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FAQs

Here are some of our most commonly asked questions when it comes to owning, buying and maintaining an industrial heat treat oven or furnace.

Maintenance, Repair & Troubleshooting

Manuals and electrical wiring diagrams are made individually for each piece of equipment with the exception of the Laboratory Ovens. A copy of the electrical wiring diagram is included in the operating manual and a second copy is bolted to the inside of the control panel door. Replacement operating manuals and wiring diagrams can be purchased here. The equipment serial number will be required when placing an order.

Please follow this link for our General Operating Instructions. General Operating Instructions for Laboratory Ovens include an electrical wiring diagram. All other electrical wiring diagrams are made individually for each oven.

  • Lab Ovens: Small silver plate on back of oven.
  • Bench Ovens: Older ovens have a small silver plate on side or on the back of the oven. Newer ovens have electrical specification nameplate on oven door or beneath control panel on side of oven.
  • Large Ovens and Furnace: Serial Number is located on electrical specification nameplate located on face of control panel or adjacent to control panel.
  • Serial Numbers can also be found in the Operators Manual.

Refer to our Resource Library which contains component manuals with information on error code displays and troubleshooting.

Typically our equipment can be serviced by your maintenance department. If additional help is required our technical support department can provide further assistance over the phone. As an alternative you can contact your local Grieve area sales representative who will put you in touch with a local mechanical service group.

(Even though the heating elements or burner are not on, any equipment with recirculating blower will heat up to about 30°F above room temperature due to the energy added by the blower.)

  • Check the Temperature controller is set above room temperature.
  • If Temperature controller displays a high temperature or an error code, the controlling thermocouple may have broken. Temperature controllers include “upscale break protection” which will not allow heating if the thermocouple junction has failed.
  • Check the Excess Temperature Limit Interlock, it may have tripped. Push reset button. The excess temperature limit interlock should be set at least 15ºF higher than operating temperature to prevent nuisance tripping.
  • If Excess Temperature Limit Interlock will not reset and/or displays an error code, the controlling thermocouple may have broken. Excess Temperature Limit Interlock includes “upscale break protection” which will trip and not allow resetting if the thermocouple junction has failed.
  • Heat will not come on unless exhauster (if installed) and blower are running. If exhauster or blower pilot light will stay on only when the START button is pushed and held, it indicates the motor starter overload has tripped. Reset starter overload block inside control panel. Determine reason for overload tripping-see additional FAQ’s below.
  • If exhauster and blower are running, check circuit to make sure that air flow switches (pressure differential switches) installed across exhauster and blower are closing. If they are not, determine cause-see additional FAQ’s below.

For Electrically Heated Equipment:

  • Is the HEAT switch turned on and the HEAT pilot light on? If HEAT pilot light does not come on, it indicates a possible control circuit issue outlined below.
  • Determine if heater fuses in control panel are blown. If so, make sure there is not a short to ground on any of the heater lines and replace fuses. If there is a short to ground it indicates shorted wires or failed heating elements.
  • Measure for correct line voltage between all phases at the heater fuses. The voltage of each phase to ground is not important, only the voltage between phases. If voltage is not correct (see equipment nameplate or wiring diagram for design voltage) determine cause.
  • If there is no voltage between phases at heater fuses, check voltage between phases at incoming wires to contactors or SCR power controllers. If there is power incoming to contactors or SCR power controller but not out of them to the heater fuses, there is a control circuit issue, blown coil in contactor(s) or a failed SCR power controller.
    • If it appears to be a control circuit issue and equipment uses contactors, hook one end of a volt meter to ground (terminal or wire marked 2 in control panel) and using wiring diagram trace control circuit backwards from contactor coil until voltage is displayed on the volt meter. The point prior to voltage being displayed is the cause of control circuit voltage not making it to the contactors. It is possible that the purge timer (if installed) has not completed the purge time period or purge timer is defective.
    • If equipment uses an SCR power controller, the 4to 20 milliampere signal to the SCR control circuit must be checked. Interpose (connect in series) an ampere meter in one of the control wires to the SCR and determine if there is 4 to 20 milliampere present. If there is no signal present, the temperature controller or the SCR control board is defective.

For Gas-Fired Equipment:

  • Flame Safety is not sequencing correctly and the burner is not igniting.
    • Determine that there is gas pressure at the equipment.
    • Gas ¼ turn hand valves are open (handle parallel with the valve body). There are hand valves at main line and the pilot line.
    • Gas pressure is incorrect and high or low gas pressure switches are not closing.
    • Sufficient time has not passed for purge time period determined by flame safety relay to have completed.
    • Check for error codes at flame safety relay.

The decision whether to stock replacement parts is based on how critical the equipment operation is to production. If equipment is critical and a few days to a week of down time would not be acceptable, we would suggest stocking heating elements, heating element contactors, thermocouple, blower and exhauster (if equipped) motors, V-belts (if equipped), door gasket, fuses, bearings (if equipped), latches and hinges. Most parts are available from our stock. Some parts such as non-standard temperature controllers, SCR power controllers, entire gas burners and special blower wheels are not stocked and availability is based on our vendor’s delivery. Some of these parts could have long delivery, but also may be able to be repaired by our vendor.

  • Has there been any change in the area where the equipment is located?
    • Check that the voltage supply agrees with that shown on the equipment nameplate. Lower voltage will result in low heat input for example running a 230 volt oven on 208 volts resulting in 80% of design heat input.
    • Make sure that the exhauster (if installed) and blower are rotating in the correct direction as indicated by arrow on motor mount. Most exhauster and blowers are 3-phase and interchanging any two incoming leads will reverse rotation. Make any change at the incoming power to equipment, not individual motor starters, or some motors end up running in correct rotation and others in wrong rotation.
    • Check or excessive exhaust from the equipment due to change in exhaust system or damper having been opened. Dampers are drilled and screwed in place before living the factory.
    • Change in load (larger loads take more time to heat up) or in loading (load blocking air flow will increase heat up time by restricting air flow)
  • Determine if one or more heater fuses in control panel are blown. If so, make sure there is not a short to ground on any of the heater lines and replace fuses. If there is a short to ground it indicates a shorted wire or failed heating element.
  • On gas-fired equipment, the gas pressure is correct.
  • Air flow switch (pressure differential switch) installed across either exhauster or blower could be opening as the oven air heats up and becomes less dense resulting in the heat turning off. This will make the heat cycle on and off at too low a temperature. On ovens with a purge timer, or gas-fired, the purge cycle will reset.

Some voltage supply variance is acceptable. For example, equipment built to function on 460V will work on 440 as well as 480 volts. Changing the phase (1-phase or 3-phase), frequency (50 Hz or 60 Hz), or a large change in voltage (between 208 volts, 230 volts, 380 volts, 460 volts, 600 volts) will require equipment retrofit kits. Not all changes will be economically feasible. Please locate the serial number of your equipment and contact our sales team or contact your local representative for further assistance and a quotation.

  • Equipment can be moved by forklift truck. Handle from the bottom; do not lift up by the top of the equipment. Make sure forks do not crush conduit or any components while lifting. If necessary to get forks beneath equipment, use a crowbar to pry up one of the corners of the equipment to maneuver forks beneath. Pick up from the edges, not push fork tips up into the middle of the equipment bottom or floor. If using machinery rollers, make sure they are positioned under edges of walls, not in the middle of the floor. Pick up from the sides; do not lift directly under the doors on walk in ovens.
  • Removable heat chambers may be lifted from the top and are factory equipped with lifting eyes. Please note only the chamber is designed to be lifted via lifting eyes, do not lift the entire oven by heat chamber lifting eyes once the heat chamber is installed.
  • Lifting chains or slings used to lift heat chamber should lift at approximately a 45 degree angle to avoid crushing the top of the heat chamber.
  • This is due to the setting of the tuning constants (PID) in the temperature controller. Refer to the controller set up sheets in the equipment manual to make sure the tuning constants (PID) set in the temperature controller are set the same as when the equipment was shipped. There is a tradeoff between slow approach to set point and overshooting set point. Decide which is important for your process. To approach set point more quickly, reduce P (proportional band), increase I (Integral or Reset), reduce D (Derivative or Rate).

The ovens are expected to run under a slight positive pressure. It is expected that the area immediately around the doors and at truck track seals will run hotter than the rest of the oven walls. There should be minimal heat leaking around the doors unless the door gaskets have deteriorated or the doors are damaged.

Door seal can be checked by closing a piece of paper between the gasket and oven face to make sure the gasket is touching the face of the oven. There should be resistance to pulling out the paper all around the perimeter of the doors. Doors can be adjusted at the hinges or by adjusting catch standoffs. Check to make sure that the oven is level and on a firm floor. To some extent the oven will form fit to the floor resulting in a warped oven face that is hard to seal to. If the top corners at the gap between double doors do not line up, the oven is not level. The oven should be shimmed to correct this.

Operating an oven under negative pressure will cause colds spots where room air is pulled in around the door seals. Oven negative pressure can be caused by the room where the oven is located being under negative pressure. This results in the room pulling air down the oven exhaust stack, through the oven and hot air into the room.

Internal oven pressure can be adjusted by setting of the fresh air inlet and exhaust outlet. Increasing fresh air into the oven by opening the fresh air inlet will increase pressure in the oven. Increasing exhaust by opening the exhaust outlet will decrease pressure in the oven.

Please contact our sales team or contact your local representative for further assistance.

  • Is this a new development? If so, have changes been made to the oven?
    • Make sure that the exhauster (if installed) and blower are rotating in the correct direction as indicated by arrow on motor mount. Most exhauster and blowers are 3-phase and interchanging any two incoming leads will reverse rotation. Make any change at the incoming power to equipment, not individual motor starters, or some motors end up running in correct rotation and others in wrong rotation.
    • Have the fresh air or exhaust dampers been changed resulting in oven running under negative pressure? Operating an oven under negative pressure will cause colds spots where room air is pulled in around the door seals.
    • Have the setting of the air adjustment louvers on the duct work been changed?
    • Have the parts changed? Larger parts will take longer to heat up causing transient cold areas around them.
    • Are parts being loaded differently? Placing the large cross-section of part across the air flow will block the air flow to other parts. Parts should be loaded so heated air can move between the parts.
  • To improve temperature uniformity,
    • Adjust doors for a good seal-see FAQ regarding hot areas around doorway.
    • To isolate any effect on uniformity caused by part loading, measure uniformity in an empty oven not a loaded oven. Position test leads 4” to 6” from edges of work space, 12” above insulated walk in oven floor, 18” above uninsulated oven floor. Positioning leads closer than this to work space edges is not realistic.
    • Balance the oven internal pressure to slightly positive by adjusting the oven exhaust and fresh air dampers. Increasing fresh air into the oven by opening the fresh air inlet will increase pressure in the oven. Increasing exhaust by opening the exhaust outlet will decrease pressure in the oven. Slight positive pressure is indicated by hot air just pushing past loosest area on door seal. Do not reduce exhaust on ovens with exhaust rate set for safety ventilation. On these ovens, open the fresh air inlet.
    • After measuring the uniformity, adjust the louvers on the duct work by opening louvers at cold spots and closing at hot spots. The rule is the same for both supply and return duct work.
    • It may be necessary to close all of the louvers on the duct in order to make a big enough change when opening at the hot or cold spot.
    • Make a big adjustment. Too small an adjustment will result in never making a measurable change. If temperature at a test lead swings too far the other way, you can always go backwards.
    • Don’t worry about bending the louvers too many times. They won’t break off.
    • Louvers are paired with alternating louvers blowing air in opposite directions. If there is a cold spot that just won’t go away, aim the heated air towards the cold spot by closing louvers blowing away from the cold spot and opening those blowing toward the cold spot.
    • If all the test temperatures are either above or below the set point, the temperature at the controlling thermocouple must be adjusted. Heating up the controlling thermocouple with lower the measured temperatures at test leads; cooling it off will raise all the temperatures. Controlling thermocouple can be heated or cooled by directing more or less heated air toward it or by pulling it toward the oven wall to cool it; moving it away to heat it. This adjustment can be made while oven is running.
    • Measure, adjust, and repeat.

If after taking these steps, uniformity is still in question please contact our tech support for further steps

  • This is due to the setting of the tuning constants (PID) in the temperature controller. Refer to the controller set up sheets in the equipment manual to make sure the tuning constants (PID) in the temperature controller are set the same as when the equipment was shipped. There is a tradeoff between overshooting set point and slow approach to set point. Decide which is important for your process. To reduce overshoot of set point, increase P (proportional band), decrease I (Integral or Reset), increase D (Derivative or Rate).
  • Temperature controllers controlling contactors are typically set with a cycle time of 15 seconds. This means that the total time from when the contactors close through the open time period to when they close again is 15 seconds. If the cycle time is less than 15 seconds, the cycle time in the controller has been changed. Or, not set correctly when a new controller is installed. Refer to the controller set up sheets in the equipment operating manual.
  • A bad connection or component in the control circuit could be interrupting the control circuit voltage to the temperature controller and contactors. Intermittent signal could be caused by a loose connection at a contactor coil or an air flow switch “fluttering” open and closed.

Contactor with something caught in the coil or failing contacts can cause “chattering”. If this is the case, the contactor should be cleaned out or replaced.

Our sales team will be happy to review the feasibility of your new process taking place in existing equipment. They will go over all key aspects and provide a solution on modification or recalibration of your existing equipment. Please locate the serial number of your equipment and contact our sales team or contact your local representative to discuss your application.

  • Motor could be defective and pulling excessive current (high amperage).
  • New motor installed of incorrect size (horse power too low) or motor wired incorrectly.
  • The motor or blower could be binding on something, make sure blower and motor turn freely and are not contacting any surfaces.
  • Sheaves on belt driven blowers have been changed resulting in blower rotating too fast.
  • Use whatever will dissolve and remove the residue. Do not use flammable liquids for cleaning as they will penetrate oven seems and soak into insulation. When the oven is heated after cleaning and flammable liquid in the oven or insulation may create a flammable mixture with air and explode resulting in damage to surrounding and personal injury.
  • Some residues can be removed by heating the empty oven up to maximum temperature and burning off the residue. Allow oven to cool after burning off residue, scrape and vacuum what is left from the interior of the oven.
  • If equipped, take care not to change setting of air adjustment louvers while cleaning or removing the ductwork. Louver position sets temperature uniformity within the oven, if altered temperature uniformity will be compromised. If ductwork is removed for cleaning make sure to mark the sections while removing and replace them in the same location after cleaning.
  • Refer to the Maintenance section of the General Operating Instructions located in operating manual or at our Resource Library.

Oven Purchasing & Customer Service

If your operating temperature is above 1250F Grieve will be providing a furnace solution. If you’re operating temperature is 1250F or below we will provide an oven solution.

The Grieve Corporation, an OEM manufacturer of Industrial Oven & Industrial Furnaces, does not buy and resell used equipment. However, we are aware that there is a large market in used industrial ovens and industrial furnaces.

We are often contacted, after a used oven or used furnace has been purchased, to help the new owner get the unit up and running. For this reason, we are very aware of the pitfalls of purchasing used industrial equipment. Before purchasing a used industrial oven or a used industrial furnace, reference the following link: New versus Used equipment

Our ovens and furnaces can be equipped and tested to comply with AMS 2750E. Yes, the “Furnace class” and “Instrumentation type” will need to be provided in order for us to quote correct equipment with proper instrumentation.

 

TIP: Use Our Oven Finder Tool

We have a handy oven finder tool that can help you narrow down a type of oven based on the various temperatures and specifications for your worksite. Once you find the oven you think may work, add it to the quote cart, and submit the form to request more information. This will start the conversation with our consultation team. browsE ovens

Calculators for Oven Design Requirements

Clicking a link below will navigate you to a page with detailed instructions for the calculations.

oven-manufacturing-process-home

Glossary of Terms for Industrial Heat Treat Ovens

AMS2750 is a heat treatment standard predominantly used in the aerospace industry. It covers temperature sensors, instrumentation, thermal processing equipment, system accuracy tests, and temperature uniformity surveys. These are necessary to ensure that parts or raw materials are heat treated in accordance with design requirements. The AMS 2750E specification has specific requirements for recording, calibration of controlling thermocouple, location of fixed permanent reference thermocouples and temperature uniformity testing. There are different requirements on recording and temperature uniformity depending on the use of the equipment being tested.

Inert atmosphere is used to minimize Oxygen contacting parts during heating. Most common use of inert atmosphere is to avoid discoloration or scaling of parts that would occur if heated in presence of Oxygen. There are other processes that require inert atmosphere during heating due to a specific nature of the product being treated.

Annealing is a process that is used to change hardness and strength of a product, typically made from metal. Annealing makes a product easier to work with by reducing the hardness. It is typical for an annealing furnace to have an inert atmosphere to protect product from discoloration.

Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid.

Curing is a chemical process employed in polymer chemistry and process engineering that produces the toughening or hardening of a polymer material by cross-linking of polymer chains.

Heat treating is a process used to alter the physical, and sometimes chemical, properties of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing and quenching.

Stress relief reduces the internal material stresses within a part or welded assembly caused by manufacturing processes like forming, machining, cutting or welding. By heating the component or assembly and holding for sufficient time the internal stress can be reduced.

Passes heated air across each shelf level. Use when processing flat sheets or parts with the least restriction to airflow from left to right within workspace.

Use when processing flat sheets or parts with the least restriction to airflow from front to rear within workspace. Accommodates virtually any oven loading without restricting air passage

For workloads where the heated air must pass upward through the load. Use when processing parts with the least restriction to airflow vertically within workspace.

Used for applications that are above 1400 °F.

Natural rise of heated air. Used to reduce air movement within workspace.

Blower assisted airflow. Used to improve temperature uniformity within workspace and, accelerates heat transfer.

Our industrial design and manufacturing process begins with a consultation. Let’s get started.

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