Burlington, August 18, 2014 - VAC AERO shipped a VAH 6660 HV-2 horizontal vacuum furnace to an international company’s plant in Mexico to process aerospace parts. This customer has a long history with VAC AERO, having purchased many vacuum furnaces for its plants all over the world over the last few decades. The furnace features an all-metal hot zone with a work chamber of 48” x 48” x 60” with a 4,000-pound load capacity. It utilizes gas cooling to 2-bar absolute pressure and operates at temperatures of 1,000 °F to 2,200 °F. The furnace is also equipped with a 35” diffusion pump and VAC AERO’s HC900 control system. A key control feature is the ability to independently control the work chamber zones for optimal work-load uniformity as well as the ability to program heat-treatment cycles that can then be run automatically and accurately allowing the operator to achieve the specific structure and properties required for their application. MORE INFO ON OUR VACUUM FURNACES
Low temperature heat treatments that involve a vacuum purge at the onset of the cycle have become increasingly popular throughout the industry. These operations are conducted in vacuum furnaces and furnaces that employ a vacuum purge prior to the beginning of the heat process with parts placed inside a special vacuum tight vessel or in a retort. Processing being run using these methods take advantage of a highly controlled environment designed to minimize surface interactions. Low temperature vacuum heat treatment is used by both captive and commercial heat treaters and spans such diverse markets as Aerospace, Automotive, Electronics, Optics, Housewares, Industrial Products, Tool & Die, Military/Defense and Farm Implement to name a few. Most processes run in the temperatures range of 175°C – 730°C (350°F – 1350°F). Special applications extend these ranges down to as low as 120°C (250°F) and up to as high as 925°C (1700°F), but this is unusual.
In my opinion, based on my experience, the amount of actual braze coverage in a joint is more important than the number of voids in that joint! As discussed in last month’s blog-article, a lap-joint with an overlap of “3T-to-6T” (where “T” is the thickness of the thinner of the two members being brazed) is all that is needed to provide full strength and hereticity in a properly designed brazed joint (1T-to-3T for aluminum alloys). By this I am saying that we need to look at the amount of GOOD braze coverage, rather than being overly concerned with trying to count the number of voids in a joint! Counting voids is really the wrong way to approach the “goodness” of a brazed joint. Please note, that if someone brazed a lap-joint that used a 6T-overlap, and it contained about 50% void content (assuming the voids to be randomly distributed throughout the joint), that would still leave a net-overlap (after deducting all the areas of voids) of about 3T.
The microstructure of iron-base alloys is very complicated and diverse, being influenced by chemical composition, material homogeneity, processing and section size. This article offers a brief explanation of the terminology describing the constituents in ferrous alloys, and offers a basic review of steel microstructures. Microstructures of castings look different from those of wrought products, even if they have the same chemical composition and are given the same heat treatment. In general, it is easiest to identify heat-treated structures after transformation and before tempering. For example, if a mixed microstructure of bainite and martensite is formed during quenching, these constituents will become more difficult to identify reliably as the tempering temperature used for the product increases toward the lower critical temperature. Further, ferrous metallographers tend to use nital almost exclusively for etching, but nital is not always the best reagent to use to properly reveal all microstructures.
Oil diffusion pumps remain in popular use in the vacuum heat treating industry, possibly one of the few applications remaining for this type of high vacuum pump in the western world. The main reasons for their continued use are their longevity the lack of other options. When your process requires a pressure below that of a mechanical pump or mechanical pump and Roots pump combination a secondary vacuum pump has to be used. These are oil diffusion pumps, turbomolecular pumps and possibly cryogenic pumps. Turbomolecular pumps are limited in physical size due to the high rotor speeds needed to create molecular flow into the pump mechanism; and both “turbos” and “cryos” are very susceptible to process contamination. Large cryos are often used in vacuum coating applications but, as far as I am aware, not in vacuum heat treating applications.
VAC AERO offers complete turnkey services, including planning, designing, building and installation of vacuum furnace systems and controls. VAC AERO’s experience, proven through decades of service in commercial heat treating, has provided us with valuable insight into the changing needs and rigorous demands of our furnace customers. As a result, VAC AERO has developed a keen understanding of the design and performance of vacuum furnace systems built to meet the most stringent requirements for reliability. VAC AERO’s vacuum furnace design innovations are thoroughly tested in our own heat treating facilities before being offered to our customers. That means better quality, reliability and efficiency to maximize uptime and productivity. Horizontal vacuum models provide great flexibility for general heat treating and brazing applications and Vertical bottom-loading models are ideal for processing large circular and/or long parts.