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: 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: 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: Engine / transmission / brake parts Tools Anything that needs hardening

Quench Tanks – Fire Protection

• Fire Hazard: 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: 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: 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.

• 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.

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

Quench Tanks – Fire Protection

Quench Tank – CO2

Enclosed Quench Tank

This particular installation has exposed flames to burn the ‘off gases’ when the vestibule door opens.

Hood

Off Gas Igniters

Finished Product Area

Quench Tank in Pit

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 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 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