FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 2 4 8 trogen gas and a vacuum pump on the vestibule increases operating costs. The gear manufacturing cell would benefit from localizing heat treat furnaces in the same area, but the operating costs and capital equipment costs alone do not justify this concept. Material handling, housekeeping, and safety would need to be evaluated to justify this investment in a flameless type BIQ. When considering batch versus continuous furnaces, the capacity of batch furnaces has increased to batch loads of 6000 lbs and work zones of 36 x 72 x 36 in. (w x l x h). Using large batch furnaces is a preferred method for the flexibility of BIQ furnaces. Heat treat capacity of the larger BIQs is 1000 lbs/hr, so up to three large BIQs can be utilized instead of choosing continuous pusher furnaces. Batch furnaces allow manufacturing to grow without the large capital investment of continuous pusher furnaces. Maintenance costs for batch furnaces are low, and lifetimes are greater than 20 years. The maintenance costs for continuous furnaces are greater on a complete overhaul basis. CONCLUSION Processes available for gear heat treatment are well established and controllable with atmosphere carburizing, while vacuum carburizing is modeled on a case by case since it is empirical. The technologies that have improved distortion are high pressure gas quenching, but better material grades are required, and both add costs. Other advances are better insulation and heating technologies, improved process control sensors and better quench modeling/design. As such, the temperature uniformity, carburizing or nitriding potential uniformity and quenching are significantly better than in the past. Comparing BIQ rated capacity today to continuous pusher furnaces shows batch loads are highly productive. Today it is advisable to invest in the flexibility of up to three BIQ furnaces before considering continuous pusher type furnaces. It is expected that better material grades (alloying, powder metallurgy, additive manufacturing) will be developed for lightweighting in automotive, aerospace, and defense industries. Until these advanced alloys are cost justified, atmosphere carburizing and oil quenching remain the preferred heat treat method for gears. ~HTPro For more information: Benjamin T. Bernard, vice president global sales, Surface Combustion Inc., 1700 Indian WoodCircle, Maumee, OH43537, 419.891.7134, bbernard@ surfacecombustion.com, surfacecombustion.com. References 1. Y. Wei, Atmosphere vs. VacuumCarburizing, Center for Heat Treating Excellence, Worcester Polytechnic Institute, 2013. TABLE 1 — OPERATING COST COMPARISON OF VARIOUS FURNACES Heating source Quench method Cost per load Energy cost per load Multiple chamber vacuum Gas Oil $8.12 $7.37 BIQ Gas Oil $9.65 $7.92 Flameless BIQ Gas Oil $13.15 $7.37 Two-chamber vacuum Electric Oil $25.26 $23.76 Multiple-chamber vacuum Gas High-pressure gas quench (HPGQ) $27.01 $12.06 Single-chamber vacuum Electric High-pressure gas quench (HPGQ) $50.30 $37.80 Interested in advertising with the ASMHeat Treating Society? Contact Kelly “KJ” Johanns at kelly.johanns@asminternational.org. 12
RkJQdWJsaXNoZXIy MTYyMzk3NQ==