Fig 5 wsLast time (The Fundamentals of Vacuum Theory – Part 1) we talked about the Kinetic Theory of Gases and how it can be used to calculate gas properties. We also considered the relationship between molecular density, mean free path, molecular velocity and pressure. Now we turn our attention to a discussion about temperature and kinetic energy, pressure and kinetic energy, and types of flow in vacuum systems. Again, we will focus on the basics, using fundamental comparisons to explain the concepts significant to industrial vacuum systems

Relevance of Temperature to the Kinetic Theory of Gases - Based on an atomic understanding of the world we live in, the Kinetic Theory reveals that gas properties are highly dependent on the speed of their molecules, which determines their kinetic energy, and therefore the gas pressure. When considering the effects of the Kinetic Theory, it is also important to understand the influence of temperature. Specifically, the speed of the molecules in a gas is dependent on its temperature (the higher the temperature the faster the gas molecules move). Another way to think of it is that the temperature of a gas is a measure of the average kinetic energy of that gas. By Dan Herring

Fig 4 wsAs in any discipline, understanding the underlying scientific principles has profound practical implications when properly understood. In this series of articles we will review the first principles of vacuum technology and explain them using real world illustrations. Most industrial vacuum systems can, in broad based terms, be categorized in terms of low (i.e., “soft”), medium, high (i.e., “hard”) and ultra-high vacuum. 

These ranges are very useful in describing the various pressure, flow, and other phenomenon encountered, which leads to a better understanding of vacuum pump selection and operation, and system operational requirements at the different vacuum levels. As shown by the difference in pressure from low to ultra-high vacuum, industrial vacuum systems must operate under an extremely wide range of pressure. In fact, the range is so large it is hard to actually comprehend. Consider a volume of gas at a pressure of 1000 mbar (atmospheric pressure) in a 1 meter by 1 meter by 1 meter container sealed so that no molecules can escape or enter. It is easy to understand that if the container is expanded in volume while still remaining sealed, the pressure will decrease (and a vacuum will be created) in direct proportion to the increase in volume (in accordance with Boyle's law). If, for example, the container volume is doubled to 2 cubic meters, the pressure will decrease by half, to 500 mbar. When this relationship is expanded to the scale of industrial vacuum systems, the result is striking. If we take this same 1 cubic meter volume of gas and increase its volume sufficiently for the pressure to be reduced to 10-12 mbar (ultra-high vacuum), the container will be a staggering 99 km long x 99 km wide x 99 km high, or 200 times the volume of the grand canyon!. By Dan Herring 

Figure 2 ws nQuestion: Staining of titanium parts after vacuum heat treatment following a gas quench, your thoughts on possible causes and remedies? 

In response to this question, phenomenal suggestions by everyone! A wealth of great information here. So, what else could be happening? Let The Doctor add a few thoughts to the discussion. First, the fact that the discoloration (staining) is brown in coloration suggests that the oxide is forming on the part surface during cooling when the temperature is in the range of (approximate) 245ºC – 270ºC (475ºF – 520ºF). This is supported by the fact that the oxidation does not occur “during natural cooling” (which we assume to mean cooling under vacuum). Second, the fact that the discoloration is more evident at the bottom of the load suggests the phenomenon is (gas exposure) time dependent, that is, the longer the parts take to cool through the critical range, the greater the chance for discoloration. Third, a “steel-copper-stainless steel” test will be helpful in isolating if it is a water or air leak. Leaks in heat exchangers have been known to “open up” during the cooling cycle when exposed to hot gases and close up again at room temperature. The writer has personally experienced this – the solution being the replacement of the old heat exchanger at which time the problem went away. Fifth, look in all the places suggested by those who responded, but remember to make only one change at a time and evaluate its impact in order to find then correct the problem. Finally, as an unabashed promotion of my books on Vacuum Heat Treatment (Volume II of which comes out this fall), there are a number of sections that discuss this very issue in considerable detail covering subjects such as “Vacuum Furnace Contamination and Cleanup Cycles”, “Leaks External to the Vacuum Furnace Proper” and “Factors Affecting Performance: Discolored Work” to name a few. Good luck!. By Dan Herring

Figure 1 wsThe automotive, aerospace, medical device and construction industries rely heavily on the use of fasteners to secure component assemblies. For example, medical devices (e.g. dental & orthopedic implants, instruments) employ literally hundreds of different types fasteners to hold their assemblies together

Even though the components in the medical devices are small or even tiny, when a fastener fails, the device will almost always fail as well. The correct fastener ensures that the device goes together and stays together for the intended life of the assembly, and that the device performs as desired. Fasteners can overcome challenges in assembly, solve quality problems and significantly reduce the total cost of the device. By Dan Herring 

Figure 2a wsWe study vacuum science and vacuum engineering in order to better understand the role vacuum technology plays in creating useful engineered products (Fig. 1, Table 1). Manufacturing as we know it, and research and development as we have come to depend upon it, would not exist without the creation and control of the vacuum “atmosphere”.

Vacuum techniques are important in both the industrial setting and for the scientific community, whether it be in heat treatment or high-energy physics. At the heart of vacuum processing for manufacturing is the modern vacuum furnace. Ever since the introduction of the electric light at the beginning of the 20th century, society and manufacturing have been linked to advances in vacuum science and engineering. Examples include the development of modern computers to advanced transportation systems; the very fabric of modern society depends on vacuum technology. By Dan Herring 

figure 4 wsVacuum furnaces are available in numerous styles and sizes and come in both standard and custom configurations. They are designed to process an almost limitless number of both semi-finished component parts as well as raw materials using a diverse set of thermal processes in equipment available from a wide variety of different equipment manufacturers located around the world.

The intent here is to provide a brief overview of some of the more common designs and applications found throughout the heat-treatment industry. The hope is that the reader will come away with an understanding that there is a vacuum furnace solution to virtually any design, application or specification encountered.. By Dan Herring

vacaero vacuum furnace wsThe role of materials science (Fig. 1) is to study, develop, design, and perform processes that transform raw materials into useful engineering products intended to improve the quality of our lives. It is said by many that material science is the foundation upon which today’s technology is based and that real-world applications would not be possible without the materials scientist. The discipline has expanded to encompass materials for many highly specialized product applications.

The industrial revolution thrust metals into the forefront of technology, and they have stayed there ever since becoming the very foundation on which our modern society is built. One cannot envision a life where our transportation and communications systems, buildings and infrastructure, industrial machines and tools, and safety/convenience devices that are not an integral part of our daily lives. By Dan Herring 

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