RAW MATERIAL PREPARATION
A ball mill wet-grinds the quartz sand with water to a sand slurry. The sand slurry is stored in slurry tanks and pumped into the slurry weighing hopper in the mixer tower. The binders (lime, cement and anhydrite) are stored in silos. It is also possible to mill the anhydrite together with the sand in the ball mill. 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. 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 AND MOULD CIRCULATION
The mould consists of four fixed sides and one detachable platform. The inner mould surfaces are covered with demoulding release oil before casting. This oil is applied either manually or automatically. The mix is then poured into the moulds. A mould circulation system conveys the moulds to the rising area, where the cake pre-cures for 2-3 hours after which it is ready for cutting. Depending on the plant design, the moulds are handled by a mould traverser or by the tilting-manipulator.
The HESS systems are also ideal for the production of large format reinforced panels. Depending on the required capacity, the reinforcement cages are outsourced or welded on site. The cages are then assembled per mould and hung onto holding frames with cross bars and needles. A corrosion protection is then applied. Immediately after the mix has been poured into the mould, the waiting reinforcement frame assembly is inserted. Before cutting of the cake the holding frames with needles are lifted, leaving the reinforcement in the cake.
The tilting manipulator tilts the mould by 90°. The manipulator unlocks the mould and removes the mould body, so that the cake remains on one mould side/platform for cutting. This tilting system has proven to be the safest method for tilting the cake into the vertical cutting position, as the cake is remaining on the platform / mould side for the cutting process.
The cake in cut by high precision cutting machines. Cutting is done by pneumatically tensioned cutting wires.
the pre-cutter and vertical cutter cut the block length and panel width. In this station the profiling (tongue and groove) can be cut into the cake with profiling knives;
the horizontal cutter cuts the block and panel thickness;
the cross cutter cuts the block height and the panel length. Optionally hand-grips can be milled into the cake in the green stage..
BACK-TILTING AND BED WASTE REMOVAL
In most tilt-cake systems the cake is autoclaved in the vertical position. The HESS plants have combined the advantages of the tilt-cake and flat-cake system.
After the cutting is completed, the cake is tilted back by 90° onto a cooking frame. In the HESS system no part of the mould or platform, used for cutting, goes into the autoclaves. After the cake has been tilted back into the horizontal orientation, the bottom/bed waste will be removed before autoclaving. Autoclaving the cake while lying horizontally on the cooking frames allows efficient autoclave loading and most importantly, will prevent most of the sticking of the layers, which is a typical disadvantage of the traditional tilt-cake systems.
One of the HESS innovations is the green separator. Here the horizontal cuts (now lying vertical) are carefully separated before autoclaving, leaving a small gap in between the layers. This innovation eliminates any sticking, which is typical for other tilt-cake systems. Further this green separation substantially improves the autoclaving process as steam can penetrate into the cake more effectively.
FRAME CIRCULATION AND AUTOCLAVING
The green cakes on the cooking frame are stacked three high onto autoclaving cars, referred to as bogeys. Autoclave buffer tracks in front of the autoclaves ensure that the cutting and packaging processes are less dependent on one another. An autoclave traverser is used for loading and unloading the autoclaves, ensuring that this process is performed in the shortest possible time, in order to optimise autoclaving capacity.
In the autoclaves the cakes are cured for ca. 10 - 12 hours at a temperature of 190° C with saturated steam at a pressure of 12 bar. The fully automatic autoclave control system ensures a safe and optimal autoclaving process, also allowing for steam transfer and energy reutilization in combination with the condensate system.
UNLOADING AND PACKAGING
After autoclaving is completed, the cakes are destacked and unloaded from the cooking frames. HESS offers a large variety of packaging solutions, ensuring that the finished products are packed according to local market requirements. Usually blocks will be delivered as packs on wooden pallets, strapped and/or covered in foil.
HESS also offers a wide range or post-autoclaving handling for reinforced products, such as packaging lines, sawing and shaping systems.
PROCESS CONTROL AND PLANT AUTOMATION
The entire production process is controlled by modern automation systems designed by HESS on the basis of Siemens S7 control system using standard components that are available world-wide. User-friendly, multi-lingual operator interfaces with touchscreen monitors allow easy and understandable operation. The HESS remote diagnostic system allows for the possibility of online support.
HESS 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 gain important information on raw material production behaviour and final product quality.