A build-ahead is the packaging engineer’s worst assignment. The plant is going to build months or years of product in advance, put it in a warehouse nobody is going to heat or dehumidify, and expect every unit to roll onto the assembly line later without a rust spot. Rust preventive oil is out, because the engines have to be clean when they come out. Desiccant alone is out, because the bag will get opened and resealed for inspection. And the line cannot slow down for whatever you specify.
Two Cortec case histories from the late 1990s are still the reference recipe for this job. A Big Three automaker packed engines and components worth close to 2 billion US dollars in Michigan, then 25,000 to 30,000 truck engines worth more than 200 million US dollars in an uncontrolled Ohio warehouse for two years, using nothing but VpCI bags, foam emitters, emitter cups and VCI stretch film. The engines came out clean.
Five levels of testing in a 40-foot trailer
Cortec Case History #107 (1998) starts in May 1997, when the automaker’s powertrain division came to Cortec with a build-ahead program launching the following year. The requirement was 100 percent assurance of corrosion protection for completed engines and components using packaging products only, inside the constraints of a robotic assembly line. The company had already tried a competitor’s VCI papers and films and judged them inadequate.
The two sides went through five levels of testing. Full pallets of engines and parts were tested at Cortec’s facility and at the Michigan plant in a converted 40-foot trailer used as a humidity chamber, cycling temperature and humidity between 80 and 100 percent RH. The pack recipe that came out of the trailer is worth reproducing, because it is the most detailed one Cortec has published.
| Load | Pallet | VpCI-126 8 mil HP | VpCI-131 foam strips | VpCI-111 emitters | Outer wrap |
|---|---|---|---|---|---|
| Complete V-8 engines, 3 per pallet | – | 68 x 68 in bag per engine | 2 per engine, one each side | – | Cor-Pak VpCI stretch film |
| Partial V-8 engines, 3 per pallet | – | 68 x 68 in bag per engine | 2 per engine, one each side | – | Cor-Pak VpCI stretch film |
| Cylinder heads, 50 per pallet | 48 x 48 x 32 in | 72 x 78 in sheet top and bottom | 15 strips, 2 x 40 in | – | Cor-Pak VpCI stretch film |
| Crankshafts, 36 per pallet | 56 x 48 x 28 in | 72 x 78 in sheet top and bottom | 15 strips, 2.5 x 40 in | 24 cups | Cor-Pak VpCI stretch film |
| Blocks | 42 x 58 x 46 in | 69 x 56 in bottom, 72 x 78 in top | 6 strips, 2.5 x 40 in | 12 cups | Cor-Pak VpCI stretch film |
Every engine also got a shot of VpCI-238 aerosol on its open electrical connectors before bagging. The program launched on schedule and the system went to other plants with build-ahead programs or long inventory transfers.
Thirty thousand engines, two years, no climate control
Cortec Case History #164 (1999) is the follow-on. In May 1999 the same automaker had sold an engine plant and was contractually obliged to build 25,000 to 30,000 truck engines before the end of 2000, then hold them up to two years before they went into vehicles. The engines were worth more than 200 million US dollars. The project had to start in June, so there was no time to repeat the trailer testing; the plant relied on the Michigan data. The one difference was that the Ohio warehouse was uncontrolled, with no heat and no humidity control, for the full two years.
The pack was simpler because each engine was a single unit. Three engines went into each metal shipping container, each bagged in a custom VpCI-126 bag with four VpCI-131 foam emitters positioned on its four sides. The bag was sealed with a packing tape rated to stick to polyethylene through extreme temperature and humidity swings, and the containers went to the warehouse. Periodic inspections checked for bag damage and any sign of corrosion.
Through June 2000 there was no corrosion on any Cortec-packaged engine. The case notes this was the automaker’s third successful build-ahead program on the same system, which had become the only packaging system the company accepted for build-ahead work.
Why the recipe works
The pack has three layers that back each other up. VpCI-126 film releases vapor-phase inhibitor from the bag walls, and at 8 mil it survives forklift handling. The VpCI-131 foam strips carry roughly ten times the inhibitor per square foot of a film or paper, so they saturate the air space inside an engine bag quickly and re-saturate it after an inspection reseal; each 2 by 10 inch pad is rated for 1.5 cubic feet. The VpCI-111 cups on the crank and block pallets do the same for a dense stack of parts, 11 cubic feet each. Cor-Pak stretch film is not a barrier, but it unitizes the load and adds inhibitor outside the sheets. None of it leaves a residue, so the engines went to the line without a wash.
How to do this in your plant
- Get the parts clean and dry before they go in the bag; a film of coolant or a wet casting will rust inside the best bag made. If you are washing before pack-out, a Build-All or Magido cabinet washer running a VpCI cleaner leaves the flash-rust film you want.
- Bag each unit. For sub-assemblies and housings the 24 by 30 inch VpCI-126 Blue zip-close bag lets you open for inspection and reseal; for a complete engine or a full pallet use a VpCI-126 gusseted liner up to pallet-shroud size.
- Add emitters by volume. One VpCI-131 foam pad per 1.5 cubic feet of bag volume, doubled for a two-year hold or an ocean crossing; the engine case used four per bag. For a dense pallet of parts add VpCI-111 emitter cups at one per 11 cubic feet.
- Spray open electrical connectors with ElectriCorr before bagging, as in #107.
- Seal and mark. Heat seal or use a tape rated for polyethylene, then label the bag as VpCI protected with the pack date so nobody slits it open to check.
- Stretch wrap the pallet in Cor-Pak VpCI stretch film with a VpCI-126 sheet under and over the load. The machine-grade roll runs on a standard turntable wrapper.
- Inspect on a schedule: open one bag a quarter, look, reseal with a fresh foam pad. Our VpCI product selection guide covers the film gauges and emitter sizes for longer or harsher storage.
Which Cortec products
- VpCI-126 Blue zip-close bags: sub-assemblies, housings and kits that will be opened and resealed; up to 5 years depending on gauge and conditions.
- VpCI-126 gusseted bags: the liner that encloses a whole engine or pallet in one layer of film.
- VpCI-131 foam pads: the extra inhibitor source inside a bagged engine; 1.5 cubic feet each, antistatic.
- VpCI-111 emitters: self-stick cups for dense pallets and electrical boxes; 11 cubic feet, up to 24 months.
- Cor-Pak VpCI stretch film: unitize and add inhibitor in the same pass on the wrapper.
We stock VpCI-126 bags, VpCI-131 foam, VpCI-111 emitters and Cor-Pak stretch film in Elmhurst, Illinois, and can quote custom bag sizes for an engine or a full pallet. If you have a build-ahead, a plant move or a long inventory hold coming, contact us for samples and we will help you pack a test pallet first.
Sources: Cortec Case History #107 (1998), Cortec Case History #164 (1999); Cortec product data sheets for VpCI-126, VpCI-131, VpCI-111 and Cor-Pak VpCI Stretch Film.
