From the Archives: “Fundamentals of Vacuum Heat Treating” by Harold Ipsen

Harold Ipsen portraitPublished in 1962 by Harold Ipsen, this manual provided readers with an introductory look into vacuum heat treatment. Today, it offers a unique perspective on an industry that, while much changed in the past 55 years, still values innovation and continued learning.

And much like Harold Ipsen – who believed that innovation has the capacity to change the world – we remain committed to strengthening and accelerating innovations in almost every industry.

Whether we are investing $1,000,000 in the heat-treating industry or developing cutting-edge technology that transforms how you experience your heat-treating system, everything we do is designed to further the industry as a whole. Learn more about our recent innovations, including predictive maintenance software with augmented reality, at booth #1801, ASM Heat Treat/Gear Expo 2017.

With that in mind, enjoy Harold Ipsen’s thoughts on the industry and where he believed it was headed, as well as his description of vacuum and why we use it.


Advent of the Space Age and the ensuing role of modern metals in its wake has catapulted the science of vacuum technology out of the laboratory and into production lines throughout the country almost overnight.

These same vacuum techniques in heat treating so little understood just a decade ago are now indispensable tools of the industrial heating industry. So to keep pace with the rapid increase in vacuum usage a better understanding of this comparatively new science is imperative, not only for more successful applications, but also to uncover a vast potential of untried uses.

In recent years furnace design has paralleled the tremendous strides in vacuum metallurgy, techniques, and practices. We at Ipsen Industries, Rockford, Illinois, are only too aware of our responsibility to continue in the vanguard of vacuum research by furthering the development of heat treating equipment as processing becomes more critical.

This manual deals with the fundamental principles that apply directly to vacuum heat treating furnaces and their uses. As the material was compiled from a variety of sources as well as our own research team, we are conscious of divergent values given by different authorities for the same constants.

With this in mind the reader should be cautious in his application of the data contained in this manual.

On Vacuum: What It Is And Why We Use It

Simply stated, a perfect vacuum is the lack of atmosphere. A void. A nothing. In a perfect or absolute vacuum there are no vapors, no substances, and no gases. And consequently no pressure. When we speak of atmosphere at sea level we mean that the enveloping vapors and gases exert a pressure of 14.696 lbs. per square inch. As we approach higher altitudes the atmosphere becomes more rarefied, pressure declines until ultimate vacuum is reached – in outer space.

Even with the best possible equipment today, this condition of absolute vacuum is not achievable on earth. In this respect, therefore, we must consider our manufactured vacuum in relative terms beginning at atmospheric pressure. As the pressure decreases from atmosphere, the degree of vacuum becomes higher. Present equipment is capable of reaching high vacuums, a billionth of atmospheric pressure or less, but even at this efficiency the remaining gas molecules exceed 10 billion per cubic centimeter in number. (There are 16.4 cubic centimeters per cubic inch.) Fortunately, however, attainable vacuums are well within the correct operating pressures for most present day heat treating applications as vacuum pressure is variable and dependent on the characteristics of the materials being processed. This will be discussed more fully in the following sections.

Why vacuum? While vacuum melting has been practiced for several years, the method of heat treating the resulting products has been confined largely to baths and atmospheres, prepared or natural. Basically, vacuum is the foster child of the Space Age, and the subsequent preoccupation with metals of high melting points. Though many of these metals such as tantalum, columbium, molybdenum, tungsten, (the so-called refractory metals) were well known in the laboratory, they were considered unworkable mainly due to their affinity for contaminant gases at high temperatures. Even a small amount of contamination caused embrittlement and impaired their properties. Vacuum proved a useful means, in fact the only means of removing these impurities, and eventually demonstrated further versatility in the processing of the more conventional materials, including standard steels and alloys. Other applications were subsequently uncovered: the vacuum stream degassing of large steel ingots, the annealing of continuous strip, the refining of iron and nickel-base superalloys for heavy duty in jet engines, the brazing and bright tempering of many grades of stainless, hardening and tempering of high speed steels and so forth. The scope of vacuum is boundless.

New Horizons in Vacuum Heating

To set down remarks on future trends in vacuum heat treating in advance of forthcoming developments in the field is subject to risk. However, continued advancement takes cognizance of these trends, and the effect they can have on the commercial aspect of industrial heat treating.

The immediate future promises a continuing pattern of increased demand for safe high temperature and high purity processing of metals such as the stainless and special alloy steels, heat treating, brazing, and sintering.

The principal advantages of vacuum furnaces for these processes are:

  1. Easier control of atmosphere.
  2. No hazardous atmospheres required to maintain high purity at high temperatures.
  3. Lower operating costs to achieve high purity and high temperatures.
  4. Less maintenance and “down-time” due to material failures at high temperatures.

We shall find vacuum heat treating equipment competing with conventional methods in original cost as well as its present advantage of lower operating costs. Actual liquid quenching will be done within the vacuum chamber without the necessity for removal to air.

Briefly, vacuum heat treatment of metals will gradually replace controlled atmosphere methods as the greatest volume production heat treating method.

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