Ultrasonic cleaning of precision tubes#.

Case Study Rototronic plant

Order: cleaning air conditioning components | Challenge: complex geometries and high cleanliness requirements | Implementation: multi-step Rototronic® system for cleaning and drying | Process: ultrasound cleaning and pressure flooding

No particle > 200 micrometer inside and outside

For an internationally active supplier to the automotive industry, air conditioning components have to be cleaned for smooth installation. These are thin-walled, straight and three-dimensionally very complex bent aluminum tubes. After soldering, they must be cleaned inside and out free of particles, rinsed and dried. Purification takes place in PURIMA’s own specially developed plants, which are designed for high throughputs with demanding cleanliness requirements.

Increasing complexity and purity requirements

For many years, the automotive supplier has been using ultrasonic cleaning systems in its plants worldwide to treat the brazed aluminum tubes. The tubes are installed in air conditioning systems of vehicles. From the very beginning, PURIMA, formerly RPE Pape Anlagentechnik, has been a reliable partner for the implementation of customer-specific process solutions as a supplier of aqueous cleaning systems and special designs. The requirements for cleaning results increased continuously. Over the years, pipes, like many other components of a vehicle, have become increasingly complex. Today, these components are partly manufactured with double walls and additionally take over the functions of a heat exchanger. Continuous further development of cleaning technology is therefore absolutely necessary, which increases the complexity of the processes and technologies used.

In this specific example, residue-free removal of the soldering process

Cooperative research and development work

Before a cleaning system for the treatment of complex components is designed, extensive washing tests and elaborate residual dirt investigations are required. PURIMA carried this out in close cooperation with the automotive supplier’s project managers at its own technical center in Porta Westfalica. The challenges of the task set stood out clearly. Soldered components have internal undercuts, where particles persistently deposit. The complex 3D bent tubes do not fill completely with cleaning liquid. Air pockets mean that they cannot reach certain parts of the component. Simply swiveling the pipes did not solve this problem, neither when filling, nor when emptying. Even pipes that were manually blown out with oil-free, dry compressed air had too much residual moisture for the downstream process. In addition, residual contamination with particles larger than 200 µm was repeatedly found in the cleanliness analyses.

The results from the tests showed that the pipes can only be cleaned with a complex cleaning technology. In the pilot plant, the components were treated with rotation and in various angular positions in the treatment basins. It was quickly apparent that this was the only way for the air to escape from the pipes and for the cleaning fluid to reach all points. Furthermore, it became apparent that the pipes could only be emptied in a rotational process with stopping at certain angular positions above the bath level. Drying proved to be very difficult. Even with rotation of the tubes in a circulating air dryer, the residual moisture was too high in the required cycle time. The desired results were only achieved with post-drying in a vacuum dryer at 1 mbar.

Case Study Rototronic plant

Problem solver: Flexible rotation technology

The Rototronic® cleaning system developed by PURIMA serves as the basis for solving the task. The systems of this series are available as customized single-chamber and multi-stage cleaning systems. Depending on the requirements, the plants are therefore equipped with one or more process tanks. Within these basins, different cleaning technologies are used, which in combination ensure an optimal cleaning result. The items to be cleaned are transported through the cleaning process in specially designed pick-up racks and washing baskets. In a multi-stage cleaning process, the goods are moved via a multiple handling system with automatic basket covering. The wash racks can rotate, swivel or be positioned at precise angles in all treatment stages, both in the basins and above the liquid level for emptying.

Different washing programs can be created via the system control, which stores the best positions and the holding time for the bent tubes so that the liquid can run out of the tubes. Only in this way is it possible to flush particles that have been dissolved by ultrasound out of the pipes. The superposition of rotational movements and movements in the vertical direction increase the effectiveness of particle removal and rinsing. In addition to the use of ultrasound in the cleaning stage, the sinks are equipped with pressure circulation. Since both straight and bent pipes have to be cleaned, the flow direction can be selected from the side walls or from a front side when pressure is circulated.

The same movements take place in the drying with hot circulating air. Moving liquid in the pipes is moved past the hot surfaces and can evaporate more easily. To ensure absolute dryness, the final treatment stage involves drying in a vacuum. Depending on the plant configuration, the vacuum dryer is integrated as an external module in the unloading zone or in the common frame system of the plant.

After cleaning, all pipes are leak tested, as they are used in closed circuits. The test is carried out with helium, as water or moisture is an n.iO criterion in this test process.

In addition to multiple handling, there is also a variant with single handling, which is used as a converter. In this case, rotation, swiveling or precise angular positioning is performed via drives directly in the basins. After the treatment time has elapsed, the handling system picks up the wash rack and performs exactly the programmed movements above the liquid level. This plant technology is enormously flexible and also suitable for the treatment of parts with critical treatment times.

All plants supplied by PURIMA are equipped with the latest filtration technology for the removal of oils, greases and particles in accordance with the requirements. As far as possible, specially developed systems are used for this purpose, which function without wearing parts. By means of targeted media treatment, be it via softening plants, reverse osmosis, microfiltration, ultrafiltration or the use of evaporators, it has been possible to reduce ongoing operating costs to a minimum.

Case Study Rototronic plant
Case Study Rototronic plant