Vacaero

Manufacturers of heat treating and brazing vacuum furnaces and controls, complete hot zone and vacuum furnace retrofits, thermal spray coatings, plasma, HVOF and paint coating services.

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The Role of Lubricants in Vacuum Furnace Seals

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Lubricants for vacuum service are a diverse family of highly formulated products. The types of lubricants for vacuum service fall into three general categories: (a) wet, organic or silicone-compound based oils and greases, (b) dry lubricants including PTFE (Teflon®) and metal dichalcogenide compounds (e.g. molybdenum disulfide, tungsten diselenide) and (c) metal on metal combinations.

The choice of lubricant depends on a number of considerations that are highly dependent on the specific end-use applications including; operating temperature and vapor pressure, the presence or absence of sliding or rolling motion, the presence or absence of reactive species (e.g. plasma), loading characteristics and frequency of usage. Lubricants are used in a vacuum system for three primary reasons: (1) in an “O” ring sealed system to help minimize externally applied forces on the ring material, (2) between moving surfaces to reduce the coefficient of friction, minimize wear and/or reduce/eliminate the formation of particular matter and (3) as anti-seizing agents where mating surfaces are likely to seize.

Simple Physics for the High Vacuum Processing Industry

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States of Matter – All matter consists of atoms, and some atoms combine with others in a chemical reaction to form molecules. For example, water consists of two atoms of hydrogen combined with one atom of oxygen (H2O). Some gases such as argon (Ar), helium (He) and neon (Ne) are unlikely to combine with a similar or dissimilar atom, while others such as hydrogen, nitrogen, and oxygen and usually combine with an identical atom forming a molecule (H2, O2 and N2) and are called diatomic.

Matter is divided into three states: solid, liquid and gaseous. Some matter can exist in each of the three states, for example, water that can be ice (solid), water (liquid) and steam (vapor) depending on the surrounding pressure and temperature (Fig. 1). Another example is carbon dioxide that can also exist in all three states.

The Solid state (Not to be confused with “solid state” electronic components)

In a solid, the atoms are bound tightly together in fixed positions relative to each other by interatomic forces. Therefore a solid has a fixed volume at a specific pressure and temperature. Changes in temperature will change the energy in the atoms and cause tiny vibrations about their position but the bonds are relatively strong and most solids can withstand reasonable temperature changes without breaking down apart from small expansion or contraction if the temperature changes. Even though a solid appears “solid” there are very small spaces between individual molecules. Metal solids, which are ones most prevalent in the vacuum furnace and heat treating industry, all have a melting point and if enough heat is applied the solid will eventually change to a liquid. This liquid, if more heat is added will eventually evaporate and change to a vapor.

Metallographic Examination of Bronze Bracelets from Hasanlu

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Hasanlu is an early Iron Age settlement located in northwestern Iran. It dates back to the second millennium B.C., ~1450 B.C., until it was destroyed around 800 B.C. Although the site attracted the attention of the British archeologist Sir Aurel Stein due to artifacts recovered from burial mounds in the 1930s, it was not given substantial attention until the discovery of the “Hasanlu Golden Bowl” in 1958. The Hasanlu archeology project began in 1957 and was greatly stimulated by this discovery. It ended in 1977. The excavations were sponsored by The University of Pennsylvania Museum and the Metropolitan Museum of Art of New York in cooperation with the Archeological Service of Iran.

The author obtained six specimens from the University of Pennsylvania Museum. The six specimens consisted of three cast (No. 1) and three wrought bronze bracelet sections (Nos. 2-4), as defined in Table 1. The three cast specimens were from the same bracelet. For simplicity, they will be referred to as specimens 1, 2, 3 and 4. As there are three specimens of the cast bracelet in mount 1 (HAS 60-617), they will be referred to by their size. The chemical analysis shows that they are similar in composition although the tin content of the fourth specimen is somewhat higher than the other three.

A Brief History of Vacuum Technology

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The history of vacuum technology is a fascinating one. It seems to have begun in ancient Greece when the philosopher Democritus (circa 460 to 375 B.C.) proposed that the world was made up of tiny particles that he called atoms (atomos, Greek: undividable). Democritus proposed that empty space (in other words, in modern terminology, a vacuum) existed between the atoms, which moved according to the general laws of mechanics. Democritus, together with his teacher Leucippus, may be considered as the inventors of the concept of a vacuum. Our modern view of physics is heavily influenced by the ideas of Democritus.

However, it was the thinking of Aristotle (384 – 322 B.C.) that dominated the scientific community up until the 16th century. Aristotle denied the existence of a vacuum as it conflicted with the idea that the universe was comprised of countless individual particles. According to Aristotle, nature consisted of the four basic elements namely water, earth, air, and fire.  In fact, the word vacuum comes to us from the Latin word “vacuus” meaning empty or “vacare” meaning “to be empty”.

A Curious Case of Part Contamination in a Vacuum Furnace

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A manufacturer of quartz products for the lighting industry was curious as to the origin of black “flakes” (particles) found on the outside and inside surfaces of their quartz tubes after heat treatment. These flakes appeared to be “fluffy bits of carbon”. The thought process to investigate this phenomenon presents a unique learning experience for us all.

One of the last steps of the quartz-production process is the heat treatment of the quartz tubes, which takes place in one of several vacuum furnaces at this manufacturer’s facility. The quartz tubes are heated under vacuum to 1050°C (1220°F) and held at temperature for several hours. This is followed by a quench with nitrogen. The vacuum furnaces in question have graphite heating elements, a combination ceramic fiber/felt insulation pack with a molybdenum hot face and stainless steel cold face and a graphite hearth. The quartz tubes themselves are placed onto graphite fixtures (racks).

Obtaining Consistent Vickers Hardness at Loads ≤ 100 Grams Force

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One of the most serious limitations to Vickers hardness testing in the micro-load range (10-1000 gf or 0.098-9.81 N) has been the variability in measured hardness with loads ≤ 100 gf (≤ 0.98 N). In the literature four HV-load trends have been reported for this range.  In the order of most common to least common, the trends are: the hardness decreases with decreasing load; the hardness increases slightly and then decreases; the hardness increases with decreasing load; and, the hardness is constant. Many publications have concentrated on the most common trend and attributed it to material factors. Samuels [1] stated, however, that these problems were due to microscope limitations, such as limited contrast and resolution, and visual perception limitations. At the same symposium, Westrich [2] showed that the SEM could be used to measure small Vickers indents and yield virtually constant hardness as a function of load.

VAC AERO Specializes in Custom Designed Vacuum Furnaces

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VAC AERO provides custom furnace designs and process capabilities to suit your specific requirements.

In addition to standard vacuum heat treating and brazing furnaces, VAC AERO also manufactures custom vacuum systems for a wide variety of special processing applications. VAC AERO’s skilled team of engineers works closely with the customer from concept through design, final manufacture and installation. VAC AERO designs and builds standard Gas Quench furnaces for maximum durability, reliability and trouble-free operation and provides an outstanding level of training, field and technical support based on decades of commercial heat treating experience.