How to Keep Machined Parts From Rusting?

Rusting of machined parts plagues manufacturers, distributors, and end-users worldwide. It ruins part aesthetics, cripples performance, shortens service life, and drives up maintenance costs. For CNC machined parts—which demand ultra-high precision—rust can render components entirely useless, leading to costly production delays and financial losses.

If you’re tired of battling rust on your machined parts, you’re not alone. This guide breaks down the science behind rust, actionable prevention steps, real-world success stories, and myth-busting tips—all to help you protect your parts long-term.

Before fixing rust, you need to understand its root cause. Rust (scientifically iron oxide) forms when iron or iron-containing alloys react with oxygen and moisture—a chemical process called oxidation. Several factors speed up this reaction, turning small spots into widespread corrosion:

●  Moisture: Even tiny amounts (like condensation on part surfaces or high humidity) provide the water molecules oxidation needs. Humidity above 60% drastically raises rust risk.

●  Oxygen: Abundant in air, oxygen reacts quickly with iron. More exposure (e.g., poor packaging or open storage) accelerates rust.

●  Contaminants: Dust, dirt, oil residues, or acidic/alkaline chemicals stick to part surfaces. They break down protective layers—for example, oil traps moisture, while acids directly eat away at metal.

●  Temperature Fluctuations: Rapid temperature changes (e.g., moving parts from a cold warehouse to a warm workshop) cause condensation. Enclosed, poorly ventilated spaces make this worse.

●  Rough Surface Finish: Machined parts with rough surfaces have pores and crevices that trap moisture and contaminants. Smooth, polished surfaces resist rust far better.

Pre-processing is your first line of defense. By prepping parts before use or storage, you eliminate rust triggers early. Here’s how:

▶  2.1 Thorough Cleaning

Contaminants like metal shavings, oil, or dust are rust’s best friends. Choose a cleaning method that matches your part material and complexity:

●  Solvent Cleaning: Uses organic solvents (e.g., mineral spirits) to dissolve oil and grease. Ideal for small parts with simple shapes.

●  Aqueous Cleaning: Uses water-based solutions with biodegradable detergents. Eco-friendly and safe for most metals (avoid on sensitive alloys like aluminum).

●  Ultrasonic Cleaning: Uses high-frequency sound waves to reach tight spots (e.g., threaded holes or complex CNC features). Removes even microscopic contaminants.

Pro Tip: Always dry parts completely after cleaning—leftover moisture will restart rust formation. Use compressed air or a low-heat dryer for hard-to-reach areas.

▶  2.2 Deburring

Burrs (sharp, tiny edges from machining) trap moisture and contaminants. Remove them with:

●  Manual Deburring: Files, sandpaper, or deburring tools for precision parts (e.g., aerospace components).

●  Mechanical Deburring: Brushes, grinders, or tumblers for high-volume parts (e.g., automotive bolts).

●  Chemical Deburring: Uses mild acids to dissolve burrs on delicate parts (e.g., medical devices).

▶  2.3 Surface Activation (For Coating Adhesion)

If you plan to apply a protective coating, activate the part surface to ensure the coating sticks:

●  Chemical Activation: Acid etching (removes thin oxide layers) or alkaline cleaning (neutralizes contaminants).

●  Physical Activation: Sandblasting (creates a rough surface for better grip) or plasma treatment (ideal for aluminum or stainless steel).

Surface treatments create a barrier between metal and the environment, stopping oxidation entirely. Below are the top options, with their pros, cons, and best uses:

Expert Tip: For parts exposed to saltwater (e.g., marine components), combine zinc electroplating with a clear epoxy coating for double protection.

Even well-treated parts rust if stored or shipped poorly. Follow these rules:

▶  4.1 Optimize the Storage Environment

●  Keep relative humidity below 60% (use dehumidifiers in warehouses).

●  Maintain a consistent temperature (avoid fluctuations that cause condensation).

●  Store parts away from moisture sources (water pipes, windows) and contaminants (oil drums, chemicals).

●  Use raised pallets (keep parts off damp floors) and ventilated shelves (prevent stagnant air).

▶  4.2 Choose the Right Packaging

●  Moisture-Proof Packaging: Plastic bags, vacuum-sealed bags, or moisture-proof paper for most parts.

●  Anti-Rust Packaging: VCI (Volatile Corrosion Inhibitor) paper/film releases a chemical that forms a protective layer on metal. Ideal for stainless steel or CNC parts.

●  Separate Parts: Use dividers or foam inserts to prevent scratches (scratches break protective coatings).

▶  4.3 Transport With Care

●  For sea shipping: Use waterproof containers and add desiccants (silica gel packets) to absorb moisture. Treat parts with a rust inhibitor spray before packing.

●  For land shipping: Cover parts with tarps to protect from rain/dust. Avoid stacking heavy parts on top of delicate ones.

●  Loading/Unloading: Use forklifts with soft pads to avoid dropping or scraping parts.

Rust prevention doesn’t end after treatment—regular checks keep parts in top shape:

▶  5.1 Clean & Lubricate

●  Clean parts every 3–6 months (or more often for high-use parts) with a mild detergent and soft cloth.

●  Lubricate moving parts (e.g., gears, bearings) with a water-resistant lubricant (e.g., lithium grease) to repel moisture.

▶  5.2 Inspect for Rust

●  Visual Checks: Look for discoloration (orange/brown spots) or pitting on surfaces.

●  Non-Destructive Testing: Use ultrasonic testing (for internal rust) or magnetic particle testing (for steel parts) on critical components (e.g., engine parts).

▶  5.3 Repair or Replace Protective Coatings

●  If paint chips or plating wears off, sand the area lightly, clean it, and reapply the coating immediately.

●  For galvanized parts with small rust spots, use a zinc-rich paint to touch up the area.

Case 1: Automotive Parts Manufacturer Cuts Rust by 90%

A U.S.-based automotive supplier struggled with rust on CNC-machined engine components. Their solution:

1.  Installed dehumidifiers to lower warehouse humidity to 45%.

2. Switched to VCI packaging for all parts.

3. Improved cleaning (added ultrasonic cleaning for complex parts) and deburring processes.

Result: Rust rate dropped from 25% to 2.5%, and part service life increased by 50%.

Case 2: Aerospace Supplier Protects Parts for Space

An aerospace company needed parts that could withstand extreme space conditions (vacuum, temperature swings). Their steps:

1.  Anodized all aluminum parts (for lightweight corrosion resistance).

2. Used vacuum-sealed bags with desiccants for storage/transport.

3. Added a strict quality check (measured anodize layer thickness with a micrometer).

Result: Zero rust reported after 5+ years in space.

Don’t let these myths ruin your rust prevention efforts:

●  Myth 1: Stainless steel never rusts.

     Fact : Stainless steel resists rust but isn’t immune. If its chromium oxide layer is scratched (e.g., by a tool) or exposed to saltwater, it can develop “pitting corrosion.”

●  Myth 2: Painting is enough to stop rust.

     Fact : Paint chips or peels over time, and rust can form under the paint if the surface wasn’t cleaned properly. Always combine painting with pre-processing (cleaning, deburring).

●  Myth 3: Removing surface rust fixes the problem.

     Fact : Surface rust is a sign of deeper oxidation. If you only sand off the surface, rust will spread from inside the metal. Always treat the area with a rust inhibitor and reapply a coating.

1.  Use the Right Material: For high-moisture environments, choose stainless steel (304 or 316 grade) or aluminum instead of carbon steel.

2. Train Your Team: Teach employees to handle parts with gloves (oils from hands cause rust) and to inspect parts before storage.

3. Document Processes: Keep records of cleaning, coating, and inspection dates—this helps track what works (and what doesn’t) for future batches.

Rust prevention is a long-term investment, but it pays off: longer part life, lower maintenance costs, and happier customers. If you need help with CNC machining or custom rust prevention solutions for your parts, contact our team today—we’ve helped 500+ manufacturers solve their rust problems.

What’s your biggest rust challenge? Let us know in the comments!