When John Ozog’s phone rings, once in a while it might be a frustrated foundry mold manager who’s having a bad day. Ozog, who is technical director at United Erie, a resin maker serving the metalcasting industry, says when molds aren’t coming together as they should, the foundry’s binder supplier is usually the first one who gets the call. And the first question they’ll ask, he says, is predictable: “Did you change the resin formula?!”

Naturally, it’s a tense situation. When sand molds don’t cure fast enough or manifest performance defects, casting production is directly impacted––the pace of casting output is slowed and/or the scrap rate increases; either way, it’s costing the foundry money. Whatever the molding problem is, the widespread assumption at the foundry is, it’s got to be the binder. 

Turns out, that’s part of some widely-accepted myths about sand mold issues. According to Ozog, foundry mold-makers commonly but mistakenly believe:

Molding problems are never caused by sand, because “sand is sand.”
Angular sand is better than round grain sand.

Ozog has studied resins for 30 years and more recently has embarked on focused research of sand properties that adversely influence sand’s interaction with binders and the strength of a sand mold. Specifically, he has identified how the presence of iron, calcium, and magnesium (Fe, Ca, Mg respectively) have detrimental impact on the quality of sand for use in sand molds. And the presence of these three elements create negative results regardless of alloy poured or alloy melt temperature. 

He is planning to co-author a paper about the research with Penn State Behrend Associate Professor of Industrial Engineering Dr. Paul C. Lynch (AFS Student Chapter Co-advisor), and he delivered a sort of “trailer” preview of his work at the March 18 meeting of the AFS Northwest Pennsylvania Chapter in Erie. 

For the present, what Ozog most wants foundries to know is, sand is not sand.

The Accidental Dog Bone

The story of Ozog’s initial discovery about sand, which became the catalyst for further study, begins with a dog bone. These are bone-shaped sand-resin test molds he has used for decades in the pursuit of improving resins for his company’s customers. Using a control batch to which a modified-resin batch is compared, Ozog says he’s always looking for trends. 

“That’s where it really started. I was always using the same sand in those early years,” he said. “I always thought sand was sand––I just assumed it was always the same. But one day, I made a modification to a resin, and it was better than the original resin. I tested them side by side on that sand, and then I tested it with another sand and the performance advantage disappeared. I didn’t understand why. At that point, I started thinking to myself, maybe sand isn’t sand, and I need to start paying more attention to it.”

Indeed, he did pay attention in the lab to see what was really happening. “The results are pretty surprising,” he added. 

Ozog conducted tests to discover the mineral makeup of sand from a wide variety of sources. He isolated Fe, Ca, and Mg, which are present in varying degrees in sandstone throughout North America and serve as a cementing agent in the sandstone. The greater the cementing caused by these minerals, the more energy is required to process the sandstone into sand. The weaker the cementing in sandstone, he found, the easier it is to produce sand grains. Through extensive research, he concluded that less sandstone processing results in rounder grains, which, he discovered, bind better with resins. 

He performed analytical sand tests, using a sample of clean St. Peters Sandstone as a control, and separately mixed only iron, then only calcium, then only magnesium with urethane and furan, the two main types of binders used in mold-making. Ozog discovered Fe, Ca, and MG interfere with chemical binders and greatly reduce speed of resin curing––a major cause of mold-making problems in the foundry. 

Proof Testing 

Ozog’s research extends outside of the lab and onto the plant floors at a few different foundries, where his hypothesis has been proven out consistently. Where problems arise and resin has not been altered, changing the sand, at his recommendation, provides immediate resolution. 

Conversely, he still occasionally receives those calls from anxious mold-makers pointing the finger at the binder. But, says Ozog, when he questions them a little further, the truth frequently emerges: The foundry changed their sand just before the problem cropped up. 

Perhaps the most frustrating foible about Ozog’s sand revelations is that sand inconsistencies can occur from within the same state, the same sand mine, and even the same truckload of sand delivered to the foundry. Complicating the issue, sand mines that own multiple sites in different states sometimes call their sand by the same name. 

Does that mean the foundry doesn’t know the content or quality of their sand at any given time? It’s a possibility. For the present, Ozog is on a mission to raise awareness about sand and its direct correlation to problematic molds. But in the absence of continuous sand testing of every incoming batch, there doesn’t appear to be a ready solution to know whether you’ll have mold trouble until the day you do.