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Please check out our Newsletter Archives to access dozens of published articles since 2007, or check out our online Educational Resources for a more complete list of educational and training materials.
Highly distortion prone gearing was the subject of an investigation into the dimensional changes which result from utilizing either oil or high pressure gas quenching following a low
pressure vacuum carburizing process. For comparative purposes, the gears in question were also atmosphere gas carburized and plug quenched, which is standard practice for these geometries. Full production loads were run using two (2) different carburizing methods (atmosphere, vacuum) in combination with free quenching in either oil at 75°C (165°F) or high pressure gas (nitrogen) at 11 bar. Gears were taken from multiple locations throughout each load for analysis. Parts for metallurgical evaluation were selected from the center of each load. Multiple areas on each part were then analyzed for microstructure, case depth, and hardness (surface, profile, core). Dimensional checks (out of round, gear tooth profiles) were conducted on the gears before and after heat treatment. For brevity, only a portion of the complete test program is presented here (see Reference 4 for more detail).
In Over the years it has shown that the best surface for brazing, generally speaking, is the "as-received" (as-rolled, as-drawn, as-machined, etc.) surface roughness of the material coming into the brazing shop. An illustration of what this surface roughness might look like, under high magnification. Surface roughness obviously increases the total surface area of each faying surface inside the joint, when compared to a flat, polished surface. And, due to this “roughness”, it can be seen that there are many capillary paths for brazing filler metal (BFM) to follow between all the valleys and “peaks” on that roughened surface. Surface roughness refers to the “texture” of a surface, the measurement of which is often expressed in several different ways, including Ra (Roughness average), RMS (Root Mean Square), AA (Arithmetic Average), and CLA (Center Line Average). I’ve found RMS to be a frequently used measure in my brazing experience. Others may perhaps have found otherwise.
Formation of martensite in fine-grained steels is probably the most common goal in heat treatment of components. The carbon content of the parent austenite phase determines whether lath (low-carbon) or plate (high-carbon) martensite, or mixtures of the two will be produced, assuming the quench rate and steel hardenability are adequate for full hardening. Lath martensite produces higher toughness and ductility, but lower strengths, while plate martensite produces much higher strength, but may be rather brittle and non-ductile. For a given alloy content, as the carbon content of the austenite increases, the martensite start, Ms, temperature and the martensite finish, Mf, temperature will be depressed which results in incomplete conversion of austenite to martensite. When this happens retained austenite, which may be either extremely detrimental or desirable under certain conditions, is observed. The amount of retained austenite present depends upon the amount of carbon that can be dissolved in the parent austenite phase and the magnitude of the suppression of the Ms and Mf temperatures. This paper examines the conditions under which austenite is retained and the problems associated with it presence, with detecting it and with measuring it.
The Edwards “RV” (simply meaning Rotary Vane) laboratory sized oil sealed rotary vane vacuum pumps have been in the market for 21 years. They have a very unique design with no equal. This article will attempt to show the reasons for its design and introduction in 1993 and then explain the features of the vacuum pump that make it one of the best small vacuum pumps available today. This is not an official Edwards account, although the engineering related content is based on Edwards information, it contains my personal knowledge, experience and understanding from working with these pumps for many years. As I mentioned in a previous article, European vacuum pump companies were the first to develop direct drive oil sealed rotary vane vacuum pumps. These are the pumps capable of reducing the pressure to around a two thousandth part of one Torr total pressure (2 x 10-3 Torr or 2 microns) as shown in their catalogs.
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.