How do we make... things watertight?

Posted on April 27, 2016 by Caren-Malina Butscher, Images by Robert Hack

To ensure that electrical equipment is not exposed to moisture, mtu uses a special process to protectengine cabling.
Friedrichshafen, Deutschland

Are mtu engines watertight? Actually, most of them aren't! But they don’t need to be, because the engine compartment is sealed to keep water out. However, the situation is different for tracked vehicles. They do not have sealed engine compartments, and their engines sometimes get wet. To ensure that its electrical equipment is not exposed to moisture, mtu uses a special process to protect engine cabling.

These cables may be anywhere from one to 15 meters long. They have to withstand temperatures from below zero to 450°C and to carry voltages from 24 to 400V. In short, mtu engine cables have to be robust. “These cables provide the interfaces between the high-tech components on our engines and gensets,” said Georg Haas, master craftsman in the cable production section at MTU Friedrichshafen. They have to be sealed absolutely tight to ensure that they are impermeable to dust and water
and that no engine control or monitoring faults can occur. However, the cables obviously have to be manufactured before mtu technicians can test the engines for leak tightness.

Zoran Krucican needs a steady hand to fit the cores and their pins in the round connector.

One pin for each core

To start the process, Zoran Krucican cuts several long, slender white cores to length. Later on, these cores will conduct the signals for the engine electronics. Krucican fits a pin – a sort of silver sleeve – over the end of each insulated core to provide a cable connector. Using these pins, he then inserts up to 64 cores into a round connector. mtu assembly technician Johannes Hecht then fits a gray rubber sleeve over the cores before the sealing process takes place and a drop of liquid adhesive sealant is applied between the connector and the connector housing.

More than just hot air: Johannes Hecht uses a special hot-air blower to soften the heat-sensitive components and form a sealed connection.

Starting the sealing process

Hecht then fits a braided silver shield over the entire length of the cores to protect against electromagnetic waves. “What we are using here is a tinplated copper alloy that will prevent signal interference later,” explained Haas. So the cores are electronically sealed, as it were. Once Hecht has drawn the braided copper shield over the cores, he pushes it over the connector housing, secures it with a stainless steel strip, winds it around and presses it back in again. Finally, he fits a black shrink-fit sleeve over the connection as a protective cable sheath before using a specially designed molding to join the sleeve and the connector housing. A hot-air blower then shrinks the heat-sensitive components to form a watertight connection between the connector housing and the cable sheath.

Daniel Angele conducts an immersion test to ensure the cables are watertight.

Under water

At this stage, the cables are finished and watertight. However, electrician Daniel Angele still has to immerse the cables to ensure they are tight and will withstand water pressure. Angele places the cable harnesses in an empty bath and lets water in. He uses a pump to simulate pressure – as if the cables were immersed several meters below the surface. “If any air bubbles rise to the surface now, it means the cable is not tight,” said Angele. The cable harnesses are kept under water for 60 minutes to ensure there is no possibility of even the tiniest leak.

Point of contact

Georg Haas
+49 7541 90 8231
+49(0)7541 908190
+49(0)7541 90908231

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