For a flawless finish, snow

Tailored partial cleaning for a new production step

A novel coating solution was developed for a new implant in collaboration with a customer. To mask parts of the product that don’t need coating, a new masking system was developed that withstands the high temperatures required by the plasma coating process. When this is removed from the implant after coating, patches of discoloration caused by the masking system are evident on the small contact points. To achieve a flawless finish, which is essential for such medical products, these residues must be removed.

“We needed a solution that could clean these contact points selectively without altering the roughness of the pre-treated surface in any way. We also needed a non-toxic cleaning medium that doesn’t leave any residues,” says Dr. Sebastian Mihm, head of medical coating at Medicoat, describing the requirements.

CO₂ snow in the liquid phase

Due to its process and non-toxic properties, carbon dioxide (CO₂) snow-jet cleaning is ideal for this task. Initially, tests were performed with a system that uses blocks of dry ice to generate the snow crystals, but this proved to be extremely complicated to handle.

“In our search for a system that isn’t only easy to handle but also suitable for use in series production, we got to hear about the quattroClean snow-jet technology from acp systems. This uses liquid carbon dioxide from cylinders as a cleaning medium,” Mihm says.

The CO₂ has an indefinite shelf life and is generated as a by-product from various industrial processes, making it climate neutral.

The key to the cleaning system is a wear-free, two-component ring nozzle. Liquid carbon dioxide is fed through this nozzle and expands on exiting to form fine CO₂ snow, which is then bundled by a separate jacket jet of compressed air and accelerated to supersonic speed. When the easy-to-focus and non-abrasive jet of snow and compressed air impacts the surface to be processed at a temperature of -78.5°C, a combination of thermal, mechanical, sublimation, and solvent effects takes place. The interaction removes the discoloration due to the masking in a dependable, reproducible cleaning process while not affecting the structure of the jet-cleaned surface.

“In cleaning trials at the manufacturer’s technical center, this cleaning solution convinced us of its capability to reliably meet our requirements,” Mihm reports.

A further advantage is that the crystalline CO₂ is fully converted to gas during the cleaning step so it doesn’t leave any residues on the surface.

Standalone system for manual cleaning

To establish the quattroClean process in the company and obtain its approval for the product, Medicoat opted for a manually operated JetStation-HP system in cleanroom design.

The compact stand-alone unit comes with a sound-insulated stainless-steel cabin. The cabin interior only contains components and materials used in cleanroom applications. The media preparation system for the carbon dioxide and compressed air is similarly designed. The process chamber is constructed to counteract dirt pocket formation and prevent recontamination of the cleaned parts. The design also promotes rapid removal of detached impurities and sublimated carbon dioxide by the integrated extraction unit, which is connected to a central extraction system at Medicoat. The concentration of CO₂ in the working area is monitored by a sensor system integrated as standard. If the defined limit value is exceeded, the CO₂ supply is automatically switched off and an error message displayed.

“The professional, closed concept of the JetStation and its clean design certainly played a role in the decision,” Mihm notes.

The implants are loaded and unloaded via a front flap with manual access. The operator positions the implant’s contact points to be cleaned underneath the fixed jet nozzle and starts the process via a foot pedal.

“We’ve been working with the system in series production since the beginning of 2020, cleaning between 50 and 100 implants a day, and the results are outstanding. Consequently, we are now thinking about automating the process to make it more efficient. We are also considering using this solution to clean other medical products,” Mihm concludes.

acp systems: https://www.acp-systems.com; Medicoat AG: https://www.medicoat.com