Metalworking fluids present a direct challenge when it comes to rust, said Joe Purnhagen of Lubrizol Metalworking Additives in Spartanburg, S.C. In our industry, rust is a type of corrosion, the corrosion of an iron-containing alloy. A pure cast iron will have more rust than steel, but all iron-containing metals need rust control.

The problems have become more acute as water-containing metalworking fluids – synthetics, semi-synthetic and soluble oils – gained in popularity for their excellent cooling properties, and because they can be diluted on-site by end users. Careful attention is needed because the water content of these fluids will promote rust quickly. So while some cutting fluids, especially neat mineral oils, contain little to nothing as pure rust preventives, most contain a hefty slug of rust-preventing additives.

For rust prevention, alkanolamine chemistry is the dominant type. That includes alkanolamines, and carboxylic and/or boric acid salts, which are polar in nature and show good surface affinity, so they form a protective shield.

In a synthetic metalworking fluid concentrate, as much as 30 percent of the package may be rust preventive chemistry, said Purnhagen, who is Lubrizols metalworking marketing manager. Remember, that will be diluted with a lot of water, usually 20 parts water to one of concentrate. Semi-synthetics may contain 5 to 20 percent rust preventive, and soluble oils up to 10 percent.

And of all the metal removal processes, grinding operations are probably the most challenging for rust and corrosion control, Purnhagen continued. With grinding, the fluids job is to cool and flush; theres less true lubricity needed, so rust prevention is a key property. As soon as you grind the fresh surface theres more area to protect. And this fresh surface is especially prone to corrosion.

Its the fluids job to prevent the piece from rusting in the time between the grind and the next step – however long that takes. Residue on the part is also an issue. You want to have as little residue as possible so theres less to clean off, Purnhagen said.

Lubrizol has built a large stable of rust preventives. Seven years ago, it acquired Alox and its specialized rust preventives known as oxidates. In February, it strengthened its position by acquiring the competing Lockguard products from Lockhart Chemical, the second leading maker of oxidates as well as other additives. It now fields a deep lineup, including natural and synthetic sulfonates, carboxylates, boric acid salts, and more.

Dave Pristic, Lubrizol global business manager, metalworking, told LubesnGreases, When we combine the Lockhart and Lubrizol Metalworking Additives product lines for rust prevention, if you include emulsions, solvent based, temporary and intermediate components, plus metalworking additives, its about 200 products. The Lockhart addition certainly enhances us in a couple of areas, and it improves our North American position in sulfonates. Lockhart also had gelling capabilities and some industrial rust-preventive coatings. One area with enhancements is the low-V.O.C., water based rust preventives we acquired.

We were both trying to prevent rust on metal, but not all the chemistries are identical. Putting Lubrizol and Lockhart together broadens our capabilities and the options that we can offer to our customers, Pristic said.

Field Work

Additives alone dont do the job of course; they must be formulated into finished metalworking fluids or concentrates. Soman Dhar, global range product line coordinator at Castrol Industrial North America in Naperville, Ill., generally classifies these fluids into three types: solvent based, neat oils or aqueous based. Castrol has more than 30 of these products in its global range for rust and corrosion. Solvent based products, such as our Safecoat and Rustilo range, usually contain hydrocarbons, solvents and additives that form a film to protect the surface. These are often used where a dewatering action is desired, to remove water from the metal surface after a part is machined, he explained. This is especially important if you use water soluble coolants, which leave corrosion-promoting moisture on the part.

Neat oils, by contrast, are largely straight mineral oil, used at ambient temperatures and often non-drying. Neat oils typically are used in processes such as strip rolling, tube forming, wire drawing and finishing operations.

Finally, Dhar said, there are aqueous rust inhibitors, which may be a water soluble oil or wax emulsion, or even be fully synthetic. These are still a very small part of the market, Dhar said.

Another consideration is how well the fluid protects the machinery that is performing the operation, in addition to protecting the workpiece. The fluid is protecting the part, yes, but it also must take care of the machine itself, said Eric Kielts, vice president of laboratory services at Wallover Oil in Strongsville, Ohio, which has a full line of rust preventives, including solvent, oil and water-based products.

In metalworking machinery theres a lot of splashing, he pointed out, which if youre using an oil-containing fluid creates a layer of oil on machine parts, so they tend not to rust. Youll see more rust issues in machine areas of high humidity, behind shields and under panels, and synthetics add to that because they contain no oil at all.

Kielts continued, A lot of fluid suppliers will go to Lubrizol or Lockhart to get their formulating expertise, especially the smaller players who get them to pick the rust inhibitor, but the additive companies are short on application expertise. The fluid supplier is the one who sees how it works as part of the system out in the field. Its a mistake to look at the individual components alone; you have to see how its all related to the tool, to the other fluid components, the equipment and the part being worked.

Post-process Aids

Another category of rust preventives are so-called post-process coatings, used to protect parts stored in warehouses, storage yards and during transport. These contain a higher percentage of rust preventive additives, and may stay on the surface for a week, a month or longer. Bill Kingston is technical marketing manager for Na-Sul rust preventives at King Industries in Norwalk, Conn., where post-process rust preventives are a specialty. King is basic in dinonyl naphthalene sulfonate, and also offers a variety of other polar chemistries, such as carboxylates.

Post-process coatings need to be durable but also environmentally safe and cleanable for when the part goes into service or to its next processing step, Kingston explained. It all depends on what you want them to do, how long the parts will be stored, and where. Will they be indoor, outdoors, outdoors under shelter, or transported over seas? Also, what is the substrate being protected: steel, multi-metals, or is there a yellow metal as well?

These days, he sees some formulators attempting biodegradable fluids, perhaps using vegetable oil as a carrier, which can be tricky. For additive response, the naphthenic oils are best, followed by Group I, Group II, then Group III. If you need to use polyalphaolefin, the additive response is tough, but with some vegetable oils like canola (rapeseed), its pretty good.

Kingston sees many competing requirements from customers. They want rust preventives to be biodegradable, and to last a long time. They want them to be aggressive on the surface, and easily removed. And price is always a concern – they always want it for less.

Tried and True

Most rust preventive chemistries in use today have been around for a while, says Frank Ressa, chairman of Ideas Inc. in Lombard, Ill., which makes the Ida-Sol series of rust inhibitors. Early water-based metalworking fluids contained triethanolamines and sodium nitrite, he said – good at preventing rust, but outlawed when they were found to generate harmful nitrosamines. The next generation of formulations relied on paratertiary butyl benzoic acid; it in turn was banned because it was found to cause testicular atrophy in lab mice.

The next up were carboxylic acids and salts, which are still current, Ressa said. The acid reacts with the amines, which creates a salt or amide to combat rust. They include boresters and boramides, which are good but can have a tendency to built a glass-like film which can cause machining problems. These products can be purchased from a number of sources, such as Ideas or Lubrizol, and some fluid manufacturers make them in-house for their own proprietary use as well.

There are no huge black flags near term for any components used today, but Lubrizols Purnhagen did note that in Europe boric acid may be facing an increased health hazard rating. The reacted salts present no problems, but some blenders are trying to get away from handling boric acid per se, he said. They might consider a pre-processed, pre-reacted boric acid salt. It costs more, but can offer processing efficiencies since its an easy-to-handle liquid and doesnt require an on-site reaction. Having a reliable quality and supply can be key, but it still may present a challenge economically, Purnhagen said.

At Castrol, Dhar sees a number of trends in the market, beginning with an ongoing shift away from products compounded with barium. We see this in the U.S. but even more so in Europe, where theres a lot of push away from barium.

The market also is moving to low-V.O.C.-emitting products, to meet air quality standards. If youre trying to substantially reduce V.O.C.s, the best answers are solvent-free corrosion preventive oils or an aqueous based product, but a water based fluid will always need to be followed by good corrosion protection, Dhar said. Most solvent based rust preventives release a lot of volatile organic compounds. However, there are alternatives, such as Rustilo 4135 HF, which is solvent based yet has low V.O.C.

Supply Questions

Wallovers Eric Kielts said, Rust itself isnt any tougher, but there are always new issues out there, such as regulatory concerns – Do I use barium or no? – and physical issues such as demulsibility for fluid disposal. For rust, the current customer concern is whether the solvent used is flammable. In talking with customers I hear issues that are not focused on rust inhibition, but rather on can I use mineral spirits? in the formulation.

The biggest concern now, from our standpoint, is about oxidates, Kielts said, turning to the Lubrizol/Lockhart deal. There used to be two suppliers, and now theres just one. I can guarantee you that prices will go up, its what always happens, and the only comfort is that everyone I compete with will be in the same boat, so no one will have or lose an advantage on it.

It really makes no difference to us, shrugged one fluid formulator, but others were somewhat glum. Not good for end-users, worried one, who declined to be named. Absolutely youre going to see prices go up. Other companies are going to have to rise up to offer alternatives.

Greg Jorjorian of Additives International in Evanston, Ill., said he is preparing to do just that. His company already makes rust preventives from wax esters, calcium soaps, sulfonates and other proprietary components, and now hes developing a line of oxidates which should be ready for introduction by mid-year, he said.

People are looking hard at costs and alternative chemistries, Jorjorian said. And were going to be offering one.

Lubrizols Pristic outlined some of his companys plans for the Lockhart products. Both the Lubrizol and Lockguard brands will continue, and everything from Lockharts Flint, Mich., plant will be moved by year end to Lubrizols plant in Painesville, Ohio, he said. Care will be taken that the products remain identical, despite the shift in production site, he added.

When Lubrizol has a product name, if its Alox or Lockguard, the products are what they are. We must support them as they are and cannot change them without notification to the customers. We bought the entire Lockhart product line because it made sense to, that was part of their appeal. The goal is to give our customers – the formulators – the capability to offer new products for their end users.

Look at it from a bigger picture, Pristic continued. There are a number of external forces at play in the market that make size and capacity very important. For example theres REACH [Europes stringent chemical registration and testing program], and companies who are trying to comply with it will need to have the financial wherewithal to work through its requirements. This acquisition will help keep the Lockhart products in a range where they might get through it better.

The supplier range may be smaller, but in the long run, having a healthier supplier will be better for the users.