Retaining walls may seem like a niche in the precast market but are among the most common and widely used elements in the non-residential building industry. These elements are produced in various shapes and sizes and find application in many fields such as agriculture, soil and terrain management, water channels, fencing, road works, silage clamps, storage, and others. Despite appearing rather simple both in geometry and composition, the design and manufacturing of these elements can be quite challenging, as they often must comply with strict tolerances, withstand heavy loads, flexural stress, wet or chemical environments, contact with soil, and are also subject to weathering.
In order to last long in these circumstances (50+ years), the quality of concrete must be very high, and reinforcement carefully arranged, especially in the weak point which is in the sharp 90° angles of the foot. Additionally, in common with many other types of precast elements (walls, slabs..), great importance is given to weight reduction and thus quantities of raw materials, to save on costs and be more competitive on the market, while keeping the on-site performance of the elements unaffected.
When it comes to retaining walls, The Netherlands are definitely the reference market in Europe, along with the neighbouring countries, due to their geography, abundance of water canals, waterways, famous agriculture, soil management and highly developed road and rail networks. And within this market company, Bosch Beton is surely the manufacturer and supplier of reference.
Bosch Beton is a family-run company started back in 1968, based today in a beautiful and state-of-the-art factory in the city of Barneveld, built just 5 years ago and equipped with cutting-edge technologies for precast. With a workforce of about 100, the company accomplishes over 4.500 projects throughout Northwest Europe every year, which translates to more than 50.000 pieces of retaining walls. For the most used and common types, about 7.000 walls are always in stock and ready to be delivered to construction sites, but there are also custom projects where the walls are designed and produced for specific needs.
Sustainability and innovation are top priorities for the company: the roof of the factory is covered with solar panels that power the whole plant, rainwater is collected and used when needed, and internal research is focused towards 100% circular production, with huge gains already obtained for cement-free products. Needless to say, the resulting quality of the walls is superior, and for this reason, Bosch Beton is able to give huge warranties, even up to 20 years, on their products.
On the reinforcement side, Bosch used to buy all their mesh from the market and therefore kept a huge stock in the factory. All mesh is special, with variable wire spacing, different diameters and different lengths of the bars in the same mesh. A large number of products were manually shaped on several manual bending stations, with some of the benders being so customized that were unavailable on the market and had thus been handcrafted by skilled Bosch technicians, to produce the special shapes.
As obviously, the big mesh suppliers don’t cope well with special mesh types and custom orders in small batches, delivery periods became longer and longer over time. With the intention to reduce stock, free some space in the factory and reduce manual jobs for the workers, Bosch finally decided to invest in a fully automatic mesh welding and bending line between 2020 and 2021, in spite of the covid global pandemic.
Staying in contact with only a few selected suppliers capable to manufacture such a demanding plant, the technical discussion went on for quite some time. Reinforcement drawings of the retaining walls were analysed and reviewed in great detail, to understand their feasibility and try to find the best configuration for the machine, optimising the workflow and reducing downtime as much as possible.
Eventually, the job was awarded to the Italian manufacturer AWM Srl.
AWM manufactured the machine model “Flexiweld SF”
, part of the very well-known Flexiweld family with a long innovation history on its back and the first specimen dating back to the year 1991.
Tracing only the highlights, this machine is fed from compact 5-ton coils of wire with different diameters; wires are straightened with rotors and flying cut with two straightening machines, to separate the cross from long bars and increase productivity. The welding process is immediately followed by bending with the Autobend unit and the machine ends with a long roller conveyor on which the products are stacked.
This type of machine is nowadays completely automatic and works unmanned or with little supervision, requiring a few seldom manual operations such as coil change and unloading of the finished products.
Even if custom machines and tailored solutions have been usual business for AWM ever since the project presented several challenges on the technical side and new features have been developed with extreme success.
In the first place, due to the specific design of retaining walls, reinforcement is often intricate and very dense in the foot where mesh are combined together; for this reason, the machine can weld longitudinal wires at stepless (“free” or “gridless”) pitch, meaning positioning of the bars is controlled every millimetre.
Most mesh Bosch uses in his production are obviously bent automatically in-line, sometimes the cross bars must stay inside and sometimes outside of the bent shape.
The machine is therefore equipped with a large longitudinal mesh tilter that can turn any mesh up to a length of 8 meters. AWM developed this unit specifically to be fast, avoiding any possible downtime, however, very short mesh are welded so quickly that turning is conveniently delegated to another handling unit further down the line which
is even faster.
In order to reduce downtime caused by bending mandrel changes, a mobile bench was designed to store 7 types of mandrels, including one for virtual bending.
Additionally, to match any configuration of the longitudinal wires with the stepless pitch mentioned above, the position of each mandrel needed to be adjusted.
For accurate positioning of each bending pin, AWM developed an automatic system that can automatically change the position of any mandrel installed on the bending beam as well as change the bending beam to store the sizes not currently used on the side, on the movable bench.
This Flexiweld model features innovations and optionals specifically developed for the Bosch Beton customer.
Installed in June 2022, the machine is working at full capacity and, to date, has achieved 90% productivity during the work shift.