Right: Evonik’s MLT 4840 multi-layer tubing system uses a polyamide inner layer in place of a fluoropolymer

newly developed grade of polyamide 612 for the inner layer. Crucially, the system uses aliphatic polyam-

ide in the inner layer. In the past, only aromatic PA grades – and fluoropolymers – had a good enough low-extractable performance. “This is a special material that we’ve developed

power, the systems operate well below permitted legal thresholds. The system can be used in conjunction with

iXact diameter-measuring systems, which can make up to 16,000 measurements per second per axis. They are often used for pipe or tube diameter measurement at the end of the extrusion line.

Auto extrusion Maillefer says that its multi-layer co-extrusion cell provides high enough flexibility to produce modern automotive tubes.

Demand for plastic pipe within the automotive sector is growing, but emission standards can be highly restrictive – meaning that products such as fuel vapour return tubes must have a sufficient barrier to prevent emissions. At the same time, electric vehicles also require tubes that work at raised temperature, in applications such as cooling tubes that keep batteries at the optimal temperature. Maillefer says that an array of five or six of its single screw extruders – with a multi-layer ECH crosshead at the centre – can be used as the basis to extrude pipes up to six layers. Production flexibility, combined with the possibility of swap- ping layer positions, gives manufacturers many choices, says the company. “Mathematically, more than 150 combinations

are possible with the five-layer head, while many more are possible with the six-layer version,” said Mailleer.

Allowing operators to prepare for the next

product run by optimising set-up and clean operations at the head makes for faster product changes. The head’s indexing feature allows layer positions to be assigned with a simple twist. Reduc- ing the number of layers to be extruded is made possible by using thicker distributors or by combining extruder flows. The head has an improved design that allow easy removal of parts, which is appreciated during cleaning.

Conductive inner layer Evonik has developed a conductive, low-extracta- ble multi-layer tubing system for automotive fuel lines – which uses a polyamide inner layer in place of an expensive fluoropolymer. Its MLT 4840 multi-layer tubing system uses a

22 PIPE & PROFILE EXTRUSION | November/December 2019

from previously existing grades,” said Klaus Gahlmann, director of tubing systems in the company’s automotive and mobility division. The three-year development project began by adding conductive fillers to the material, but in time the plastic itself also had to be modified. “It’s not just about the fillers,” said Gahlmann. The other advantage of using an aliphatic

material is that it can be extruded at relatively high speed without suffering a ‘sharkskin’ effect. MLT 4840 retains its antistatic properties even

after long-term contact with alcohol-containing fuels, and is more cost-effective than systems that use fluoropolymers, said the company. Alcohol-containing fuels, such as ethanol-con- taining biofuels, can dissolve components from the inner walls of conventional fuel lines. These substances can clog the nozzles in sensitive fuel systems that use small-diameter nozzles to create an atomised spray of fuel and air for fuel injection, in order to reduce fuel consumption. To reduce this possibility, Evonik has expanded its range of multilayer tubing systems to include some with reduced extraction. The new material also ensures that swelling

effects – which might destroy the conductive effect – are avoided.

Gahlmann added that it is crucial for the adhesive layer to be low extractable – and this material had already been developed for the earlier MLT 4800 system.

Although the system was showcased at K2019, it

is already being trialled by customers. “They are already testing it to their own require-

ments,” said Gahlmann. “It’s being assessed on several platforms. We hope it will start being used commercially next year.” The company says that it now has both conduc- tive and non-conductive vers ion of the multi-layer pipe. The non-conductive version is the earlier MLT 4800, launched at K2016.


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