US3708351A - Blackening process - Google Patents

Blackening process Download PDF

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Publication number
US3708351A
US3708351A US00007505A US3708351DA US3708351A US 3708351 A US3708351 A US 3708351A US 00007505 A US00007505 A US 00007505A US 3708351D A US3708351D A US 3708351DA US 3708351 A US3708351 A US 3708351A
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United States
Prior art keywords
gas
furnace
combustion
masks
oxidizing
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US00007505A
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English (en)
Inventor
N Dallas
R Uzumecki
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Tubal Ind Inc
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Tubal Ind Inc
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Publication date
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/10—Oxidising

Definitions

  • Aperture masks and shadow masks made of steel are conventionally used in the manufacture of television receivers. To minimize internal reflection in the receiver it is necessary to blacken such pieces, and it has been the practice to blacken them by oxidation at elevated temperatures in a furnace chamber in combustion gases derived from the air combustion of natural gas.
  • the oxidation process is controlled to provide in the combustion gas contacted with the masks a controlled amount of free oxygen and live steam.
  • the gas introduced into the furnace chamber is controlled in composition to contain at least about 1/z% by Volume of oxygen, and preferably from about 1% to about 2%, and at least about 1/2% by volume of added live steam, and preferably from about 1% to about 2% thereof.
  • the gas should also contain from about 2% to about 7% of combustible gas (carbon monoxide and hydrogen, combined) and preferably from about 41/2 to about 61/2 thereof.
  • the combustion gas of the desired composition is preferably introduced into the blackening furnace chamber at a midpoint thereof so that the freshest gas with the highest oxygen and steam content comes into contact with fully heated masks.
  • the steam content of the combustion gas should be at a level such that the gas is not below its dew point even at the coolest part of the furnace. Otherwise condensation on the masks can occur with consequent unevenness of the coatings.
  • FIG. 1 is a partially schematic side elevation of the blackening apparatus
  • FIG. 2 is a side elevation in cross section of the furnace of FIG. 1;
  • FIG. 3 is a transverse view of the furnace in cross section, taken along plane 3-3 of FIG. 2;
  • FIG. 4 is a plan View of the furnace in cross section, taken along plane 4--4 of FIG. 2;
  • FIG. 5 is an enlarged perspective View of the entrance curtains used to seal the furnace ends.
  • FIG. 6 is an enlarged perspective view of a gas distribution manifold in the furnace.
  • the blackening apparatus comprises a mesh belt 11 on which the pieces to be blackened 12 are mounted to move successively through entrance tunnel 13, furnace 14 and exit tunnel 16.
  • a series of entrance curtains 17a, 17b, 17c and 17d each made of a plurality of hanging stainless steel strips 18 which flex to allow entrance of the pieces to be blackened and immediately recover to keep the tunnel end sealed.
  • a series of electrical heating elements 19, situated in the upper and lower portions of the furnace provide heat to the pieces to be blackened and to the gases within the furnace.
  • Combustion gas is generated in gas generator 21 by the combustion of natural gas in air and is generally cooled to about ambient temperature to remove most of its moisture before reaching feed line 22.
  • Air, or oxygen is introduced through line 23 to produce the desired oxygen content in the gas, as discussed in more detail below, and the combined gas passes to the side of the furnace where live steam is added through line 24.
  • the combined gas stream is split in two, with a portion going directly into the furnace through manifold 26 below belt 12 and the remainder passing through branch line 27 to manifold 28 above the belt.
  • Manifold 26 contains a plurality of apertures in two parallel rows spaced apart and directed upward, and manifold 28 has similar rows of apertures directed downward.
  • exit tunnel 16 As the pieces pass through furnace 14, they pass into exit tunnel 16, the downstream portion of which has a cooling jacket 29. Cooling water passes through jacket 29, being fed thereto through line 31 and withdraws through line 32.
  • a series of exit curtains 33a, 33h, 33C and 33d, are similar in construction and function to entrance curtains 17a-17d.
  • the oxidizing gas introduced to the middle of furnace 14 through manifolds 26 and 28 moves toward the opposite ends thereof with a portion going through entrance tunnel 13 before passing out through the entrance curtains and with the remainder going through exit tunnel and being cooled before passing out through the exit curtains.
  • Exhaust tunnel 34 at the entrance end and exhaust tunnel 36 at the exit end draw olf the exhaust oxidizing gas, in each case blending it with ambient air from outside the curtains.
  • Gas generator 21 is of known construction and design and does not per se constitute part of this invention. It comprises air and gas flow meters, a proportioning mixer, a compressor, a fire check, a burner, a combustion chamber, and a cooler with a condensate separator and trap.
  • Combustion in gas generator 21 is generally carried out at air/natural gas ratios between 8:1 and 10:1.
  • air/gas ratios in excess of 10:1 tend to produce temperatures too high for the burner to handle with safety, and air/gas ratios below 8:1 tend to raise the hydrogen concentration of the combustion gas to the lower explosive limit and the carbon monoxide concentration to the point where it can be dangerous to health.
  • air/gas ratios outside 0f air/gas ratios outside 0f the above limits may be employed.
  • the cooler u'sed in gas generator 21 uses water to cool the hot combustion gas and is preferably operated to cool the gas to about 70 F. rather than to a higher temperature which would deposit lime in the water lines.
  • the combustion gas is cooled to this low temperature, it loses most of its moisture content; and a portion thereof must be replaced through line 24 to obtain optimum oxidation in the blackening apparatus.
  • the pieces are loaded onto belt 11 prior to its entry into entrance tunnel 13. As the pieces pass through curtains 17a-17d, the curtains close behind each piece to help keep the oxiding gas of the desired composition within the oxidizing zone and to keep ambient air out.
  • the time for passage of the pieces through the entrance tunnel, furnace and exit tunnel is a function of the weight and configuration of the parts to be blackened. In a typical operation, thirty minutes of process time may be required.
  • the process is applicable to iron-containing articles other than television tube aperture masks and shadow masks, and works well with both low carbon and high carbon steels. It may be used, for example, for blackening steel elements used in vacuum tubes.
  • the temperature in the furnace is suitably maintained between about 1100 F. and 1200 F. and cooling in the exit tunnel may bring the temperature of the pieces down to about 250 F. to 300 F. at curtain 33a, and to lower temperatures at curtain 33b.
  • the amount of oxygen is generally maintained below about 3%, although 1 to 2% is preferred.
  • said oxidizing gas contains from about 2% to about 7% by volume of combustible gas comprising hydrogen and carbon monoxide.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Furnace Details (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
US00007505A 1970-02-02 1970-02-02 Blackening process Expired - Lifetime US3708351A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US750570A 1970-02-02 1970-02-02

Publications (1)

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US3708351A true US3708351A (en) 1973-01-02

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US00007505A Expired - Lifetime US3708351A (en) 1970-02-02 1970-02-02 Blackening process

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US (1) US3708351A (fr)
BE (1) BE762442A (fr)
DE (1) DE2104809A1 (fr)
GB (1) GB1309725A (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3958530A (en) * 1972-08-14 1976-05-25 Dart Industries Inc. Apparatus for coating an article
US4035200A (en) * 1974-08-23 1977-07-12 Smit Ovens Nijmegen B.V. Process for making an oxide-layer
US4425868A (en) 1981-12-28 1984-01-17 Thatcher Glass Corporation Coating hood
US4612061A (en) * 1984-03-15 1986-09-16 Kabushiki Kaisha Toshiba Method of manufacturing picture tube shadow mask
US4859251A (en) * 1987-03-07 1989-08-22 Kabushiki Kaisha Toshiba Furnace for formation of black oxide film on the surface of thin metal sheet and method for formation of black oxide film on the surface of shadow mask material by use of said furnace

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4425383A (en) * 1982-07-06 1984-01-10 Xerox Corporation Process for oxidation of carrier particles

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3958530A (en) * 1972-08-14 1976-05-25 Dart Industries Inc. Apparatus for coating an article
US4035200A (en) * 1974-08-23 1977-07-12 Smit Ovens Nijmegen B.V. Process for making an oxide-layer
US4425868A (en) 1981-12-28 1984-01-17 Thatcher Glass Corporation Coating hood
US4612061A (en) * 1984-03-15 1986-09-16 Kabushiki Kaisha Toshiba Method of manufacturing picture tube shadow mask
US4859251A (en) * 1987-03-07 1989-08-22 Kabushiki Kaisha Toshiba Furnace for formation of black oxide film on the surface of thin metal sheet and method for formation of black oxide film on the surface of shadow mask material by use of said furnace

Also Published As

Publication number Publication date
DE2104809A1 (de) 1971-08-19
BE762442A (fr) 1971-07-16
GB1309725A (en) 1973-03-14

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