One of the most popular exhibits at Cast Expo ‘05 last month in St. Louis was demonstration of a new approach to cleaning castings. Called NitroJet, it involved manipulating a casting over a jet of liquid nitrogen to remove core sand.
The demonstration took place in the Vulcan Engineering exhibit. Vulcan is partnering with NitroCision to develop the latter’s nitrogen jet technology into a process for decoring castings. The demonstration used a Vulcan-integrated ABB robot, a Fox compliant cut-off saw, and NitroCision’s NitroJet. The robot picked up the casting and moved it over the NitroJet’s rotating nozzle to remove the core sand from the cut-lines. (This was done to extend the life of the cut-off blade.) Next, the robot positioned the casting to allow the Fox Compliant cut-off saw to remove the gating and flash. This process opened access to the internal core areas. Finally, the robot moved the casting back to the NitroJet’s rotating nozzle to complete the decoring operation.
Founded in 2001, NitroCision LLC is a private company in Idaho Falls, ID. It has patented a method of cooling and pressurizing liquid nitrogen to create an ultra-high-velocity jet that has a density comparable to water. By regulating the temperature and velocity, the jet of liquefied nitrogen can be used in a range of industrial applications, including precision cutting and drilling, in addition to the cleaning of castings.
The NitroJet system compresses liquid nitrogen from 5,000 to 55,000 psi with temperatures ranging between -240° and -500°F. For the Cast Expo demonstration, the liquid nitrogen left the nozzle at 50,000 psi or about 2,000 mph. It had a temperature of -220°F and was in the state of a supercritical fluid with a density comparable to water.
As the robot positioned the casting over the rotating nozzle the liquid nitrogen was propelled into the casting’s sand core, where it penetrated and followed the path of least resistance. Within milliseconds after leaving the nozzle the liquid nitrogen changed from a supercritical fluid to a gas. As this change occurred, the liquid nitrogen expanded to five times its volume and literally ruptured the core without damaging the casting.
Additional cleaning was achieved when the displaced core material and the speed of the liquid nitrogen stream were combined. This combination created an additional erosive agent that further cleaned the casting.
In production applications, different nozzles can be used to optimize cleaning or cutting effects, including rotary heads, fan nozzles, multiple jets, or concentrated single nozzles.
According to Vulcan Engineering officials, the NitroJet approach offers several benefits. For one, it is a totally dry process because the liquid nitrogen turns to a gas, and no heat is introduced into the casting.
The technology is revolutionary in that it eliminates all secondary waste created or generated by conventional cleaning technologies, thereby eliminating environmental hazards and significant time and cost associated with the capture, treatment, and disposal of secondary waste streams.
The process can remove sand, ceramic, or lost-foam cores. When used to remove sand cores, the sand can be reused immediately.
Finally, the safety zone for an operator is within 18 in. of the nozzle. Beyond that zone, an operator would only feel a cold, strong breeze, even when the operating pressure at the nozzle is as high as 55,000 psi.
Temperature tests conducted by NASA on 0.016-in. thick aluminum sample showed a drop of 40°F from ambient and then a return to ambient within 3-4 seconds. Metallurgical tests showed no metal fatigue or other changes.