Every plant between Ohio and Iowa knows the calendar. Sometime in June the dew point climbs, the doors are open, the parts washer is running hot, and machined steel that sat clean on the rack all winter starts showing orange spots overnight. Maintenance calls it humidity. Cortec’s field people call it rust season, and it runs through September. If you already buy VCI paper and film and still lose parts in July, the packaging is not doing what the sales sheet said.
An Illinois transmission plant, a Michigan stamping plant and a Midwest transmission OEM each solved a different version of this problem, and the answers add up to one method: CorShield VpCI-146 paper between the parts, a VpCI-126 bag around them, and, where liquids are allowed, a dry-film rust preventative that lasts longer than 30 days. Cortec Case Histories #777, #740 and #625 are the sources.
Illinois: paper and bag beat a competitor’s VCI
Cortec Case History #777 (2022) describes a transmission plant in Illinois that rusted transmission components every summer despite packing them in VCI paper and film from a well-known competitor. Liquid rust preventatives were not an option because of what the parts were. In spring of about 2015 the plant ran a real-world test: it packed parts in Cortec materials, left them in the shop for three to four months through the worst of the season, and looked at them. By that summer it was switching over.
The packaging that has been in place since is simple. Parts go into bins or trays with a sheet of CorShield VpCI-146 paper between each layer, and the whole bin is closed inside a VpCI-126 bag. The same pack is used in-process, between production stages, and in storage. The plant reported no major corrosion problems in the seven years since. The paper puts inhibitor in direct contact with every layer; the bag keeps the vapor in and the humid shop air out.
Michigan: the hot parts were the problem
Cortec Case History #740 (2021) is the root-cause story. A Warren, Michigan producer of stamped automotive components had parts rusting on ocean shipments to Germany and China and on LTL freight to Mexico, against a customer requirement of 60 days rust-free. Cortec walked the line and found the cause before recommending a product: hot stampings were going straight off the press into closed dunnage. Warm steel in a sealed box sweats as it cools, and no VCI is designed to cope with standing condensation.
The fix had three parts. Add airflow on the line so parts cool partly before they are packed. Put VpCI-146 paper between the parts. Line the container with a VpCI-126 bag. The manufacturer reported that corrosion stopped, that it saved the cost of the rejected shipments, and that its customer was satisfied. If your parts are rusting in transit, take a thermometer to the packing station before you change suppliers.
Midwest OEM: a wash additive is not six months of protection
Cortec Case History #625 (2019) covers a large OEM transmission manufacturer in the Midwest that stored finished transmissions one to nine months in a warehouse with no temperature or humidity control before they went to another site to be wrapped in VpCI-126 for export. The only protection in that gap was the flash-rust inhibitor in the final wash. A standard wash additive is good for roughly 30 days, and less in a Midwest summer, so the transmissions were rusting in the warehouse.
The plant needed something compatible with transmission fluid, nearly residue-free, and easy to rinse off later. After a long approval process it adopted BioCorr ATF, the transmission-fluid-compatible grade of Cortec’s biobased BioCorr rust preventative, sprayed on after the wash, leaving a dry film that is close to invisible. The transmissions then go through the normal VpCI-126 wrap and bulk box for export. At the time of writing the program had run for about eight months without the warehouse rust.
| Case | Where the rust happened | Fix | Result |
|---|---|---|---|
| #777 (2022) | In-process and storage, Illinois | 146 paper interleaf plus 126 bag | No major issues in 7 years |
| #740 (2021) | Ocean and LTL transit | Cool parts, 146 paper, 126 bag liner | Corrosion stopped; 60-day requirement met |
| #625 (2019) | 1 to 9 months in an uncontrolled warehouse | Dry-film RP after wash, then 126 wrap | 8 months clean at time of writing |
How to do this in your plant
- Start with a clean, dry, cool part. VCI protects clean metal; it does not clean it. Parts should leave the washer free of coolant and salts and be at room temperature before they are closed in anything.
- Interleave with VpCI-146. Use pre-cut 36 by 36 inch sheets for trays and bins, or a 36 inch by 1,200 foot roll on a dispenser at the packing station. Coated side toward the parts; one sheet per layer.
- Close the bin or tray in a VpCI-126 bag. Gusseted bags fit tote bins and pallet boxes; zip-close bags suit sub-assemblies that get opened for inspection. Fold or seal the top; the bag only works closed.
- If parts wait more than a month before packaging and liquids are allowed, add a dry-film rust preventative after the wash. Standard BioCorr is ready to use, leaves a near-invisible film, and rinses off at the next operation; ask us about the ATF grade if the parts see transmission fluid.
- Run your own rust-season test. Pack a few parts in April, leave them in the worst corner of the shop until August, and open them. That is what the Illinois plant did, and it is more convincing than any data sheet. Our VpCI product selection guide shows which papers, films and preventatives are rated for each metal and exposure.
Which Cortec products
- VpCI-146 sheets, 36 by 36 inch: interleaving in bins and trays; multimetal, MIL-PRF-3420 family.
- VpCI-146 roll, 36 inch by 1,200 feet: for a dispenser on a busy packing line.
- VpCI-126 gusseted bags: bin and box liners; up to five years of protection depending on gauge.
- VpCI-126 zip-close bag, 24 by 30 inch: reclosable, for assemblies and kits.
- BioCorr: water-based dry-film rust preventative for the gap between wash and packaging.
The next rust season starts in June, and a packaging test should be packed in spring to be believed. We stock VpCI-146 paper, VpCI-126 bags and BioCorr in Elmhurst, Illinois, and will send sample sheets and bags for a parts trial. Contact Solvent Recycling Systems and tell us what the parts are, how long they wait and where they ship.
Sources: Cortec Case History #777 (2022), Cortec Case History #740 (2021), Cortec Case History #625 (2019); Cortec product data sheets for VpCI-146, VpCI-126 and BioCorr.
