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Archives for July 2014

Vacuum Furnace Quenching Systems: External versus Internal

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For heat treating purposes, “quenching” can be defined as the rapid cooling of a metal to impart some desired property such as hardness. Different metals and alloys require different quenching rates to achieve their optimum properties. Regardless of equipment design, gas quenching in vacuum furnaces involve the same basic principles.

The gas quenching process normally consists of the following sequence of events. First, the power to the heating elements is shut off. Next, the furnace chamber and quench loop are backfilled with a non-reactive gas, commonly nitrogen or argon. The quench blower then activates, forcing the gas through quench nozzles located circumferentially in a manifold that is part of the hot zone and into the hot load. As the gas passes over the load, it picks up heat. The hot gas then exits the main chamber and travels through the quench piping to a water-cooled heat exchanger, where it is cooled. After exiting the heat exchanger, the cooled gas is drawn back through the blower to be recirculated through the chamber in a continuous cooling loop. BY JEFF PRITCHARD

VAC AERO Kalisz Receives Several Nadcap Coating Approvals

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 […]

Metallographic Preparation of Titanium and Its Alloys

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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, α-ß alloy specimens are significantly easier to prepare than a single-phase α specimen. The method does yield perfect polarized light response with α-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. Titanium, like iron, is allotropic and this produces many heat treatment similarities with steels.  Moreover, the influences of alloying elements are assessed in like manner regarding their ability to stabilize the low temperature phase, alpha, or the high temperature phase, beta.  Like steels, Ti and its alloys are generally characterized by their stable room temperature phases – alpha alloys, alpha-beta alloys and beta alloys, but with two additional categories: near alpha and near beta.

A Layman’s Guide to Understanding The Theory of Gases

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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). Molecular collisions occur between molecules and if contained, these molecular collisions against the walls of their container result in a pressure rise (which always occurs in a closed container when a gas is heated). In other words, pressure is simply the force per unit area that a gas exerts on the walls of its container.