Accelerating particle removal

Litton Guidance and Controls manufactures advanced inertial navigation and guidance systems for military and commercial aviation industries.

“At Litton, one product we produce is the accelerometer assembly for inertial navigation and guidance systems in missiles and aircraft,” said Bob Bauman, manufacturing/process engineer for Litton Guidance and Controls.

“Within the accelerometer there is a strong magnet that attracts metallic particles, and there are small gaps between moving parts within the instrument.  This particulate contamination is devastating to the performance of the instrument and was the largest cause for accelerometer failures during testing.  We can tolerate no particulate contamination on the magnet prior to, or after, assembly.”

According to Bauman, the company had previously used chemical sprayers to try to remove the particulates.  While the sprayers worked well on residue-type contamination and loose foreign material, they were relatively in effective in removing particulates held by the magnetic field.  “We resorted to hand cleaning particles out manually using sticky picks, which was time consuming and inconsistent,” Bauman stated.  “During our evaluation of the new options, we came across the CO₂ composite spray cleaning process, and it is the best particulate removal method we have found.”

“With the CO₂ composite spray cleaning system, Litton Guidance and Controls consumes approximately 50 pounds of CO₂ every 10 to 14 days, depending on production.  The management team has found the new system to be cost effective as well as user friendly.  Regarding cycle time, a sub-assembly (containing three magnets, other components, nooks, and crannies) can now be cleaned in less than one minute compared with the 10 to 15 minutes it once took by hand.”

“We had not been able to achieve the same result with the other cleaning methods, especially cleaning the magnetically held particles.  We had established that particulate contamination was the primary cause of the failures and are convinced the yield improvement is significant,” concluded Bauman.

Source:
“Today’s Forecast: It Looks like Snow”, Precision Cleaning, May 1999