Energy-efficient automation in construction chemistry

For more than 60 years ARDEX has been the competent brand of the specialist craft and wholesale trade in the building industry. With excellent products of optimum workmanship, the company has evolved into a quality leader of a whole business line. The company ARDEX manufactures a wide range of construction chemistry products (Fig. 1). For applications in carcassing, these are, for example, concrete fillers, screeds and grouts. In addition they also produce tile adhesives, natural stone adhesives, grouts, wall and façade fillers. All products must have functions that are optimally attuned to the working processes and are distinguished by a constantly uniform and high quality.

With over 37 subsidiaries the ARDEX Group is represented in more than 50 countries on all continents. The Witten-based family-owned business has been an internationally operating enterprise for a long time and is one of the leading suppliers of high-quality special building materials all over the world. At their development center ARDEX continuously research and work on new ideas and innovative product systems within the framework of precisely controlled research processes. Whether this concerns primers, fillers, sealants or coating materials – all product developments at ARDEX have only one goal, i.  e. to facilitate systematically the work of the specialist craftsmen and to widen the range of creative possibilities. The extensive ex-
perience gained with materials and working processes as well as the permanent dialogue with the customers are, in any case, the most important sources of inspiration.

It goes without saying that the high ARDEX quality is also a protection against consequential costs. Due to their tremendous reliability the systems always ensure maximum working safety. This is a factor that should not be underestimated because in this way complaints and incalculable costs for repairs are ­
avoided. Each order which is perfectly carried out will positively contribute to the good reputation of the processing ­
company.

The product quality comes first as regards the aims of capital spending: ARDEX customers can always rely on the product function promised, e.g. easy, efficient and quick workability. Another important criterion is flexibility of production.

The new plant should ensure the continuous improvement and optimization of the products as well as the manufacture of newly developed products. The long-term reliability should be ensured by landmark process control and visualization technology in addition to innovative automation technology. Targets were:

1. Automation of more than 50 raw materials, in particular the integration of the medium and small components, in more than 50 formulations with up to 20 components.

2. Maximum throughput in compliance with maximum dosing and weighing precision.

3. Energy-efficient handling of large product quantities in a tower concept with vertical material flow.

4. Control screening of all raw materials used to avoid a “comet formation” during working

5. Highest flexibility when changing the product due to very easy cleaning systems with extremely short production downtimes.

6. Change of product in case of special products and pre-blended materials without residues.

7. Low-dust, ergonomic workplaces due to closed systems.

8. Gentle, trouble-free conveying of difficult raw materials, such as titanium dioxide.

9. Transparent process, product safety and documentation of all formulations including connection to the superior host system.

10. Maintenance and service friendly overall system ensuring a high availability with future-proof components.

“During the project phase we already realized that the key to successful production lies before the actual mixing process because there is the cornerstone for the proverbial quality of our products.” says Peter Kawka, plant manager with ARDEX ­Witten. “Screening of all the raw materials used was a must for us. In addition to the vibrating screens for large quan-
tities, cyclone screeners from AZO are convincing because of their compact design and efficiency.” continues Klaus Behrendt, Manager Corporate Engineering with ARDEX.

After a detailed project study ARDEX decided in favour of a vertical tower concept (Fig. 2) according to which the raw materials are pneumatically conveyed to the top and then dosed and weighed in free fall and fed to the mixing and the following filling processes. The entire plant is subdivided into seven sections:

1. Automation of large quantities

2. Handling of pre-blended materials and special products

3. Provision of the medium material components

4. AZO COMPONENTER^® for automatic weighing of additives

5. Mixers

6. Filling of the finished products and pre-blended materials

7. Process control and visualization of the entire plant.

There are 15 silos of standard steel for the storage of large quantities that are arranged at various levels. These silos are fed via filling lines from bulk container vehicles. Monitoring and plausibility checks are carried out via preselection in the receiving department and by the sensor technology at the connections of the conveying line. This kind of monitoring ensures that the right products get to the silos intended for them. Specific compressed air is stationary available for the discharge of the bulk container vehicle. This prevents air humidity from being blown into the hygroscopic products, which would inevitably lead to clotting. The filling lines are equipped with spherical bends since in many cases the products, such as cement, fibrous materials, chalk, gypsum, dispersing powder and sand are abrasive. The lines are mounted and integrated in such a way that they could quickly be replaced by means of a hoisting gear in case of possible wear. This is done as a preventive measure every three months.

All silos are equipped with large filters and level measurement systems. Depending on the product, some of the silos are explosion-proof providing a maximum of safety. The design of the silo outlets is also adapted to the product properties. The alternatives range from a simple outlet cone and vibrating bottoms up to vibrating bottoms additionally equipped with aerating nozzles (Fig. 3). This ensures that all products are discharged on a “first in – first out” basis. Adequately dimensioned, frequency-controlled dosing screw feeders are used for metering of the products into the hopper weighers. Since both large and small quantities of the various products are handled, in part the screws are designed “pickaback”, i. e. the big screw is followed by a small one that doses the small quantities.

For exact dosing of all components, the screws are frequency controlled so that even with large amounts, very high precision with simultaneously very high outputs are achieved. A control screening machine is installed between the dosing screw feeder and the weighing machine to dissolve clottings or discharge them. The exactly weighed batches are discharged into a preliminary hopper for finished mixtures above the mixers.

According to the experiences of ARDEX, AZO DOSITAINERS^® offer maximum flexibility when changing the product and ensure, amongst other things, an ideal change of pre-blended products without any residue. Safe raw material handling without any mistakes in the phase of material provision is achieved by operator control at monitors and bar code monitoring of all raw materials.

To produce pre-blended materials, various types of gypsum are taken from the giant silos and dosed into the corresponding hopper weigher. Also in this case coarse-fine switching for dosing and control screening is part of the operation. Further raw materials belonging to the formulation are preliminarily weighed and directly fed into the mixer via a feed ­hopper including an integrated control screen. After producing the ­homogeneous mix, it can be filled into both Big Bags and AZO DOSITAINERS^®. They can be used for the further process as changing components in the AZO ­COMPONENTER^®.

The medium components are supplied in bags or Big Bags at ground level. The bagged material is filled into the feed hopper with low dust formation. From there it is transported by means of a suction conveying system gently and dust-free into the daily service silo above the AZO COMPONENTER^®. The material can be distributed to the corresponding storage bins via a coupling station. The supplied Big Bags are docked at the Big Bag discharge stations and discharged there (Fig. 4). These raw materials are also transported to the daily service silos by pneumatic suction conveying systems. A separate station offers the possibility to transfer the bagged material to the AZO DOSITAINER^®. Theses containers with integrated feed screw can be put on the AZO COMPONENTER^® as changing components. When the product is changed, the AZO ­DOSITAINER^® can be replaced easily and quickly without any major cleaning expenditure, which is a special advantage of this system. Paints and special control additives, which cannot be conveyed ­pneumatically, are fed via the feed hopper directly above the AZO ­COMPONENTER^®. All components supplied are ­safely discharged and screened with control cycloscreeners. The components are exactly proportioned by proportioning screw feeders into the mobile weighing machines of the AZO ­COMPONENTER^®.

The AZO COMPONENTER^® including the change weighers provides boundless flexibility for the automatic provision of additives for ARDEX. Maximum dosing precision for control additives is a unique selling point of our company in international competition. At the beginning of the project we were looking for a strong company as regards the dosing of small quantities (Fig. 5). With AZO we found a partner that integrated all components in the automation process. Almost none of AZO’s competitors thought that it was possible to automate the paints and control additives like the AZODOS^® systems.

The AZO COMPONENTER^® is equipped with two mobile weighing machines that approach the corresponding dosing points according to the formulation. There a dustproof connection is established and an aspiration system is connected automatically. Now the components can be dosed exactly into the weighing machines designed as containers. Protective slide valves prevent the material from flowing out from the dosing points. Since control additives and paints have to be fed very accurately, AZODOS^® dosing devices are used in this field as negative weighing machines. They have a smaller weighing range than the mobile weighers and, therefore, can weigh small product quantities very accurately (Fig. 5). As soon as a formulation has been executed and all components are inside the mobile weighing machine, the latter is moved to a discharge station. A dustproof connection is established by means of a docking device and a patented docking sleeve, and the complete batch is discharged into the mixer below to produce the finished mix. To save time during a product change, the containers on the mobile weighing machines can be replaced by cleaned ones. Thus, no delay will occur since production can be continued immediately.

Two horizontal mixers are available to produce the finished mixtures. A further mixer of similar design is used for preblending. Feed hoppers above the mixers make it possible to add material by hand. After sampling this can be used to adjust the batch. In this connection also the overall concept leaves nothing to be desired as regards flexibility.

“The close consultation between the project planning and production departments of ARDEX and the AZO engineers led to an optimum concept tailored to our requirements yielding a high profit, ensuring further growth and setting no capacity limits for us.” says Peter Kawka. As in the receiving department, when filling many different kinds of packaging are possible (Fig. 6). For instance, the finished mixtures can be filled in bags and stored via a fully automatic bagging and palletizing system. ­Furthermore it is also possible to fill containers and Big Bags at corresponding filling stations.

It was particularly important for ARDEX to have a partner for the entire project as regards process and control engineering. Clear responsibilities between AZO and hsh made it possible to adapt the production in an optimum way to the MES and host system. The operators overlook the entire production from the central control room (Fig. 7). The clearly arranged process visualization informs the operator at any time as regards the current state of production. For example, the levels, parameters or the mixer status can be identified at a glance. It is possible to work without interfaces due to the connection to the host computer. The operators in the production department receive exact instructions at clearly designed, coloured monitors, as to which products have to be filled and where. In this case mistakes are prevented by the bar code system. Furthermore, there is the possibility to intervene in the automatic process via operator terminals. In this way, it is possible to change from the automatic process to a semi-automatic or an individually controlled process. The corresponding protocols for the formulation docu-
mentation are printed out as well as the consignment notes, labels etc. Only the optimum interplay of process and control engineering offers maximum production safety and transparency as well as the documentation of all goods produced.

“As regards energy efficiency, the new plant in Witten is an example for our plants worldwide. Both as regards process and control engineering the module idea will become world stand-
ard for application”, concludes Peter Kawka.