When you walk into a heat-treating department and see your first vertical vacuum furnace, you’d be forgiven for staring openly at the jaw-dropping sight.

There, perched a story or more in the air on metal legs, is a gigantic vacuum pressure vessel. Wires and hoses, pumps and controls—all attached at various angles—could draw comparisons to science-fiction icons like the Iron Giant or the alien spacecraft from H.G. Wells’ War of the Worlds. They are magnificent machines. Awe inspiring. And, most importantly, very useful.

Looking Closer – Why Buy a Vertical Vacuum Furnace?

Abar Corporation started producing large bottom-loading vertical vacuum furnaces in the 1960s, most notably building the largest of its kind at the time in 1969 with a gigantic 96-inch by 96-inch work zone (pictured above). “Aerospace companies on the east coast started buying multiple Abar vertical furnaces, lining them up in a row to meet the demands of the space race and the growing commercial aircraft business,” said Mark Heninger, Ipsen’s Director of Equipment Sales. By the time Abar and Ipsen merged in 1985, vertical vacuum furnaces had a steady demand.

While these furnaces could do just about everything their horizontal counterparts could do—annealing, carburizing, hardening, tempering, etc.—the vertical furnaces could uniquely handle delivering heat and quenching with a high level of control for very large or very long cylindrical parts with varying thicknesses. Picture a cross-section of an aircraft fuselage, or the engine nozzle of an orbital rocket.

“Heat-treaters were looking for more capacity out of a furnace in one load. Trying to load a part that’s big or deep into a horizontal furnace becomes a problem,” added Jim Grann, Ipsen’s Technical Director. “When you have a piece that’s six feet in diameter and 25 feet deep, how do you load and unload that into a horizontal furnace?”

Bottom loading vertical vacuum furnaces allowed huge pieces like this to be sitting flat on the hearth or suspended from the top on a jig within the hot zone. This allowed engineers to take advantage of the geometry of the whole diameter of the chamber, not be restricted by the cross-section width of the pressure vessel at different elevations above the hearth like they might in a horizontal furnace.

“If I have a part that I’m laying down in a cradle on a hearth, and it’s going to grow in a way where I can’t control the expansion coefficient, the weight may cause the piece to warp. However, if I can hang the part, and let gravity allow for it to grow down with neutral loading, I’ll have more consistent uniformity through both the heating and cooling process.” Jim Grann, Technical Director

“When it comes to handling these large parts, vertical vacuum furnace owners are often able to rely on existing overhead crane infrastructure for loading and unloading parts onto the hearth mounted on the traversing bottom head,” Heninger explained.

“Compare that to a horizontal furnace that would require a loader with long forks feeding these gigantic pieces deep into the hot zone. Ensuring the forks remain rigid and parallel over a long travel distance to place the load without colliding with hot zone elements can be expensive,” Grann added. Buying or building a loading system that can handle that rigidity over a long span can add significant cost to the expense of the setup. Storing such a loader when not in use further adds to the overall footprint.

Looking for More – Beyond Big Parts

Not everyone who buys a vertical vacuum furnace has a constant stream of gigantic parts, however. “We had an assumption that we changed about three years ago. We believed that people would buy these vertical furnaces so that people could put big parts into it. Now, we see users building fixtures with big round plates on it like a pizza oven,” Grann explained of the trend. The demand to handle smaller parts between orders for the larger piece work drove systemic innovation in fixture design. In addition to the multi-tiered platforms, basket systems and hanging racks took advantage of the larger usable overall volume available in a vertical vacuum furnace for parts with strange dimensions.

“This demand to use fixtures to handle smaller parts changed the way we looked at the design of the control zones,” Grann noted. Due to the demand in the aerospace industry for accurate temperature readings and process monitoring, additional positions for thermocouple monitoring within the designs of vertical vacuum furnaces made managing processes that handled parts with a wide range of geometries at the same time possible.

“Even though a vertical furnace may be very tall, a lot of the mass of the parts may be at the bottom of the chamber, with the hearth and the fixture,” Heninger explained. “Customers may run a partial load with parts only going so far up into the chamber. So you’re more likely to see top and bottom elements and ring elements for better temperature control throughout the chamber.”

Companies in global locations where ground square footage was at a premium looked at vertical furnaces as a way to build upwards instead of outwards, reducing the footprint of each furnace while maintaining the capabilities of handling large workloads.

Look Out Below: What Are Top-Loading Vertical Furnaces?

A rarer counterpart to the bottom-loading vertical vacuum furnace, Ipsen’s VTL top-loading furnace also emerged as a solution for incredibly long parts. “Top-loaders and bottom-loaders are distinct furnace types. Top-loaders excel at handling exceptionally long components, such as tubes exceeding 300 inches in length,” said Heninger.

Sometimes lowered into a pit beneath ground-level, these furnaces could handle hardening massive driveshafts for everything from big trucks to oceangoing vessels. “For a top-loader, you need an area for the furnace, but then you also need an area for the part to be lowered into the furnace,” said Heninger.

Imagine gargantuan pistons the size of semi-trailers pushing camshafts that run the entire length of a ship. For every ship that crosses the ocean, each piston and shaft requires heat treatment. In those cases, top-loading vertical vacuum furnaces can often be the solution.

A Critical Eye – When Not to Select a Vertical Furnace

“Vertical furnaces are flexible, but that doesn’t mean that they’re a universal solution,” explained Janusz Kowalewski, Ipsen’s Sales Director for Southeast Asia. Most notably, hot zone maintenance is more complicated when your technicians need to be a story or two above the shop floor to replace consumable parts. There are extra considerations that come with managing the human interface—ladders, catwalks and handrails. And, of course, the height of the facility’s roof will limit the size of the furnace. “One cautionary tale taught installers and riggers to be mindful of the location of the overhead crane, so that it doesn’t get stuck on the wrong side of a vertical furnace or lose half of its travel span,” Kowalewski recalled.

Fixtures in a vertical vacuum furnace tend to be more elaborate to take advantage of the space, and typically cost more than what is used in a horizontal furnace. And while bottom-loading furnaces may take up less floor space while operating, there are still additional space demands. “Bottom-loading vertical furnaces still need space for the hearth to drop down and move away from the base of the furnace for loading and unloading the parts payloads,” Kowalewski noted.

“Also, recipes for vertical and horizontal are not necessarily interchangeable. Moving a process from a horizontal machine to a vertical machine may require a recertification of the process before production can continue,” Grann added.

Looking Ahead – Vertical Vacuum Trends

“While traditionally, we’ve seen clients using our vertical vacuum furnaces for annealing and brazing parts, requiring only a 2-bar quench, aerospace companies are starting to approach us for higher pressure quench solutions,” Heninger observed. “We have started to see more demand for 6-bar up to 15-bar furnaces from aerospace companies and we’re building more of these as the demand increases.”

What Ipsen has seen over the years is a tendency for customers who buy one vertical vacuum furnace to add more to their fleet over time. Once the maintenance team is trained, the recipes are approved, the fixtures and procedures are in place, and the orders start coming in, the demand for vertical vacuum furnace production remains strong.