Plastic pipes for protecting cables in the ground are available in a wide variety of diameters and wall thicknesses. One thing is the same in all cases: the cables inside the pipe are to be protected from environmental influences and damage. To ensure this, appropriate standards must be met that clearly specify the properties of the conduit.

Among other things, these standards specify the diameter/wall thickness ratio, which fixes the amount of material per running meter of pipe. To save costs, recyclates or B-goods are often used, whose property profile and processing characteristics are highly dependent on the batch.

Saving costs by using environmentally friendly gases
Another approach to reducing costs and plastic consumption is to physically foam the pipes. Here, environmentally friendly gases such as carbon dioxide or nitrogen are injected into the plastic and mixed with it in the extruder. In the subsequent pipe extrusion process, these gases form a fine-pored foam that leads to weight reduction and thus to savings in plastic.

Joint venture - working together for the best result
In a joint project of the companies Hans Weber Maschinenfabrik GmbH and Promix Solutions AG, the feasibility, practicality and savings potential have now been determined. For this purpose, Weber provided a grooved barrel extruder type “NE7.40” for the foamed middle layer and a grooved barrel extruder type “NE5.40” for the inner and outer layers. A Weber “PKM250” 3-layer pipe head was used as the die. In addition, the downstream equipment available in the technical center of Hans Weber GmbH: Cooling section, haul-off and saw were used. Promix Solutions provided an “N400” gas dosing station with adapted injector for precise metering of the nitrogen and a “P1 180” melt cooler for homogenization and temperature reduction of the melt. In the initial trials, Borealis' “HDPE HE3490 LS” was used for a DN110 x 6.3 cable protection tube and foamed with nitrogen.

After production of a non-foamed reference sample, the metered gas quantity was gradually increased, resulting in a weight reduction of up to 26% for virgin material and approx. 15% for recycled material - based on the entire pipe. The pipe produced in this way was subsequently tested in accordance with DIN 16876 and GA KSR 2010 (Switzerland) and was able to meet all requirements. Particular attention was paid to the ring stiffness and the drop test according to DIN EN 744. Based on these positive results, the test was repeated with a foamed inner layer made of recycled HDPE. This also showed good feasibility with a stable process.

More sustainability through physically foamed cable conduits
In view of the current supply situation for polymers and the ever increasing material prices, microcellular foaming of plastic pipes is a perfect way to save material and reduce the CO2 footprint for the pipes. In contrast to foaming with exothermic chemical blowing agents, no SVHC (substances of very high concern) listed additives are used and an accumulation of additives via regrind recycling is also avoided. Of course, this technology can also be used for other pipe systems. The experts from Hans Weber Maschinenfabrik GmbH and Promix Solutions AG will be happy to provide more information on this topic.

In the coming months, the joint tests of Weber and Promix will be continued to foam further pipe variants, throughputs, and other polymers with this technology. Furthermore, they are working together on a solution for physically foamed PVC extrudates.

Promix Solutions AG
Technoparkstrasse 2
 8406 Winterthur, Switzerland
Contact person is Andrea Schwarz
Tel.: +41 52 2678085
a.schwarz@promix-solutions.com
www.promix-solution.com

About Promix Solutions AG
Promix Solutions AG is the leading supplier of unique key components and solutions in the area of mixing, foaming and cooling in plastics processing and polymer production. Promix serves the industry with effective solutions for the reduction of the environmental footprint, cost savings and quality improvements in extrusion and injection molding. A motivated team with long standing experience and extensive process and application know-how ensures excellent consultancy and service. The product portfolio includes Foam Extrusion Systems, CO2/N2 Gas Dosing Stations, nucleation additives, Key Components for the production of Light Foams, Mixing Nozzles, Melt Blenders, Melt Coolers and Inline-Viscosity Measurement Systems.