This is the 20th article in our Vacuum Heat-Treatment Series. Here we discuss oil quenching in vacuum furnaces, a technology that has been used for over 50 years and has both broad appeal and some very unique characteristics.

Many components use oil quenching to achieve consistent and repeatable mechanical and metallurgical properties and predictable distortion patterns. The reason oil quenching is so popular is due to its excellent performance results and stability over a broad range of operating conditions. Oil quenching facilitates hardening of steel by controlling heat transfer during quenching, and it enhances wetting of steel during quenching to minimize the formation of undesirable thermal and transformational gradients, which may lead to increased distortion and cracking. By Dan Herring

Next Time: Part 21 of this series begins a discussion on various vacuum applications by discussing the hardening process.

This is the 19th article in our Vacuum Heat-Treatment Series. Gas quenching from sub-atmospheric to ultrahigh pressures is a technique used to achieve both proper part hardness (surface and core) and optimize part microstructure. Understanding this technology and the factors that influence quenching performance is critical.

What is Pressure Quenching? The description most often used to define high-pressure gas quenching is “accelerating the rate (speed) of quenching by densification and cooling of gas.”[2] One of the many reasons for the intense interest in this quenching technique is related to improved part distortion with full hardness. A critical concern in using this technology is to avoid sacrifice of metallurgical, mechanical or physical properties, that is, retain the ability to transform a material to a microstructure that is similar, identical or superior to that of a known quenching medium (e.g., oil or salt). By Dan Herring

This is the 18th article in our Vacuum Heat-Treatment Series and looks at various vacuum-furnace maintenance practices and procedures as well as offers tips from industry experts on what areas need to be maintained, how often, and why certain components should be inspected and/or replace.

To ensure reliability and repeatability of operation as well as uncompromising safety, maintenance practices need to be well defined, understood by all, and implemented in a prudent and well-thought-out manner. Only trained personnel experienced in vacuum technology should be allowed to service vacuum furnace systems. By Dan Herring

Next Time: Part 19 of this series discusses gas pressure quenching from sub-atmospheric to ultrahigh pressure, including a discussion of the factors that influence the heat-transfer coefficient.

This is the 2nd part of the "Vacuum Process Instrumentation and Controls" article (Part 1). This subject is complex and in a constant state of flux, changing as advances in technology are made. As such, we have surveyed the current state of the industry and report our findings here. In part two we discuss some of the vacuum processing challenges that original equipment manufacturers (OEMs) are facing today.

Temperature control in a vacuum heat-treating environment can be difficult because of the changing heat-transfer characteristics of the furnace as it moves from convection to radiation and conduction. The rapid heating rate of a vacuum furnace demands precise control, including setpoint program control with soak guarantee inputs. Vacuum furnaces are often used for a variety of products and processes by the heat treater making recipe management an important function. By Dan Herring

Next Time: Part 18 of this series looks at various vacuum furnace maintenance practices and procedures and offers tips from industry experts on what areas need to be maintained, how often and why certain components should be inspected and/or replaced.

This is the 17th in a series of articles about vacuum heat treatment and looks at instrumentation and controls in two parts. This subject is complex and in a constant state of flux, changing as advances in technology are made. As such, we have surveyed the current state of the industry and report our findings here.

Instrumentation and process controls used on vacuum furnaces in the heat treatment industry are extremely diverse due in large part to the fact that the life of a vacuum furnace can range from 20 to 50 years. The intent here is to report the results of a survey of major equipment manufacturers to better understand their product offerings today and to look at the current and future state-of-the-art with respect to instrumentation and controls. By Dan Herring

Next Time: Part two of this series will discuss some of the vacuum processing challenges that original equipment manufacturers (OEMs) are facing today.

This is the 16th article in our Vacuum Heat-Treatment Series. Water systems ensure that the vacuum furnace runs properly and that the quenching system operates at maximum efficiency.

All vacuum furnaces require some form of cooling either by water or by a suitable fluid (e.g., ethylene glycol) with high heat-transfer characteristics. Cooling systems can be designed as either open systems (discharging to a sewer) or closed (recirculation) types. There are a number of factors to consider when selecting a vacuum furnace cooling system, including the type, treatment methods and system maintenance. The importance of each of these factors cannot be overstated, and neglecting any one of which can have disastrous consequences on the performance and life of the vacuum furnace and cooling system. By Dan Herring

Next Time: Part 17 of this series discusses the process controls and instrumentation used on today’s vacuum furnaces to enable them to operate at peak efficiency.

This is the 15th article in our Vacuum Heat-Treatment Series. Heat exchangers are an important part of the vacuum gas-cooling system, yet most users do not understand the critical role these units perform or have a clear understanding of the type of maintenance required to keep them operating at peak efficiency.

Most heat exchangers used in vacuum furnaces are essentially fin cooling units (Fig. 1), which depend on the surface area of their coolers as well as the temperature of the incoming water supply to achieve a given cooling rate. Factors to consider when designing these units include the total surface area as well as the type and design of the individual elements that make up the surface since there can be many types of finned tubes with differences in shape, arrangement and relative dimensions between the fins and the tubes. By Dan Herring

Next Time: Part 16 of this series discusses water systems and their importance to the overall ability of a vacuum furnace to operate properly as well as efficiently quench workloads.