Metalcasters are among the many manufacturers that must protect their materials and finished parts from corrosion for varying periods of time. And, while there are many options for corrosion protection there’s not much standard information.
There is a general agreement that poor corrosion protection carries a penalty, including the costs of additional cleaning and surface preparation as well as material and product rejects, and loss of time. Of course, those are the costs before the finished product is shipped.
According to research by Battelle Labs, and later supported in a study by the National Assn. of Corrosion Engineers, corrosion damage to products and materials ranges from $276 billion to $300 billion/year in the U.S. At that level of risk, investing in corrosion protection is becoming more than discretionary; it’s an effort to enhance finished-product quality and improve customer service. It is a way to protect investments in equipment, products, and raw materials-items that determine the integrity and standard of excellence in finished goods.
Buyers of castings and other products know the importance of corrosion protection. On the other hand, some manufacturers overlook the importance of quality in their selection of corrosion protection products. While there’s not much standard information to guide this selection, one product area that is widely recognized for effectiveness is volatile corrosion inhibitor (VCI) packaging.
There’s another problem. Some users and suppliers of VCI packaging imply that “good enough is good enough” when it comes to VCI performance; that “conforming” to stringent scientific testing to establish a standard is the same as complying with them. At the core of this debate, then, is the issue of the value of scientific test methods and how to determine what level of performance is sufficient for VCI. Also under consideration is what happens when “good enough” does not perform well enough.
It works like this
Corrosion inhibitor compounds vaporize from the paper or film and are attracted to the charged surface of the metal by virtue of their polar orientation. The VCI molecules align on the surface of the metal to a depth of 3-5 molecules. This molecular layer passivates the charged surface and creates a barrier that prevents oxidation for years. The corrosion cell (the flow of electrons in the metal and the flow of ions in the electrolytic surface layer) is unable to establish itself. Corrosion is prevented, or halted; airtight packaging is not necessary. The metal remains clean, corrosion-free and ready to use; no washing, dipping or cleaning is necessary.
A metalcaster, or any manufacturer, that adopts VCI packaging for its products will need to become familiar with the materials and technologies available: How can, and should, VCI products be applied to a specific operation and product line? That’s the recommendation of Mike Bentley, Mid-Central regional sales manager for Daubert Cromwell one of the leading suppliers of VCI products and materials.
Bentley observed that VCI is being used in some form by most major metalcasters, particularly the producers of gray and ductile iron products, but also the producers of zinc-alloy materials that can also be prone to oxidation.
Most of these producers are being encouraged to adopt product-protection capabilities by their customers, Bentley confirms. Just as castings buyers want on-time deliveries, they expect their purchases to be ready for processing. For “precision, high-value parts” like automotive water pumps or rotors that may need specialized machining, that means the surface conditions must match specifications exactly.
For the metalcasters adopting VCI packaging, the investment should not be considered extraordinary. Typically there is no specialized equipment needed, according to Bentley, but rather a new packaging material or design.
There are a number of VCI packaging suppliers, but because theirs is a fairly recent innovation, and because its how’s and why’s are rather esoteric, there is little understanding of what protects best, and what is the appropriate standard for measuring the efficacy of corrosion prevention packaging?
No organization understands the need for corrosion protection better than the U.S. Dept of Defense. The Pentagon has established a process to certify that all assets in its complex and critical distribution system are protected by VCI products that comply with the most demanding standards for quality and performance. Products that make the cut are placed on the DOD’s Qualified Product List. Because the approval process is thorough and stringent, QPL sets the standard for VCI product reliability and performance. Given the disruptive potential of corrosion, it’s clear that protection against degradation is an essential part of the effectiveness of DOD’s assets.
The selection process
There are VCI packaging suppliers that challenge the need to adhere to such stringent parameters. Obviously, more rigorous testing increases research costs, and the resulting product costs. In efforts to maintain price-based market share, some VCI producers downplay the importance of product performance. They allege that the high QPL-type standards established for VCI materials represent a classic case of overkill providing little or no reciprocal value to justify the research and production costs. They also contend that VCI materials need only to provide a minimal standard of performance — which may or may not meet actual needs — because the VCI product “conforms” with QPL-type testing and has similar VCI chemical composition even though it does not comply with it.
Some efforts have been made to assess VCI effectiveness by ways other than strict performance testing. In the automotive industry, for instance, a chemical-deposition standard is a common method. It uses the Wash Off Test, an indirect test that avoids actual performance testing.
In the Wash Off Test, a sample of VCI packaging paper is rinsed under water and the materials applied to the paper, including VCI chemicals, are washed off, collected, and weighed. The weight of the residue must meet a specified weight criterion to pass the test. Less than scrupulous suppliers, however, have found a way to meet the weight criterion of the Wash Off Test by substituting clay or other fillers for some of the more expensive VCI chemicals. So, even though the weight of the residue meets the criterion, corrosion protection may be sacrificed.
VCI products are widely available, and VCI materials can be applied to work effectively in most shipping and packaging operations. But, not all VCIs are equally good, nor are they equally effective in every application. Often, one VCI formulation that works under one set of conditions will not work under another. And, they must have sufficient VCI chemicals to allow the formation of a three- to five-molecule layer. There is a need to take into account all aspects of the process, metal compositions, packaging, storage, and shipping, in order to select the right packaging media and VCI formulations.
When VCI formulations or products are selected, the VCI packaging should be tested with the metals to be protected in conditions that nearly simulate the actual protection environment. Only the actual performance test should be used to validate the packaging’s efficacy.
There are a number of suppliers of VCI materials. In the metalcasting industry one of the most visible is Daubert Cromwell, the result of a recent merger between Daubert VCI Inc. and Cromwell Phoenix Inc. It maintains that its product developments have been steadfast in the effort to maintain the highest standards of quality and effectiveness; it has 13 products (and one more pending) among 13 categories on the DOD’s QPL. Daubert Cromwell says the QPL criteria keeps it in the R&D mode, and it offers multiple formulas of VCI chemicals and many “near-custom” products.
Another prominent supplier is Cortec Corp. It promotes its expertise with packaging materials for metal products that are recyclable and degradable, and also emphasizes its branded packaging for manufacturers that customize their shipments that way. Branded packages may carry a company logo, as well as part ID number, verification receipts, etc.