by
Lisa Chamoff, Contributing Reporter | November 12, 2014
From the September 2014 issue of HealthCare Business News magazine
X-ray tube insert final seal
Photo courtesy of Varian
3. Final seal
This is the most visual part of the process, and for anyone who has toured an X-ray tube factory, it can be as interesting as a visit to the Simon Pearce glassblowing facility in Vermont (though without the gourmet food). The assembled cathodes and anodes are placed depending on the product, into metal or glass inserts (also called envelopes).
“Forming the glass envelope is fascinating and requires a high level of glass technology as some glass doesn’t seal to the metal parts and requires ‘transition’ glass to be used,” says Tom Spees, director of sales, North America for Dunlee, the GTC division of Philips Healthcare. “The welding of the tube parts into the metal frame construction of high-end CT tubes is equally as fascinating, although perhaps not as visually stimulating, as watching the glass blowing,” he says.
Vacuum processing
Photo courtesy of Dunlee
4. Pump
At this stage, the anode and cathode are heated and cooled repeatedly to remove unwanted gasses. The length of the pumping process varies by the size of the tube and the application, and can range from eight hours to three days, using equipment that’s about the size of a large closet. Because tubes are run actively and produce X-rays during the process, the equipment housing the tubes during the process is lead lined for the safety of the operators. The vacuum is very strong to create a stable high voltage environment. According to Dunlee, the vacuum levels achieved in their processing is better than those which surround the International Space Station. At this point, it is sealed off from the atmosphere.
Baron vacuum oil fill station
Photo courtesy of Varian
5. Tank testing/housing load
Once the final seal is in place, all of the gas has been removed and the insets are placed in their lead housings, which have small windows that allow X-rays to exit, Dielectric oil, nonconductive oil that acts as a cooling agent, is added, and the oil is specially processed so X-rays don’t break it down. The fully assembled tubes are then put into test tanks and are exposed to the type of voltage they will run on, on a gantry system similar to one used in the field, preparing the tube for its role in a medical application. Varian always exposes the tubes to 50 percent more voltage, so if the tube will run on 140 kV then it’s exposed to 210 kV. Dunlee also exceeds the high voltage rating.
