Castings in the Belfry
By Shea Gibbs, Senior Editor
Tim Verdin is a sixth generation bell man. His family’s business, the Verdin Company, Cincinnati, has been making bells since 1842. It’s the oldest family owned manufacturing company in Cincinnati and the 52nd oldest in the country. But Verdin’s family history only scratches the patina of the history of bell making.
As early as the 1200s, European metalcasters began producing bells by molding molten metal. The process has remained remarkably constant since then, but a few critical changes along the way have resulted in the shape of the modern bell making industry.
Today, bell makers produce castings primarily in sand processes, though some manufacturers have experimented with other processes with mixed results. Green sand is a popular medium, but other metalcasters use chemically bonded sands. Verdin and his company find that material more suitable for their needs, which include bells up to 2,000 lbs.
While the bell making industry today isn’t as large as it once was, and it no longer claims heads of state and Paul Revere as members, the metalcasting process is still the preferred method of producing the ornate and functional pieces.
Two Kinds of Bells
A metalcaster could produce infinite types of bells, and the Arcosanti Foundry, Arcosanti, Ariz., is out to prove it.
“All the bells we have here are handmade and unique,” said Erin Jeffries, a spokesperson for the company. “They are similar but different and one of a kind in both sound and look.”
To be fair, Arcosanti is a special case. The metalcasting facility is one of two that is used to produce artistic bells in the vision of architect Paolo Soleri’s art. Each bell is made unique through the practice of imprinting abstract, pastoral images directly into green sand molds after they have been formed and removed from standard metalcasting patterns. But in the end, all of the unique bells a metalcaster can produce essentially fall into one of two categories. Is it a bell that looks good, or is it a bell that sounds good?
Arcosanti is focused on the former, as are producers of larger bells that go into bell towers, like the Verdin Company. But bells designed to sound good, such as the hand bells played in church choirs, must be handled differently.
The Precision of Hand Bells
Keith DiGrazio, general manager of Richmond Industries Inc., Dayton, N.J., has made a lot of bell scrap. When he first started making the musical castings, it was easy to do.
“The process of making a bell is different from making production castings,” he said.
DiGrazio is owner of a company that makes bells for Malmark Inc., Plumbsteadville, Pa., a hand bell producer established in 1973. But his company is primarily in the business of making commercial castings. By day, it’s a 40,000-sq. ft. plant pouring nonferrous alloys on two automatic green sand lines. So when Richmond Industries began to pour the alloys that are necessary to make Malmark’s mellifluous bells, things were difficult at first.
“Bell metal historically is unique,” said Jake Malta, president and owner of Malmark. “It’s a special bronze alloy—80% copper and 20% tin with only trace amounts of contaminants. That percentage of tin produces the brilliant sounds [but it also] makes it extremely hard and brittle.”
Maintaining that lack of contaminants can be difficult, DiGrazio said, but through patience and considerable time spent working closely with Malta, Richmond Industries has developed an efficient bell making system. The company inventories a range of matchplate patterns designed to produce bells in several sizes (the size dictates the sound produced). Each pattern is used to produce a multi-cavity mold, yielding about a dozen bells, depending on the size. The bells are gated with a circular runner around their base and poured from the top down on an automatic green sand molding machine.
The most common defect that confounds Malta is shrink at the centerline, though DiGrazio said his company has reduced its scrap rate from the early days to typical production metalcasting levels. It is through the finishing process, which remains tedious and manual, that Malta finds the rare unacceptable level of shrink at the centerline while machining into the walls of the bells.
The bells are cast with excess metal on the inside diameter—the surface that will be struck by the clapper. To tune them, trained acousticians machine away layers of metal, judging by ear when the bell produces the desired sound. It is in the course of this process that subsurface defects sometimes are found. But according to Malta, the cost of metalcasting scrap is minimal enough to avoid the need for non-destructive testing prior to machining.
The inner surface of a concert bell is machined to a pitch about 40% higher than the desired note. This gives the bell maker a bit of leeway when beautifying the outer surface, the surface that gleams brightly in the low light of church sanctuaries and concert halls. To achieve that signature shine, the surface undergoes a multi-step sanding process, starting with larger grit paper and progressing toward finer grits.
“That’s why we leave them a little higher,” Malta said. “[Tuners] read between each of these operations and bring them down slowly to the desired pitches.”
The Beauty of Large Bells
When the Foundry on Wheels rolls into your town, you’re probably not in line for a perfectly tuned bell, but you are in line for a fine looking noisemaker. The large rolling metalcasting facility is just one of the Verdin Company’s many toys, but the bells it produces are similar to most of the products it makes at its full scale bell manufacturing plant in Cincinnati.
“Depending on the application, the customer will say, ‘we want one that looks very nice, or one that sounds very nice,’” Verdin said. “You can have a single bell where all you’re looking for is to make a sound. Those bells don’t have to make a perfect pitch note. Ninety-nine percent of our customers don’t care what sound it makes.”
The Foundry on Wheels does on location what the Verdin Company’s main plant does several times a week back at headquarters. Using a large aluminum pattern, molders create a nobake mold using extra fine sand intended to produce a smooth surface finish and intricate detail. The metalcasters then invert the bell, run the gating system from the top of the mold to the bottom and pour the bell from the bottom up, which is top to bottom with respect to the orientation of the bell. The alloy is typical bell bronze (80% copper, 20% tin). The Verdin Company pours it at about 2,200F, the upper limit of the typical temperature for that alloy, to avoid defects. With these non-concert bells, the metalcasters have less concern for shrink.
“The shrink is so minimal,” Verdin said. “Sometimes you can see some in the walls, but we never have a problem with it splitting or opening up.”
Jim Hornberger, manager of Arcosanti Foundry, said his plant achieves the aesthetic and tonal quality it desires by using a coarser sand than production metalcasters and pouring a slightly different alloy than most bell makers (94% copper, 3.5% silicon, 1% manganese and other trace elements).
“Solari’s work is generally organic, so a rougher surface fits in with that well,” he said.
Malta has tried a number of casting processes other than sand to improve the quality of his bells, but he continues to come back to the old standby.
“We tried permanent mold, lost foam and lost wax, but we’re back with sand,” Malta said. “Cost is part of it, but if you don’t get better quality with the higher cost, then you go back.”
With lost wax, Malta said he saw a bit of savings on finishing operations. The lost foam process yielded far better surface finish. But in the end, for Malta, grain structure is the central driving factor for a quality bell. Neither of those processes maintained the grain consistency needed to produce the desired tonal quality.
Malta has even looked at processes outside the metalcasting industry, attempting to break with hundreds of years of tradition. But because of the metal’s lack of ductility, metal forming processes other than casting have failed. Forging, while effective when bell metal is at its peak temperature, quickly becomes destructive as the metal cools, fracturing the surface of the raw bell.
“You could just machine the entire bell,” Malta said. “But then the labor and time would be so great that it would be prohibitive. The cost of them would be out of sight.”
For now, Malta remains shackled by the long history of casting quality bells. ECS