Do’s and don’ts guides are an engineer’s best friend. They’re an objective instruction tool that helps system architects and fabricators to navigate processing minefields. In that regard, hot zone maintenance procedures employ a highly organised sequential approach. That systematic methodology begins with a pre-processing phase, a maintenance checklist that governs the heat treatment operation before a single piece of equipment receives a wisp of ignitable fuel.
Do Manage Preprocessing Work
A baseline must be established. That baseline starts with metal parts that are clean and blemish-free. The conveyed workpieces are handled with corresponding care, with a level of workpiece-conserving prudence that delivers an absolutely viable initial heat load.
Don’t Accept Soiled Parts
The goal of the heat treatment work is to uniformly alter the microstructure of a metal part, but that uniformity becomes difficult if the part’s exterior is coated with foreign matter. Hot spots form, especially in vacuum furnaces, so don’t allow that part access until it’s thoroughly cleaned.
Do Wash After Sandblasting
For the most stubborn surface marks, sandblasting is the logical solution. However, that sandy material can’t be allowed into the furnace, not when it’ll affect the production cycle. The furnace will inevitably cook these unwanted particulates and corrupt the stringently monitored process. Wash all traces of this residue away before continuing any further.
Do Maintain a Clean Buffer Zone
A clean cool area enters the process chain when the parts are ready for the cooling phase of the operation. Emulate that stage by using a clean hot zone, a reserved area that acts as a hot buffer outside of the furnace. In here, certain process variables can be corrected. They include water vapour eviction, material cleanup work, and other hot phase operations. Integrated correctly, the hot buffer zone extends the working life of the vacuum furnace system.
Don’t Forget Transferrable Materials
Oils and greases enjoy something of a charmed life. They’re absorbed into the hands of workers or conveyed on the part’s carrying equipment. That’s a process reality that negatively impacts heat treatment technology. Conduct a vacuum washing or hydrocarbon rinse, a stringently observed wash stage that targets these oily materials before the workpiece enters the furnace.
Heat treatment environments are undoubtedly classed as industrial sites. Foreign matter accumulates in here. Still, a hot zone maintenance plan must counter that environmental reality. It must systematically eliminate the oils, greases, and particulates before they corrupt a process that relies on a predetermined viability factor. Enforce these Do’s and Don’ts. Better yet, document the maintenance strategy by recording the corrective steps and generating a preventive maintenance program.
Does a factory full of furnaces look like some industrial hell? In point of fact, nothing could be further from the truth. Science-lab accuracy and high-tolerance engineering exactitude rule every processing stage. In those heated furnaces, temperature uniformity is a beyond critical quality, one that comprehensively eliminates heat treatment inconsistencies. Let’s really draw a line under the importance of temperature uniformity by examining a working heating system.
Delivering Atmospheric Fuel
In catering equipment and powder coating ovens, powerful convection fans push large quantities of air throughout the cooking space. At first, that sounds like an efficient air supply solution, but then the heat treatment furnace gets pulled into the debate. This equipment operates on a higher level. In here, regenerative blowers distribute thermal energy. Air intake channels and special manifolds control the pressure, and a filtration system eliminates airborne contaminants. Beyond this carefully arranged air ducting architecture, there are pressure switches and metering devices, ancillary mechanisms that actively manage the air-to-gas ratio inside the furnace. Kept steadily at a 10:1 gaseous relationship, the atmospheric part of the heat treatment equation is therefore finitely controllable.
Examining Heat Furnace Technology
As has been clearly demonstrated by the impeccably designed air supply system, heat treatment science values uniformity. Next, the combustible fuel supply needs to match the air management system. It does so by regulating the piped fuel. In this case, the chosen combustible fluid is natural gas. That gas is passed through a filtered series of NFPA 86 validated valves, a network that’s constantly monitored to ensure an unvarying flame is generated by the burner elements. In short, when that fastidiously controlled fuel stream ignites, these valves and monitors generate a flame that will evenly heat the entire furnace.
Assessing Burner Mixer Efficiency
If we picture the filtered air and filtered fuel meeting in a mixing head, the high-velocity flame can be visualised as it rushes headlong down an array of tubes. Uniform heat erupts from the burner channels to heat treat every hidden recess, every surface feature, and every contour on and around any workpiece. The uniformity factor is assured at this point, with thermal energy evenly touching the unique profile of any conceivable geometrical outline. Meanwhile, back at the monitored burner valve train, exhaust energy is recycled until the furnace achieves full self-recuperative functionality.
If we’ve proven anything, it’s that the furnaces used in a heat treatment facility are technologically superior. The equipment controls every possible part of the combustion process. The atmospheric intake, the filtered fuel, the burner assemblies, every system and subsystem inside the furnace is regulated by electronic instrumentation. Controlled in this manner, the uniform distribution of furnace heat is absolutely assured.
As stated in our earlier articles, flame hardening technology selectively heats and hardens parts of a metal workpiece. Imagine the teeth of a spur gear being subjected to the flame, or perhaps it’s the leading edge of a chisel that experiences the focused flame. Looked at from the perspective of the subject steel or iron part, how do we quantify these hardening effects? Well, we begin by recruiting the Rockwell Scale.
What is The Rockwell Scale?
Used to measure metal hardness, the Rockwell test is defined as an alloy’s ability to resist indentation. More accurately, the test uses a set load and a specially engineered indentation tool to measure how deeply the strike registers. Incidentally, Rockwell engineering data tends to go hand-in-hand with a hardness curve, a heat treatment signature that’s every bit as unique as a fingerprint.
Flame Hardening Effects: Ferrous Materials
Thermal gradients and Rockwell tables provide a great deal of information. The data illustrates temperature and hardenability relationships, it shows how many millimetres of material hardness have been applied to a subject steel or iron part, and it also depicts carbon content changes. As the oxy-acetylene torch closes on the workpiece, a thin, hard transformative layer is imparted. Importantly, this is not an additive process, so no dimensional expansion takes place. No, the process actually converts the microstructure of the existing surface into an austenite, then that processed grain changes again during the quench phase until a full martensite shell surrounds an untouched ferrous core.
Executing a Dramatic Phase Change
The effects of the flame hardening work only tell half the story. Obviously, this is the stage of the process where the metal part is heated rapidly, but, if left to cool, that state change won’t produce a properly case hardened shell. In order to achieve the gradient curves and Rockwell numbers detailed above, the quench station must also rapidly cool the alloyed part so that the martensite phase is quickly reached. In other words, those data-illustrating thermal gradient curves tell a story, one that’s based on applied thermal energy, the period that temperature was maintained, and the length of the quenching interval.
The final component in this material-centric formula is the composition of the ferrous material. The amount of carbon in the alloy, the steel family used in the heat treatment process, even the use of nearly pure iron, all of these processing factors impact the hardening curves. In the latter instance, iron, the carbon-exempt metal gains fatigue resistance and localised strength when the flame hardening torch gets to work.
Metal fabricators employ numerous tooling stations, which is as it should be because complex geometrical profiles are processed within these expert workshops. Some tools bend, others drill, then, waiting in the wings, there are bandsaw cutters and shop presses waiting. In essence, the workpieces are exposed to enormous stresses. These cold work stresses steal away part’s ductility. With that drawback in mind, let’s talk about workpiece recovery.
Annealing Equipment: Resetting Workpiece Ductility
It may take an arsenal of metal fabrication tools to produce a certain geometrical profile, but the effects of this cold-worked processing environment needn’t be permanent. Intransigent microcrystalline damage, a sort of metal memory, is deletable. To eliminate this effect, annealing equipment enters the workshop tooling chain at a predetermined point, then the physically inflexible part is slowly heated until its microstructure softens. As it softens, the part regains its former pre-cold worked properties.
A Metal Fabrication Facilitator
As we can see, without annealing equipment, a machined part may as well have a countdown clock stamped into its hardened material. A bend here, a cut there, each additional processing stage slices form-manipulating seconds off of the figurative timepiece. When that clock is in the red, the partially finished part becomes rigid, perhaps even brittle. Any further bends or cuts stand a good chance of sending fractures through the part. Even if fractures don’t develop, invisible weaknesses proliferate while ugly ripples grow along the inner turn of a bend. In short, for lack of an annealing station, the plastic deformation feature attached to the part has taken a leave of absence. Again, that absence is temporary, but it’s only temporary if this heat treatment process is properly plugged into the metal fabrication chain.
The Importance of Normalising
This heat treatment solution varies the functions of annealing equipment ever so slightly. Primarily, the normalising variant is geared towards ferrous alloys, so steel parts are subjected to this ductility resetting process. As for procedural differences, normalised parts are typically cooled by air or under a protective gas. In this way, parts decarburization is circumvented while grain uniformity and plasticity is regenerated.
When metal fabrication shops are responsible for forming complicated workpieces, some degree of cold worked inflexibility is inevitable. In order to sidestep this potentially expensive issue, time has to be turned backwards within the material. Annealing equipment acts as the time machine, a heat treatment solution that heats the part slowly until all of its workable mechanical properties are reset.
The flame hardening process is a cost-effective heat treatment technique. Primarily, it’s the high-intensity oxy-gas flame that keeps project expenditure low. The flame hardens localised workpiece areas, so application economy exists right there. Next, the movable flame head controls hardening depth, which is yet another cost-saving benefit. Now that we’ve begun investigating, the budget-centric benefits are coming thick and fast, with that mobile flame head really burning away the costs.
Cost Friendly by Design
There are engineering issues to solve here and logistical problems that ride alongside those mechanical puzzles. Flame hardening technology provides an immediate solution for the practical problems and those abstract but still very real monetary concerns. Basically, that single focused flame holds enough hardening sway to heat treat parts that are much larger than that lone tool. Known collectively as “Progressive Flame Hardening,” this wide surface area process variant moves like the beam on an old television set. It “scans” along the steel sheets or large cross-sectional area of a steel component to uniformly harden big areas, material segments that would otherwise require large amounts of widely distributed thermal energy.
The Ubiquitous Heat Treatment Solution
In an age where large industries create entire cityscape-like silhouettes, steel parts have scaled to meet demand. Post-processing technology emulates that scalability by using huge amounts of heat to harden unwieldy parts. Conversely, the scanning process we just outlined does the same job at a fraction of the cost. The flame head carries out its voyage across the part one line at a time. If the workpiece is a cylinder, then the flame head mounts on a spinning armature, one that spirals down the length of the cylindrical steel segment until it’s fully hardened.
A Perfect Match for Targeted Applications
The focused oxy-gas tool is also designed to work selectively. Remember, the outer teeth on a helical gearing assembly will require depth hardening, which works out well since this white-hot flame is quite capable of transmitting enough energy to case harden a set of gear teeth down as far as 10-mm. Similarly, the cost-effective flame hardens load-critical areas and intersections on steel frames and while leaving non-loaded sections malleable. Again, the result is an economical operation that nonetheless satisfies the project specs.
A single scanning torch is inexpensive to run. The head requires maintenance, and a fuel source needs to be reloaded occasionally. The spinning machine variant costs more, probably because multiple flame hardening heads work in tandem around that long cylinder. In conclusion, however, this affordable hardening solution is versatile. It accommodates complex geometries, larger workpieces, and is controllable, so depth hardened process consistency is as addressable as any uniform coverage strategy.