This is the 13th article in our Vacuum Heat-Treatment Series. What follows is a discussion of cleaning, one of the most important subjects in vacuum processing. Understanding the need for cleaning parts, fixtures and the cleaning system itself is critical to success, as is measuring how good a cleaning job we have done.

When vacuum furnaces were first introduced, many in the industry felt that the only acceptable part and fixture cleaning method was solvent vapor decreasing. Over the years, however, environmental and other factors have necessitated the use of aqueous systems. Therefore, it is important to understand how each method can successfully get the job done. Cleaning is the application of time, temperature, chemistry and energy to remove contamination from the surface of a part to a level appropriate for the intended application. In other words, cleaning is simply moving contaminants from where they are not wanted (on the parts) to where they should be (in the waste disposal system). READ MORE by Dan Herring

Next Time: Part 14 of this series discusses diffusion bonding, eutectic melting, outgassing and other topics related to what can go wrong inside the vacuum furnace as we process parts.

This is the 12th in a series of articles in our Vacuum Heat-Treatment Series. What follows is a discussion about acceptable leak rates, leak detection and leak repair methods used on most vacuum vessels. Controlling the leak rate is of major importance in producing sound metallurgical components.

A common problem experienced by almost every vacuum user is that, over time, leaks develop that are both damaging to product quality and to furnace internal components. In extreme cases, the problem is obvious: the furnace will not pump down and/or the hot zone (or heating elements) shows obvious signs of oxidation. Small leaks, which are more common, often go undetected because the pumping system can overcome any air infiltration. However, even small leaks can cause continuous and sometimes catastrophic damage. Thus, routine leak checking should become a part of any good vacuum furnace maintenance program. READ MORE by Dan Herring

Next Time: Part 13 of this series discusses the importance of cleaning and discusses/compares solvent-based systems to aqueous solutions as well as talks about alternative cleaning methods that have been used over the years.

This is the 11th in a series of articles in our Vacuum Heat-Treatment Series. This part discusses vacuum valves, penetrations and flanges found on most vacuum vessels; where they are used, how they operate and a little about how they should be maintained.

Valves intended for vacuum service are subjected to a variety of special conditions (Fig. 1), ranging from high and ultrahigh vacuum levels to low, high and ultrahigh pressures, differentials in pressure and differentials in temperature as well as variable frequencies of mechanical operation. They can be supplied in a number of configurations: ball valves, gate valves, butterfly valves, needle valves, isolation valves, pressure-relief valves and control valves just to name a few. The type of valve in use is typically identified by its design or function, and each type can be actuated in a variety of ways (manually, electro-magnetically, pneumatically, electro-pneumatically or via electric motor). Position indicators and limit switches located on the valves are common. READ MORE by Dan Herring

Next Time: Part 12 of this series discusses leak testing and leak detection and also reviews the choices available for leak repair.

This is the 10th in a series of articles in our Vacuum Heat-Treatment Series. This part continues a discussion begun in Part Seven (Vapor Pressure) and focuses on the use of partial pressure and related areas necessary to control vaporization and prevent damage to both the parts and the equipment.

One of our goals in vacuum furnace processing is to minimize both alloy depletion from the part surface and subsequent hot zone contamination. Many of the materials we run are processed at temperatures and pressures at which individual elements can volatilize (leave the part surface). Partial pressure systems (Fig. 1) are designed to prevent this from happening by establishing a combination of pressure-temperature-time that minimizes the vaporization of the more volatile alloy constituents. READ MORE by Dan Herring

Next time: Part 11 of this series discusses vacuum valves, penetrations, feedthrus and flanges; where they are used, how they operate and how they should be maintained.

This is the ninth in a series of articles in our Vacuum Heat-Treatment Series. This part talks about heating elements used in vacuum furnaces, the materials and temperatures of operation, forms and maintenance practices. The design and location of the heating elements is critical to achieve proper heating and uniformity of temperature.

Almost all high-temperature vacuum furnaces are electrically heated. Resistance heating elements are constructed from metal or graphite in a variety of styles. In general, one of the following materials is used: Stainless steel alloys – 300 series alloys (e.g., 304L, 316L) can be used for heating elements up to approximately 760°C (1400°F). Nickel/chromium and iron-aluminum based alloys – These typically operate up to temperatures of 1150°C (2100°F) and exhibit good-to-excellent oxidation resistance, making them useful for a number of applications including hot wall-type furnaces. READ MORE by Dan Herring

This is the eighth in a series of articles in our Vacuum Heat-Treatment Series. This part talks about vacuum hot zones, their history, construction and maintenance. The type of hot zone construction is often important both to the material and to the process.

The first commercial vacuum furnace was sold to industry in 1929. In these early years vacuum furnaces were hot-wall retort designs; that is, alloy retorts placed inside atmosphere furnaces in which a vacuum was pulled on the retort interior. By the late 1950s, vacuum furnaces were gaining wider acceptance, particularly within the commercial heat-treatment industry. Larger sizes were especially in demand, prompting furnace manufacturers to consider alternative designs. The early 1960s saw the introduction of the first all-graphite-felt hot zone with graphite (cloth) heating elements. READ MORE by Dan Herring

Part nine of this series discusses the types of heating systems available for vacuum furnaces and explains how temperature uniformity is achieved in various styles of furnaces.

This is the seventh in a series of articles in our Vacuum Heat-Treatment Series. Here we talk about vapor pressure and how it is influenced by the various materials of construction used in a typical vacuum furnace as well as the materials we process.

All solids and liquids have a tendency to evaporate into gaseous form, and all gases have a tendency to condense back into their liquid or solid form. In other words, all materials have a characteristic vapor pressure that varies with temperature. Formally, vapor pressure is the pressure of a vapor in (thermodynamic) equilibrium with its condensed phase(s) in a closed container or vessel. READ MORE by Dan Herring

Next time, we will begin a discussion of the interior construction of vacuum furnaces by considering hot-zone designs.