Identifying Issues with Your Furnace

Vacuum furnace systems may be designed in order to help refine operations and perform specific processes which produce results of the highest quality, but they are also made with the safety of users in mind.

Consequently, various precautions and system status indicators are built into these systems.

However, with the number of components and pieces that comprise a heat-treating system, it can often be hard to recognize an issue or know exactly what the different vacuum furnace alarms and buttons mean.

A list of the range of switches and indicators located on the vacuum furnace system is given below, as well as some common alarms or issues which may occur.

Emergency Shutdown/Alarms

  • Emergency Stop: This shuts off power to ancillary equipment such as the pumping system, the hot zone, or the VRT, enacting an emergency shutdown.
  • Alarm Indicator: This indicates a specific alarm condition as it lights up in conjunction with an audible alert.
  • Alarm Acknowledge: This silences the alert after acknowledging the alarm.

Below Safe Levels

  • Pump Water Pressure Switch: When the water pressure of the vacuum pump drops below a safe level, this activates.
  • Furnace Water Pressure Switch: When the water pressure of the furnace drops below a safe level, this activates.
  • Inert Gas Pressure Switch: When the inert gas pressure drops below a safe level, this activates.

Exceeds Safe Operating Parameters

  • Furnace Shell Over Temperature Switch: When the temperature of the outer jacket of the furnace goes above safe operating levels, this activates.
  • Pump Over Temperature Switch: When the diffusion pump goes above safe operating temperatures, this activates.
  • Furnace Over Temperature: When the over-temperature thermocouple of the furnace exceeds the over-temperature controller setting, this activates.

No Actuation

  • Heat Exchanger Flow Switch: Unless there is a sufficient flow of cooling water to the heat exchanger, this will not activate.

On/Off Indicators

  • Roughing Pump Start: This is a combination switch/light which starts the roughing pump as well as indicating that it is running.
  • Roughing Pump Stop: This halts the roughing pump and switches off the Roughing Pump On
  • Holding Pump Start: This is a combination switch/light which starts the holding pump as well as indicating that it is running.
  • Holding Pump Stop: This starts the holding pump and switches off the Holding Pump On
  • Diffusion Pump Start: This is a combination switch/light which starts the diffusion pump as well as indicating that it is running.
  • Diffusion Pump Stop: This halts the diffusion pump and switches off the Diffusion Pump On
  • Valve Limit Switch: This helps to display the valves’ current positions on the pumping, vent, and backfill (i.e., quench) manifolds.
  • Diffusion Over Temperature: When oil inside the diffusion pump goes above the maximum temperature previously set by the user, this actuates.

Modes of Operation

  • Heat Cycle Indicator: When the vacuum level reaches 80 microns (crossover), this lights up and applies heat to the work zone.
  • Partial Pressure Indicator: When the system is in partial pressure operation, this lights up.
  • Cooling Cycle: When the system is in cooling mode, this lights up.
  • Vacuum/Partial Pressure Switch: This selector switch is for selecting the system mode of operation (partial pressure event must also be programmed in the DCP).
  • Gas Select Switch: This selector switch is for selecting the type of backfill/cooling gas.
  • Vacuum/Static/Forced Switch: This selector switch is for determining the cooling mode.

In addition to seeing an overall list of common switches and indicators on the vacuum furnace, it is also useful to know the kind of alarms which can commonly be triggered, as well as the reasons they activate. A common alarm activates when parts are held for an excessive period of time. This alarm may activate for the following reasons:

  • Poor temperature uniformity
  • Degradation in the hot zone
  • The use of load thermocouples (TCs) which are beyond the acceptable specifications
  • The load TCs being defective
  • The load TC jack panel being contaminated.
  • The dead-band on load soak requirements being overly tight

Another common alarm which may activate during quenching is the chamber water jacket over temperature alarm. This alarm may activate for the following reasons:

  • The water supply temperature being set incorrectly
  • The water pressure being too low
  • The water balancing valves being adjusted incorrectly
  • Aging and excessive heat loss in the hot zone
  • The drain manifold running over five pounds per square inch before the quenching cycle begins

Several problems can occur which do not have specific alarms indicating a problem exists. For instance, the furnace door may fail to open. This may happen for the following reasons:

  • The cycle being incomplete
  • The furnace not being at atmospheric pressure
  • The inside temperature exceeding 200º
  • The door drifting off the closed-limit switch

Another example of a frequent problem which does not have an alarm is when a recipe fails to start. This can happen for the following reasons:

  • The door of the furnace being improperly closed
  • The vacuum pumps not running, or if they are set to automatic mode
  • The load TCs being selected and programmed but not installed
  • The emergency stop button being hit, or if the emergency stop reset button has not been pressed
  • Other alarms being activated which have not been addressed
  • The auto/manual key switch not being set to auto position
  • The VRT circuit breakers not being reset
  • The over-temperature setting not being reset

In order to monitor and prevent alarms and issues, a good option is to install software systems designed specifically to control heat-treatment processes and equipment. These particular software types are able to maximize uptime and reduce the potential for human error, thereby allowing users to operate at improved efficiencies.

Although vacuum furnaces have a number of precautionary indicators and alarms, a familiarity with common issues or frequently activated alarms in advance can help to ensure that the equipment is operated safely and successfully.

This information has been sourced, reviewed and adapted from materials provided by Ipsen.

For more information on this source, please visit Ipsen.

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