In many vacuum systems, especially those where the chamber is large, has a large internal surface area and

the chamber load adds extra surface area, the pump down can be slowed substantially when the chamber pressure drops to the range where the water vapor molecules on the surface desorb and have to be pumped away.

Pressure and temperature dete

rmine when this vapor desorbs, but at ambient temperature around seventy two degrees Fahrenheit or twenty degrees Centigrade the vapor desorbs from about 50 Torr down to about 0.1 Torr. The vapor pressure of water at ambient temperature is about 18 Torr, so that is where maximum desorption may occur. By Howard Tring

Techniques that have been developed for iron and steel specimens are directly applicable to meteorites. Sections must be removed from the parent mass with as little damage as possible. This may be difficult to achieve when very large masses must be sectioned. The gross macrostructure of meteorites can be very dramatic, as shown in Figure 2. Octahedrites obtained their name from this very striking macrostructural growth pattern of the kamacite (ferrite) phase, which is visible to the unaided eye.

Octahedrites generally contain from ~5 to 10 weight percent Ni. The as-solidified microstructure is FCC taenite (austenite). With subsequent cooling, kamacite nucleates on the prior-taenite grain boundaries producing the Widmanstatten pattern shown in Figure 2. Determination of the prior-taenite grain size has been rarely donwe due to the need for exceptionally large specimens. Vagn Buchwald, in his study of the 20,140 kg Agpalilik Cape York meteorite (Figure 1), measured a prior-taenite grain size of ~2 X 1.5 X 1.5 m – yes, meters, not millimeters!. By George Vander Voort

Many brazing shops use graphite fixtures on which to set parts that are to be brazed. Graphite fixtures have excellent thermal stability, enabling them to be used again and again through many brazing cycles. This high thermal stability is often coupled with low cost compared with some metals used for making fixtures (such as the high nickel/chromium or moly- alloy type fixtures).

If you are using graphite fixtures, or intend to consider doing so, it is VERY important to remember that graphite is carbon, and pure carbon likes to react chemically/metallurgically with metals containing iron (such as steel), to form low-melting eutectic compositions at temperatures just under 2100°F/1150°C, as shown in the iron-carbon (Fe-C) phase diagram illustrated in Fig. 1. This temperature is often lower than some of the brazing temperatures being used in many brazing shops today! by Dan Kay

By now, most maintenance departments should have a plan in place for schedules repairs and maintenance during the summer months, especially if the plant has a shutdown for vacation. The part of the vacuum furnace system that I know best is the vacuum system, so I will concentrate on this.

The summer maintenance schedule should cover all the vacuum pumps on a vacuum furnace. For some it will just be mechanical pumps, the rotary piston pumps and the Roots booster (or blower); for others it will include the oil diffusion pump or pumps and the small rotary vane holding pump, if used. By Howard Tring

The Canyon Express Pipeline System (CEPS) was started up in November 2002 in the Gulf of Mexico, south of Louisiana. It is owned by six oil companies and collects hydrocarbons from ten wells at depths of ~6100, 7100 and 7200 feet.

The flow line system consists of two 12” diameter gas pipelines (“east” and “west”) connected to a header system, which carries the hydrocarbons 57 miles north to a fixed platform, the Canyon Station, in about 500 feet of water. Tankers come into the Canyon Station to fill up and carry the hydrocarbons to refineries. Just west of the “east” flow line is a 2.875” diameter, X-70 line pipe that carries methanol from the station to the header where it is injected to prevent freezing of the hydrocarbons. To the left of the methanol line is a 6” diameter umbilical line containing electrical power and hydraulic lines. By George Vander Voort

The correct use of the Gas Ballast valve on a mechanical oil sealed rotary vacuum pump has always been seen as “black science” or just plain guesswork. It is a very simple device and when used correctly can keep a vacuum pump working well even though it may be used on a very wet process and the oil becomes contaminated with condensed vapors.

One series of vacuum pumps I worked with had a gas ballast valve that had no stop when opened. If you unscrewed it enough the ballast knob would come off in your hand allowing maximum air to enter the pump, the pump to become noisier and a blast of oil mist to come out of the exhaust. I always thought that if a lab technician ever did that they would replace the knob and never ever touch the gas ballast valve again. By Howard Tring

Low temperature vacuum heat treatment offers unique advantages to a variety of industries including Aerospace, Automotive, Electronics, Household Appliances, Machine Tools and Tool and Die as well as Commercial Heat Treaters who must serve all of these customer.

This article will discuss the key factors required to optimize processing parameters in low temperature heat treatments (e.g. tempering, stress relief) by focusing on a variety of topics. Low temperature processing can be batch or continuous, either as stand-alone units or “modules” incorporated into a continuous vacuum furnace system. The following is a basic description of the operation of a typical batch vacuum furnace. By Dan Herring

Vacuum furnaces can use a variety of different gases during the processing cycle in partial pressure operation, for backfilling to atmospheric pressure at the end of the processing cycle and for cooling/quenching. The most common of these gases (in order of frequency of use) are nitrogen, argon, hydrogen and helium. Other common gases include various hydrocarbons and ammonia (for vacuum carburizing/carbonitriding) and specialty gases such as neon (for certain electronics applications).

In vacuum heat treatment nitrogen is used primarily for cooling/quenching, as a partial pressure gas and for backfilling to atmospheric pressure at the end of the heat treating cycle. A common misconception, however, is that nitrogen gas is a true inert gas. It is not and under the wrong circumstances it can react with the surface of the material being heat treated with deleterious effects. By Dan Herring

Boucherville, Quebec (June 10, 2013) –VAC AERO Coatings division recently received approvals from Pratt & Whitney USA, Rolls-Royce Canada, Bell Helicopter and The SAFRAN Group (Messier-Bugatti) for a variety of thermal spray coatings. The facility was qualified to the stringent standards of Pratt & Whitney PWA 53-5 plasma spray coatings for steel, nickel and cobalt base alloys, and is an approved Rolls Royce RR Energy Gas Turbine Sub Tier Supplier. The facility is also approved for Bell Helicopter’s BPS 4463 tungsten carbide coatings as well as The Safran Group’s WC/Co/Cr 86-10-4 and IFC 40-818-02 HVOF coatings.

For more information on VAC AERO’s Coating Services please click here.

Over the past forty-plus years, steelmakers have introduced improved practices for reducing the inclusion content of steels. The success of these practice changes can be monitored in a variety of ways. Chemical analysis of the bulk sulfur and oxygen contents provides a relatively simple means to assess the impact of these changes. However, microscopical test methods are still needed to assess the nature of the inclusions present.

Traditional chart-based measurement methods have wide acceptability, and their data are well understood by both purchaser and producer for heat acceptance purposes. These methods do have inherent weaknesses which limit their usefulness for quality control, SPC, and database applications. Image analysis-based chart measurements are an improvement over manually generated chart ratings, but the data still does not lend itself to databases and statistical comparisons. ASTM Committee E-4 on Metallography has developed a stereologically-based image analysis standard test method, E 1245, which provides the necessary data in a form which is easily databased and analyzed statistically. The presentation will describe E 1245 and show how data from different heats and melting practices can be compared statistically to ascertain valid test differences. By George Vander Voort