Top coating extruder

A specially designed main extrusion system, which melts the HDPE or PP granules to a homogeny mass, after which the coating material can be applied onto the pipe. A pressure roller system prevents air entrapments underneath the top-coat layer. A weld seam compensation system, used when processing longitudinal welded pipes (LSAW- pipes) reduces the material consumption. The system can be used on a large variety of pipe diameters.

• Suitable for flat-head and cross-head(ring) extrusion dies: Depending on the required pipe diameter range the extruder can either be equipped with a flat-head extrusion die in a side-extrusion (wrapping) process, or for pipe diameters up to 24” a cross-head extrusion die can be provided, suitable for a sleeve/hose extrusion pipe coating process.
• Screen & screen changer: A screen is installed between the extruder and extrusion die, preventing unmolten particles in the applied coating layer. In case the screen gets polluted too much, an alarm signal will appear, and the screen can be changed during production by means of a hydraulic screen changer.
• Pressure roller system: A pressure roller system ensures the top-coat layer is properly applied onto the pipe surface and prevents air entrapments.
• Weld seam compensation system: A weld seam compensation system will reduce the amount of HDPE or PP to be applied on the pipe surface. Such system is suitable for LSAW-pipes. A system with an acceleration roller is available, as well as an injection system which achieves additional material savings.
• Granules drying & pre-heating system: A drying system removes moisture from the granules, which otherwise could cause gas-forming in the molten HDPE or PP material, resulting in holidays (defects in the coating layer). Pre-heating of the granules will result in more efficient extruder output and avoids the risk of unmolten granules particles.
• Additives: When required, the extruder system can be extended with a gravimetric granules feeding system, e.g. for colour batching or recycled coating materials.
• Orientation: In a wrapping application, the sheet can be applied from side, or alternatively from top for which the extruder will be installed on a lifting platform.
• Controls: Modern control with HMI panel of the complete extruder system.

• Special designed extruder: In general extruders have a higher output capacity for LDPE materials compared with HDPE materials. Selmers’ special extruder design is designed for pipe coating application for which HDPE materials are most often used. The screw design provides a high output for PP materials as well, at a very competitive price level.
• Complete system: Selmers not only supplies the extruder, but can supply the complete system from granules feeding up to the application onto the pie surface. One stop shopping instead of different suppliers for different items if the extrusion system.
• Wide output range: Apart from the maximum output, the extruder can rum at low rpm as well for plants where a wide range of pipe diameters can be processed.
• Multi purpose extruder design: The extruder is suitable for processing HDPE materials and PP materials, but LDPE and MDPE materials can be processed as well.
• Bushing zone: Bushing water-cooling design without O-rings.
• Space requirement: frame design for less built-in space
• Maintenance: Easy maintenance due to module construction

The top coating extruder system applies a layer of High-Density Polyethylene (HDPE) or Polypropylenes on the external pipe surface, typically used in a multi-layer pipe coating system.

The top coating extruder is typically used in a pipe coating line combined with various other process equipment, such as pipe handling system, pipe-heating system, FBE powder application, adhesive extruder system and quench system.