Quenching

Report
Heat Treating Facilities - Quenching
The purpose of quenching is to control the normal
metallurgical transformation that occurs when metal is
cooled, thereby producing the desired hardness.
Water in most cases cool the material to quickly.
Typically oil is used.
Oil is circulated at a specific rate and temp. to achieve
the desired results.
Heat Treating Facilities - Quenching
• The process:
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Objects are heated in an oven and submerged into
an oil bath.
This oil is circulated around the object to cool it
When completed, the object is raised out of the oil
bath.
Heat Treating Facilities - Quenching
• Two types of quenching:
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Enclosed (Objects are lowered directly from a
chamber in a furnace into a quench tank by an
elevator or conveyor)
Open (oil bath is a separate process fed from a
external conveyor, crane, etc.)
• What gets quenched:
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Engine / transmission / brake parts
Tools
Anything that needs hardening
Quench Tanks – Fire Protection
• Fire Hazard:
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Overheating of oil
Quenching system and/or oil integrity compromised
Introduction of water – causes boiling and oil to
spread outside of quenching area
Oil evaporation from hot metal being submerged
causes flame ups if oil temp is above auto-ignition
temp.
Quench Tanks – Fire Protection
• Enclosed Quench Areas of Concern:
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Exhaust Hoods (located at exit of furnace)
Exhaust Ducts (located atop of the hood)
Oil Catch Pans (located at exit of furnace)
Vestibule area where treated product is exposed to
the atmosphere when leaving the furnace
Oil handling / cooling pumps
Oil filtering devices
Pit areas subject to spilling, splashing, condensation,
leakage or dripping
Quench Tanks – Fire Protection
• Open Quench Areas of Concern:
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Oil Coolers
Hood / Exhaust systems
Entry and exit conveyors (if present)
Areas subject to spilling, splashing, condensation,
leakage or dripping
Quench Tanks – Types of Systems
• Types of protection:
 If oil is less than 212°F, a water spray system can be used.
 Above 212°F, A Carbon Dioxide or Dry Chemical system may be used. This is
because the water could boil at these higher temps maker a more severe hazard.
Type of
Protection
Extinguishing
Method
Temperature
sensitive
Contaminates
Oil
System
Cost
Water Spray
Removes heat
Yes
Yes
Low
Dry Chemical
Removes Oxygen
No
Yes
Moderate
Carbon Dioxide
Removes Oxygen
No
No
High
• CO2 is preferred by most companies due to the lack of loss business
• CO2 uses Local Application design principles (See FSSA Design Guidelines for Local
Application)
• Systems are typically automatically actuated
• Fire is typically detected by industrial rate compensated heat detectors.
• Very large Installation using CO2 at the Chrysler Transmission Plant in Kokomo, IN.
Quench Tanks – Fire Protection
Quench Tank – CO2
Hood
Off Gas
Igniters
Finished
Product
Area
Quench
Tank in Pit
Enclosed Quench Tank
This particular installation
has exposed flames to
burn the ‘off gases’ when
the vestibule door opens.
Quench Tank – CO2
Open Quench.
This particular installation
has an overhead crane
drop the items into this oil
bath.
Quench Tank – CO2
Oil Handling Equipment
Drippings under conveyors
needs to be protected.
CO2 Fire Protection – Enclosed Quenches
• Protection System Arrangement
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Exhaust Hood – local application, rate x area
Exhaust Ducts – total flood deep-seated, 65%
Adjacent Oil Handling Equipment – local application, rate x volume
Pit Areas (if any) – total flood surface fire, 34%
Conveyer Area (leaving the quench), local application, rate x area
Vestibule Door (Screening Nozzle) - local application, rate x area
CO2 Fire Protection – Enclosed Quenches
CO2 Fire Protection – Open Quenches
• Protection System Arrangement
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Oil Surface – local application rate x area
Adjacent Oil Handling Equipment – local application, rate x volume
Pit Areas (if any - enclosed) – total flood surface fire, 34%
Pit Areas (if any – open-top) – local application, rate by area for open
top pits*
Tote Bin (if any), local application, rate x volume
Conveyor (if any) - local application, rate x area
Exhaust Hood (if any) - local application, rate x area
Exhaust Ducts (if any) – total flood deep-seated, 65%
* 4#/min /sq.ft. Refer to NFPA-12, 2011 edition B.5
CO2 Fire Protection – Open Quenches
REFERENCES
• References:
 NFPA -12
 NFPA-13
 NFPA-17
 NFPA-34
 NFPA-86C
 FM Loss Prevention Guide 7-41

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