Graphite Hot zone parts

Which spare parts should you keep on hand for a furnace?

High temperature furnaces are a relatively large investment and often have a life span of several decades. As is the case with any piece of machinery, parts wear out and will need to be serviced, replaced or maintained. With the JIT attitude in today’s manufacturing environment, some parts may have large lead times and could cause extended periods of down time were they to fail and none are on hand. Other parts may become obsolete due to the ever shorter product cycles especially in electronics. These include controllers, motors, PC’s, sensors with integrated electronics, etc. To avoid costly down-time and be prepared for maintenance, what should you have on hand, what are your furnace recommended spare parts?

 Heating elements and shielding

Heating elements and shielding are especially important to have on hand as spares, as they are the heart of a furnace and due to the many different sizes and configurations, are not often a readily stocked item. These parts slowly degrade over time depending on the temperatures, gases and contaminants they are exposed to. An easy way to check the efficiency of your heater and shielding is by comparing power usage of the hot zone at a given temperature with the power usage listed in the operation manual. If the overall KVA usage has increased, or the voltage and amperage deviates substantially from those numbers, it may indicate a worn out hot zone. A temperature uniformity test may also provide valuable data regarding the condition of the hot zone. An MRF hot zone typically has a uniformity of +/-10C over the usable hot zone, an increase in deviation may indicate degradation in efficiency and insulating characteristics of the heating element and shielding. A visual inspection of shield conditions and heating element condition can easily confirm this.

Graphite Hot zone parts

Graphite hot zone parts

metallic shields 710px

Metallic heat shields

Temperature Thermocouples

Temperature Thermocouples

Other items exposed to extreme heat are fixtures, heart plates, retorts, etc. While typically these items will easily exceed the life of the hot zone itself, some may need to be replaced eventually as well.


Thermcouples are often the primary sensor used to measure the temperature. While they are usually sheathed for prolonged life, they are prone to drift over time and need regular replacement in order to ensure accurate feedback. Vacuum and pressure sensors also need to be checked periodically for accuracy and performance. Many users have a calibration schedule to do just this.


Seals such as Viton, Buton or other o-rings, are relatively cheap and are recommended to be replaced when doing maintenance to ensure vacuum integrity. For furnaces running in positive pressure, the chamber gas exhaust valve is another item that should be kept as a spare. These valves may be exposed to numerous volatile substances, and they tend to collect on this valve as they cool down while exiting the furnace.

Electronics too?

Product life cycles of electronics and instruments are ever decreasing, with faster, newer and enhanced versions flooding the market more rapidly with each succession. Over the years, the majority of components that have changed the most are easily identified as the control components such as PLC’s, instruments, controllers, smart sensors, PC’s, display panels, etc. As an indirect supplier of these components, we only choose components that are industrial and have a proven track record of functionality, reliability and availability. As such they have a much better life expectancy than for example you average cell phone. Do we recommend keeping spare control components on hand? It depends, but in general we don’t see the need except for sensors. Even if your current control instruments may no longer be available in some years, most manufacturers will still support and repair them and/or offer newer updated replacements. As such it doesn’t seem the best use of resources especially for smaller labs.



As the old saying goes, an ounce of prevention is worth a pound of cure. MRF furnaces are built from reliable quality components, and are built to withstand the test of time, yet certain components subject to the wear and tear from thermal cycling or mechanical motion will eventually need replacement. Every MRF furnace is accompanied with a recommended maintenance schedule as well as a list of the specific spare parts for the model purchased. Adhering to a regular maintenance schedule and keeping a relevant supply of furnace consumables is the best way to prevent unexpected down time.



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