Autoclaved Aerated Concrete Technology Plants and ... - HESS Group

Autoclaved aerated concreteThe Autoclaved Aerated Concrete (AAC) materialwas developed in 1924 in Sweden. It hasbecome one of the most used building materialsin Europe and is rapidly growing in manyother countries around the world.Autoclaved Aerated Concrete, also known asAircrete, is a lightweight, load-bearing, highinsulating,durable building product, whichis produced in a wide range of sizes andstrengths.AAC offers incredible opportunities to increasebuilding quality and at the same time reducecosts at the construction site.AAC is produced out of a mix of quartz sandand/or pulverized fly ash (PFA), lime, cement,gypsum/anhydrite, water and aluminium andis hardened by steam-curing in autoclaves. Asa result of its excellent properties, AAC is usedin many building constructions, for example inresidential homes, commercial and industrialbuildings, schools, hospitals, hotels and manyother applications.The construction material aircrete contains60% to 85% air by volume. The solid materialpart is a crystalline binder, which is calledTobermorite by mineralogists. Besides the bindingphase Tobermorite aircrete contains grainsof quartz and in minor amounts some otherminerals. The chemical composition of Tobermoriteshows silicium dioxide, calcium oxideand water.The silicium dioxide is obtained from silicasand, fly ash (PFA), or crushed quartzite. It ispossible to obtain silicium dioxide as a by-productfrom other processes, e.g. foundry sand.The calcium oxide is obtained from quick lime,hydrated lime and cement. Gypsum/Anhydriteis added in small quantities as a catalyst and foroptimizing the properties of AAC. Aluminiumpowder / paste is used as expanding agent.Advandayes of AAC• Large variety of sizes: AAC can be producedin a large variety of sizes, from standardblocks to large reinforced panels;• Excellent thermal insulation: AAC has avery low thermal conductivity and thereforea very high thermal energy efficiencyis achieved.This results in cost savings forheating and cooling;• Extremely lightweight: AAC weighs approximately50% less than other comparablebuilding products;• High compressive strength: AAC is a solidproduct, therefore making it highly loadbearing. The entire surface area is used instructural calculations;• High dimensional accuracy: As a result ofits dimensional accuracy, AAC is extremelyeasy to install, as no thick set mortar isrequired;• Great acoustic insulation: The porousstructure of AAC provides a high acousticinsulation;• High fire resistance: AAC has an extremelyhigh fire resistance rating of at least 4hours and more;• Termite resistance: AAC can not be damagedby termites or insects;• High workability: As a result of the excellentsize/weight ratio, AAC allows rapidconstruction work. Even though AAC is asolid building material, it can be cut, sawn,drilled, nailed and milled like wood, makingit an easily workable product2 3

Production processReinforcement preparationThe HESS systems are also ideal for the production of large format reinforced panels. Dependingon the required capacity, the reinforcement cages are outsourced or welded on site. The cagesare then assembled per mould and hung onto holding frames with cross bars and needles. A corrosionprotection is then applied. Immediately after the mix has been poured into the mould, thewaiting reinforcement frame assembly is inserted. Before cutting of the cake the holding frameswith needles are lifted, leaving the reinforcement in the cake.Raw material preparation and mixingA ball mill wet-grinds the quartz sand with water to a sand slurry. The sand slurry is stored in slurrytanks and pumped into the slurry weighing hopper in the mixer tower. The binders (lime, cementand anhydrite) are stored in silos. It is also possible to mill the anhydrite together with the sand inthe ball mill. The aluminum powder or paste is prepared in a separate building where it is dispersedin water.All the components are accurately weighed, and are released into the mixer in a pre defined order.The HESS recipe and temperature control system constantly monitors this process.HESS also has the knowledge and the experience to produce AAC with alternative raw materials,for example with fly ash.Casting, rising/pre-curing andmould circulationThe mould consists of four fixed sides and one detachableplatform. The inner mould surfaces are coveredwith demoulding release oil before casting.This oil is applied either manually or automatically.The mix is then poured into the moulds. A mouldcirculation system conveys the moulds to the risingarea, where the cake pre-cures for 2-3 hours afterwhich it is ready for cutting. Depending on the plantdesign, the moulds are handled by a mould traverseror by the tilting-manipulator.TiltingThe HESS systems are also idealfor the production of large formatreinforced panels. Dependingon the required capacity,the reinforcement cages are outsourcedor welded on site. Thecages are then assembled permould and hung onto holdingframes with cross bars and needles.A corrosion protection isthen applied. Immediately afterthe mix has been poured into themould, the waiting reinforcementframe assembly is inserted.Before cutting of the cake theholding frames with needles arelifted, leaving the reinforcementin the cake.6 7

CuttingThe cake is cut by high precision cutting machines.Cutting is done by cutting knives andby pneumatically tensioned cutting wires.• the pre-cutter and vertical cutter cutthe block length and panel width. Inthis station the profiling (tongue andgroove) can be cut into the cake withprofiling knives;• the horizontal cutter cuts the block andpanel thickness;• the cross cutter cuts the block heightand the panel length. Optionally handgripscan be milled in the blocks in thegreen sdaye.8 9

Back-tilting and bed removalIn most tilt-cake systems the cake is autoclaved inthe vertical position. The HESS plants have combinedthe advandayes of the tilt-cake and flat-cakesystem.After the cutting is completed, the cake is tilted backby 90° onto a cooking frame. In the HESS systemno part of the mould or platform used for cuttinggoes into the autoclaves. After the cake has beentilted back into the horizontal orientation, the bottom/bedwaste will be removed before autoclaving.Autoclaving the cake while lying horizontally on thecooking frames allows efficient autoclave loadingand most importantly, will prevent most of the stickingof the layers, which is a typical disadvandayeof the traditional tilt-cake systems.HESS SYSTEMS PRODUCE NOPROCESS RELATED WASTE!Green separationOne of the HESS innovations is the green separator.Here the horizontal cuts (now lyingvertical) are carefully separated before autoclaving,leaving a small gap in between the layers.This innovation eliminates any sticking, whichis typical for other tilt-cake systems. Further thisgreen separation substantially improves the autoclavingprocess as steam can penetrate intothe cake more effectivety.Frame and bogey circulationThe green cakes on the cooking frame are stackedthree high onto autoclaving cars, referred toas bogeys. Autoclave buffer tracks in front of theautoclaves ensure that the cutting and packagingprocesses are less dependent on one another. Anautoclave traverser is used for loading and unloadingthe autoclaves, ensuring that this process isperformed in the shortest possible time, in order tooptimise autoclaving capacity.AutoclavingIn the autoclaves the cakes are cured for ca. 10 – 12hours at a temperature of 190° C with saturatedsteam at a pressure of 12 bar. The fully automaticautoclave control system ensures a safe and optimalautoclaving process, also allowing for steam transferand energy reutilization in combination with thecondensate system.10 11

Process control and plant automationThe entire production process is controlled by modern automation systems designed by HESSon the basis of Siemens S7 control system using standard components that are available worldwide.User-friendly, multi-lingual operator interfaces with touchscreen monitors allow easy andunderstandable operation. The HESS remote diagnostic system allows for the possibility of onlinesupport.Unloading and packingAfter autoclaving is completed, the cakesare destacked and unloaded from the cookingframes. HESS offers a large variety ofpackaging solutions, ensuring that the finishedproducts are packed according to localmarket requirements. Usually blocks will bedelivered as packs on wooden pallets, strappedand/or covered in foil.HESS also offers a wide range or post-autoclavinghandling for reinforced products,such as packaging lines, sawing and shapingsystems.Process know-howHESS has a modern laboratory equippedwith all necessary equipment and apparatusto perform vital raw material tests. Not onlythe raw material characteristics are checked,but also small scale AAC productionis possible, allowing HESS to gain importantinformation on raw material production behaviourand final product quality.12 13

ModificationsTechnical Data - AAC PlantsCompact Line – CBTCBT-200 CBT-300 CBT-400Theoretical capacity 200 m³ / day 300 m³ / day 400 m³ / dayCakes / day 75 112 150Cycle time 18,0 min / cake 12,0 min / cake 9,0 min / cakeNo. of autoclaves (32 m) 2 3 4No. of rising places 9 13 17Net cake size 3,0 x 1,5 x 0,6 m = 2,7 m³Keen-Crete® Line – KBT-SKBT-S-450 KBT-S-650 KBT-S-900Theoretical capacity 450 m³ / day 650 m³ / day 900 m³ / dayCakes / day 84 126 167Cycle time 16,1 min / cake 10,7 min / cake 8,1 min / cakeNo. of autoclaves (43.7 m) 2 3 4No. of rising places 10 14 19Net cake size 6,0 x 1,5 x 0,6 m = 5,4 m³Keen-Crete® Line – KBTKBT-900 KBT-1100 KBT-1350 KBT-1550Upgrade of existing Hebel type cutting systemsIn order to increase the quality of the productas well as the reliability of the plant, withoutinvesting in a complete new cutting machine,the modification of the Hebel technologybased cutting machine is possible.• cutting table with moving bridges• needles with rectangular design• ballance opposed double set of cross cuttingshafts• vertical wire tensioning system• top crust removal system• horizontal cutting system for lintel cutting• counter pusher with pusher package• bottom and top profiling system• control system• hydraulic systemHighlights• short installation time• proven technology• the existing logistics and production technologydo not require major changesHESS can also undertake the modification ofother AAC plant systemTheoretical capacity 900 m³/ day 1.100 m³/ day 1.350 m³/ day 1550 m³/ dayCakes / day 167 204 250 288Cycle time 8,1 min / cake 6,5 min / cake 5,3 min / cake 4,6 min / cakeNo. of autoclaves (43.7 m) 4 5 6 7No. of rising places 19 24 28 33Net cake size 6,0 x 1,5 x 0,6 m = 5,4 m³Keen-Crete® Line – KBT-LKBT-L-1550 KBT-L-1750 KBT-L-2000Theoretical capacity 1550 m³/ day 1750 m³/ day 2000 m³/ dayCakes / day 288 330 370Cycle time 4,7 min/ cake 4,1 min/ cake 3,7 min/ cakeNo. of autoclaves (43.7 m) 7 8 9No. of rising places 32 37 41Net cake size 6,0 x 1,5 x 0,6 m = 5,4 m³Based on a pre-curing time of 2,5 h and on 2 autoclave cycles/day. These are dependent on raw materials and product mix. Other autoclave lengthsand net cake volumes are possible and will change the capacity data. Reinforced products with a length of max. 6 meters can be produced on allKeen-Crete® Lines14 15

We put concrete into shapeHESS Group – Successful for more than 6 decadesThe HESS group provides you the competitive edge in the field of concrete block and pipe makingmachines, plants for the production of autoclaved aerated concrete as well as the associated componentsand mixing plants.HESS AAC Systems B.V. possesses specific know-how on the building of machines and plants forthe autoclaved aerated concrete and sand-lime brick industry.More than 40 years ago HESS AAC became active on the AAC market, concentrating mainlyon manufacturing, installing and maintaining the production machinery for the world marketleaders in AAC. During this relationship HESS built several production lines for key customers inEurope.Today HESS is known worldwide for its excellent craftsmanship, engineering know-how and highquality of the products and services it supplies. The machinery is robust and equipped with firstclass components, at a very competitive price level.HESS AAC Systems B.V.Aluminiumsteden 107547 TN Enschede, The NetherlandsPhone:Fax:E-mail:Internet:+31 (0) 53 460 1700+31 (0) 53 460 1799info@hess-aac.comwww.hess-aac.comENG V2 2013 / SaGRights to changes with regards to technical modifications and contentsare reserved.The pictures on the preceding pages are partially withoutsafety devices due to illustrational reasons!16