Stay Up-to-Date with Our Vacuum Heat Treating Newsletter! SUBSCRIBE NOW
With an ever-increasing need for knowledge of vacuum processing and the intricate functions of complex vacuum furnaces, better training and education means having the necessary tools for the continued success of your heat treat operation. We here at VAC AERO want to continue keeping you informed through valuable and relevant information on topics such as vacuum processing, operations, maintenance and troubleshooting, as well as hints, tips and real world advice from our panel of industry experts.
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.
The movement of gases is an important and interesting subject but one often dismissed as a topic best left to scientists. However, the Heat Treater needs to know something about the basic nature (theory) of gases and in particular how they behave in vacuum. The main difficulty is that too much theory tends to become a distraction. Our focus here will be to better understand what goes on inside a vacuum furnace. One definition of a gas is that it is simply a collection of molecules in constant motion (Fig. 2). The higher the temperature, the faster these molecules move, and as one might expect, the motion of gas molecules stops or dramatically slows down at or near absolute zero (0°K). As molecules speed up with an increase in temperature, there is an increase in their kinetic energy (or energy of motion).
A half century ago (back in the early 1960’s) a lot of research work was done by The American Welding Society (AWS) Committee on Brazing and Soldering to determine appropriate criteria for brazing lap joints (the preferred type of joint design for assemblies requiring the ability to withstand high pressure in service, such as gas bottles, etc.). The results were published in their committee report: AWS C3.1 in 1963, one of the recommendations of which was that joints should have an overlap of 3T or more, where “T” is the thickness of the thinner of the two sheet metal pieces being brazing together. Here’s how that recommendation came about. The AWS C3 committee arranged to conduct a series of round-robin testing in ten different laboratories around the country, using two different shear-type joint designs, four different base metals, and three different types of brazing filler metals (BFMs), for a total of about 1200 brazed shear test specimens.
Experiments were conducted using three-step preparation procedures for titanium and its alloys. For CP titanium and alpha-titanium alloys, use of an attack-polishing agent in the third step was required to obtain good results. The experiments defined optimum surfaces for each step and operating conditions. Two-phase, a-ß alloy specimens are significantly easier to prepare than a single-phase a specimen. The method does yield perfect polarized light response with a-phase alloys, such as commercial-purity titanium. Titanium and its alloys have become quite important commercially over the past fifty years due to their low density, good strength-to-weight ratio, excellent corrosion resistance and good mechanical properties. On the negative side, the alloys are expensive to produce.
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.
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.