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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Vacuum Science and Engineering

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We study vacuum science and vacuum engineering in order to better understand the role vacuum technology plays in creating useful engineered products (Fig. 1, Table 1). Manufacturing as we know it, and research and development as we have come to depend upon it, would not exist without the creation and control of the vacuum “atmosphere”.. 

Vacuum techniques are important in both the industrial setting and for the scientific community, whether it be in heat treatment or high-energy physics. At the heart of vacuum processing for manufacturing is the modern vacuum furnace. Ever since the introduction of the electric light at the beginning of the 20th century, society and manufacturing have been linked to advances in vacuum science and engineering. Examples include the development of modern computers to advanced transportation systems; the very fabric of modern society depends on vacuum technology.

Dry Pumps: Claw Pumps

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Every industrial vacuum furnace system uses a primary (aka mechanical) pump, which is also commonly referred to as a “backing” pump when either used in series with a booster pump, or used with both a booster and secondary (“high vacuum”) pump combination, such as a diffusion pump. These primary pumps are further divided into “wet” pumps (e.g., oil sealed rotary vane style or liquid ring pumps) or “dry” pumps (e.g., claw, hook or screw). Of the dry primary pumps, the most common types are the claw pump and the screw pump. 

Dry pumps are being increasing popular as an alternative to oil sealed rotary vane pumps for many medium and high vacuum applications (e.g., in low-pressure vacuum carburizing where fine granular soot is carried from the process into the pump). Designers and users of vacuum furnaces must have a good understanding of how claw and screw pumps operate. This includes the principles of operation, pump design, sealing, operating characteristics, features, purging, and ancillary devices.

Overview of Common Vacuum Furnace Equipment

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Vacuum furnaces are available in numerous styles and sizes and come in both standard and custom configurations. They are designed to process an almost limitless number of both semi-finished component parts as well as raw materials using a diverse set of thermal processes in equipment available from a wide variety of different equipment manufacturers located around the world.

The intent here is to provide a brief overview of some of the more common designs and applications found throughout the heat-treatment industry. The hope is that the reader will come away with an understanding that there is a vacuum furnace solution to virtually any design, application or specification encountered.

Why Vacuum?

Historically, vacuum heat-treating applications were classified in one of four areas, namely processes that could be:

  • Performed using no technology other than vacuum
  • Done better in a vacuum from a metallurgical perspective
  • Done better in a vacuum from an economic standpoint
  • Done better in a vacuum from a surface enhancement perspective

Metallurgy for the Vacuum Heat Treater

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The role of materials science is to study, develop, design, and perform processes that transform raw materials into useful engineering products intended to improve the quality of our lives. It is said by many that material science is the foundation upon which today’s technology is based and that real-world applications would not be possible without the materials scientist. The discipline has expanded to encompass materials for many highly specialized product applications.

The industrial revolution thrust metals into the forefront of technology, and they have stayed there ever since becoming the very foundation on which our modern society is built. One cannot envision a life where our transportation and communications systems, buildings and infrastructure, industrial machines and tools, and safety/convenience devices that are not an integral part of our daily lives. Metallurgy is that part of materials science and materials engineering which studies the physical and chemical behavior of metallic elements, intermetallic compounds and their alloys. This definition is all-encompassing and includes the study of processes run in furnaces and ovens, the forging and rolling of metals, foundry operations, electrolytic refining, creation and use of metal powders, welding, heat treatment and much more. One might say that metallurgy is the application of knowledge of materials while materials science focuses on the theory of the structure, properties, processing, and performance of engineering materials.

An Introduction to Vacuum Pumps

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When designing or operating a vacuum system, it is critical to understand the function of the vacuum pumps. We will review the most common types of vacuum pumps, their principles of operation and where in the system they are used.

Vacuum pumps are categorized by their operating pressure range and as such are classified as primary pumps, booster pumps or secondary pumps. Within each pressure range are several different pump types, each employing a different technology, and each with some unique advantages in regard to pressure capacity, flow rate, cost and maintenance requirements. Regardless of their design, the basic principle of operation is the same. The vacuum pump functions by removing the molecules of air and other gases from the vacuum chamber (or from the outlet side of a higher vacuum pump if connected in series).

Cleanup of Contaminated Vacuum Furnaces

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When operating vacuum furnaces, situations may arise in which the hot zone and/or cold walls may become contaminated (Fig. Nos. 1 – 2). This can occur from a variety of sources: air leaks, outgassing from residues left on the parts as a result of the manufacturing or cleaning processes, vaporization of sensitive materials (e.g., chromium-bearing materials), process induced contaminations such as carbon in the form of soot or tar, fluxes from brazing pastes, excess braze alloy as well as many other sources. Often times the work being processed is also affected (Fig. 3). The question becomes, how do we attempt to clean up our contaminated vacuum furnaces?

The leak test should be performed as part of routine operation and maintenance of equipment and typically consists of isolating the heating chamber (i.e., no pumping on the chamber) for a period of one (1) hour and measuring the increase (if any) in vacuum level. For single chamber vacuum furnaces, 10 – 20 microns per hour is considered an acceptable leak rate for general heat treatment (Note: specific materials, parts and/or processes may require a significantly lower leak rate). The vacuum level should be recorded before and after the test. Detailed procedures can be found in Reference 1.

Conductance in Vacuum Pumping Systems

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When designing a vacuum system it is important to take into account the system conductance. What is Conductance and Why Does it Matter? Conductance is the characteristic of a vacuum component or system to readily allow the flow of gas and can be thought of as the inverse of resistance to flow. It must be closely considered when designing a vacuum system and selecting the pump and other components, otherwise, your vacuum chamber will take too long to reach the pressure required.

Well-designed piping of vacuum equipment, as well as proper component selection, increases production efficiency by minimizing the vacuum pumping time. It also minimizes energy use, making your equipment less expensive to operate. Ignoring the principle of conductance and designing the system with only physical configuration and flow rates in mind, can cause delayed equipment startup, plant downtime, and process inefficiency because if a problem is found after startup, it can take considerable time and money to correct.