The Selmers Extruder: at the heart of the coating process

With motor powers even reaching up to 1 Megawatt, Selmers extruders can be mighty machines. But according to Jan Peter Biersteker, Sales Director Linepipe Division, power is only part of the story. What really matters is understanding the coating material, the machine and the process in which they come together. That is why Selmers decided to develop its own extruder specifically for pipe coating.

From granules to coating

In a typical three-layer coating system, the pipe is first cleaned before a powder coating is applied for corrosion protection, followed by an adhesive layer and a plastic topcoat. Selmers extruders are designed for both these adhesive and topcoat layers.

Jan Peter compares the basic principle of an extruder to a very large, highly sophisticated meat grinder. Plastic granules, such as polyethylene (PE) or polypropylene (PP), enter the machine and are transported by a rotating screw. Under high temperature and pressure, they melt into a thick, homogenous syrup-like material that eventually leaves the extruder as a thin, continuous film.

What sounds straightforward requires precise process control. The characteristics of the coating material must be understood and considered in the design and operation of the extruder.

The heart of the coating line

Selmers originally purchased extruders from external suppliers but later decided to design and build them in-house. This allowed Selmers to develop its own knowledge of the machine, the materials and their behavior during the coating process. “We really build our extruders specifically for pipe coating applications and pipe coating materials. That is key,” Jan Peter explains.

He describes the extruder as the heart of a coating process line.  That heart does not operate in isolation. Pipe speed, rotation, temperature and the condition of the preceding coating layer all influence the moment at which the extruded material is applied. According to Jan Peter, there is only a small process window in which the extruded material can be applied correctly. Understanding the complete coating line is therefore an important part of integrating the extruder into the process.

Flexibility and process control

Selmers extruders are designed to operate across a broad output range, allowing different coating capacities to be handled with the same machine. A frequency converter and optimized screw design help stabilize the output, while controllable heating and cooling provide further process control.

Process data also plays a role. Machine and process information can be stored and used to repeat specific settings, supporting continuous and measurable coating quality. “The customer gets a very flexible machine that can work with different types of coating materials and at different speeds,” Jan Peter explains.

Smarter use of material

Process optimization can also reduce material consumption. One example is Selmers’ hydraulic weld seam compensator for specific offshore pipe coating applications. According to Jan Peter, this can reduce coating material use by around 10% or more, lowering both material costs, raw material consumption and last but not least lower the overall footprint of pipeline construction.

Built for the long run

Selmers extruders are used for a range of applications, including PE and PP application, color marking, flat-film, sleeve and jacket extrusion, for example in pipe insulation processes.

And they are built to stay. According to Jan Peter, Selmers extruders can remain in operation for 20 to 30 years and generally require very little maintenance. “It really is a quality product,” he says.

Want to know more about Selmers’ extruders or how they can be integrated into your coating process? Get in touch with our team.