AMP_04_May_June_2021_Digital_Edition

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 | M A Y / J U N E 2 0 2 1 5 7 H eat treating is often the last step in themanufacturing process. It is also very often the last step considered when designing the line. Companies usually have a good handle on mechanical and spatial requirements, but few have design-level experience of heat treating. All too of- ten it’s necessary to call in experts to redesign an inadequate process that was hastily designed and specified because heat treatingwas considered an afterthought, or “just throw- ing some heat at it.” It’s no wonder that cracks, inconsistent patterns, and inadequate depths happen. Without the proper controls, “throwing heat” results in the Wild Wild West of heat treating: inconsistent pat- terns, varying hardness levels, and safety issues. Today’s flame hardening, perhaps the heat treat method most often associated with “just throwing heat,” employs pro- grammed controls that make sure the heat is distributed safely and consistently part after part, shift after shift. This article describes some general ideas of the control meth- ods used in building various flame hardening machines designed for in-house production use. These guidelines will help anyone who finds themselves part of a team hav- ing to design a line that will use a heat treating station, particularly if flame hardening is used, and will present in- formation to caution coworkers whomight say, “just throw some heat at it.” Controls must be the center of the design phase. They must ensure: (1) the hardness spec is met each time a part runs, without any cracking; and (2) the operator is protected and has the ability to address any flow problems that arise. FLAME HEADS ARE KEY TO PATTERN AND QUALITY Developing a hardness specification in-house that specifies the material grade and pretreatment/stress relief of the piece prior to heat treating, in addition to the hard- ness pattern and Rockwell level and depth required for each part that needs hardening, is a good first step to op- timizing quality and control (Figs. 1 and 2). Don’t just buy steel. Specify the material and pretreatment condition. Know exactly the amount of hardness a part needs, where it goes, and how deep—so that the amount of heat is con- trolled only to what is specified. DON’T ‘JUST THROW SOME HEAT AT IT’ Precise controls are at the heart of today’s flame hardening processes and design, delivering consistent, measured, and accurate heat treatments. Mark Sirrine Flame Treating Systems Inc., Durham, North Carolina With the desired pattern and hardness levels estab- lished, the design of the flame head ensures that the heat “thrown” at the part reaches only the area specified by the Fig. 1 — Hardness specification for a roller chain guide made from 4140 steel. Fig. 2 — Flame head design to achieve hardness pattern (58-60 Rc, .200-in. deep) from specification. 5