REFRACTORY CASTABLES BY GUNNING DESIGN AND INSTALLATION MANUAL
Thermal Ceramics
TABLE OF CONTENTS A. Preface I ntr od uct ion B. Refractory Castables by Gunning 1 . Ge n e r a l 2. Pre-Installation 2. 1 S to r a ge 2.2 Surface Preparation Prior to Refractory Placement 2. 3 A n c ho r s 3 . I n s ta l l a t i o n 3.1 Te mper atu re 3.2 Jo ints 3.3 Equip ment 3.4 Multilayer Linings 4. Firing 4. 1 P re wet 4. 2 N o z z e l W a t e r C o nt ro l 4. 3 G un ni ng 4.4 Fin ishi ng 4. 5 Cu ri ng 5. Firing List of Figures F ig ur e 1 G un nin g F ig ur e 2 Proper Bag Storage F ig ur e 3 Construction Joints F ig ur e 4 Expansion Joints F ig ur e 5 Rotary Gun F ig ur e 6 Do ubl e Cha mber Gun F ig ur e 7 Multilayer Linings F ig ur e 8 Ca Castable Gun Surface F ig ur e 9 B o o s te r P u mp F i g u r e 1 0 S ta n d a r d N o z z l e F i g u r e 1 1 D o ub l e B u b b l e N o z z l e F i g u r e 1 2 C o r r e c t G un n i n g T e c h n i q u e Figure 13 Gunning with Rebound Falling Clear F i g u re 1 4 Ove rhead Gun ning Tech nique F i g u re 1 5 Gunning Pattern and Distance F i g u re 1 6 Gu agin g Dep th o f Gun ned P anel F i g u re 1 7 Cu tting B ack Gunn ed Mate rial
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DESIGN & INSTALLATION MANUAL REFRACTORY CASTALBES BY GUNNING
INTRODUCTION
1 . G EN ENE RA RA L
Over the past 75 years, Thermal Ceramics has proven to be a world leader in solving heat intensive problems.
Thermal Ceramics provides a wide range of products designed for application by pneumatic gun. This method involves refractory castables being pneumatically conveyed through suitably designed flexible hoses to the installation position, whereupon they are projected through a handheld nozzle at the target area. This type of installation is well suited for the following:
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.
• Where Where large large volumes volumes of refract refractory ory are involv involved, ed, gunning may reduce installation time and costs. • Where Where there there is no need need for shutt shuttering ering,, further further reducreducing the cost of the job. • Where Where access access is difficult, difficult, provid provided ed a nozzlem nozzleman an and and hose can be accommodated, a lining can be gunned. • For elevat elevated ed po positio sitions, ns, ma materia terials ls can be conveyed conveyed vertically for reasonable distances, solving logistic problems. • Where Where multilaye multilayered red walls walls are required required,, it is often often easier and more cost effective to gun two layers rather than use two sets of formwork. • Where Where space space for refrac refractory tory is limited limited,, thin linings linings are are easier to place. • For odd odd or irregula irregularr contoure contoured d shapes shapes which which are difdifficult to form up.
Figure 1 - Gunning
There are two types of gunning – wet and dry.
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Wet (or slurry) gunning involves mixing all of the required water with the mix in a paddle mixer prior to conveying to the nozzle. This method usually requires a higher water content and thus density of the placed material may be lower. However, there is little or no dust caused by this method and low rebound, lamination-free linings result. Dry gunning is the much more popular of the two methods. It allows the nozzleman to operate up to 300 yards horizontally and 150 yards vertically away from the feed station. Desired air pressures at the nozzle are 35-50 psi for dense castables, 25-35 psi for medium weights and 20-25 psi for lightweights, depending on the product. Higun materials require higher air volumes than conventional dense castables (50-75 psi) to ensure adequate mixing in the nozzle extension and sufficient compaction on the walls. Due to the pressure drop between the nozzle and the gun, the gun operator should as a guide add 5 psi for every 50 feet of hose length more than the standard two lengths, and 5 psi for every 50 feet of elevation above the gunning machine. For lightweights add 3 psi. If the pressure is too high, material density and rebound will increase; low pressure results in low strength and lack of consolidation. Since the amount of water added is determined by the nozzle operator, the person gunning should have eno ugh experience with the particular refractory being used to know how much water to add to get the correct consistency on the wall. Too much water and the material will have low density and strength and could slump off the wall; too little, and the rebound and dusting losses are high.
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. 2.2 Preparati Preparation on Prior to Refracto Refractory ry Placement. Placement. The work surface shall be substantially free of dust, scale, oil, water, dirt and loose foreign material and should be cleaned by sandblasting if necessary.
2. PRE-I PRE-INS NSTAL TALLA LATI TION ON 2.1 Stor Storag age e Castables should be stored in a dry, well-ventilated area and held off the floor on pallets (Figure 2). If stored outside, the bags must be protected from rain or dripping water by a fixed cover. Stor age temperature is not a consideration as long as the castable is in the desired temperature range prior to use. 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 pallets. December 2002
Figure 2 - Proper Bag Storage
2.3 Anchors Both ceramic and metallic anchors are appropriate for use with gunning grade castable refractories. This sub ject is treated in a separate procedure “Anchoring of Monolithic Refractories” (M 150). 3. INST INSTAL ALLA LATI TION ON 3.1 Temp Temper erat atur ure e Ambient conditions as well as material and gunning water temperatures can significantly affect the ease of gunning and initial setting time of the castable. In very cold conditions, the bags should be kept in warm storage, not less than 60°F, for at least 48 hours before use.
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DESIGN & INSTALLATION MANUAL REFRACTORY CASTALBES BY GUNNING
Cold material retards the activation of the cement binder thereby increasing rebound during gunning and may also cause slumping. The ideal mix temperature lies between 60°F and 80°F. When gunned in place and until thoroughly dried, the castable and environment preferably should not fall below 50°F and certainly not below 40°F. If the castable freezes before the hydraulic set is completed, the ultimate strength of the material can be reduced by 50% or more. In very hot weather, the bags should be kept in cool storage and cool water used for gunning. The steel shell may also need cooling prior to gunning. This can be done by spraying the shell with water from the gun, ensuring that the water does not pool where the refractory is to be installed. 3.2 Join Joints ts The two types of joints used in gunning, although sometimes linings are gunned without any joints, are construc tion joints and expansion joints.
Figure 4 - Expansion Joints
3. 3.3 3 Equi Equipm pmen entt Equipment used is conventional conventional concrete guniting equip ment. This involves an air operated gun forcing material through a flexible hose and a nozzle where water is added to it. Most Thermal Ceramics gunite contractors typically use a rotary gun (Figure 5) with 8 to 10 pockets, although pressurized double chamber guns (Figure 6) are also used.
Construction joints (Figure 3) are designed to break the job up into conveniently conven iently sized panels. Adjoining Adjoin ing panels are gunned against each other without leaving any gaps using the set face of previously gunned sections as the formwork edge. Panels are generally 10-15 ft 2. This size can generally absorb stresses without cracking. The construction joint can be regarded as placing a crack where you require it, rather than leaving the castable to stress relieve itself in a random crack pattern.
Figure 5 - Rotary Gun
With a rotary gun, material is placed in the gun hopper where it feeds into a wheel with pockets at the base of the hopper. The wheel turns by motor driven gears powered by compressed air.
Figure 3 - Construction Joints
For expansion joints (Figure 4), adjacent panels are sep arated and offset during installation by materials such as cardboard or plastic which will burn out during firing and eave a gap, or by high temperature materials such as ceramic fiber which remain in the gap, but have some degree of recovery after compression.
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When the feed wheel rotates, the loaded pockets pass under an air inlet section which forces the material to the outlet neck and into the feed hose in a steady flow. The material passes along the hose to the nozzle, where it is mixed with water (if needed) and sprayed onto the wall. 1 Generally, two 50-foot lengths of 1 / 2 inch I.D. hose are used. If more lengths are required, air pressure at the gun must be increased as previously noted. The quantity of material able to be conveyed is only limited by the inside diameter of the hose and the quantity of air available.
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slumpage on the wall). The drawback of prewetting is potential clogging of the nozzle. Material should be mixed in a paddle type or high intensity ribbon mixer for one to two minutes with a fraction of the t otal water needed (see bag or data sheet for further information). Kao-Plas™ and Higun products are especially prone to nozzle clogging and are not pre-wet before gunning. 4. 4.2 2 Nozzle Nozzle Water Water Cont Control rol Control of the water addition by the nozzleman is a critical factor and one based largely on his experience. Appearance of the gunned refractory surface is the only indicator of correct water/mix ratio (Figure 8). Freshly placed material should have a wet, silky sheen which rapidly disappears when the nozzle is moved away from the area. The coarse aggregate should make small craters on the surface on impact. A sandy, gritty surface indicates too little water is being used. Slumping, ripples or a washboard surface indicates too much water.
Figure 6 - Double CHamber Gun
An 18 inch flexible nozzle extension (“whip”) is required for some products like Higun to provide better water/material intermixing during gunning. 3. 3.4 4 Multilay Multilayer er Linings Linings Where an insulating lining has previously been installed, a coating with an impermeable membrane should be used to prevent premature moisture loss from the fresh castable into the insulating layer (Figure 7). 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.
Figure 8 - Castable Gun Surface
Water pressure at the nozzle must be at least 10 psi higher than the air pressure to ensure that the water is able to completely wet the material as it passes the water ring. A water booster pump may be required to increase plant water pressure (Figure 9). For Higun prod ucts high pressure water feed is needed to drive the water into the material at the water ring so the water pump should be used capable of a minimum of 200 psi.
NOTE:
Figure 7 - Multilayer Linings
4. GUN GUNNIN NING 4.1 P re re we we t Prewetting castables before being placed in the gunning hopper cuts down on dusting at the nozzle, allows better water control and accelerates the set of the material in cold temperatures (process called “slaking” to stop December 2002
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Figure 9 - Booster Pump
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The nozzleman should break up the installation into conveniently sized panels, which allows construction joints to be put in (Figure 15). Upon completion of a panel, the edges are cut back at right angles to the shell, removing all waste and rebound before proceeding to the next panel.
Figure Figure 10 - Standard Nozzle
Inconsistent mixing of water is often caused by either too low pressure or blocked holes in the ring. This should be periodically checked and cleaned. Higun products require a 16 hole water ring to allow for the higher pressure and to help resist blockage.
Figure 12 - Correct Gunning Technique
Figure 11 - Double Bubble Nozzle
4.3 Gunn Gunnin ing g The nozzle is held between 45° and 90° perpendicular to the wall and approximately 18-24 inches away from the work surface (Figure 10 and 11). It is moved in a circular motion building up the full thickness over the whole area of the designated panel starting from the bottom of the wall and working up, then from the top down and filling the center section last (Figure 12). Lower sections and corners are generally gunned first so that rebound does not become entrapped there. Care needs to be taken to ensure that the rebound falls clear of the target area and does not become entrapped (Figure 13). This causes laminations or spots of low density in the panel. When gunning overhead, water addition should be reduced slightly to prevent slumping prior to initial set of material material (Figure 14). 14). An increase increase in rebound should also be expected when gunning in this orientation. The nozzle should be at an angle of about 45°. December 2002
Figure 13 - Gunning with Rebound Falling Clear
If, for any reason, an interruption delays application in excess of 10 minutes, any area which has been partially gunned shall have the edges cut back at right angles to
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as a guide since the end face of the anchor brick is required to finish flush with the lining. When metallic anchors are used, they are generally set back one to three inches from the hot face. In this 1 method, the nozzleman’s trowel-hand uses a rod of / 16 16 inch wire, bent at right angles to the required depth (Figure 16). This is inserted in the lining at right angles to the working face and turned full circle. If the lining is too thick, a circle remains on the wall, indicating the correct thickness and giving the troweler a level to cut back to. If too thin, then there is no mark and the wall needs further building. The third method involves using gauge boards set at the lining thickness. The lining is gunned then cut back with a levelling board held on the gauge boards. This method is used where accurate thicknesses are a must.
Figure 14 - Overhead Gunning Technique
When gunning around anchors, avoid “shadowing” as this is detrimental to the lining, causing laminations. When this occurs, the material should be removed and re-gunned. Similarly, any overspray on anchors or steelwork should be removed on a continual basis. If the lining consists of two layers, e.g. an insulating castable back-up lining and a hot face, the hot face can be gunned onto the first layer after the back-up has set. Generally, the back-up layer is given a coating of a concrete curing compound to prevent loss of water of hydration from the hot face material to the back-up. Preferably, the back-up lining should be cured before the hot face lin ing is installed. 4. 4.4 4 Fini Finish shin ing g The as-gunned finish of the refractory is quite acceptable, but if a smoother surface is required, it can be scraped with the edge of a trowel or wooden board as soon as possible after the completion of gunning (Figure 17). The rough, open texture should be left. Smooth troweling to
Figure 15 - Gunning Pattern and Distance
Figure 16 - Guaging Depth of Gunned Panel
the work face where full thickness has been achieved. Any areas not built-up to full thickness shall be removed and replaced. To control the thickness of the lining, several methods may be used. When ceramic anchors are used, they act December 2002
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Figure 17 - Overhead Gunning Technique
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slick the surface is unacceptable as this draws a fine fin ish of cement rich segregated material to the surface, which can spall off during heating. 4.5 Curi Curing ng Curing the castable prevents the premature loss of moisture from freshly gunned refractory concrete during the chemical changes associated with hydration of the calcium aluminate binder. When mixed with water, an exothermic hydration reaction takes place which drives off water at an early stage. Loss of water from the surface of the castable before the cement is fully hydrated results in a weaker lining. To prevent this, various methods of moist curing should be used. Exposed refractory can be 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. Moist curing needs to be performed for a minimum of 24 hours. Curing is essential to the achievement of maximum strength in the green unfired state and will effect the ultimate fired strength. After the initial 24-hour moist cure, a further 24 hours of air-curing should be allowed before the lining is fired to further increase the final strength. 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 warm, humid environment. Unless the castable can be heated, it should be sprayed or brushed with Kao-Seal™ surface coating to resist the onset of alkali hydrolysis attack. 5 . F I RI N G 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). 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.
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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, 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:
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