Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
  • C21D1/773—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material under reduced pressure or vacuum

Definitions

• Metal foil as it is received from a rolling mill, has a coating of rolling oil deposited on it during the rolling operation.
• This oil coating or film must be removed totally or partially from the foil, particularly from aluminum foil, to render it suitable for many of its uses, such as, for example, household uses and use as a vapor barrier in packaging materials.
• oil film was removed by heat alone during an annealing process.
• the coils of foil were placed in an annealing furnace, having a protective atmosphere, and heated to a temperature which was sufi'iciently high to vaporize the oil film and drive the vapors from the coil.
• a typical rolling oil has a critical temperature of 550 F. at 14.7 pounds per square inch absolute (PSIA) and a critical temperature of 340 F. at l PSIA.
• the aluminum foil was readily stained or tarnished by components of the oil film and other vapors or moisture within the coil. Also, at this temperature the evolution of the oil vapor from the coil was often rapid and uncontrolled. Sometimes the vapor pressure was sufficiently excessive to cause the foil to become wrinkled or distorted.
• the present invention solves the above mentioned by providing a process which promotes the scavenging of gases and vaporizable liquids such as rolling oil from a coil of foil at a temperature which is lower than the normal boiling point temperature of the oil.
• a coil of foil By subjecting a coil of foil to a partial vacuum during at least a portion of the cleaning and annealing process, a partially annealed foil which is substantially free from oil film may be readily produced.
• Partially annealed foil is stronger than fully annealed foil and is therefore superior to fully annealed foil for many purposes.
• the coil is then heated so that it attains an annealing temperature substantially uniformly throughout the coil.
• Annealing temperatures vary with the type of metal foil being processed and the amount of annealing desired.
• the annealing temperature range for aluminum extends between about 500 F. and 750 F.
• a coil of aluminum foil heated to 750 F. 1 20 F. will be fully annealed.
• heat should be applied at a rate which keeps the temperature difference small between the interior portion of the coil and the surface portions of the coil, particularly when the interior portions of the coil reach a temperature at which the vapor pressure of the rolling oil exceeds the pressure of the atmosphere within the furnace
• the heating cycle may include a soak period during which the coil is subjected to a substantially constant heat environment. It is generally advantageous to provide such a soak period when the coil temperature is approximately at least equal to the boiling point of the rolling oil at the existing furnace pressure.
• the heat transfer in a coil of foil, particularly in a coil of highly reflective foil is primarily through the end surfaces of the coil longitudinally towards the center of the coil. As a result, the longitudinal center of the coil is the last portion to attain heat. The oil film on this portion is therefore the last to be vaporized and removed.
• the vapor produced from the oil film must pass the hotter outer ends of the coil. Therefore, if the end portions of the coil are allowed to become excessively hot before the fluids are removed from the coil, the foil in these end portions may react with the exiting fluids and become stained or tarnished by them.
• the protective atmosphere in the furnace preferably is circulated and continuously replenished or maintained. If the coil is heated principally by radiation, then the entire heating cycle may be performed with a partial vacuum in the furnace However, if a substantial portion of heat is transferred to the coil by means of convection, the first portion of the heating cycle may be performed at about atmospheric pressure and the last portion of the heating cycle may be performed at a reduced pressure. such as about 1.0 to 0.1 p.s.i.a.
• the first portion of the heating cycle is the portion wherein the coil temperature is raised from ambient temperature to about the boiling point of the rolling oil contained in the coil.
• the remaining portion of the heating cycle is the last portion wherein the coil temperature is raised to the desired annealing temperature.
• the heating means may be turned oh and then the coil may be cooled to about 400 F. or less and removed from the furnace
• the cooling is accomplished in a protective atmosphere at about atmospheric pressure or above.
• a cooled stream of protective atmosphere may be directed against and around the foil coil and circulated past a cooling means, such as a water-cooled heat exchanger.
• a method of annealing a tightly wound coil of aluminum foil and scavenging gases and vaporizable liquids therefrom comprising the steps of placing said coil in a vacuum furnace, sealing said furnace, partially purging said furnace and said coil of contaminating gases by evacuating said furnace to about 1.0 to 0.1 p.s.i.a. in backfilling said furnace with a protective atmosphere to about 14.7 p.s.i.a.
• said annealing temperature is between 500 F. and 700 F. but is less than the temperature required for a full anneal of said foil.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=25089919

Family Applications (1)

Country Status (3)

Cited By (3)

• 1968
  • 1968-10-25 US US770859A patent/US3615907A/en not_active Expired - Lifetime
• 1969
  • 1969-09-29 GB GB47815/69A patent/GB1273191A/en not_active Expired
  • 1969-10-20 SE SE14384/69A patent/SE368722B/xx unknown

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