Particle limit value of 400 micrometers stably achieved with dry final cleaning

The manufacturer was looking for a suitable solution for cleaning the inside of an oil pressure line in which an elastomer component encased in a metal mesh is integrated. The decisive factor in the decision for the dry QuattroClean snow blasting technology was the process-reliable compliance with the cleanliness specification of “no particles larger than 400 micrometres” and the fact that no waste water is produced during dry cleaning.

It was 1885 when the Pforzheim jewelry manufacturer Heinrich Witzenmann invented the first metal hose together with the French engineer Eugène Levavassèur. The model for this robust and flexible product was the goose necklace. Witzenmann subsequently developed all the notable profiles for hose production that are still technically valid today. This was followed by further developments such as the mechanically corrugated metal hose, bellows and expansion joints. Today, the family-owned company is the world’s leading manufacturer of these flexible metallic elements for the safe conduction of media and energy for mobility and industry. They are used to absorb movement and decouple vibrations and are used in vehicle construction as well as in industry, technical building equipment and aerospace. As a development partner to its customers, Witzenmann works on innovative solutions for a wide range of applications and markets. These include products in the field of new mobility and for hydrogen applications in industry and the energy sector, as well as high-purity components for microelectronics and semiconductor production.

High cleanliness limits require new cleaning solution

In oil, petrol or cooling circuits, the advantages of flexible metal pipes are absolute gas and diffusion tightness, durability and temperature resistance. This is a key criterion, especially when they are installed close to the manifold, turbocharger or exhaust system. “In addition, the products usually have to have a very high level of particulate cleanliness,” adds Andrea Krause, expert for technical cleanliness at Witzenmann. This was also the case for an oil pressure line, for which the vehicle manufacturer’s specification was “no particles larger than 400 µm”. Not really a challenge for the company if this line did not have an integrated elastomer component around 100 mm long with an internal diameter of 8 mm, which is braided with a metal mesh to stabilize the pressure. During its assembly, particles are produced that can get into the component. “The line therefore has to be finally cleaned,” reports the cleanliness expert. “Achieving this 400 µm reliably poses a certain challenge, especially as the parts have to be cleaned on the inside. There were no suitable systems available at the production sites for this application, so we had to invest in new cleaning solutions.”

Dry snow jet cleaning prevails over wet cleaning

Alternative solutions included wet cleaning systems with various process technologies that work in narrow capillaries and the dry QuattroClean snow blasting technology from ACP Systems AG. The decisive factor in opting for the dry cleaning solution was that it solved several problems. “On the one hand, it saves us having to completely wet, rinse and dry the parts again. On the other hand, this cleaning process does not produce any waste water that we would not have been able to dispose of at one of the two production sites for environmental reasons,” explains Andrea Krause. The snow jet technology uses liquid, recycled carbon dioxide as the cleaning medium, which is fed through a wear-free two-substance ring nozzle. As it leaves the nozzle, the carbon dioxide expands into fine CO2 snow, which is bundled by a separate, ring-shaped jet of compressed air and accelerated to supersonic speed. When it hits the surface to be cleaned, the jet of compressed air develops a combination of thermal, mechanical, solvent and sublimation effects. The interaction of these four mechanisms ensures that particulate contamination down to the sub-micrometer range and filmic contamination are removed reliably and reproducibly. As the crystalline carbon dioxide completely sublimates during the process, the cleaned surfaces are dry and residue-free.

Coordinated system concept ensures high process reliability

The decision was preceded by very extensive cleaning tests in the system manufacturer’s technical center. On the one hand, this proved that the required cleanliness could be achieved with process stability. On the other hand, APC worked out the system concept for the internal cleaning of the components based on the results. “The collaboration with ACP was extremely pleasant and was very easy, not least due to the close proximity,” recalls Andrea Krause. The cleaning system consists of a standard cell in which a linearly movable capillary with adapted nozzle technology is integrated. For cleaning, the lower open end of the component is fixed in the process chamber, then the capillary moves into the tube at a precisely defined speed, blasting with carbon dioxide and compressed air. The speed and pressure of both media are monitored by sensors. This makes it possible to prove that each component is cleaned with the defined parameters. On the “return path”, the nozzle blasts with heated compressed air to counteract condensation on the outside. Detached particles are removed by a suction unit positioned above the upper end of the component to reliably prevent recontamination. “When monitoring the cleaned parts, we found that a particle size of 300 µm was achieved in 90 percent of cases. I think the process also has potential for cleaning components for new mobility. Especially if other particles are reliably removed in addition to metallic ones,” concludes the cleanliness expert.

author Doris Schulz, Korntal Web: www.acp-systems.com