Surface technology process: Inside Rinsing of coolers

The internal rinsing of the cooler forms the background for the conductivity rinsing in fuel cell applications. The requirements of the OEMs for the conductivity in the cooling circuit are usually between 5 and 100 µS / cm. The conductivity of a coolant is around 2 - 6 μS / cm, deionized water is around 5 - 8 μS / cm. Since an unflushed cooler soldered with flux has a coolant conductivity of 150 - 250 μS / cm, we at Heiche have developed a process with which this value can be reduced to 5 - 50 μS / cm. An efficient rinsing process is required to achieve the required conductivity. This process takes place in two steps:

- Step 1 rinsing the inside of the heat exchanger with a large volume of rinsing medium
- Step 2 conversion coating inside the heat exchanger to prevent further, uncontrolled reaction of the surface.

The conversion treatment binds the free potassium, aluminum and fluorine ions and contributes to the passivation of the component. In order to complete the process of surface refinement, the surface that is active after rinsing is given a passivation afterwards. The flux residues have a similar solubility as the base material and the inorganic acids strongly attack the aluminum. That is why we have developed a rinsing medium made from organic acids with which, in combination with the conversion coating, the required low conductivity can be safely achieved.


This process is offered at the following locations:

Heiche Oberflächentechnik GmbH

Heiche Schwaigern
Schwaigern / Germany

phone: +49 7138/9717-0
fax: +49 7138/9717-77