Summary for alkaline wash staining Discussion
Staining of hydraulic manifold blocks after alkaline wash is described as brown and sometimes blue marks that appear when wash solution dries on ductile iron blocks after ultrasonic cleaning. The manufacturer says the blocks are deburred, cleaned in a heated alkaline bath, then blown off before rinsing, but stains still show up near drain holes and on the wash platform contact points. They have tried another cleaning solution during a run-off test and have kept aluminum and iron work separated, yet the problem has persisted for years. The thread excerpt provided does not include any replies or diagnosis, so no specific cause or remedy is stated in the source. The practical issue is that drying before rinsing seems to be linked to the staining, but the excerpt stops before any expert answer is given.
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
A. Hi,
Maybe you can install a “fog rinse” over the cleaning tank. This is just a manifold of PVC pipe with fog nozzles. The nozzles are designed to provide very little water, just enough to maintain 100% humidity so the manifold doesn’t dry and, with luck, will add no more water to the cleaning tank than is lost to dragout and evaporation.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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