1917 to the present day – over 90 years of centrifugal casting in Wetzlar

A ductile cast-iron pipe comes to life

For over 90 years, Duktus has been producing cast-iron pipes using a centrifugal casting process – creating quality products based on tradition and expertise. We guarantee our pipes for 100 years.

At the first stage of the process, various types of scrap are mixed and melted in the cupola furnace at temperatures of up to 2000 °C. We then conduct a precise chemical analysis to ensure that the properties of the final material satisfy the required high standards of quality. The vonRoll Group generally does not use crude iron to produce its cast-iron pipes. This approach reduces CO2 emissions by around 65 % as it removes the need to melt iron ore. The pipe production line becomes a recycling process with no limitations on the achievable quality of the material.

 

diagram of cupola furnace

Thanks to the use of scrap metal as a raw material in the manufacturing process, and the long operating life of the resulting product, Duktus ductile cast-iron pipes are a highly sustainable solution. Our product is exceptionally environmentally friendly – and is 100 % recyclable at the end of its life.

The next stage – a magnesium treatment that takes place in a converter – gives the pipes their ductile quality. Cast iron (grey cast iron with lamellar graphite) used to be a very brittle material. By swapping the lamellar graphite for graphite balls, the material becomes as flexible as steel.

The molten metal is then poured into rotating permanent moulds and cooled quickly with water, which hardens the 6 m-long pipes in a matter of seconds. This centrifugal casting process is known as the De Lavaud process.

 

diagram of centrifugal casting

 

Due to the rapid cooling process, the pipes are left with a very hard microstructure on the surface. This structure is softened in an annealing process, which takes place at 950 °C in a 50 m tunnel furnace.

To provide the pipes with lifelong protection against corrosion, the exterior surface is coated with metallic zinc or a zinc/aluminium alloy. Today, this method is also used in the production of car panels.

At Duktus, 100 % quality is our top priority, so we carry out a number of checks on our products to verify the material properties and dimensions. Each pipe is also checked for leaks at pressures of up to 50 bar; we take no shortcuts when it comes to safety.

On pipes with a BLS® joint, a welding bead is applied to the spigot so that the holding bar forms a longitudinal positive locking joint during the pipe’s subsequent installation.
To safely transport drinking water in a way that maintains potability, all pipes are given a cement mortar lining (CML). This process takes place as part of procedure I in accordance with DIN 2880.
Now, all that remains to do is apply the outside coating. There are a number of different exterior coating options. The standard process is to apply an epoxy resin finishing layer.

A cement-mortar coating can also be applied to the galvanised pipe as an alternative. Pipes coated with a cement-mortar coating (CMC) can be installed in substrates with a grain size of up to 100 mm, aggressive soils or in trenchless systems. The CMC also extends the expected technical operating life to up to 140 years.

For years, Duktus has been following these processes to create top-quality products.

To ensure that our products are easily recognisable and traceable, the pipes are labelled before they leave production. They are then passed on to dispatch for delivery to our customers.

Our expertise, your products. You can rely on us.

Diagram of pipe manufacturing process

 

diagram of pipe manufacturing process

 

Our video “How is a cast-iron pipe produced?”

 How are cast iron pipes made?

The Duktus foundry in Wetzlar