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 8 hardness spec and only up until the time the desired depth and Rockwell levels are reached (Fig. 3). Failing this level of control, throwing heat at a part for too long or into areas that compromise the integrity of the whole, and problems invariably result. MAINTAINING DISTANCE The next crucial control step is managing the relation- ship between the flame head and the part during the heat treating process. If the flame head is too far away, it will re- duce the hardness depth and level perhaps out of spec. If it is too close, the reverse is true. Either the part or the flame head will be traveling during the heat treating process so the integrity of that relationship must be maintained for every run (Fig. 4). After the correct relationship is estab- lished during the manufacturing process, it is programmed into the machine control panel. CONTROLLING FLOWS OF FUEL AND OXYGEN It’s been shown how the flame hardening process is controlled at the part. Now consider how it’s controlled from the sources of fuel and oxygen. Whatever the source—natural gas, propane, tanks, or lines—the fuel and oxygen coming into a flame hard- ening machine needs to be tightly controlled. This is not only for safety reasons, but also quality. The flame head is designed to deliver the correct amount of heat based on a precise calculation of flows. There are two ways to con- trol the flows, manually (Fig. 5) or with a mass flow meter (Fig. 6). CONTROLLING THE QUENCH Hopefully this article has given a 30,000-foot view of controls necessary to “throw heat” at steel or cast iron parts in production. In fact, only an overview of controls re- lated to the actual flame head and delivery of fuel and oxy- gen has been described thus far. There is more to this type of targeted, surface heat treating than pointing a torch at a general area of a part and hoping it’s good enough. Con- trols are just as necessary in the next step of the heat treat- ing process: the quench. Because a heat treated part wants to retain its heat, the method and rate of quench needs to ensure that the heat is taken out of the part at the correct rate. If the pro- duction process uses a spray quench, the flow rate of the quench must be controlled. If the production uses a quench tank, the rate at which the part enters the tank must be controlled. The temperature of the quench must also be controlled; if it is in a quench tank, it may need a chiller to keep it at the correct temperature as each part introduces more heat into the tank. When using a polymer quench, it’s critical to know the percentage of polymer to water that is necessary for the materials and the mass. Failure to correctly design and control the cooling process causes quality issues and cracks. If a part cools too slowly, it may not reach the hardness level specified. If a part cools too quickly, the part can crack, introducing safety risks and failure in the manufacturing process. CONTROLLING FOR SAFETY Ignition and extinguish- ing get a lot of attention for operator safety. Both process- es should be stabilized with timers and solenoid valves. 7 Fig. 4 — Correct relationship between flame head and part, including distance and speed of travel if scanning. Fig. 3 — Result of actual run with prototype flame head and sample part. 6