitive to slight increase inwater). This may be varied only at the manufacturersrepresentatives direct instruction.

3.2 Temperature

Ambient conditions as well as casting water and materialtemperatures can significantly affect the setting time ofhigh technology castables. In very cold conditions, thebags should be kept in warm storage, not less than 60F,for at least 48 hours before use. The ideal temperature ofmixed low cement castables lies between 62F and 77F.When cast in place until thoroughly dried, the castableand environment preferably should not fall below 60Fand certainly not below 50F as the castable will takemuch longer to set.

If the castable freezes before the hydraulic set is com-pleted, the ultimate strength of the material can bereduced by 50% or more. Therefore, until the cast mate-rial is fired, freezing conditions must be avoided.

In very hot weather, the bags should be kept in cool stor-age (a temperature-controlled container may be required)and the outer steel shell and formwork should be cooledwith water sprays. When spraying, extreme care needs tobe taken to ensure that no cooling water seeps into thecasting cavity. If it does, it must be dried before castingcommences. Cool water should be used for mixing. Athigh temperatures, the time available to place the mater-ial is dramatically shortened; e.g. at 100F, the workingtime can be as little as two minutes.

3.3 Mixing

Mixing combines the dry materials and water into ahomogenous mass. Mixing must be done in a high inten-

sity or continuous augur type paddle mixer of sufficientcapacity to ensure thorough mixing (generally half thenominal capacity) (Figures 3 and 4). The drive systemmust have sufficient horsepower to allow the mixer toachieve 40 rpm when loaded. Small cement drum typemixers do not have enough energy to get thorough mix-ing. The level of dry product in the mixer must not beabove the center paddle shaft. Paddle type mixers incor-porate rotating shafts with paddles attached. The pad-dles, which put a high level of work energy into the mix-ing operation, must be made of steel and have no morethan 34 inch clearance from the mixer walls. Theyassure a rapid, thorough mix and virtually clean them-selves from batch to batch.

The mixer and tools used in casting must be clean. Somesubstances like lime or portland cement, found in dirtymixers, can cause flash setting or otherwise lower theultimate strength of the castable. The mixer should alsobe washed periodically during the course of mixing to pre-vent buildup of material.

Do not mix more material than can be placed within 15minutes from the start of mixing and do not combine dif-ferent types of material.

Add all of the mixing water to the mixer and begin itsoperation. Then add the castable in full bag lots. After themix becomes uniform in color, the remainder of the wateris added in small increments to bring the mix to the cor-rect consistency. Do not use more than the recommend-ed amount of water without direct authorization from themanufacturers representative. When using a bottom dis-charge mixer, discharge at least two buckets of productfrom the mixer to clear the gate. This material can beimmediately returned to the mixer and re-mixed. The dis-charge gate should be cleaned out after every mix to pre-vent 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



Figure 3 - Paddle Mixer


have been added to the mixer. The fibers should beintroduced by sprinkling them into the mixer or by shak-ing them through a wire basket. If the fibers are alreadycontained in the castable, the water addition should bemade on the basis of the powder weight, not the bagweight.

The weight of fibers present in the mix needs to be sub-tracted from the bag weight before calculating the castingwater needed. Care needs to be taken here since theaddition of fibers will cause a lowering of the mix fluidity.NO EXTRA WATER needs to be added to compensatefor this loss in fluidity.

The high technology castables should be mixed for a min-imum of six minutes when using a paddle mixer.

Excess mixing generates heat causing a decrease in thesetting time, whereas insufficient mixing will result in anon-homogenous batch and reduce the strength.

For the high technology castables, the ball in hand testis unsuitable since these castables do not develop fluidi-ty until the vibrator is inserted into the mass. Only experi-ence can show when the castable is suitable for place-

ment, but when the correct water addition is made, thecastable will place well.

3.4 Placement

The work of placement of the mixed refractory castablecovers several functions:

To position and consolidate freshly mixed materialwithin 15 minutes of it leaving the mixer

To work in a manner which minimizes material segre-gation

To fill all voids, particularly around obstructions and incorners and to eliminate all air bubbles.

Once the installation has started, it should proceed with-out interruption until the lining of the part or section con-cerned is completed. Consolidation of the castable is pro-duced using a high frequency vibrator (Figure 6). Thevibrator must have a minimum rated speed of 14000 VPM(vibrations per minute) when immersed in the mass. Apoker type vibrator gives maximum strength and densifi-cation in the finished casting and assists flow aroundanchors and into recesses.

Continue vibrating until the mass has settled into place,the surface gives an appearance of oily wetness and airbubbles have stopped rising. If water collects on the sur-face, reduce the water addition in subsequent batches.

Best results are achieved by inserting the poker to adepth of no greater than 12-16 inches, keeping it vertical,and letting the vibrator move slowly through the entirecastable mass. DO NOT force the vibrator through thematerial as this will cause pockets of air to be left behind.The vibrator head should be suited to the size of the sec-tion being cast generally a 2-21/2 inch diameter head isused for large casts, while a 1-11/2 inch diameter headcan be used in smaller casts. Smaller vibrators require ahigher VPM rating. When removing, the vibrator should

Figure 4 - Typical Large Paddle Mixer

Figure 5 - Continuous Mixer

Figure 6 - High Frequency Vibrator

be drawn upwards very slowly through the castable so itdoes not leave any holes or channels behind.

When vibrating around anchors and other obstructions,add fresh material from one side and allow the vibrator tofeed the material around and under the obstruction toavoid the formation of air pockets. For deep cavitiesrequiring successive layers of castable mix, the pokershould pass through the freshly added mix into the previ-ously cast material to ensure a homogenous lining free oflaminations.

3.5 Multilayer Linings

Where an insulating lining has previously been installed,if possible, the lining should be coated with an imperme-able membrane to prevent premature moisture loss fromthe fresh castable into the insulating layer (Figure 7). Themembrane used should burn out at low temperaturewhen the drying cycle is started. Alternatively, the back-up layer may be dampened prior to casting by lightlyspraying with water.

3.6 Joints

The two types of joints used in casting are constructionjoints and expansion joints.

Construction joints (Figure 8) are designed to break thejob up into conveniently sized panels. Adjoining panelsare cast against each other without leaving any gapsusing the set face of previously cast sections as the form-work edge. Panels are generally 10-15 ft2 in size. Thissize can generally absorb stresses without cracking. Theconstruction joint can be regarded as placing a crackwhere you require it, rather than leaving the castable tostress relieve itself in a random crack pattern.

For expansion joints (Figure 9), adjacent panels are sep-arated and offset during installation by materials such ascardboard or plastic that will burn out during firing andleave a gap, or by high temperature materials such as

ceramic fiber which remain in the gap, but have somedegree of recovery after compression.

3.7 Finishing

When finishing the exposed surface of the refractorycasting to the necessary level or shape, it is important toavoid excessive troweling of the surface. This drawswater to the surface and produces a fine finish of cementrich segregated material which is easily dislodged underalternate heating and cooling.



Figure 7 - Multilayer Linings

Figure 8 - Construction Joints

Figure 9 - Expansion Joints

Figure 10 - Finishing

3.8 Curing

Curing prevents the loss of moisture from freshly castrefractory concrete. Loss of water from the surface of thecast before the bond is fully hydrated results in a weakercast. To prevent this, various methods of moist curing canbe used.

Formwork should be left in place for a minimum of 24hours and exposed refractory concrete either sprayedwith water, covered with plastic sheeting, or sprayed witha concrete curing compound (Figure 12). This is calledmoist curing. The concrete curing compound forms animpermeable membrane to prevent moisture loss duringcuring but will burn out at low temperatures during firing.Curing is essential to the achievement of maximumstrength in the green unfired state which will effect theultimate fired strength.

The lower the ambient temperature, the longer the curingtime required for proper strength generation. Curing atlow temperatures also increases the risk of steamspalling during initial heat up. External heating (using asmall space heater or similar) may be required to keepthe ambient temperature high enough for effective curingand also casting.

After the initial 24-hour moist cure, formwork can bestripped away, being careful not to damage the lining asthis could possibly occur. A further 24 hours air curingshould be allowed before the lining is fired to furtherincrease the final strength.

4. FIRING

Detailed firing schedules are separate from this proce-dure. They are available from any Thermal Ceramicsoffice or representative.

Notice:

Some of the products described in this literature containRefractory Ceramic Fiber (RCF) and/or crystalline silica(cristobalite or quartz). Based on experimental animaldata, the International Agency for Research on Cancer(IARC) has classified RCF, along with fibrous glasswooland mineral wool, as a possible human carcinogen(Group2B) and respirable crystalline silica as a probablehuman carcinogen (Group 2A).

To reduce the potential risk of health effects, ThermalCeramics recommends engineering controls and safework practices be followed by product users. Contact theThermal Ceramics Product Stewardship Group (1-800-722-5681) to request detailed information contained in itsMSDSs and product literature and videos.


Figure 11 - Cast with Forns in Place

Figure 12 - Spraying with Curing Compound

12.02/M147/1.5M COPYRIGHT 2002 THERMAL CERAMICS INC.

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For further information, contact your nearest Thermal Ceramics technical sales office. You may also fax ustoll-free at 1-800-KAOWOOL, or write to Thermal Ceramics, P. O. Box 923, Dept. 140, Augusta, GA30903.

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high tech castables by casting - usa

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