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Preventing iron contamination on non-ferrous parts
Ferrous residue on aluminium, zinc, copper or stainless rusts, stains and can start galvanic corrosion months after shipment.
Every blasting operation embeds a trace of the medium into the surface it strikes. On a steel part that is invisible and harmless. On a non-ferrous part it is a different metal, sitting in electrical contact with the substrate in the presence of moisture, which is the definition of a galvanic couple.
The visible symptom is usually rust spotting, appearing days or weeks later as the embedded iron oxidises. On an anodised or painted part it appears through the coating, which makes it a rework rather than a clean.
The complete solution is to match the medium to the substrate: stainless, aluminium, zinc or copper media according to the part. Partial solutions such as passivation after blasting treat the symptom and add a process step.
Where a plant genuinely cannot dedicate a machine, the practical control is separation: a dedicated media charge, a documented changeover and a cleaned recovery system. That is harder to sustain than it sounds, which is why dedicated machines are the norm where non-ferrous work matters.
Specifications
| Cause | Ferrous media embedded in a softer surface |
|---|---|
| Symptom | Rust spotting days or weeks later |
| Fix | Match media alloy to substrate |
| If sharing a machine | Dedicated charge, documented changeover, cleaned recovery |
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