AAC Technology - Plants and Systems - HESS Group

AAC Technology - Plants and Systems

The Autoclaved Aerated Concrete (AAC) materialwas developed in 1924 in Sweden. It has becomeone of the most used building materials in Europeand is rapidly growing in many other countriesaround the world.Autoclaved Aerated Concrete, also known asAircrete, is a lightweight, load-bearing, highinsulating,durable building product, which isproduced in a wide range of sizes and strengths.AAC offers incredible opportunities to increasebuilding quality and at the same time reduce costsat the construction site.AAC is produced out of a mix of quartz sand and/or pulverized fly ash (PFA), lime, cement, gypsum/anhydrite, water and aluminium and is hardenedby steam-curing in autoclaves. As a result of itsexcellent properties, AAC is used in many buildingconstructions, for example in residential homes,commercial and industrial buildings, schools,hospitals, hotels and many other applications.The construction material aircrete contains 60%to 85% air by volume. The solid material part isa crystalline binder, which is called Tobermoriteby mineralogists. Besides the binding phaseTobermorite aircrete contains grains of quartzand in minor amounts some other minerals. Thechemical composition of Tobermorite showssilicium dioxide, calcium oxide and water.The silicium dioxide is obtained from silica sand,fly ash (PFA), or crushed quartzite. It is possible toobtain silicium dioxide as a by-product from otherprocesses, e.g. foundry sand. The calcium oxide isobtained from quick lime, hydrated lime and cement.Gypsum/Anhydrite is added in small quantitiesas a catalyst and for optimizing the propertiesof AAC. Aluminium powder / paste is used as expandingagent.

Advantages of AACLarge variety of sizes: AAC can be produced ina large variety of sizes, from standard blocks tolarge reinforced panels;Excellent thermal insulation: AAC has a very lowthermal conductivity and therefore a very highthermal energy efficiency is achieved.This resultsin cost savings for heating and cooling;Extremely lightweight: AAC weighs approximately50% less than other comparable buildingproducts;High compressive strength: AAC is a solidproduct, therefore making it highly load bearing.The entire surface area is used in structuralcalculations;Great acoustic insulation: The porous structure ofAAC provides a high acoustic insulation;High fire resistance: AAC has an extremely highfire resistance rating of at least 4 hours and more;Termite resistance: AAC can not be damaged bytermites or insects;High workability: As a result of the excellentsize/weight ratio, AAC allows rapid constructionwork. Even though AAC is a solid building material,it can be cut, sawn, drilled, nailed and milledlike wood, making it an easily workable product.High dimensional accuracy: As a result of itsdimensional accuracy, AAC is extremely easy toinstall, as no thick set mortar is required;

212224272526161719181514131210The HESS AAC plants offer a high degree of flexible design, tailored to the specific requirements interms of capacity and product range. The systems are based on know-how and experience in both tiltcakeand flat-cake production systems, hereby combining the advantages of the two systems.Standard HESS AAC plant systems:COMPACT LINE – designed for lower output and reduced automationCBT version – capacity range from 200 – 400 m³/dayKEEN-CRETE® LINE – intended for medium and large output and high automationKBT-S version – capacity range from 350 – 900 m³/dayKBT version – capacity range from 900 – 1550 m³/dayKBT-L version – capacity range from 1350 – 2050 m³/day

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, cement andanhydrite) are stored in silos. It is also possible to mill the anhydrite together with the sand in the ballmill. The aluminum powder or paste is prepared in a separate building where it is dispersed in water.All the components are accurately weighed, and are released into the mixer in a pre defined order. TheHESS recipe and temperature control system constantly monitors this process.HESS also has the knowledge and the experience to produce AAC with alternative raw materials, forexample with fly ash.Casting, rising/pre-curing andmould circulationThe mould consists of four fixed sides and onedetachable platform. The inner mould surfaces arecovered with 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.

Reinforcement preparationThe HESS systems are also ideal for the production of largeformat reinforced panels. Depending on the required capacity,the reinforcement cages are outsourced or welded on site. Thecages are then assembled per mould and hung onto holdingframes with cross bars and needles. A corrosion protectionis then applied. Immediately after the mix has been pouredinto the mould, the waiting reinforcement frame assembly isinserted. Before cutting of the cake the holding frames withneedles are lifted, leaving the reinforcement in the cake.TiltingThe tilting manipulator tilts themould by 90°. The manipulatorunlocks the mould and removesthe mould body, so that thecake remains on one mouldside/platform for cutting. Thistilting system has proven to bethe safest method for tilting thecake into the vertical cuttingposition, as the cake is remainingon the platform / mould side forthe cutting process.

CuttingThe cake is cut by high precision cuttingmachines. Cutting is done by cutting knives andby pneumatically tensioned cutting wires.the pre-cutter and vertical cutter cut theblock length and panel width. In this stationthe profiling (tongue and groove) can becut into the cake with profiling knives;the horizontal cutter cuts the block andpanel thickness;the cross cutter cuts the block height andthe panel length. Optionally hand-grips canbe milled in the blocks in the green stage.

Back-tilting and bed removalIn most tilt-cake systems the cake is autoclavedin the vertical position. The HESS plants havecombined the advantages of the tilt-cake andflat-cake system.After the cutting is completed, the cake is tiltedback by 90° onto a cooking frame. In the HESSsystem no part of the mould or platform usedfor cutting goes into the autoclaves. After thecake has been tilted back into the horizontalorientation, the bottom/bed waste will beremoved before autoclaving. Autoclaving thecake while lying horizontally on the cookingframes allows efficient autoclave loadingand most importantly, will prevent most ofthe sticking of the layers, which is a typicaldisadvantage of the traditional tilt-cakesystems.HESS SYSTEMS PRODUCE NOPROCESS RELATED WASTE!Green separationOne of the HESS innovations is the green separator.Here the horizontal cuts (now lying vertical) are carefullyseparated before autoclaving, leaving a small gap inbetween the layers. This innovation eliminates anysticking, which is typical for other tilt-cake systems.Further this green separation substantially improves theautoclaving process as steam can penetrate into the cakemore effectivety.

Frame and bogey circulationThe green cakes on the cooking frame are stacked threehigh onto autoclaving cars, referred to as bogeys. Autoclavebuffer tracks in front of the autoclaves ensure thatthe cutting and packaging processes are less dependenton one another. An autoclave traverser is used for loadingand unloading the autoclaves, ensuring that thisprocess is performed in the shortest possible time, in orderto optimise autoclaving capacity.AutoclavingIn the autoclaves the cakes are cured for ca. 10 – 12 hoursat a temperature of 190° C with saturated steam at apressure of 12 bar. The fully automatic autoclave controlsystem ensures a safe and optimal autoclaving process,also allowing for steam transfer and energy reutilizationin combination with the condensate system.

Unloading and packingAfter autoclaving is completed, the cakes are destacked and unloadedfrom the cooking frames. HESS offers a large variety of packagingsolutions, ensuring that the finished products are packed according tolocal market requirements. Usually blocks will be delivered as packson wooden pallets, strapped and/or covered in foil.HESS also offers a wide range or post-autoclaving handling forreinforced products, such as packaging lines, sawing and shapingsystems.

Process control and plant automationThe entire production process is controlled by modern automation systems designed by HESS on the basis of Siemens S7control system using standard components that are available world-wide. User-friendly, multi-lingual operator interfaceswith touchscreen monitors allow easy and understandable operation. The HESS remote diagnostic system allows for thepossibility of online support.Process know-howHESS has a modern laboratory equipped with all necessary equipment and apparatus to perform vital raw material tests.Not only the raw material characteristics are checked, but also small scale AAC production is possible, allowing HESS to gainimportant information on raw material production behaviour and final product quality.

Upgrades of existing Hebel-type cutting systems.In 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 technology basedcutting machine is possible.cutting table with moving bridgesneedles with rectangular designballance opposed double set of cross cutting shaftsvertical wire tensioning systemtop crust removal systemhorizontal cutting system for lintel cuttingcounter pusher with pusher packagebottom and top profiling systemcontrol systemhydraulic systemHighlightsshort installation timeproven technologythe existing logistics and productiontechnology do not require major changesHESS can also undertake the modificationof other AAC plant systems.

Development – Design – FabricationHESS machinery is designed on modern 3-D CADsystems. In the production only materials andcomponents of the highest standards are used.Continuous in-house control ensures this highquality standard.Machine components are made out of certifiedsteel types and manufactured with the help of CNCcontrolled welding-, milling- and drilling machinery.This results in machinery and systems with accuratedimensions and a high quality standard.ServiceEven after the installation and commissioning of theplant, HESS customers benefit from the first-class knowhow of our engineers.Experienced and trained service engineers can assistin resolving problems by access to the machinery viaremote diagnosis.Also regular service inspections on site can be offered toensure that the productivity and product quality remainat a constantly high level.Storage facilities worldwide with original spare andwearing parts guarantee availability and ensurecontinuous productivity of your systems.

We put concrete into shapeHESS Group – Successful formore than 6 decadesHESS AAC Systems B.V. possesses specificknow-how on the building of machines andplants for the autoclaved aerated concreteand sand-lime brick industry.More than 40 years ago HESS AAC becameactive on the AAC market, concentratingmainly on manufacturing, installing andmaintaining the production machinery forthe world market leaders in AAC. During thisrelationship HESS built several productionlines for key customers in Europe.Today HESS is known worldwide for itsexcellent craftsmanship, engineering knowhowand high quality of the products andservices it supplies. The machinery is robustand equipped with first class components, ata 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.comWith the reservation of technical modifications and as regards contents!The pictures on the preceding pages are partially without safety devicesdue to illustrational reasons!