When people talk about heat treating, they usually start with how hot a furnace needs to get to transform metal parts. But it’s often the quenching (or cooling) process that largely determines the final results.
What is Quenching?
Quenching is the process of cooling metal parts after reaching and holding at a specific temperature during heat treating. The method and speed of quenching typically determines the category of a heat-treating process. The most common processes of heat treating are annealing, normalizing, hardening, tempering, and surface hardening. Each process creates a resulting quality that will have different uses or be a part of a different process of making a multi-step end product.
A slower quench time, as seen in annealing or normalizing, can result in metal parts that are springy, bendable, or can be extruded into wire. On the other hand, a more rapid cooling process can result in surface-hardened or through-hardened parts, necessary for making anything from bolts to drill bits to camshafts. Tempering a hardened piece by reheating the metal to slightly lower temperatures with a slower cooling time can help relax some of the internal stress of the metal while adding strength, generating a less brittle, highly ductile material.
Often, a single part may undergo multiple heat-treating operations. It’s helpful to think of a multi-step heat-treating process like this: Imagine taking a disc of pliable metal and cutting teeth into it to give it the profile of a gear, then hardening the gear in a high-temperature furnace, grinding it to achieve required tolerances, and finally tempering it to add ductility. The quality of the metal changes throughout each process to make machining easier, define an edge with pinpoint accuracy, or ensure longevity of the completed piece.
Each process and corresponding end product play an important role in manufacturing today. As a result, Ipsen has continued to find ways to deliver more options and better control of the quenching process to its customers.
It’s Kind of a Cool Story
In 1978, when Craig Moller, Chief Engineer for Ipsen USA, started working at Ipsen, vacuum furnaces had the capacity to handle a positive-pressure gas cooling solution of up to ten psi using 40-horsepower motors. That’s roughly the equivalent of diving to the deep end of a ten-foot pool, or the air pressure inside a very flat car tire. “That was cutting-edge technology at that time,” Moller recalled.
Today, Ipsen has manufactured furnaces with 600 HP cooling motors providing up to 15 bar of quenching pressure. That’s roughly ten times the pressure of machines from 45 years ago.
Gas pressure matters because of thermodynamics. The denser a material is, whether solid, liquid, or gas, the easier heat can transfer from one substance to another. It’s why a vacuum insulated thermal mug can keep hot drinks hot and cold drinks cold longer than a plastic cup – the vacuum minimizes the heat transfer.
Moller explained why quenching pressure is such an important aspect of innovation over the years, “When you triple the gas pressure, you double the cooling rate of a quenching system and the parts being quenched.”
And when it comes to hardening specific metals used to make dies, a rapid and clean quenching system is essential. For example, “when customers are looking for dies for aluminum extrusion to make parts used in an electric vehicle, these high-pressure vacuum furnaces deliver clean dies that are surface hardened for the longevity of the die,” Moller explained. Those clean dies can ensure a high level of accuracy in the extruded parts.
Playing it Cool
For a while, the race to create a faster quench process was all about pressure – more pressure meant parts got cooler, faster. Early on, 90 percent of the focus of heat-treating innovation was the heating process. Eventually, the need to reduce scrap parts stemming from cracks and thermal distortion required better solutions to the quenching process. “It’s been a big change,” Jim Grann, Technical Director for Ipsen explained. “Right now, the balance is closer to 50/50 when it comes to developing heating and quenching technology.”
Grann has been a part of the innovation process since 1978 when he went to work for Abar before their merger with Ipsen. “What’s driving innovation in quenching is the need to create the fastest cooling possible, while affording the controllability of the process. Uncontrolled cooling rates can add inherent stress to the parts. Cooling faster without distortion is the key.”
Today’s PLC controls can react in real time to make modifications to a recipe mid-process if the thermocouples notice an anomalous reaction during the quench. “For example, a recipe may indicate that the core temperature and the surface temperature of a part may not have more than a very specific temperature differential. The PLC can monitor the temps and slow down the quench through reducing pressure, gas circulation, or even by reheating the furnace. Parts heat up on the outside first, but also cool from the outside first, so the furnace can be told to react accordingly,” Grann explained.
Ipsen’s different lines of vacuum furnaces, combined with modern PLC systems, give end users greater control over their process than ever before. The TITAN, MetalMaster and TurboTreater lines have a wide range of quenching capabilities using a 360-degree flow design that can serve dozens of different heat-treating processes. Specialty lines like the Turbo²Treater and VUTK can be designed to solve specific, frequently repeated recipes that require significant quenching gas flow control, providing directional gas cooling from just about any angle within the chamber.
“Sometimes a single-direction gas flow makes sense. Think of quenching a long pipe. If gas is flowing in from both ends simultaneously, they meet in the middle and create a static dead zone. Alternating gas flow from one end, followed by the other, minimizes temperature differentials,” Grann explained.
Directional quenching gas options, variable pressure controls, and active temperature monitoring can allow operators to ensure parts with either simple or complex geometries have the same success rate. “If you tell us what you want to do, what material you’re using, how many pieces you want to process over a day, a week or a month – tell us what you want to accomplish, and we can find a solution.”
With a range of furnace designs and PLC control options, Grann is certain that Ipsen can design a furnace for just about any process. “There are still some quenching rates that we can’t do for the same reason my Toyota 4Runner can’t go 240 mph… we can’t defeat physics,” Grann mused.
Quenching innovations, like the ones witnessed by Moller and Grann over their careers, largely came about by working to meet unique customer demands in an ever-changing market.
If you have a unique quenching problem that needs a customized solution, reach out to us at sales@ipsenusa.com or by calling 800-727-7625.