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Staining of hydraulic manifold blocks after alkaline wash

Q. Hello, I am a manufacturing engineer working at a company that makes hydraulic manifold blocks. (Basically a block of ductile iron with a bunch of holes drilled in it.) After machining, the blocks are deburred manually with various hand tools / sand paper / scotch brite. Then they enter an ultrasonic bath to be cleaned. The bath uses an alkaline cleaning solution heated to 140-145 degrees. When the cycle ends, the platform rises out of the solution. The operator then blows off the block and inner cavities with clean air before placing in rinse tank. If any of the wash solution dries on the surface it leaves brown and sometimes blue stains. This is mostly noticeable near draining holes and where the blocks rest on the wash platform.

     

Ideally, I would like to get the freshly washed block into the rinse tank before any drying occurs, but this is not feasible with our current setup. We have also tried a different cleaning solution during a "run-off" for our new ultrasonic washer.

FYI: We are machining the blocks with a semi-synthetic coolant, the blocks are blown out by the machinist before moving to the de-burring area. We also manufacture steel and aluminum blocks, but we have made efforts to keep the aluminum and iron in different areas of the shop. This issue has been occurring for years, and we have not been able to figure out the cause.

Michael Michalgyk
Manufacturing Engineer - Bethlehem, Pennsylvania
March 14, 2025