We conclude our vacuum preventive-maintenance (PM) discussion this month. See November’s issue for part 1.


Establishing a PM Plan

Divide and conquer. Begin by understanding the heat-treat process(es) you will be asking the unit to perform and compare these to the design ratings/limitations of the equipment. These items include:

  • Temperature rating
    • Normal and maximum operating temperature
    • Cyclic operating conditions
    • Idling conditions
  • Loading
    • Load size including volume or weight limitations
    • Load distribution and the necessity for load ballast
    • Maximum and minimum gross load weight as a function of temperature
  • Atmosphere requirements
    • Type and function of gas(es) – partial pressure and backfill
    • Gas flow rate, pressures, etc.
  • Quench requirements
    • Type of quenchant
    • The volume of quenchant, if a liquid (in relation to gross load weight)
    • Quenchant temperature
    • Flow characteristics of the quenchant around the part
  • Special requirements
    • Baskets and fixturing
    • Quench restrictions
    • Access and site ports
    • Water systems
  • Design-specific features
    • Special features
    • Support/ancillary items (heat exchangers, water circulating systems, etc.)

Next, take the time to divide the equipment into logical “sections” so that the maintenance on each of these areas focuses on those components or assemblies that are critical to their functionality (and ultimately that of the entire machine). Then walk around the exterior and inspect the interior. Note: Confined-entry training/permits may be required.

Observe how all components interact. This takes a surprisingly short amount of time and yields a significant amount of information. Next, understand the “external” constraints being placed on the equipment (usage, budget, etc.). These factors are important in tailoring your plan to meet the expectation. Identify critical spare parts and have them in stock. Understand which spare parts must come from the OEM manufacturer and which ones can be purchased through alternative suppliers.

Steps you can take include:

  1. Intelligent equipment purchases – Taking the time to select the right equipment and features (standard and custom hardware and software), including consideration of future growth plans.
  2. Commitment to a robust maintenance program – Using a planned PM approach rather than a haphazard fix-it-when-it-breaks approach.
  3. Having user-friendly HMI, instrumentation and controls – Taking full advantage of today’s technology, including remote access capability, intelligent sensors and anticipatory controls (such as cloud-based reporting of abnormal operating conditions), is almost mandatory. This allows one to manage data through an intuitive, graphical interface so that changes to the system in real-time can be observed and corrective actions (including maintenance) can be initiated.
  4. Safety – Safety is mandatory and cannot be compromised at any time. This can be following a set of company rules (e.g., confined-entry regulations) or plain common sense and respect for the equipment and processes being run. There is a myriad of safety issues that must be considered when maintaining vacuum furnaces to avoid physical injury, electrocution, asphyxiation, burns and other injuries to yourself or others.

Code requirements, such as NFPA standards, must be followed by the OEM. In addition, there are several unique considerations specific to vacuum furnace equipment. For example, on furnaces equipped with oil diffusion pumps, maintenance should only be attempted after the pump has been allowed to cool to ambient temperature. The diffusion pump works by boiling oil to form a vapor. Heated by coils in the base of the pump, oil temperatures reach 240ºC (464ºF) and higher. At these temperatures, vapors from hydrocarbon-based oils can react explosively with air. As a result, the fill port in the pump should never be opened while the pump is operating. Silicone-based pump oils eliminate this explosive risk.

Maintenance of furnace-chamber internals should only be conducted using approved confined-space entry and electrical lockout procedures. Residual quench gases remaining in the tank even after the door is opened can cause asphyxiation. Particular care should be taken entering furnace chambers after argon has been used as a quench gas. Argon is heavier than air and can remain in low-lying areas for some time. It has no discernable odor, and there is usually no advanced warning before unconsciousness occurs. Vacuum conditions in a furnace tank are even more lethal. Lockout procedures to prevent furnace operation must be in place before entering any furnace chamber.


What You Should Expect of Your Furnace OEM or Third-Party Supplier

In this day and age, one should expect support from their supplier partners in the form of:

  1. Technical support (24/7) – Internet and/or telephone support by personnel trained in supporting vacuum equipment. A prompt response and courteous reply followed by rapid resolution of the problem should be expected, especially if a critical issue is involved.
  2. Diagnostic help (remote dial-in) – The ability of the OEM to access the vacuum furnace to aid in the troubleshooting process (this often requires the installation of a dedicated telephone line). Today, a number of cloud-based reporting systems are available so that the system can be monitored for abnormal operating conditions in real-time with alerts sent to both users and the OEM. Predictive analytics help determine an optimal PM schedule because tasks are carried out only when needed.
  3. Root-cause analysis – Taking the time to determine the root cause of a failure and analyzing the various ways in which it can be corrected is essential to equipment uptime and ultimately high productivity. Temporary fixes to keep the equipment running in the short term may be necessary, but these should be instituted only with the understanding (and preset timetable) of shutdown for a permanent repair and/or replacement.
  4. Availability of spare parts – Anticipation as well as availability of critical spare parts is an important aspect of a proper planned PM program. This should include both “standard” spare parts as well as specially designed components that may require extended lead times. Evaluation of which spares to keep in stock or on consignment at the OEM or third-party supplier is as critical as any aspect of the PM plan.
  5. Field support – Components fail and systems malfunction. This happens in the real world, but dealing with an unanticipated breakdown of your vacuum furnace can bring operations to a standstill despite the best-laid plans. If the issue is significant enough to require service by an OEM or third-party provider, they must be available, have individuals with the right skill sets (mechanical/electrical/process) and be familiar with the style and type of vacuum furnace. This is essential to a quick resolution of the problem.
  6. Period service visits – Setting up quarterly service visits by the OEM or third-party maintenance provider serves as a wellness check and helps prevent more serious problems from occurring before they become critical and produce unanticipated downtime. A suitable maintenance program, which includes regular inspection, lubrication, testing (Fig. 3), repairs and fine-tuning adjustments (Fig. 4), will ensure safe and efficient operations.
  7. Training – The OEM or third-party maintenance provider should be able to train your maintenance staff on routine service issues so that they can do the work themselves. In addition, they should be able to provide safety alerts and information on product upgrades, obsolescence and the like. Choosing a partner that will guarantee a level of professionalism and quality in the performance of their work is critical to success.



Successful use of a vacuum furnace should be measured in terms of uptime productivity. Today, uptime should be in the range of 90% or greater and depends ultimately on a leak-free and well-functioning vacuum system. While there are numerous factors that influence uptime (e.g., planning, scheduling, identifying the root cause of a failure, having the tools and spare parts needed for the repair), fixing problems correctly the first time is critical to success. 


  1. Herring, Daniel H., Vacuum Heat Treatment, BNP Media, 2012
  2. Pritchard, Jeff, “Maintenance Procedures for Vacuum Furnaces,” Vac Aero International (http://www.vacaero.com), 2008
  3. “Maintenance of Vacuum Furnaces,” Vac-Aero International, 2018
  4. “Technical Support and Maintenance Services,” Furnacare (http://www.furna.care)
  5. “The Harold – Blogging for the Heat Treatment Industry,” Ipsen (http://www.ipsenharold.com)
  6. “The Vacuum Furnace Blog – Maintenance,” TAV Vacuum Furnaces (http://www.tav-vacuumfurnaces.com/blog/category/2/en/maintenance)