For metalcastings, heat-treating is simply any method of altering physical or metallurgical properties of a product, but as applications for finished components become more complex and demanding, the treating processes are anything but simple. Recent heat-treating installations are fine-tuned to the particular design criteria of the finished products.
For example, earlier this year Can-Eng Furnaces International Ltd. commissioned a complete, modular solution treating system for Albany Chicago Co. LLC, a custom aluminum diecaster and machining operation in Pleasant Prairie, WI. The installation includes two solution treatment furnaces, Can-Eng’s PAQ™ precision air quenching system, and three artificial aging ovens, and it was specifically designed to heat treat high-integrity aluminum structural castings for automobile manufacturing.
Parts and processes
Solution heat treatment allows the component’s alloys to diffuse through the metallurgical microstructure and form intermetallic structures, increasing the strength of the alloy. Albany Chicago Co. selected the system as part of a program to fulfill an order to supply high-integrity structural castings for a global automotive manufacturer.
Can-Eng Furnaces designs and manufactures a wide variety of industrial heat-treating equipment, and its commissioning process at Albany Chicago included installing and starting up a Level 2 automation system that supports product traceability, process control, system diagnostics and historical archiving of process related data.
Another new heat-treating installation for automotive parts has been ordered from Consolidated Engineering Co. by Nemak. It plans to install a basketless system for treating aluminum engine blocks and cylinder heads at its metalcasting operations in Monterrey, Mexico.
The developments are not only in the automotive sector. Manufacturers in the aerospace markets make very particular demands on their component suppliers, such as a 2009 order for a natural gas-fired batch furnace designed by Wisconsin Oven , with a quench tank to perform solution treatment on aluminum aerospace parts. The installation is designed to receive a 4-ft3 baskets, and the oven is rated for a 1,250°F maximum operating temperature and a 1,100°F normal operating temperature.
The aerospace customer required temperature uniformity of ±10°F at 600°F and 1,100°F, per AMS 2750D Class 2 furnaces and Type C instrumentation. Wisconsin Oven developed a nine-point temperature uniformity survey using calibrated wire in an empty chamber under static operating conditions. The results exceeded the design requirements (+5.4°F/ -1.8°F at 600°F and +5.3°F / -6.1°F at 1,100°F).
The oven is fabricated with 6 in. of insulation, with an inner shell and ductwork in 18-gauge, 304 stainless steel. The hearth consists of two rows of wheels, with a heating system that features a 500,000 BTU per hour air-heat burner and a motorized gas control valve. The recirculation system includes combination airflow and uses a 10,000 CFM@15 HP blower. Most of the air is delivered under the load so that it flows vertically upward past and through the product, for even heating.
An unheated, manual quench tank is fabricated in stainless steel and has water-level control. An agitation pump keeps water in motion, with a manifold for more uniform cooling, pulling the heated quenchant from the load. A push-button station allows the oven operator to raise and lower baskets into and out of the quench tank, and opening and closing the vertical lift door.
The horizontal solution treat system includes a UL-certified, NEMA 12-rated control panel with IEC style push buttons and pilot lights. Oven temperature is controlled by a Honeywell DCP100 programmable temperature controller and recorded by a Honeywell DPR100 strip chart recorder. Both the oven temperature controller and recorder provide flexibility for treating a wide variety of parts with multiple recipes.
Component parts supplied to defense manufacturers have still another range of design parameters. Specialty heat-treater Solar Atmospheres reports it recently vacuum carburized a 60-in. gear for a defense application — a product that had never before been processed successfully using atmospheric equipment.
Solar Manufacturing specializes in vacuum heat treating and brazing for surgical instruments, aircraft and aerospace components, among other products.
Solar modified one of its large 10-bar quenching furnaces so that it can vacuum carburize larger and more extensive loads. Carburizing involves heat treating a product in the vicinity of another metal that frees carbon as it decomposes. When the process is complete the part’s outer surface, the case, will have a higher carbon concentration than the interior, which retains its original properties.
Solar added new instrumentation, carburizing nozzles, an improved backfill system, so that the 487238-in. furnace with a 10,000-lb load capacity is capable of performing carburizing cycles on very large parts and loads not previously thought possible in vacuum.
The large gear, 60-in. diameter 13-in. high, was made of 9310 steel and weighed 1,900 lb. It was low-pressure vacuum carburized to achieve an effective case depth of 0.070 in., followed by a temper, a -225°F freeze, and a second temper operation. Quenching was accomplished with a mixture of nitrogen and helium gasses.
Flatness on the finished part was within 0.100 in. and roundness within 0.050 in., Solar reports, well within acceptable tolerances. It says such results will expand the range of applications for low-pressure vacuum carburizing.
As each of these examples demonstrates, the variety of heat-treating process and capabilities is growing rapidly. One area of development, laser technology, is not new but an expanding number of applications make it an interesting option, at least for highly specialized products.
Laser heat-treating has been in development for several decades, and though it is not a feasible treatment for large-scale production it’s gaining in applications as laser processes get more sophisticated and widely applied. For example, lasers are an effective way to perform remelting as a surface hardening technique: A beam is scanned across the surface of a component, with controls capable of maintaining process uniformity to achieve requisite hardness with little to no variation.
But lasers need not “remelt” the component’s surface; more recognizable heat-treating effects can be accomplished, too. Lasers can be used to anneal metal parts, for example to provide localized heat treatment for parts that need machining or repair.
Even more common, lasers can be used in a hardening process to “re-crystallize” the surface of a steel component. A laser beam scans across the surface and heats the component to a controlled depth, without melting it. The conditions are controlled so that carbon in the steel diffuses and becomes uniform, creating a hard surface that leaves the component more wear- and fatigue-resistant.
Setting up a laser system to perform surface treatment is not especially difficult, and various types of lasers (CO2, neodymium YAG, direct diode, and fiber lasers) can be used. Systems of this type are used to treat products like diesel engine cylinder liners, pistons, and power steering components.
The speed at which the laser beam moves controls the sdepth to which the component is case hardened, though the amount of carbon in the steel also affects the final hardness.