Application closeup: Extreme cleaning application for medical tubing

By Control Engineering Staff December 6, 2006

Products in medical devices have very critical cleaning and sanitation requirements prior to use with patients. Even something as simple as Teflon tubing has to go through a sophisticated cleaning process after being extruded. Arion Engineering has designed and built a system to etch tubing that will ultimately be used for catheter applications.

The cleaning process takes three steps:

  • The initial etching process uses a heated, super-saturated solution of metallic sodium dispersed in naphthalene. Since this is highly reactive with oxygen, the solution and this whole stage is kept under a nitrogen blanket to prevent any chemical degradation. The reservoir and treating trough is fabricated from stainless steel with an external jacket to circulate heated oil. This maintains the process at an even temperature throughout. A pump keeps the solution flowing from the reservoir to the trough while the newly extruded tubing passes through. Oxygen sensors monitor the nitrogen blanket constantly to ensure that there has been no loss of reactivity in the etchant.

  • The second stage is an alcohol wash that floods the tubing to neutralize any remaining sodium solution. The alcohol also circulates from a reservoir to keep a fresh supply on the product.

  • The third stage is a final hot water rinse to ensure the tubing is clean and there is no sodium or alcohol residue. The water circulates through a heated reservoir.

Since the operation is continuous, the cleaning solutions can be replenished while running as needed. One PLC controls and monitors the operation, collecting data from temperature, pressure, and oxygen transducers. This information feeds back to the machine operation and alarm circuits if any process variables move out of appropriate ranges. All motors and electrical connections are explosion resistant.

Control Engineering Daily Daily News Desk
Peter Welander
, process industries editor