Come Visit us at Furnaces North America – Booth 418, Nashville, TN – October 6-8, 2014

We’re excited to head down to Nashville for the Furnaces North America Conference and Expo.  If you plan on attending the show, please be sure to stop by our booth number 418 to learn more about our latest vacuum furnaces, and most importantly… we’re interested in learning about you, your business, and your needs. Our sales reps will be available to answer questions about how VAC AERO can help your business with exactly the vacuum processing solutions that you’re looking for.

See you there!  Date: October 6-8, 2014!

Knowledge of vapor pressure and rates of evaporation of various materials is valuable information for those operating vacuum furnaces, whether we are heat treating or brazing at high temperature and low vacuum levels or dealing with outgassing at very low temperatures and pressures.

When we think about a solid or liquid in a sealed vessel, we find that, even at room temperature and atmospheric pressure, there are molecules that leave the surface and go into the gaseous phase. The gas phase thus formed is called a vapor. The process of forming a vapor is known as evaporation and the rate of evaporation is determined by the temperature of the substance involved. In time, some of the evaporated molecules will, in all likelihood in the course of random movement, strike and stick to the surface of the vessel. This process is known as condensation and the rate of condensation is determined by the concentration of gas molecules (that is, the pressure of the evacuated gas). Eventually, the number of molecules leaving the surface of the substance is equal to the number returning to it (that is, the evaporation rate equals the condensation rate) and we have dynamic equilibrium. The (partial) pressure at which this occurs is known as the vapor pressure of the substance.² Below this pressure, surface evaporation occurs faster than condensation, while above it, surface evaporation is slower. By Dan Herring

A number of people have inquired about how to keep tubing or piping centered in holes or fittings prior to brazing, thinking (erroneously) that if the tubing/piping does not remain centered in the joint, but instead touches one surface or another inside the joint (due to lack of centering) that the joint therefore may be weakened thereby, or that the molten brazing filler metal (BFM) will not be able to penetrate the area where the tubing/piping contacts one of the surfaces inside the joint.  That is incorrect thinking, because molten brazing filler metal (BFM) is able to penetrate extremely tight joints, even when there is metal-to-metal contact in some portions of the joint.  The microscopic surface roughness of the mating surfaces inside the joint will allow the liquid BFM to penetrate completely.

But, if you are in that group that feels that you must take steps to keep the tubing or piping centered in the joint to be brazed, and want to take steps to prevent any joint surfaces from touching, then there is a simple way by which to insure that the tubing/piping will remain centered in the joint throughout the braze-cycle. The simplest way is to “dimple” the OD surface of the tubing/piping using a prick-punch, a tool that is illustrated in Fig. 1. by Dan Kay

Revealing the prior-austenite grain boundaries in heat treated steel is probably the most difficult, and frustrating task, faced by the metallographer or metallurgist. Grain boundaries, regardless of the type, are generally impossible to see in cast metals, as they solidify dendritically and segregation is present and often substantial. After deformation and annealing, if recrystallization occurs, grain boundaries in the product may be visible, but they are not necessarily prior-austenite grain boundaries.

In a deformed, partially recrystallized specimen, it is usually possible to see both recrystallized and non-recrystallized grain boundaries. But, prior-austenite grain boundaries are those of the steel when it was austenitized prior to quenching and tempering. If the steel’s microstructure is fully martensitic after hardening, or contains some retained austenite or lower bainite, the prior-austenite grain boundaries may be revealed. They can often be revealed in specimens isothermally processed to obtain fully lower bainitic microstructures; but they cannot be revealed if the transformation microstructure consists of upper bainite, pearlite and/or ferrite. Composition also is important in trying to reveal the prior-austenite grain boundaries, as is the tempering temperature. In general, steels with low carbon contents and low phosphorous contents are very difficult subjects.  This article summarizes the state-of-the-art in revealing prior-austenite grain boundaries. By George Vander Voort

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. I think that many oil diffusion pumps are still used for industrial and some scientific applications in the eastern parts of the world where the cost of a turbomolecular pump is still very high based on the local costs of doing business. By Howard Tring

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.

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. Temperature uniformity in dedicated furnaces is considered excellent throughout the standard temperature ranges listed. By Dan Herring

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. by Dan Kay

This article continues the series of five reasons that vacuum is used in science and industry; to provide a working force, to remove active and reactive constituents, to remove trapped and dissolved gases, and to decrease thermal transfer.

If you commute to work by car and your drive is an hour or so, you may well take a coffee or another hot or cold beverage in your own personal container to drink on the way. Often this type of container is a vacuum insulated cup with a lid. A step up from that, if you work on a jobsite for example, would be a vessel that holds several cups of liquid for all day use. You may know these as “Thermos” or “Aladdin” flasks which are two of the trade names for vacuum insulated containers. Let’s discuss the thermodynamics of vacuum insulated vessels and then look at other uses for them. By Howard Tring

Kalisz, Poland, July 14, 2014 – VAC AERO’s Kalisz, Poland division has recently been awarded a Nadcap coatings certificate in accordance with SAE Aerospace standard AS7003. Scope of Accreditation: In recognition of the successful completion of the PRI evaluation process the accreditation was granted to the Kalisz, Poland facility to perform the following: AC7108/1 Rev B – Nadcap  Audit Criteria for Painting and Dry Film Lubricant Coatings when performed with AC7109/1, /2 or /3 – Ceramic/metallic Spray & Thermal Coatings; AC7109 Rev D – Nadcap Audit Criteria for Coatings; AC7109/1 Rev C – Nadcap Audit Criteria for Thermal Spray – High Velocity Oxy Fuel (HVOF) / High Velocity Air Fuel (HVAF) Plasma Thermal Spray; AC7109/4 Rev C – Nadcap Audit Criteria for Stripping – Chemical; AC7109/5 Rev E – Nadcap Audit Criteria for Coating Evaluations – Bond Strength, Hardness, Metallography/Microstructure and Microindentation Hardness.