Reliably cleaning X-ray tube parts

Shortly after Wilhelm Conrad Röntgen discovered X-rays in 1895, Philips Medical Systems DMC GmbH began developing and manufacturing X-ray tubes with Carl Heinrich Florenz Müller, a glassblower born in Thuringia, Germany. By March 1896, he made the first X-ray tube in his workshop and three years later was granted the first patent for a model with water-cooled anti-cathode. The speed of tube development and X-ray technology success spurred worldwide demand, turning the craftsman’s workshop into an X-ray tubes specialty factory. In 1927, Philips, the only shareholder at the time, took over the factory and has been shaping X-ray technology with innovative solutions and continuous improvements ever since.

Clean, precise manufacturing

Products used in Philips Healthcare systems, and those sold under the Dunlee brand, contribute significantly to advances in diagnostic imaging, computer tomography (CT), and interventional radiology.

“Besides modern manufacturing technologies, high precision, and ongoing process optimization, component cleanliness plays an important role in ensuring the functional reliability and longevity of our products,” says André Hatje, senior engineer for process development in the X-ray Tubes division. Residual particle contamination specifications must be met when cleaning the various X-ray tube parts – two or fewer 5µm particles and one or fewer 10µm size – underlining the cleanliness required in the process.

Removing molybdenum grinding dust

When a Philips spiral groove bearing components cleaning plant needed to be replaced, the company set meeting high cleanliness requirements as a main criterion. Molybdenum bearings form the heart of high-tech X-ray tubes, and after the groove structure has been applied by laser, a dry grinding step is performed. This is followed by cleaning, during which the grinding dust and traces of smoke left in the grooves from the laser process must be removed. To simplify process validation, a compact standard machine was needed for cleaning. Against this backdrop, a process developer approached several cleaning equipment manufacturers, including Ecoclean GmbH in Filderstadt.

After conducting cleaning tests with various manufacturers, researchers determined that required cleanliness for the spiral groove bearing parts was only possible with the EcoCwave from Ecoclean.

Equipped for fine cleaning

The machine for immersion and spraying processes operates with the same acidic cleaning medium previously used at Philips and has a 6.9m2 footprint. Fitted with three flood tanks, one for washing and two for rinsing, the flow-optimized, cylindrical design, and upright position of the tanks prevent dirt accumulation. Each tank has a separate media circuit with full-flow filtration, so cleaning and rinsing fluids are filtered during filling and emptying and in the bypass. Deionized water used for final rinsing is treated in the integrated Aquaclean system.

Frequency-controlled pumps allow flow volume to be adapted to parts during flooding and emptying. This allows the working chamber to be filled to different levels for more intensive media exchange in critical areas of components. Parts are then dried by hot air and vacuum.

“We are very satisfied with the cleaning result. All parts come out of the plant so clean that we can transfer them directly into a cleanroom for further processing,” Hatje says, noting the next steps include annealing and coating the components with liquid metal.

Ultrasonic system

The spectrum of parts cleaned at Philips in an 18-year-old, multi-stage ultrasonic machine from UCM AG range from small screws and anode plates to cathode sleeves and housing pots with a 225mm diameter. The metals from which the parts are made are equally diverse – nickel-iron materials, stainless steel, molybdenum, copper, tungsten, and titanium.

“The parts are cleaned after different processing steps, such as grinding and electroplating, and before annealing or brazing. Therefore, this is the most frequently used machine in our material supply system, and it continues to deliver satisfactory cleaning results,” Hatje says.

However, the company reached its capacity limits and decided to invest in a second machine from UCM, a division of the SBS Ecoclean Group specializing in precision and ultra-fine cleaning. Even though the existing machine could handle the process, the number of cleaning and rinsing steps, and the drying process, Philips wanted a new cleaning system that would be faster, more versatile, and deliver better results.

Some components were not optimally cleaned in the intermediate cleaning stage with their current system, which doesn’t impair the subsequent processes.

Fast, flexible processes

Including loading and unloading, the fully enclosed ultrasonic cleaning system features 12 stations and two transfer units. They are freely programmable, as are the process parameters in the various tanks.

“To meet the different cleanliness requirements for the various parts and downstream processes, with this system we use around 30 different cleaning programs, which are automatically selected via an integrated barcode system,” Hatje explains.

The system’s transport racks are equipped with varying grippers, which can pick up cleaning containers and perform functions such as lifting, lowering, and rotating at the treatment stations. Depending on the program, the feasible throughput is 12-to-15 baskets per hour in three-shift operation six days a week.

Optimal cleaning results

After loading, the first four tanks are designed for cleaning processes with intermediate rinsing steps. For better, faster results, the cleaning tanks are fitted with multi-frequency ultrasound (25kHz and 75kHz) at the bottom and on two sides. With plate transducers flange-mounted in the tank, there are no components in the tanks for dirt to collect. Additionally, the cleaning tanks feature a bottom filtration system and a two-sided overflow for discharging suspended and floating particles. This ensures that any removed impurities accumulating on the bottom are detached by a flushing nozzle and sucked off at the lowest point of the tank. Fluid from the surface and bottom filtration systems is treated via separate filter circuits. The cleaning tanks are also equipped with devices for electrolytic degreasing.

“We already developed this function together with UCM for the old machine because it also enables us to get parts clean that have dried polishing paste on them,” Hatje says.

A new addition, however, delivers significantly better cleaning results. A spray rinsing device with deionized water is integrated into the fifth treatment station to remove very fine dust still sticking to the surface after cleaning and the first immersion rinse.

Spray rinsing is followed by three immersion rinsing stations. For components made of ferrous materials, a corrosion inhibitor is added to the deionized water used in the last rinse cycle. All four rinse stations have separate lift-out equipment for removing baskets after the defined dwell time and and agitating the parts while rinsing. The next two part-drying stations are fitted with combined infrared vacuum dryers. In the unloading station, an enclosure with integrated laminar flow box prevents component recontamination.

“The new cleaning system gives us a lot more cleaning options, enabling us to achieve better cleaning results with shorter cycle times. That’s why we are planning to have our old machine appropriately modernized by UCM,” Hatje concludes.

Ecoclean Group
https://ecoclean-group.us

Philips Medical Systems DMC GmbH
https://www.philips.com/healthcare

UCM AG
https://www.ucm-ag.com